Lighting Voltage Supprestion in Gis

7/28/2019 Lighting Voltage Supprestion in Gis

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Approaches for Suppressing of Lightning

Overvoltage in the Gas-Insulated Substation (GIS)

AbstractGas-insulated substations (GIS) have different

specifications in proportion to air-insulated substations. Due to

space limitation in the field of the gas-insulated substation (GIS),

it is difficult to install extra arresters near the power

transformers. Voltage magnification is due to reflections oftransient waves in various junctions, low surge impedance and

decrease in the length of conductors in the GIS. These problems

cause to increase the propagation of transmitted and reflected

waves within the conductors in proportion to air-insulated

substation; thereby overvoltages in GIS are more important than

air-insulated substation. In air-insulated substations, probability

of failures across insulator strings or bushings is acceptable since

air insulation is self restoring. In GIS, the entire gas insulated

assembly must be protected because the gas insulated system

must be considered as non-self-restoring. According to

aforementioned reasons, it follows that insulation coordination

design of the GIS has been critically important. This paper

presents practicable and beneficial approaches to the industry to

look for the optimum approaches for lightning incoming surge

mitigation. These approaches are included effects of number of

surge arrester in the each feeder, system configuration and

decreasing of number of surge arrester and as costs, location of

surge arrester and cable, and terminal components. Lightning

overvoltages due to direct lightning stroke with varying intensity

current have been investigated. For accurate calculations,

ATP/EMTP software has been used.

Keywords- Insulation Coordination; lightning; gas insulated

substation (GIS); surge arrester; cable; the terminal component;

switchgear arrangement

I. INTRODUCTIONGas Insulated Substation (GIS) has been developed for

wide range, because of their benefits. These benefits are suchas compactness, protection from pollution, high reliability, a

few maintenance, etc [1]. Gas-Insulated Substations (GIS) are

exposed to the same variety of overvoltages as air-insulated

substations (i.e., lightning. switching, and temporary

overvoltages) [2].

However, in air-insulated stations, primary concern is placed

on the protection of transformers and some risk of failures

across insulator strings or bushings is accepted since air

Insulation is self restoring. In GIS on the other hand, theentire gas insulated assembly (including enclosures, circuit

breakers, disconnect and grounding switches) must be

protected because the gas insulated system must be viewed as

non-self-restoring. In the insulation coordination design of the

GIS, lightning overvoltages are found to be critically

important. Voltage magnification due to reflections of suchlightning surges at various junctions within the GIS is often

the determining criteria for selection of surge arrester rating

and locations [2].Though lightning surges have been reduced to an acceptable

level in modern substation insulation coordination, still

transformer failures related to lightning are often reported.

Two possible transformer failure modes may happen if a

lightning surge appears at the transformer terminals. The

transformer main insulation (the insulation between HV

winding and LV winding, HV winding and core, or HV

windings) will be threatened because of the large magnitude of

the lightning surge. On the other hand, the insulation between

turns at the beginning of the HV winding is oftendisproportionally more stressed because of the large potential

gradient appearing in the initial voltage distribution. Similar to

switching overvoltages and VFT, it is possible that lightning

overvoltage may excite partial winding resonance in the

transformer windings. The distance between the arrester and

the transformer will determine the overvoltage magnitude at

the transformer HV terminals [3],[4].Several factors may contribute to a transformer failure due to

lightning strokes including: 1) very high magnitude of the

overvoltage; 2) nonlinear voltage distribution along the

winding, which could result in high voltage between turns; 3)

Resonance or partial-winding resonance in the HV winding if

they coincide with the excitation frequencies [4],[5].This paper presents beneficial approaches to the industry to

look for the optimum approaches for lightning incoming surge

mitigation, including number of surge arrester, location of

surge arrester/cable, system configuration and decrease

number of surge arrester, the terminal component.

