Ct Sizing XL

Calculation of CT Parameter Description

Parameter

Remark

From generator Data sheet

From generator Data sheet

(i) Generator parameter Rated Voltage(kV) Rated Current(Amp) Sync. Reactance Xd is 1/SCR Subtransient Reactance Xd"(Saturated) Transient Reactance Xd' (Saturated) Rated Voltage at -5% FL current at -5%of rated Voltage=

19 9116.3 200.0 12.0% 20.0% 18.05 9596.1

Voltage at + 5% FL current at +5% of rated Voltage=

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

3571.43

Fault contribution from system in MVA considering 40KA system Impedence on 220KV Side. Source impedence in Percentage at 300 Base

2024.10

Taking higher of the above two values =

3571.43

1.97%

108.52

Fault Current in KA Taking higher value of the fault contribution from i.e. fault contribution from system / fault contribution from gen 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 Im  15 mA at Vk/2

Page 1 of 20

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

0.4 7 Total 10Nos Analogue meter connected & max 4 nos of transducer per CT

Max. Burden margin Consider for future use Total Burden on CT = Lead Burden+ Meter Burden 2

Lead Burden for lead length of 100M= I x(Rct+2RL) Rct Assumed for CT Sec.1A is 15 ohm for 11000/1Amp Total Burden on CT = Lead Burden+ Meter Burden+burden margin Consider for future use 30 VA, CL-0.2

2 =Sqr(1)*(Rct+2Rl) =Rct+1.774 16.774 26.174 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) 512.40

GT HT side current (current on 400 kV side) = = 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) 600/1A Total Burden on CT = Lead Burden+ Relay Burden Lead Burden for lead length of 270M= I2x(Rct+2RL) Rct Assumed for CT Sec.1A is 6 ohm Total Burden on CT = Lead Burden+ Relay Burden 15 VA, CL5P20

R relay= 0.1 (from relay catalogue of ABB)

=Sqr(1)*(Rct+2Rl) =Rct+4.79 10.79 10.89 Cater the Load burden of Numerical Relay

Page 2 of 20

iii) Core –3 (metering) 600/1A Typical Meter burden in ohm (from catalogue of Conzerv model) Typical Anolgue Meter burden in ohm (from catalogue of AE/Rishab) & Transducer

0.4 4.5 Total 5Nos Analogue meter connected & max 4 nos of transducer per CT

Max. Burden margin Consider for future use Total Burden on CT = Lead Burden+ Meter Burden 2

Lead Burden for lead length of 270M= I x(Rct+2RL) Rct Assumed for CT Sec.1A is 6 ohm for 600/1Amp Total Burden on CT = Lead Burden+ Meter Burden+burden margin Consider for future use 20 VA, CL-0.2

iv)

2 =Sqr(1)*(Rct+2Rl) =Rct+4.79 10.79

17.69 20 VA arrived at considering all the meter connected

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 GT full load current on HV side = 512.40

14.50% Considering SPAE 10 relay with 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

Page 3 of 20



VR = If (RCT + 2RL + R relay) = 6.01 ( RCT + 2 x 1.242 + 5.4/1)

2

VK ` = 6.01 RCT + 47.38

2.5 mm 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

ii)

Same CT parameter is applicable for neutral REF CT

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) Total Burden on CT = Lead Burden+ Meter Burden

0.2

2

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

Lead Burden for lead length of 140M= I x(Rct+2RL) Rct Assumed for CT Sec.1A is 6 ohm for 600/1Amp Total Burden on CT = Lead Burden+ Meter Burden+burden margin Consider for future use 10 VA, CL-5P20

B

8.4836 8.6836 As relay used is Numerical type, hence 10 VA considered is more than Sufficient.

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 = Zgt with 10% negative tolerance 1 0 0 1 0 0 X 1 0 0

System contribution = Base MVA / (Zspu+Zgt)

1.15%

1.152

13.05%

13.05



2499.49

= 2499.49 MVA

Page 4 of 20

Total fault MVA(Contribution from Generator & GT system) = 3252.91+2499.49 = 5752.40 MVA Fault current

6701.17

= 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. (ii)

Vdesin=BurdenxALF/CT Secondary

Core – 2 (51 UAT – HV side) CT chosen – 800/1A 10VA, CL 5P20 Typical Relay burden in ohm (from ABB catlogue) Total Burden on CT = Lead Burden+ Relay Burden

0.1

2

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

Lead Burden for lead length of 125M= I x(Rct+2RL) Rct Assumed for CT Sec.1A is 7 ohm for 600/1Amp Total Burden on CT = Lead Burden+ Meter Burden+burden margin Consider for future use 10 VA, CL-5P20

(iii)

9.2175 9.3175 As relay used is Numerical type, hence 10 VA considered is more than Sufficient.

