Chiller Problems

[brian john]

Received a call from an electrical contractor today, they have been struggling with this issue for a week.

They have a chiller that is going out on current imbalance, at 50% load a 50% current imbalance from the average currents will shut the chiller down. Above 50% load the chiller shuts down at 30% from the average (this is the average of all three phases. The percentages seemed high to be. They have been going down several times a day. Finally they installed a generator to handle just the chiller.

This is a WYE, DELTA starter.

What we did

Measured all phases

VAC
A-215, B-210, C-216

IAC
A-49, B- 69, C-74

We then rolled the phases and the current followed the conductor.

The chiller remained on line with this phase imbalance.

They has previously (prior top me arriving on site) connected the chiller to generator, they had been running off generator for several days. But restored the operation to utility today


While on generator this was what they recorded

VAC
A-209, B-209, C-209

IAC
A-75, B-75, C-75

These are the largest motors on site but I checked other smaller 3 phase motors and there was phase imbalance but the percentages were not nearly so severe. Additionally as the chiller loaded up the current imbalance was not as significant as at the lower loads.

I know phase voltage imbalance will result in current imbalance but the voltage phase imbalance is about 3% (varies during the day, I am told) and for the voltage imbalance the current imbalance we see seems excessive.

The day this started the utility had an issue on the network feeding this facility, they have not said what the issue was. The site was down about 13 hours before power was restored. This issue started after the power was restored.

The mechanical contractor says all systems on the chiller checked out OK.

We are in the process of monitoring the service and feeder for the chillers, and the utility is starting an investigation as well.

Any help would be appreciated.

 

[iceworm]

Brian -
208Y correct? Are the motors 200V. If they are 240V this guess is no good. And it is a wild guess.

If the voltage on the motors is high and the motors are tight in the volts per turn ratio, they could be saturating a bit. This will magnify the current imbalance. Can you turn down the xfm tap and get closer to 208V?

I've only seen this once, testing MIL-spec motors in a lab. At 480V the motors un-loaded currents were out of spec for imbalance. We dropped to 460V and adjusted the supply so the voltages were real close - the imbalance went away.

Nothing says you didn't get the same low bid motors supplied to our submarines and space program.

ice

 

[tesi1]

phase imbalance

phase imbalance

i have seen this several times lately, each time we contacted the power co to have them check all three phases of the primary and as usual they checked and said
everything was okay, a few days later each time an another problem would arise and when they checked further down the street and or transmission line they would find a phase out, the area where the phase was out was just after other 3 phase banks of larger transformers were located, so i believe the phase which was out was being balanced
thru the other transformers and mainly showed the problem when the load was inbalance the other transformers or they were fully loaded.
it always amazes me how the power co never has a problem till it afects others.

 

[brian john]

Iceworm 208 VAC motors operating fine before the outage, operating fine off a 208 from a stand by generator, The site is a 208/120 Wye.

 

[brian john]

i have seen this several times lately, each time we contacted the power co to have them check all three phases of the primary and as usual they checked and said
everything was okay, a few days later each time an another problem would arise and when they checked further down the street and or transmission line they would find a phase out, the area where the phase was out was just after other 3 phase banks of larger transformers were located, so i believe the phase which was out was being balanced
thru the other transformers and mainly showed the problem when the load was inbalance the other transformers or they were fully loaded.
it always amazes me how the power co never has a problem till it afects others.

You are saying there was an issue with the primary in the street and due to other transformers on the circuit voltage was present as three phase?

I have checked phase angle and all looks ok, I have heard of chillers that were running losing a phase and continue to operate fine until shut down but never what you are describing.

 

[iceworm]

Iceworm 208 VAC motors operating fine before the outage, operating fine off a 208 from a stand by generator, The site is a 208/120 Wye.

Yes, I figured that - each of the three statements.

Here is what I saw in your data.

...
VAC
A-215, B-210, C-216

IAC
A-49, B- 69, C-74

We then rolled the phases and the current followed the conductor.

The chiller remained on line with this phase imbalance. ...

........
While on generator this was what they recorded

VAC
A-209, B-209, C-209

IAC
A-75, B-75, C-75

Lower voltage, balanced voltage = balanced currents

higher voltage, 3% out-of-balance voltage = un-balanced currents.

208 VAC motors operating fine before the outage,...

208 volt motors are usually 200V nameplate. But sometimes the vendor will supply 240V motors.

