circuit breaker application & distribution systems - 2014

ABB Group March 12, 2014 | Slide 1

Lionel Ng, LPBS - Low Voltage Products

Welcome Technical Sharing Session


Lionel Ng, LPBS - Low Voltage Products, 2014

Electrical Installation Circuit Breaker Selection

As to be able to protect LV/MV transformers LV side, we must mainly

take into account:

Rated current of the protected transformer, LV side, from which

the rated current of the circuit breaker and the setting depend on

(In);

The maximum estimated short circuit current in the installation

point which defines the minimal breaking power of the protection

circuit breaker (Isc).

Protection of Transformers

Sn

In

Isc

U20

Protection of Transformers Switchboards with one transformer

The rated current of the transformers LV side is defined by the

following expression

where

Sn = rated power of the transformer [kVA]

U20 = rated secondary voltage (no load) of the transformer [V]

ln = rated current of the transformer, LV side [A]

In = Sn x 103

3 x U20

The full voltage three-phase short circuit current immediately after the LV

side of the transformer can be expressed by the following relation once we

suppose infinite power at the primary:

where

Ucc % = short circuit voltage of the transformer [%]

ln = rated current, LV side, [A]

lsc = three-phase rated short circuit current, LV side, [A]

Isc = In x 100

Ucc %


The short circuit current is normally lesser than the deduced value if

the circuit breaker is installed at a certain distance by means of a cable

or bar connection, according to the connection impedance.

Circ

uit b

reaker B

I1 I2 I3

1 2 3

Isc2 + Isc3

Isc1 + Isc2 + Isc3

I4 I5

Circ

uit b

reaker A

Isc1

Protection of Transformers Switchboards with more than 1 transformer in Parallel

As far as the calculation of the rated current of the transformer is

concerned, the rules beforehand indicated are completely valid.

The minimum breaking capacity of each circuit breaker LV side must be

greater than the highest of the following values: (the example refers to

machine 1 of the figure and it is valid for the three machines in parallel):

lsc 1 (short circuit current of transformer 1) in case of fault

immediately downstream circuit breaker 1;

lsc2 + lsc3 (short circuit currents of transformer 2 and 3) in case of

fault immediately upstream circuit breaker 1;


Circuit breakers l4 and l5 on the load side must have a short circuit

capacity greater than lsc1 + lsc2 + lsc3; naturally every transformer

contribution in the short circuit current calculation is to be lessened by the

connection line transformer - circuit breaker (to be defined case by case).

The choice of the circuit breakers for switching and protection of cables

means the perfect knowledge of:

rated operating line current lB

max admissable cable current lZ

presumed short circuit current in the point of installation of the circuit

breaker Icc

Protection of Cables

The correct circuit breaker must be selected to satisfy the following

conditions:

It must have a short circuit breaking capacity (lcu or eventually lcs) greater

or equal to the short circuit current lcc

It must use a protection release so that its overload setting current ln (l1)

satisfies the relation lB < ln < lZ (Oveload protection)

The let through energy (l2t) that flows through the circuit breaker must be

lesser or equal to the maximal one allowed by the cable (KS) (Short-

circuit protection)


It

Icc

Cable KS

Circuit breaker It

Icc max


As far as the verification required by IEC 60364, according to which

the overload protection must have an intervention current (lf) that

assures the operation for a value lesser than 1.45 lz (lf < 1.45 lz), we

must state that it is always verified for ABB Circuit breakers, since

according to IEC 60947-2 the required value is less than 1.3 ln.


LV protection devices

L function protection against

overload

Circuit Breaker Curves

S function protection against

delayed short-circuit





I function protection

against instantaneous

short-circuit



G function protection

against earth-fault

A

B

C

Protection of Primary & Secondary Distribution

Selective Protection

The example emphasizes the need for co-

ordination between circuit breakers A and

B, such that in case of fault in C, only circuit

breaker B trips, thus leaving complete

continuity to the rest of the plant supplied

by the circuit breaker A.

Selectivity might be Total or Partial:

Total selectivity: only the circuit breaker B

trips for every current value lesser or equal to

the max short circuit current foreseen in C;

Partial selectivity: the circuit breaker B opens

only according to fault current lower than a

certain value; values that are equal or greater

than this will give the intervention of both

circuit breakers A and B.