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 = 577.35 607.74 800/1A

At the lowest tap 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 mm2 cable / phase, L = 100 meters) 2.661W VK = 40x1(RCT + 1.774 + 0.1) = 40RCT+74.96

=

1.774

74.96

Page 5 of 20

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 0.1

R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden Lead Burden for lead length of 50M= I2x(Rct+2RL)

=Sqr(1)*(Rct+2Rl) =Rct+0.887

Rct Assumed for CT Sec.1A is 6 ohm Total Burden on CT = Lead Burden+ Relay Burden 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)

6.887 6.987

Core –4 (Metering) 2000 / 1A , 10VA , CL 0.5 , ISF  5 Typical Meter burden in ohm (from catalogue of Conzerv model) Burden margin Consider for future use Total Burden on CT = Lead Burden+ Meter Burden Lead Burden for lead length of 50M= I2x(Rct+2RL)

0.2 2 =Sqr(1)*(Rct+2Rl) =Rct+0.887

Rct Assumed for CT Sec.1A is 12 ohm Total Burden on CT = Lead Burden+ Meter Burden+burden margin Consider for future use 20 VA, CL5P20

12.887 15.087 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)

1 0 0 1 0 0 X 1 0 0



22292

Page 6 of 20

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




Taking into consideration 25MVA(Rated Installed Capacity) Current is 2187Amp

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

0.2

Burden margin Consider for future use Total Burden on CT = Lead Burden+ Meter Burden Lead Burden for lead length of 50M= I2x(Rct+2RL)

2 =Sqr(1)*(Rct+2Rl) =Rct+0.887

Rct Assumed for CT Sec.1A is 15 ohm Total Burden on CT = Lead Burden+ Meter Burden+burden margin Consider for future use 2500 / 1A , 20VA , CL 0.5 , ISF  5

ii)

15.887 18.087 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.

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) 2500/1A Total Burden on CT = Lead Burden+ Relay Burden Lead Burden for lead length of 50M= I2x(Rct+2RL)

0.1

=Sqr(1)*(Rct+2Rl) =Rct+0.887

Rct Assumed for CT Sec.1A is 15 ohm Total Burden on CT = Lead Burden+ Relay Burden 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.

15.887 15.987

11KV 110V 37 . 4204 1.81063

iv)

Core –4 (87- ST- LV) 


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

Page 7 of 20

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  40 I

3 2 3 2 2 X 0 . 2 5 6 6 X % Z 1 0 0 x 1 0   1 1 2 8 2 x 1 0 1 K 1 V 1    x x x 2 R 3 x 1 1   1 M 0 0 V A 9 4 . 1 5 2 4 8 . 6

R 1 0 0 0 . 0

1

2



0 . 5 9 1 . 6

4

Page 8 of 20

CT sizing for 6.6 kV System SNo.

Type of switchboard

Feeder Rated Load current rating (kW)

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 i.

Boiler Feed Pump-1A, 1B For Differential Protection Motor rated Current = 5400/Sqrt(3)/6.6/0.9 Differential CT for Motor Protection Vk = 40xIx(Rct+2RL+ Rrelay)

5400

CT ratio

Remark

600/1

524.86

= 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) Total Burden on CT = Lead Burden+ Relay Burden Lead Burden for lead length of 40M= I

0.1

2

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

x(Rct+2RL)

Rct Assumed for CT Sec.1A is 7 ohm Total Burden on CT = Lead Burden+ Relay Burden 10 VA, CL5P20

iii.

7.7096 7.8096 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.

For Metering Core Typical Meter burden in ohm (from catalogue of Conzerv model) Typical Anolgue Meter burden in ohm (from catalogue of AE/Rishab) & Transducer Burden margin Consider for future use Total Burden on CT = Lead Burden+ Meter Burden Lead Burden for lead length of 40M= I

0.2 1 2

2

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

x(Rct+2RL)

Rct Assumed for CT Sec.1A is 7 ohm for 750/1Amp

7.7096

Total Burden on CT = Lead Burden+ Meter Burden+burden margin Consider for future use 15 VA, CL-0.5

2 i.

Condensate Extraction Pump-1A, 1B For Differential Protection Motor rated Current = 1100/Sqrt(3)/6.6/0.9 Differential CT for Motor Protection Vk = 40xIx(Rct+2RL+ Rrelay) = 40*1*(Rct+2x0.7983+0.1) = 40Rct+67.864V

ii.