II. LIGHTNINGLightning overvoltage is a phase-to-ground or phase-to-phaseovervoltage produced by one specific lightning discharge. The

Ahmad Tavakoli

Iran University of Science and

Technology, Center of Excellence for

Power System Automation and

Operation, Tehran, Iran

[email protected]

Ahmad Gholami




Operation, Tehran, Iran

[email protected]

Ali Parizad




Operation, Tehran, [email protected]

978-1-4244-4813-5/10/$25.00 2010 IEEE


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lightning overvoltages have duration bet

microseconds and a wave front between 1 anThe wave shape of the lightning current is

voltage produced at the point of contact

stroke. The lightning condition and

specifications are shown in the table. I. Th

stroke current and its rate of decay were de

the guide lines given in References [2].

TABLE . THE LIGHTNING CONDITION AND THE APP

Peak Current (kA) 50 75 100

Time to Crest (s) 1.5 1.75 2.0

III. MODELING OF GIS COMTo model GIS components, lumped elemeparameters can be used, that is defined by

wave velocity and lengths of GIS section.

The surge arresters model recommended b

(IEEE Working Group 3.4.11, 1992) is sho

model the non-linear V-I characteristic is rep

sections of non-linear resistances designate

two non-linear resistances A0 and A1 are s

filter. For currents discharge in arrester witthe influence of the filter is negligible; th

essentially in parallel and characterize the

the MOSA. For the fast rising of su

impedance of the filter becomes more signi

inductance L1 derives more current into the

A0. Since A0 has a higher voltage for a givethe model generates a higher voltage b

terminals, what matches the dynamic

MOSAs. The inductance L0 represents

associated with the magnetic fields in the i

of the arrester. The resistor R0 is used tooscillations when running the model with

The capacitance C0 represents the ext

associated to the height of the arrester [8], [9

Figure 1. The IEEE Frequency-Dependant

Table.II shows the electrical equivalent circof GIS component [6]. Fig.2 shows the sing

a 420 kV GIS. Characteristics of the trans

and the electric power line and the ground

the table.III and Fig.3.

een 1 and 100

d 5 microseconds.different from the

of the lightning

the apparatus

e steepness of the

ermined based on

RATUS SPECIFICATION

150 200

2.25 2.5

ONENTS

ts and distributedurge impedances,

IEEE W.G3.4.11

n in Fig.1. In this

resented with two

d A0 and A1. The

parated by a R-L

slow rising time,s A0 and A1 are

static behavior of

ge currents, the

ficant, indeed the

non-linear branch

n current than A1,etween its input

characteristics of

the inductance

mmediate vicinity

avoid numericaldigital program.

rnal capacitance

], [10].

Model [8]

uits for mode lingle-line diagram of

ission line tower

ire are shown in

Figure 2. Single-line d

Figure 3. Transmissi

TABLE I. ELECTRICAL

Component

GIS Bus Bar

CB, DS, and Earthing Switch

Potential Transformer (PT)

Current Transformer (CT)

Capacitive Voltage Transformer

(CCVT)

Bushing

Power Transformer

Arrester

cable

CT

LA

T1

LA

PT

PT

CT

CT

PT

Transmi

Ca

iagram of a 420 kV GIS

n Line and Substation

QUIVALENT CIRCUIT[5],[6],[7]

Notes

z0 = 90 ohm

v = 270 m/us

In the closed position: impedance

(42 ohm)

In the open position: capacitance

(4pF)

300pF

300pF

5 nF

100pF

2 nF

Discharge Voltage (10kA):870kV

R0 = 0.0010679 ohm/m

z0 = 30 ohmv = 165m/us

CT

LA

LA

CT

T2

PT

PT

sion Line

ble


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TABLE II. SPECIFICATION OF TRANS

Conductor resistance at DC (with skin

effect) ohm/km

Power

Ground

Outer radius of one conductor

Power

Ground

Inner radius of one conductor. Only

available with skin effect

Power

Ground

Vertical bundle height at tower PowerGround

Vertical bundle height at mid-spanPower

Ground

Distance between conductors in a

bundle

Power

Ground

Angular position of one of the

conductors in a bundle

Power

Ground

Number of conductors in a bundlePower

Ground

The time step for simulation is 2.5 ns and

100s. Computer simulation has been

alternative transients program (ATP), a wide

EMTP. For simulation of surge arrester c

exponential current-dependent resistor

ATP/EMTP.

