Neutral resistance usage

[mayoz66]

Dear All,

Consider 2 generator . These generators are 6.3 kV and They are connected to 34.5 kV system with power transformer ( delta(6.3 kV )/star (34.5 kV) ( Dyn11).

In some application, I see that each transformer neutral point are earted with a resistor independantly.(Aplication1)

But some other application , Two transformer neutral point are connected in a point. Only one resistor is used for two transformer. (Application 2 )

What is the advantages and disadvantages of both
Application 1 and Application 2.

With my best regards

 

[vima]

Application 1: when these two transformers may or may not feeding one system.

Application 2: These two transofrmers are feeding one system.

 

[Marmite]

One problem with a shared resistor is if you need to be able to isolate each transformer independently to work on it, whilst the other remains in service, then you would need to provide some switchgear to isolate the transformer neutral from the resistor. The resistors are relatively inexpensive items and it's probably more economic to have two rather than one plus neutral switchgear. Also,if you have one resistor and it fails, then you lose your system earthing. Personally I can't see any benefit from having the resistor shared between 2 transformers.
Regards
Marmite

 

[slavag]

Hi.
Totally agree with Marmite.
Regards.
Slava

 

[waross]

Are you concerned with rounding the transformers or with grounding the system?
Grounding the system neutral with one resistor makes ground fault detection and protection easier.
This is in accordance with the oft stated principal of a single grounding point or connection between the neutral and ground.
If you have system ground fault protection you may wish to consider a single point ground connection.
If each transformer has extensive protection, including ground fault protection, you may wish to use an independant resistor for each transformer.
If the transformer neutrals are floating, then by all means use a resistor for each transformer.
If the transformer neutrals are solidly connected, you may consider a single resistor.

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