Surge arrester MCOV
Surge arrester MCOV
(OP)
Hi,
I need to specify a surge arrester in the neutral circuit of a 99MVA 138kv-34.5kv (14.4kv tertiary) auto transformer. The arrester will be located in the neutral circuit of the secondary winding (34.5kV) and is placed between the transformer neutral and a neutral grounding reactor (1ohm, 600A 10sec).
How would one select the MCOV rating of a station class surge arrester in this application? The X0 winding BIL is 200kV.
Regards.
I need to specify a surge arrester in the neutral circuit of a 99MVA 138kv-34.5kv (14.4kv tertiary) auto transformer. The arrester will be located in the neutral circuit of the secondary winding (34.5kV) and is placed between the transformer neutral and a neutral grounding reactor (1ohm, 600A 10sec).
How would one select the MCOV rating of a station class surge arrester in this application? The X0 winding BIL is 200kV.
Regards.






RE: Surge arrester MCOV
If your reactor rating is any indication, 600 A and 1 ohm gives you 600 V. Above 600 V, I'm not sure what the next available arresters are. I've used some 3 kV duty cycle ratings and they have an MCOV of 2.4 kV I believe.
RE: Surge arrester MCOV
RE: Surge arrester MCOV
RE: Surge arrester MCOV
I am thinking 24.4kV MCOV station class in the neutral.I have based this on the recommendation shown on page 16 (of 19) in the attached file. See "selection of surge arrester" at the bottom right.
Your choice of 2.4kV MCOV against system overvoltage due to fault current seems reasonable too.
RE: Surge arrester MCOV
Normally, the line arresters are based on around 80% of the line-to-line voltage or 1.25 times the line to neutral voltage. For the neutral to ground, particularly with a neutral reactor, it's a different story. I think you can go much lower. There's an IEEE standard on the subject of neutral grounding so I'll have to check to see if it says anything different than my opinion.
RE: Surge arrester MCOV
Regards
Marmite
RE: Surge arrester MCOV
GE publication that recommends sizing the arrester rating at 70% of line-to-line system operating voltage for solidly grounded system. In ungrounded system it will be 100%.