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 & 8.87
GRP the resistance of 2.5 sq.mm Cu cond cable at 70oC in W / km (from
KEI catalogue)

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 2024.10

Impedence on 220KV Side.
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. 108.52
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) 0.4
Typical Anolgue Meter burden in ohm (from catalogue of AE/Rishab) & 7 Total 10Nos
Transducer 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
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 100M= I x(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 26.174
Consider for future use
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= I2x(Rct+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
Relay

Page 2 of 20
 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) & 4.5 Total 5Nos
Transducer 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
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 270M= I x(Rct+2RL)
=Rct+4.79
Rct Assumed for CT Sec.1A is 6 ohm for 600/1Amp 10.79
Total Burden on CT = Lead Burden+ Meter Burden+burden margin 17.69
Consider for future use
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

Page 3 of 20
 

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

VK ` = 6.01 RCT + 47.38 2

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 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

Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 140M= I x(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 8.6836
Consider for future use
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

100

100 X 100

System contribution
= Base MVA / (Zspu+Zgt) 2499.49

= 2499.49 MVA

Page 4 of 20
 Total fault MVA(Contribution from Generator & GT system) = 6701.17
3252.91+2499.49
= 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 Vdesin=BurdenxALF/CT Secondary
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) 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
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 125M= I x(Rct+2RL)
=Rct+2.2175
Rct Assumed for CT Sec.1A is 7 ohm for 600/1Amp 9.2175
Total Burden on CT = Lead Burden+ Meter Burden+burden margin 9.3175
Consider for future use
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 18451
and U1B taken from UAT sizing calculation)

Total running load in Amp on the 6.6 kV bus ( higher of the two buses U1A 1614.04
and U1B taken from UAT sizing calculation)


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) = 1.774
2.661W

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

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= I2x(Rct+2RL) =Sqr(1)*(Rct+2Rl)
=Rct+0.887
Rct Assumed for CT Sec.1A is 6 ohm 6.887
Total Burden on CT = Lead Burden+ Relay Burden 6.987
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

Typical Meter burden in ohm (from catalogue of Conzerv model) 0.2

Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter 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 12 ohm 12.887
Total Burden on CT = Lead Burden+ Meter Burden+burden margin 15.087
Consider for future use
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
100

100 X 100

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 22292
and C1B taken from ST sizing calculation)

Page 6 of 20
 Total running load in Amp on the 6.6 kV bus ( higher of the two buses C1A 1950.04
and C1B taken from ST sizing calculation)


CT chosen – 2500/1A 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 2

Total Burden on CT = Lead Burden+ Meter 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 15 ohm 15.887
Total Burden on CT = Lead Burden+ Meter Burden+burden margin 18.087
Consider for future use
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) = 4.435
4.435W

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
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 15 ohm 15.887
Total Burden on CT = Lead Burden+ Relay Burden 15.987
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.
11KV
110V
37 . 4204
1.81063

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) = 4.435
2.661W

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
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Page 8 of 20
 CT sizing for 6.6 kV System

SNo. Type of switchboard Feeder Rated CT ratio Remark

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 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) RL = 8.87X0.09 (Considering 90m Length
= 40Rct+67.864V 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 0.1
SPAJ)
Total Burden on CT = Lead Burden+ Relay Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 7 ohm 7.7096
Total Burden on CT = Lead Burden+ Relay Burden 7.8096
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
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 7 ohm for 750/1Amp 7.7096

Total Burden on CT = Lead Burden+ Meter 10.9096

Burden+burden margin Consider for future use
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

i. For Differential Protection
Motor rated Current = 1100/Sqrt(3)/6.6/0.9 113.21
Differential CT for Motor Protection
Vk = 40xIx(Rct+2RL+ Rrelay)
= 40*1*(Rct+2x0.7983+0.1) RL = 8.87X0.09 (Considering 90m Length
= 40Rct+67.864V 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 0.1
SPAJ)
Total Burden on CT = Lead Burden+ Relay Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is <=6 ohm 6.7096
Total Burden on CT = Lead Burden+ Relay Burden 6.7096

Page 9 of 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.
iii. For Metering Core
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 6 ohm for 750/1Amp 6.7096
Total Burden on CT = Lead Burden+ Meter 9.9096
Burden+burden margin Consider for future use
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-1A, 1B 2240 300/1

i. For Differential Protection
Motor rated Current = 1100/Sqrt(3)/6.6/0.9 222.67
Differential CT for Motor Protection
Vk = 40xIx(Rct+2RL+ Rrelay)
= 40*1*(Rct+2x1.996+0.1) RL = 8.87X0.225 (Considering 225m Length
= 40Rct+163.66 V from Motor terminal to Relay)=1.996, R relay
= 0.1
Vk>= 40Rct+175V, Im<=30mA at Vk/2
ii. For O/C & E/F Protection
R relay in ohm (from relay catalogue of ABB model 0.1
SPAJ)
Total Burden on CT = Lead Burden+ Relay Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is <=6 ohm 6.7096
Total Burden on CT = Lead Burden+ Relay Burden 6.7096
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
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 6 ohm for 750/1Amp 6.7096
Total Burden on CT = Lead Burden+ Meter 9.9096
Burden+burden margin Consider for future use
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

