NOAMUNDI POWER

BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0

CALCULATIONS FOR CT & PT PARAMETERS FOR 132KV GIS IN 6.0

MTPA KALINGANAGAR PROJECT

SR. NO. TITLE SHEET NO.

A. 132 KV BUS-SECTIONALISER 1

B. 132 KV BUSCOUPLER WITH BUS PTS 4

C. INCOMER FROM 220/139kV 200MVA MT 6

WITH LINE PT

D. 132KV FEEDER TO 132 KV/34.5 100 MVA 11

TRANSFORMER AT MRSS

E. 132KV FEEDER TO 132 KV/34.5 100 MVA 17

TRANSFORMER AT MSDS AND CRM

F. 132KV FEEDER TO 132 /6.9KV 20 MVA 21

STATION TRANSFORMER AT CPP

G. INCOMER FROM 11/132KV 115MVA GENERATOR 24

TRANSFORMER AT CPP

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0

CALCULATIONS FOR CT & PT PARAMETERS FOR 132KV GIS IN 6.0

MTPA KALINGANAGAR PROJECT

REFERENCE DATA

1) Catalogues for various Relays and meters

2) Short Circuit Study report

3) General Site Layout -

4)

5) Main One line diagram dwg no TCE-5668B-737-AU-3012

ASSUMPTIONS :

1) Presuming usage of Numerical relays for differential protection,

Aux CTs are not used.

DESIGN CRITERIA

1) Bus differential protection Cts will be single ratio;

Metering CT ratios shall be of dual ratio type.
Main protection and back up protection CTs shall be dual rato type.
Numerical relays are only considered for CT & PT burden. CTs are not for static or
electromagnetic protection.

A. 132 kV Bus Coupler

BUS 1 BUS 2

CT4 Bus differential

Bus differential for Bus 1(TYP)
CT1
for Bus 2(TYP)

CT2 Backup O/C

Bus PT 2
& E/F
Bus PT 1 CT3 Metering Core 1- Directional O/C of transformer
Core details same as feeders, overfluxing relays of
of Bus PT 2 transformers, undervoltage relays

Core 2- Voltmeter, multifunction

meter of transformers, synchronising
1250A scheme.

MVA A
Outgoing transformer rating 12.5/15 0.656
Max. capacity in phase 1 30 131
Contract demand in phase 1 9 39.37
Max. capacity in phase 3 60 262
With 20% margin 72 315
Bus rating selected 1250 Amps

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
1) CT parameters for Busbar Differential Protection 87B Main-1, 87B Main-2,
CT1 & CT4 (Voltage Class : 132kV)
CT ratio chosen = 1200 /1 Amp ( close to bus rating) (with 120% thermal capability)

132kV Bus Design Fault Level = 31.5 kA

Vk = If x 1/CTratio x (Rct + Rl+Rrelay)

If = fault current on CT secondary = 31500/1200 = 26.25 A

Considering 4 sq.mm copper conductor cable between CT and relay, resistance of

4 sq.mm copper cable ~ 5.5 Ohms / km

Maximum cable length = 75 M (from site plan)

Cable Lead Resistance for the loop Rl = 2 x 5.5 x 0.075
= 0.83 Ohms

R relay = 0.1 VA (ABB Relay REB500)

Winding res. of CT sec, Rct = 6 Ohms (Assumed)

Therefore Vk > = 26 *(6+0.825+ 0.1)

= 181.781 Volts

Keep Vk twice the value required >= 363.563 or 375V

Therefore CT chosen for Bus differential = 1200 /1 Amp

Vk>= 375V
Rct<= 6 ohm
Magnetising Current (Im) Calculation
Bus rating = 1250 Amps
Formula for calculating CT magnetising current Im.
Im = 1/n [PFSC x (1/CT ratio) - Ir]

Where n = Nos. of CTs in parallel = 7

PFSC = Primary Fault Setting Current = 400 Amp
(Assuming 10 times of Ifull load in phase 1)
Ir = Relay current at set point in Amp = 0.1 Amp
Im = Magnetising Current in Amps

Im = 1/7[ 400 x ( 1/1200) - 0.1]

= 0.033 Amp
= 33 mA
Hence Im at Vk/2 = 33/2 = 16.5 mA.

As standard rating, Im at Vk/2 <= 15 mA is selected

Selection of Class of CT
As the CT is meant for differential protection, Class Px CT is selected.

CT Class = PS

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
Therefore, parameters for 87B-Main-1, 87B-Main-2 and 87B-Check zone are

CT RATIO = 1200 /1 Amp

Knee Point Voltage Vk >= 375V
CT Wdg. Res. Rct =< 6ohm
Mag. Current Im at Vk/2 =< 15 mA
CT Class = PS
CT Cable to be used = 4 sqmm copper cable

2) Calculation of CT parameters for (50 BF, 51/51N relays)-CT2

(Voltage Class : 132kV)

Full load capacity of 132 kV GIS Bus = 1250 Amps

(maxm. rating available in 132 kV GIS system)
Bus rating = 1250 A
CT ratio selected = 600 - 1200 / 1 Amp
(in line with busbar rating)
Relay Burden :

Relay Burden= 0.05 VA (Seimens Relay SIP-7SJ62)

Since the secondary Current is 1A, the above burden can be taken as the total burden in ohms.
i.e., Rrelaytotal in ohms = Relay Burden total in VA/(I s2),
where Is = Secondary Current of CT.
Therefore Rrelaytotal in ohms = (0.05 /1*1)
= 0.05 ohms

Formula for calculating Knee point voltage requirement at 600 A tap:

Vk = If x 1/CTratio x (Rct + Rl+Rrelay)

Where If = CT Primary fault current in Amps = 31500 A

( 132kV Bus fault current)
Rct = CT winding resistance = 3 ohm (Assumed)
Rl = Cable resistance between CT & Relay

