International Symposium on Standards for UHV Transmission

1

3.1System Impacts on UHV Substation Equipment

On behalf of CIGRE WG A3.22

29-30 January 2009, New Delhi, India

Hiroki ItoMitsubishi Electric

Covenor, CIGRE WG A3.22

Scope: Review the state-of-the-art of project specific and national technical specifications for all substation equipment within the scope of CIGRE Study Committee A3 at voltages exceeding 800 kV. Recommend future specifications and standardizations of 1100 kV and 1200 kV equipment and provide technical backgrounds on the collected information to IEC TC17.

Publications of CIGRE WG A3.22

2007Technical paper presented at IEC-CIGRE UHV symposium in Beijing2-4-1 “Technical requirements for UHV substation equipments”

2008First Technical Brochure submitted to CIGRE CO in February & published in DecemberTB 362 “Technical requirements for substation equipments exceeding 800 kV”

CIGRE Session paper presented at 2008 CIGRE session in ParisA3-211 “Technical requirements for UHV substation equipments”

Recommendations submitted to IEC TC17 in November“Summary of technical backgrounds of UHV equipment specifications”

2009Technical paper presented at IEC-CIGRE UHV symposium in New Delhi3-1 “System impacts on UHV substation equipment”4-1 “CIGRE state of the art & prospects for equipment”

Second Technical Brochure will be submitted to A3 chairman in March“Background of technical specifications of substation equipment exceeding 800 kV”

2

3

Specific issues for UHV AC systems

Prominent Ferranti effect and TOV due to large capacitance of overhead lines

Phenomena peculiar to UHVEquipment

Surge arresterShunt reactor

CIGRE investigations

Severe voltage factor and breaking current for capacitive current switching is not appeared.

Prolonged secondary arc extinction time due to higher induced voltage

4-legged reactorHSGS

Large time constant of DC component in fault current due to low losses of transformers and lines

Circuit breaker Reduced first-pole-to-clear factor due to small zero-sequence impedance in the UHV systems

Reduced line surge impedances due to multi-bundle conductors with large diameter

Circuit breaker

Severe VFTO due to geometry and topology of UHV substation

High TRV peak value for out-of-phase due to low damping of traveling waves

Circuit breaker

Possibly reduced corona onset voltage with increased corona losses and audible noise

LineSubstation (AIS)

Circuit breakerGIS, Transformer

High amplitude factor in TRVs due to low losses of power transformers and transmission lines

Circuit breakerSurge arresterCircuit breakerSurge arrester

Increased Insulation levelsSubstationequipment

Various mitigation schemes are applied to suppress the SIWV levels as much as possible.4-legged shunt reactor can attain successful auto-reclosing in case of 1LG condition for single circuit.

Resistor-fitted DS can effectively suppress VFTO for GIS substation.Time constants in the UHV systems are 100 ms for India, 120 ms for China and 150 ms for Japan.

Line surge impedance is suggested as 330 ohm for 8 bundle conductors designed for UHV OH-lines.

First-pole-to-clear factors are 1.1 for Japan, 1.2 for India and 1.0-1.23 for China.RRRV for TLF exceeds the existing standard value. MOSA can suppress TRV peak for terminal faults.Further investigations are expected to provide some solutions for out-of-phase phenomenon.

UHV lines employ 8 conductors with 400-810 mm2

depending on the allowable level of corona noise.

The applications of multi sub-conductor bundles with large diameter as well as large capacity transformers affect the technical requirements for UHV substation equipment, those will not be simply extrapolated from the existing standards up to 800 kV.

Chapter 2: System requirements2.1 Insulation levels (LIWV / SIWV)2.2 Temporary Overvoltage (TOV)2.3 Secondary arc extinction2.4 Out-of-phase2.5 DC time constant2.6 MOSA impacts on equipment

Chapter 3: Equipment requirements (GCB)3.1 Terminal faults3.2 Transformer limited faults3.3 Long-line faults3.4 Short-line faults3.5 Capacitive current switching3.6 Requirements for auxiliary equipment of CB

4

Scope of CIGRE WG A3.22(Contents of second Technical Brochure)

Chapter 4: System requirements (DS,ES)4.1 Capacitive current switching by DS4.2 Bus-transfer switching by DS4.3 Requirements for resistor-fitted DS4.4 Induced current switching by ES

Chapter 5: Equipment requirements (MOSA)

Chapter 6: Equipment requirements (VT,CT)

Chapter 7: Factory &Lab. Testing experience

Chapter 8: Field testing experience

WG A3.22 will provide the scientific backgrounds on the collected technical specifications to IEC TC17 based on precise predictions with digital simulation techniques

LIWV>1.25 x LIPL, providing LIPL with the residual voltage of MOSA at 20 kA. LIWV requirements for transformers in Italy, Russia, India and China are comparable.LIWV requirements for other equipment are fairly close.Japan studies the insulation levels in UHV systems using the EMTP analysis with a lightning current of 200kA-1s/70sWG A3.22 is investigating a limited survey on utilities’ policies on the insulation level.

