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P o w e r T e c h n o l o g y

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High Voltage

Circuit Breakers

General



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AGENDA

GENERAL

Introduction/ Physics of the electric arc

Breaking an alternate current

Circuit breaker characteristics

BREAKER TYPES

Breaker technologies

Oil circuit breakers

Sf6 circuit breakers

Vacuum circuit breakers MAINTENANCE/ DRIVING/ TESTS

Maintenance

Driving systems

Tests



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AGENDA

GENERAL




BREAKER TYPES




Vacuum circuit breakers MAINTENANCE/ DRIVING/ TESTS

Maintenance

Driving systems

Tests



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Introduction The circuit breaker is the last, larger and more important

element of the system constituted by the protection

equipment. It is responsible of the ultimate clearance of all present

disturbances and of the switching manoeuvres involved innormal operation of the system.

All this tasks must be performed without the insertion of secondary disturbances by the breaker.

In order to fulfil these requirements, the breaker must behighly reliable, both electrically and mechanically.



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The switching of the configuration of an electrical system operating acircuit breaker is not generally a simple process.

The operation of a breaker in a circuit with a current flow, implies thenecessity of extinguishing the electric arc which appears betweenthe contacts.

The arc extinction, which must be done under very severe physicaland time conditions, may itself provoke transient phenomenaaccompanied with overvoltages.

Introduction

According to the standard IEC 265-1:1983, a circuit breaker is a

mechanical device of connection, capable of establish, withstand

and break the current under the normal operation of the circuit and

occasionally, under specific overload in-service conditions, as wellas endure specific abnormal circuit currents (e. g. short circuit

currents) during a given time (generally fractions of second).



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The main function of circuit breakers is hence to interrupt currents.

Its operation consist of: The physical separation of two points named contacts.

The extinction of the arc which inevitably appears, taking theopportunity of the zero pass of the current (AC).

Finally the circuit breakers must: When open, to endure the voltage among contacts without

restriking.

At closing, to withstand the making load or fault currents.

When closed, to withstand the permanent flow of load current At opening, to interrupt currents without failure

Nevertheless it is not usual that circuit breakers visibly isolatezones for working, hence something else is necessary.

Introduction


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Physics of the electric arc

In order to turn gases into electric conductors their temperature shouldreach a certain limit.

Thus, their molecules and atoms begin to lose electrons and the gasesbecome conductors.

Metals have their own conductive properties due to the existence of free electrons in their inside.

In their surface there is a potential barrier produced by a layer of positiveions in the metal’s inside, which prevents electrons from escaping thesurface, unless their kinetic energy is greater than its charge multiplied bythe potential barrier.

When the temperature in the metal is raised, energy is transmitted to

electrons that may lead them to overcome the potential barrier, thuscausing the thermionic emission.

Other forms to extract electrons from a metal is to expose it to a strongelectric field or to a luminous radiation (photoionic emission)



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Discharge phenomena in a gas

When the electric arc appears, the electrons are released due to thethermoelectric emission of the cathode.

The electric field in front of the cathode accelerates the positive ions;

this process heats the metal in the cathodic electrode and generates thenecessary temperature in the cathode (22000k).

This electric field leads to the release of electrons in the cathode.

The electric arcs present the properties of great mobility and easyshifting due to the effect of air currents, magnetic fields, etc.

The voltage drop in the arc may be expressed by AYRTON’s formula:

Where A and B are linear functions of the arc length For i o; U A = Ue (extinction voltage)

For strong currents: Ua = A

I

B + A=U a



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Arc temperature

The curve in Fig. shows the temperatureof the medium surrounding the arc as afunction of the distance to its axis. Thetemperatures depend on the contactsmaterial.

The arcs shows up as an incandescentgas column with an almost straight-linetrajectory between the electrodes, whichcore reaches temperatures between6,000 and 10,0000 ºC. The surface of contact of the arc with the electrodesappears incandescent.

The collision of the molecules with theelectrons emitted by the cathodegenerates the ions of the arc column.



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Voltage drop in the arc

The arc can be divided in three zones.

Close to the electrodes, there are two very short zones with high gradientsand pronounced voltage drops: U A (anodic) y Ue (cathodic).

The third zone presents a smaller voltage drop, U, proportional to the lengthof the rest of the distance between electrodes.

The cathodic drop is lower than the anodic and includes a very small zone.

U A and Ue depend on the current intensity (Fig. 1).



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Voltage drop in the arc

In the zone of the cathodic drop there aremetallic vapours proceeding from thecathode with many positive ions and fewelectrons.

These electrons have great mobility and theyare able to transport from 10% to 20% of thecurrent.

In the arc zone, the shifting of electronsgives place to intense currents.

When the ions go toward the electrodes of opposite sign they accumulate toward thenearby zones causing the voltage dropsshown in Fig. 1.

These voltage drops are associated topowerful fields that provide the ions enoughenergy to release new ions.

In the anodic zone, a negative chargegenerates a voltage drop.



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Power and energy in the arc

The power absorbed by the arc is equal to multiply the current of thearc Ia by the voltage drop in the column:

The energy absorbed by the arc is the integral of the former product,extended to the whole duration of the arc:

This energy is transformed in heat and is dissipated to the environmentdue to conduction, radiation and convection. Part of this heat is

absorbed by the dissociation of the flow that surrounds the arc. A high thermal conductivity and an improvement of the refrigeration

conditions will reduce the temperature and increase the voltage drop.

The rise of the pressure also produces an increase in the voltage drop.

dt U I =dt P =W aa

T

oa

T

o

U I = P aaa



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Characteristics of the arc

The relationship among voltage andcurrent in an electric arc is very differentfrom that of metallic conductors.

In metallic conductors, the voltage isproportional to the current, and itscharacteristic is a straight line er .

The voltage U A between the electrodesof the arc decreases when the currentrises to a limit value and then it risesagain when the current decreases.

The initial breakdown of the space between electrodes requires a high

voltage of ignition for i = o. The growth of current increases tª and the ionisation of the medium

that surrounds the arc, consequently raising the conductivity of thecolumn of the arc, which decreases the voltage of the arc.



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Characteristics of the arc

When the current increases, the

curve shows a very considerabledecline at the beginning and then itdecreases more slowly.

This is because the arc subsists at aconstant current density, which

implies a section growth when thecurrent rises and an increase of theair conductivity.

If the current of the arc decreases under a given value, the points of thecurve do not match, but they are below the curve.

This phenomenon is due to the calorific inertia of the arc.

The surface of the cathodic stain, the arc diameter, the ionisation currentand the tª do not adapt instantly to the new values of current and theygive place to a lesser voltage of the arc.



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Characteristics of the arc The extinction voltage is smaller than the

restriking voltage, because when the

extinction takes place (following aninstant of strong dissipation of heat dueto thermal inertia), the column of the archas thermodynamic and conductiveconditions superior to those preceding

the restriking. The restriking occurs after a very short

time without arc, of about millionths of second, in which a cooling and an intensedeionisation of the arc take place.

The arc restriking, with the current in the opposite direction, is producedwhen the inverse voltage of recovery applied between the electrodes ishigher than the restriking voltage.

The value of the restriking voltage depends on the separation betweenelectrodes, the pressure of the medium and the concentration of chargecarriers, influenced by the refrigeration and thermal conductivity of the

medium and the electrodes.



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The arc in alternate current In an AC circuit the current passes through zero twice in a cycle. If the

voltage and current of the arc are registered by an oscillograph, the

obtained “voltage-current” curves present forms that depend on the kindof gas, the material of the electrodes, the arc length and the frequency of the current.

The difference of ordinates between the curve of rising current and thecurve of decreasing current is due to the thermal capacity of theelectrodes and of the gas of the arc and, in particular, of the calorificinertia of the arc (arc hysteresis).



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The arc in alternate current RESTRIKING VOLTAGE (Ur )

It is the voltage between electrodes needed to restrike the arc after it

extinguishes when the current naturally crosses zero. If the voltage betweenelectrodes is lower than the restriking voltage of the arc, the circuit staysdefinitely open.

EXTINCTION VOLTAGE (Ue) It is the peak voltage of the arc when the current reaches zero value.

The decreasing shape of the characteristic of the arc and the smaller concentration of charge carriers (resultant from the current decrease) justifythe rise of the arc voltage Ua, which peak is the extinction voltage Ue.



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AGENDA

GENERAL




BREAKER TYPES




Vacuum circuit breakers

MAINTENANCE/ DRIVING/ TESTS

Maintenance

Driving systems

Tests



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Breaking an alternate current If the circuit breaker is capable to open its contacts at the instant when

the current crosses zero fast enough so that the voltage between

contacts does not reach the restrike voltage, the circuit remains openand, since the electromagnetic energy is null in that instant, noovervoltages are present between contacts.

For this to happen in 50 Hz networks, the circuit breaker should be able toopen in less than ten thousandth of second.

