generator neutal connection for stability

[vranac]

Hello....
Can anybody tell me is it neccessary to connect neutral of the Diesel generator if we want to use diesel generator
as a source to inject 400v on three phase transformer on delta side. The point is to test stability of transformer
injecting 400v from generator. Fault on the high wolage side is 3pg to ground.
We can connect fases, but what to do with neutral. Is it neccessary to connect it
(and where) or we can leave it unconnected? What can happen if it is not connected.???
Thank you in advance....

 

[ScottyUK]

Normally the neutral of an LV machine is connected to an earth electrode and to the frame of the machine. You don't need the neutral to undertake your test, but you should earth the machine.

 

[vranac]

Thank you ScottyUK. Now it's clear for me.

 

[waross]

The ground connection on the neutral is a safety issue. You probably don't need it unless something goes wrong. It may be a code issue.
In my area, anything less than 260 Volts (150 Volts to ground) must have the neutral grounded. At higher voltages an approveda ground detection scheme must be provided. A jumper is a lot cheaper. Impedance grounding is another accepted method if there are no line to neutral loads.

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

 

[krisys]

If the generator is directly connected to a step up transformer, the neutral earthing may not be essential. The code requirement comes, when the generator is connected at its generation voltage level.

Having said this, connecting the generator neutral to ground is always recommended for the following reasons:

a) To detect the earth faults at early stage and clear the fault.
b) To avoid fire hazard
c) To prevent over voltages and arcing grounds

Here you can have a high resistance grounding, so that the earth fault detection becomes easy. If it is floating neutral, at least provide a conductor earth detection system with alarm and trip. First conductor earth fault will alarm. For the second conductor earth fault, it will tripping, unless someone fails to act for the first earth fault alarm.

From the description, it appears to be a generator with a unit transformer. You may also ask the basis for neutral earthing from the supplier or the consultants, if any.

 

[ScottyUK]

krisys,

Read the OP again - he's using this machine as a source of primary injection current for test purposes.