Ct Sizing XL

(1)

Calculation of CT Parameter Parameter Remark

Description From generator Data sheet From generator

Data sheet (i) Generator parameter

Rated Voltage(kV) 19

Rated Current(Amp) 9116.3

Sync. Reactance Xd is 1/SCR 200.0

Subtransient Reactance Xd"(Saturated) 12.0%

Transient Reactance Xd' (Saturated) 20.0%

Rated Voltage at -5% 18.05

FL current at -5%of rated Voltage= 9596.1

Voltage at + 5% 19.95

FL current at +5% of rated Voltage= 8682.2

Choose CT ratio = 11000/1

105% of rated current at (-)5% of rated voltage 10075.94

Choose CT ratio = 11000/1A 11000

This gives an over load capability 1.21

% O/L Capability of Full Load Current 120.66

1) Calculation of CT parameter for generator differential protection (87G)

Relay setting VR = If (RCT + 2RL + Rrelay) where ,

Where If = fault current on CT sec, RCT = CT secondary resistance, Rrelay = Relay resistance in ohms, RL = Resistance of cable in ohms,

RL in W for 100m of 2.5mm2 0.887

(Considering 100 m of 2.5 sq.mm Cu cond. cable between busduct CT & GRP the resistance of 2.5 sq.mm Cu cond cable at 70oC in W / km (from KEI catalogue)

8.87

Relay resitance/phase Assumed Rrelay from SEC 0.1

Fault contribution from Gen in MVA= 3571.43

Taking 30% - Ve tol on Xd” as per IEC-34 part –I

Fault contribution from system in MVA considering 40KA system Impedence on 220KV Side.

2024.10

Source impedence in Percentage at 300 Base 1.97%

Taking higher of the above two values = 3571.43

Fault Current in KA Taking higher value of the fault contribution from i.e. fault contribution from system / fault contribution from gen

108.52

Secondary Fault Current 9.87

VR = 9.87 (RCT +2x0.887+0.1) E47*(RcT+2*E31+E35)

Vk = 2 VR 2*9.87* (RCT +2x0.887+0.1)

Expressing VK term of +40V 19.74Rct+36.99

Vk = 20RCT + 37

(2)

CT with group-1/group-2 protection

11000/1A, CLPS, Vk  20RCT + 36V Im  15 mA at Vk/2

(ii) METERING CORE

CT chosen 11000/1A, 30VA, CL 0.2 ISF  5

Typical Meter burden in ohm (from catalogue of Conzerv model)

_0.4

Typical Anolgue Meter burden in ohm (from catalogue of AE/Rishab) &

Transducer

7

Total 10Nos Analogue meter connected & max 4 nos of transducer per CT

Max. Burden margin Consider for future use

₂

Total Burden on CT = Lead Burden+ Meter Burden

Lead Burden for lead length of 100M= I2

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl) =Rct+1.774

Rct Assumed for CT Sec.1A is 15 ohm for 11000/1Amp 16.774

Total Burden on CT = Lead Burden+ Meter Burden+burden margin Consider for future use

26.174

30 VA, CL-0.2 As meter used is Multifunction type,

hence 30 VA considered is more than Sufficient also Lead burden is less than above assumed buden as Meter & CT are at the same Switchgear.

Calculation of CT parameter for (87- 0A) on 19 kV side

Same as generator differential protection CT core 11000/1A, CL-PS, Vk ≥ 20Rct + 36V, Im ≤ 15mA at Vk/2

2 CT on 220 KV side of Generator Step up transformer Bay

i)Core –1 (87- 0A)

GT HT side current (current on 400 kV side) = 512.40

= 513 A

RL = 8.87x0.27 (considering 270m)= 2.3949

Rrelay = 0.1 CT ratio chosen = 600/1A

VK = 40xIx(RCT+2RL+Rrelay) Fault current on 400KV side taken

as 40KA = 40x1 (RCT +2x2.3949+0.1) =40 RCT+195.592 = VK 40 RCT+200V CT ratio 600/1A CLPS , VK  40 RCT+200V Im  30 mA at VK/2 ii)Core –2 (50 LBB, 51GT)

R relay= 0.1 (from relay catalogue of ABB) R relay= 0.1 (from relay catalogue of ABB)

