Partial Discharge Detection

Hello k241,

Could you explain what you mean by "partial discharge"? Are you talking about an RF circuit of some kind?

Hi,

What i mean by partial discharge (PD) is the transient discharges which occur in high voltage cables and transformers aswell as other low and medium voltage systems. An RF circuit can be used to detect these transient effects as PD's have a high frequency response.But i do not know exactly how the cicuits would operate to detect partial discharges. I am hopeing to get more information on such circuits and how they would work to detect this phenomina.

For example i have found information which states that coupling capacitor can be used to detect partial discharge in transformers by attaching it to the bushing of a transformer but i would like to understand how this works, what type of cicuit is required and how external signals are filtered out.What type of capacitors are needed and why,high voltage ones for these high voltage systems. Alternatively a radio frequency current transformer (RFCT) can also be used to measure the transient current from a partial discharge and again i am interested to know how this can be done and implemented.What would the frequency response and bandwidth have to be?Also which of these methods is better and how cost effective each one could be and is there other methods which can be used to detect PD.

I will endevour to find more information but if anyone can explain how these circuits operate or point me towards information which can assist me that would be great

Thanks for the reply and i hope i have clarified myself but if not please say so and i will attempt to do so further.

K

It seems to me that you are looking for leakage current in some electrified system. The question that comes to mind is what is the fundamental frequency of the system you are monitoring. If it is a power distribution system, it is likely to be 50Hz, 60Hz, or 400Hz. However, if the system leakage is via some RF cable, then the problem is quite different.

In any case, it is important to know something about the transient in order to detect it. In most cases you will be dealing with a tuned circuit of some kind or another. Your ability to detect the transient will depend greatly on your matching of the frequency characteristics of your detection circuit to the transient and where you connect it with respect to the overall circuit (including cable losses).

In general, I would use the term "leakage current" rather than "partial discharge" since a cable can not store energy. A discharge implies that something was first charged but that language is confusing except for very special and unusual cases of an experimental test. So, I hope you will understand why I am confused about your problem. Please tell me what the source of power is to which your cables are connected and anything you know about the transients. Thanks!

In our power plant we use the coupling capacitors.

Works fine . Offered by a company who manufactures the capacitors and electronic box to do the filtering and signal conditioning.

A laptop with the software is coupled to the electronics annually for 15 minutes and data gathered.

From the analysis , you can tell if the partial diacharge activity has increased hence giving an indication of the cabling and other HV equipment.

In generator the insulating wedges which holds the winding in place on the generator can become loose with wear and an increase leve of PD results.

In the case of a generator in a power plant , two capacitors are installed approx 1 metre apart.

This is required so that if you read a PD spike, you can tell is it was generated in the generator or the power system busbar by the propogarion delay between the spikes.

Remember you will see the spike from both couplers, just that the capacitor on the source side will show the spike first.

To detect it perfectly is still a difficult job, I was told.

Beside yoiu metioned above, infrared and ultravoilet camera shoots, ultrasonic testing etc. are alos used in the field.

Some of them use x-ray radiograph+ultrasonic or acoustic emission method to detect it.

a tiny capacitor can be used for capture instant sparkling energy in cable.

It is easier to comprehend partial discharge as a bubble in the insulation wall on a conductor. The bubble has a lower breakdown voltage then the solid wall of the conductor. When the bubble flashes over a partial discharge has occurred.

A high frequency oscilloscope with appropriate coupling capacitor is a way to observe partial discharge.

hehe, leakage current is distinctly differ from partial dischage.

Thanks for the info thus far. Regarding generators i have seen that RTD's (resistive temperature sensors) also used. Could these be also used for transformers?