Is an ATS a passive device?

[elec_eng]

Situation: 2000A ATS (480V, 4-pole, contactor based bypass Isolation type) is fed from 2000A LVPCB. ATS’s UL 1008 Withstand and Close On Rating (WCR) is 100KA but STD rating is only 36KA for 18-cycle.

In order to achieve selectivity with a downstream CB, STD was imposed on the 2000A LVPCB. The issue is ATS did not have a high enough STD rating. STD is less than 18-cycle, so ATS's duty-cycle is OK, though.

A proposed solution was to add a current limiting fuse before the ATS and reduce the fault current. I think this is a so called “Up-Over-and Down” method?

So, my questions are
1. Does this seem right?
2. I know “Up-Over-and-Down” method can be used on a passive device. Is the ATS a truly passive device?
3. Any other ways to resolve this issue?

 

[dkidd]

You can use breakers and fuses as documented by the manufacturer. Have a look at the GE document http://www.gegridsolutions.com/prod...ity/TB-1102 - Withstand & Closing Ratings.pdf

It states in one paragraph

Some switch designers analyze “blow-on” and “blow-off” effects
and force vectors (due to electromagnetic repulsion) to claim
increased WCR capability of their product. Such calculations are
very rough approximations because of inherent errors in estimating
“domain” size and number, current “pinch” effect and the problem
of complex geometry of actual contact structures when compared
to idealized models. The only proof of a successful design are
tests, uniformly performed and consistently reported all to the
same criterion such as UL 1008.

so the ATS is not necessarily passive.

There is also a good white paper at

http://power.cummins.com/sites/defa...echnicalpapers/PT-9005-30-CycleDangers-en.pdf

 

[jim dungar]

The ATS has a published short circuit current rating. Your installation needs to comply with the standards used to develop that rating.
I know that UL tests for series-combination ratings between an ATS and specific protective devices, including fuses.

 

[elec_eng]

You can use breakers and fuses as documented by the manufacturer. Have a look at the GE document http://www.gegridsolutions.com/prod...ity/TB-1102 - Withstand & Closing Ratings.pdf

It states in one paragraph

Some switch designers analyze “blow-on” and “blow-off” effects
and force vectors (due to electromagnetic repulsion) to claim
increased WCR capability of their product. Such calculations are
very rough approximations because of inherent errors in estimating
“domain” size and number, current “pinch” effect and the problem
of complex geometry of actual contact structures when compared
to idealized models. The only proof of a successful design are
tests, uniformly performed and consistently reported all to the
same criterion such as UL 1008.

so the ATS is not necessarily passive.

There is also a good white paper at

http://power.cummins.com/sites/defa...echnicalpapers/PT-9005-30-CycleDangers-en.pdf

dkidd,

So what you are saying is that ATS is not necessarily passive device but a fuse can be used to increase the WCR of ATS, if the fuse is tested with the ATS?

Does the fuse have to be in the ATS (mfgr installed) or can be anywhere upstream of the ATS (field installed)?

 

[dkidd]

dkidd,

So what you are saying is that ATS is not necessarily passive device but a fuse can be used to increase the WCR of ATS, if the fuse is tested with the ATS?

Does the fuse have to be in the ATS (mfgr installed) or can be anywhere upstream of the ATS (field installed)?

Yes

It can be and usually is upstream.

 

[elec_eng]

The ATS has a published short circuit current rating. Your installation needs to comply with the standards used to develop that rating.
I know that UL tests for series-combination ratings between an ATS and specific protective devices, including fuses.

Just curious...The UL test is only between an ATS and specific protective devices, whether it is fuse or cb. right? But in a real world distribution system, there are other protective devices, either up stream or downstream..how do thy come into play? Won't they create a dynamic impedance that was not in the UL test?

 

[jim dungar]

Just curious...The UL test is only between an ATS and specific protective devices, whether it is fuse or cb. right? But in a real world distribution system, there are other protective devices, either up stream or downstream..how do thy come into play? Won't they create a dynamic impedance that was not in the UL test?

If you have selective coordination, the other protective devices should not be operating.