Current transformer size 2

[eleecsunil1965]

We are trying to use one spare feeder for energising one new Transformer(750KVA,13.8kV/480Volts,60Hz.6%(Z), using feeder 1200Amps,breaker(VCB) having 600/5, ANSI C200 class current transfomer(Bus bar mounted) for protection relaying and measuring purpose. Is there any accuracy issue with this CT ratio?

 

[dpc]

So what is the load expected to be? If you will have over 600A of load, you need to verify the thermal rating of the 600/5.

Is your concern relaying or metering accuracy. If relaying, you'll need to know the available fault current. If metering, you will need to determine the metering accuracy rating, if any.

"An 'expert' is someone who has made every possible mistake in a very narrow field of study." -- Edward Teller

 

[stevenal]

C200 is a relay accuracy designation. Unless rated for metering as well, it will not be suitable for revenue accuracy metering.

 

[eleecsunil1965]

Connected load will be around 300KW on 480 volts bus(lighting, small power and HVAC units( maximimum motor size 20KW only. Fault rating on 13.8KV side bus is 500MVA.I am concerned about only protection relaying purpose. Metering is just for indication purpose only.

 

[dpc]

Assuming standard overcurrent relaying, I don't think the CT performance will be an issue. C200 is better than the majority of CTs in metal-clad switchgear.

"An 'expert' is someone who has made every possible mistake in a very narrow field of study." -- Edward Teller

 

[pwrtran]

It possibly 10% or 2.5% accuracy at 100A at secondary, for protective relaying it is ok.

 

[stevenal]

You need to know the available current at the CT location.

Rule of thumb is use within 20* the 600 A rating. For more detailed analysis, use

http://www.nxtphase.com/documents/CT_SAT_Calculator - IEEE Version.xls

Relays will differ in how they respond to saturation.

 

[pwrtran]

stevenal has a good point - are you concerning about accuracy for measuring purpose or you are concerning about the CT saturation during a fault?
A star for stevenal, great calculator!

 

[eleecsunil1965]

AS i told before only concern is protection requirements.Thanks stevenal.