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barevadiya
Participant

Join Date: Feb 2011
Posts: 1

Motor Differencial CT

02/04/2011 11:40 PM

We have motor differencial protection for motor. For that we have provided specification of Class PS CT (350/1 A) to Motor Vendor & switchboard vendor which is as below,

Motor Vendor:

Rct <= 2 ohm

Vk >= 200 V

Imag = 30ma @ Vk/2

Switchboard vendor:

Rct <= 4 ohm

Vk >= 400 V

Imag = 30ma @ Vk/2

However calculated Vk value is 127.83 V

My doubt is that whether differencial protection work correctly
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Pathfinder Tags: Two different type of CT for motor differential p
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Tornado
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 21017
Good Answers: 795
#1

Re: Motor Differencial CT

02/04/2011 11:52 PM

???????

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TonyS
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United Kingdom - Member - New Member

Join Date: Aug 2010
Location: Resting under the Major Oak
Posts: 4347
Good Answers: 181
#2

Re: Motor Differencial CT

02/05/2011 12:27 AM

Just get the switchboard vendor to talk to the motor vendor.

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mountk2
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Join Date: Jun 2010
Posts: 348
Good Answers: 10
#3

Re: Motor Differencial CT

02/05/2011 12:40 AM

Differential protection can be there for a large motor but what Class PS CT has got to do with switchboard vendor?

Did not the switchgear vendor reply to you "HA HA HEE HEE HA HA ... Oops"

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ecsales
Member

Join Date: Jan 2011
Posts: 8
#4

Re: Motor Differencial CT

02/05/2011 11:49 PM

Hi,

The calculated Vk is 127 then the CT will be sufficient since the Vk rating is 400V.

As for motor differential, so long there is a CT connected to the neutral and the phase, it will work.

Hope this helps

ecsales
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electricalexpert65
Guru

Join Date: Oct 2009
Posts: 2061
Good Answers: 169
#5

Re: Motor Differencial CT

02/07/2011 10:51 AM

I would like to study the excitation curves of both the CTs before answering. I feel that there could be stability problems. Because going by the date given at 127 V through-fault voltage, the excitation currents of both the CTs would differ and the relay might act.
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ecsales (1); electricalexpert65 (1); mountk2 (1); TonyS (1); Tornado (1)

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