600/1A

Total Burden on CT = Lead Burden+ Relay Burden Lead Burden for lead length of 270M= I2_x(R

ct+2RL) =Sqr(1)*(Rct+2Rl)

=Rct+4.79

Rct Assumed for CT Sec.1A is 6 ohm 10.79

Total Burden on CT = Lead Burden+ Relay Burden 10.89

15 VA, CL5P20 Cater the Load burden of Numerical

(3)

iii)Core –3 (metering) 600/1A

Typical Meter burden in ohm (from catalogue of Conzerv model) 0.4

Typical Anolgue Meter burden in ohm (from catalogue of AE/Rishab) & Transducer

4.5Total 5Nos Analogue meter connected & max 4 nos of transducer per CT

Max. Burden margin Consider for future use 2

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl) =Rct+4.79

Total Burden on CT = Lead Burden+ Meter Burden+burden margin

Consider for future use

17.69

20 VA, CL-0.2 20 VA arrived at considering all the

meter connected

iv) Core –4 (87 B1/B2)

Fault level of switchyard = 40 kA for 1 sec.

CT ratio chosen 600/1A

CT sec lead resistance with 2.5 mm2

Cu cond cable 270 m length (max) RL = 8.87x0.27 = 2.3949W

VK = If (RCT + 2 Rlead + Rrelay) RCT value from CT manufacturer Bus bar protection is a numerical relay

VK = 40x1 (RCT +4.79+0.2) = 40 RCT + 199.6

Knee point voltage selected is 40 RCT + 200V

CT ratio chosen 600/1A

CLPS , VK  40 RCT + 200V, Im  15 mA at VK/2

v) Core –5

Spare core . Parameters same as core-4,

VK  40 RCT + 150V

Im  15 mA at VK/2

A GT Bushing CTs

i) Core-1 Phase CT for REF protection (64 GT)

% Impedence of GT is 14.50%

GT full load current on HV side = Considering SPAE 10 relay with

512.40 Setting relay burden =5.4 VA

Considering the Source impedance based on 40kA, max. earth fault current I = F.L current / % Z x 0.9 ( -ve tol of 10%)

3457.15

= 3607.70 as GT impedance Zt = 14.5%

Choosing bushing CT of 600/1 on GT HV side & neutral side CT sec. equiv. thro'fault current = 3607.70 x1/600 5.76

(4)

VR = If (RCT + 2RL + R relay) = 6.01 ( RCT + 2 x 1.242 + 5.4/1) VK ` = 6.01 RCT + 47.38 2.5 mm2 Cu cond, 140 m length VK read = atleast 2 VR VK = 2x(6.01 RCT + 47.38)V VK = 12.5 RCT + 100V CT parameters chosen CT ratio 600/1A

VK  13 RCT + 100 V Im < 30 mA at VK/2 Same CT parameter is applicable for neutral REF CT

ii) Core - 2 Neutral CT-GT inverse time ground O/C relay (51NGT)

CT chosen 600/1A 20 VA, CL 5P20 P20 because Chracteristic will get

smoothen after 20 times of rated current

Typical Relay burden in ohm (from ABB catlogue)

_0.2

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl) =Rct+2.4836

Rct Assumed for CT Sec.1A is 6 ohm for 600/1Amp

_8.4836

Total Burden on CT = Lead Burden+ Meter Burden+burden margin

Consider for future use

8.6836

10 VA, CL-5P20 As relay used is Numerical type,

hence 10 VA considered is more than Sufficient.

B UAT BUS DUCT MOUNTED CTS

Formula used / reference / design assumption (87UAT) (HV side)

i) Core –1 (50 UAT – HV side) For a fault at UAT HV terminals

Fault contribution from generator

Base-MVA 355

Generator Xd” sat From Generator data sheet 0.120

Zg with 30% neg tolerance

Zg (pu) = 0.155X0.7= 10.85% 0.084

Zg (pu) with 355MVA base= 0.0845

Fault contribution from generator is Base MVA/Fault MVA 4201.68

Fault contribution from 400KV system in MVA 27712.8

Zspu with 10% negative tolerance = 1.15% _1.152

Zgt with 10% negative tolerance 13.05% 13.05

System contribution

= Base MVA / (Zspu+Zgt) 2499.49

= 2499.49 MVA   100 X 100100

(5)

Total fault MVA(Contribution from Generator & GT system) = 3252.91+2499.49

6701.17 = 5752.40 MVA

Fault current = 166.06 KA 203.63

CT Chosen = 8500/1A Cl 5P20, 10VA 10181.38

Ratio of fault current to CT ratio < 20 times 23.96

However the ratio of rated burden of CT & the connected burden is about 10 times. Therefore the voltage, developed by the CT (200V) will be increased by that ratio, therefore the CT does not saturate and hence CT chosen is ok.

