Odd voltage level

[tulum]

If you have a contactor that is rated 18kA on a 1500V system,what is it rated for on a 1000V system?

Is there a rule of thumb? Does the rule work for other components, breakers, etc?

I will check with the manufacturer to make sure, however, for design estimating it would be nice to know.

Regards,
TULUM

 

[buzzp]

I would think it would still be rated for 18kA.

 

[JBD]

Is that 18kA the symmetrical fault rating? Is this a motor starting contactor?

 

[tulum]

The contactor is on the secondary of a 750/940kVA delta to grounded wye dry type transformer. It is a disconnect means for the secondary feeders. The primary has an S&C mini-rupter fused with din fusing. The contactor is an AB 1500V 400A vacuum contactor.

The reason I asked was that on a previous job for a Toshiba vacuum circuit breaker the manual gave the the following formula to evaluate interrupting rating;

New Short Cicuit rating = old SC x (Rate Voltage/actual Voltage).

Just wonder if it applies as a "blanket" rule of thumb.


I will have to check the 18kA rating...

 

[davidbeach]

That formula works for every piece of equipment that the manufacturer's instructions say it works for and not for any others. Frankly, a linear relationship seems a bit surprising, but presumably the manufacturer tested the device enough to know that the formula worked.

 

[cuky2000]

Tulum

The actual ANSI/IEEE standard C37.09 was revised in 1999 with fix factor K=Rate Voltage/actual voltage = 1. This means that the standard do not longer support changing the interrupting rating as a function of the voltage at which the vacuum of FS6 interrupting breaker was applied.

_{[blue]NOTE: In the past was common to manufacture oil or air interrupting devices. Today, virtually all MV circuit breakers are either vacuum or SF6 insulated. Those gases are more closely represent a constant current interrupting device, independent of the nominal system voltage.
Since MV vacuum contactor are similar to MV breaker vacuum bottle, will be safe to assume that their interrupting ratings is constant and independently of the operating voltage. .[/blue]}

In short, I will vote to consider the interrupting rating constant independent of the operating voltage.

 

[tommom]

Such adjustments to interrupting rating were intended to work within a narrow range of voltage values, I believe, and are not intended to allow use of the equipment on much lower voltage systems.

 

[dpc]

Even when allowed (k factor > 1) this is for a specific voltage range as tommom states. There is a lower limit below which there is no increase in SC capability.