Amperometric (Current) selectivity is obtained

by setting on different values the

instantaneous tripping currents of the circuit

breakers chain (greater values for upstream

circuit breakers)



A B

ImB ImA

ImA is the selectivity limit

Chronometric (Time) selectivity is obtained by

introducing intentionally always greater delays in

the intervention tripping timings of the upstream

circuit breakers in the chain.



Total selectivity

B A

t

Switchboard A

Switchboard B

400V

400V

2500 kVA

(fault current 57,5 kA)

E2N20 MS (disconnector)

E4S40

with PR121

E2N20

with PR121

T5H 630

with PR222


A

B

C


Back-up Protection

In the figure, the circuit breaker B, downstream in respect

with A, might have a short circuit breaking capacity lesser

than the presumed short circuit current in case of fault in

C if the circuit breaker A satisfies at all the two following

conditions:

It has a short circuit rating greater or equal to the

presumed short circuit current in its installation point and

obviously greater than the short circuit current in C

In case of fault in C with short circuit values greater

than the short circuit breaking capacity of circuit breaker

B, the circuit breaker A must limit the let through energy

by limiting it to a correct value than can be stood by

circuit breaker B and by the protected lines

The back-up protection is used in electric plants where operation continuity

is not a main need. This means that the up stream breaker will always trip

with or without the help from the down stream protection device. This

means the whole system including the sound parts of the installation will

be without power.

This co-ordination solution is used by those who need to contain the plant

costs by reducing the general performance in case of a fault.


Back-up Protection

U Load

B

A

Ib = 1300 A

Icc = 65 kA

Icc 30 kA

Ib = 300 A


Back-up Protection

Electrical characteristics of the employed circuit breakers

Reference Rated Type Rated Breaking Selectivity Back-up

current uninterrupted capacity limit limit

current

[A] Iu [A] Icu [kA] [kA] [kA]

A 1300 SACE Emax E2L16 1600 130

B 300 SACE Tmax T4N 320 320 36

36 (T) 65

50 kA !!!

T4S 250

T1N 160 * T1N 160 is 36 kA only mccb


Back-up Protection

T6H 800 (70kA)

70 kA

T4H 250 (70kA)


Selectivity

Rated operational voltage Ue: the value of voltage which

determines the application and to which all the other

parameters are referred to.

Rated uninterrupted current Iu: the value of current which the

device is able to carry for an indefinite time. It defines the size

of the CB

Rated current In: the value of current which characterizes the

protection release installed. Is often related to the rated

current of the load protected

T5N400 PR221DS-LS/I In 320

Iu In

Selection of Protective Devices Main electrical parameters

Rated ultimate short-circuit breaking capacity Icu: it is the

r.m.s. value of the symmetrical component of the short-circuit

current which the circuit-breaker is able to break (test cycle O-

t-CO)

Rated service short-circuit breaking capacity Ics: it is the r.m.s.

value of the symmetrical component of the shortcircuit current

which the circuit-breaker is able to break (O-t-CO-t-CO)


Icu


Rated short-circuit making capacity Icm: it is the maximum

prospective peak current which the circuit-breaker must be

able to make Icm=n x Icu


Icu 36kA Icm 75.6 kA @415V


Rated short-time withstand current Icw: it is the r.m.s. value of

the alternate current component which the circuit-breaker is

able to withstand without damages for a determined time,

preferred values being 1s and 3 s

Defined for category B only


Generalities about the main electrical parameters Dont forget

Ue Un Icu or Ics Ik Icm Ip

Ue, Icu, Ics, Icm?



Lionel Ng, Low Voltage Products, 2014

Distribution systems Protection against indirect contact and earth fault

Agenda

Main definitions

Distribution systems and protection

against indirect contact and earth fault

ABB solutions for protection

against earth fault

Discrimination of the protections

against earth fault

Definitions

Indirect contact

Electric contact of persons with exposed-conductive-parts which have become live under fault condiction (deterioration)

Direct contact

Electric contact of persons with live parts

Definitions

Earth fault

The loss of insulation between normally live conductors and exposed-conductive-parts may generate a earth fault

Main causes of the loss of insulation:

time decay of dieletric properties

mechanical breaking

particularly aggressive environments

rodent action

overvoltages of atmospheric origin or due to switching

Definitions

Main effects of the earth fault current

energizing of exposed-conductive-

parts

localized electric arcs and consequent

overheatings

disturbances to telecommunication systems

erosion phenomena of earth electrodes

Definitions

Time-current zones of the effects of alternating current on the human body

A contact with a live part causes the flowing of current through

the human body, the danger of this current depends on its :

duration

size

Reversible pathological effects

No reaction

No physiological effect

Fibrillation risk greater than

50%

1

2

3

4

Definitions

Live part

Conductor or conductive part intended to be enegized in normal operation

Including a neutral conductor

By convetion not a PEN.

