Feeding 2 panels from generator, one is 3 phase 200 amp and the other single phase 100 amp

[harrykerry]

My customer has a gas station with 2 meter panels. One is 3 phase 200 amp and the other single phase 100 amp. Could I run one conduit to a splitter box and feed 2ea auto transfer switches? the first 200 amp panel feeds walk in coolers, the second 100 amp single phase feeds miscellaneous light loads.

 

[waross]

Yes.
I would use the three phase ATS to control the generator. The refrigerators are probably the most critical loads.
You may have low voltage issues with any single phase 240 Volt equipment. It will get 208 Volts instead of 240 Volts.
240 Volt heating equipment will be slower to come up to temperature and will have longer on cycles.
208 Volts is a common commercial voltage and is also found in many larger apartment buildings.
A lot of 240 Volt rated equipment will work on 208 Volts, but it is something to watch for.

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

 

[crshears]

Hmmm...

The OP doesn't state what voltage the 3 ph 200 A equipment operates at; might it be 240V delta? There may not be any low voltage issues at all, but might there not be phase imbalance issues?

And might it not be important to specify / stipulate a generator winding / output configuration?

Just asking...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[waross]

Good points CR.
If there is a 480 volt three phase service the OP will have to install transformers between the generator and the three phase transfer switch.
Generator connections: I have seldom used a four wire delta connection on a standby set but this may be a case for a four wire delta connection. That will give 240 Volts three phase and 120:240 Volts single phase with almost equal currents in all three generator windings.
That is assuming balanced single phase loads.
Given a choice between supplying three phase 208 Volt equipment with 240 Volts and supplying single phase 240 Volt equipment with 208 Volts I tend to opt for the 208 Volt solution.
But take your pick.
A wye generator connection for 120:208 Volts.
A delta generator connection for 120:240 Volts.
Load balance: The four wire delta connection does provide better load balance on the generator but single phase loading on a three phase set is never perfect. There is a paradox in that when a single phase load is supplied by a delta source,
each of the delta windings will see equal current and equal KVA, but unequal kW sharing.
When a single phase load is supplied from a wye source tao of the wye windings supply all of the load.
In both instances tha single phase KVA rating is 2/3 of the three phase KVA rating.
How important is the unbalances on the generator?
On a standby set, not very important.
Example: a 1500 KVA set in prime power duty.
Chronic phase current unbalances. The unbalance shifted from phase to phase depending on the time of day and the weather.
After about 5 years of almost continuous service the supplier's techs came out and did a megger test of the rotor.
I was not involved but was informed later.
I did not see the test results.
They stated that the rotor insulation was degraded and sent the rotor back to the shop for rewinding.
I always felt that their findings were suspect and an excuse to do a rewind job.
This was not a warranty repair.
The set probably had between 15,000 and 25,000 hours and was not showing any problems.
We had failed stators but never a failed rotor on much older sets in the same plant with upwards of 50,000 hours. Some may have had in excess of 100.000 hours.
From that perspective, I don't see a problem with unbalances on a standby set.

Note: when a single phase load causes equal currents in all three windings that means numerically equal.
Two of the windings will be seeing current at 50% PF. (Hence the discrepence between KVA and kV)
Single phase loading on a three phase set will cause rotor currents.
How important is this? Virtually 100% of single phase sets of over about 20 KVA capacity are re-connected three phase sets.
The question about unbalances is valid. The answer is, "You can live with it."

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