240v generator polarity for walk-in freezer

[Backcountry802]

I installed a generator hookup on a farm with a walk in freezer. The generator attaches to a tractor 3 point hitch and has 90A 240v rating.
When testing the generator we got it running, tested for voltage (244v) and transferred just the load for the freezer, the generator struggled for just a second or two when freezer inrush started, the the freezer operated on generator power for about twenty minutes. When power transferred back to utility power the freezer’s main contactor fried.
my understanding is that 240v motors do not have polarity, is the an inrush polarity that could have caused this? If I just swap the poles on the transfer switch from the generator does this have any affect on the freezer?
The freezer compressor is on a 50A breaker and only runs at 12.7a when active. This freezer had capacitor problems a couple months ago and the HVAC installer had to change them out.

 

[GoldDigger]

The phase relationship between the generator and utility is not controlled, so swapping polarity will do you no good.
My guess is that the contactor dropped out momentarily during an open transfer, and while current from the motor was still either arcing across the contacts or flowing in a snubber the contactor poles were connected onto an opposite polarity utility source, greatly increasing the current.
A time delay on the contactor coil might or might not help. A delayed transition to utility until after the generator has stopped, stopping the compressor, will be more like normal compressor operation.

PS: If the contactor had stayed closed, it probably would not have been damaged, but similar damage might have happened at the transfer switch.

 

[Hv&Lv]

Were you trying to parallel them to do a closed transition?
Are you using some sort of transfer switch?
As stated above, it’s the phase relationship between the utility generator and your generator.
they won’t ever match up without some serious components to sync them together.

 

[hbiss]

Were you trying to parallel them to do a closed transition?
Are you using some sort of transfer switch?

My question also but I don't get that's what happened.

If not, it sounds like it was just time to replace the contactor. When the generator struggled there was a low voltage condition and compressors don't like that. (I wouldn't do that again.) If the contactor contacts weren't in good shape as most aren't after years of use, they burn up.

-Hal

 

[GoldDigger]

My question also but I don't get that's what happened.

If not, it sounds like it was just time to replace the contactor. When the generator struggled there was a low voltage condition and compressors don't like that. (I wouldn't do that again.) If the contactor contacts weren't in good shape as most aren't after years of use, they burn up.

-Hal

Ideally the generator would be sized large enough that the rotating mass stores enough energy to carry through the motor starting.

 

[infinity]

If the generator has an ouput of 90 amps and the freezer is only 12.7 RLA there should not be any problems. Reversing the phase condcutors on a 1Ø circuit will do nothing. What type of transfer equipment are you using?

 

[ptonsparky]

I suspect the contactor should have been replaced along with the capacitors.

 

[LarryFine]

Shouldn't there a 5-minute delay in re-starting a compressor?

 

[Backcountry802]

Were you trying to parallel them to do a closed transition?
Are you using some sort of transfer switch?
As stated above, it’s the phase relationship between the utility generator and your generator.
they won’t ever match up without some serious components to sync them together.

It has a mechanical interlock at the panel. We followed normal generator starry up procedure as well, and all other loads were shut off.

 

[Backcountry802]

My question also but I don't get that's what happened.

If not, it sounds like it was just time to replace the contactor. When the generator struggled there was a low voltage condition and compressors don't like that. (I wouldn't do that again.) If the contactor contacts weren't in good shape as most aren't after years of use, they burn up.

-Hal

There is a mechanical interlock and we were following normal generator start up procedures. All other breakers were off, and the main purpose of the generator is supposed be to keep the freezer running. There was probably five minutes of off time between both energy transfers. The freezer is less than six months old. I didn’t like how much the generator bogged down considering that it’s sized for a much larger load, but it also didn’t seem completely abnormal. Brown energy for a second or two while the generator slowed from 60 hertz.
I’m going to meet with the freezer installer in a month to try and do a controlled transfer, perhaps we can establish a manual start up procedure within the freezer itself. The whole idea is to keep thousands of pounds of free range chickens frozen, if the generator causes problems, it is essentially useless.
As long as there is no polarity issue, which I’ve always understood there is none with single phase, then I’ve done my job correctly.
I assume that there are hundreds of thousands of freezers running on backup generators in this country, so my issue may not be unique. Thank you

 

[Backcountry802]

Ideally the generator would be sized large enough that the rotating mass stores enough energy to carry through the motor starting.

To me, it seemed like a very well sized generator. The freezer

If the generator has an ouput of 90 amps and the freezer is only 12.7 RLA there should not be any problems. Reversing the phase condcutors on a 1Ø circuit will do nothing. What type of transfer equipment are you using?

Mechanical interlock. Everything was done according to normal generator start up and this was the only load we were dealing with as I had all the other breakers in the panel off.
There were multiple minutes of off time between both transfers as I was testing voltages etc…. This was our initial start up and it was being monitored closely.
As long as there’s not a phase issue, which has always been my understanding with 240v, then my end was done right and we can problem solve what happened with that in mind.

 

[Hv&Lv]

What’s the locked rotor amps from the data plate?
it does fine on utility because the utility has no problem delivering the 10-13 times amp draw for startup.
A 90 amp generator doesn’t have much rotational mass for sudden draws

 

[LarryFine]

There was probably five minutes of off time between both energy transfers.

That should be enough time for the high-side pressure to drop.

I’m going to meet with the freezer installer in a month to try and do a controlled transfer, perhaps we can establish a manual start up procedure within the freezer itself.sands of freezers running on backup generators in this country, so my issue may not be unique.

Ask if a soft-start kit might help.

 

[Backcountry802]

What’s the locked rotor amps from the data plate?
it does fine on utility because the utility has no problem delivering the 10-13 times amp draw for startup.
A 90 amp generator doesn’t have much rotational mass for sudden draws

I’ll have to check when I make it over next time, it’s being turned by a 40hp tractor, but this is a possibility. It seemed big enough to me that I didn’t look to hard into it. “Sizing generator for walk in freezer” google search will probably have some insights for me in the meantime. Thank you, appreciate the feedback.

 

[kwired]

What’s the locked rotor amps from the data plate?
it does fine on utility because the utility has no problem delivering the 10-13 times amp draw for startup.
A 90 amp generator doesn’t have much rotational mass for sudden draws

Since it was a tractor PTO driven generator, this sort of depends on tractor's abilities.

Seen cases where a much larger tractor than necessary was driving a generator and had a line to line fault end up breaking input drive shaft U joints.

Voltage drop from generator impedance still occurs though.

 

[kwired]

To me, it seemed like a very well sized generator. The freezer

Mechanical interlock. Everything was done according to normal generator start up and this was the only load we were dealing with as I had all the other breakers in the panel off.
There were multiple minutes of off time between both transfers as I was testing voltages etc…. This was our initial start up and it was being monitored closely.
As long as there’s not a phase issue, which has always been my understanding with 240v, then my end was done right and we can problem solve what happened with that in mind.

Sounds coincidental to me that it happened to fail when it did, and that the contactor likely was failing sometime soon even if you never would have run off the generator.