We are having some issues with volt
We are having some issues with volt
(OP)
We are having some issues with voltage at our facility. We had the power company check the incoming and this is what they came up with. Does any of this make sense?
Sorry to send this to you on a Friday. Do you have an electrical engineer on staff? If not, you will probably need to contact a power quality consultant. You can give them the attached charts for reference.
The voltage and KVA are okay at the transformer; well within the voltage limits. You have the 5Th harmonic above 3% and the THD slightly above 5%. High 5th harmonics are usually from 6 pulse rectifiers. You also have a load that has sub cycle events above 1000 amps. You should hire a power quality electrical contractor Hunt / Olympia Tech. > Parsons > Etc.
Sorry to send this to you on a Friday. Do you have an electrical engineer on staff? If not, you will probably need to contact a power quality consultant. You can give them the attached charts for reference.
The voltage and KVA are okay at the transformer; well within the voltage limits. You have the 5Th harmonic above 3% and the THD slightly above 5%. High 5th harmonics are usually from 6 pulse rectifiers. You also have a load that has sub cycle events above 1000 amps. You should hire a power quality electrical contractor Hunt / Olympia Tech. > Parsons > Etc.






RE: We are having some issues with volt
With that said, based on what the utility said, do you have DC loads that you are supplying through rectifiers? Has anything changed with those loads or the configuration of your facility?
I'd first try to figure out when the problems started happening and if anything else happened at around the same time, whether unexpected or planned.
RE: We are having some issues with volt
RE: We are having some issues with volt
To provide answers we need some information on what the voltage problem might be. Power factor does not have anything to do with voltage imbalance. Power factor is the relation between voltage and current, Voltage imbalance is the relation between the 3 phases of voltage.
RE: We are having some issues with volt
RE: We are having some issues with volt
You really do need to identify whatever is responsible for the "sub cycle events above 1000 amps". Fast, high current switching can cause impulse voltages which might explain the high casualty rate among your power supplies. Do you have any 'difficult' loads such as a large welder or similar which might be the origin of these transient events?
As others have suggested, a half-decent power quality consultant will be able to make some rapid inroads into identifying the causes of the problems. Fixing them is sometimes a little harder.
RE: We are having some issues with volt
The transient's is another issue that Scotty has given you some pointers on.
RE: We are having some issues with volt
The utility is saying that the voltage is well within limits. I would ask them for what the limits are and ask them for a printout or trend of the voltage and load readings. This will help you decide if you need to adjust taps on your downstream tranformers etc. Based on the informatin you gave of 467 volts this represents about a 2.7% vcltage drop which is a little high if its at your main incoming bus. It would be better to be closer to 2% or less. One way to compensate for this on the incoming side is to have load tap changers on your incoming transormers to keept the voltage within a tight limit. One concern is you say on your secondary circuits you are going down to 98 volts wich represents almost 14% drop. this is much more then the 2.7% drop on the primary. If this is a sustained situation you might either have a down stream transformer that is overloaded or the taps are not set properly. If its a momentary sag then you may have a large piece of equipment that is starting up and pulling the voltage down. You could attack this by looking into soft start methods of starting this equipment as well as putting ciritical 120 volts loads on UPS equipment to keep it from being affected by the momentary start. There are recommendations by IEEE in their red book on voltage regulation, voltage flicker etc. that you might find helpful. They have charts that based on the size of a motor you are starting what size transformer you would need to prevent voltage flicker when the unit starts across the line.
It sounds like your harmonics are a little high but not too bad. I would speak to the vendor of your VFDs or other equipment to see if they can recommend local line reactors or filters at the pieces of equipment that are generating the harmonics. They can do some quick modeling what the affect of adding line reactors to their equipment would due to improve the overall harmonic content at both your incoming as well as down at the secondary level.
The other issue could be your distribution. If you find from your metering that your incoming switchgear voltage is staying fairly stable around +/- 2% but your down stream readings are fluctuating much higher you may need to add more down stream distribution rather then have everything fed off of one or two feeders that are overloaded or connected to the heavy starting equipment.
I know I threw out a lot of ideas. I hope this helps you get started.