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Breaking an alternate current In fast medium-voltage circuit breakers, the current breaks after two or

more hundredth of second. Ac tual ly, the current b reaking always has

place through an arc, with th e except ion of very weak cu rrents or extremely sm all vol tages.

The breaker goes fromconductive condition toinsulating condition with a

given puncture voltage or dielectric strength, whichgrows with time.

The conductive condition isprovoked by the ionisation

of the gas that surroundsthe arc. The ionisation isdue to the high temperaturethat the gas reaches and bythe electrons released by

the cathode.

Em

u

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u a

u rd

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Breaking an alternate current The voltage drop in the arc brings the power required to keep the high

temperatures (due to the Joule effect), balancing the heat losses of the

arc due to conduction, convection and radiation. As the current decreases when it approaches to zero, the thermal power

of the Joule effect is lower than the thermal power given to theenvironment. This leads to the cooling of the arc and produces arecombination of ions and electrons, which diminish the conductance of

the path of the arc. If the curve Up is constantly above the curve Utr , the arc will not restrike

and the circuit opening will be definitive. Nevertheless, if the voltagecurve Utr crosses the curve Up, at that instant the dielectric puncture of the medium will occur and a new arc suddenly restrikes.



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Breaking an alternate current The final extinction of the arc will be possible in one of the instants when

the current crosses zero, providing that the voltage between contacts in

those instants is unable to restrike a new arc toward the remainder plasma (between contacts), more or less deionised.

The possibility of an arc restrike or its definitive extinction depends onthe rate of rise of the TRANSIENT RECOVERY VOLTAGE (TRV), andof the dielectric strength of the zone surrounding the arc at such time.

The dielectric strength is a function of tª and the fractional ionisation of the plasma in the instant of the zero crossing of the current.

The arc trajectory should acquire briefly a dielectric strength enough toresist the recovery voltage between electrodes.

The rate of rise of the transient recovery voltage (TRV) is very importantfor the value of the breaking capacity of a circuit breaker. In the highvoltage circuits, the TRV may reach initial values of around kV/Ts.



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Breaking an alternate current The rate of recovery o f the dielectr ic s trength o f the arc’s medium

is an attr ibute of the circui t breaker, since it depends on the

refr igerat ion condit ion s, the deionisat ion rate of the zone of the arc and the speed of the separat ion o f the contacts .

The problem consists in a race between tw o voltages: the dielectr ic

strength and the transient recovery vo ltage. If the second does not

reach the f irst , the breaking is def in i t ive and happens when the

cu rrent crosses zero



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When a circuit breaker is

closed, a pressure amongcontacts exists and the currentdensity is minimal.

Arc extinction process



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At the opening maneuver, at

the moment of contactparting, the thin layer of fluid(air, oil, SF6, etc) betweenthem is crossed by thecurrent, which implies a veryfast rising of the temperaturein the contacts originatingmetallic vapours.

The isolating mediumsurrounding the arc suffers a

violent heating whichoriginates its transformationinto conductor.




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The gaseous column

strongly ionised turns intoplasma

Its ionisation and electricalconductivity extremely risewith temperature




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The renewal of the quenchingmedium and the zero cross of the current extinguish the arc




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The simplest case of current interruption is the one corresponding to

the normal load current. They are small currents, compared to the high short circuit currents,

and its phase angle is close to zero (cosΦ aprox. 0,8).

The interruption will take place at the first zero cross of the current.

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Arc extinction process. Load current interruption



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The case of close-in faults is characterized by a high current, with ahigh phase angle close to 90º (load strongly inductive).

It can lead to several arc restrikings and the arc extinction does nottake place before the 2º or 3º zero cross of the current.

Em

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The arc is established by contact parting.The voltage drop is Ua.

At the first zero cross the TRV rises veryquickly trying to reach the grid voltage buta restrike occurs because the dielectricstrength is not high enough.

At this zero cross, the dielectric strength ishigher than the TRV and the arc is finallyextinguished.

Arc extinction process. Fault current interruption




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When the short circuit is at the far end of the line, a transientovervoltage may add to the TRV, which can cause restrikings eventhough the current is not very high.

The case of interrupting small inductive currents may also cause sometroubles since the arc may extinguish even before the zero cross of thecurrent, hence generating voltage peaks by induction effect, andconsequent restrikings.

Arc extinction process. Other cases




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AGENDA

GENERAL

Introduction/ Physics of the electric arc Breaking an alternate current


BREAKER TYPES






Maintenance

Driving systems

Tests




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Circuit Breakers According to the standard IEC 265-1:1983, a circuit

breaker is a mechanical device of connection,

Capable of establish, withstand and break the currentunder the normal operation of the circuit

Occasionally, under specific overload in-serviceconditions,

Endure specific abnormal circuit currents (e. g. shortcircuit currents) during a given time (generallyfractions of second).




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Circuit Breakers The main nominal characteristics of circuit breakers are:

Rated voltage

Insulation level

Rated current

Rated frequency

Breaking capacity

Making capacity

Short-time current

Sequence of operationThermal short-time current rating

Mechanical short-time current rating




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Rated voltage The rated or nominal voltage of a network (Un) is the standard value of

voltage for which the network’s operation and insulation have been

designed. The limit values of a network’s voltage (excluding all transitory or

abnormal conditions) are the highest and lowest value of voltage thatmay be present in the network at a given instant or place under normaloperation conditions.

Generally, those limit values are around ± 10% from the nominal voltage of the network.

The highest voltage for a circuit breaker is the maximum specified for itrelated to:

Its insulation

Other attributes associated to this voltage




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Insulation level

The insulation level of a circuitbreaker is given by:

Nominal power-frequencywithstand voltage

Nominal lightning withstandvoltage

And eventually by: Nominal switching withstand

voltage

These values characterize the

device’s insulation regarding itsaptitude to withstandovervoltages at power frequency,lightning overvoltages andswitching overvoltages of steepwavefront.




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Insulation level. Lightning wave

Lightning overvoltage waves in overhead lines may have severalforms, but those registered by a cathode-ray oscillograph during

storms had shown that they might be represented by a non-periodicunidirectional wave of steep front, attenuated afterwards.

In order to typify the insulation of a given device, this wave can bestandardized as a 1.2/50 waveform;

this is, a waveform which front has a conventional duration T1 = 1.2 s,

and the conventional duration of the waveform afterwards until itreaches half its amplitude in the tail is of 50 s, according to thestandard DIN VDE 0432.




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Insulation level. Switching wave In high and medium voltage lines, the breaking of the current in a

circuit provokes overvoltages, with an unidirectional wave of steep

front, attenuated afterwards, that be standardized as a 250/2500 shockwave, this is, a waveform which front has a conventional duration T1 =250 s and T2 = 2500 s.

These shock voltages are generally triggered by an arrangement inwhich a given number of capacitors are charged in parallel by a high-

voltage direct current source and then discharged in series over acircuit composed by the tested device in parallel with a pure resistanceR and a linear inductance L.




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Nominal or rated current It is the current assigned by the manufacturer that the device can

endure indefinitely (or for a given time) under normal operation

conditions, without suffering any heating higher than that fixed by thestandards, and without undergo any modification in its functionalfeatures.

The values in the former table are for circuit breakers operatingoutdoors. For circuit breakers operating indoors, these limits of temperature rise are related to the temperature indoors and should notexceed 40 ºC if the circuit breaker contacts are made of silver or silvery

copper.

PART LIMITS OF RISE OF TEMPERATURE IN ºC

Oil circuit breakers Other circuit breakers

Contactors in air 30 35

Contactors in oil 30 --

Oil 30 --

Voltage coils with insulation type 0* 35 35

Series coils with insulation type 0* 50 50

Series and voltage coils with insulation type A 50 50

Series and voltage coils with insulation type B 70 70

All the other parts of the circuit breaker 70 70

S t i l d t i l b ki t




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Symmetrical and asymmetrical breaking current

Besides, the delay of the relays (whichsend the opening signal to the breaker after the short-circuit starts) should betaken into account.

For this the actual value of the currentcleared by the breaker is lower thanthe initial value of the short-circuitcurrent.

When a sudden short-circuit takes place, the initial current reaches ahigh value that progressively diminish until it attains the steady state

short-circuit value.

The IEC defines breaking current as follows:

The breaking cu rrent of a circu i t breaker pole is the value of the cu rrent in the pole in the instant of con tact separat ion and is

expressed by two values:

Symmetrical current

Asymmetrical current





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The asymmetrical current is the RMS value of the total currentcomposed by the AC and DC components in a pole in the instant of contact separation and its value is given by :

The symmetrical current is the effective value of the AC component inthe pole at the instant of contact separation and its value is given by:

2

x = I sim

)(Y +2

x = I

2

2

asim




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The extent of the asymmetrical period and its importance of theasymmetry depend, for each phase, on the instantaneous value of the

electromotive force (e.m.f.) in the initial moment of the short-circuit andits maximum value when the initial instant corresponds with a zero of the e.m.f.