Considering 4 sq.mm copper conductor cable between CT and relay, resistance of

4 sq.mm copper cable = 5.50 Ohms / km
Maximum cable length = 75 M (Site Plan layout)

Cable Lead Resistance for the loop Rl = 2x 5.5 x 0.075

= 0.83 Ohms
Considering 600 /1 A ratio,

Vk required = 31500 x 1/600(3 + 0.83 + 0.05)

= 204 Volts

Selection of Class of CT
By choosing 5P20 , 10 VA CT,
Vk available = 20 x 1 (3+10)
= 260 Volts

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0

ALF(actual) = ALF(rated) x (Rct + Rb)/(Rct + Rc)

where Rct= CT resistance= 3
Rb = Rated Burden = 10
Rc= Connected Burden= 0.88

ALF (actual)= 67
ALF (required)= If/CTR = 53
Since, ALF (actual) > ALF (required), CT dimension is ok.

Hence, the following CT Parameters are selected

CT RATIO = 600-1200/ 1 Amp

CT Class = 5P20
VA burden required = 10 VA
CT Cable to be used = 4 sq.mm copper cable

3) CT Parameters for metering CT- CT3

(Voltage Class : 132kV)
Purpose: Metering
CT ratio chosen
600-1200/1 A.
Meter VA Burden
Multifunction meter 0.5
Ammeter 1.5
Total = 2
Considering a 4 sq. mm lead length of 75 m
R(lead)= 0.83 1.875
Burden= 0.83 as sec. current is 1A
Total burden= 2.83 VA
7.5 VA is chosen to account for any future additions etc.
25%(rated) < connected burden < rated burden
ISF (actual) = ISF(rated) x (Rct + Rb)/(Rct + Rc)

Considering an ISF (rated) <5,

ISF (actual) = 9 (safe)

Therefore CT chosen = 600-1200/1 A.

7.5VA
CL.0.2
ISF <5.

2) Calculation of parameters for 132kV Bus PT1 & Bus PT2

Core1 -- To be used for Directional overcurrent protection of transformer feeders.

VA
Directional overcurrent protection -- 1.5 (Siemens relay 7SJ531 catalog)
of max. five transformers
Undervoltage relay 5
No voltage relay 5
Fuse failure relay 3
Synchronising relay 0.5
Under voltage relay 1.5
No voltage relay 1.5
Underfrequency relay 0.5
Overfluxing relay of two transformers 0.5
17.5

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
Considering future additions 50 VA is chosen.
As it will used for protection, Class 3P is selected.
The Parameters for PT core1 is 3P, 50 VA

Core 2 -- To be used for Metering

VA
Voltmeters(two nos.) 3
Multifunction meter of five. nine transformers 0.5
Synchroscope 0.5
Voltmeter 5
Frequencymeter 2
Total 11
Considering future additions, 50VA is chosen.
As it will be used for metering, Class 0.2 is chosen.

Therefore PT chosen
Ratio 132 110 110
√3 √3 √3
Class 0.5/3P 0.5/3P
Burden 100 50/ 50/
Core 1/ 2/

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
C. 132kV Incomer from JSEB
BUS 1

BUS 2 Indicating purpose

1250A

P1

CT 1 Line Differential

CT 2 Directional (IDMT) O/C & E/F, Local Breaker Backup

CT 3 Metering & Indication

CT 4 Tariff Metering

CT 5 Bus Differential - Main

CT 6 Bus Differential - Check

P2

Line EMVT

Core 1- Directional overcurrent & Earth fault, Line Differential relay

Core 2- Multifunction meter, voltmeter, Check synchronising scheme,

undervoltage relay
Core 3- Tariff metering

Incomer from Noamundi JSEB substation

1) CT parameters for 132 KV Line Differential

Protection (87L ) -CT1 (Voltage Class : 132kV)
CT Ratio Selection :

Line Rating = 450A (Panter conductor)

Minimum projected load = 4.5 MVA = 19.68 A = 6.56099

Therefore full load currrent on 132kV Side =

540
CT ratio selected on 132kV side is = 600 - 300 /1 Amp
(considering 15% margin)

Knee Point Voltage Calculation (For 87L ) :

Formula for calculating Knee point voltage requirement for differential protection
Vk = If x 1/CTratio x (Rct + Rl+Rrelay)

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
Where If = CT Primary fault current in Amps 40000 A
( 132kV Bus fault current)
Rct = CT winding resistance = 1.5 ohm
Rl = Cable resistance between CT & Relay

Considering 4 sq.mm copper conductor cable between CT and relay, resistance of

4 sq.mm copper cable = 5.50 Ohms / km

Maximum cable length = 75 M (from site plan)

Cable Lead Resistance for the loop Rl = 2 x 5.50 x 0.075

= 0.83 Ohms

Relay Burden < = 0.1 (SIP catalogue 7SD610)

Therefore, Since the secondary is 1A, RRelay = 0.1 ohms

CT knee point requirement = 40000x 1/300x (1.5+0.825+0.1)

= 323 Volts

We choose Vk >= 2 X Vk (required) to account for DC component during fault,

variation in CT, lead lengths and resistances, relays etc.

Hence, Vk >= 650 V

Magnetising Current (Im) Calculation (For 87L):

Formula for calculating CT magnetising current Im.

