CB Operation Time Versus Velocity

What sort of breaker? Please give the forum something to go on. Maker? Part number? How about voltage and current?

The more information that can be provided during the initial posting, the more concise and quicker will come the answers.

Of course, by the factor of distance. (Which makes the distinction between velocity and time.)

OK. Let see: rated closing time (from technical documentation) =50 mS. Measured closing time (field measurement by CB analyser) 49 mS. What can i learn more about CB health by velocity measuring ?

Simply that the closing time is 2% faster than specification.

Measure or compute the velocity, and see if it also conforms to specification.

For instance, time relates to total let-through energy; velocity relates to arc quenching and possible contact bounce.

If kvsridhar is observing, he can surely amplify on these brief comments.

Thanks for the vote of confidence Tornado

Closing velocity, if high at the point of contact-touch, causes bounce. Today's contactors have electronically controlled coils, which regulate closing force so that bounce is practically eliminated. As opposed to old contactors which used to slam shut bouncily.

Fast opening is mostly desirable, to quench the arc quickly. Won't help in zero-current devices like contactors, but current-limiting devices (eg. MCCBs) are helped by a high opening velocity.

My two cents, for what it is worth.

It's a long time since I've had trouble with contact bounce.

Thanks kvsridhar for reminding me of some long weary shifts on old switchgear.

Regarding the opening velocity, there's something nagging in the back of my mind about the zero current point being used to stop the arc being drawn out before the end of contact travel.

Old age is getting to me

Velocity is the in distance travelled in a unit of time.

Close/Open time is the time it took to execute the open action completely.

The difference: if the distance = 10mm, and it took 50ms, then the velocity is 200 mm/sec. This is needed in relation to the arcing potential during opening, i.e. how efficient it is in preventing any arcing.

!!!

Next time, put all that in the original post.

PWSlack! I'm really trying to find arguments. What's wrong with how I built my question? There are some rules on construction issues in the forum?

Maybe the money guys know how to do arithmetic better than you do.

Er...i did mention that the time/distance calculation gives AVERAGE speed. What is important is the instantaneous speed at the point of contact-touch and contact-parting. The transducers can tell you that. Best argument for convincing higher-ups. Depends on your passion in needing to find out this speed.

"I'm really trying to find arguments"

Many here don't care to waste time arguing with unqualified people on subjects about which they demonstrate ignorance.

"close/open operation time" is the period of time that it takes for a CB to transition from one state to another. "open position-to-close position" and "close position -to open position".

"close/open velocity" is the speed at which the CB contacts are moving.

"close/open operation time" is directly affected and is a result of CB "close/open velocity" and contact gap.

Yes it is possible that "close/open time" is fine but the "close/open velocity/speed" is wrong.

Given Conditions:

1. The contact gap is set at less than CB design value.

2. A mechanical malfunction condition exists that decreases the "close/open speed" value.

Resultant:

Because the pole piece has less distance to travel the "close/open time" could still within acceptable limits even though the "close/open velocity/speed" is defficient.

The condition of a faster speed can also occur with the incorrect springs installed in an air circuit breaker. I went out for a factory recall for this condition on AM type indoor 15 KV units. The tighter springs moved the contacts too fast and the arc never made it to the proper position in the arc chute. Most had never interupted a fault and were a simple fix, but a few were quite damaged. The QA foreman had decided that even though the speed and opening time were under spec, it would not cause a problem. It turned out to be a very big problem.

Vacuum bottles are much easier and more dependable.

Many thanks to all who responded to my question! The discussion reinforced my belief that the checks at the time of commissioning and periodic inspections must include not only the response time measurement, but also the definition of the speed of the main contacts.