How to calculate CT ratio

[hallmg]

Hi,

I am trying to find the CT ratios for my 33KV switchgear protection relays, as the equipment is very old i cannot find much information so far.

Is there a way to calculate what the turns ratios should be?

Any help would be much appreciated.

Regards,
Melvin.

 

[TestMonkey]

Transformer Turns Ratio (TTR) test

 

[waross]

35kV/120V >> 35000V / 5V = 292:1
Under some fault conditions the line to ground voltage may rise to the line to line voltage. All protection PTs should be rated for line to line voltage.
There may be exceptions for line metering PTs.
The primary voltage should be equal or greater than the highest expected line to line voltage.
The turns ratio is generally multiplied by 120 and the transformers are rated as (Primary voltage):120 Volts

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Variac200]

To know the CT ratio in the absence of reliable nameplate data, your best option is to do a CT primary injection; injection of current of known magnitude into the primary side.

 

[stevenal]

Waross, I think the question was about CTs.

I agree that testing may be your only option.

 

[hallmg]

Hi,

Thank you everyone for the help, its much appreciated.