Im = 1/n [PFSC x (1/CT ratio) - Ir]
Where n = Nos. of CTs in parallel = 1
PFSC = Primary Fault Setting Current = 45 Amp
(Assuming 20% of Ifull load)
Ir = Relay current at set point in Amp = 0.1 Amp
Im = Magnetising Current in Amps
Im = 1/1[ 45 x ( 1/300) - 0.1]
= 0.050 Amp
= 50 mA

Hence Im at Vk/2 = 50/2 = 25.0 mA. Im at Vk/2 <= 30 mA is selected

Selection of Class of CT
As the CT is meant for Line differential protection, Class Px CT is selected.
CT Class = PX

Therefore, CT parameters for 87L are

CT RATIO = 600-300 /1 Amp

Knee Point Voltage Vk >= 650 V
CT Wdg. Res. Rct =< 1.5 ohm
Mag. Current Im at Vk/2 =< 30 mA
CT Class = PX
CT Cable to be used = 4 sq.mm copper cable

As per Siprotec,

Vk>= Ktd x Issc*(RCT + Rb') /(1.3*CTR)

where Ktd = 1.2

= 298 V

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
2) Calculation of CT parameters for (50 BF, 50/67 relays)-CT2
(Voltage Class : 132kV)

CT ratio selected = 600 - 300 /1 Amp

Relay Burden :

Relay Burden= 0.1 VA (Seimens Relay SIP-7SJ600 )

Since the secondary Current is 1A, the above burden can be taken as the total burden in ohms.
i.e., Rrelaytotal in ohms = Relay Burden total in VA/(I s2),
where Is = Secondary Current of CT.
Therefore Rrelaytotal in ohms = (0.1 /1*1)
= 0.1 ohms

Formula for calculating Knee point voltage requirement :

Vk = If x 1/CTratio x (Rct + Rl+Rrelay)

Where If = CT Primary fault current in Amps 40000 A

( 132kV Bus fault current)
Rct = CT winding resistance = 2 ohm (Assumed)
Rl = Cable resistance between CT & Relay

Considering 4 sq.mm copper conductor cable between CT and relay, resistance of

4 sq.mm copper cable = 5.50 Ohms / km
Maximum cable length = 75 M (Site Plan layout)

Cable Lead Resistance for the loop Rl = 2x 5.50 x 0.075

= 0.83 Ohms
Considering 300/1 ratio,
Vk required = 40000 x 1/300(2 + 0.83 + 0.1)
= 391 Volts

Selection of Class of CT
By choosing 5P20 , 20 VA CT,
Vk available = 20 x 1 (2+20)
= 440 Volts

Hence, the following CT Parameters are selected

CT RATIO = 600-300/1 Amp

CT Class = 5P20
VA burden required = 20 VA
CT Cable to be used = 4 sq.mm copper cable

ALFact = ALFrat * (RCT + Rb')/(RCT + Rb)

where Rb = Connected Burden

Rb' = Rated Burden

= 150

ALFreqd = 133 ALFact > ALFreqd CT satisfactory

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
3) CT Parameters for metering CT-CT3 (Voltage Class : 132kV)

CT ratio chosen 600-300 - 150 /1 Amp

All burdens are chosen from reputed manufacturers of these equipment like
SATEC

Meter VA Burden
Multifunction meter - 2nos. 1
Ammeter 1.5 Assumed
Lead Burden 0.83
(Considering 75 M length, 4 sq.mm Cu. Conductor )
Total 3.33 VA
7.5 VA is chosen to account for any future additions etc.
25%(rated) < connected burden < rated burden
Therefore CT chosen = 600-300-150/1 Amp
7.5
CL.0.5s
ISF <5.

ISF (actual) = ISF(rated) x (RCT + Rb')/(RCT + Rb)

Considering an ISF (rated) <5,

ISF (actual) = 9 (safe)

For Tariff metering CT,

CT chosen 600-300-150/1 Amp
7.5
CL.0.2s
ISF <5.

4) CT parameters for 132 kV Busbar Differential Protection 87B Main-1, 87B

Main-2 & 87C - CT5 & CT6 in 132 kV Bus
(Voltage Class : 132kV)
The CT parameters are identical to the parameters of Bus differential protection
CTs for Bus Coupler. -- Refer Sl. No. 1 of Section A.

Therefore the CT parameters for 87B Main-1/Main-2 & 87C are

CT RATIO = 1200 /1 Amp

Knee Point Voltage Vk >= 375V
CT Wdg. Res. Rct =< 6ohm
Mag. Current Im at Vk/2 =< 15 mA
CT Class = PS
CT Cable to be used = 4 sqmm copper cable

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
5) Calculation of Line PT parameters

Core1 -- To be used for Directional Overcurrent and Earth fault protection.

VA
Directional O/C & E/F protection -- 0.1 (Siemens relay 7SJ512 catalog)
Undervoltage relay 5
No voltage relay 5
Fuse Failure relay 0.5
Total 10.6
Considering future additions 50 VA is chosen.
As it will be used for protection, Class 3P is selected.

Core 2 -- To be used for Metering and Synchronising scheme

VA
Voltmeter (2nos.) 5
BCU 0.5
MW meter 5
MVAR meter 5
Fuse failure relay 3
Synchronising relay 0.5
Synchroscope 6
Voltmeter 5
Frequencymeter 2
Fuse failure relay 3
Total 16.5

Considering future additions, 50VA is chosen.