Exposed-conductive-part

Conductive part

Can be touched

Is not normally live

Can become live when basic insulation fails

Definitions

Basic insulation

Isolation of live part

Base protection against direct and indirect contact

Supplementary isolation

independent insulation applied in addition to basic insulation

Insures the protection when the basic insulation fails

Double isolation

comprises both basic insulation and supplementary insulation

Reinforced insulation

provides a degree of protection against electric shock equivalent to double insulation (unique insulation)

Fault current current which flows across a given point of fault resulting from an insulation

fault

Definitions

Live part

functional isolation: in an electrical device it insulates the parts at different potentials thus enabling operations

basic insulation is the insulation of the normally live parts

supplementary insulation is applied in addition to basic insulation in case of a failure of the last

reinforced insulation, a unique insulation which can guarantee the equivalent protection degree which can be provided by basic insulation plus supplementary insulation

Double insulation: comprises both basic insulation and supplementary insulation

+

Definitions

Reference earth

part of the Earth considered as conductive, the electric potential of which is conventionally taken as zero

Earth electrode

conductive part, which may be embedded in a specific conductive medium, e.g. concrete or coke, in electric contact with the Earth

Earthing resistance

resistance between the main earth collector (or node) and the Earth

Definitions

L1

L2

L3

N PE

Protective conductor PE

conductor provided for purposes of safety (protection against electric shock)

it connects:

exposed-conductive-parts

main earth collector (or node)

earth electrode

earthed point of the source or artificial neutral

PEN conductor

combines the functions of both a PE conductor and a neutral conductors

Residual current:

vectorial sum of the values of the electric currents in all live conductors

Id = IL1+ IL2+ IL3+ IN

Classification of electrical distribution systems

Protection against indirect contact

Protection throught automatic disconnection :

CBs with thermomagnetic or electronic releases;

CBs with electronic releases with G function against earth fault

CBs with residual current devices integrated

Residual current circuit breaker

Residual current releases

protection without automatic disconnection:

Protection by double or reinforced insulation;

Protection by earth-free local equipotential bonding;

Protection by electrical separation for the supply of only one item of current-using equipment

Protection by electrical separation for the supply of more than one item of current-using equipment


The IEC 60364-3 classifies the electrical systems with the combination of two letters

The first letter indicates the relationship of the power system to earth

T direct connection to earth of one point

I all live parts isolated from earth or one point connected to earth through an impedance

The second letter indicates the relationship of the exposed-conductive- parts of the installation to earth

T direct connection to earth

N direct electrical connection of the exposed-conductive-parts to the earthed point of the power system


Subsequent letters, if any, indicates the arrangement of neutral and protective

conductors

S neutral and protective functions provided by separate conductors

C neutral and protective functions combined in a single conductor (PEN

conductor)

PE N

PEN


TT system

the neutral and the exposed-conductive-parts are connected to

earth electrodes electrically independent


TT system

The earth fault current returns to the power supply node through the soil


TT system

The exposed-conductive-part assumes the potential UT = Ik RA

The person touching the exposed-conductive-part is subjected to the voltage UT

Ik


Condition to be fulfilled :

Ra is the total resistance of the earth electrode and of the protective conductor of the exposed-conductive-parts

IDn is the rated residual operating current of the residual current circuit- breaker

the time defined in the following table for the terminal circuits with a rated current In32A

0UIR na D


Thanks to a more sensitive residual current device, from a pratical point of view it will be easier to realize an earthing system coordinated with the characteristics of the device itself. This table shows the maximum values of earth resistance which can be obtained with residual current devices and making reference to a common environment (50V)

toroid

trip coil

test button

main contact

resistance

electronic circuit (if any)

How an RCD works

How an RCD works

How the RCD works

TEST



Zs is the total impedance of the loop;

Ia is the disconnection current in these time:


0UIZ as

Conclusion about TT system

Domestic installations and similar, small industries with LV power supply

Typical value of earth fault currents 10 ~ 100A

The standards allow the use of:

