Step up transformer voltage problems?

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Hi! I have a chiller that's giving me problems. The compressor is 230 VAC and I have a 208 VAC service. I have the power stepped up with a 75 KVA transformer from 208 to 240. With the chiller off, I have about 246 volts phase to phase. When I power it up, the voltage drops to about 226. During the summer, the voltage drops so low (about 198, I'm told) it kicks the compressor out from overcurrent. I have another chiller set up the same way. The voltage drops from about 246 to 243 when I power it up. I have checked all connections. Any input is appreciated. Thanks.
 
A drop from 246 to 243 is perfectly acceptable (1.2%). I am guessing that you are considering that to be normal, and that you are not experiencing any problems with that second chiller.

A drop from 246 to 226 is not acceptable (8.1%). But before I can make a guess about causes and corrective actions, I would like to know what problems you are experiencing. For example, a chiller designed to operate at 230 volts, but that is only getting 226 volts (due to whatever is giving you the 20 volt drop from the original 246 volts of the transformer) should still operate just fine. That 226 is only 1.7% below the nominal rating of 230.

So other than not getting 246 volts with the chiller running, what problems are you experiencing? Does it stall out? Not run at all? Run hot? Run loud? Run for congress?
 
It has been known to drop well below 226. That's the lowest I have seen myself. I have inherited this problem. I have been told it has dropped below 200 and caused the compressor to kick out. The compressor itself has some type of over current protection module on it. I checked the distance today. It's only about 50' from the transformer. The wire looks to be 3/0.
 
could either be a loose connection/undersized wires or
could be an undersized transformer

the loose connection/undersized wires could account for the voltage drop during operation

the chiller must not reach 2/3 of the transformer capacity for it to run properly. I had experienced fuse blowouts when starting a compressor that exceeded 2/3 the transformer rating
 
What's the dataplate amp draw of the chiller? It sure sounds like an undersized xfmr to me at this point. Either that, or the primary of the xfmr has a heck of a long or undersized circuit feeding it.
 
I have another chiller set up the same as this one. Same model chiller, same size transformer, same size wire, it's about 70' from the transformer.
 
stevie5150 said:
I have another chiller set up the same as this one. Same model chiller, same size transformer, same size wire, it's about 70' from the transformer.
That's interesting... but are both those chillers loaded the same? That is to say, do they both condition spaces with the same heat load to the same temperature? If the other chiller is more lightly loaded than the one you're having trouble with, it might be squeaking by. As I understand, the one that you're having troubles with is only intermittantly locking out on over-current. I'd be more interested in learning the data plate information on this chiller, and less interested with the fact that a similar setup seems to perform okay.
 
Have you measured the amperage of the two motors and compared them?
If they are identical and one is pulling more amperage, I would look at the pump itself as maybe causing the problem. Are these ammonia compressors? Could be a problem with excess head pressure on the pump...Maybe icing in the expansion valve. Refridgerant compressors are positive displacement pumps. Any increase in the discharge pressure results in a increase in motor load.
Just a thought
steve
 
Here's the nameplate info:
Air Cel
Mod: CH 3500
Max Cfm: 55
Voltage: 208/ 230 3 ph 60 hz
Max Fuse: 275
Max Breaker: 200
No. RLA: 1 107
LRA EA: 565
HP: 35
Fans: 4 6.5
Min Circuit Ampacity: 27.6

Suction: 65 psi
Discharge: 215 psi

Note: This is not the original compressor.
Compressor: 230 V/ 165 Amps
The transformer is 75 kva, 208/ 240 step up
wire size is 4/0

Thanks for the help!
 
Have you measured the running voltage and amps on the problem compressor?
In my Opinion....If you have that 165 Amp motor (which equates to about 75 HP) running off a 208/230V/3Ph 75KVA transformer, the transformer capacity is marginal.

If my math is correct...The transformer is rated at about 188 Amps on it's 230V secondary. Simply starting the compressor motor requires a lot more than 188 Amps, and I'm sure that alone is dragging the voltage down considerably during start (which is not good). After the motor starts, any problem with excessive pump load (head pressure, mechanical problems, etc.) could lead to higher motor current which would also drag the voltage down and lead to further current rise and resulting increase in motor temperature.

I'm thinking....You either have a problem with the compressor, or the transformer is too small (obviously, you're thinking).