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

i. For O/C & E/F Protection
R relay in ohm (from relay catalogue of ABB model 0.1
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

Page 10 of 20
 Rct Assumed for CT Sec.1A is <=4 ohm 6.7096
Total Burden on CT = Lead Burden+ Relay Burden 6.7096
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.
ii. For Metering Core
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 4 ohm for 100/1Amp 4.7096
Total Burden on CT = Lead Burden+ Meter 7.9096
Burden+burden margin Consider for future use
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.

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

i. For Differential Protection
Motor rated Current = 1100/Sqrt(3)/6.6/0.9 164.66
Differential CT for Motor Protection
Vk = 40xIx(Rct+2RL+ Rrelay)
= 40*1*(Rct+2x0.887+0.1) RL = 8.87X0.1 (Considering 100m Length
= 40Rct+74.96V from Motor terminal to Relay)=0.887 R relay
= 0.1
Vk>= 40Rct+80V, Im<=30mA at Vk/2
ii. For O/C & E/F Protection
R relay in ohm (from relay catalogue of ABB model 0.1
SPAJ)
Total Burden on CT = Lead Burden+ Relay Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is <=5 ohm 5.7096
Total Burden on CT = Lead Burden+ Relay Burden 5.8096
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
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 5 ohm for 200/1Amp 5.7096
Total Burden on CT = Lead Burden+ Meter 8.9096
Burden+burden margin Consider for future use
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.

6 Coal Mill-1A, 1B, 1C, 1D, 1E, 1F 400 43.74 50/1 3C x 185 mm2
i. For O/C & E/F Protection
R relay in ohm (from relay catalogue of ABB model 0.1
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

Page 11 of 20
 Rct Assumed for CT Sec.1A is <=1 ohm 1.7096
Total Burden on CT = Lead Burden+ Relay Burden 1.8096
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.
ii. For Metering Core
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 5 ohm for 50/1Amp 1.7096
Total Burden on CT = Lead Burden+ Meter 4.9096
Burden+burden margin Consider for future use
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.

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

i. For Differential Protection
Motor rated Current = 1100/Sqrt(3)/6.6/0.9 144.08
Differential CT for Motor Protection
Vk = 40xIx(Rct+2RL+ Rrelay)
= 40*1*(Rct+2x3.548+0.1) RL = 8.87X0.400 (Considering 400m Length
= 40Rct+287.84V from Motor terminal to Relay)=3.548 R relay
= 0.1
Vk>= 40Rct+290V, Im<=30mA at Vk/2
ii. For O/C & E/F Protection
R relay in ohm (from relay catalogue of ABB model 0.1
SPAJ)
Total Burden on CT = Lead Burden+ Relay Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is <=5 ohm 5.7096
Total Burden on CT = Lead Burden+ Relay Burden 5.8096
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
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 5 ohm for 200/1Amp 5.7096
Total Burden on CT = Lead Burden+ Meter 8.9096
Burden+burden margin Consider for future use
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.

8 Main Incomer from Unit Transformer 2000/1

i. For O/C & E/F Protection
R relay in ohm (from relay catalogue of ABB model 0.1
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

Page 12 of 20
 Rct Assumed for CT Sec.1A is <=12 ohm 12.7096
Total Burden on CT = Lead Burden+ Relay Burden 12.8096
15 VA, CL5P20 As relay used is numerical(SPAJ-140C) type,
hence 15 VA considered is more than
Sufficient also Lead burden is less than
above assumed buden as relay & Ct are at
the same Switchgear.
ii. For Metering Core
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
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 12.7096
2000/1Amp
Total Burden on CT = Lead Burden+ Meter 15.9096
Burden+burden margin Consider for future use
20 VA, CL-0.5 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.
9 Unit Service Transformer-1A & 1B 2500 219.79 300/1 3C x 240 mm2
i. For O/C & E/F Protection
R relay in ohm (from relay catalogue of ABB model 0.1
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
Rct Assumed for CT Sec.1A is <=6 ohm 6.7096
Total Burden on CT = Lead Burden+ Relay Burden 6.8096
10 VA, CL5P20 As relay used is numerical(SPAJ-140C) type,
hence 15 VA considered is more than
Sufficient also Lead burden is less than
above assumed buden as relay & Ct are at
the same Switchgear.
ii. For Metering Core
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 6 ohm for 6.7096
2000/1Amp
Total Burden on CT = Lead Burden+ Meter 9.9096
Burden+burden margin Consider for future use
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.
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 CT Details same as Unit service Trans.
12 ESP Service Transformer Feeder-1A & 1B feeder 2500 219.79 300/1 feeder
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
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)