Vdesin=BurdenxALF/CT Secondary

(ii) Core – 2 (51 UAT – HV side) CT chosen – 800/1A

10VA, CL 5P20

Typical Relay burden in ohm (from ABB catlogue) 0.1

Total Burden on CT = Lead Burden+ Relay Burden

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl) =Rct+2.2175

9.3175

10 VA, CL-5P20 As relay used is Numerical type,

hence 10 VA considered is more than Sufficient.

(iii) Core – 3 (87 UAT-HT side) 800/1A , CL PS , Im  15 mA at VK/2 UAT rating – 20 MVA

Current on 20 kV side = 577.35

607.74 At the lowest tap

800/1A i.e – 5%, CT ratio will be

VK = 40xIx(RCT + 2RL + R relay) CT ratio choose CT = 800/1A

= 40x1x(RCT +2x8.87x0.125 +0.1)

VK >40RCT+92.7

VK 40RCT+92.7V 2x8.87x100/1000

Im 15mA AT VK/2

C UAT LV side CTs

i) Core –1 (87- 0A) (UAT-LV)

Total running load in KVA on the 6.6 kV bus ( higher of the two buses U1A and U1B taken from UAT sizing calculation)

18451

Total running load in Amp on the 6.6 kV bus ( higher of the two buses U1A and U1B taken from UAT sizing calculation)

1614.04

CT chosen – 2000/1A This also cater the installed

Capacity of UAT i.e. 20MVA

VK = 40 x I (RCT + 2RL + R relay)

2 RL = 2 x 8.87 x 0.1 (1 run 2.5 mm 2

cable / phase, L = 100 meters) = 2.661W

1.774

VK = 40x1(RCT + 1.774 + 0.1) = 40RCT+74.96 74.96

(6)

VK selected is  40RCT+80V

CT chosen 2000/1A, CLPS, Vk  40RCT+80V

Im  15 mA at Vk/2

ii) Core - 2 64-UAT - LV side & 87-UAT

20/16 MVA , 20/6.9 KV

Rated Current of Unit Transformer at nominal Tap 1749.55

Fault Current limited by transformer impedance of 10% at -5% 18416.28

= 18.416 KA

Fault Current reflected on CT Secondary 9.21

VK = 9.21x(Rct+2x0.887+0.1)

= 9.21 RCT + 17.26

=10Rct+20V Im  15mA at Vk/2

Since the phase side CTs for REF protection will be same as that used for 87 UAT, same parameters as that of core-2 will be provided for neutral CT to be located in NGR or Neutral Bushings of transformer.

iii) Core –3 (51 UAT - LV) 2000/1A, 10VA, CL 5P20

R relay in ohm (from relay catalogue of ABB model SPAJ) 0.1

Total Burden on CT = Lead Burden+ Relay Burden Lead Burden for lead length of 50M= I2_x(R

=Rct+0.887

10 VA, CL5P20

As relay used is numerical(SPAJ-140C) type, hence 10 VA considered is more than Sufficient also Lead burden is less than above assumed buden as relay & Ct are at the same Switchgear.

iv) Core –4 (Metering)

2000 / 1A , 10VA , CL 0.5 , ISF  5

Burden margin Consider for future use 2

Lead Burden for lead length of 50M= I2x(Rct+2RL) =Sqr(1)*(Rct+2Rl) =Rct+0.887

15.087

20 VA, CL5P20 As meter used is Multifunction type,

hence 10 VA considered is more than Sufficient also Lead burden is less than above assumed buden as Meter & CT are at the same Switchgear.

v) 51 N – UAT- LV.

