Did you guys have any luck in detecting an impending failure in power factor correction capacitors ( I do not mean detection of a poor wire connection)?

If yes, what is a reasonable inspection interval?

Thanks,
David

Hi David,

Pertaining to your PFC, the only way is to do physical inspection on the capacitor bank condition. However, it is fixed term replacement usually every 8-10 years to replace the whole bank. I did experience the PFC blown out due to partial replacement. It is subjected to the PFC operating mode whether under stress mode or comfortable zone.

To avoid the PFC problem, it is recommended to do inspection every 3 years by visual inspection and ultrasound detection....

LAMMIE,

Are you saying that you HAVE tried infrared inspection on PFC and it PROVED to be ineffective?

Also, does an impending failure in PFC give you a visual warning at least 3 years in advance?

David,

Infrared inspection PFC will not able to scan the heat as it is encapsulated component. Normally, the PFC will fail prematurely if the PFC work very stressful to correct the PF and also depend on the PFC manufacturer quality. PFC is a hardly maintenance attention be given but it fails can cause fire outbreak. Either you can Operate to Fail or Fixed Term Replacement to overcome this failure unless manufacturer has the dielectric strength testing method to determine remnant life of this PFC. It is recommended to keep the PFC in separate room with fire protection also separate protection to prevent the whole electrical system being pulled down.....

LAMMIE,

Did you try infrared on PFC yourself or used any published reference?

David, yes I have tried to carry out some infrared scanning but only detect the heat profile on the terminal but not extend to the encapsulated cap as it did not capture the heat profile accurately. Internal dielectric strength heating is difficult to measure unless embedded temp sensor is taking over the role. This is only design out most probably able to give better view internally. Maybe you have better ideas on this?

I think there are two things you can reasonably hope to capture:
1 - high resistance connections
2 - shorted or open elements within a single capacitor housing or within a bank.

I do know that many capacitors used as surge arresters consist of a number of series capacitor elements within a single housing (as far as you can tell from the outside, it looks like a single capacitor). Shorting of a series elements results in slight increase in current flow. I don't know to what extent power factor correction capacitors follow the same construction. I do know that power factor correction capacitors are often connected in bank. It may be either series or parallel bank - whatever is necessary to build the required capacitance from off-the-shelf capacitors. Comparison among three phases would be a good comparision. If see a difference, investigate current and voltage readings if they can be safely obtained. Current and temperautre difference may be caused by voltage difference (not related to the capacitors), or may be caused by impedance differences due to shorted or open element of the capacitors.

This message has been edited. Last edited by: electricpete,

I agreed with electripete statement the measurement can also provide some good info but will not able to do the predictive maintenance strategies. Generally in the industries used parallel arrangement depend on the KVA available size in the market.