CBs with inverse time tripping characteristics

CBs with instantaneus tripping characteristics

Residual current devices

If automatic disconnection cannot be obtained in compliance with the disconnection times of the table or within the conventional time, it shall be necessary to provide supplementary equipotential bonding connnected to earth, however the use of supplementary protective bonding does not exclude the need to disconnect the supply for other reasons, for example protection against fire, thermal stresses in equipment



TN-S system

the neutral and the exposed-conductive-parts are connected to the same earthing arrangement

the exposed-conductive-parts are connected to the earth electrode by means of the PE

N

PE


TN-C system

the neutral and the exposed-conductive-parts are connected to the same

earthing arrangement

the exposed-conductive-parts are connected to the earth electrode by

means of the PEN

PEN


TN system

the earth fault current returns to the power supply node without practically

affecting the earth electrode

the current is limited by the impedance of the fault loop


TN system

It is necessary to interrupt the fault because person touching the exposed-conductive-part is subjected to the voltage UT



Zs is the impedance of the fault loop

U0 is the nominal voltage to earth

Ia is the diconnection time in ampere of the protective devices within:


0aS UIZ


TN system: example

Un = 400 V (U0=230V)

This system supplies a terminal circuit with In>32A

Earth fault = 3 kA


Conclusion about TN system:

Industries and big installations with MV power supply

Fault current values similar to those of the single-phase fault

The standard allow the use of:

Automaic devices against overcurrents

RCD or CBs with G function

In the TN-C systems disconnection of the neutral and use of the residual current devices or devices with similar operating principle (function G against earth fault) is not possible

if automatic disconnection cannot be obtained in compliance with the disconnection times of the table or within the conventional time, it shall be necessary to provide supplementary equipotential bonding connected to earth, however the use of supplementary protective bonding do not exclude the need to disconnect the supply for other reasons, for the example protection against fire, thermal stresses in equipment


Why in TN-C system it is not possible to use RCD or

function G against earth fault?

TN-S

TN-C


IT system

has no active parts directly earthed

may have live parts connected to earth through high value impedance

the exposed-conductive-parts are connected to an independent earth electrode


Dieletric insulator+air

Electric field

Plate

Plate area

IT system

The earth fault current returns to the power supply through the earthing arrangement of the exposed-conductive-parts and the capacities to earth of the line conductors

the fault current value depends on the size of the installation

capacities to earth of the line conductors

capacitor

cable

plate area

dielectric insulator+air

plate area

electric field

electric field

plate area

plate area

dielectric



IT system

the automatic disconnection of the circuit is not necessary

condition to be fulfilled:

RE is the sum of the resistance, in ohms, of the earth electrode and protective conductor for exposed-conductive-parts;

Id is the fault current, in amperes, of the first fault of negligible impedance between a line conductor and an exposed-conductive-part; such value takes account of the leakage currents and of the total earthing impedance of the electrical installation

an insulation monitoring device shall be provided to indicate the presence of

fault.

VIR dE 50


IT system

the occurrence of a first earth fault modifies the distribution system

two situations may occur in the event of a fault to earth


according to TT system

IT system

in the event of a second fault, the supply shall be disconnected


according to TN system

IT system

in the event of a second fault, the supply shall be disconnected

Neutral distribuited:


a

sI

UZ

2a

sI

UZ

2

0'

Neutral not distribuited:

U0= is the nominal voltage between line conductor and neutral conductor

U = is the nominal voltage between line conductor

Zs = is the impedance of the fault loop comprising the line conductor and the protective conductor of the circuit

Zs= is the impedance of the fault loop comprising the neutral conductor and the protective conductor of the circuit

Ia = is the current causing the operation of protective device within the time required for TN system


Conclusion about IT system:

chemical and petrochemical industries, i.e. plants for

which service continuity is fundamental

fault currents A ~ 2A dependent on the size of the

installation

system suitable for the cases in which service continuity

must be assured

The presence of a first fault does not cause high current and/or currents dangerous for the people

A reliable and safe protection is realized by combining:

The protection functions against overcurrent with those against earth faults

An effective earthing arrangement

This choice allows to obtain:

Protection against indrect contact

A timely protection against earth falts of small value where prevention from fire risks is absolutely necessary

Protection Solution

Protection Solution

For an adequate protection against earth faults ABB has designed the following product categories:

Miniature circuit breaker

Residual current operated circuit-breakers with integral overcurrent protection DS201 & DS202;

