Generator earthing (standby generator)

[Jk1996]

Hi guys just trying to get my head round generator earthing. I understand we earth the alternator to earth usually by means of electrode and have the neutral tied to this. This then goes through the changeover switch or ACB through to the installation. I don’t know if I’m overthinking this one but what’s in place for earth fault protection between the generator and breaker. Say if an earth fault occurred at the generator I can see the earth electrode will be pulled up to whatever voltage it’s exposed to but what prevents persons receiving a shock in these instances?

 

[TugboatEng]

It sounds like your earth connection is made in your supply transformer. With a standby generator you now have two sources of power. The best solution is to make the earth/neutral connection in your switchboard. The generator and transformer enclosures should be electrically bonded to the switchboard to prevent shock hazard and provide a fault current patch back to neutral in the event of a fault.

 

[waross]

If you ground the generator neutral at the generator, you must then switch the neutral in the transfer switch.
If you ground at the switchboard you may use a solid neutral in the transfer switch.
Then ground fault current will return to the generator through the existing ground fault protection.

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

 

[Jk1996]

Thanks guys for your replies. I’m just trying to get my head round what protects the actual outgoing cables from the generator before the overload protection. So if there was an earth fault before the main breaker. I hope my question makes sense.

 

[waross]

I hope that your generator has a breaker on the output as part of the generator skid.
On many standby and some prime sets, there is no protection between the windings and the first breaker, wherever the first breaker is located.
On larger sets you may use differential protection but that is rare on smaller sets.
I remember a 75 KVA set with a ground fault in the windings.
The set ran to destruction.
I was responsible for a small existing power plant with sets up to 1500 KVA that had no protection between the sets and the breakers in the main switchboard.
I recommended differential protection on a new 1500 KVA set, but was overruled by the budget department.

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