Ct Vt Calculations r1

FICHTNER Consulting Engineers (India) Private Limited, (FI) Chennai VENDOR DRAWING REVIEW STATUS

Action - 1 : Approved Action - 2 : Approved except as noted on drawing. Revise drawing and resubmit for records. Action - 3 : Returned with comments. Resubmit for approval Action - 4 : Not approved. Resubmit for review Information noted. Retained for reference and records

This document has been reviewed as noted with regard to general conformity with the Contract specifications and requirements. The Vendor / Contractor is responsible for correctness of design calculation and details. Approval of this document does not relieve the Vendor / Contractor of his responsibility in carrying out the work correctly and fulfilling the complete requirements of the contract nor does it limit the purchaser's rights under the contract. FI Letter Ref.No.

Date

CNT 2310710001/E9/6263 dt 14.12.10 Signature

Initials

AE

CT & VT CALCULATIONS FOR GENERATOR, GT AND UT METERING AND PROTECTION

1.0

DOCUMENT NO. : PE-DC-348-510-E003 REV NO. : 01 DATE SHEET

: 28/10/10 : 1 of 16

SCOPE : This document covers the following : CT parameters calculations for :-





CTs of Generator Neutral & Line side.



CTs on GT HV side having interface with GRP.



CTs on GT HV neutral side.



CTs on GT LV side.



CTs on UT HV side.



CTs on UT LV neutral side.



CTs on UT LV side having interface with GRP.

VT parameters calculations for :-





IVT parameters calculations for



2.0

VTs on Generator line side.



Generator Inter turn fault relay (64GlT)



110 V AC auxiliary supply to 20 Hz Generator

REFERENCE DRAWING : DRAWING TITLE : SLD for Generator, GT & UT Metering and Protection. DRAWING NO.

3.0

: PE-DG-348-510-E001

LEGEND : CT

:

Current transformer

I

:

Relay rated current

IVT

:

Interposing voltage transformer

Ie

:

Excitation current

If

:

CT secondary current corresponding to fault current

L

:

Length of cable between CT and relay

RL

:

One way lead resistance between CT and relay

Rct

:

Resistance of secondary winding of main CT

Vk

:

Knee point voltage

VT

:

Voltage transformer


4.1

DATE SHEET

: 28/10/10 : 2 of 16

MAIN EQUIPMENT DETAILS (I)

(II)

(III)

4.2

DOCUMENT NO. : PE-DC-348-510-E003 REV NO. : 01

GENERATOR : Rated Output

: 600 MW

Rated Voltage

: 21 KV

Subtransient reactance (Xd’’) (saturated)

: 17.8%

Voltage variation

: ± 5%

Rated power factor

: 0.85 LAG

GENERATOR TRANSFORMER : Rating

: 3 single-phase units of 240 MVA each.

Percentage Impedance [Tentative]

: 14.5% at 240 MVA base

Voltage ratio

: (420/√3)/21KV

UNIT TRANSFORMERS : Rating

: 31.5 MVA

Percentage Impedance [Tentative]

: 10 %

Voltage ratio

: 21/11.5KV

CONTROL CABLE DETAILS Material

: Copper

Size

: 2.5 mm2

Resistance of conductor

: 8.87 /kM (for 2.5 mm2 cable)

5.0

CTs PARAMETER CALCULATIONS

5.1

CTs Ratio On Gen Neutral & Phase Side : Generator current at normal operating voltage IGnormal

= =

600  1000

3  21x 0.85 19407.3A

Generator current at minimum continuous operating voltage (i.e. at 95% of normal voltage) IGmax

= =

600  1000

3  21x0.85  0.95 20428.7A

Hence CT ratio for CTs located on generator neutral side and phase side for protection, metering, load transducers and AVR is selected as 22000/5 A



: 28/10/10 : 3 of 16

For the purpose of calculation, distance from GRP to Gen Busduct CTs marshalling box, L is taken as 175M 

Lead Resistance, RL

=

8.87 x 0.175

=

1.55 ohm

=

52 x 1.55 VA

=

38.8 VA

=

19.4 VA

Hence , Lead Burden Lead Burden (for 2 cores)

5.1.1

CTs ON GEN. NEUTRAL SIDE

CT 1

:

For Overall differential protection (87OA)

CT 2

:

For ‘Load transducer’ & ‘Performance testing’

CT 3

:

For composite generator protection relay ‘GR1’

CT 4

:


CT9

:

For 100% stator E/F Protection (64G3)

