Multiple sources, voltages, & transfer switches - solid neutral?

[bentov]

A customer has a 60hp pump supplied by a remote (300ft away) 480/277V service, so the neutral conductor is not present at the pump (ground only). 125ft from that is a 600a 240/120V 3ph 4W delta service supplying (2) greenhouses on separate 200a branch feeder breakers. Next to that service they've parked a new 150kw 480/277 4 lead generator - pump company plans to pull power from there to the 60hp pump, locating a manual transfer switch over at the pump panel. My job is to use the same generator to supply the greenhouses (total load for both around 100a, looks like).

So I see how to add a 45kva delta delta (or wye delta) transformer with primary and secondary protection to the genset. I'll need to use (2) 200a manual transfer switches for the greenhouses(cause have to pull from the load side of the existing feeder breakers, can't access the line sides supported by the buss standoff hardware, likewise can't access the losd side of the main switch - all bolted together).

So right next to each other I'll have the 600a 240/120 service mid tapped neutral, the 250a 480/277 generator neutral (with factory jumper to genset frame ground), and my new transformer mid tapped neutral. I guess there's also a 4th neutral, back at the 200a service for the pump, though no conductor is present. I should just tie all those neutrals together, right, then bond them to the service entrance earth rod? Been reading threads, and the code, not really finding a similar situation . . .

 

[cuky2000]

What is the benefit to add this transformer over Delta-wye unit?
Beware of the NEC grounding and bonding rules for generator/ATS separately and non-separately derived system. For reference check the NEC 250.30(A)(1) and 250.30(A)(2).

 

[waross]

Look at it as two systems.
Pump:
Consider a transfer switch based on circuit breakers.
A suitable sized circuit breaker will provide overload protection for the feeders from the transformer to the transfer switch.
The generator main breaker may be suitable for over current protection.
You may be able to save the price of a circuit breaker.
Check your code.

Green houses
This does not compute; Two, 200 Amp transfer switches transfer switches and two 200 Amp breakers for a 100 Amp load?
I would combine the feeders onto one 100 Amp breaker and to a 100 Amp transfer switch, fed from one of the 200 Amp breakers.

Now the issue of voltages:
60 HP equals approximately 60 KVA.
100 Amps at 240 Volts = 44 KVA
Running the generator at 480 Volts will allow a smaller transformer to be used to drop to 240 Volts.




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

 

[bentov]

Hey Bill,

The genset is 480 only, has a 250a CB. The pump guys are tapping bottom of that, taking it the 125ft to the 60hp panel, installing a transfer switch there.

The 200a 240V greenhouse branch feeder circuits are bigger than needed at the moment, not my call though to reduce that capacity since UG wire & conduit & distribution panels already in.

Sizing for the stuff already bought then, I figure the 150kw genset can operate the 60hp pump, and also (via transformer) supply about 100a @ 240V for the greenhouses. I'll need a 70a breaker on the primary of that transformer, then a single 150a breaker on the secondary side to feed the bridged 200a transfer switches.

cuky2000, I'm using the delta secondary transformer with the mid-tap neutral to maintain the same 240 3 phase 120 single phase as supplied by the utility, being careful of course where we land the stinger leg.

Pretty cobbled up, for sure, but will work ok I think. Mainly I'm worried about unexpected neutral current loops or voltage backfeeds between services and the genset, all of which will be energized simultaneously at some point (isolated by the transfer switches on the phase conductors of course).