Usually the relationship between the symmetrical and asymmetricalshort-circuit currents is expressed by a factor of asymmetry K:

K depends on the relationship between the inductive reactance and theresistance of the circuit where the circuit breaker will be mounted. It isgenerally tabulated in tables.

The breaking capacity of a circuit breaker is calculated as:

I K = I simasim

R

x f = K

I U 3= ASIM P

I U 3= SIM P

ASIM ncc

SIM nccSIM P K = ASIM P cccc

Sh t i it ki t



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Short circuit making current

This value distinguishes the capacity of a circuit breaker to close itscontacts under short-circuit conditions in the system.

The making current of a breaker when its contacts close under short-circuit conditions is the value of the total current (including alternateand direct components) and which are measured from the envelope of the current waveform in its first peak value.

The making current of a breaker is that associated to its closing at

service voltage. If this value is not present in the nameplate, should becalculated as follows:

Making current = 1,8 Isim = 2,55 Isim

P i ibl t d h t ti t



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Permissible rated short-time current

The permissible rated duration of the short-circuit current is the timeduring which the closed circuit breaker can endure a current equal to

its rated breaking capacity under short-circuit conditions. The rated value of the permissible rated duration of the short-circuit is 1

second, or, if a superior value is needed, 3 seconds.

For short-circuits that last more than one second, the relationshipbetween current and duration, unless the manufacturer specifies it

otherwise, complies with the following expression:

constant =t I 2

R t d f ti



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Rated sequence of operation

The rated sequence of operation of a circuit breaker consists in anumber of operations established in a certain succession and in given

ranges of time. According to the IEC standards, the sequence of operation of a circuit breaker not specified as a recloser can beexpressed as follows:

o - t - co - t' - co

o - t² - co

Where:

o = opening operation, c = closing operation

co = closing operation followed by an opening operation

t, t', t² time ranges, t y t' expressed in minutes, t² expressed in seconds

For example, a circuit breaker with a double operation sequence o -0,15seg – co, means than when the fault takes place, the circuitbreaker opens, waits 0,15seg, closes and, if the fault continues, itopens again.



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High Voltage

Circuit Breakers

Breaker

Types



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AGENDA

GENERAL



BREAKER TYPES






Maintenance

Driving systems

Tests



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Breaker types

The main way to distinguish thedifferent types of breakers is that

related with the mediun they useas a dielectric and to break thecurrent.

In accordance with that we candistinguish :

Oil breakers

Dead tank

Low content

Magnetic blast breakers

Air blast breakers

SF6 breakers

Vacuum breakers

Voltage Puncture in OIL, AIR

and SF6



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1900 Contacts in oil without breaking chamber

Breaking chamber

Oil as dielectric and isolation

Dead tank, reaches ratings of 330 kV 63 kA

1930 Low content of oil

Porcelain isolator

1973 Low content oil reaches 765 kV y 63 kA

1979 At HV becomes not competitive against SF6

Breaker technologies. History. OIL

S



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1930 Breaking with single and multiple chambers

1955 Very well accepted and introduced into the market

1965 Becomes not so popular because maintenance,compressors, noise, etc.

Breaker technologies. History. AIR BLAST

B k t h l i Hi t VACUUM



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1920 First development at laboratory

Difficulties with manufacturing

1963 Still manufacturing difficulties

1973 17 breakers installed at U.S.A

6 Chambers for 138 kV 40 kA

1990 Becomes rather popular at MV

Breaker technologies. History. VACUUM

B k t h l i Hi t SF6



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1950 Beginning of instalation with GIS

1973 Hidro-Quebec complete an instalation with GIS for 765 kV

1984 Beyond 123 kV becomes the most popular technologywith auto-puffer breakers

1990 Continues expansion at M.V. y H.V.. New designs with

low energy operating mechanisms

Breaker technologies. History. SF6

Selection of the breaking technology



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Selection of the breaking technology

In order to select the appropriate breaking technology, the followingaspects should be taken into account:

The highest security for personnel and material The fewer requirements of maintenance

The best treatment of switching overvoltages in order to keep theminto secure levels (less risk for the material)

The best economical conditions, considering cost of acquisition andassembling, as well as maintenance yearly expenses, cost of renewal of damaged material (due to repeated arcs) and cost of indispensable auxiliary systems (like air compression systems inairblast circuit breakers)

P di t bl f t f h t h l



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Predictable future of each technology

The predictable development of vacuum breaking, even when it has beenlong an uncertainty.

The impressive development of SF6 breaking, which dominates nowadaysthe hole range of medium to high voltage (from 3 kV to 800 kV)

The hypothetical birth of static breaking, with a promising but doubtful future.

Accordingly to experience it

is possible to establish: The continued monopoly

of air breaking for all lowvoltage applications.

The expected decrease(that has already started)of two formerly successfultechnologies: airblastbreaking and oil breaking.

P di t bl f t f h t h l



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Number of breakers by Voltage and thecnology used

Predictable future of each technology

K.V. AIRE G.V.A. P.V.A. SF6 VACÍO TOTAL

380 1 0 0 4 7 1 4 0 7 1

220 6 6 2 2 6 0 1 4 7 0 4 7 5

132 4 3 7 3 4 4 3 4 5 1 0 1 0 1 0

66 0 1 4 3 5 8 2 4 3 3 0 1 1 5 8

45 9 4 4 9 0 0 6 2 2 0 1 0 3 5

30 6 7 7 4 8 6 3 3 2 9 6 3 1

20 4 3 2 3 2 6 1 2 9 2 0 2 1 6 6 4 4 2

15,13,11 2 0 2 3 3 1 3 2 0 1 5 9 1 5 9 7

TOTAL 1 9 7 5 7 4 7 2 9 9 4 0 7 5 2 7 4 1 2 4 1 9

%TOTAL AÑO 2000

1 , 5 9 4 , 6 2 5 8 , 7 7 3 2 , 8 1 2 , 2 1 1 0 0

AÑO 1997 2 5 , 8 5 6 4 , 7 5 2 5 , 7 9 1 , 6 1 1 0 0

M ti bl t i it b k



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Magnetic blast circuit breakers

Arc extinction by means

of a magnetic fieldcreated by the current tointerrupt

The arc is displaced andelongated by the effect

of that magnetic field Only used in LV and MV

No flammability hazard

M ti bl t i it b k



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El principio del soplado magnético consisteen producir, por la acción de un campo

magnético excitado por la propia corrientea cortar, un más rápido alargamiento delarco, el cual es canalizado hacia el interior de una cámara de extinción de materialaislante, refractario, de gran capacidadcalorífica.

En base a este principio, es posible lograr la ruptura de muy elevadas corrientes enbaja tensión y aún en media tensión,siempre y cuando se cuente con una

potencia de refrigeración suficiente en lazona del arco como para impedir elembalamiento térmico post-arco.

Interruptores de A..T. Interruptores para el Interior.


Magnetic blast circ it breakers



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Es condición fundamental, en uninterruptor de soplado magnético, que el

arco se extinga dentro de la cámara deextinción, sin salirse de ella. La misión deesta cámara es laminar el arco y enfriar enérgicamente el plasma de gasesionizados, al paso por cero de la corriente.

Conviene destacar que el sopladomagnético en los interruptores de corrientealterna, es nulo en el momento deextinguirse el arco (paso por cero de lacorriente), no ejerciéndose en estosinstantes acción electromagnética algunasobre los iones y electrones presentes enla columna del mismo, lo cual limita lautilización de este tipo de aparatos paratensiones muy altas.

Interruptores de A..T. Interruptores para el Interior.





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SECCIÓN DE UN POLO DEL INTERRUPTOR AUTOMATICO

Interruptores de A..T. Interruptores para el Interior. Ruptura con solapado Magnético





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SECUENCIA DE CORTE DE UNPOLO DEL INTERRUPTOR

AUTOMATICO






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Ua =Tensión de arcoe = F.E.M. del circuitoi = Corriente

r a = Resistencia del aire

La figura ilustra este proceso, en el caso de un circuito de corriente alterna.La técnica utilizada en estos interruptores no pretende cortar bruscamenteel arco al paso por cero de la corriente, sino que aprovecha los instantesque preceden y suceden a ese instante para cambiar el régimen defuncionamiento del interruptor, pasando de un arco de pequeña resistencia

a un arco de elevada resistencia. La ruptura sobreviene a continuación, alincrementarse esta resistencia hasta el infinito, tal como se tiene en losinterruptores de corriente continua.

El éxito de esta técnica, inicialmente aplicada a los interruptores de baja tensión y muy especialmente en los interruptoresde corriente continua ultrarrápidos hasta 3 kV, llevó a los constructores a extrapolar su utilización a los aparatos de alternade media tensión, hasta tensiones de 24 kV.