CT 1 : Vk



50I (Rct + 2 RL)

Ie



0.03 I at Vk/2

I

=

5A

Vk



50 x 5 (Rct + 2 x 1.55 /2) [2 cores of 2.5mm2 cable]

Vk



250Rct + 387.5 V

Ie



150mA at Vk/2

SELECTED PARAMETERS FOR CT 1 : CT RATIO

:

22000/5 A

ACCURACY CLASS

:

PS

KNEE POINT VOLTAGE

:

 250Rct + 400 V

MAGNETISING CURRENT

:

 150mA at Vk/2



DATE SHEET

: 28/10/10 : 4 of 16

CT 2 : Source of burden

Burden (in VA)

Ammeter (*)

3.0

Wattmeter (*)

5.0

VARmeter (*)

5.0

PFmeter (*)

5.0

KWHmeter (*)

5.0

Load Transducer

0.5

Lead burden [2 cores of 2.5 mm² cable]

19.4

Total Burden

42.9

* : Performance testing meter


:

22000/5 A

ACCURACY CLASS

:

0.2

BURDEN

:

60 VA

I.S.F.

:

≤ 5.0

CT 3 & CT 4 : Maximum through fault current of generator

=

600 1000 3  21 0.85  0.178  0.85

=

128270.3 A

=

128270.3  5 21000

=

30.54 A

Vk



5If (Rct + 2 RL)

Vk



5 x 30.54 (Rct + 2 x 1.55/2)

If

[2 cores of 2.5 mm2 cable] Vk



152.7Rct + 236.685 V

Ie



0.03 I at Vk/2

I

=

5A

Ie



150mA at Vk/2



: 28/10/10 : 5 of 16

SELECTED PARAMETERS FOR CT 3 & CT 4 : CT RATIO

:

22000/5 A

ACCURACY CLASS

:

PS

KNEE POINT VOLTAGE

:

 160Rct + 250 V

MAGNETISING CURRENT

:

 150mA at Vk/2

CT 9: PARAMETER TO BE FINALISED LATER AFTER RECEIPT OF NGR RATING FROM CUSTOMER. 5.1.2

CTs ON GEN. PHASE SIDE CT 5

:


CT 6

:


CT 7

:

For Load transducer, Load shedding relay and AVR

CT 8

:

For ‘Metering’, Load transducer & AVR.

CT 5/CT 6 : Particulars shall be similar to CT 3/CT 4

SELECTED PARAMETERS FOR CT 5 & CT 6: CT RATIO

:

22000/5 A

ACCURACY CLASS

:

PS

KNEE POINT VOLTAGE

:

 160Rct + 250 V

MAGNETISING CURRENT

:

 150mA at Vk/2


Burden (in VA)

AVR

20.0

Load transducer

0.5

Load shedding relay

0.85


19.4

Total burden

40.75


:

22000/5 A

ACCURACY CLASS

:

0.2

BURDEN

:

60 VA

I.S.F.

:

≤ 5.0



DATE SHEET

: 28/10/10 : 6 of 16


Burden (in VA)

MWH/MVARH meter

1.0

Current transducer (3 Nos.)

0.2 x 3 =0.6

Watt transducer (1 Nos.)

0.5

VAR transducer (1 Nos.)

0.5

PF transducer

0.6

Load transducer

0.5

AVR

20.0


19.4

Total Burden

43.1

SELECTED PARAMETERS FOR CT 8 :

5.2.0

CT RATIO

:

22000/5 A

ACCURACY CLASS

:

0.2

BURDEN

:

60 VA

I.S.F.

:

≤ 5.0

CTs ON GT LV SIDE Phase Current on GT LV side

=

240 x 1000 A 21

=

11428.57 A

Hence CT ratio for CTs located on GT LV line side for protection is selected as 12500/5 A. For the purpose of calculations, Distance from GRP to GT M.Box, L =  Lead Resistane, RL 5.2.1

230M

=

8.87 x 0.23

=

2.04 ohms

CTs on GT LV line Side: CT 10

:

For GT differential Protection (87GT)

CT 11

:

For GT differential Protection (87GT)

CT10/ CT11 : Vk



50I (Rct + 2 RL)



: 28/10/10 : 7 of 16

Ie



0.03 I at Vk/2

I

=

5A

Vk



50 x 5 (Rct + 2 x 2.04 /2) [2 cores of 2.5mm2 cable]

