Battling Voltage Fluctuations

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dha

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Hello Everyone,

A facility that I'm working is suffering from severe problems due to voltage unbalance and voltage sags from the utility supply.

The supply to the facility is (or supposed to be) 3 phase 480 VAC, the voltage dips to below 410 VAC at sometimes and there is unbalance of 30 VAC on a frequent basis. I have been asked to come up with some suggestions as to how we can combat this problem, the utility company is not very eager to do anything. This problems is wreaking havoc with or motors.

I was thinking about looking at some kind of transformer with automatic voltage regulation to maintain 480 VAC on the secondary. Can anyone suggest the approved/accepted means of overcoming this problem.

Thanks.
 
If you are in the US and the utility is not cooperating, you can contact the state utility commission. There are standards that the utility must comply with as far as the voltage they supply to you.
 
The proper way to calculate voltage unbalance is to calculate the average of the phase to phase voltages, then find the maximum deviation from the average, and finally divide the deviation by the average in percent.

For example: If my three phse to phase voltages are 475, 480, and 487 V:

Average = 480.67 V
Max deviation = 487-480.67 = 6.33

(6.33/480.67)*100 = 1.3% unbalance

Like Don said, if you are in the United States, you can file a complaint with your state's public utility commission. That should get you a response. Also, the utility commission may have rules in place for maximum voltage unbalance.

The voltage sags can be a bit tricky. Many states have limits on steady state voltage ranges, but sags are usually exempt. Do you know for sure that the sags are from the utility and not from a large load coming on in your facility? How often are the sags happening?

Before investing money in voltage regulation equipment, I would want to look more into what is causing the sags.
 
dha said:
Hello Everyone,

A facility that I'm working is suffering from severe problems due to voltage unbalance and voltage sags from the utility supply.

The supply to the facility is (or supposed to be) 3 phase 480 VAC, the voltage dips to below 410 VAC at sometimes and there is unbalance of 30 VAC on a frequent basis. I have been asked to come up with some suggestions as to how we can combat this problem, the utility company is not very eager to do anything. This problems is wreaking havoc with or motors.

I was thinking about looking at some kind of transformer with automatic voltage regulation to maintain 480 VAC on the secondary. Can anyone suggest the approved/accepted means of overcoming this problem.

Thanks.
Click to expand...

Is the transformer suppling this facility (At 480V) utility owned or does your facility own it? That is the first thing to figure out. If the utility owns it you need to follow the recommendations made here already, typically they will need to respond to anything > +/- 5%. You will need to install some monitors to document the sags.

If your company owns the transfomer then you need to figure out of ot os a transformer problem or utility problem, again, start with the data loggers.
 
Hi All,

The transformer is owned by the utility company, we're fed from a spur in the distribution system. We have tried getting through to the utility and even to the state officials but were a small country, the utility company is state owned and the facility is not located in one of the more developed parts of the country, typical 3rd world syndrome.
The owners of the facility are will to spend what they need to in order to improve the situation so any suggestions will be greatly appreciated.

Thanks.
 
If they are willing to spend the money, you might look into either one large motor-generator (MG) set with a flywheel or a large UPS (battery) for the entire facility, or if you can determine which loads are sensitive to the utility sags, and install smaller MG sets or UPS's (battery) for the sensitive loads. Before you spend any money, it would be wise to determine what depth of voltage sag and how long the sag typically is, so sag mitigation devices will be sized appropriately.
 
The problem with a UPS with no generator is you would deplete the battery in short period of time. Battery life is based upon the number of discharges, and in a place like this that would be quick it seems.


What size service?

Is there specific equipment you need to protect or the whole facility?

Is this consistent, where you could adjust taps on a transformer to over come the deviations?
 
Hi All,

Thanks for all of the encouraging responses.

I have been speaking to the persons who are based on the facility on a permanent basis, this problem of low voltage is persistent it seems. The voltage is below 430 VAC on most days, some days as low as 410 VAC but never close to 480 VAC.

The most critical loads to protect are 3 phase motors.

I believe that a transformer will do the job, but I need some adivice.
 
dha said:
Hi All,

Thanks for all of the encouraging responses.

I have been speaking to the persons who are based on the facility on a permanent basis, this problem of low voltage is persistent it seems. The voltage is below 430 VAC on most days, some days as low as 410 VAC but never close to 480 VAC.

The most critical loads to protect are 3 phase motors.

I believe that a transformer will do the job, but I need some adivice.
Click to expand...

As I mentioned earlier, you need to knowwhat is going on the primary side of the transformer, do some monitoring before you go buy anything, this may be a simple fix. If the primary voltage is what it is supposed to be test the transformer (Full NETA tests) , specifically a TTR test, sounds like you may have a transformer issue, open or shorted windings.

If the primary voltages are low and the transformer tests good match the tap setting to the actual primary voltage and you should get 480V on the secondary.
 
First step is to prove your problem. To do that you need a certified data logger that produces writen reports concerning the problem. If you don't own one you will have to rent one and monitor the service for at least a week. Then set up a meeting with the power company and your customer and ask them what they can do???? Possibly they can increase the secondary tap on the transformer ??? Or increase the transformer size to accomidate the load.....
 
090327-2001 EST

I believe dha is in a country that has very poor electrical quality, and the government there does not care. See his is comment in post #5.

.
 
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