Since used for dual purpose, dual class 0.5/5P is chosen

Therefore PT chosen
Ratio 132 110 110 110
√3 √3 √3 √3
Class 3P/ 0.5/ 0.5/3P
Burden 50/ 50/ 100
Core 1/ 2/ 3

D. 132kV Feeder - 132/34.5kV 100MVA Transformer at MRSS

BUS 1

BUS 2

2500A

P1

CT 1 Transformer Differential

CT 2 Directional (IDMT) O/C & E/F, LBB,

Instantaneous O/C

CT 3 Metering

CT 4 Bus Differential - Main

CT 5 Bus Differential - Check

CT 6 Restricted Earth fault

Bushing CT C T7 Spare
Bushing CT
CT 8 Spare

CT 9 CT 10

IPT HV Restricted E/F Standby E/F

LV Restricted E/F Standby E/F

P2

Bushing CT
To 33 kV Bus at MRSS

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
1) CT parameters for 100 MVA Transformer Differential
Protection (87IPT ) - CT1 (Voltage Class :132kV)
CT Ratio Selection :

Transformer Rating = 63/80/100 MVA @ 50deg.C, ONAN/ONAF/OFAF

132/34.5kV, YNynd5, Z=16% at100 MVA

Therefore full load currrent on 132kV Side = (MVAx 1000)/(1.732 x kV)

= 100 x 1000 / 1.732 x 132
= 437 Amps
CT ratio selected on 132kV side is = 500 /1 Amp
(considering 15% margin)

Knee Point Voltage Calculation (For 87IPT) :

Formula for calculating Knee point voltage requirement for differential protection
Vk = If x 1/CTratio x (Rct + Rl+Rrelay)

Where If = CT Primary fault current in Amps 40000 A

( 132kV Bus fault current)
Rct = CT winding resistance = 2.5 ohm
Rl = Cable resistance between CT & Relay

Considering 4 sq.mm copper conductor cable between CT and relay, resistance of

4 sq.mm copper cable = 4.61 Ohms / km 5

Maximum cable length = 50 M (from site plan)

Cable Lead Resistance for the loop Rl = 2 x 5 x 0.05

= 0.50 Ohms

Relay Burden = 0.1 (ABB catalogue RET 316)

Therefore, Since the secondary is 1A, RRelay = 0.1 ohms

CT knee point requirement = 40000x 1/500x (2.5+0.5+0.1)

= 248 Volts

We choose Vk >= 2 X Vk (required) to account for DC component during fault,

variation in CT, lead lengths and resistances, relays etc.

Hence, Vk >= 450V

Magnetising Current (Im) Calculation (For 87IPT ):

Formula for calculating CT magnetising current Im.

Im = 1/n [PFSC x (1/CT ratio) - Ir]
Where n = No. of CTs in parallel = 2
PFSC = Primary Fault Setting Current = 87.48 Amp
(Assuming 20% of Ifull load)
Ir = Relay current at set point in Amp = 0.1 Amp
Im = Magnetising Current in Amps

Im = 1/2[ 87 x ( 1/500) - 0.1]

= 0.037 Amp
= 37 mA

Hence Im at Vk/2 = 37/2 = 18.5 mA.

Im at Vk/2 <= 15 mA is selected
Selection of Class of CT
As the CT is meant for Transformer differential protection, Class PS CT is selected.
CT Class = PS

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
Therefore, CT parameters for 87IPT are

CT RATIO = 500/1 Amp

Knee Point Voltage Vk >=450V
CT Wdg. Res. Rct <= 2.5ohm
Mag. Current Im at Vk/2 <= 15 mA
CT Class = PS
CT Cable to be used = 4 sq.mm copper cable

2) Calculation of CT parameters for (50 BF, 50/67IPT relays)-CT2

(Voltage Class : 132kV)
Transformer Rating = 63/80/100 MVA @ 50deg.C, ONAN/ONAF/OFAF
132/34.5kV, YNynd5, Z=16% at100 MVA

Therefore full load currrent on 132kV Side = (MVAx 1000)/(1.732 x kV)

= 100 x 1000 / 1.732 x 132
= 437.40 Amps

CT ratio selected = 500 / 1 Amp

Relay Burden :

Relay Burden (0.1 + 0.1) = 0.2 VA (Seimens Relay SIP-4 7SJ60 and 7SV)

Since the secondary Current is 1A, the above burden can be taken as the total burden in ohms.
i.e., Rrelaytotal in ohms = Relay Burden total in VA/(I s2),
where Is = Secondary Current of CT.
Therefore Rrelaytotal in ohms = (0.2 /1*1)
= 0.2 ohms

Formula for calculating Knee point voltage requirement :

Vk = If x 1/CTratio x (Rct + Rl+Rrelay)

Where If = CT Primary fault current in Amps= 35000 A

( 132kV Bus fault current)
Rct = CT winding resistance = 2.5 ohm (Assumed)
Rl = Cable resistance between CT & Relay

Considering 4 sq.mm copper conductor cable between CT and relay, resistance of

4 sq.mm copper cable = 4.61 Ohms / km
Maximum cable length = 50 M (Site Plan layout)
Cable Lead Resistance for the loop Rl = 2 x 4.609 x 0.05
= 0.46 Ohms
Considering 500/1 ratio,
Vk required = 35000 x 1/500(2.5 + 0.46 + 0.2)
= 221 Volts

Selection of Class of CT

By choosing 5P20 , 15 VA CT,

Vk available = 20 x 1 (2.5+15)
= 350 Volts

Hence, the following CT Parameters are selected

CT RATIO = 500/ 1 Amp

CT Class = 5P20
VA burden required = 15 VA
CT Cable to be used = 4 sq.mm copper cable

3) CT Parameters for metering CTs- CT3

(Voltage Class :132kV)
Purpose: Metering
CT ratio chosen 500 /1 A.

Meter VA Burden
Digital Multifunction meter 0.5 VA
Ammeter 0.6 VA
Considering a 4 sq. mm lead length of 50 m
R(lead)= 0.46
Burden= 0.46 as sec. current is 1A
15VA is chosen to account for any future additions etc.

Therefore CT chosen = 500 /1 A.

15 VA
CL.0.5
ISF <5.

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
4) CT parameters for Busbar Differential Protection 87B Main-1, 87B Main-2
& 87C - CT4 & CT5 (Voltage Class : 132kV)

The CT parameters are identical to the parameters of Bus differential protection

CTs for Bus sectionaliser. -- Refer Sl. No. 1 of Section A.

