70KVA Generator Keeps Tripping Out

[CathalX]

I am supplying a 3 phase board with from a 70kva 3 phase generator.
The board is protected by a 100A screw in fuse on each phase. The generator unfortunately keeps tripping out without MCBs, RCDs tripping in the board or any of the 100A fuses blowing. The house has passed all earth and resistance tests.

Any ideas

 

[pdcelec]

where are you getting your neutral and earth from?

 

[CathalX]

Neutral and earth are coming from the generator

 

[pdcelec]

Why are you using a genny instead of mains?

 

[CathalX]

Main supply will take a week to install - customer has moved in.

 

[pc1962]

Do you mean the genny engine is shutting down or the MCB on the genny is tripping, or perhaps the alternator voltage is dropping off?

What make is the alternator, stamford ?

pc

 

[plugwash]

hmm house? 70KVA genny? something just doesn't make sense there

 

[CathalX]

Engine is fine and doesn't shut down. The generator within was tested by an engineer from the hire company as delivering correct voltage and capable of delivering 70KVA.

The house or load in this situation has an underfloor heating system that draws 30KW of power across the three phases.

There are 45 circuits, 7 lighting circuits and 7 power circuits, 20 heating elements etc. It's a very big house and needs a 3 phase supply

In total the max load will be no more than 45 KW

ALL earth tests have ben passed, EVERY cable was tested for insulation and continuity. The installation has been signed off. Post tests will be carried out in the next couple of weeks.

When the generator trips out, none of the three 100A fuses protecting each phase blow!

None of the RCDs protecting the socket circuits trip!

None of the MCBs in the board are tripping!

Sequence is as follows:

Generator is switched on with main isolator to board in ON position and ALL MCBS in board in th OFF position. One by one all 45 circuits are brought on. Always after fifteen minutes, the generator trips.

I am certain of the following:

the load from the house comes nowhere near the capacity of the generator
There are no short circuits in the insulation (all insulation tests passed no tripping on board)
No earth leakage on power circuits (no tripping of RCBO)

My question is this:

Do you think it is logical that if there is a fault in the installation, it kicks in after fifteen minutes. Surely it would happen straight away.

Sorry for the long reply, I needed to be clear

 

[Chris.J]

A logical approach night be something like : --
Start up & engage breakers as usual, but only switch in half of them. Run for 30 min, has it tripped?: --
if yes, then allow to cool off & repeat with only half of those first half on.
if no, then repeat with the other (first) half on.
And so on, and on.
This way you narrow the fault "zone" down.
Tedious but logical.

 

[CathalX]

should I expect problems when the main supply is connected? Logic tells me no!

 

[kendor]

Engine is fine and doesn't shut down. The generator within was tested by an engineer from the hire company as delivering correct voltage and capable of delivering 70KVA.

The house or load in this situation has an underfloor heating system that draws 30KW of power across the three phases.

There are 45 circuits, 7 lighting circuits and 7 power circuits, 20 heating elements etc. It's a very big house and needs a 3 phase supply

In total the max load will be no more than 45 KW

ALL earth tests have ben passed, EVERY cable was tested for insulation and continuity. The installation has been signed off. Post tests will be carried out in the next couple of weeks.

When the generator trips out, none of the three 100A fuses protecting each phase blow!

None of the RCDs protecting the socket circuits trip!

None of the MCBs in the board are tripping!

Sequence is as follows:

Generator is switched on with main isolator to board in ON position and ALL MCBS in board in th OFF position. One by one all 45 circuits are brought on. Always after fifteen minutes, the generator trips.

I am certain of the following:

the load from the house comes nowhere near the capacity of the generator
There are no short circuits in the insulation (all insulation tests passed no tripping on board)
No earth leakage on power circuits (no tripping of RCBO)

My question is this:

Do you think it is logical that if there is a fault in the installation, it kicks in after fifteen minutes. Surely it would happen straight away.

Sorry for the long reply, I needed to be clear

Does the genny have an undervoltage protection sensor and when a heavy load switches in (underfloor heating on stat) it drags the output volts down for enough time to trigger what may be a faulty or badly calibrated sensor?

 

[CathalX]

don't think so, but I did run the heating on full (30KW) for hours on a different genny one month ago. No probs.

 

[kendor]

don't think so, but I did run the heating on full (30KW) for hours on a different genny one month ago. No probs.

which then suggests this genny is faulty?

 

[CathalX]

That's the thing! The trip on the genny is a 3 phase MCB, which can only blow if its load capacity is exceeded 70KVA +
The house without heating would hit no more than 15KVA. The genny is experiencing some sort of surge in my opinion.

However the genny engineer is asking us to investigate a surge from the house as it COULD NOT be his machine. He tested it with a meter with the house disconnected. He stated that the same genny ran a small site for a week without a problem.

If there was a surge going to his generator, why doesn't it blow one of my MCBs or 100A fuses?

 

[kendor]

That's the thing! The trip on the genny is a 3 phase MCB, which can only blow if its load capacity is exceeded 70KVA +The house without heating would hit no more than 15KVA. The genny is experiencing some sort of surge in my opinion.

However the genny engineer is asking us to investigate a surge from the house as it COULD NOT be his machine. He tested it with a meter with the house disconnected. He stated that the same genny ran a small site for a week without a problem.

If there was a surge going to his generator, why doesn't it blow one of my MCBs or 100A fuses?

Not necessarily, remember that the 3 phase MCB is interlocked across the phases and your load may be unbalanced and tripping one of the linked MCB's which may be weaker than the others and being interlocked trips all of them. what the engineer shoud have done was stayed and tested the genny under load to see the fault happening.