19 ruben grund praesentation

7/28/2019 19 Ruben Grund Praesentation

1/17

Steckbare feststoffisolierte berspannungsableiterfr Hochspannung

Pluggable, Solid State Insulated Surge Arresters

for High Voltage

Ruben Grund, Michael Zerrer, Stuttgart, March 7th, 2012


2/17

Page 2 of 17

Content

Obervoltages and Insulation Coordination

Voltage Limitation by Metal Oxide Varistors

Design of Surge Arresters

Rating of Surge Arresters

Protective Zone

Pluggable Surge Arresters


3/17

Page 3 of 17

Overvoltages and Ins. CoordinationEquipment Damage by Overvoltage

Example: Transformer (Very Expensive!)

Lightning stroke hits power line

Overvoltage travelsover power line to transformer

Insulation withstand voltage exceeded

Dielectric breakdown

Short circuit

Severe equipment damage

Protection by Surge Arresters


4/17

Page 4 of 17

Lightning Overvoltages

Cause: Atmospheric discharge Duration: Microseconds, e.g. 1,2/50 Magnitude: > 5 Um Can be limited by surge arresters (SA)

Switching Overvoltages (incl. line discharge) Cause: Switching in power system Duration: Milliseconds Magnitude: 2 to 3.6 Um Can be limited by surge arresters (SA)

Temporary Overvoltages (TOV) Cause: Load flow variations in power system Duration: Seconds Magnitude: 1 to 1.3 Um Can not be limited by SA,

SA must be rated to withstand TOV

Overvoltages and Ins. CoordinationTypes of Overvoltages


5/17

Page 5 of 17

Voltage Duration

Lightning

overvoltage

(Microseconds)

Switching

overvoltage

(Milliseconds)

Temporary

overvoltage

(Seconds)

Highest voltage

for Equipment Um(Continuously)

MagnitudeofVol

tageinp.u.ofU

m

5

4

3

2

1

0

Overvoltages and Ins. CoordinationVoltage Limitation by Surge Arrester

Basic insulation level (BIL),i.e. lightning impulse withstand voltage 1,2/50 s,e.g. 3.4 p.u.

Withstand voltage of equipment

Voltage limited by arresterVoltage w/o arrester


6/17

Page 6 of 17

Voltage Limitation by MOVPhysical Principle

Voltage limitation by MO surge arrester bases on electronic effect in MO grain structure.

Interface between zinc oxide (ZnO) grain and bismuth oxide (Bi2O3)acts as unidirectional potential barrier of 3.5 Volts (Diode).

Multitude of statistically connected diodes acts as bidirectional varistor.

MO: Metal Oxide

MOV: Metal Oxide Varistor

Varistor: Variable ResistorTypical MOV element range (TDK EPCOS)

Diameter 32 mm to 99 mm


7/17

Page 7 of 17

Example:TDK EPCOS MOV E78 SR 123

Diameter 78 mm, Ures = 12*103 kV

16

14

12

10

8

6

4 10-4 10-3 10-2 10-1 1 10 102 103 104

PeakValueofVoltageinkV

Peak value of current in A

Factor 100,000,000 = 108

Voltage Limitation by MOVElectric Characteristic

Factor2.4

Residual voltage Ures = 12 kV@ nominal discharge current 10 kA

Continuous operating voltage Uc = 5 kV@ leakage current 100 A


8/17

Page 8 of 17

Environment

Dry, wet

Clean, polluted

Design of Surge ArrestersGeneral Design Options

Surge arresters consist of MOV element column inside a housing.

MOV element column is determined by electrical requirements:

Length of column (= quantity of elements)according to voltage.

Diameter of column (MOV type)according to energy requirements.

Housing type is determined by application, mechanicaland environmental requirements:

HV, MV, Outdoor, Indoor, AIS, GIS

GIS substation, transformer:GIS surge arrester, pluggable surge arrester

AIS, standard mechanical requirements:porcelain, polymer cage design

AIS, high mechanical requirements:

polymer tube design

AIS, low pollution: porcelain

AIS, high pollution: polymer cage or tube design

Length

(voltag

e)

Head force

Diameter (energy)


9/17Page 9 of 17

Design of Surge Arresters

GIS Pluggable

AIS, Porcelain

AISPolymer Tube

AISPolymer Cage


10/17Page 10 of 17

Rated voltage (Ur)

Voltage which can be applied to surge arrester for 10 seconds during operating duty test. Most important key data, NOT to be confused with Uc (see below).

Continuous operating vol tage (Uc or MCOV) Maximum voltage which can be applied to surge arrester continuously. Uc = Um /3 Usually, Uc = Ur /1.25

Nominal discharge current (In) Permissible peak value of lightning impulse current 8/20 s through arrester. Usually 5, 10 or 20 kA

Protection level Residual voltage Ures at nominal discharge current. Rating factor = Ures / Ur for every arrester / MOV type.