IV. EFFECT OF VARIOUS FACTDIRECT LIGHTNING S

In this section, lightning overvoltages

lightning that directly striking the transmissi

is corresponding to the situation where

opened and lightning is struck on the tower

(Fig. 3). Also, in order to simulation

condition, it is considered that lightning waphase A in tower No.2 and at the crest of

Table.IV describes the lightning overvoltage

intensity current at the power transformer,

near the lightning struck.

TABLE V. LIGHTNING OVERVOLT

Peak Current

(kA)

Transformer

(MV)

Tower

(kV)

50 1.1221 67.17

75 1.1401 101.19

100 1.2841 142.98

150 1.3573 208.61200 1.3635 274.96

These factors are included effects of the

arrester in the each feeder, system c

decreasing of number of surge arrester and

surge arrester and cable, terminal compon

resistance of tower. The impact of various

discussed above, were investigated undcurrent levels.

ISSION LINE

ine 0.069

Wire 0.44

ine 1.45cm

Wire 0.77cm

ine 0.7cm

Wire 0.5cm

ine 25.1mWire 39.7m

ine 10.1m

Wire 24.7m

ine 60cm

Wire 0cm

ine 45deg

Wire 0deg

ine 4

Wire 1

alculating time is

done using the

ly used version of

n be using ZnO-

(TYPE 92) in

ORS UNDER

ROKE

re simulated for

on line. This part

bus coupler was

o.2 from the GIS

under the worst

s happened on thenegative polarity.

s with the various

T, PT and tower

AGES

CT

(MV)

PT

(MV)

1.1361 1.3044

1.1584 1.3731

1.3208 1.4442

1.3544 1.56851.4049 1.6158

number of surge

onfiguration and

costs, location of

nt and grounding

odeling details as

r various stroke

A.Effect of Number of SurgeThis part is corresponding towas opened and lightning stru

the GIS (Fig. 3).The lightning

six cases.

Case(A-1): the arreste Case(A-2): the arr

transformer feeder, Case (A-3) : original

as Shown in Fig. 2

Case (A-4): an extrtransformer feeder ba

Case (A-5): an extrafeeder based on case (

Case (A-6): an extrtransformer feeder a

case (A-3).

Fig.4 shows the effect of nu

overvoltage at the power tran

lightning stroke. Its clear that

cause decreasing of the overvobserved that peak magnitude

power transformer terminal

current is fixed. Fig.5 shows cthe lightning overvoltage at t

The observed overvoltage at

can reach up much more than t

when the arresters are disabl

feeder. But disabled arresters

than disabled arresters in thexistence of arrester at the i

Fig.5, case (A-3) shows clearl

transformer terminal is still v

and can be up to 4.21 Pu. It isarrester installed, the lightnin

transformer terminal is still hithe studied case. Hence, ins

necessary for suppressing har

Figure 4. Effects of number of surge

transformer due to direct lightning stro

the line feeder, case (A-2): the arrestercase (A-3): original arrester configura

(A-4): an extra arrester is installed in t

3), case (A-5: an extra arrester is insta3) and case (A-6) is that an extra arres

and in the line feeder based on case (A

Arrester

he situation where bus couplerk on the tower No.2 away from

overvoltages are investigated in

rs are disabled in the line feeder

sters are disabled in the

arrester configuration is applied

a arrester is installed in the

ed on case (A-3),

arrester is installed in the line

A-3)

a arrester is installed in the

d in the line feeder based on

mber of surge arrester on the

sformer terminal due to direct

existence of extra arrester can

oltage. In the cases 4, 5, 6 areof overvoltage variation at the

with increasing of lightning

learly effect of extra arrester one power transformer terminal.

he power transformer terminal

he transformer BIL of 1230 kV,

ed in the line and transformer

in the line feeder can be worse

transformer feeder. Howevercoming feeder is emphasized.

y that the voltage at the power

ery high because of reflection,

orth noting, that even with theovervoltage seen at the power

her than the transformer BIL inalling extra surge arresters is

ful lightning overvoltages.

rrester on the overvoltage at the power

ke. Case (A-1): arresters are disabled in

s are disabled in the transformer feeder,ion is applied as Shown in Fig. 2, case

e transformer feeder based on case (A-

led in the line feeder based on case (A-ter is installed in the transformer feeder

-3).


