Voltage problems/Block Plant

[fredpar]

Hi:

I got a call from one of our customers complaining about voltage spikes that are burning electronics and machines. It's a Block plant [CEMEX], we have a 500KVA transformer to feed them at 480/277V. They say voltage goes up to 530V even 580V. They have their own dry type xfmr to feed drives controls and computers at 120/240V. I'm planning to monitor the 480V bus with a power analyzer. I'm guessing it's going to be harmonics for the most part created by their own drives and plc's. I think providing them with an additional 120/240V service from one of our overhead tranformers for their electronics and control needs is going to help. What do you think?

 

[waross]

Do you have any permanently connected capacitors for power factor correction? Does the utility have any power correction capacitors nearby on the primary lines?
respectfully

 

[wareagle]

Had a similar problem. The substation feeding the load had
capacitors on a time clock. Every morning about 7:00am when
the load was low, the caps were energized and the voltage
rose to 520 volts. Before the regulator could adjust the voltage back to 480 volts, the drives were fried. Solution was to remove the time clock and leave the caps online.

 

[fredpar]

There is no capbank around. This plant is 4000ft away from the sub. Tried to install a pa9 power analyzer but something is wrong with it. Have to wait til next week,
Thanks!

 

[apowerengr]

fredpar - does the customer have internal capacitors or is there switching of capacitors on the transmission system? Perhaps the revenue meter can answer the former question and the bulk supplier the latter? Sometimes providing multiple services to one customer can cause other code/operating issues.

 

[waross]

If the voltagw pulses are coming in on the primary, and you connect a new service to the same primary, you will still have voltage spikes and a very unhappy customer.
Look for capacitors somewhere.
respectfully