I want to use a regulator capacitor bank in a small facility that has a machine so based on the power factor it insert the capacitors. Each 30 seconds the motor power factor is 0.4 and for 10 seconds is. 77.
Would I have a problem with the contactors(should be AC-6b) because less than a minute it switch 3 time for 24/7?

Also apparently the bank should be out of the circuit before turning off the motor, how should we do!???

  • \$\begingroup\$ If your duty cycle is fixed as you say, you can insert capacitors to correct the average power factor and omit the switch. \$\endgroup\$
    – skvery
    Mar 6 '17 at 18:58
  • \$\begingroup\$ Ask the contractor. Who on this forum would know what contract have you signed? \$\endgroup\$ Mar 6 '17 at 19:10
  • \$\begingroup\$ Every week the cycle will be changed. And the bank is for the building not just the machine \$\endgroup\$ Mar 6 '17 at 19:14
  • \$\begingroup\$ If the bank is for the building, it is probably not a good idea to size it so that turning off one machine will result in overcorrection. It also doesn't seem like such a good idea to allow a contactor based automatic power factor correction system to switch that often. \$\endgroup\$ Mar 6 '17 at 21:24
  • \$\begingroup\$ Thanks Charles you are right. Except putting inverter for the machine what would be the best solution with this set up with minor changes. \$\endgroup\$ Mar 7 '17 at 4:34

You can probably find contactors that would be ok with that duty. You will need to consider the make and break current in addition to the duty cycle. You should be able to get detailed application data from the contactor manufacturer. You may also need to consider stress caused to the capacitors and transients created on the power distribution system.

It is difficult to envision how this scheme can provide any benefit.

You probably need to gather data for the entire building load and the largest individual loads over a period of time. Record watts, reactive volt-amperes and harmonic volt-amperes. Determine how the energy charge is calculated. Then decide what sort of effect various reactive VA compensation schemes will have on the operating cost.


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