summary of insulation coordination standard

7/23/2019 Summary of Insulation Coordination Standard

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National Transmission and Despatch Company Limited

TRANSMISSION SCHEME FOR DISPERSAL OF POWER FORM

2X660MW COAL FIRED POWER PLANTS AT THAR

Insulation Coordination

（2015‐

B09‐

PK‐

500‐

DO‐

003）

NEPC II CONSORTIUM



Insulation Coordination

(1) Basic insulation level

The system insulation level is as follows:

Standard Rated Switching Impulse Withstand Voltage Standard RatedLightening Impulsewithstand voltagekV (Peak Value)

LongitudinalInsulation

kV (Peak Value)

Phase to EarthkV (Peak Value)

Phase to Phase(ratio to the phase

to earth PeakValue)

1050 1175 1.50 1550

Based on actual tower spotting, the highest altitude of all tower is less than 1000m, In this case

we use the altitude factor Ka based on 1000m.

(2) Clearances according to EPRI

Refer to “ EPRI AC Transmission Line Reference Book-200kV and Above, Third Edition”

The primary method to calculate the strike distance (ST) at the tower can be calculated by

Equation 3.5-3 for lines with voltages above 50kV.

ST=0.280+0.005*(VLL-50)

Where:

VLL is the phase-phase voltage in kV,

ST=0.280+0.005*(550-50) = 2.78m

(3) Clearances according to IEC 60071-1 and IEC 60071-2

The minimum phase-to-earth clearances follow from IEC 60071-2, table A.1 and table A.2

2015-B09-PK-500-DO-003 Insulation Coordination Page 1 of 6

NEPC II CONSORTIUM



From the table above, we find as follows:

The minimum phase-to-earth clearance (Conductor - Structure) is 2.9m in 1550kV (standard

lightning impulse withstand voltage)

The minimum phase-to-earth clearance (Conductor - Structure) is 3.1m in 1175kV (standard

switching impulse withstand voltage)

(4) Clearances according to EN 50341-1

In EN 50341-1 [8], Annex E, formulae for the calculation of the clearances Dpe for slow front and

fast front overvoltages are presented.

where:

U90%_ff is the fast front overvoltage being withstood with 90% probability (kV):

U90%_ff = U50%_ff ⋅ kz_ff;

kz_ff is the deviation factor of the fast front withstand voltage: kz_ff = 0,961;

kz_sf is the deviation factor of the slow front withstand voltage. For switching

impulses: kz_sf = 0,922;

ka is the altitude factor

kcs is the statistical coordination factor taken as 1,05.

The gap factor kg (1.45 for conductor-structure) depends on the type of gap

In EN 50341-1 [8], Annex E, formulae for the calculation of the clearances Dpe_pf

between live and earth parts is as follows:

where:

kz_pf is the deviation factor being 0,910 for power frequency voltages;

kg_pf is the power frequency factor.


NEPC II CONSORTIUM



The system insulation level is as follows:

Dry Lighting Impulse Withstand Voltage: 1550kV

Wet Switching Impulse Withstand Voltage: 1175kV

Insulation Coordination Calculation(EN 50341-1:2001)

1 The highest system voltage Us kV 550

2 Phase to earth(fast front overvoltage):U90%_ff_is kV 1550

3 slow front overvoltage:U2%_sf kV 1175

3.1 phase to earth:KCS*U2%_sf kV 1234

3.2 phase to phase:1.40*KCS*U2%_sf kV 1727

4 The altitude factors

4.1 slow and fast front overvoltages:

phase to earth and phase to phase Ka 0.978

4.2 power frequency voltage:

phase to earth Ka 0.946

phase to phase Ka 0.959

5 The deviation factors Kz

5.1 fast front overvoltages:Kz_ff 0.961

5.2 slow front overvoltages:Kz_sf 0.922

5.3 power frequency voltage:Kz_pf 0.910

6 Conductor-window configuration(Kg_sf =1.25)

for fast front overvoltages Del

gap factor Kg_sf 1.45

6.1 for fast front overvoltages Del m 2.79

the clearance distance between the extremities of the insulator string dis m 2.63

