Back up generator on domestic

[scammell man]

Can't see need for earth link. We use large industrial back up gens all the time and never do this . Just need to know what Ze is when DNO earth is available and what Ze is on your local spike. Then make sure installation works for both scenarios. Generators should have the earth neutral bond in place at manufacture, although you need to check otherwise the earth rod does nothing.

As a matter of discussion, if you are worried about no DNO earth during a power cut, how do you know you have the earth back when the power comes back on?

 

[Engineer54]

Can't see the point of that set up at all, the link between main and standby, unless physically removed each time you go onto generator supply. But if that's what you want to do, then surely better to use use a 3 pole C/O switch for a single phase set-up.

But what do i do with a 3 phase set-up, which is what i deal with?? That would need a 5 pole C/O switch or a 4 pole with a linked Aux contacts linked SP contactor (4 pole + E)..... Never done so, and i can't see myself ever doing so either!! So tell me what i'm doing wrong??

 

[Knobhead]

The only 3Ph backup generators I’ve dealt with were on private 11KV networks.
Basically we didn’t have to worry about exporting the earth as any work on the system was under our control. The incoming to the intake was at either 11 or 33KV on OH lines so as regards earthing arrangements we were independent.

Out of interest E54, if you have more than one DG set what do you do about the star point earthing of your setup?

As for the reason I mentioned the link, it was in a UKPN document sent to me when I got involved in installing a LV generator. They seemed a bit worried about their staff getting fried.

 

[Engineer54]

Out of interest E54, if you have more than one DG set what do you do about the star point earthing of your setup?

Not really a problem Tony, at least not from my standpoint as our gensets come ordered as matched pairs with the same winding pitch, so both sets can have paralleled neutral point earthing.

Normally more of a problem with gensets with differing winding pitches, in that case a reactor can be included in the commoned neutral, there are other methods that can also be used...

 

[Knobhead]

This is why I asked. We used automatic earth transfer switching to the common earth bus. The bus grounded via a NER.

 

[shanky887614]

This is why I asked. We used automatic earth transfer switching to the common earth bus. The bus grounded via a NER.

Whats a NER?

Im curious after what happened today.

Do you normally use buz bar changeover switches usinh castel keys?

Is this more an industrial application or common?

 

[Engineer54]

This is why I asked. We used automatic earth transfer switching to the common earth bus. The bus grounded via a NER.

Ah, i should have realised you were talking about MV, yes we use NER's on MV gensets, even on single units, to reduce the available fault current...

 

[Engineer54]

Whats a NER?

Im curious after what happened today.

Do you normally use buz bar changeover switches usinh castel keys?

Is this more an industrial application or common?

NER = Neutral Earthing Resistor!!

I rarely use castel key's on our installations as they are all fully automatic, on both the MV and the LV Switchboards, as i tend to work on large hospital installations. Only ever use them on the downstream MV side, when distribution is via RMU's....

And yes, you could say this is found more within the Larger commercial and industrial sectors...

Tony has used mechanical castell and other interlock key system far more than myself

 

[Knobhead]

Shanky, It’s mainly industrial. Unlike E54’s systems ours were all manual switches.

A typical situation would be two incoming supplies and a bus section switch.
Three locks, two keys. This would give you three options:
Supply A & B CLOSED bus section switch OPEN
Supply A CLOSED bus section switch CLOSED Supply B OPEN
Supply B CLOSED bus section switch CLOSED Supply A OPEN
You can’t parallel supply A & B

There are ways around this. I have a couple of Castell master keys. These were kept locked away at all times and never left my sight.
I just know E54 will shout at me for this.

 

[Engineer54]

Shanky, It’s mainly industrial. Unlike E54’s systems ours were all manual switches.

A typical situation would be two incoming supplies and a bus section switch.
Three locks, two keys. This would give you three options:
Supply A & B CLOSED bus section switch OPEN
Supply A CLOSED bus section switch CLOSED Supply B OPEN
Supply B CLOSED bus section switch CLOSED Supply A OPEN
You can’t parallel supply A & B

There are ways around this. I have a couple of Castell master keys. These were kept locked away at all times and never left my sight.
I just know E54 will shout at me for this.

No not at all, they are in the hands of someone that KNOWS what they are doing!!

 

[scammell man]

I still have some castell master keys. Which apparently don't exist :smiley2::smiley2::smiley2:

 

[Knobhead]

Still got mine even though I'm retired. No one will get their hands on them.

 

[Knobhead]

No not at all, they are in the hands of someone that KNOWS what they are doing!!

You shouted at me for paralleling two 1600KVA transformers and exceeding the boards maximum fault current.
Two guys working together, one on the each ACB. It will take me longer to type “OPEN” “CLOSE” than it took for the switches to operate. We would have been damned unlucky for a fault to occur in that split second. I did take the precaution of putting the 11KV on to one feeder, that needed my 2[SUP]nd[/SUP] naughty key.

Normal operation A, B, D, E closed C & F open.

 

[scammell man]

Standing instruction is to never potentially over stress equipment, even for switching time, except in exceptional circumstances that are fully risk assessed and appropriate action taken. This would certainly include preventing any access to switch gear etc

how did you know you had exceeded the boards max fault current in your example? You can't just add the fault currents together!