Earth Fault current to be restricted to 300Amp. For neutral CT to be located in NGR. 300/1A, 15VA, CL 5P20

D ST LV side CTs

i) Core –1 ( metering)

Total running load in KVA on the 6.6 kV bus ( higher of the two buses C1A and C1B taken from ST sizing calculation)

22292  100 X 100 100

(7)

Total running load in Amp on the 6.6 kV bus ( higher of the two buses C1A and C1B taken from ST sizing calculation)

1950.04

CT chosen – 2500/1A Taking into consideration

25MVA(Rated Installed Capacity) Current is 2187Amp

18.087

2500 / 1A , 20VA , CL 0.5 , ISF  5 As meter used is Multifunction type, hence 20 VA considered is more than Sufficient also Lead burden is less than above assumed buden as Meter & CT are at the same Switchgear.

ii) Core - 2 (ST - 64 RST - LV side)

25 MVA , 220/6.9 KV

Rated Current of Station Transformer at nominal Tap 2186.93

Fault Current limited by transformer impedance of 14.5% at -15% 25728.62 = 25.73 KA

Fault Current reflected on CT Secondary 10.29

2 RL = 2 x 8.87 x 0.20 (1 run 2.5 mm2 cable / phase, L = 250 meters) = 4.435W

4.435

Vk = 10.29x(Rct+4.435+0.1) 46.67

= 10.29 RCT + 46.67

= 11RCT+46.67 V

i.e. CTR chosen - 2500/1A, 11RCT+50V, Im 15mA at Vk/2

iii) Core –3 (51 ST - LV)

2500/1A, 20VA, CL 5P20 From Above Full Load Current

R relay in ohm (from relay catalogue of ABB model SPAJ) 0.1

2500/1A

20 VA, CL5P20

As relay used is numerical(SPAJ-140C) type, hence 20 VA considered is more than Sufficient also Lead burden is less than above assumed buden as relay & Ct are at the same Switchgear.

iv) Core –4 (87- ST- LV)

CT chosen – 2500/1A From Above Full Load Current

VK = 40 x I (RCT + 2RL + R relay)

2 RL = 2 x 8.87 x 0.15 (1 run 2.5 mm2 cable / phase, L = 250 meters) = 2.661W

4.435

1.81064204.373110V311KV

 

(8)

VK = 40x1(RCT + 4.435 + 0.1) = 40RCT+181.4 VK selected is  40RCT+200V CT chosen 2500/1A, CLPS, Vk  40RCT+115V Im  15 mA at Vk/2      MVKV1ARX2 x 100%Zx 100 11294112.3110x11 100xx 3 40404040R282IRXX0.2566RX5248100.012x.623 0.5941.6

(9)

SNo. Type of switchboard Feeder Load rating (kW) Rated current CT ratio Remark

A 6.6 kV Unit switchgear (U1A & U1B) comprising of the following panels with ratings and accessories as indicated in single line diagram, specification & data sheet.

Motor Feeder

1 Boiler Feed Pump-1A, 1B 5400 600/1

i. For Differential Protection

Motor rated Current = 5400/Sqrt(3)/6.6/0.9 524.86 Differential CT for Motor Protection

Vk = 40xIx(Rct+2RL+ Rrelay) = 40*1*(Rct+2x0.7983+0.1) = 40Rct+67.864V

RL = 8.87X0.09 (Considering 90m Length from Motor terminal to Relay)=0.7983 R relay = 0.1

Vk>= 40Rct+70V, Im<=30mA at Vk/2

ii. For O/C & E/F Protection

R relay in ohm (from relay catalogue of ABB model SPAJ)

0.1 Total Burden on CT = Lead Burden+ Relay Burden

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl) =Rct+0.7096

10 VA, CL5P20 As relay used is numerical(SPAJ-140C) type,

hence 10 VA considered is more than Sufficient also Lead burden is less than above assumed buden as relay & Ct are at the same Switchgear.

iii. For Metering Core

0.2 Typical Anolgue Meter burden in ohm (from

catalogue of AE/Rishab) & Transducer

1

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl) =Rct+0.7096

10.9096

15 VA, CL-0.5 As meter used is Multifunction type, hence

15 VA considered is more than Sufficient also Lead burden is less than above assumed buden as Meter & CT are at the same Switchgear.