0

1

2

3

4

IEC 800 kV

Hydro Quebec

765 kV

2.76

3.21

FURNAS

800 kV AEP

800 kV Russia

1200 kV

(With MOSA)Ligh

ting

Impu

lse

With

stan

d Vo

ltage

(p.u

.)

x1.34

LIPL:2.41

2.993.21

Tran

sfor

mer

Oth

er e

quip

men

t

x1.47

LIPL:2.18

3.21 3.21

Tran

sfor

mer

Oth

er e

quip

men

t

x1.46

LIPL:2.20

3.14 3.14

Tran

sfor

mer

Oth

er e

quip

men

t

x1.44

LIPL:2.17

LIWV = (1.25-1.48) x LIPL

Japan

1100 kV

2.172.51

Tran

sfor

mer

Oth

er e

quip

men

t

x1.39

LIPL:1.80

x1.14 x1.20

India

1200 kV

2.302.45

Tran

sfor

mer

Oth

er e

quip

men

t

x1.35

LIPL:1.82

x1.26

China

1100 kV

2.51 2.67

Tran

sfor

mer

Oth

er e

quip

men

t

x1.48

LIPL:1.80

x1.39

2.302.45

Tran

sfor

mer

Oth

er e

quip

men

tLIPL:1.89

x1.30

x1.22

Italy

1050 kV

2.62 2.62

Tran

sfor

mer

Oth

er e

quip

men

t

x1.25

LIPL:2.10

5

Insulation level: LIWV and LIPL

SIWV>1.07 x SIPL, providing SIPL with the residual voltage of MOSA at 2 kA. SIWV requirements for 1200 kV in Russia and India have the same values.SIWV requirements for 1100 kV in China and Japan are slightly different.The applications of new technologies such as MOSA with higher performance, CB with opening/closing resistors, DS with switching resistor can effectively suppress the switching surges, which is a predominant factor to reduce the construction cost of UHV transmission. 6

Insulation level: SIWV and SIPL

0

1

2

3

4

IEC 80

0 kV

Hydro Q

uebec

765 kV

1.992.18

FURNAS

800 kV AEP

800 kV

Switc

hing

Impu

lse

With

stan

d Vol

tage

(p

.u.)

x1.18

SIPL:1.85

2.482.28

Tra

nsfo

rmer

Oth

er e

quip

men

t

x1.25

SIPL:1.83

2.372.37

Tra

nsfo

rmer

Oth

er e

quip

men

t

x1.28

SIPL:1.85

2.602.60

Tra

nsfo

rmer

Oth

er e

quip

men

t

x1.42

SIPL:1.83

SIWV = (1.07-1.42) x SIPL

x1.07 x1.36

Russia

1200 k

V

(With MOSA)

1.841.84

Tra

nsfo

rmer

Oth

er e

quip

men

t

SIPL:1.65

x1.11

Italy

1050 k

V

2.101.95

Tra

nsfo

rmer

Oth

er e

quip

men

tSIPL:1.83

x1.07

x1.15

India

1200 k

V

1.841.84

Tra

nsfo

rmer

Oth

er e

quip

men

t

SIPL:1.55

x1.11 x1.23

China

1100 k

V

2.002.00

Tra

nsfo

rmer

Oth

er e

quip

men

tSIPL:1.63

J apan

1100 k

V

1.591.73

Tra

nsfo

rmer

Oth

er e

quip

men

tSIPL:1.60

x1.08

WG A3.22 will investigate how the secondary arc current can be effectively extinguished in UHV systems with double circuits and also provide advantages and disadvantages for HSGS and Four legged shunt reactor more in depth.

