In the past few years, facilities that have capacitors installed for power factor correction have been experiencing quite a few problems with the units failing. Whether it be a few individual cells or the entire bank failing, these problems have started to show up now on a more frequent basis.
I guess if I think back, this has been happening for the past eight or more years but seem to be worse in the last two years than ever before. Most of the failures are on “fixed” bank units. That leads me to a few conclusions about what may be going on at these facilities:
- The load profile has changed either up or down
- A Main Transformer has been changed out
- More Non-Linear load has been added to the system
In any case, something has changed at these facilities that is now causing the capacitors to fail.
Let’s take the Load Profile for example:
When originally installed, the capacitor sizing is based on the kW load of the facility. What also comes into play is the Transformer size, Impedance, existing Power Factor, Site Voltage and other things that we look at such as Linear verses Non-Linear load.
Factoring in all of the above information, we calculate how many kVAR will be needed to correct the power factor. Also the placement of the capacitor bank(s) is looked at very closely. We determine where it will be best suited electrically (depending on system) for survival in the facility. We also make sure that we are not “tuning” the system to a frequency that is close to critical frequencies that are generated by most non-linear loads, such as the 5th, 7th, 11th harmonic.
In most every instance that we have had capacitor failures after a few years of service, I have found that the user has added Variable Frequency Controllers to the system or some other non-linear device(s) that are now causing harmonics that become detrimental to the existing capacitor bank. In one instance, I found that the Main Transformer had been changed out to a different size unit. This caused a rise in voltage that is bad for the power factor and also re-tuned the system close to the 5th harmonic.
In conclusion, what I am trying to say is that if you have power factor capacitors at your facility; pay close attention to changing, adding or deleting anything on the electrical system as this can cause you major headaches in the long run.
If you want more information, you know where to get it.