My experience is in Low Voltage so I would appreciate if someone could expand on the following comment I read in a report:


"Caues of PD has been positively established as flourescants in
substation causing PD across all switchgear."

Should "flourescants" be "fluorescents" and if so how does this cause partial discharge.

I suspect so.


They don't. What they may do is put inteference onto the metalwork which either the test instrument or the operator is mis-interpreting as PD. In such a scenario, it would be usual to switch off the fluorescents to see if that removes the signal being measured.

Regards,

Alan.

Fluorescents usually produce harmonics. In particular the third harmonic will combine to produce high earth currents in the three phase supply which is undesirable, especially if it isn't reinforced enough.

In addition the there may be back emf and ringing issues with the higher frequencies, particularly if they lock onto each other.

I've also heard of situations where switch gear contacts have burnt out due to HF ringing because of low circuit capacitance in small systems (results in not enough zero crossing time to quench the switched current's plasma in the arc).

These tidbits picked up from IET committee colleagues who do work that side of the low power / high power divide - another IET benefit ;-)

-------------------------
philip oakley

As alancapon says the methods of testing PD can be interfeared with by certain external influances. The more accurate methods measure ultrasonic waves, and its usually left to the knowlage and experience of the operator to identify the cause and origin of the scource. Any PD will normally be at the points of stress in the system, bushes, cable boxes and connection points are likley points. The front of the panel usualy has few "likley" points, this is obviously dependant on the switchgear type. The results of any PD survey need to be interprated by somone who has experience of these surveys.