Vk



250Rct + 510 V

Ie



150mA at Vk/2

SELECTED PARAMETERS FOR CT 10/ CT11 :

5.3.0

CT RATIO

:

12500/5 A

ACCURACY CLASS

:

PS

KNEE POINT VOLTAGE

:

250Rct + 550 V

MAGNETISING CURRENT

:

 150 mA at Vk/2

CTs ON GT HV SIDE Current on GT HV side

=

3 x 240 x 1000 3x420

=

989.77 A

Hence CT ratio for CTs located on GT HV neutral side and GT HV line side for protection is selected as 1200/1 A and 1200/5 A respectively. For the purpose of calculations, Distance from GRP to GT M.Box, L =  Lead Resistane, RL

230M

=

8.87 x 0.23

=

2.04 ohms

=

12 x RL

=

2.04 VA

Hence, Lead burden 5.3.1

CTs on GT HV Neutral Side: CT 12 (CORE-1)

:

For GT HV side Backup Earth Fault Protection (51NGT)

CT 12 (CORE-2)

:

For GT HV & overhead line differential Protection (87HV)

CT 12 (CORE-1) : Source of burden

Burden (in VA)

51 NGT

0.30

Lead burden( 2.5 mm² cable)

2.04

Total Burden

2.34

SELECTED PARAMETERS FOR CT 12 (CORE – 1): CT RATIO

:

1200/1 A


ACCURACY CLASS

:

5P20

BURDEN

:

15 VA


: 28/10/10 : 8 of 16

CT 12 (CORE-2) : Maximum through fault current on HV side of GT

=

720 1000 3  420  0.95  0.145

=

7185.28 A

 Fault on secondary side of CT, If

=

7185.28 1 1000

If

=

7.185 A



2If (Rct + 2RL)



2 x 7.2 (Rct + 2x 2.04)

Knee point voltage, Vk Vk

(2.5 mm² cable) Vk



14.4 Rct + 58.75 V

Ie



0.03 I at Vk/2

CT sec. current , I

=

1A

Ie



30mA at Vk/2



SELECTED PARAMETERS FOR CT 12 (CORE-2) :

5.3.2

CT RATIO

:

1200/1 A

ACCURACY CLASS

:

PS

KNEE POINT VOLTAGE

:

 20 Rct + 100 V

MAGNETISING CURRENT

:

 30 mA at Vk/2

CTs on GT HV line Side : CT 13

:

For GT differential protection (87GT)

CT 13 : Vk



50I (Rct + 2 RL)

Ie



0.03 I at Vk/2

I

=

5A

Vk



50 x 5 (Rct + 2 x 2.04 /2) 2

[2 cores of 2.5mm cable] Vk



250Rct + 510 V




Ie


: 28/10/10 : 9 of 16

150mA at Vk/2


:

1200/5 A

ACCURACY CLASS

:

PS

KNEE POINT VOLTAGE

:

250Rct + 550 V

MAGNETISING CURRENT

:

 150 mA at Vk/2

CT 14(CORE-1) :

For Overall differential protection (87OA) to be covered in 400kV switchyard document [customer scope] documents.

CT 14(CORE-2) :

For GT HV & overhead line differential protection

(87HV) to be covered in

400kV switchyard document [customer scope] documents. 5.4.0

CTs FOR UT #1A/2A & UT #1B/2B

5.4.1

CTs on UT #1A/2A & UT #1B/2B HV Line side :CT15A/ CT15B

:

For UT Differential Protection (87UTA / 87UTB)

CT16A/ CT16B

:

For UT HV Over Current Protection (51UTA / 51UTB)

CT17A/ CT17B

:

Overall differential protection (87OA)

Current on UT HV side

=

31.5 x 1000 3x21

=

866.05 A

[At normal voltage]

Hence CT ratio for CTs located on UT HV side for protection is selected as 1000/1 A. For the purpose of calculations, Distance from GRP to UTs Tap Off Busduct CT marshalling box is taken as 210m. L = 

Lead Resistance, RL

210M

=

8.87 x 0.21

=

1.86 ohm

=

I2 x RL

=

12 x 1.86

=

1.86 VA

Vk



40 I (Rct + 2 RL)

Ie



0.03 I at Vk/2

I

=

1A

Vk



40 x 1 (Rct + 2 x 1.86)

Hence, Lead burden

CT 15A & CT 15B:



: 28/10/10 : 10 of 16

[2.5 mm2 cable] 