Does the pump make any un-usual sounds? Is it cooling OK?
Any excess ice forming on the expansion valve, low pressure side or anywhere else?
Is it possible that water might have gotten into the refridgerant?
Can you measure the gas pressure (high/low and differential)?
I would measure motor current and voltage (transformer in and out) during operation to try and locate the origin of the problem.
Just a thought
hope this helps
steve
 
hillbilly said:
Have you measured the running voltage and amps on the problem compressor?
In my Opinion....If you have that 165 Amp motor (which equates to about 75 HP) running off a 208/230V/3Ph 75KVA transformer, the transformer capacity is marginal.

If my math is correct...The transformer is rated at about 188 Amps on it's 230V secondary. Simply starting the compressor motor requires a lot more than 188 Amps, and I'm sure that alone is dragging the voltage down considerably during start (which is not good). After the motor starts, any problem with excessive pump load (head pressure, mechanical problems, etc.) could lead to higher motor current which would also drag the voltage down and lead to further current rise and resulting increase in motor temperature.

I'm thinking....You either have a problem with the compressor, or the transformer is too small (obviously, you're thinking).

Does the pump make any un-usual sounds? Is it cooling OK?
Any excess ice forming on the expansion valve, low pressure side or anywhere else?
Is it possible that water might have gotten into the refridgerant?
Can you measure the gas pressure (high/low and differential)?
I would measure motor current and voltage (transformer in and out) during operation to try and locate the origin of the problem.
Just a thought
hope this helps
steve

hillbilly,
There's no ice or funny noises. I ran both chillers to compare them this morning.
Chiller #1 (the problem chiller)
Turned on the chiller, 2 out of 4 fans kicked on, the compressor was off. I was at 245 volts at 13 amps.

Chiller #2 (the good one)
Turned on the chiller, 2 out of 4 fans kicked on, the compressor was off. I was at 248 volts at 13 amps.

Chiller #1, I turned on the compressor, it jumped up to 149 to 155 amps for about 4 - 5 minutes before dropping down to 107 - 108 amps.

Chiller #2, I turned on the compressor, it jumped up to about 120 - 125 amps. I shut off because it reached the temperature setpoint before it stabilized. I have measured it at about 105 amps after it has ran for a while.

I was pulled off of this to work on another machine, so I didn't get to let #2 run as long as I wanted to. I'm really starting to think it's the compressor though. What do you think? Thanks.
 
the rise in amps is due to the starting current of the compressor. if both have wye-delta starters, some minor adjustments may be needed in the first chiller's starter. this current draw could be more than the transformer can handle, hence the drop in voltage
 
Quote: stevie5150
"There's no ice or funny noises."

"Chiller #1, I turned on the compressor, it jumped up to 149 to 155 amps for about 4 - 5 minutes before dropping down to 107 - 108 amps."

Is this a 40HP motor? IMO...149-155 amps for 4-5 minutes is much too long for normal starting on a 40 HP motor. If it's a 35HP, it's running overloaded constantly.
Sounds like the compressor is starting against too much head pressure. I'm suprised that it doesn't trip out on start. What size is the starter and heaters? I would look for some problem that is causing the compressor head pressure to be too high. Is the condensor air cooled?
If the compressor starts and finally runs at a amperage consistent with the motor nameplate, I would look for something that causes the amperage to spike at intermittent times and trip the motor overload. Is the thermal tripping on the starter or is it the breaker (fuses?) that's tripping?
I'm thinking you have a problem with the expansion valve. Either (internal water) ice formation or trash that is clogging it. Is it regulating or fixed orifice? If regulating, is it opening properly (not stuck)?
Do you have gages on the high and low sides? What are the readings?
steve
 
stevie5150 said:
Hi! I have a chiller that's giving me problems. The compressor is 230 VAC and I have a 208 VAC service. I have the power stepped up with a 75 KVA transformer from 208 to 240. With the chiller off, I have about 246 volts phase to phase. When I power it up, the voltage drops to about 226. ..I have another chiller set up the same way. The voltage drops from about 246 to 243 when I power it up. I have checked all connections. Any input is appreciated. Thanks.

Some people are accused of one track minds dominated by ??X. Until I learn better, for performance of electrical systems, my minds eye lusts for Z.

Because of measurements provided here, evidence of higher upstream impedance, Z=(Et-Er)/I, and lower wattage, W=Er*Ir, (less mechanical friction) applies to Chiller #1 (the problem chiller), relatively to Chiller #2.

Assuming these stabilized measurements for Chiller #1 (the problem chiller):
Et=246vac, Er=226vac, Ir=107A
And these stabilized measurements for Chiller #2:
Et=246vac, Er=243vac, Ir=105A

If the actual measurements correctly show Z is higher for the problem chiller, perhaps the least obvious culprit is reactance between different cable lengths, ferrous raceways, shielded cable, odd-spacing gaps between phases, or different Xfmr's %Z.
 
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