Therefore the CT parameters for 87B Main-1/Main-2 & 87C are

CT RATIO = 2500 /1 Amp

Knee Point Voltage Vk >= 300V
CT Wdg. Res. Rct =< 10ohm
Mag. Current Im at Vk/2 =< 15 mA
CT Class = PS
CT Cable to be used = 4 sqmm copper cable

5) Parameters for 132/34.5kV Transformer HV bushing CTS and HV Neutral

side CT used for HV Restricted earth fault protection 64R-CT6, CT9 & CT10
(Voltage Class : 132 kV )
Full load on 132kV side = 437 Amps
CT ratio chosen = 500 /1 Amp
Knee point voltage Calculation (64R)

Formula for calculating Knee point voltage requirement for differential protection
Vk = If x 1/CTratio x (Rct + Rl+Rrelay)
Where If = CT Primary fault current in Amps 40000 A
( 132kV Bus fault current)
Rct = CT winding resistance = 2.5 ohm
Rl = Cable resistance between CT & Relay
Considering 4 sq.mm copper conductor cable between CT and relay, resistance of
4 sq.mm copper cable = 4.61 Ohms / km 5
Maximum cable length = 100 M (from site plan)
Cable Lead Resistance for the loop Rl = 2 x 5 x 0.1
= 1.00 Ohms
Relay Burden = 0.1 (ABB catalogue RET 316)

Therefore, Since the secondary is 1A, RRelay = 0.1 ohms

CT knee point requirement = 40000x 1/500x (2.5+1+0.1)
= 288 Volts
We choose Vk >= 2 X Vk (required) to account for DC component during fault,
variation in CT, lead lengths and resistances, relays etc.
Hence, Vk >= 575V

Magnetising Current (Im) Calculation (For 64R ):

Formula for calculating CT magnetising current Im.
Im = 1/n [PFSC x (1/CT ratio) - Ir]

Where n = No. of CTs in parallel = 4

PFSC = Primary Fault Setting Current = 131.22 Amp
(Assuming 30% of Ifull load)
Ir = Relay current at set point in Amp = 0.1 Amp

Im = Magnetising Current in Amps

Im = 1/4[ 131 x ( 1/500) - 0.1]

= 0.041 Amp
= 41 mA
Hence Im at Vk/2 = 41/2 = 20.5 mA.

Im at Vk/2 <= 15 mA is selected

Selection of Class of CT
As the CT is meant for Transformer differential protection, Class PS CT is selected.
Therefore, CT parameters for 64R are

CT RATIO = 500/1 Amp

Knee Point Voltage Vk >=575V
CT Wdg. Res. Rct <= 2.5ohm
Mag. Current Im at Vk/2 <= 15 mA
CT Class = PS
CT Cable to be used = 4 sq.mm copper cable

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
8) Parameters for Transformer Neutral side CT used for 51SN protection -
Neutral Bushing CT10

CT ratio chosen = 500 /1A

Fault current on 132kV side = 40000 A

Vr = If(Rct + Rlead + Rrelay)

If = fault level on CT secondary = 40000/500 = 80 A
Considering 4 sq.mm copper conductor cable between CT and relay, resistance of
4 sq.mm copper cable = 4.61 Ohms / km
Maximum cable length = 100 M (from site plan)
Cable Lead Resistance for the loop Rl = 2 x 4.61 x 0.1
= 0.92 Ohms
R relay = 0.1 VA (Assumed)
Winding res. of CT sec Rct = 2.5 Ohms 1.75
Therefore Vr (Vk required) = 80 *(2.5+0.922+ 0.1)
= 281.76 Volts
Selection of Class of CT
To take into account variations in CT parameters etc.,
By choosing 5P20 , 15 VA CT,
Vk available = 20 x 1 (2.5+15)
= 350 Volts

Therefore CT chosen for 51SN protection

CT RATIO = 500/1A
CT Class = 5P20
Rated VA of CT = 15 VA
CT Cable to be used = 4 sq.mm copper cable

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
E. i) 132kV Feeder - 132/34.5kV 100MVA Transformer at MSDS 1/2/3
ii) 132kV Feeder - 132/34.5kV 100MVA Transformer at Cold Rolling Mill
BUS 1

BUS 2

2500A

P1

Transformer Feeder Differential

Directional O/C & E/F, LBB, Instantaneous O/C

CT 2

CT 3 Metering

CT 4 Bus Differential - Main

CT 5 Bus Differential - Check

P2

To 132/34.5 kV 100 MVA Transformer at MSDS/ Cold Rolling Mill

1) CT parameters for 100 MVA Transformer Feeder Differential Protection
(87T FDR ) - CT1 (Voltage Class :132kV)
CT Ratio Selection :

Transformer Rating = 63/80/100 MVA @ 50deg.C, ONAN/ONAF/OFAF

132/34.5kV, YNynd5, Z=16% at100 MVA

Therefore full load currrent on 132kV Side = (MVAx 1000)/(1.732 x kV)

= 100 x 1000 / 1.732 x 132
= 437.40 Amps

CT ratio selected on 132kV side is = 500 /1 Amp

(considering 15% margin)

Knee Point Voltage Calculation

CT 1 (For 87T FDR ) : 1.025702
0.503009
Formula for calculating Knee point voltage requirement for differential protection
Vk = If x 1/CTratio x (Rct + Rl+Rrelay)

Where If = CT Primary fault current in Amps= 40000 A

( 132kV Bus fault current)
Rct = CT winding resistance = 2.5 ohm
Rl = Cable resistance between CT & Relay
Considering 4 sq.mm copper conductor cable between CT and relay, resistance of
4 sq.mm copper cable = 4.61 Ohms / km ~ 5 Ohms / km

Maximum cable length = 75 M (from site plan)

Cable Lead Resistance for the loop Rl = 2 x 5 x 0.075

= 0.75 Ohms

Relay Burden = 0.1 (ABB catalogue RET 316)

Therefore, Since the secondary is 1A, RRelay = 0.1 ohms

CT knee point requirement = 40000x 1/500x (2.5+0.75+0.1)

= 268 Volts

We choose Vk >= 2 X Vk (required) to account for DC component during fault,

variation in CT, lead lengths and resistances, relays etc.