2 Condensate Extraction Pump-1A, 1B 1100 150/1

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

Rct Assumed for CT Sec.1A is <=6 ohm

6.7096

_6.7096

(10)

10 VA, CL5P20 As relay used is numerical(SPAJ-140C) type, hence 10 VA considered is more than Sufficient also Lead burden is less than above assumed buden as relay & Ct are at the same Switchgear.

Typical Meter burden in ohm (from catalogue of

Conzerv model)

0.2

1

Burden margin Consider for future use

2 x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

6.7096

Total Burden on CT = Lead Burden+ Meter

Burden+burden margin Consider for future use

9.9096

10 VA considered is more than Sufficient also Lead burden is less than above assumed buden as Meter & CT are at the same Switchgear. Also Rct is max typical value for 750Amp Primary

3 ID-1A, 1B 2240 300/1

Vk = 40xIx(Rct+2RL+ Rrelay) = 40*1*(Rct+2x1.996+0.1) = 40Rct+163.66 V

RL = 8.87X0.225 (Considering 225m Length from Motor terminal to Relay)=1.996, R relay = 0.1

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

6.7096

0.2

1 ₂

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

6.7096

9.9096

4 FD-1A, 1B 800 87.48 100/1

i. For O/C & E/F Protection

Lead Burden for lead length of 40M= I2_x(R

(11)

Rct Assumed for CT Sec.1A is <=4 ohm 6.7096

ii. For Metering Core

Conzerv model)

0.2

1 ₂

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

4.7096

7.9096

5 PA-1A, 1B 1600 200/1

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

_5.7096

5.8096

Conzerv model)

0.2

1

2 x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

5.7096

8.9096

6 Coal Mill-1A, 1B, 1C, 1D, 1E, 1F 400 43.74 50/1 _{3C x 185 mm}2

(12)

Conzerv model)

0.2

1 ₂

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

1.7096

4.9096

7 CWP-1A, 1B 1400 200/1 3C x 185 mm2

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

5.7096

_5.8096

0.2

1

2 x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

_5.7096

8.9096

8 Main Incomer from Unit Transformer 2000/1

(13)

1

Total Burden on CT = Lead Burden+ Meter Burden Lead Burden for lead length of 40M= I2_x(R

=Rct+0.7096 Rct Assumed for CT Sec.1A is 12 ohm for

2000/1Amp

12.7096 Total Burden on CT = Lead Burden+ Meter

Burden+burden margin Consider for future use

15.9096

9 Unit Service Transformer-1A & 1B 2500 219.79 300/1 3C x 240 mm2

0.2

1 ₂

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

Rct Assumed for CT Sec.1A is 6 ohm for

2000/1Amp

6.7096

9.9096

10 Spare motor feeder on all the Unit-1 buses 5400 590.47 600/1 CT Details same as Feedpump Motor feeder

11 Spare transformer feeder on all Unit-1 buses 2500 219.79 300/1

12 ESP Service Transformer Feeder-1A & 1B feeder 2500 219.79 300/1

13 Tie to C1A & C1B 2000/1 CT Details same as I/C feeder from Unit Transformer

B 6.6 kV Unit switchgear (U2A & U2B) comprising of the following panels with ratings and accessories as indicated in single line diagram, specification & data sheet.

Motor Feeder

1 Boiler Feed Pump-2A, 2B 5400 600/1 CT Details same as above Feedpump Motor

feeder

Vk = 40xIx(Rct+2RL+ Rrelay)

CT Details same as Unit service Trans. feeder

(14)

= 40*1*(Rct+2x0.7983+0.1) = 40Rct+67.864V

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

Rct Assumed for CT Sec.1A is 7 ohm

_7.7096

7.8096

Conzerv model)

0.2

1 ₂

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

7.7096

10.9096

2 Condensate Extraction Pump-2A, 2B 1100 150/1

0.2

1 ₂

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

6.7096

(15)

10 VA, CL-0.5 As meter used is Multifunction type, hence 10 VA considered is more than Sufficient also Lead burden is less than above assumed buden as Meter & CT are at the same Switchgear. Also Rct is max typical value for 750Amp Primary