Page 13 of 20
 = 40*1*(Rct+2x0.7983+0.1) RL = 8.87X0.09 (Considering 90m Length
= 40Rct+67.864V 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 0.1
SPAJ)
Total Burden on CT = Lead Burden+ Relay Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 7 ohm 7.7096
Total Burden on CT = Lead Burden+ Relay Burden 7.8096
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
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 7 ohm for 750/1Amp 7.7096
Total Burden on CT = Lead Burden+ Meter 10.9096
Burden+burden margin Consider for future use
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-2A, 2B 1100 150/1

i. For Differential Protection
Motor rated Current = 1100/Sqrt(3)/6.6/0.9 113.21
Differential CT for Motor Protection
Vk = 40xIx(Rct+2RL+ Rrelay)
= 40*1*(Rct+2x0.7983+0.1) RL = 8.87X0.09 (Considering 90m Length
= 40Rct+67.864V 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 0.1
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
Rct Assumed for CT Sec.1A is <=6 ohm 6.7096
Total Burden on CT = Lead Burden+ Relay Burden 6.7096
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
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 6 ohm for 750/1Amp 6.7096
Total Burden on CT = Lead Burden+ Meter 9.9096
Burden+burden margin Consider for future use

Page 14 of 20
 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

i. For Differential Protection
Motor rated Current = 1100/Sqrt(3)/6.6/0.9 222.67
Differential CT for Motor Protection
Vk = 40xIx(Rct+2RL+ Rrelay)
= 40*1*(Rct+2x1.995+0.1) RL = 8.87X0.225 (Considering 225m Length
= 40Rct+163.66V from Motor terminal to Relay)=1.995 R relay
= 0.1
Vk>= 40Rct+175V, Im<=30mA at Vk/2
ii. For O/C & E/F Protection
R relay in ohm (from relay catalogue of ABB model 0.1
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
Rct Assumed for CT Sec.1A is <=6 ohm 6.7096
Total Burden on CT = Lead Burden+ Relay Burden 6.7096
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
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
Lead Burden for lead length of 40M= I2x(Rct+2RL) =Sqr(1)*(Rct+2Rl)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 6 ohm for 750/1Amp 6.7096

Total Burden on CT = Lead Burden+ Meter 9.9096

Burden+burden margin Consider for future use
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

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

i. For O/C & E/F Protection
R relay in ohm (from relay catalogue of ABB model 0.1
SPAJ)
Total Burden on CT = Lead Burden+ Relay Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is <=4 ohm 6.7096
Total Burden on CT = Lead Burden+ Relay Burden 6.7096
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.
ii. For Metering Core
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 4 ohm for 100/1Amp 4.7096

Page 15 of 20
 Total Burden on CT = Lead Burden+ Meter 7.9096
Burden+burden margin Consider for future use
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.

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

i. For Differential Protection
Motor rated Current = 1100/Sqrt(3)/6.6/0.9 164.66
Differential CT for Motor Protection
Vk = 40xIx(Rct+2RL+ Rrelay)
= 40*1*(Rct+2x0.887+0.1) RL = 8.87X0.1 (Considering 100m Length
= 40Rct+74.96V from Motor terminal to Relay)=0.887 R relay
= 0.1
Vk>= 40Rct+80V, Im<=30mA at Vk/2
ii. For O/C & E/F Protection
R relay in ohm (from relay catalogue of ABB model 0.1
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
Rct Assumed for CT Sec.1A is <=5 ohm 5.7096
Total Burden on CT = Lead Burden+ Relay Burden 5.8096
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
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 5 ohm for 200/1Amp 5.7096
Total Burden on CT = Lead Burden+ Meter 8.9096
Burden+burden margin Consider for future use
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.

6 Coal Mill-2A, 2B, 2C, 2D, 2E, 2F 400 43.74 50/1 3C x 185 mm2
i. For O/C & E/F Protection
R relay in ohm (from relay catalogue of ABB model 0.1
SPAJ)
Total Burden on CT = Lead Burden+ Relay Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is <=1 ohm 1.7096
Total Burden on CT = Lead Burden+ Relay Burden 1.8096
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.
ii. For Metering Core
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
Lead Burden for lead length of 40M= I2x(Rct+2RL) =Sqr(1)*(Rct+2Rl)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 5 ohm for 50/1Amp 1.7096

Page 16 of 20
 Total Burden on CT = Lead Burden+ Meter 4.9096
Burden+burden margin Consider for future use
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.