Como sea que, para alcanzar una tensión de arco del orden de la tensión de la red, la longitud de aquel debe ser muy

importante; y una elevada tensión de arco con corrientes fuertes sería causa de un considerable desarrollo de energía (por defecto Joule), que además de inútil sería perjudicial. Es necesario que en tanto la corriente sea fuerte el arco sea corto,forzando su alargamiento únicamente al ir aproximándose la corriente a cero. Esto se ha conseguido jugando con lassecciones de paso ofrecidas al arco, por ejemplo, disponiendo en las pantallas de las cámaras de ruptura rendijas deanchura variable.



Air blast circuit breakers



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Air blast circuit breakers Arc extinction by high pressure air blast

Advantages:

No flammability hazard

Disadvantages:

Compressed air system is needed

Noisy operation

Expensive maintenance

It was competitive at high voltages and highbreaking capacities

Other characteristics:

Always multiple breaking Dielectric strength rises with pressure

It must be re-closed to prevent emptying.

AGENDA



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AGENDA

GENERAL



BREAKER TYPES






Maintenance

Driving systems

Tests

Breaking an alternate current in oil



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Breaking an alternate current in oil In the instant of electrodes separation, a considerable resistance named

appears between them. Since the current cannot changeinstantaneously, a voltage takes place between electrodes, forming anarc.

This arc is constituted by a mixture of metallic particles and volatilised oil,hence forming a blend of gases partially dissociated and ionised andbecoming a conductor path of weak resistance when the arc is stable.

This resistance gets weaker when the current gets higher, and increaseswhen the arc is enlarged.

Breaking an alternate current in oil



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Breaking an alternate current in oil When the electrodes start to separate, as soon as the arc is established,

the resistance is very low and does not sensibly modify the condition of current I, which follows its normal variation and until it reaches zero.

The arc extinguishes at this instant, but the gaseous path does notdisappear and the arc restrikes when the voltage between electrodesreaches the appropriate value.

The phenomenon repeats with every change of sign of the current;

however, as the arc enlarges, the resistance of the arc grows, thecurrent amplitude diminishes slightly, and the restriking voltageincreases noticeably.

Finally, the restriking voltage gets to be higher than the voltage betweenelectrodes, hence the arc does not restrike anymore and the circuit is

opened.

Arc extinction using oil blast



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Arc extinction using oil blast To extinguish an arc it is required to deionise its

path in a very short time (µs). Then, the blast of turbulent gases should be thrown to the ionisedfiles that constitute the arc.

Consider two electrodes A and B inside aninsulating enclosure cross by a transversalchannel. If a given amount of oil is thrown

through the channel in the direction of the arrow,the oil will penetrate the arc. At the instant whenthe current passes through zero, the voltage willstay at its normal value, since an insulating layer had been introduced between electrodes, andthis layer would be able to stand that voltage.

For the extinction to be ultimate, it is alsorequired that the insulating layer would becapable to endure the recovery voltage Ur for aslong as it is present.

This is, the fluid speed must be proportional to theradient of the recover volta e.




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The dielectric strength Ur to beintroduced is that of the fluid relative tothe shock voltages. For oil, even if it ishighly contaminated, it is around 220kV/cm.

In the circuit breakers with transversalblast, the extinction of the arc is aided

by the fact that the dielectric strength of oil, under shock voltage, is greater thanthe dielectric strength of the arc columnat the instant of extinction, which isaround 7 kV/cm.

The speed of the oil is inevitably limited(20 to 40 m/s), however, when thegradient g gets too large, after thevoltage rise in a circuit of a givenfrequency f o, the artifice of multiplechannels in parallel is used.


Operation of low oil content CB



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Breaking chamber

Fixed contact

Mobile contact

Oil

Current collector

Insulating material

Current collector

The extinction of the arc happens in the breaking chamber, in which ablast takes place due to the pressure generated by the arc itself.

The breaking chambers present the property that the breaking effect

rises as the current to be interrupted increases. The breaking power is limited only by the pressure of the gases product

of the arc which must be endured by the breaking chamber.

This is manufactured with an insulating material, epoxy resin, built up withfibreglass. The insulation from ground is obtained by standoff insulators.

Operation of low oil content CB When the mobile contact

moves away from the fixedcontact, the oil provokes a fastcooling of the arc betweencontacts. The procedure of arcextinction has two stages:

Enlargement and cooling of the arc

Self-extinction of the arc.

Interrupting chambers Axial blowout



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Interrupting chambers. Axial blowout

In this kind of chambers, the gasesescape through the passage gap of the

fixed contact.

Since the section of the opening is small,the pressure in the chamber is high evenwith small currents.

Interrupting chambers Transverse blowout



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Interrupting chambers. Transverse blowout

In this kind of chambers, the gasesescape through side gaps.

The heat of the arc vaporises the oil andthe gases formed (mainly hydrogen)increase in pressure and force the arc tobow into the vents.

Gas

evacuation

Interrupting chambers Mixed blowout



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Interrupting chambers. Mixed blowout

For high breaking capacities, theblowout of gases towards the arc is

perpendicular to the contacts axis;meanwhile for low capacities, theblowout is axial.

The contacts of these circuit breakerscan stand, according to the statisticsprovided by the manufacturers, thefollowing number of operations withoutneed of replacement.

At rated current 4000 operations.

At half of the maximum short-circuitpower 8 operations.

At full short-circuit power 3 operations.

Gas

evacuation




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The most used since 1900

Advantages:

Lower arc length than in air

Better isolation

Disadvantages:

Flammability hazard

Oil contamination by arc effect

Explosive mixture of gases and air

Bulk oil/ Dead tank:

Oldest technology and obsolete

Big oil tank where the contact parting off takes place

Arc extinction by oil pressure on gasses bubble

Improvement with arc extinction chamber

Low content oil circuit breakers



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Low content oil circuit breakers

Reduced chamber containing thecontacts and the oil

Oil blast at pressure in the arc

Several chambers used as voltagerises

Advantages:

Self-regulation (Higher blasting for higher arc intensity)

High breaking capacity

Fast deionization

Low overvoltages Reduced energy dissipation

Reduced carbonization

Reduced contact wearing



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High Voltage

Circuit Breakers

Breaker Types

SF6

AGENDA



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AGENDA

GENERAL




BREAKER TYPES






Maintenance

Driving systems

Tests

The sf 6 as a dielectric gas



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6 g

Under a few bars of pressure its dielectric strength reaches 5

times that of air . This is due to two reasons:

First, the dimension of its molecule, which effective section of collision withan accelerated electron inside an electric field is higher to that of thenitrogen or oxygen, for example. This means that the electron will endurestatistically a greater number of collisions in SF6 than in air.

But mainly, the second, which results from the property of the SF6 moleculeto capture an electron in an electron-molecule collision, thus forming a

negative ion.

This property of capturing electrons comes from the extraordinarilyelectronegative nature of the fluorine atom. When this atom lacks anelectron to complete its external layer, it generates an elevated level of attraction towards any electron inside its influence field. This provides this

element its well-known chemical reactivity. This point will be further developed when analysing the deionisation

phenomena..

Hence, in the field of current breaking, SF6 is the ideal gas, as it willbe analysed below.

The SF6 as the breaking gas. Thermal features



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6 g g

In the breaking process of an electric arc,

two main qualities are required from the

dielectric used as a breaking agent:

the cooling capacity

the capacity of deionisation of the arc.

The application of SF6 for this purpose is

evident under two features: Thermal and

Electronic Given an electric arc formed inside a

cylindrical tube containing a gas and crossedby a constant current, it can be demonstratedthat the temperature of this arc is maximum in

the axis of the tube, and it decreases towardsthe walls until it reaches the temperature of the tube in the walls.

The SF6 as the breaking gas. Thermal features



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6

When the current increases, it can beobserved in most gases the appearance of a thermal threshold and the developmentin the centre of the tube of a cylindricalzone in which the temperature rapidlyrises, called central core.

The thermal conductivity of SF6 presents apeak near the thermal threshold thattranslates in an important heat release.

In SF6 the temperature of the threshold(2.200ºK) is close to the temperature of recombination of the SF6 atoms inmolecules.

Therefore, there is an important absorptionof energy that causes a new descend intemperature, which goes below 2100ºK.

At this temperature, the SF6 is basically aninsulator and impedes the restrike after the

current crosses zero.

The SF6 as the breaking gas. Deionisation



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SF6 has another notable feature, related to the strongly

electronegative nature of fluorine.

In fact, the atom of fluorine lacks an electron to fulfil its external layer, whichcreates a high level of attraction over any electron inside its influence field.

There is a noticeable decrease in the number of free electrons (responsibleof the arc conductivity) below 6,000ºK.

Such electrons are captured by the fluorine atoms to form negative ions F-,

185 times slower. Hence, for every captured electron, the current isautomatically divided by 185.