Vk



40Rct + 148.8 V

Ie



30mA at Vk/2

SELECTED PARAMETERS FOR CT 15A & CT 15B : CT RATIO

:

1000 / 1 A

ACCURACY CLASS

:

PS

KNEE POINT VOLTAGE

:

 40Rct + 200 V

MAGNETISING CURRENT

:

 30mA at Vk/2

CT 16A & CT 16B : Source of burden

Burden (in VA)

51UT

0.3

Lead burden [2.5 mm² cable]

1.86

Total Burden

2.16

SELECTED PARAMETERS FOR CT16A & CT 16B : CT RATIO

:

1000/1 A

ACCURACY CLASS

:

5P20

BURDEN

:

15VA

CT17A/ CT17B : Praticular shall be similar to CT1: SELECTED PARAMETERS FOR CT 17A/17B :

5.4.2

CT RATIO

:

21000/5 A

ACCURACY CLASS

:

PS

KNEE POINT VOLTAGE

:

 250Rct + 400 V

MAGNETISING CURRENT

:

 150mA at Vk/2

CTS ON UT LV SIDE: Current on UT LV side

=

31.5 x 1000 3x11.5

=

1581.48 A

Hence CT ratio for CTs located on UT LV side for protection is selected as 2000/1 A. 5.4.2.1 CTs on UT LV Neutral side:



DATE SHEET

: 28/10/10 : 11 of 16

NOTE: FOR CALCUALTION PURPOSE, NGR RATING IS CONSIDRED AS 300A FOR 10 SEC. CUSTOMER TO CONFIRM. CT18A/ CT18B (CORE - 1) :

For UT LV Backup Earth Fault Protection (51NUTA / 51NUTB)

CT18A/ CT18B (CORE - 2) :

For UT Restricted Earth Fault Protection (64RUTA / 64RUTB)

Max. distance from GRP to UT MB  Lead Resistane, RL Hence, Lead burden

=

210M

=

8.87 x 0.21

=

1.86

=

I2 x RL

=

12 x 1.86

=

1.86 VA

CT 18A & CT18B (CORE-1) : Source of burden

Burden (in VA)

51NUT

0.3

Lead burden [2.5 mm² cable]

1.86

Total Burden

2.16

NGR is rated for maximum E/F current of 300 A. SELECTED PARAMETERS FOR CT 18A & 18B (CORE-1) : CT RATIO

:

300 / 1 A

ACCURACY CLASS

:

5P20

BURDEN

:

15 VA

CT 18A & CT 18B (CORE-2) : Maximum through fault current on LV side of UT =

31.5 1000 3 11.5  0.10  0.9

=

17572 A

 Fault on secondary side of CT, If

=

17572 1 2000

If

=

8.78 A



2If (Rct + 2RL )



2 x 8.78(Rct + 2 x 1.86)

Knee point voltage, Vk Vk

[ 2.5 mm2 cable] 

17.56Rct + 65.32 V



0.03 I at Vk/2

CT sec. current , I

=

1A

Ie



30mA at Vk/2

Vk Magnetising current , Ie 



: 28/10/10 : 12 of 16

SELECTED PARAMETERS FOR CT 18A & 18B (CORE-2) : CT RATIO

:

2000 / 1 A

ACCURACY CLASS

:

PS

KNEE POINT VOLTAGE

:

 20Rct + 100 V

MAGNETISING CURRENT

:

 30mA at Vk/2

5.3.2.2 CTs on UT LV Line side: CT19A/ CT19B (CORE-1) :

For UT Restricted Earth Fault Protection (64RUTA / 64RUTB)

CT19A/ CT19B (CORE-2) :

For UT Differential Protection (87UTA / 87UTB)

Average Distance from GRP to Unit Switchgear I/C Busduct CT marshalling box  Lead Resistane, RL

=

90 M

=

8.87 x 0.09

=

0.8 ohm

CT19A/ CT19B (CORE-1) : Particulars shall be similar to CT 18A/CT18B (CORE-2) i.e. SELECTED PARAMETERS FOR CT 20A & 20B (CORE-1) : CT RATIO

:

2000 / 1 A

ACCURACY CLASS

:

PS

KNEE POINT VOLTAGE

:

 20Rct + 100 V

MAGNETISING CURRENT

:

 30mA at Vk/2

CT19A/ CT19B (CORE-2) : Vk



40 I (Rct + 2 RL)

Ie



0.03 I at Vk/2

I

=

1A

Vk



40 x 1 (Rct + 2 x 0.8/2) [2 cores of 2.5 mm2 cable]



