Nct Sizing

HPCL-MITTAL HPCL-MITTAL ENERGY ENERGY L IMITED PROJECT

220/33kV BAY EXTENSION AT HMEL BHATINDA

JOB No.

220/33kV 220/33kV BA Y EXTENSION EXTENSION AT HMEL BHATINDA DOC NO

NAC/HMEL/NCTSIZE/01 SIZE/01 21/2/2012

Doc Issue Date

NCT SIZING CALCULATION FOR 16/20MVA TRANSFORMER

Contr Contractor actor :

BECP BECPL L

Consult Consultant ant :

N_Arc N_Arc Consult Consultiing, New New Del Delhi

2 1

21/2/2012 15/2/2012

Third Submission Second Submission

PRADEEP PRADEEP

AJAY AJAY

0 Rev.

20/1/2012 Date

First Submission Description

PRADEEP Prepared By

AJAY Checked By

SAMIR SAMIR SAMIR Approved By

1of5

DOC.

HMEL Project

220/33 kV Bay Extension at HMEL Bhatinda

Project No

 A.

NAC/HMEL/NCT SIZE/01

DOC NO Rev

2

TRANSFORMER NCT

220 kV Side Core-I

CT RATIO :100-50/1A VA-30, CLASS 5P20 220kV Side NCT Primary current(Ip)

=

100

A

220kV Side NCT Secondry current(Is)

=

1

A

CT Resistance(RCT)

<

5

Ω

=

100

m

Resistance of 2.5mm  Cu. Cable(R)

2

=

9.48

Ω/km

Lead Resistance(RL)

=

RxL/1000

RL

=

0.948

Lead Burden

=

I (Rct + 2RL)

=

1 (5+(2*0.948))

=

6.896

VA

0.25

VA

2

Length of 4mm  Cu. Cable(L)-1Way LEAD BURDEN CALCULATION

Relay Burden Total CT Burden

Ω

2

2

= Relay Burden +Lead Burden =

7.146

VA

Considering 10% extra for inter-panel wiring

=

7.861

VA

VA Recommended For CT

=

30

VA

Hence CT is Safe

2 of 5

DOC.

HMEL Project

220/33 kV Bay Extension at HMEL Bhatinda

NAC/HMEL/NCT SIZE/01

DOC NO

Project No

Rev

2

220 kV Side Core-II KNEE POINT VOLTAGE CA LCULA TION (V kp ) NCT RATIO :100-50/1A VA-30, CLASS PS 33kV NCT Primary current(Ip)

=

100

A

33kV NCT Secondary current(Is)

=

1

A

CT Resistance(RCT)

<

5

Ω

=

100

m

=

9.48

Ω/km

2

Length of 2.5mm  Cu. Cable (L) 2

Resistance of 2.5mm  Cu. Cable (R) No. of runs/phase

1

Two way lead loop resistance (RL)

1.896

Ω

A

System fault level (IF)

=

40000

Sho rt c ircu it fa ult cur re nt a t Se c. o f NC T( If)

=

IF/Ip

=

400

A

0.25

VA

If Relay Burden Knee Point Voltage(VKP)

=

0.5*If(Rct+RL+Rb)

Knee Point Voltage(VKP)

=

1429.2

Volts

Recommended Knee Point Voltage

>

1500

Volts

Magnetising current(Imag) at VK/2

<

30

mA

3 of 5

DOC.

HMEL Project

220/33 kV Bay Extension at HMEL Bhatinda

NAC/HMEL/NCT SIZE/01

DOC NO

Project No

Rev

2

33 kV Side Core-I VA BURDEN CALCULATION FOR CORE-I CT RATIO :600-300/1A VA-30, CLASS 5P20 33kV Side NCT Primary current(Ip)

=

600

A

33kV Side NCT Secondry current(Is)

=

1

A

CT Resistance(RCT)

<

5

Ω

=

100

m

Resistance of 2.5mm  Cu. Cable(R)

=

9.48

Ω/km

Lead Resistance(RL)

=

RxL/1000

RL

=

0.948

Lead Burden

=

I (Rct + 2RL)

=

1 (5.0+(2*0.948))

=

6.896

VA

Relay Burden

=

0.25

VA

Total CT Burden

= Relay burdern +Lead Burden

2

Length of 4mm  Cu. Cable(L)-1Way LEAD BURDEN CALCULATION 2

Ω

2

2

=

7.146

VA

Considering 5% extra for inter-panel wiring

=

7.503

VA

VA Recommended For CT

=

30

VA

Hence CT is Safe

4 of 5

DOC.

HMEL Project

220/33 kV Bay Extension at HMEL Bhatinda

NAC/HMEL/NCT SIZE/01

DOC NO

Project No

Rev

2

33 kV Side Core-II KNEE POINT VOLTAGE CALCULATION (V kp ) NCT RATIO :600-300/1A VA-30, CLASS PS 11kV NCT Primary current(Ip)

=

600

A

11kV NCT Secondary current(Is)

=

1

A

CT Resistance(RCT)

<

5

Ω

Length of 2.5mm2 Cu. Cable (L)

=

100

m

Resistance of 2.5mm2 Cu. Cable (R)

=

9.48

Ω/km

No. of runs/phase

1

Two way lead loop resistance (RL)

1.896

Ω

A

System fault level (IF)

=

40000

Sho rt c ircu it fa ult cur re nt a t Se c. o f NC T( If)

=

IF/Ip

=

66.66666667

If Relay Burden

0.25

A VA

Knee Point Voltage(VKP)

=

0.5*If(Rct+RL+Rb)

Knee Point Voltage(VKP)

=

238.2

Volts

Recommended Knee Point Voltage

≥

500

Volts

Magnetising current(Imag) at VK/2

≤

30

mA

5 of 5