Voltage transformer sizing (protection)

[epesmh]

When sizing a VT for generator neutral protection - what is important to have in mind?

How to determind the rated VA?

 

[cranky108]

Usually the size of the loading resistor tied to the secondary.

 

[Kiribanda]

It looks like you are talking about the "DISTRIBUTION TRANSFOMER" connected to the
neutral of the generator for transformer HRG. If yes, please refer IEEE C62.92.2 for sizing.
But if you are talking about Voltage Transformers for the gen protection scheme,
then it is different.

 

[waross]

The transformer should be sized and rated based on line to line voltage rather than line to neutral voltage for most applications.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[epesmh]

I'm talking about a VT for generator neutral protection purpose yes. The ratio of the VT is 11 000:v3 / 110:3, but the size in VA I dont know what to consider. Cant find any litterature mentioning this

 

[scottf]

The VA rating, which is called burden rating, should be a function of what device(s) you are connecting the VT's secondary.

In this case, you would need to look at the rated burden of the relay being used. In general, modern electronic relays are generally <= 1VA.

 

[epesmh]

Scottf:

Yes the relay has a very low burden, but do I need to size the VT bigger if there's a "primary resistance" connected to the generator neutral, and a VT in parallell over the resistance?

The resistance is sized to lower the fault current to 10A.

 

[scottf]

epesmh-

No...the burden rating of the VT only pertains to what is connected to the secondary winding of the VT.

 

[Kiribanda]

epesmh,
I donot understand your method of using just a VT (voltage transformer) for generator grounding.
I am sure that you are referring to using a single phase transformer for neutral
grounding. In the industry standards it is named as generator HR grounding using a single phase
"DISTRIBUTION TRANSFORMER". As I mentioned in my previous post you have to refer
to C62.92.2 for its sizing.

 

[waross]

Is this a distribution transformer supplying an Neutral Grounding Resistor, with a PT across the resistor?
Or is the PT from the neutral point to ground?

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!