Vk



40Rct + 32 V

Ie



30mA at Vk/2

SELECTED PARAMETERS FOR CT 20A & CT 20B (CORE-2) : CT RATIO

:

2000 / 1 A

ACCURACY CLASS

:

PS

KNEE POINT VOLTAGE

:

 40Rct + 50 V

MAGNETISING CURRENT

:

 30mA at Vk/2



6.0.0

DATE SHEET

: 28/10/10 : 13 of 16

VOLTAGE TRANSFORMER PARAMETER CALCULATIONS VT 1

:

For Gen. Protection, AVR, Frequency Transducer, Load transducer & Load shedding relay.

VT 2

:

For Gen. Protection, AVR, Load transducer & gen. Synchronising.

VT 3

:

For metering, performance testing & Load transducer.

Primary connection

:

Star

Secondary connection

:

Star

Primary voltage

:

21000

V

3 Secondary voltage

:

VT ratio

:

110 V 3

21000 110 3

VT 1: Source of burden

Burden (in VA)

60VT1

11.0

AVR

20.0

Frequency transducer

3.00

Load transducer

0.13

Load shedding relay

2.1

GR1

0.3

Total Burden

36.53

Lead burden is negligible for VT

SELECTED PARAMETERS FOR VT 1 : VT RATIO

:

21000 110 3

ACCURACY CLASS

:

0.5/3P

BURDEN

:

100 VA

3

V

3

V



VT 2 : Source of burden

Burden (in VA)

60VT2

11.0

AVR

20.0

Load transducer

0.125

Voltage transducer for incoming voltage(*)

0.22

Frequency transducer for incoming

3.0

frequency(*) Synchroscope(*)

6.0

GR2

0.3

Total Burden

40.645

Lead burden is negligible for VT * synchronising equipment SELECTED PARAMETERS FOR VT 2 : VT RATIO

:

21000 110 3

VT 3:

ACCURACY CLASS

:

0.5/3P

BURDEN

:

100 VA

3

V

: 28/10/10 : 14 of 16


Source of burden

Burden (in VA)

60VT3

11.0

MWH/MVARH meter

2.0

Transducer for VAR

0.22

Transducer for Watt

0.22

Transducer for PF meter

2.5

Transducer for Frequency

3.0 x 2 = 6.0

Transducer for Voltmeter (2 Nos.)

0.22 X 2 = 0.66

Load transducer

0.125

AVR

20.0

Wattmeter (*)

5.0

Varmeter (*)

7.5

PFmeter (*)

5.0

KWH meter (*)

7.5

Total Burden

62.325


: 28/10/10 : 15 of 16

* Performance testing meter Lead burden is negligible for VT

SELECTED PARAMETERS FOR VT 3 : VT RATIO

:

21000 110 3

7.0.0

IVT1

ACCURACY CLASS

:

0.2

BURDEN

:

100 VA

V

3

INTERPOSING VTs PARAMETER CALCULATIONS IVT 1

:

For Gen. Interturn fault protection (64GIT)

IVT 2

:

For 110V AC auxiliary supply to 20Hz Generator

Primary connection Secondary connection

: :

Star Open delta

Under fault condition, 64GIT should get no voltage. NGT secondary and open delta secondary of IVT1should give equal and opposite voltages. NGT ratio is 21kV/240V, i.e. it gives an output of 240/√3 for a single line to earth fault. to get 240 /√3 V, IVT1 secondary rating shall be (240 /√3) / 3 V. IVT Primary voltage IVT ratio

: :

(110/√3) V (110/√3) / (80/√3) V



Source burden 64GIT Total Burden SELECTED BURDEN

DATE SHEET

Burden (in VA) 0.3 0.3 15 VA

SELECTED PARAMETERS FOR IVT 1 : IVT RATIO

:

ACCURACY CLASS BURDEN

110

80

3

3

: :

3P 15 VA

Primary connection

:

Star

Secondary connection

:

star

Primary voltage

:

V

IVT 2 :

415

V

3 Secondary voltage

110

:

V

3 IVT ratio

415 110 / 3 3

:

Source of burden

Burden (in VA)

20 Hz Generator

45.0

Total Burden

45.0

SELECTED PARAMETERS FOR IVT 2 : VT RATIO

:

415 110 V / 3 3

ACCURACY CLASS

:

1.0

BURDEN

:

100 VA

: 28/10/10 : 16 of 16

Ct Vt Calculations r1

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