stored energy motor operating mechanisms 4

[paliha]

When testing a motor control centre, i came across a stored energy motor operator (ABB ISDAO for S6-57 or some thing like that) The closing operation is instantaneous after applying signal on "close" input. The open operation takes plase after few seconds of "open"input signal as there is no stored energy for opening operation.

I can understand practical difficulties for not having instantaneous action on both "open" and "close" operations. But my logic is, it is the " open" operation the one that need fast response. (In fact i instructed the emergency off button to be connected to the tripping circuit as few seconds delay can not be allowed.)

I do not think ABB has overlooked this point, but beleve there is a strong reason against my logic.

Can any one of you have any explanation?

 

[slavag]

Hi Paliha.
First of all, You are totally right!!!
Somthing starnge.
Maybe it's some misunderstanding, try ask to ABB.
standard cycles are O-C or O-C-O ( open, close).
Best Regards.
Slava

 

[dpc]

I'm not familiar with the device mentioned, but there is a difference between opening a molded case breaker and tripping it. The motor operators I have seen for MCCBs are a messy looking affair that connects to the breaker operating handle. I wouldn't trust one of these to protect my dog. They are strictly used for remote switching and perhaps automatic closing, but never for protection or emergency tripping. If a remote emergency trip is required, the breaker should have a shunt trip device that will work regardless of the motor operated switch.

 

[slavag]

Hi Paliha.
I see it's new ABB Tmax MCCB.
If you have some problem ask ABB, tommorow I'll ask our local ABB person.
Regards.
Slava

 

[ScottyUK]

I think the instant close operation is to allow MCCBs to be controlled by an automatic synchroniser, or that is how it was explained to me. I am not sure how much faith to put in this explanation but it is the most convincing one I have heard. The slow open relies on the breaker internal mechanism to provide a rapid opening of the contacts in response to the gradual winding open of the handle. They are OK for functional switching, for example an automated load shed / load add arrangement on a standby generator. I agree with dpc's comments regarding tripping as opposed to opening the breaker with one of these things.


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If we learn from our mistakes I'm getting a great education!

 

[jraef]

Yes, the general rule on stored energy operators for MCCBs is to NOT use the trip mechanism for every day opening of the breaker because it stresses the critical trip components. So for motorized opening, it literally moves the handle as if you were doing it yourself and that takes time. But if you energize the "Trip" input, it will instantly trip the breaker independently of the motor operator, usually with a shunt trip coil.

 

[gepman]

I agree with jraef and have done what he has described for some automatic control of field breakers in hydropower plants. Just remember to set up your automatic circuit to "open" the switch after you "shunt trip" it. You can't "close" the MCCB after a shunt trip (or any other type of trip), you must "open" it and then "close" it.

 

[jraef]

Good point, I forgot to mention that.

 

[JBinCA]

If the device is one of motor operators that mount on the front of MCCBs (as DPC thinks), it's worth pointing out that while the closing evolution is slow, the actualy closing of the contacts is not. The handle is moved slowly, but the contacts close rapidly once the handle gets to the right position (over top dead center).

Regards,

JB