Experience with MV Contactors

[wbd]

Hello,

I am working on replacing 1950's vintage circuit breakers on the output of 800 kW hydro generators. One proposal I have received is using MV contactors instead of circuit breakers. The generator output is 2400V delta and the system fault current is around 6kA.

Does anyone have any experience using MV contactors in this type of application?

Thank you

 

[dpc]

I've seen it done, but never been a proponent. If the contactor can handle the fault current, it will certainly be less expensive.

 

[Skogsgurra]

Be careful if you are looking to use vacuum contactors. They produce a lot of overvoltage when switching. I had a case recently where a 9 MVA generator flashed over after less than five years of operation. Reason: vacuum contactors and no overvoltage protection. Surge arresters are a must.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[LionelHutz]

Rack-out breakers are the most common. The breaker provides the means to trip for protection and the rack-out provides the means to isolate the load. If you don't need load isolation for maintainence then a vacuum contactor could work.

 

[RalphChristie]

wbd

Be very careful if you wanting to use vacuum-contactors, even more so in this case, because you want to use it on an old machine. Due to different contact materials and operating speeds, (contactors vs circuit breakers) contactors are much more prone to pre-strike (switching on) and re-strike (switching off) voltages, which may stress and puncture the coil insulation. Although the vacuum-technology has improved a lot over the last years, it might be a problem due to lower BIL-ratings (BIL = breakdown insulation level) on older machines. Modern machines are normally designed to have a much higher BIL-rating than previously.
Nicely picked up, Gunnar. Like Skogs said, if you are going to use it, do not use it without arresters.

Regards
Ralph

[red]Failure seldom stops us, it is the fear for failure that stops us - Jack Lemmon[/red]

Make the best use of Eng-Tips.com
Read the Site Policies at FAQ731-376