momentary overvoltages- not transients

[MIEngineer]

Hello All,

I have a small 1500VA APC UPS that has been reporting overvolages periodically, line voltage reading approx. 129V on 120V supply. There is no set time when this happens. A couple of weeks ago it was getting this about 5 times a day, now it's down to once per day, usually in the morning 6a-7a. These can last as long as 20 minutes, when it was happening often or as short as 4 seconds, more recently. Voltage sags I can pretty easily understand; motors, etc. Does anyone know of a possible approach to find out where the problem is? This is a small building mostly office and a service small garage.

Thanks for any help.

 

[petersonra]

I would not worry about it a whole lot. It won't hurt anything, except maybe burn out your incandescent lights a little faster, if you have any.

If it bugs you, you will need to see if it is coming to you that way from the power company. If it is, they will have to deal with it. I think it is enough out of spec that the tariffs might require them to actually deal with it rather than ignore it.

 

[ron]

I would first verify that it is actually happening. We had a 10kVA APC UPS that reported overvoltages and it turned out to be a programming/firmware issue.

 

[brian john]

I have have had several of these with smaller UPS's, utilized a high speed recorder and captured nothing.

 

[Pierre C Belarge]

I would first verify that it is actually happening. We had a 10kVA APC UPS that reported overvoltages and it turned out to be a programming/firmware issue.

Hello Ron
How were you able to ascertain that it was a software issue?

 

[ron]

We metered the feeder, saw no swells or significant transients and called APC. They said it was a software/firmware problem and came out to fix it.

 

[robbietan]

utilities are allowed to have a plus/minus 10% variation in their voltage. this is due to the fluctuating demand for power.

if you have a 120V service, plus 10% of that is 132V. If your equipment is tripping at 129V, the protection is a little too sensitive. Maybe you can increase the level a little, say up to 131V, just to get rid of the nuisance trippings.

 

[petersonra]

utilities are allowed to have a plus/minus 10% variation in their voltage. this is due to the fluctuating demand for power.

if you have a 120V service, plus 10% of that is 132V. If your equipment is tripping at 129V, the protection is a little too sensitive. Maybe you can increase the level a little, say up to 131V, just to get rid of the nuisance trippings.

I have been down this road once or twice. IIRC, the real number is +/- 10% of 117VAC, which would make a trip point of 129V sound pretty reasonable.

 

[don_resqcapt19]

The permitted voltages are set by the state's utility commission and may very from state to state. Here is the rule for Illinois:

Section 410.300 Voltage Regulation
a) Standard voltage. Each entity supplying electrical energy for general use shall adopt a standard service voltage of 120 volts (when measured phase to neutral) and shall maintain the service voltage within the allowable variations from that value at all times.

b) Allowable voltage variations. For service rendered at the standard service voltage, voltage variations as measured at any customer's point of delivery shall not exceed a maximum of 127 volts nor fall below a minimum of 113 volts for periods longer than two minutes in each instance. For service rendered at voltages other than the standard voltage value, voltage variations as measured at any customer's point of delivery shall not exceed 10% above or below the service voltage for a longer period than two minutes in each instance.