Line discharge class (LD-Class) Characterises energy absorption capability by classes 1 to 5. Depends on Um and power line length. Difficult calculation (simulation of power system) or just follow standard tables.

Short circuit current Power frequency short circuit current of 200 ms duration.

Rating of Surge ArrestersKey Data

Um

Um/3


11/17Page 11 of 17

Rated frequency

Usually 50 or 60 Hz. Different consideration for harmonics e.g. in HVDC required.

Energy absorption capability (in kJ/kV per Ur or Uc)

Thermal energy absorption capability during operating duty test.

Current impulse energy absorption capability at different waveshapes.

High current impulse capability in kA

Permissible peak value of high current impulse 4/10 s through arrester.

Temporary overvoltage (TOV) capability

Withstand temporary overvoltage of different voltage(1 s, 10 s, 100 s)

Derating curves available for every arrester type.

Creepage distance in kV/cm

Ur / distance between terminals across shed profile.

Withstand voltage of housing in kV

AC, lightning impulse, switching impulse

Dry, wet

Mechanical strength

Permissible cantilever strength in kNm

Permissible headload in kN

Dynamic (short term) and static (continuously)

Rating of Surge ArrestersKey Data


12/17Page 12 of 17

Fast transient overvoltages (e.g. lightning impulse) travel along the power line like waves.

Waves are reflected when hitting higher impedance and then increase their peak value. Arrester cuts off wave, however, wave base travels to equipment, is reflected and increases peak value.

Example from MV power system:

Overvoltage wave is shaped like a voltage ramp, steepness 1000 kV/s (1 kV/ns)

Wave travels at speed of light 300 m/s.

Distance from arrester to transformer is 3 m

Arrester limits voltage to 80 kV at its terminals

Protective ZonePhysical Background

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100 110 120

t [ns]

u[kV]

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100 110 120

t [ns]

u[kV]

Voltage at transformer

up to 100 kV

Voltage at arrester

limited to 80 kV


13/17Page 13 of 17

Example 1:

Distribution system, insulated neutralUm = 24 kV, BIL = 125 kVArrester Ur = 30 kV, Ures = 80 kV

(125 / 1,15) - 80

21000 300 m =4.3 mxs =

Due to travelling wave effects of fast transient overvoltages,

surge arresters are effective only within limited distance to arrester location In other words: Do not install arresters too far away from equipment to be protected!

Simplified calculation of the protective zone (Details see IEC 60099-5, 60071-1, 60071-2):

xs Protective zone m

BIL Basic insulation level kV

1.15 Safety factor

Ures Protection level of the arrester kV

s Front steepness of the overvoltage kV/s

(usually about 1000 kV/s)

vtw Speed of travelling wave:

300 m/s on overhead line (speed of light c")

200 m/s in cables

(BIL / 1,15) - Ures

2s vtwxs =

Protective ZoneCalculation

Example 2:

Transmission system, groundedUm = 420 kV, BIL = 1425 kVArrester Ur = 336 kV, Ures = 806 kV

(1425 / 1,15) - 806

21000 300 m =65 mxs =


14/17Page 14 of 17

Pluggable Interface for HVDesign and Advantages

Connection element is completely protected from the environment by the housing.At the same time, the housing provides electric shock protection.

Pluggable connection is easy to plug/unplug and installation is quickly done.

Cable section to be prepared for installation of a plug is relatively short.

Socket of equipment to be connected with plug can be terminated with dummy plug.

Thus, equipment may be tested w/o cable attached. No gas or oil handling required at switchgear or transformer on site.

Pluggable connections are dry, mechanically stable all around and can be installed in any position.

Field grading in socket and plug are manufactured and routine tested in the factoryand thus have high reliability and robustness.


15/17Page 15 of 17

Pluggable Surge ArrestersDesign

Plug includingcontact and

insulating part

Polymer insulatingpart incl. field

gradingFRP tube housing

Head flange incl.pressure release

system


16/17Page 16 of 17

Minimum distance and thus maximum electrical protection of equipment

(e.g. GIS busbar, tansformer etc.) by integration of the arrester into the insulating system. Fast installation and fast change after overload by pluggable connection.

No pressure vessel, no gas monitoring, no environment hazardous substancesby dry insulation made from elastomer material.

Pluggable solid state insulated surge arresters for high voltage combine the advantages of GIS arresters

(maximum electrical protection)

Pluggable technology(easy connection/disconnnection)

Solid state insulation

Pluggable Surge ArrestersFeatures and Application


17/17

Questions and Answers

Thank you for your attention

19 ruben grund praesentation

Documents