10.9096 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. 1100

150/1

113.21


Vk>= 40Rct+70V, Im<=30mA at Vk/2 For O/C & E/F Protection R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden Lead Burden for lead length of 40M= I

2

x(Rct+2RL)

Rct Assumed for CT Sec.1A is <=6 ohm Total Burden on CT = Lead Burden+ Relay Burden

0.1

=Sqr(1)*(Rct+2Rl) =Rct+0.7096 6.7096 6.7096

Page 9 of 20

10 VA, CL5P20

iii.


3 i.

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.

0.2 1 2

2

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

x(Rct+2RL)


6.7096


9.9096

ID-1A, 1B For Differential Protection Motor rated Current = 1100/Sqrt(3)/6.6/0.9 Differential CT for Motor Protection Vk = 40xIx(Rct+2RL+ Rrelay)

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 2240

300/1

222.67

= 40*1*(Rct+2x1.996+0.1) = 40Rct+163.66 V

ii.

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


0.1

2

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

x(Rct+2RL)

Rct Assumed for CT Sec.1A is <=6 ohm Total Burden on CT = Lead Burden+ Relay Burden 10 VA, CL5P20

iii.



0.2 1 2

2

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

x(Rct+2RL)


6.7096


4 i.

FD-1A, 1B For O/C & E/F Protection R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden Lead Burden for lead length of 40M= I2x(Rct+2RL)

9.9096 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 800

87.48

100/1 0.1

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

Page 10 of 20


ii.



0.2 1 2

2

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

x(Rct+2RL)


4.7096


5 i.

PA-1A, 1B For Differential Protection Motor rated Current = 1100/Sqrt(3)/6.6/0.9 Differential CT for Motor Protection Vk = 40xIx(Rct+2RL+ Rrelay)


200/1

164.66

= 40*1*(Rct+2x0.887+0.1) = 40Rct+74.96V

ii.



0.1

2

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

x(Rct+2RL)


iii.



6 i.

5.7096 5.8096

0.2 1 2

2

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

x(Rct+2RL)


5.7096


8.9096

Coal Mill-1A, 1B, 1C, 1D, 1E, 1F For O/C & E/F Protection R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden Lead Burden for lead length of 40M= I2x(Rct+2RL)

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. 400

43.74

50/1

3C x 185 mm2 0.1

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

Page 11 of 20


ii.



0.2 1 2

2

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

x(Rct+2RL)


1.7096


7 i.

CWP-1A, 1B For Differential Protection Motor rated Current = 1100/Sqrt(3)/6.6/0.9 Differential CT for Motor Protection Vk = 40xIx(Rct+2RL+ Rrelay)


200/1

144.08

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

ii.



0.1

2

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

x(Rct+2RL)


iii.



8 i.

3C x 185 mm2

0.2 1 2

2

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

x(Rct+2RL)


5.7096


8.9096

Main Incomer from Unit Transformer For O/C & E/F Protection R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden Lead Burden for lead length of 40M= I2x(Rct+2RL)

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. 2000/1 0.1

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

Page 12 of 20


ii.


For Metering Core Typical Meter burden in ohm (from catalogue of Conzerv model) Typical Anolgue Meter burden in ohm (from catalogue of AE/Rishab) & Transducer Burden margin Consider for future use Total Burden on CT = Lead Burden+ Meter Burden

0.2 1 2

Lead Burden for lead length of 40M= I2x(Rct+2RL)

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

Rct Assumed for CT Sec.1A is 12 ohm for 2000/1Amp Total Burden on CT = Lead Burden+ Meter Burden+burden margin Consider for future use 20 VA, CL-0.5

9 i.

ii.

Unit Service Transformer-1A & 1B For O/C & E/F Protection R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden

12.7096 15.9096

2500

219.79

300/1

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. 3C x 240 mm2 0.1


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




0.2 1 2

2

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

x(Rct+2RL)

Rct Assumed for CT Sec.1A is 6 ohm for 2000/1Amp Total Burden on CT = Lead Burden+ Meter Burden+burden margin Consider for future use 10 VA, CL-0.5

6.7096 9.9096 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. CT Details same as Feedpump Motor feeder

10

Spare motor feeder on all the Unit-1 buses

5400

590.47

600/1

11 12 13

Spare transformer feeder on all Unit-1 buses ESP Service Transformer Feeder-1A & 1B feeder Tie to C1A & C1B

2500 2500

219.79 219.79

300/1 300/1 2000/1

CT Details same as Unit service Trans. feeder 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 Boiler Feed Pump-2A, 2B

600/1

CT Details same as above Feedpump Motor feeder

1 i.

