## How to calculate VT Ratio with the given information

## How to calculate VT Ratio with the given information

(OP)

20125/34500GY/115

which Voltage should I use to divide by 115 to get my VT Ratio?

which Voltage should I use to divide by 115 to get my VT Ratio?

## RE: How to calculate VT Ratio with the given information

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If we learn from our mistakes I'm getting a great education!

## RE: How to calculate VT Ratio with the given information

Not sure where you got the information from and what are you trying to do, specify a VT or use VTR in a relay programming or do some calcs?.

You still need to know the VT connections, Y or delta and number of VTS to specify a VT correctly. For all I know you can have a single phase VT on a 3 phase system, connected either L-L or L-N.

As a side note, the rating 20125/34500Y does not exactly match up to 1.732 multiplier so once you select a VT, you need to use the actual VTR on the VT nameplate, and not what you might have calculated.

Rafiq Bulsara

http://www.srengineersct.com

## RE: How to calculate VT Ratio with the given information

FYI...the system voltage is 34.5KV.

## RE: How to calculate VT Ratio with the given information

115/(sqrt 3) = 66

34500/115= 300 or 20125/66=304.

For a 34.5 kV, L-N voltage would be 19919. 19919/66=302.

I would still ask for the relay and VT schematics.

Rafiq Bulsara

http://www.srengineersct.com

## RE: How to calculate VT Ratio with the given information

20125/34500 Grd Y 175/300:1

From IEEE C57.13 for indoor bushings:

20125/34500 Grd Y 175:1

ScottyUK is correct, use the smaller number. 175:1 corresponds to a 115 V secondary and 300:1 gives 67 V.

## RE: How to calculate VT Ratio with the given information

The ratio is 20125:115V, which is 175:1. It doesn't matter how the VT is connected. The rated primary voltage is 20125V and the rated secondary voltage is 115 kV...as it's written.

Also, because the rating lists "GY" it means it's a single-bushing unit meant for line to ground connection only.

You're correct that 34500/sqrt3 is not 20125, but that doesn't mean the ratio is not still 175:1, but rather means that the secondary voltage is not exactly 115V when the system voltage is 34500V.

## RE: How to calculate VT Ratio with the given information

Rafiq Bulsara

http://www.srengineersct.com

## RE: How to calculate VT Ratio with the given information

If that is what is on the PT, yes it is 175.

Rafiq Bulsara

http://www.srengineersct.com

## RE: How to calculate VT Ratio with the given information

## RE: How to calculate VT Ratio with the given information

You can certainly have delta connected VTs or single phase line to line VTs.

Rafiq Bulsara

http://www.srengineersct.com

## RE: How to calculate VT Ratio with the given information

## RE: How to calculate VT Ratio with the given information

## RE: How to calculate VT Ratio with the given information

Rafiq Bulsara

http://www.srengineersct.com

## RE: How to calculate VT Ratio with the given information

The rated voltage is the voltage that the primary winding is rated to have applied across it. How that voltage gets there (line-to-line, or line-to-neutral/ground) doesn't really matter to the VT. All other considerations are insulation-based, etc...

## RE: How to calculate VT Ratio with the given information

Rafiq Bulsara

http://www.srengineersct.com