Therefore, in the temperature range of 6,000 and 3,000ºK, in which

almost all free electrons had been captured, the conductance

decreases very faster than in gas without the electronegative

properties of fluorine. Summarizing, in SF6, even before the central core has completely

disappear while the cooling of the arc, its conductance is almost

null, due to the capture of the free electrons by the fluorine atoms,which become electrons traps below 6,000ºK.

Breaking technologies in sf6 . Self-compression



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The breaking technology of self-compression inSF6 was first used in high voltage circuitbreakers, and then it moved on medium voltage,following its own evolution.

The active elements are mounted inside thesealed terminal boxes that constitute the poles.




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1 Lid

2 Gastightness system

3 Driving axle

4 Crankshaft

5 Insulating rod

6 Conical roller bearing

7 Top current tap

8 Casing

9 Bottom10 Spring

11 Valve

12 Piston

13 Mobile arc contact

14 Mobile main contact

15 Fixed arc contact

16 Insulating nozzle

17 Fixed main contact

18 Molecular sieve

19 Bottom current tap

The current breaking isperformed through thecontacts of the arc:

The fixed contact is rigidlymounted above the bottomtap.

The mobile contact has

two parts: The contact in the

centre

A contact rod thatslides inside a fixedbase leaned againstthe top tap.




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A piston is rigidly mounted over the contact rod

with the purpose of compress the SF6 duringthe opening of the contacts.

A Teflon nozzle tightly jointed to the piston hasthe purpose of channelling the SF6 towards thebreaking zone.

The permanent current crosses the maincontacts.

The fixed main contact, mounted around the arccontact, is constituted by a ring of silvery fingers

that are articulated and assembled over springs.

The springs exert a strong centrifugal force,assuring a good contact.




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The mobile main contact has an almosttruncated-cone shape, is silvered and firmly

linked to the piston.

This contact technology has the doublepurpose to avoid corrosion in the maincontacts due to the arc and to keep the devicefeatures after a high number of breaks.

Breaking technologies in Sf6. Self-compression



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In the first phase of current break, themain contacts separate, while the springkeeps the pressure over the arc contacts,which remain closed.

This separation of contacts is simply asectioning and works without arc forming.

At the same time, the relative movement

of contacts generates a compression of SF6.




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In the second phase of current break, theseparation of the arc contacts takes placeand an arc appears between them.

The compressed SF6 is released andchannelled towards the zone betweencontacts, sweeping away the arc extremes,rapidly deionisating the zone.

When the current crosses zero, the arcextinguishes.




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Once the arc contacts are separated, an electrical arc is establishedamong them with a temperature higher than 10,000ºK, which keeps thecurrent flow.

During this period, it is essential to evacuate the thermal energy of the arc, given by the network. The evacuated energy will be higher as the gas density and its specific heat increase.

The heat evacuation during the arc duration is obtained mainly by

convection, due to the replacement of a given quantity of hot gas bycold gas.

Due to the high temperatures, an important heat exchange byradiation could be expected.




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During the closing manoeuvre, the

valve rigidly attached to the pistonis opened to allow the gasexchange among the differentparts of the pole, aiding themovement of pieces.




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The empty tubular contacts ease the fast circulation of hot gases andlead to instability in the arc extremes, which avoid the wearing out of arc contacts.

The breaking process by self-compression is especially effective, sinceit works with the injection of a small quantity of gas between contacts.

In the case of a break of 25 kA at 20 kV, the energy to be evacuated is of around 30,000 Jules, which is the energy provided by the arc to keep it at atemperature from 10,000 to 15,000ºK.

1 g of SF6 will be enough to achieve this.

The break by self-compression in SF6 is used in high voltage in outdoor circuit breakers up to 800 kV and in gas-insulated sealed substations(GIS), where the SF6 is used not only as the break medium but also as

the insulator in buses and switches. In medium voltage, the self-compression in SF6 is used in circuit

breakers up to 36 kV.

Extinction chambers with a low consumption of driving energy



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g gy Recent technological advances allow to obtain extinction chambers of

automatic circuit breakers in SF6 which require 40% less mechanicalenergy to disconnect than the former self-compression chambersbased in the pressure generated between a mobile cylinder and a fixedpiston.

The arc extinction is currently achieved by the following effects:

Self-compression.

Arc thermal effect.

Effect of assistance to disconnection by expansion gases, patentedby GEC ALSTHOM.




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CLOSED

POSITION

OPEN POSITIONTHERMAL

EFFECT

BEGINNING OF

DISCONNECTION

EFFECT OF ASSISTANCE

TO DISCONNECTION

g gy Beginning of Disconnection:

The parallel contacts 3 are separated from the mobile contact 4 and

the current is commuted to the arc contacts 7. Thermal Effect:

When the contacts 7 separate, the arc takes place and its energycauses the pressure rise of volume Vt closed by contact bar 8 andinsulating nozzle 9.




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CLOSEDPOSITION

OPEN POSITIONTHERMALEFFECT

BEGINNING OFDISCONNECTION

EFFECT OF ASSISTANCETO DISCONNECTION

g gy Effect of Assistance to Disconnection

When the contact bar 8 exits the throat of nozzle 9, the thermaloverpressure present in volume V

tis released, which creates a blowout

just before the zero crossing of the current, ensuring the arc extinction.

At the same time, the rise of pressure originated close to the arcspreads towards piston 10, exerting a driving force over the mobilesystem, providing the required energy for the manoeuvre in the

disconnection springs.




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g gy The arc extinguishes and the molecules of SF6 dissociated by the arc

are instantly recombined.

The secondary products of the breaking end up deposited in themolecular sieve 11 without affecting negatively the circuit breaker.

In the particular case of breaking weak currents, such as those presentin switching capacitor banks or unloaded lines or transformers, thethermal energy of the arc is too small to generate enough

overpressure. To obtain the adequate blowout of the arc, the classicaleffect of self-compression that takes place in volume Vp is used.

Consequently, these chambers have a blowout that depends on thecurrent to be opened, causing:

Maximum blowout in case of short-circuit currents.

Reduced blowout in case of small currents; hence, the extinction of such currents generates weak overvoltages.

Advantages of the use of Sf6



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g Lack of maintenance.

Electrical and mechanical endurance.

Great reliability Reduced size and weight related to its features

Adaptable to all kind of installations.

Public and industrial networks

Motor switching

Capacitors switching and protection

Reduced prices.

The SF6 appears as a technology favourably applied to the wholerange of electric installations.

Disadvantages of the use of SF6



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g At pressures higher than 3.5 bars an temperatures lower than –40ºC

the gas becomes liquid.

Due to this, in the case of circuit breakers of two pressures, it is required toheat the gas of the extinction chamber to keep the equilibrium at roomtemperatures lower than 15ºC.

The gas is odourless, colourless and tasteless.

In closed places, care should be taken to avoid leaks, since it may provoke

suffocation in personnel by lack of oxygen (due to its higher density, thegas is displaced by air).

In some places it may be convenient to set up extractors that shouldoperate before the personnel entry.

The secondary products of the arc are toxic, and combined with

humidity produce hydrofluoric acid, which attacks porcelain and thecement that seals the nozzles.

Effect of the impurities in SF6



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This impurities come from the manufacturing technique or the depositspollution.

Test most be performed to detect the different impurities specifying thelimits of its content in the gas and the methods to control suchimpurities (see IEC 376).

Nature of impurities

Toxic impurities

Impurities that affect the apparatus security

Impurities that dilute the product

Impurities and odour

Impurities have an unnoticeable effect over the dielectric strength of the sulphur hexafluoride

Breakdown in SF6 circuit breakers



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The main breakdowns in this type of circuit breakers are the gas leaks,which require special devices to be detected.

In a well-installed apparatus, the gas losses should be less than 2% annualof the total volume of the gas inside the apparatus.

In case of total loss of the gas pressure and due to the high dielectricstrength of SF6 the voltage that the contacts can bear when opened isequal to double the phase-to-ground voltage.

Anyways, it is not convenient to operate an SF6 circuit breaker when itspressure has been reduced by a leak and the control circuit should beblocked to avoid an accident.



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High Voltage

Circuit Breakers

Breaker Types

SF6 Dead tank

AGENDA



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GENERAL

Physics of the electric arc



BREAKER TYPES






Maintenance

Driving systems

Tests

SF6 Dead tank circuit breakers



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The design of this type of circuit breakers, called “dead-tank”, consists in three

aluminium tanks mounted ina sole support. Inside thetanks are included SF6breaking chambers.

The switching drives can bemechanical (by springs) or hydraulic for higher voltages,and are located inside acontrol cabin placed in the

circuit breaker support




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The SF6 gas has rated conditions of 6 bars at 20ºC and each SF6chamber has a densimeter associated. The use of SF6 technology insealed chambers causes that this type of circuit breakers requires low

maintenance.

The compact and simple design of the dead-tank circuit breaker considerably reduces the support structure and the space required for itslocation in the installation. Besides, this design allows factoryassembling and testing, noticeably diminishing mounting time andcomplexity.

