how do you size current transformers

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vladimirRM said:
how do you size current transformers for protection and metering for 138kV substation?
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Please advise what you application is as there are countless was to address you question. What's the voltage, current, cable bus, meter, relay, etc. And what class would the CT be? Is it a bar or widow CT?
Because for question is so vague is this a class or test question
 
how do you size current transformers for protection and metering for 138kV substation

how do you size current transformers for protection and metering for 138kV substation

the voltage is 138kv, for protection and metering purposes
 
vladimirRM said:
how do you size current transformers for protection and metering for 138kV substation?
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You will most likely need both metering accuracy and relaying accuracy CTs but an extended range transformer might work depending on what you are doing. The metering CTs will be accurate at low current readings but will probably saturate for fault conditions. The relaying CTs will be sized to not saturate for available fault current but probably will not be accurate enough for low load currents (if metering for revenue).

You use burdens, ambient temperatures, mechanical stress, amp rating of equipment connected to the CT secondary, accuracy requirements, load current ranges, fault current ranges, and rating factors.

You have asked a very broad question but if you have a specific question, ask away. Most manufacturers have application guides covering sizing so check with your supplier. I know CT manufacturers like GE & ABB both have application guides as well as the relay manufacturers like Schweitzer, Cooper, Basler, etc.
 
Besoeker said:
Maybe 138kV?
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Yes, another instance where the OP tells you as little as possible and everybody guesses what the real question is. You must be a soothsayer to have guessed 138kv out of the clear blue sky, a voltage that is a utility voltage unless you a dealing with an extremely large industrial facility with a 138kv service. Needless to say I'm impressed.
 
kingpb said:
Unless you are asking just for your own curiosity, I would highly recommend you contact an engineering firm knowledgeable in HV substation design.

Some additional reading material:
http://www05.abb.com/global/scot/sc...7b130057ba48/$file/138000 section_updated.pdf
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I guess that's why I completely misread what the OP stated because the topic as so bizarre and I didn't take it seriously. But there it was 138kv with no reference as to why the question is being asked.
 
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