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Figure 5. Effects of extra arrester on the lightni

B.Effect of System ConfigurationInstalling extra surge arresters is necessar

harmful lightning overvoltages. But it is

extra arresters near transformers due to spac

site.

In order to suppressing harmful lightning otransformer terminals, it can be used an

installation of extra arresters. In this waycircuit breaker of bus coupler; on the other h

associated with together and more tran

connected to the substation. In this sectovervoltages are investigated in three cases.

Case (B-1): the arresters are disfeeder and bus coupler is closed

Case (B-2): the arresters aretransformer feeder and bus coupler

Case (B-3): original arrester conand bus coupler is closed.

Fig.6 shows effect of system configuration

at the power transformer terminal when bus

If bus coupler is closed, the lightnintransformer terminals can be reduced to a le

in the studied case. Fig.7 compares effects onew configuration (bus coupler is closed

associated with together). Its clear that c

than case (A-4) and case (A-5). H

configuration is better than even extra arrest

With more transformers connected to tharresters must be also connected to the GI

absorbing more lightning energy by the a

cause to reduce the maximum overv

transformer terminal.

g overvoltage.

for suppressing

ifficult to install

e limitation in the

vervoltages at theapproach without

ne can be closedand, all of feeders

sformers can be

ion the lightning

abled in the line

disabled in the

is closed

iguration applied

nthe overvoltagecoupler is closed.

overvoltage atel below the BIL

extra arrester andor all of feeders

se (B-3) is lower

nce, appropriate

r in the feeder.

e network, more, it is helpful for

rresters; hence, it

oltages at each

Figure 6. Effects of System Configutransformer terminal when bus couple

disabled in the line feeder and bus co

are disabled in the transformer feederoriginal arrester configuration is appl

(A-3) is that original arrester configura

Figure 7. Compares etween effect

configuration (bus coupler is closed or

C.Effect of Location of SurgeDue to absorbing more lightni

negative reflection of cable,ef

and cable is imported. This

situation where bus coupler

on the tower No.2 away fro

arrester configuration is app

lightning overvoltages are inve

Case(C-1): the surgincoming cable

Case(C-2): the surgeincoming cable.

Case(C-3): the surgeincoming cable

Case(C-4): the surgeincoming cable

Case (C-5): the surincoming cable.

Fig.8 shows effect of location

the overvoltage at the powerwhen the surge arrester is pl

lightning overvoltages are

reflection.

Figure 8. Effects of location of surge

power transformer terminal. Case (C-

incoming cable, Case (C-2): the surge

ation on the overvoltage at the poweris closed. Case (B-1): the arresters are

pler is closed, Case (B-2): the arresters

and bus coupler is closed, Case (B-3):ed and bus coupler is closed and case

tion applied as Shown in Fig.2.

of extra arrester and effect of new

all of feeders associated with together)

Arrester and Cable

ng energy by the arresters and

fect of location of surge arrester

ection is corresponding to the

as opened and lightning struck

m the GIS (Fig. 3). Original

lied as shown in Fig.2. The

stigated in five following cases.

arrester situated in next of

arrester situated in 3/4 after



ge arrester situated in before

of surge arrester and cable ontransformer terminal. Its clearced before of incoming cable,

decreased due to negative

rrester and cable onovervoltage at the): the surge arrester situated innext ofarrester situated in3/4 after incoming


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cable Case (C-3): the surge arrester situated in2/4 afte(C-4): the surge arrester situated in1/4 after incomingsurge arrester situated inafter incoming cable.

D.Effect of the Terminal ComponentThe peak magnitude of lightning overvolta

terminals depends on the terminal compone

GIS. The terminal component can be an

overhead transmission line or a gas-insulate

(GITL). To understand the effect of differe

the peak magnitude of the lightning ovesubstation layouts have been considered and

V. The attenuation of the lightning overv

with time is found to depend on the switc

and the terminal component connected to the

Fig.9 shows variation in peak magnitudes

overvoltages for various substation layouts.