Secondary Arc Extinction

7

0 50 100 150 200 250 300

Recovery voltage after secondary arc extinction (kV)

Extin

ctio

n tim

e of

sec

onda

ry a

rc (se

c)

0

1

2

3

4

5

6

7

8

1100kV-210kmline with HSGS

Arc extinction time of secondary arcGap distance: 5.5m, Primary arc: 10kA,

Arcing time: 0.1sec, Wind velocity: 2m/sec

765kV-240km compensated linewith modified 4 legged reactors (40A)

230-765kV compensated lineswith 4 legged reactors (20A)

1100kV-210km uncompensatd line(150A-140kV)

1200kV-500km compensated linewith 4 legged reactors (106A)

765kV-350km compensated linewith 4 legged reactors (64A)

765kV-90km compensated linewo neutral reactor (38A-94kV)

550kV-100km uncompensated line (30A-60kV)

Secondary arc current

10 A

20 A

40 A

80 A

160 A

1100kV-359/281km compensated line with 4 legged reactors (China pilot)

0

50

100

150

200

0 50 100 150 200 250 300 350 400

Line length (km)Se

cond

ary

Arc

Curre

nt (A

)

Highest voltage Single circuit Double circuits

1100 / 1200 kV

765 / 800 kV

765 / 800 kV

Single circuit with 4-legged shunt reactor

Secondary arc can be extinguished less than one second if the current does not exceed 60 A. 4-legged shunt reactor can reduce the secondary arc current by a half.

Surveys on DC time constants in fault currents

Tower and conductor designs

Calculations predict a large DC time constants in fault current in UHV transmission systems due to usage of multi sub-conductor bundles and the existence of large capacity power transformers.

16.5m

16m

15.5m

19m

72.5

m90

m10

7.5m

120m

810mm sq. -8 conductors

1100kV transmission lines

27.4

m40.3

m

15.24m

42.7m

1360mm sq. -4 conductors

800kV transmission lines

35 (5

4.5)

m22

.6 (4

2.1)

m

12m 12m

20.12m

1360mm sq. -4 conductors

800kV transmission lines

Influences of the high DC component on test-duty T100a does not show any significant difference when the constant exceeds around 120ms. Therefore, it is recommended to use a special case time constant of 120 ms for rated voltages higher than 800 kV.

ConductorsHighest voltage

( kV)Size

( mm 2 ) Bundle

DC time constants

( ms )800

Canada 686 4 75

800USA 572 6 89

800South Africa 428 6 67

800Brazil 603 4 88

800China 400 6 75

1200Russia 400 8 91

1050Italy 520 ( 100)

1100Japan 810 150

1100China 500 120

8

8

8

1200India 774 1008

8

Further investigations:WG A3.22 will try to provide scientific explanations for these proposals.Verification of MOSA clipping level and comparison with the analytical TRVLong-term reliability of high-performance MOSA 9

MOSA clipping levels on TRV

Proposals and recommendations from A3.22 members1) 1460 kV (1.63 p.u.) for the SIPL value of 1100 kV MOSA2) 1526 kV (1.70 p.u.) based on the maximum switching surge level of 1100kV system3) 1615 kV (1.80 p.u.) provided with 10% margin to the SIPL level4) 1715 kV (1.91 p.u.) considered with additional 10% design margin

0 4Time (ms)

1 52 3

Uc=1635kV (Kpp=1.3, Kaf=1.4)

0

500

Volta

ge (k

V)

1000

1500

2000 T60, Breaking current : 26.2kATRV for T60 with twice TRV peak value of existing 550kV standard

Without MOSAWith MOSA (A type characteristic)With MOSA (B type characteristic)

Uc=1751kV (Kpp=1.3, Kaf=1.5)

0 4Time (ms)

1 52 30

500Vo

ltage

(kV)

1000

1500

2000 T100, Breaking current : 33.8kA

TRV for T100 with twice TRV peak value of existing 550kV standards

Without MOSAWith MOSA (A type characteristic)With MOSA (B type characteristic)

TRVpeak=1586kV

TRVpeak=1411kV

Uc=1635kV (Kpp=1.3, Kaf=1.4)TRVpeak=1502kV

TRVpeak=1380kV

Bus-charging current switching by DS

IEC62271-102 Japan (GIS) China pilot (GIS or MTS)

0.5 A for 550 kV0.8 A for 800 kV

0.5 A for 1100 kVLoad side capacitance correspond to 2000 pF

0.5, 2.0 A for 1100 kVLoad side capacitance

correspond to 10000 pF

Interruptingcurrent

1100 kV / 3Ur / 3 1100 kV / 3Voltage

The length of the busbar in the Jindognan substation (China pilot) is 96.2 m at the first stage, which corresponds to 4200pF of load side capacitance and provides the bus-charging current of 0.84 A.The substation is planned to be expanded with the busbar up to 420 m at maximum in the future, which corresponds to 19300pF of load side capacitance and provides the bus-charging current of 3.9 A.