Hence, Vk >= 500V

Magnetising Current (Im) Calculation (For 87T FDR ):

Formula for calculating CT magnetising current Im.

Im = 1/n [PFSC x (1/CT ratio) - Ir]

Where n = No. of CTs in parallel = 1

PFSC = Primary Fault Setting Current = 87.48 Amp
(Assuming 20% of Ifull load)
Ir = Relay current at set point in Amp = 0.1 Amp
Im = Magnetising Current in Amps

Im = 1/1[ 87 x ( 1/500) - 0.1]

= 0.075 Amp
= 75 mA

Hence Im at Vk/2 = 75/2 = 37.5 mA.

Im at Vk/2 <= 15 mA is selected

Selection of Class of CT
As the CT is meant for Transformer differential protection, Class PS CT is selected.
CT Class = PS
Therefore, CT parameters for 87T FDR are

CT RATIO = 500/1 Amp

Knee Point Voltage Vk >= 500V
CT Wdg. Res. Rct <= 2.5ohm
Mag. Current Im at Vk/2 <= 15 mA
CT Class = PS
CT Cable to be used = 4 sq.mm copper cable

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
2) Calculation of CT parameters for (50 BF, 50/67AT relays)-CT2
(Voltage Class : 132kV)
Transformer Rating = 63/80/100 MVA @ 50deg.C, ONAN/ONAF/OFAF
132/34.5kV, YNynd5, Z=16% at100 MVA

Therefore full load currrent on 132kV Side = (MVAx 1000)/(1.732 x kV)

= 100 x 1000 / 1.732 x 132
= 437.40 Amps

CT ratio selected = 500 / 1 Amp

Relay Burden :

Relay Burden(0.1 + 0.1) = 0.2 VA (Seimens Relay SIP-4 7SJ60 and 7SV512)

Since the secondary Current is 1A, the above burden can be taken as the total burden in ohms.
i.e., Rrelaytotal in ohms = Relay Burden total in VA/(I s2),
where Is = Secondary Current of CT.
Therefore Rrelaytotal in ohms = (0.2 /1*1)
= 0.2 ohms

Formula for calculating Knee point voltage requirement :

Vk = If x 1/CTratio x (Rct + Rl+Rrelay)

Where If = CT Primary fault current in Amps 40000 A

( 33kV Bus fault current)
Rct = CT winding resistance = 2.5 ohm (Assumed)
Rl = Cable resistance between CT & Relay

Considering 4 sq.mm copper conductor cable between CT and relay, resistance of

4 sq.mm copper cable = 4.61 Ohms / km
Maximum cable length = 50 M (Site Plan layout)

Cable Lead Resistance for the loop Rl = 2x 4.609 x 0.05

= 0.46 Ohms
Considering 500/1 ratio,

Vk required = 40000 x 1/500(2.5 + 0.46 + 0.2)

= 252.8 Volts

Selection of Class of CT

By choosing 5P20 , 15 VA CT,

Vk available = 20 x 1 (2.5+15)
= 350 Volts

Hence, the following CT Parameters are selected

CT RATIO = 500/ 1 Amp

CT Class = 5P20
VA burden required = 15 VA
CT Cable to be used = 4 sq.mm copper cable

3) CT Parameters for metering CTs- CT3

(Voltage Class :132kV)
Purpose: Metering
CT ratio chosen 500 /1 A.
Meter VA Burden
Digital Multifunction meter 0.5 VA
Ammeter 0.6 VA
Considering a 4 sq. mm lead length of 50 m
R(lead)= 0.46
Burden= 0.46 as sec. current is 1A

15VA is chosen to account for any future additions etc.

Therefore CT chosen = 500 /1 A.

15 VA
CL.0.5
ISF <5.

4) CT parameters for Busbar Differential Protection 87B Main-1, 87B Main-2

& 87C - CT4 & CT5 (Voltage Class : 132kV)

The CT parameters are identical to the parameters of Bus differential protection

CTs for Bus sectionaliser. -- Refer Sl. No. 1 of Section A.

Therefore the CT parameters for 87B Main-1/Main-2 & 87C are

CT RATIO = 2500 /1 Amp

Knee Point Voltage Vk >= 300V
CT Wdg. Res. Rct =< 10ohm
Mag. Current Im at Vk/2 =< 15 mA
CT Class = PS
CT Cable to be used = 4 sqmm copper cable

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
F. Feeder -- 132/6.9kV 20MVA Station Transformer at CPP

BUS 1

BUS 2

2500A
P1

Instantaneous O/C

CT 2 Directional O/C and E/F, LBB

CT 3 Metering

CT 4 Bus Differential - Main

CT 5 Bus Differential - Check

P2

To 132/6.9 kV 20MVA Station Transformer

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
1) CT parameters for 20 MVA Transformer Feeder instantaneous overcurrent
and earth fault- CT1 (Voltage Class : 132kV)
CT Ratio Selection :

Transformer Rating = 16/20 MVA @ 50deg.C,

132/6.9kV, YNyn0, Z=12% at100 MVA

Therefore full load currrent on 132kV Side = (MVAx 1000)/(1.732 x kV)

= 20 x 1000 / 1.732 x 132
= 87.48 Amps

CT ratio selected on 132kV side is = 150 /1 Amp

(as with CT primary = 100A, Vk required is going higher than Vk available))
CT 1

Knee Point Voltage Calculation (For 50 ) :

