5kV Breaker Operation

[rockman7892]

I have a 5kV Siemens GMI breaker that we use as a starter for our main 6500hp drive here at our plant. This breaker is opened and closed (start/stop) several times a week depending on operations.

Someone recenlty mentioned swapping this breaker with other similar feeder breakers we have in order to prevent wear and tear on the one breaker being used as a starter as mentioned above. In other words he wants to create a PM program to rotate these breakers (All 1200A Breakers) in order to prevent wear and tear on any particular one being used as the starter breaker.

My questions: Is this necessary? My argument is that the breaker would not be used as a starter breaker in the first place if it could not handle the strees of up and down operation. I am trying to prevent a situation where we would have to require power outages to switch around these breakers on some sort of routine basis.

 

[Zogzog]

Yes it is necessary, you never should have been using a GMO breaker as a motor starter in the first place. I have a dozen GMI's in my shop being rebuilt right now that failed from being used as a motor starter.

 

[rbulsara]

For frequent start/stop proper MV starters using vaccum contactors and controls would be more appropriate.

 

[burnt2x]

GMI breakers are in fact vacuum circuit breakers! I think Siemens has only 2, 5-kV class vacuum breakers; 250MVA (29kAIc) and 350MVA (41kAIc). 6500 hp means around 800 amps at 4160V and 1200A breakers should do the job.
We do swap breakers during PMS. Just be careful you dont miss the ratings of the equipment wrt the breaker rating you rack into.

 

[rbulsara]

burnt:

Yes, but breakers usually are not rated for as many mechanical operations as the contactors. Also contactors are less expensive to maintain/replace than breakers.

 

[guntherb]

Breaker

Contactor

Field Isolator

 

[oldfieldguy]

I had a client who used a GE Powervac 13.8 kV breaker as teh starter for a 7000 horsepower pump that was starter twice a day.

He wisely put it on a quarterly inspection regimen and had it checked for proper operation and most importantly for contact wear. When the original breaker got near its limits for contact wear, we swapped it out for a similar breaker that had been in transformer feeder service (one operation every three years). the transformer feeder breaker had essentially unworn contacts, and the old motor controller with its worn contacts would not see a dozen operations under load in the next five years.

old field guy

 

[Zogzog]

They just cant handle the abuse, but we sure do rebuild a ton of them.

 

[burnt2x]

I can't disagree with rbulsara re economics in using contactors. That's always the guiding principle when designing systems. But when you inherit electrical equipment, we find ways to make use of everything we have, engineer-out possible solutions to problems, etc.
As what oldfieldguy confirmed, swapping could help in avoiding greater breaker damage.
rockman7892,
BTW, I attached a published data sheet for your reference. Breaker contact wear depends on the number of breaker cycles for a period of time, the current level (make and break), and the rated interrupting capacity of the breaker contacts.

 

[edwarddo]

As manufacturer, experience is that rotating CB's is good idea. Rotating CB's, especially where large number of operations are involved, is a good policy to extend the life of the CB's. However, the need to setup outages just for this single purpose is your decision. Recommendation would be to take advantage of having the CB out of service to swap it out. The other recommendation is to have a spare.

 

[lansford]

Using MV breakers as motor starters is common in refinery and utility power plant applications that only get operated several times per year. Pipelines also use them and get started more frequently sometimes two to three times per week and they hold up reaaonably well.
Frequent operation is better handled by contactors.
JIM

 

[DTR2011]

It's not necessarily the contact wear that is the problem, but the mechanism that may not be able to handle that many switching operations. I used to work for a breaker shop and most of our repairs were not the contacts, but the mechanisms.

 

[Zogzog]

True statement smallgreek, the mechs tend to fall apart.