Standard CT & VT VA ratings? 1

[LSpark]

I've been asked to give details for some replacement CTs and VTs for one of power stations. Are there standard VA ratings for CTs and VTs?

The existing VTs are 200VA which is well in excess of what the actual burden will be (less than 5VA) so I don't want to tell them to order direct replacments.

 

[scottf]

IEC or IEEE standard?

What voltage class?

 

[LSpark]

The VTs are IEC standard and 33kV/110V.

The CTs are also IEC standard and 250A/1A & 125A/1A.

 

[scottf]

Then the answer it no...there is no "standard" va ratings per se.

Figure out what you need and specify that. Over-rating the VT burden can lead to a more expense unit that will actually perform less accurately than one sized with a more appropriate burden rating.

Over-sizing the CT burden rating won't cause a performance problem, but will potentially add cost.

 

[burnt2x]

Engineering in the reverse mode? What scottf said, start from your requirements are and specify.

 

[kalbur]

You can check pages 468; ...; 473 of ABB switchgear manual 11th edition

http://www.die.unipd.it/~gobbo/dida...BB_swithgear_manual_E11/ABB_11_E_10_druck.pdf

 

[LSpark]

Thanks for that, I usually aim to have the CTs and VTs operating between 25% and 75% of rated VA. I think 5VA will be adequate for both the CTs and VTs. Part of me wants to order 10VA VTs 'just in case' but I'd probably end up having to install burden resistors as it's for the tariff metering so needs to be in the more accurate range.

 

[koizumi]

Please check out IEC 60044-1 Instrument transformers: CT, and IEC 60044-2 Instrument transformers: VT for the ratings.