Can we use 12KV surge arrestors for Unit substations (MV switches & dry type transformer) that utilize 4.16KV service? The intent is to use 12KV arrestors so we don't have to replace it because the service, to the facility, will be upgraded in the future from 4.16KV to 12.47KV once becomes available. Thanks,
Surge Arrestor KV Rating
- Thread starter faresos
- Start date
- Status
David Castor
Senior Member
- Location
- Washington, USA
- Occupation
- Electrical Engineer
The 12 kV arrestors on a 4160 V system would mostly defeat the purpose of the arresters, which is to protect your equipment (esp transformers) from surges. I wouldn't recommend it. That future voltage upgrade, may never happen.
Dave
Dave
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The arrestors should match, the voltage rating of the other components in your system.
masterinbama
Senior Member
- Location
- Huntsville Alabama
And arrestors are cheap compared to the damage the 12kv arrestors wouldn't stop on a 5 kv system.
Sent from my moto e using Tapatalk
Sent from my moto e using Tapatalk
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
It is possible that the 12kV arrestor would have an operating threshold far in excess of the equipment, resulting in the equipment protecting the arrestor instead.
But it is also possible your 5kV equipment is actually built using 12kV spacing if it is designed to be upgraded. Ask your equipment manufacturer.
Carultch
Senior Member
- Location
- Massachusetts
A surge arrestor is there to be a protection against overvoltage. If you have a surge that is 10kV on this system, then to a 12 kV arrestor, that is ordinary grid voltage. The arrestor will remain intact and do nothing about the overvoltage. You want the arrestor to blow when there is a surge that high, otherwise it will defeat the purpose, and the equipment you are attempting to protect will get damaged instead.
It's analogous to the issue of using a 600A fuse on a 200A circuit. Sure, the 600A fuse will carry 200A of current and remain intact. But if a 500A overload occurs, the 3/0 wires are now what will melt, instead of the 600A fuses.
It will “work” but it won’t stop surges.
A modern surge arresters uses a block of sintered metal oxides. We like to think that it is an open circuit below 12 kV and dead short above but that’s not how it works. It is a voltage variable resistor. The “short circuit” region is a LOW resistance, not anywhere close to zero. This is exacerbated further by surge impedance. So without too much effort your 12 kV arrester might give you 60-80 kV surges. Easily tolerated by 95 kv+ BIL 15 kV class equipment but not your 6 kV class 65 kBIL nor 5 kV wiring that is only surge rated to 200%+1 kV or 11 kV!
- Status