What i am suggesting would not be viable if the nameplates say 240V.

ice

 

[Hv&Lv]

I understand what Tesi is saying, maybe a phase is out somewhere up the street and one transformer of the 120/208 is being fed from a backfeed on a delta bank behind the blown fuse. And it makes sense what he is suggesting, but the voltages you are recording (215, 210, 216 L-L) (124, 121, 124 L-G) seem to be inline with what would be expected if all phases are in. There seems to be some inbalance on the primary, but not terrible. Also, if the bank was too small, I would expect the voltages to go down as the amps rise. Maybe one transformer was changed out to a smaller one during the trouble? What was the trouble anyway??

 

[BJ Conner]

Check the vendor drawings.

Check the vendor drawings.

Check the internal schematics. There could be an oil heater or something that is on when it's not supposed to be.
Look at the drawing and see if there is something that could make what you see happen.
You could call/write the manufacturer.

 

[brian john]

Oil heater is minimal and off line. Plus if it was affecting the unit on utility it should cripple it in generator.

Nothing else on line in the chiller. In the building 98% lighting and most of that is incasdescent, a few small pumps, and fan coil units.

 

[mivey]

Get the POCO to check capacitor fuses and verify that the voltage regulators are stepping correctly.

 

[mivey]

Brian,

Just thinking about your problem. The issue appears to be with the POCO and you have one primary phase about 5% above the others.

My guess would be that one of the single-phase voltage regulators has stepped up to the programmed limit (probably 126-127) while the other two have stayed near 120 nominal.

You could have two fuses blown on a capacitor bank. You could then get a few volts rise on the phase with the remaining bank, depending on the bank size.

Based on the way the chiller ran with the generator, I do not think it is an issue at the retail level.

 

[mivey]

but the voltages you are recording (215, 210, 216 L-L) (124, 121, 124 L-G)

Actually, one of the L-G voltages is higher than the other two. Think about the wye: increasing one leg cause two L-L voltage to increase while one L-L voltage remains low. Brian shows two higher and one lower set of L-L voltages.

Similarly, one high and two low L-L would normally indicate two high and one low L-G set of voltages.

 

[Hv&Lv]

Actually, one of the L-G voltages is higher than the other two. Think about the wye: increasing one leg cause two L-L voltage to increase while one L-L voltage remains low. Brian shows two higher and one lower set of L-L voltages.

Similarly, one high and two low L-L would normally indicate two high and one low L-G set of voltages.

Yea, that was my screwup. I was thinking about the voltage difference on the primary instead of what I was writing.:ashamed:
Cap bank didn't dawn on me, but wouldn't it have to be a rather large bank to make that much difference? and wouldn't others be complaining also?

 

[mivey]

Cap bank didn't dawn on me, but wouldn't it have to be a rather large bank to make that much difference?

It would have to be a good size bank, or located several miles out, or be on a 4 kV system.

% Rise = kvar per phase * X_ohms per mile * miles / 10 / (kV_l-g)² = total kvar * X_ohms per mile * miles / 10 / (kV_l-l)²

Using X = 0.7/mile, 2 miles, 300 kVAR, 12 kV we get: 300 / 3 * 0.7 * 2 / 10 / 7.2 / 7.2 = 0.3%

Using X = 0.7/mile, 900 kVAR, 4 miles, 12 kV we get: 900 * 0.7 * 4 / 10 / 12.47 / 12.47 = 1.6%

Using X = 0.7/mile, 300 kVAR, 2 miles, 4 kV we get: 300 * 0.7 * 2 / 10 / 4.16 / 4.16 = 2.4%

and wouldn't others be complaining also?

Not unless they have sensitive loads.

 

[T.M.Haja Sahib]

The electrical contractor might have tried to run the chiller with a voltage regulator instead of a generator, a less costly option to run the show. Can he try it now?

 

[mivey]

The electrical contractor might have tried to run the chiller with a voltage regulator instead of a generator, a less costly option to run the show. Can he try it now?

Less costly how? The generator was already connected and ready to run.

 

[T.M.Haja Sahib]

Less costly how? The generator was already connected and ready to run.

Running cost of a generator is much higher than operation through utility.

 

[mivey]

Running cost of a generator is much higher than operation through utility.

Having the contractor to install voltage regulators is costly and would be more expensive than using the existing generator.

 

[T.M.Haja Sahib]

Having the contractor to install voltage regulators is costly and would be more expensive than using the existing generator.

Then we have to wait for the POCO to set right their problem.

 

[BillyGiug]

Utility Disclosure

Utility Disclosure

Has the utility disclosed their issue? It seems that the problem lies with the utilities disclosure. Possibly a reduced load by a local utility customer causing the phase imbalance. Has somebody "big" moved recently, causing the increased voltage?