6.2 for slow front overvoltages Del m 3.03

for power frequency overvoltages D50Hz_p_e

the power frequency gap factor of the air gap Kg_pf =1.35Kg-0.35*Kg2 1.22

6.3 for power frequency overvoltages D50Hz_p_e m 0.92

7 Conductor-conductor configuration(Kg_sf =1.60)


the lightning impulse gap factor of the air gap Kg_ff =0.74+0.26*Kg 1.16

7.1 for fast front overvoltages Dpp m 3.23

7.2 for slow front overvoltages Dpp m 4.41


7.3 for power frequency overvoltages D50Hz_p_p

m 1.57

Based on calculation above, the phase to earth clearance Dpe is 3.03m.


NEPC II CONSORTIUM



Based on bid document, the suspension and tension insulator sets is 29*170mm in Zone B.

According to the test procedures of IEC 60383-2

The suspension and tension insulator sets (29*170mm):

Dry Lighting Impulse Withstand Voltage: 2100kV

Wet Switching Impulse Withstand Voltage:1300kV

Insulation Coordination Calculation(EN 50341-1:2001)

1 The highest system voltage Us kV 550

2 Phase to earth(fast front overvoltage):U90%_ff_is kV 2100

3 slow front overvoltage:U2%_sf kV 1300

3.1 phase to earth:KCS*U2%_sf kV 1365

3.2 phase to phase:1.40*KCS*U2%_sf kV 19114 The altitude factors

4.1 slow and fast front overvoltages:

phase to earth and phase to phase Ka 0.978

4.2 power frequency voltage:

phase to earth Ka 0.946

phase to phase Ka 0.959

5 The deviation factors Kz

5.1 fast front overvoltages:Kz_ff 0.961

5.2 slow front overvoltages:Kz_sf 0.922

5.3 power frequency voltage:Kz_pf 0.910

6 Conductor-window configuration(Kg_sf =1.25)

for fast front overvoltages Del


6.1 for fast front overvoltages Del m 3.77

the clearance distance between the extremities of the insulator string dis m 3.57

6.2 for slow front overvoltages Del m 3.54 for power frequency overvoltages D50Hz_p_e


6.3 for power frequency overvoltages D50Hz_p_e m 0.92

7 Conductor-conductor configuration(Kg_sf =1.60)


the lightning impulse gap factor of the air gap Kg_ff =0.74+0.26*Kg 1.16

7.1 for fast front overvoltages Dpp m 4.38

7.2 for slow front overvoltages Dpp m 5.24


7.3 for power frequency overvoltages D50Hz_p_p m 1.57


NEPC II CONSORTIUM



(5) Live working clearance according to IEC 61467 - 2004

Refer to “ IEC 61467- 2004 Live working – minimum approach distances for

a.c. systems in the voltage range 72.5kV to 800kV – A method of calculation” Table 2.

From the table above, the live working clearance is about 3.095m when p.u. is 2.20.

p.u. is usually about 2.00 in 500kV transmission line.

(6) Live working c learance accord ing to GB 50545 -2010

Refer to China standard “ GB 50545 – 2010 Code for design of 110kV ~ 750kV overhead

transmission line” Table 7.0.10.

From the table above, the clearance of 500kV live work is 3.20m, and an additional 0.5m space

allowing movement of human body shall be available where operators need to stay for work.

So, total live work clearance is 3.20+0.5=3.70m.


NEPC II CONSORTIUM



(7) Conclusion

The clearances of d ifferent standards

EPRI IEC 60071 EN 50341IEC 61467

for live workGB 50545

for live work

(m) (m) (m) (m) (m)

2.78 3.1 3.03 3.77 3.095 3.7

From calculating above, the clearance 3.77m is enough for system insulation level.

Based on the bid document “500 kV TL CPP 01 Bidding Docs Volume II” section 2.2.3,

The minimum clearance is 4.5m > 3.77m. Therefore, we will use clearance 4.5m for

insulation design.


NEPC II CONSORTIUM

summary of insulation coordination standard

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