Another feature to consider is the low level of noise at normal operation,which added to the reduced required space, the low neededmaintenance and the utilisation of non-toxic materials, convert this typeof circuit breakers in an important alternative to diminish visual andenvironmental impact.

The dead tank circuit breakers can be used for rated voltages from 38kV up to 550 kV.




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The dead-tank circuit breakers utilise, in every breaking chamber, theprinciple of “autopufferTH”, which consists in a combined system of blowout, called “pufferTH”, and of self-blast (arc overpressure). Besides,

they add a zip gearing system of double speed. This design turns thebreaking chamber into a compact and relatively small device, whichpermits the breaking of capacitive currents.

There are main contacts and arc contacts, which execute the currentbreak. The main contacts, separated from the arc contacts, open firstand do not endure the arc erosion. By means of this system the dead-tank circuit breakers present the same maintenance requirements anddurability of the conventional circuit breakers.




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When breaking low currents, the circuit breaker utilizes the SF6 blowoutsystem; when breaking high currents, the nozzle design leads to a gasoverpressure in the arc zone when the contacts arc begin to separate.

This overpressure, added to the gearing system of double speed, makespossible the breaking of current using a small amount of energy and asimple mechanical system.

The nozzle design and the zip gearing system of double speed causethat the arc contacts move at double speed, using a small amount of energy. This reduces mechanical stresses, since the speed required tomove the connections and the switching mechanism are cut by half, incomparison with a conventional circuit breaker of the same ratedvoltage.




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Fig. shows a diagram of thebreaking chamber in closedposition, open position and low

and high currents breaking.



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High Voltage

Circuit Breakers

Breaker

Types

VACUUM

AGENDA



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GENERAL




BREAKER TYPES






Maintenance

Driving systems

Tests


Th i th i t l l f d 10 4 t 10 5



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The vacuum, meaning the air at a vacuum level of around 10-4 to 10-5 Pa (10-6 to 10-7 mmHg) reaches a dielectric strength superior to 199kV/cm.

Such exceptional dielectric strength, in addition to the fact that the arcat vacuum presents a quite low voltage (since the electrons releasedby the cathode find no obstacles in their path towards the anode) and

that the dielectric regeneration of the medium is almost instantaneous(since there are not ionised gas molecules between electrodes),motivated the research of the application of vacuum to circuit breakers.




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Even when the technology was

presented around 1920, the firstvacuum circuit breakers were notin the market until 30 years later.

The process of vacuum breakingits quite simple: it is enough to

separate the contacts, in avacuum of 10-4 to 10-5 Pa, tohave a vacuum circuit breaker.

1. Insulating casing

2.

Fixed contact3. Mobile contact

4. Piston rod of mobile contact

5. Insulating guide

6. Metallic membrane

7. Metallic screen


R h fi t i t d t bt i i l ti b ki h b bl



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Research was first oriented to obtain isolating breaking chambers ableto permanently maintain the vacuum, in which inside the contactswould be located.

The contacts should be able to cross the chamber keeping an absolutetightness in the gaskets.


O l d th bl th h i t d t th



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Once solved these problems, the research was oriented to thebreaking technology, based in the two exceptional properties of vacuum:

Its very elevated dielectric strength.

The fast deionisation of the space between contacts after thebreaking.




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The strike of a high-current arc in vacuum entails an unavoidable

vaporisation of the electrodes that rapidly leads to a dynamic pressurebetween contacts that can be equal to the atmospheric pressure.

Initially this arc is alike to that present in other devices, with the particularityof presenting a conductor column strongly concentrated and originating aunique and incandescent cathodic stain, which boiling surface emitsplentiful metallic vapours.




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When the current decreases, the pressure of these metallic vapoursquickly diminishes, due to its fast diffusion towards zones farther from the

arc, condensing over metallic screens positioned with that purpose.




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When the current reaches zero, suchas in the case of the vacuum diode, theelectrons stop travelling through thespace between electrodes; hence, theresistance of this space becomesinfinite, facing a inverse voltage, whilethe anode, now cold, is incapable to

emit electrons when acting as acathode.


The automatic vacuum circuit



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The automatic vacuum circuitbreakers are distinguished by thereduced travel of the mobile contacts

from 15 to 25 mm, according to thevoltage, and by the rather smallswitching energy.

Originally the technology of vacuumbreaking was applied to switches and

medium voltage circuit breakers withlimited functional features.

Recently this technology has beenapplied to automatic circuit breakersup to 36 kV or 50 kV




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1. Fixed contact support

2. Fixed contact terminal

3. Fixed contact

4. Mobile contact5. Insulating body

6. Mobile contact terminal

7. Mobile contact support

8. Angular connecting rod

9. Insulating arm

10. Contact pressure spring

11. Connection trigger

12. Metallic bellows



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GENERAL




BREAKER TYPES

Breaker technologies Oil circuit breakers




Maintenance

Driving systems

Tests

Maintenance of circuit breakers



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The manufacturer must provide information related to the maintenancemeasures to be observed under normal service conditions.

It is desirable that the manufacturer indicates the number of switchings(or time) following which it is convenient to perform the maintenance of the different parts of the circuit breaker.

Besides, the manufacturer must provide the information related to thecircuit breakers inspection after:

A) Short-circuit operation

B) Normal service operation

This information must include the number of switchings according to A) and B) following which the circuit breaker should be checked.




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Main Circuit

Inspection, adjustment and renovation of contacts.

Instructions to measure the transition resistance of the main circuit.

Prescriptions of the admissible wear in the contacts.

Information about the tolerances of opening and closing times.

Oil (or any other liquid) and gas for insulation or extinction of the arc

Samples, tests, drying, filling and/or substitution of the liquid or gas.

Recommendations related to quality and absence of pollution. Indicationof the required quantity of oil or liquid.

Driving mechanism

Maintenance and adjustment Whenever possible during the inspection the circuit breaker must be

operated a few times with the assistance of the drives, to ensure that thedrive mechanism operates smoothly and that everything works correctlybefore the start off of the circuit breaker .


Control circuits auxiliary circuits auxiliary equipment



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Control circuits, auxiliary circuits, auxiliary equipment

Verification of coils, relays, interlocking gears, adjustable electrical

devices, heating and drying devices. Bearings and similar pieces

Indication in the instructions of the parts to verify.

Connections

Indication in the instructions of the points to verify Compressed air and hydraulic systems

Verification of the pneumatic and hydraulic valves. Inspection andsubstitution of joints. Instructions to inspect the inner of the pressurizedcontainers regarding pollution, periodical inspection and substitution of the

air-drying devices and humidity absorption. It is advisable to periodically open the purge valve of the air containers to

eliminate condensed water .


Resistances and capacitors



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Resistances and capacitors

Verification of resistances and capacitors. The allowed tolerances must beindicated.

Lubrication and greasing

Specification of the quantity of oil and grease

Cleaning

Instructions regarding the cleaning methods. It is recommended to indicate that the insulating parts should be treated

with special care and in case of abnormal conditions, such as salinedeposits, cement powder or acid vapours, it might be needed to cleanfrequently in order to avoid possible flashovers

Spare parts and materials List of spare parts and materials that should be stored (in warehouse).

Special tools

List of special tools required to assembly or inspection (when not providedwith the circuit breaker).

Maintenance of circuit breakers. Low oil content

Each delivery of circuit breakers includes detailed instructions



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Each delivery of circuit breakers includes detailed instructionsregarding their assembly, start off and maintenance.

Care should be taken that the circuit breaker, the driving mechanismand the steel structures fit perfectly among them, in order to reduce tominimum the on-site labour.

The assembly consist mainly in place in-site the different pieces and fitthem together with bolted joints.

Manufacturers recommend to perform maintenance in the circuitbreaker after 12 to 16 years of service.

Before that it is advisable to check the bolted joints and lubricate themobile parts every 2 to 4 years.

The conditions of the contacts should be checked after switching under loads up to 10 times the short-circuit current.

The maintenance of the circuit breaker must be easily performed on-site.

The instructions should carry complete information about inspection andmaintenance.

Maintenance of circuit breakers. SF6

For the circuit breaker to require slight maintenance it is



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For the circuit breaker to require slight maintenance, it isindispensable that its extinction chamber is very simple and has fewmobile pieces.

The secondary products of decomposition that do not completelyrecombine precipitate as metallic fluorides, or deposit in a static filter thatalso absorbs the residual humidity. This diminish the maintenance costs.

The inspection of circuit breakers must be performed considering the

accumulated value of the interrupted currents, the number of switchings executed and the time in operation.

The following criteria are valid as guiding values:

An inspection should be performed, at least:

Every ten years

After 2,000 switching cycles or

After breaking an accumulated short-circuit current of 600 kA.

Maintenance of circuit breakers. SF6

In the inspection a diagnosis measurement is



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In the inspection a diagnosis measurement isperformed with the extinction chamber closed,besides general works such as visual control,check of the high and low voltage joints andverification of all screws in the rack.