Residual current operated circuit-breakers with integral

overcurrent protection DS200;


overcurrent protection DS800

Residual current blocks DDA200

Residual current blocks DDA 60, DDA 70, DDA 90 (S290)

Residual current blocks DDA 800

Residual current circuit breaker F200

Protection Solution

Miniature circuit-breaker



Protection Solution




Protection Solution


Residual current operated circuit-breakers with

integral overcurrent protection DS200

Protection Solution


Residual block DDA200

Protection Solution


Residual block DDA 60, DDA 70, DDA 90

Protection Solution


Residual block DDA 800

Protection Solution


Residual current circuit breaker F200

Protection Solution

For an adequate protection against earth faults

ABB SACE has designed the following product

categories:

Moulded case circuit breaker

RC221 residual current devices

RC222 residual caurrent devices

RC223 residual current devices

Electronic release LSIG: PR222, PR223

Electronic release LSIG: PR331, PR332

Electronic release LSIRc: PR332

Description


Residual current devices RC221, RC222, RC223

Protection Solution

Protection Solution


Electronic releases LSIG:

PR222: T2, T4, T5, T6

PR223: T4, T5, T6

PR331, PR332: T7

G function setting

I4= 0.2..1 x In

t4= 0.1.0.8 x In con I2t=k o t=k

(depending by the type of

release)

Protection Solution

G function:

currently used in MV/LV transformer substations to protect both transformers as well as distribution lines

guarantees selectivity with regard to the residual current releases located on the load side

can be used for protection against indirect contact, when allowed by the installation conditions

improve protection against earth faults with regard to the normal phase protections

Protection Solution


Electronic release PR332 LSIRc for T7

Protection Solution


Summary table

Protection Solution


ABB has designed the following product

categories:

Air circuit breakers

Electronic releases LSIG: PR331, PR332, PR333

Electronic release LSIG: PR121, PR122, PR123



Description

Protection Solution

G function setting

I4= 0.2..1 x In

t4= 0.1.0.8 x In con I2t=k o t=k

(depending by the releases)



categories:

Air circuit breakers



Protection Solution



categories:

Air circuit breaker

Electronic releases LSIRc: PR332

Electronic releases LSIRc: PR122

Protection Solution



categories

Residual current relay with external trasformer

SACE RCQ switchboard electronic residual current relay

Residual current relay for DIN rail: RD2 & RD3

Protection Solution



categories

Residual current relay with external trasformer

SACE RCQ switchboard electronic residual current relay

Protection Solution



categories

Residual current relay for DIN rail: RD2

Protection Solution



categories

Residual current relay for DIN rail: RD3

Protection Solution



categories

Front panel residual current relay: ELR

Two types of residual current discrimination

horizontal residual current discrimination

vertical residual current discrimination

Discrimination of the protections against earth fault

To ensure discrimination

for residual current CBs type S located on the supply side (in compliance with Standards IEC 61008-1 and IEC 61009)

downstream non-selective residual current CBs having In three times lower

for residual current electronic releases (RC 221/222/223, RCQ and RD2)

tripping times and currents of the device on the supply side are immediately higher than those of the device on the load side


Example

E1N 1250 PR121/P-LSIG In=1250A 4p

T5N 400 PR222DS/P-LSI In =400A con RC222

T1B 160 TMD In=160A con RC221


Example


Domestic Installation (TT)

Application of RCD

IdRCCB

MCB Load

MCB Load

Industrial installation (TN-S)

long cables

CB+RC Id

Application of RCD

Protection function G or residual current protection?

the choice can be done taking in consideration:

the distribution system

the value of the fault current

RCD:

particularly suitable for protection of people

absolutely necessary

in TT systems (small fault current to earth)

earthing of the exposed-conductive-parts is deficient

normal protections are not sufficient to provide protection that falls within the limits set by the Standards

dangerous environmental conditions (e.g. excessive humidity)

Application of RCD

G function:

currently used in MV/LV transformer substations to protect both transformers as well as distribution lines

guarantees selectivity with regard to the residual current releases located on the load side

can be used for protection against indirect contact, when allowed by the installation conditions

improve protection against earth faults with regard to the normal phase protections

Application of RCD

Typical application:

all types of construction sites (building, naval, etc.)

mobile equipment or plants

hospital environments and operating rooms

excavations and mines

campground electric installations

pools, saunas, canteens and, generally, environments with high humidity levels

aquarium and fountain lighting

agricultural premises

school laboratories

Application of RCD

circuit breaker application & distribution systems - 2014

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