0

2

4

6

8

10

12

245 300 362 420 550 800 1100 1100 1100 1100

Rated Voltage [kV]

Lo

ad

ca

pa

cit

an

ce

0

0.4

0.8

1.2

1.6

2

2.4

Bu

s-c

ha

rgin

g c

urr

en

t

Load capacitance [nF]

Current [A]

0

40

80

120

160

200

240

245 300 362 420 550 800 1100 1100 1100 1100

Rated Voltage [kV]

GIS

len

gth

0

0.4

0.8

1.2

1.6

2

2.4

Bu

s-c

ha

rgin

g c

urr

en

t

Length [m]

Current [A]

10

Bus-transfer current switching by DS

The existing IEC standard recommended 80-100 % of the rated normal currents. However, the value was introduced in 1980’s when the maximum rated normal current was 2000 A.

According to the WG survey, the value of 80% stipulated in the existing IEC standard seems to be rather conservative and the value of 60 % could be more realistic.

Since the maximum rated current is now increased up to 3150A and 4000A in the EHV systems and 8000 A in the UHV system, the bus-transfer current should be revised by reflecting the rated current specified for the UHV systems.

IEC62271-102 Japan (GIS) China pilot (GIS or MTS)

80% of rated normal current, not exceeded 1600 A

8000 A for 1100 kVMaximum rated normal

current

1600 A for 1100 kVIn accordance withexisting standard

Interruptingcurrent

300 V rms

400 V/sAIS: 300 V rms

GIS: 40 V rms 400 V rmsVoltage

11

Induced current switching by ES

Induced current interruptions duty can be easily evaluated with configurations of transmission line, line length and rated current.

Requirements for UHV ES is expected to exceed the extrapolation of the existing standards.

IEC62271-102 Japan (GIS) China pilot (GIS or MTS)

160 A rms

20 kV rms 1000 A rms

70 kV rms, 160 kV/sUnder consideration

Electromagnetic coupling

40 A rms

50 kV rms

25 A rms

25 kV rms for 550 kV

32 kV rms for 800 kV

Electrostaticcoupling

Under consideration

Japanese UHV systemsMaximum Line length: 200km, Rated current: 8000A, Double circuit transmission line- Electromagnetic coupling : 810A-65k,162V/s- Electrostatic coupling 　 : 31.8A-45.4kV

12

IEC SC17A requests for CIGRE on UHV standardizations

IEC TC17 requested CIGRE WG A3.22 to investigate the technical backgrounds of UHV substation equipment in accordance with the following IEC standards.

WG A3.22 will continuously provide technical backgrounds to support the standardization works within IEC TC17.

IEC 62271-1 Ed.1.0, HV Switchgear & Controlgear-Part 1: Common specificationsIEC 62271-100 Ed.2.0, HV Switchgear & Controlgear-Part 100: Circuit BreakerIEC 62271-101 Ed.1.0, HV Switchgear & Controlgear-Part 101: Sythetic testingIEC 62271-102 Ed.1.0, HV Switchgear & Controlgear-Part 102: A.C. DS and ESIEC 62271-110 Ed.1.0, HV Switchgear & Controlgear-Part 110: Inductive load switching

Application Guide to IEC 62271-100 and IEC 62271-1: Opening resistorNew project : High-Speed Grounding Switches

13

Summary and Considerations

Insulation levelsSuppressing switching overvoltage as much as possible is a predominant factor to reduce the height of transmission towers and the dimension of open-air parts in substations. Such technologies as MOSA with higher performance, CB with opening/closing resistors, DS with switching resistor can effectively suppress the switching surges less than 1.6pu for substation equipment and 1.7pu for OH-lines.

Secondary arc4-legged shunt reactor can reduce the secondary arc current by a half.Secondary arc can be extinguished less than 1 sec. if the current does not exceed 60 A.

First-pole-to-clear factor (FPCF)Use of a large capacity power transformer reduces FPCF (1.1 for Japan, 1.2 for India)

DC time constant / Line surge impedanceMulti sub-conductors bundles with large diameter can increase the time constants (150 ms for Japan, 120 ms for China) and reduce the line surge impedance around 350 ohm.

TRVMOSAs reduce the TRV peaks for terminal faults below the SIPL for in UHV systems.TRV for TLF appears severe RRRV only in a special case.

1429-30 January 2009, New Delhi, India