Thus, it should be checked:

Operation times.

Transition resistance of the main breakingspace.

Absorbed currents of the driving coils.

Humidity content and acids concentration inSF6.

Gastightness of the SF6 enclosures and thedriving system.

Maintenance of circuit breakers. Extinction chamber Chamber disassembly



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Chamber disassembly

When the resistance between terminals is high it is time to repair thechamber. If there is a spare chamber stored, it can be completely replaced.

To disassembly the chamber the gas must be drained through the fillingvalve or to the atmosphere until the pressure is equal to 1 bar.

If the gas is drained to the atmosphere, it is required to use mask and rubber gloves, because the used gas might content harmful decompositionproducts.

Substitution of the fixed contact

It is performed with the pole in open position. The screws that joint thecontact to the terminal plate must be removed. It can be entirely replaced or,in case of slight deterioration, it can be cleaned with fine sandpaper.

Substitution of the mobile contact It requires the disassembly of nozzles and arc contacts, and then the

dismounting of the crown of the mobile contact.

Driving maintenance

It involves the substitution of the closing/opening valves of compressed air.

AGENDA

GENERAL



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GENERAL




BREAKER TYPES





Maintenance

Driving systems

Tests

Driving systems of circuit breakers



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1. .Driving axle

2. .Opening spring

3. .Dampening device

4. .Dragging spring5. .Tie rod

6. .Gearing

7. .Holding arm

8. .Striker

9. .Cam

10. .Striker damper

11. .

Free tripping device12. .Closing coil

13. .Tie rod

14. .Free tripping device

15. .Sudden tripping device

16. .Closing springs

17. .Opening coil

18. .Coupling bar

19. .Motor 20. .Dragging spring

21. .Star

22. .Tightening axle

23. .Dragging arm

24. .Dragging arm

Driving systems of circuit breakers



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The main driving systems are the following:

By energy accumulation.

By compressed air.

By pressurized liquid.

In this system, the closing drive has a previously accumulated energy,

Driving systems of CB. Energy accumulation



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y , g p y gy,by means of a manually tightened spring or an electrical motor.

This device consist in powerful springs that accumulate the energyrequired for the connection. With this purpose they are tightenedmanually with a lever or by an electrical motor.

This drive always operate with a constant closing force, since during theclosing manoeuvre is totally independent from any external source of

energy. Besides, the closing can not start until the springs are totally tightened.

Given that the energy is stored in the springs before the closing manoeuvre,the tightening mechanism requires a moderated power, even when theclosing force has to be high and the closing, fast.

After any closing manoeuvre, the springs are automatically tightened again;hence, the mechanism is always ready to operate immediately, after anopening manoeuvre.

The closing manoeuvre is rapidly started by a




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g p y ysudden impulse, moderately strong, sent tothe closing coil, and is always completed with

any impulse duration. A voltage drop in the driving conductors or a

total lack of driving voltage have no effect over an already-started manoeuvre.

The springs of the closing mechanism can

also be tightened by a lever.

The driving voltage can be either DC or AC.

The driving mechanism can be combinedwith a simple relay set for the fast automatic

reclosing, with a minimal dead time up toonly 0.3 seconds.

The springs store elastic energy and are capable to return it without




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p g gy plosses from the moment of storing it until it has to be released.

Consequently, the energy to connect and disconnect is always ready to be

used according to the demands of the operation or protections of theelectrical system.

It is evident that, if a system of energy storage has no losses, it is notrequired any surveillance system about the storage.

The loading of the energy required for the switchings is obtained byelectrical or mechanical means. In case of emergency, the mechanicaldrives allow to manually storage the springs energy.

The energy is transmitted towards the mobile contacts (between whichthe arc is established and extinguished) by means of secure mechanical

transmissions. During the circuit breaker assembly, there is no need to connect

pressurized fluids tubes, valves or any other element for the driveservice. All that is required are electrical connections.

The driving system can be manually

Driving systems of CB. Compressed air

ecur y anometer



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g y ycommanded directly by means of avalve or an electric valve.

The connection of the circuit breaker isperformed very rapidly usingcompressed air.

The disconnection springs are tightenedduring the connection manoeuvre, thismeans, the compressed air is solelyused to connect the circuit breaker.

The driving device is activated by avalve that operates during connectionand that can be open manually or bymeans of an electromagnet, remotely.

ecur yvalve

anometer

Deposit of air

Drain valve

Holdingvalve

Compressor Motor

Pressure relay

FOR UNIPOLAR CIRCUIT BREAKER

The electrical command of connection is transmitted to the coil of the




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driving valve "CON" (4). The outlet for air evacuation (5) in the valve"CON" is closed; the compressed air can directly pass from the

pressurized deposit (3) to the driving through a tubular joint. The driving piston (7) moves from position "DES" (O) to position "CON"

(C) and the circuit breaker is connected.

1. SF6 enclosure

2. Driving bar

3. Pressurized deposit

4. Driving valve "CON"

5. Outlets for air evacuation

6. Driving valve "DES"

7. Driving piston

8. Driving cylinder

9. Auxiliary circuit breaker with position indicator

All drives are equipped with two disconnection coils "DES" independent




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from one another.

The disconnection command is electrically transmitted to the coils of thedriving valve "DES" (6). Trough the open valve "DES" the compressed air arrives to the driving of the circuit breaker pole. Simultaneously the outletfor air evacuation (5) is closed in the valve "DES" and the driving valve"CON" (4) is retained pneumatically-mechanically using a blockingsystem. The driving piston (7) moves from position "CON" (C) to position

"DES" (O) and the circuit breaker is disconnected.1. SF6 enclosure

2. Driving bar

3. Pressurized deposit

4. Driving valve "CON"

5. Outlets for air evacuation

6. Driving valve "DES"7. Driving piston

8. Driving cylinder

9. Auxiliary circuit breaker with position indicator

The pressurized liquid most commonly

Driving systems of CB. Pressurized liquid



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used is oil. The highly pressurized oilcirculates through a closed circuit. The

high pressure is provided bypressurized nitrogen.

The use of gastight gaskets at highpressure in the connected positionallows removing the mechanical

holding devices (interlocking triggers). The piston rod of the mobile contact is

directly coupled to the receivingdevice; hence, the intermediatemechanisms disappear, eliminating

any mechanical link.

Connection




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The coil 14 opens the valve 1 and thepressure of the accumulator 11 passes

to piston 10, which closes valve 2 andopens valve 3.

When opening valve 3, the pressuregoes through piping 7 to valve 5.

The high pressure passes to receiving

piston 20, which leads the mobilecontact to its connected position,compressing the springs M.

Disconnection




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When the coil 15 opens the valve 6, the highpressure over piston 10 disappears, the valve

2 is opened and the valve 3 is closed,removing the high pressure in piping 7. Thevalve 5 is opened, emptying piston 20 to thedeposit 22 through the piping 8, by means of the spring M that activates the mobile contact17 to its disconnected position.

A surveillance pressure relay automaticallyconnects and disconnects the pump-and-engine set that keeps the pressure in theaccumulators between normal levels.

Another pressure relay blocks the operationof the circuit breaker when the pressuredescends below the admissible level. Theconnection interlocking works under apressure higher than the disconnectioninterlocking, so any connection manoeuvre

can be followed by a immediate

The following table shows a statistic analysis performed in the Mexicant k

Driving systems of CB. Reliability



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network.

It can be clearly observed that the failure level for the circuit breakerswith spring-based drives is inferior to the failure level for circuit breakerswith other kinds of drives.

Type of 400 kV 230 kV

drive Nº interruptions Nº failures Nº interruptions Nº failures

Pneumatic 87 26 (29,8%) 131 31 (23,6%)

Hydraulic 50 24 (48%) 191 16 (8,4%)

Springs (1) 47 2 (4,25%) 100 0 (0%)

Oil-pneumatic 46 5 (10,8%) 25 0 (0%)

AGENDA

GENERAL



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GENERAL




BREAKER TYPES





Maintenance

Driving systems

Tests

The type tests comprise:

Tests on high and medium voltage circuit breakers



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Mechanical behaviour.

Mechanical operation.

Heating of any of the parts does not exceed the specified limits.

Insulation is according to the specified limits.

Capability to establish and break the short-circuit currents.

Capability to endure its permissible rated short-time current.

Capability to break currents on unloaded cables.

Capability to break currents on capacitors banks.

Capability to break small inductive currents.

The results of all type tests are recorded in type tests registries that

contain all required data to demonstrate its compliance to standards.They also include the data needed to identify the essentialcharacteristics of the tested automatic circuit breaker.

Each of the type tests should be performed on a new and cleanautomatic circuit breaker, and the different type tests can be carried out

in diverse times and laces

The mechanical tests exclusively comprise the execution of f i / l i ith t lt t i th i

Mechanical Tests on circuit breakers



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manoeuvres of opening/closing, without voltage or current in the maincircuits.