Formula for calculating Knee point voltage requirement

Vk = If x 1/CTratio x (Rct + Rl+Rrelay)
Where If = CT Primary fault current in Amps 40000 A
( 132kV Bus fault current)
Rct = CT winding resistance = 0.75 ohm
Rl = Cable resistance between CT & Relay
Considering 4 sq.mm copper conductor cable between CT and relay, resistance of
4 sq.mm copper cable = 4.61 Ohms / km

Maximum cable length = 75 M (from site plan)

Cable Lead Resistance for the loop Rl = 2 x 4.609 x 0.075

= 0.69 Ohms

Relay Burden = 0.1 (ABB catalogue RET 316)

Therefore, Since the secondary is 1A, RRelay = 0.1 ohms

CT knee point requirement = 40000x 1/150x (0.75+0.69129375+0.1)

= 411 Volts
By choosing 5P20 , 20VA
Vk available = 20x(20+.75)
= 415 V

Selection of Class of CT

CT RATIO = 150/1 Amp

Class = 5P20
Burden = 20VA
CT Cable to be used = 4 sq.mm copper cable

2) Calculation of CT parameters for (50 BF, 51ST relays)-CT2

(Voltage Class : 132kV)
Transformer Rating = 16/20 MVA @ 50deg.C,
132/6.9kV, YNyn0, Z=12% at100 MVA

Therefore full load currrent on 132kV Side = (MVAx 1000)/(1.732 x kV)

= 20 x 1000 / 1.732 x 132
= 87.48 Amps

CT ratio selected = 100 / 1 Amp

Relay Burden :

Relay Burden (0.1 + 0.1) = 0.2 VA (Seimens Relay SIP-4 7SJ60 and 7SV)

Since the secondary Current is 1A, the above burden can be taken as the total burden in ohms.
i.e., Rrelaytotal in ohms = Relay Burden total in VA/(I s2),
, where Is = Secondary Current of CT.
Therefore Rrelaytotal in ohms = (0.2 /1*1)
= 0.2 ohms

For fault fault on HV side of ST, the fault will be cleared by 50ST.
51ST will be required to clear a fault on LV side as a backup and so
will be designed based on LV side fault current.

Max. fault current through ST(for a fault on LV side) = If / (% Zgt )

= 87/0.12
= 729 A
Formula for calculating Knee point voltage requirement :
Vk = If x 1/CTratio x (Rct + Rl+Rrelay)

Where If = CT Primary fault current in Amps= 729 A

Rct = CT winding resistance = 0.5 ohm (Assumed)

Rl = Cable resistance between CT & Relay

Considering 4 sq.mm copper conductor cable between CT and relay, resistance of

4 sq.mm copper cable = 4.61 Ohms / km

Maximum cable length = 50 M (Site Plan layout)

Cable Lead Resistance for the loop Rl = 2x 4.609 x 0.05

= 0.46 Ohms
Considering 100/1 ratio,

Vk required = 729 x 1/100(0.5 + 0.46 + 0.2)

= 8 Volts

Selection of Class of CT
To take into account variations in CT requirements, relays, etc.
By choosing 5P20 , 10 VA CT,
Vk available = 20 x 1 (0.5+10)
= 210 Volts

Hence, the following CT Parameters are selected

CT RATIO = 100 / 1 Amp

CT Class = 5P20
VA burden required = 10 VA
CT Cable to be used = 4 sq.mm copper cable

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
3) CT Parameters for metering CTs- CT3 (Voltage Class :132kV)
Purpose: Metering
CT ratio chosen 100 /1 A.
Meter VA Burden
Digital Multifunction meter 0.5 VA
Ammeter 0.6 VA
Considering a 4 sq. mm lead length of 50 m
R(lead)= 0.46
Burden= 0.46 as sec. current is 1A

15VA is chosen to account for any future additions etc.

Therefore CT chosen = 100 /1 A.

15 VA
CL.0.5
ISF <5.

4) CT parameters for Busbar Differential Protection 87B Main-1, 87B Main-2

& 87C - CT4 & CT5 (Voltage Class : 132kV)

The CT parameters are identical to the parameters of Bus differential protection

CTs for Bus sectionaliser. -- Refer Sl. No. 1 of Section A.

Therefore the CT parameters for 87B Main-1/Main-2 & 87C are

CT RATIO = 2500 /1 Amp

Knee Point Voltage Vk >= 300V
CT Wdg. Res. Rct =< 10ohm
Mag. Current Im at Vk/2 =< 15 mA
CT Class = PS
CT Cable to be used = 4 sqmm copper cable

G. Incomer - 139/11 kV 115MVA Generator Transformer at CPP

BUS 1

BUS 2

2500A

P1

CT 1 Overall differential

CT 2 Non-Directional (IDMT) O/C and E/F, LBB

CT 3 Multifunction meter (Main & Check)

CT 4 Bus Differential - Main

CT 5 Bus Differential - Check

P2

LA C

Line EMVT
Core 1-Protective relays at CPP

Core 2- Multifunction meter, voltmeter

Core 3- Check synchronising scheme

at CPP

From 11/139 115MVA Generator Transformer at CPP

1) CT parameters for GT overall differential protection -- CT1

(Voltage Class : 132kV)
CT Ratio Selection :

These CT parameters are to match those of CTs installed at generator and

unit transformer for overall differential protection.

