Surge Arfrestors for MV

[slavag]

Dear All.
Could you please attached some link with good theoretical explanation about surge arrestors.

Shortly.
Surge arrestor for 6kV , oxid type, max operating voltage 7.5kV. 6kV ungrounded system. Ground fault on the outgoing
involved to two-phase fault, operated line protection and infeed protection too, becouse some problem, operated auto transfer and closed coupler, operated recloser on the line.
Same pict, again trip on the coupler and line. After 3min infeed closed remotly and system back to operation.
All protection are EM relays. Team checked all relays and CB's , all fine. Second fault in this system, same fault in another SS, all problem started after installation of new type of SA.
Some stuipid idea. SA operated due the overvoltage ( ungrounded system) and current is enough for the protection operation. But from other hand is unpossible, 3000A for the 2sec!!!! and SA back to operation w/o damages, for my pinion it was burnt.
Any ideas
Thanks in advance.
Best Regards.
Slava

 

[cuky2000]

I hope the enclosed information helps

http://www.cooperpower.com/Library/TheLine/pdf/99-08.pdf

http://library.abb.com/global/scot/...pplication Guide Medium voltage networks.pdf

 

[prc]

I have a query. In a steel plant, there are 50 MVA 220/33 kv and 220/11 kV transformers. LV side of transformer is connected with XLPE cable through an air fiiled cable box.Client is asking me to provide Surge arresters inside cable box.ie 12 & 33Kv arresters.
1) Does an arrester really require at this location.Cable system is not exposed one and there is no chance of any external surges coming on the cable system.Surges transferred from primary of transformer will be attenuated by the cable capacitance so that there seems no need for a arrester.What is the industry practice?

2)In case arrester is required, why and how to select the arrester rating?