Usually, 1,000 switching cycles are carried out, 10% of them are carried outbased on opening/closing cycles.

The opening is driven by closing the main contacts, being the circuit breaker equipped with its usual switching device.

In these manoeuvres the heating of the electrical components shouldnot exceed those specified by the standards.

During this test lubrication is allowed, but mechanical adjustments arenot.

After the test, all pieces must be in good condition and must not present

excessive wear-out. Any permanent deformation that could be present in the mechanical

parts must not negatively influence the circuit breaker operation; neither impedes the correct placement of the spare parts.

One of the main features of switchgear is the insulation level, defined byth l f i l f ith t d lt d i l

Dielectric Tests on circuit breakers



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the values of nominal power-frequency withstand voltage and nominallightning withstand voltage and, in switchgear for 300 kV or higher, by

the value of nominal switching withstand voltage. The standards set the effective (rms) values and the peak values in kV

for the test (nominal) voltages, as a function of the most elevatedvoltage of the material.

The voltage will be applied as following:

Dielectric Tests on circuit breakers.



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Closed position:

Among all parts of the main circuit of each pole and the frame,successively. All parts of the main circuit of the rest of the poles (if any)have to be connected to the frame.

Open position:

Among all parts of the main circuit of all poles connected among

themselves and the frame. Between the terminals of each pole successively and the frame, being

all parts of the main circuit of the rest of the poles (if any) connected tothe frame.

Between the terminals of a side connected among themselves and the

terminals of the opposite side connected among themselves and theframe. The tests will be repeated inverting the connections that link theterminals with the source and the frame, unless the distribution of theterminals of a pole is symmetrical regarding the frame.

They lie on subjecting the circuit breakers to shock waves of 1.2/50 µs.

Dielectric Tests on circuit breakers. Shock waves



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During each test, five consecutive shock waves are applied.

It is considered that the automatic circuit breaker complies the test if duringwhich neither strikes nor punctures take place.

If some puncture or two or more strikes take place, it is considered that thecircuit breaker does not comply the test.

If only one strike takes place, ten additional shock waves will be applied,and it will be considered that the circuit breaker complies successfully thetest solely if during the additional applications neither strikes nor puncturestake place.

The circuit breaker must be capable to comply the specified tests withvoltages of positive and negative polarity, even when it is enough tocarry out the test with one polarity if it is evident that such polarityresults in a lower strike voltage.

The test voltages are usually obtained by means of a pulse generator,composed by a given number of capacitors all equal that are

Dielectric Tests on circuit breakers. Shock waves



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composed by a given number of capacitors, all equal, that aresimultaneously charged in parallel through some resistances, using a

source of direct voltage (DC), and are later discharged in series througha circuit that includes the tested device (Marx Principle).

The DC voltage is generally obtained from an alternate voltage source,at 50 Hz, by means of metal rectifiers, until a spark is generated in thespark-gaps “e”, all regulated at exactly the same distance, which is

related to the voltage to be applied to the device.

The test voltage will be raised to the given value and will be maintainedby one minute It is considered that the circuit breaker does not comply

Dielectric Tests on circuit breakers. Power freq.



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by one minute. It is considered that the circuit breaker does not complythe test if during which some strike or puncture takes place.

In the test, the voltage reached in the test circuit must be stable enoughso as not to be affected by the leakage current variations or by partialdischarges or pre-discharges.

This condition is complied if the total capacitance of the tested device(including the additional capacitances of the circuit) is not higher than1,000 pF, and the value of the current permanently delivered by thetransformer when the device is short-circuited at test voltage is notlower than 1 A (rms value).

In the resonant circuit, the stability of the resonance conditions and theconstancy of the value of the test voltages depend on the constancy of the circuit impedances and the frequency of the source.

It must be ensured that the device and its main circuits do not becomeexcessively hot when the rated current is circulating through them

Heating Tests on circuit breakers.



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excessively hot when the rated current is circulating through them.

The test must be performed over a new device, with clean contacts.

Before carrying out the test, the ohmic resistance of the main circuitsmust be measured.

The test must be performed causing the circulation through all poles(with the exception of high voltage switchgear higher to 72.5 kV, in

which only one pole is tested) of the rated current at steady state and atpower frequency if it is AC, during a time range enough for the heatingto be constant (when the variation does not exceed 1ºC by hour).

For other conductors than those of coils, the tª of the different parts willbe measured using thermometers or thermocouples located in the

Heating Tests on circuit breakers.



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be measured using thermometers or thermocouples located in theavailable hottest point.

For the opening and closing coils that are excited solely during theopening and closing manoeuvres, the heating test consists in feedingthese coils at their rated voltage ten successive times with a 2 s intervalbetween the excitation instants, supposing the circuit breaker has anautomatic device to open the control circuit at the end of the

manoeuvre, or feeding them ten successive times during 1 s being 2 sthe interval between excitations.

To perform the heating test an adjustable alternate current source isrequired (exceptionally a DC source) with a capacity equal to the ratedcurrent of the tested switchgear. The pertinent measurement devices

are also required: voltmeters, ammeters, millivoltmeters, double bridge(Thomson), thermometers, thermocouples, low voltage or very lowvoltage transformers, etc.

The rated transient recovery voltage (TRV) for terminals failure,associated to the rated short-circuit breaking capacity is the

Short circuit Tests on circuit breakers. TRV



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associated to the rated short-circuit breaking capacity, is thepredictable limit voltage of reference of the circuits that the circuit

breaker must be able to clear in case of a terminals short-circuit. The waveform of the TRV changes accordingly the configuration of the

real circuits.

In networks with rated voltages higher than 100 kV and for importantshort-circuit currents (with respect to the maximum short-circuitcurrent), the TRV presents an initial period during which the risingspeed is high and a subsequent period during which such speed isreduced.

This waveform is well-enough defined by means of an envelopeformed by three straight-line segments determined by four parameters.

Before accomplishing the tests of breaking capacity and makingcapacity it is required to carry out several switchings under no load

Short circuit Tests. Breaking and making cap.



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capacity, it is required to carry out several switchings under no load,during which the accurate operation of the automatic circuit breaker will

be verified and the travel speed, closing time and opening time will beregistered.

The generated overvoltages will not exceed the maximum admissibleand external flashover will not take place.

If the automatic circuit breaker has an electrical drive, these tests mustbe performed feeding the closing device at 105% and 85% of the ratedvoltage of operation of the drive.

In case of air-compressed or pressurized oil drives, the tests must beperformed at minimum pressure with the shunt triggers fed at 85% therated voltage of operation and repeated at nominal pressure at 100%the rated voltage of operation and at maximum specified pressure at110% the rated voltage of operation.

In case of energy accumulation drives (springs), the tests must beperformed with the shunt triggers fed at 110% and 85% the rated

voltage of operation

During the tests of breaking and opening inside the given limits of breaking capacity and making capacity the circuit breaker must not

Short circuit Tests. Breaking and making cap.



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breaking capacity and making capacity, the circuit breaker must notpresent exaggerated signs of wear-out neither risk the operator

integrity. After every sequence of tests, the mechanical parts and their insulators

will be practically in the same conditions that before the tests. After thesequence of the short-circuit test, the automatic circuit breaker will becapable to close and open its steady state rated current at rated

voltage, admitting that its possibilities to open and close the short-circuit current will be considerably reduced after the tests.

It is considered that a circuit breaker does not comply the sequence of short-circuit tests if the damages in the main insulation (that issubjected to electrical stresses under normal operation conditions)

alter its insulating condition at rated voltage. The fundamental short-circuit tests in the high voltage automatic circuit

breakers consist in a series of five basic sequences of short-circuittests.

They have the purpose of evidence the imperfections of the material or the manufacturing that would alter the properties and quality of the

Individual tests in circuit breakers



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the manufacturing that would alter the properties and quality of thetested device.

They are acceptance tests performed over a given number of samplesto determine by negotiation between the manufacturer and the user.

The test site can be the installation site of the apparatus.

These tests consist on:

Voltage tests at power-frequency. Voltage tests of the driving and auxiliary circuits.

Measurement of the resistance of the main circuit.

Tests of mechanical sequence operations.

The routine tests are performed in all circuit breakers. During thesetests the circuit breaker is connected to its driving mechanism without

Routine tests in circuit breakers



n o l o g y

tests, the circuit breaker is connected to its driving mechanism withoutsupport and switching insulators. The inertia of the switching insulators

is compensated mounting special weights with equivalent inertiasbefore the test.

The routine tests include the following operations:

Adjustment of the driving mechanism.

Measurement of the limit values of the drive voltage and the motor voltage.

Voltage test of the drive circuits

Verifying the times of opening and closing, the speeds of opening andclosing, and the dampening in the final position of the contacts.

Pressure tightness tests to each breaking unit. Measurement of the resistance of the main path of current.

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