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

i. For Differential Protection
Motor rated Current = 1100/Sqrt(3)/6.6/0.9 144.08
Differential CT for Motor Protection
Vk = 40xIx(Rct+2RL+ Rrelay)
= 40*1*(Rct+2x2.4836+0.1) RL = 8.87X0.28 (Considering 280m Length
= 40Rct+202.68V from Motor terminal to Relay)=2.4836 R relay
= 0.1
Vk>= 40Rct+210V, Im<=30mA at Vk/2 Or CT details will be same as earlier Supplied
CT.
ii. For O/C & E/F Protection
R relay in ohm (from relay catalogue of ABB model 0.1
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
Rct Assumed for CT Sec.1A is <=5 ohm 5.7096
Total Burden on CT = Lead Burden+ Relay Burden 5.8096
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
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 5 ohm for 200/1Amp 5.7096
Total Burden on CT = Lead Burden+ Meter 8.9096
Burden+burden margin Consider for future use
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.

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 CT Details same as Unit service Trans.
12 ESP Service Transformer Feeder-2A & 2B feeder 2500 219.79 300/1 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.
1 BFP-1C & 2C Motor Feeder From C1A & C2A Board 5400 600/1
Respct.
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) RL = 8.87X0.09 (Considering 90m Length
= 40Rct+63.864V 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

Page 17 of 20
 R relay in ohm (from relay catalogue of ABB model 0.1
SPAJ)
Total Burden on CT = Lead Burden+ Relay Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 7 ohm 7.7096
Total Burden on CT = Lead Burden+ Relay Burden 7.8096
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
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 7 ohm for 750/1Amp 7.7096
Total Burden on CT = Lead Burden+ Meter 10.9096
Burden+burden margin Consider for future use
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 Compressor Feeders From C1A & C2A Board 500 100/1

Motor rated Current = 5400/Sqrt(3)/6.6/0.9 54.67
i. For O/C & E/F Protection
R relay in ohm (from relay catalogue of ABB model 0.1
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
Rct Assumed for CT Sec.1A is 4 ohm 4.7096
Total Burden on CT = Lead Burden+ Relay Burden 4.8096
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.
ii. For Metering Core
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 4 ohm for 750/1Amp 4.7096
Total Burden on CT = Lead Burden+ Meter 7.9096
Burden+burden margin Consider for future use
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.
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
i. For Differential Protection
Motor rated Current = 1100/Sqrt(3)/6.6/0.9 144.08
Differential CT for Motor Protection
Vk = 40xIx(Rct+2RL+ Rrelay)

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 = 40*1*(Rct+2x3.548+0.1) RL = 8.87X0.4 (Considering 400m Length
= 40Rct+287.84V from Motor terminal to Relay)=3.548 R relay
= 0.1
Vk>= 40Rct+290V, Im<=30mA at Vk/2
ii. For O/C & E/F Protection
R relay in ohm (from relay catalogue of ABB model 0.1
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
Rct Assumed for CT Sec.1A is <=5 ohm 5.7096
Total Burden on CT = Lead Burden+ Relay Burden 5.8096
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
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
2 =Sqr(1)*(Rct+2Rl)
Lead Burden for lead length of 40M= I x(Rct+2RL)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 5 ohm for 200/1Amp 5.7096
Total Burden on CT = Lead Burden+ Meter 8.9096
Burden+burden margin Consider for future use
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.

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 mm 2

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 mm 2
4 Incomer 2500/1 7Rx1Cx630 mm 2
5 Spare feeder 300/1 3C x 240 mm2
6 Incomer 2500/1 7Rx1Cx630 mm 2
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 mm 2
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) RL = 8.87X0.09 (Considering 90m Length
= 40Rct+67.864V from Motor terminal to Relay)=0.887 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 0.1
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
Rct Assumed for CT Sec.1A is 7 ohm 7.7096
Total Burden on CT = Lead Burden+ Relay Burden 7.8096

Page 19 of 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.
iii. For Metering Core
Typical Meter burden in ohm (from catalogue of 0.2
Conzerv model)
Typical Anolgue Meter burden in ohm (from 1
catalogue of AE/Rishab) & Transducer
Burden margin Consider for future use 2
Total Burden on CT = Lead Burden+ Meter Burden
Lead Burden for lead length of 40M= I2x(Rct+2RL) =Sqr(1)*(Rct+2Rl)
=Rct+0.7096
Rct Assumed for CT Sec.1A is 7 ohm for 750/1Amp 7.7096

Total Burden on CT = Lead Burden+ Meter 10.9096

Burden+burden margin Consider for future use
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.

11 Spare feeder 600/1 CT Details same as earlier main Feeder

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