For Differential Protection Motor rated Current = 5400/Sqrt(3)/6.6/0.9 Differential CT for Motor Protection Vk = 40xIx(Rct+2RL+ Rrelay)

5400

524.86

Page 13 of 20

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

ii.



0.1

2

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

x(Rct+2RL)


iii.



0.2 1 2

2

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

x(Rct+2RL)


7.7096


2 i.

Condensate Extraction Pump-2A, 2B For Differential Protection Motor rated Current = 1100/Sqrt(3)/6.6/0.9 Differential CT for Motor Protection Vk = 40xIx(Rct+2RL+ Rrelay) = 40*1*(Rct+2x0.7983+0.1) = 40Rct+67.864V

ii.

iii.


150/1

113.21


Vk>= 40Rct+70V, Im<=30mA at Vk/2 For O/C & E/F Protection R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden

0.1


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




2

x(Rct+2RL)

0.2 1 2 =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

Page 14 of 20

10 VA, CL-0.5

3 i.

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

ID-2A, 2B For Differential Protection Motor rated Current = 1100/Sqrt(3)/6.6/0.9 Differential CT for Motor Protection Vk = 40xIx(Rct+2RL+ Rrelay)

2240

300/1

222.67

= 40*1*(Rct+2x1.995+0.1) = 40Rct+163.66V

ii.

iii.


Vk>= 40Rct+175V, Im<=30mA at Vk/2 For O/C & E/F Protection R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden

0.1


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




0.2 1 2


4 i.


6.7096


9.9096

FD-2A, 2B For O/C & E/F Protection R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden Lead Burden for lead length of 40M= I

2

x(Rct+2RL)


ii.

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

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 800

87.48

100/1

3C x 185 mm2 0.1

=Sqr(1)*(Rct+2Rl) =Rct+0.7096 6.7096 6.7096 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.


2

x(Rct+2RL)


0.2 1 2 =Sqr(1)*(Rct+2Rl) =Rct+0.7096 4.7096

Page 15 of 20


5 i.

PA-2A, 2B For Differential Protection Motor rated Current = 1100/Sqrt(3)/6.6/0.9 Differential CT for Motor Protection Vk = 40xIx(Rct+2RL+ Rrelay)


200/1

164.66

= 40*1*(Rct+2x0.887+0.1) = 40Rct+74.96V

ii.

iii.

Vk>= 40Rct+80V, Im<=30mA at Vk/2 For O/C & E/F Protection R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden =Sqr(1)*(Rct+2Rl) =Rct+0.7096




0.2 1 2

2

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

x(Rct+2RL)


5.7096


8.9096

Coal Mill-2A, 2B, 2C, 2D, 2E, 2F For O/C & E/F Protection R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden Lead Burden for lead length of 40M= I

2

x(Rct+2RL)


ii.

0.1


Lead Burden for lead length of 40M= I

6 i.


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. 400

43.74

50/1

3C x 185 mm2 0.1

=Sqr(1)*(Rct+2Rl) =Rct+0.7096 1.7096 1.8096 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.

For Metering Core Typical Meter burden in ohm (from catalogue of Conzerv model) Typical Anolgue Meter burden in ohm (from catalogue of AE/Rishab) & Transducer Burden margin Consider for future use Total Burden on CT = Lead Burden+ Meter Burden Lead Burden for lead length of 40M= I2x(Rct+2RL) Rct Assumed for CT Sec.1A is 5 ohm for 50/1Amp

0.2 1 2 =Sqr(1)*(Rct+2Rl) =Rct+0.7096 1.7096

Page 16 of 20


7 i.

CWP-2A, 2B For Differential Protection Motor rated Current = 1100/Sqrt(3)/6.6/0.9 Differential CT for Motor Protection Vk = 40xIx(Rct+2RL+ Rrelay)


200/1

144.08

= 40*1*(Rct+2x2.4836+0.1) = 40Rct+202.68V

RL = 8.87X0.28 (Considering 280m Length from Motor terminal to Relay)=2.4836 R relay = 0.1 Or CT details will be same as earlier Supplied CT.

Vk>= 40Rct+210V, Im<=30mA at Vk/2 ii.

iii.

3C x 185 mm2

For O/C & E/F Protection R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden

0.1


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




0.2 1 2

2

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

x(Rct+2RL)


5.7096


8.9096 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.