Transformer Rating = 90/115 MVA @ 50deg.C, ONAN/ONAF

139/11kV, Dyn11, Z=12.5% at 115 MVA

Therefore full load currrent on 132kV Side = (MVAx 1000)/(1.732 x kV)

= 115 x 1000 / 1.732 x 132
= 503.01 Amps

CT ratio selected on 132kV side is = 600 /1 Amp

(Considering 15% margin)

Knee Point Voltage Calculation (For 87OA ) :

Formula for calculating Knee point voltage requirement for differential protection
Vk = If x 1/CTratio x (Rct + Rl+Rrelay)

Where If = CT Primary fault current in Amps 40000 A

( 132kV Bus fault current)
Rct = CT winding resistance = 3 ohm
Rl = Cable resistance between CT & Relay

Considering 4 sq.mm copper conductor cable between CT and relay, resistance of

4 sq.mm copper cable = 4.61 Ohms / km

Maximum cable length = 150 M (from site plan)

Cable Lead Resistance for the loop Rl = 2 x 4.609 x 0.15

= 1.38 Ohms

Relay Burden = 0.1 (ABB catalogue RET 316)

Therefore, Since the secondary is 1A, RRelay = 0.1 ohms

CT knee point requirement = 40000x 1/600x (3+1.3825875+0.1)

= 299 Volts

We choose Vk >= 2 X Vk (required) to account for DC component during fault,

variation in CT, lead lengths and resistances, relays etc.

Hence, Vk >= 550V

Magnetising Current (Im) Calculation (For 87OA ):

Formula for calculating CT magnetising current Im.

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
Im = 1/n [PFSC x (1/CT ratio) - Ir]

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1

 NOAMUNDI POWER
BY: PK
TATA Consulting Engineers Limited PROJECT:
DISTRIBUTION

DATE: CLIENT: TATA STEEL LIMITED DOC. NO.:TCE-5668B-EL-CALC-737-C

CT/PT Calculations
CHD.: SUBJECT:
of 132kV GIS
DATE: JOB NO.: TCE.P0833 OFFICE:DK DISC.:EL SH. OF 27 REV. NO.: P0
Where n = No. of CTs in parallel = 3
PFSC = Primary Fault Setting Current = 100.6 Amp
(Assuming 20% of Ifull load)
Ir = Relay current at set point in Amp = 0.1 Amp
Im = Magnetising Current in Amps

Im = 1/3[ 101 x ( 1/600) - 0.1]

= 0.023 Amp
= 23 mA

Hence Im at Vk/2 = 23/2 = 11.5 mA.

Im at Vk/2 <= 15 mA is selected

Selection of Class of CT
As the CT is meant for overall differential protection, Class PS CT is selected.
CT Class = PS
Therefore, CT parameters for 87TRF are

CT RATIO = 600/1 Amp

Knee Point Voltage Vk >= 550V
CT Wdg. Res. Rct <= 3ohm
Mag. Current Im at Vk/2 <= 15 mA
CT Class = PS
CT Cable to be used = 4 sq.mm copper cable

2) Calculation of CT parameters for (50 BF, 50/67GT relays)-CT2

(Voltage Class : 220kV)
Transformer Rating = 90/115 MVA @ 50deg.C, ONAN/ONAF
139/11kV, Dyn11, Z=12.5% at 115 MVA

Therefore full load currrent on 132kV Side = (MVAx 1000)/(1.732 x kV)

= 115 x 1000 / 1.732 x 132
= 503.01 Amps

CT ratio selected = 600 / 1 Amp

Relay Burden :

Relay Burden(0.1 + 0.1) = 0.2 VA (Seimens Relay SIP-4 7SJ60 and 7SV)

Since the secondary Current is 1A, the above burden can be taken as the total burden in ohms.
i.e., Rrelaytotal in ohms = Relay Burden total in VA/(I s2),
, where Is = Secondary Current of CT.
Therefore Rrelaytotal in ohms = (0.2 /1*1)
= 0.2 ohms
Formula for calculating Knee point voltage requirement :
Vk = If x 1/CTratio x (Rct + Rl+Rrelay)

Where If = CT Primary fault current in Amps 35000 A

( 132kV Bus fault current)
Rct = CT winding resistance = 3 ohm (Assumed)
Rl = Cable resistance between CT & Relay

Considering 4 sq.mm copper conductor cable between CT and relay, resistance of

4 sq.mm copper cable = 4.61 Ohms / km
Maximum cable length = 150 M (Site Plan layout)
Cable Lead Resistance for the loop Rl = 2 x 4.609 x 0.15
= 1.38 Ohms
Considering 600/1 ratio,
Vk required = 35000 x 1/600(3 + 1.38 + 0.2)
= 267 Volts

Selection of Class of CT
By choosing 5P20 , 15 VA CT,
Vk available = 20 x 1 (3+15)
= 360 Volts

Hence, the following CT Parameters are selected

CT RATIO = 600/ 1 Amp

CT Class = 5P20
VA burden required = 15 VA
CT Cable to be used = 4 sq.mm copper cable

3) CT Parameters for metering CTs- CT3

(Voltage Class :132kV)
Purpose: Metering
CT ratio chosen 600 /1 A.

Meter VA Burden
DigitalMultifunction meter (Main) 0.5 VA
Digital Multifunction meter (Check) 0.5 VA
Ammeter 0.6 VA
Considering a 4 sq. mm lead length of 150 m
R(lead)= 1.38
Burden= 1.38 as sec. current is 1A
15VA is chosen to account for any future additions etc.
Class 0.2 is chosen.

Therefore CT chosen = 600 /1 A.

15 VA
CL.0.5
ISF <5.

4) CT parameters for Busbar Differential Protection 87B Main-1, 87B Main-2

& 87C - CT4 & CT5 (Voltage Class : 132kV)

The CT parameters are identical to the parameters of Bus differential protection

CTs for Bus sectionaliser. -- Refer Sl. No. 1 of Section A.
Therefore the CT parameters for 87B Main-1/Main-2 & 87C are

CT RATIO = 2500 /1 Amp

Knee Point Voltage Vk >= 300V
CT Wdg. Res. Rct =< 10ohm
Mag. Current Im at Vk/2 =< 15 mA
CT Class = PS
CT Cable to be used = 4 sqmm copper cable

FILE NAME: F010R1.XLS TCE FORM NO. 010 R1