Crack on Surge Arresters
Crack on Surge Arresters
(OP)
Almost all the surge arresters in all the feeders of MV switchgear (6kV) got cracks as shown in the picture.
What are the reasons for it apart from dirt, moisture and inadequate capacity?. The said surge arresters were in operation for just more than a year. We have planned to replace it with another surge arrester with the same dimension with increased MCOV? will that help? In general, when the surge arrester starts conducting due to over voltage, why dont the ground fault protection activate?
What are the reasons for it apart from dirt, moisture and inadequate capacity?. The said surge arresters were in operation for just more than a year. We have planned to replace it with another surge arrester with the same dimension with increased MCOV? will that help? In general, when the surge arrester starts conducting due to over voltage, why dont the ground fault protection activate?






RE: Crack on Surge Arresters
RE: Crack on Surge Arresters
Better to subject a sample for failure analysis to know whether the failure is voltage related or current related, before going for deciding on new specs.
Rompicherla Raghunath
RE: Crack on Surge Arresters
Maybe a lightning strike in the station?
RE: Crack on Surge Arresters
Questions to consider.
Is it in an area that would be likely hit by lightning?
Are they rated line to neutral and could be exposed to line to line voltage?
Are they rated high enough for the voltage (does the switch gear operate at higher than expected voltages)
RE: Crack on Surge Arresters
RE: Crack on Surge Arresters
RE: Crack on Surge Arresters
The surge arrestor selection should consider the system neutral point earthing. If there is a selection issues, then re-verify the rating vis-à-vis system neutral earthing.
RE: Crack on Surge Arresters
if it was lightening would not you have some burns or ozone residue?
RE: Crack on Surge Arresters
RE: Crack on Surge Arresters
RE: Crack on Surge Arresters
If the cable is use from the transformer to switchboard, mostly the lightning surge gets attenuated. By the same token, the lightning struck at transformer primary, would not generally transfer to the secondary incomer, due to the attenuation, in the cable and transformer.
In an ungrounded system, an earth fault could result in such surge due to the arcing ground phenomena
Here you should also differentiate between the lighting and the surge. Though majority of the people use the term surge arrestor and lightening arrestor interchangeably, technically they are different. Normally in the cable connected switchgears you install the surge arrestor.
So review your application and the characteristics. Is it applied as lightning protection or as a surge protection? Then select the over voltage protective device accordingly.
RE: Crack on Surge Arresters
Rompicherla Raghunath
RE: Crack on Surge Arresters
RE: Crack on Surge Arresters
RE: Crack on Surge Arresters
RE: Crack on Surge Arresters
The surge arrester is mounted before the VCB in Incoming VCB and after the VCB in outgoing feeders
RE: Crack on Surge Arresters
RE: Crack on Surge Arresters
RE: Crack on Surge Arresters
RE: Crack on Surge Arresters
I don't see it appropriate to install LA with MCOV of >12kV considering that the system (i.e. all the equipment installed in 11kV system) is designed with a max system voltage of 12kV.
It is the earth fault detection and removal process that needs to be improved and instead increasing the MCOV of LA could be counter-productive (by shifting the failures elsewhere).
I haven't worked in an ungrounded system but I read why the concept of ungrounded system has gone out of popularity and is replaced by high resistance or medium resistance grounding concepts. It is the difficulty in identifying the faulty feeder and consequent delay in detecting and removal of earth faults that give rise to 'arcing grounds' which can lead to overvoltages much higher than the equipment rating.
I thought the above will be helpful to OP as he is also planning to increase the MCOV of the LAs.
Rompicherla Raghunath
RE: Crack on Surge Arresters
In the low voltage the unrounded systems are still used, for the specific (critical???) applications. But in MV and HV I don't envisage any justification to have an ungrounded system.