3 ID-2A, 2B 2240 300/1

=Rct+0.7096

1

9.9096

4 FD-2A, 2B 800 87.48 100/1 3C x 185 mm2

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

_6.7096

6.7096

0.2

1

2 x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

(16)

7.9096

5 PA-2A, 2B 1600 200/1

0.2

1

2 x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

_5.7096

8.9096

6 Coal Mill-2A, 2B, 2C, 2D, 2E, 2F 400 43.74 50/1 3C x 185 mm2

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

1.7096

1.8096

1

(17)

4.9096

7 CWP-2A, 2B 1400 200/1 3C x 185 mm2

Vk>= 40Rct+210V, Im<=30mA at Vk/2 Or CT details will be same as earlier Supplied CT.

0.2

1

2 x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

_5.7096

8.9096

8 Main Incomer from Unit Aux transformer 2000/1 CT Details same as I/C feeder from Unit Transformer

9 Unit Service Transformer-2A & 2B 2500 219.79 300/1 CT Details same as Station Service transformer feeder to SST Transformer

10 Spare motor feeder on Unit-2 buses 5400 590.47 600/1 CT Details same as Feedpump Motor feeder

11 Spare transformer feeder on Unit-2 buses 2500 219.79 300/1

12 ESP Service Transformer Feeder-2A & 2B feeder 2500 219.79 300/1

C 6.6 kV Station switchgear (C1A & C1B) comprising of the following panels with ratings and accessories as indicated in single line diagram, specification & data sheet.

1 BFP-1C & 2C Motor Feeder From C1A & C2A Board Respct.

5400 600/1

CT Details same as Unit service Trans. feeder

(18)

x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

Rct Assumed for CT Sec.1A is 7 ohm

_7.7096

7.8096

0.2

1

2 x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

7.7096

10.9096

2 Compressor Feeders From C1A & C2A Board 500 100/1

Motor rated Current = 5400/Sqrt(3)/6.6/0.9 54.67

0.2

Typical Anolgue Meter burden in ohm (from

1

2 x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

_4.7096

7.9096

3 Tie to U1A 2000/1 CT Details same as Unit Switchgear I/C

feeder from Unit Aux. Transformer

4 SST-1 feeder From C1A Board 1600 140.67 300/1 CT ratio is kept same as to maintain the

uniformity with Station Service Transformer

5 CWP-1C From C1B Board 1400 153.09 200/1 CT Details same as Other Station service

Switchgear

(19)

= 40*1*(Rct+2x3.548+0.1) = 40Rct+287.84V

0.2

Typical Anolgue Meter burden in ohm (from

1

2 x(R

ct

+2R

L

)

=Sqr(1)*(Rct+2Rl)

=Rct+0.7096

_5.7096

8.9096

6 Tie to U1B 2000/1

7 Spare feeder 300/1

8 CWPT-1 feeder From C1B Board 2500 219.79 300/1 CT Details same as Other Station service

Switchgear

9 Incomer 2500/1 7Rx1Cx630 mm2

D 6.6 kV Station switchgear (C2A & C2B) comprising of the following panels with ratings and accessories as indicated in single line diagram, specification & data sheet.

1 Compressor Feeder From C2A Board 500 54.67 100/1 CT Details same as above air compressor

Feeder.

2 CWPT-2 feeder From C2A Board 2500 219.79 300/1 CT Details same as Other Station service

Switchgear 3 Tie to U2A 2000/1 5Rx1Cx630 mm2 4 Incomer 2500/1 _{7Rx1Cx630 mm}2 5 Spare feeder 300/1 3C x 240 mm2 6 Incomer 2500/1 7Rx1Cx630 mm2 7 Tie to U2B 2000/1 _{5Rx1Cx630 mm}2

8 SST-2 feeder From C2B Board 1600 140.67 300/1 3C x 240 mm2

9 Compressor Feeder From C2B Board 500 54.67 100/1 CT Details same as above air compressor

Feeder.

10 BFP-2C Motor Feeder From C2B Board 5400 600/1 3Rx1Cx630 mm2

(20)

10 VA, CL5P20 As relay used is numerical(SPAJ-140C) type, hence 10 VA considered is more than Sufficient also Lead burden is less than above assumed buden as relay & Ct are at the same Switchgear.

1

10.9096