The attenuation rate is high if the GIS is teimpedance systems, such as XLPE cable, a

rate is low if the GIS is terminated with hig

elements such as an overhead line. Similar

terminated with a long length of GITL, ther

the transient currents for longer time durati

be noted that effect of the cable is more effeovervoltage peak than adding more arresters.

Figure 9. variation in peak magnitudes of the lightvarious substation layouts.

TABLE V. VARIOUSSUBSTATIONLAYOUTSFOR

Substation

Layouts

The Terminal Co

D-1 Overhead Li

D-2 GITL

D-3 XLPE Cab

D-4 Two XLPE Cable i

IV. CONCLUSION

Installing extra surge arresters isuppressing harmful lightning overv

difficult to install extra arresters near t

space limitation in the site.

In order to suppressing harmful lightnithe transformer terminals, it can be

without installation of extra arresters. I

be closed circuit breaker of bus co

incoming cable, Casecable, Case (C-5): the

es at transformer

t connected to the

LPE cable or an

transmission line

t terminations on

voltages, variousare listed in table

oltages amplitude

ing configuration

GIS.

of the lightning

minated with lownd the attenuation

surge impedance

ly, if the GIS are

is a possibility of

on [11]. It should

ctive to reduce the

ning overvoltages for

IFFERENTTERMINALS

mponent

ne

le

n Parallel

necessary for

ltages. But it is

ansformers due to

g overvoltages at

sed an approach

this way one can

pler; With more

transformers connected

must be also connectedabsorbing more lightning

it reduce to a level below

When the surge arrestercable, lightning overvo

negative reflection.

It should be noted thateffective to reduce the

more arresters. When

impedance becomes sm

overvoltage appearing a

reduced dramatically due

The attenuation rate is hilow impedance systems,

attenuation rate is low if

surge impedance eleme

Similarly, if the GIS are t

GITL, there is a possibil

longer time duration.

REFE

[1] C.Y. Lui J. Hiley Computatiowith special reference to effecovervoltage amplitude IEEETr1994.

[2] H. Elahi, M. Sublich, M.E.overvoltage protection of thesubstation, IEEE Transactions50, Jan. 1990.

[3] A. Greenwood, Electrical TransYork: Wiley, 1991, pp. 548554.

[4] Xuzhu Dong,Sebastian RosadoLine, Tzong-Yih Guo, "StudyEffects on GSU Transformers"vol. 18, NO. 3, JULY 2003

[5] J. P. Bickford and A. G. Heatsystems, Proc. Inst. Elect. En1986.

[6] Task Force on Very Fast Transifor very fast transients, IEEEpp.20282035, Oct. 1996.

[7] Z. Haznadar, S.CarSimamoviModeling of Gas Insulated Substof Very Fast ElectromagneticDelivery, Vol. 7 No.1, January 1

[8] IEEE working group 3.4.11, MIEEE Trans. Power Delivery, vol

[9] F. Fernndez, R. Daz, Metatransient simulations paper 14system transients, IPST01, 20 -2

[10] A. BAYADI1, N. HARID 2, K.of metal oxide surge arrester dThe international Conference onin New Orleans, USA

[11] M. Mohana Rao, M. Joy TCharacteristics of Very Fast TraTransactions on Power Delivery,

o the network, more arresters

to the GIS, it is helpful forenergy by the arresters; hence,

the BIL in the studied case.

is placed before of incoming

ltages are decreased due to

effect of the cable is moreovervoltage peak than adding

the equivalent cable surge

aller, the peak value of the

t the transformer terminals is

to negative reflection.

h if the GIS is terminated with

such as XLPE cable, and the

the GIS is terminated with high

ts such as an overhead line.

erminated with a long length of

ity of the transient currents for

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al study of very fast transients in GISts of trapped charge and risetime onns. Distrib, Vol. 141, No. 5, September

Anderson, B.D. Nelson, LightningPaddock 362-145 kV gas-insulated

n Power Delivery, vol.5, no.1, pp.144-

ients in Power Systems, 2nd ed. New

, Yilu Liu,Nien-Chung Wang,E-Lenyof Abnormal Electrical Phenomena

EEE Transactions on Power Delivery,

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nts, Modeling and analysis guidelinesTrans. Power Delivery, vol. 11, no. 4,

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Lighting Voltage Supprestion in Gis