8

Main Incomer from Unit Aux transformer

9

Unit Service Transformer-2A & 2B

2500

219.79

300/1

10

Spare motor feeder on Unit-2 buses

5400

590.47

600/1

CT Details same as I/C feeder from Unit Transformer CT Details same as Station Service transformer feeder to SST Transformer CT Details same as Feedpump Motor feeder

11 12

Spare transformer feeder on Unit-2 buses ESP Service Transformer Feeder-2A & 2B feeder

2500 2500

219.79 219.79

300/1 300/1

CT Details same as Unit service Trans. feeder

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. BFP-1C & 2C Motor Feeder From C1A & C2A Board Respct. For Differential Protection Motor rated Current = 5400/Sqrt(3)/6.6/0.9 Differential CT for Motor Protection Vk = 40xIx(Rct+2RL+ Rrelay)

1 i.

= 40*1*(Rct+2x0.7983+0.1) = 40Rct+63.864V

ii.

2000/1

5400

600/1

524.86


Vk>= 40Rct+70V, Im<=30mA at Vk/2 For O/C & E/F Protection

Page 17 of 20

R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden Lead Burden for lead length of 40M= I

0.1

2

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

x(Rct+2RL)


iii.



0.2 1 2

2

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

x(Rct+2RL)


7.7096


2 i.

ii.

Compressor Feeders From C1A & C2A Board Motor rated Current = 5400/Sqrt(3)/6.6/0.9 For O/C & E/F Protection R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden

10.9096 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. 500 54.67

100/1

0.1


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




0.2 1 2

2

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

x(Rct+2RL)


4.7096


7.9096

2000/1

3

Tie to U1A

4

SST-1 feeder From C1A Board

1600

140.67

300/1

5

CWP-1C From C1B Board

1400

153.09

200/1

i.

For Differential Protection Motor rated Current = 1100/Sqrt(3)/6.6/0.9 Differential CT for Motor Protection Vk = 40xIx(Rct+2RL+ Rrelay)

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. CT Details same as Unit Switchgear I/C feeder from Unit Aux. Transformer CT ratio is kept same as to maintain the uniformity with Station Service Transformer CT Details same as Other Station service Switchgear

144.08

Page 18 of 20

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

ii.

iii.


Vk>= 40Rct+290V, Im<=30mA at Vk/2 For O/C & E/F Protection R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden Lead Burden for lead length of 40M= I2x(Rct+2RL)

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




0.2 1 2

2

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

x(Rct+2RL)


5.7096


8.9096

6 7 8

Tie to U1B Spare feeder CWPT-1 feeder From C1B Board

9

Incomer

D

1

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. Compressor Feeder From C2A Board

2

CWPT-2 feeder From C2A Board

3 4 5 6 7 8 9

Tie to U2A Incomer Spare feeder Incomer Tie to U2B SST-2 feeder From C2B Board Compressor Feeder From C2B Board

10 i.

BFP-2C Motor Feeder From C2B Board For Differential Protection Motor rated Current = 5400/Sqrt(3)/6.6/0.9 Differential CT for Motor Protection Vk = 40xIx(Rct+2RL+ Rrelay) = 40*1*(Rct+2x0.7983+0.1) = 40Rct+67.864V

ii.

0.1

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.

2500

219.79

2000/1 300/1 300/1 2500/1

500

54.67

100/1

2500

219.79

300/1

140.67 54.67

2000/1 2500/1 300/1 2500/1 2000/1 300/1 100/1

1600 500 5400

600/1

CT Details same as Other Station service Switchgear 7Rx1Cx630 mm 2

CT Details same as above air compressor Feeder. CT Details same as Other Station service Switchgear 5Rx1Cx630 mm 2 7Rx1Cx630 mm 2 3C x 240 mm2 7Rx1Cx630 mm 2 5Rx1Cx630 mm 2 3C x 240 mm2 CT Details same as above air compressor Feeder. 3Rx1Cx630 mm 2

524.86


Vk>= 40Rct+70V, Im<=30mA at Vk/2 For O/C & E/F Protection R relay in ohm (from relay catalogue of ABB model SPAJ) Total Burden on CT = Lead Burden+ Relay Burden Lead Burden for lead length of 40M= I2x(Rct+2RL) Rct Assumed for CT Sec.1A is 7 ohm Total Burden on CT = Lead Burden+ Relay Burden

0.1

=Sqr(1)*(Rct+2Rl) =Rct+0.7096 7.7096 7.8096

Page 19 of 20

10 VA, CL5P20

iii.



0.2 1 2


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


7.7096


11

Spare feeder

10.9096 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. 600/1

CT Details same as earlier main Feeder

Page 20 of 20

Ct Sizing XL

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