Automatic Source Transfer Scheme with Switchboard?

[CuriousElectron]

Hi Folks,
Can one specify a switchboard with two main breakers(primary and redundant power sources) and controller/relay for automatic switchover in the event of primary source failure?
I'd imagine I'd need a separate compartment for the relay, and would need to work with manufacturer on this.

I know that manual switchover is an available option, however, I need auto.

Thoughts?
Thanks,
EE

 

[xnuke]

Yes.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[dpc]

Certainly can be done. Probably stating the obvious, but if doing this with circuit breakers, they need to have the ability to be electrically closed and tripped.

Also, if the loads being fed are critical, consider how a common-mode failure in the switchgear could cause a total power outage.

 

[JG2828]

What is the voltage level? 120/240v or 60kv?

 

[waross]

Good practice dictates that there be a mechanical interlock between the breakers.
While this may be challenging, don't dismiss the possibility of more than one simultaneous equipment failure that leads to an incident that would have been avoided by a mechanical interlock.
And by the way, I have seen mechanically interlocked contactors with a functioning interlock that were able to both make simultaneous momentary contact under certain conditions.
This was set up as a demonstration and flashed a light bulb rather than doing damage.
Be very wary of assumptions when safety is involved.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[GroovyGuy]

Howdy Curious Electron,
I agree with JG above. (ie what are the voltages and current involved here?).
GG
ps I have always preferred to use a actual ATS in these cases (ie a ASCO 7000 series type of AT switch for LV applications). Obviously for MV ATS applications you will need to use modified MV circuit-breakers.

"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

 

[CuriousElectron]

Greetings, Gents
This is for a Utility application, where the primary source is tapped off the generator bus via a station service step-down transformer and the redundant supply is provided from nearby MV distribution line. The Switchboard voltage level would be 480V, 3 phase, 4 wire or 208, 3 phase, 4 wire. Now, I don't believe the neutral needs to be switched here. Hmm, got to think about this one now..Maybe I can spec out a 4 pole power breaker.
I'm just thinking a relay that senses loss of voltage on either incoming line and sends a trip to the shunt of either breaker.

Thanks,
EE

 

[waross]

I have always considered switching neutrals to be a lazy solution.
I have always been able to use solid neutrals.
In some installations it is a challenge to use solid neutrals and not compromise ground fault protection.
To date I have always been able to meet the challenge.
I admit that some day I may have to switch a neutral but it hasn't happened yet.
On the other hand I have more than once had to clean up the mess after someone else's switched neutral went open unintentionally and destroyed a lot of equipment.
Remember the mechanical interlock.
If a close signal is inadvertently sent to both breakers simultaneously, they will both close before either can send an inhibit signal to the other breaker.
That can never happen, right?
Over the years I have seen to many things that "could never happen" actually happen due to an unanticipated failure of some other device.
I still remember years ago the flash, the bang and the embarrassment when I was demonstrating how an interlock could never fail and I was wrong.
As i mentioned earlier, when teaching controls I would show the students an interlock circuit and ask for their critique.
No-one ever saw a problem with the circuit.
Then we would wire it up and demonstrate the failure.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[che12345]

Dear Mr. CuriousElectron

Q. " Can one specify a switchboard with two main breakers(primary and redundant power sources) and controller/relay for automatic ..... "
A. We can not "specify" a switchboard for you as it involves legal liability...etc....
Having said that, I would like to submit the following for your information purposes:
a) depending on the current rating, use 2xACB (for >1kA), 2xMCCB (for <1kA), refrain from using 2x contactors* (they usually are NOT rated for the short-circuit kA),
b) ensure installation of [Mechanical inter-lock] in addition to the electrical inter-lock circuitry,
FYI: Mechanical inter-lock devices are available for Contactors* and ACBs (even installed in separate cubicles), but may? not be available for MCCBs,
c) tap the control supply from the individual incoming source. Use only the [Under-voltage release], do NOT use the [Shunt release] for electrical inter-lock circuitry,
d) strongly suggest to use [Four-pole] switching device (be it ACB, MCCB or Contactor*). This will simplify the earth-fault protection scheme,
e) Do NOT insert any switching device in the earthing wire, ....

Che Kuan Yau (Singapore)

 

[jraef]

You can get what is referred to as a Main-Main (or main-Tie-Main) switchboard with motorized mains and then get what is called an ATC (Automatic Transfer Controller) to do this, it's not at all uncommon. But be forewarned, 480V implies North America and there are rules in the NEC and CEC for standby or backup power systems and how power is transferred, meaning you may be FORCED to use an official Automatic Transfer Switch (ATS) like the Asco unit mentioned above by GroovyGuy.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[DTR2011]

I saw this and thought overkill. There are SEL-2411 devices that are the brains of this M-T-M set up.

 

[LionelHutz]

Yes you can.

We shipped a couple of MCC's with ASCO transfer switches installed recently. A few months back we built a main-tie-main switchboard with 2 ASCO transfer switches for generator power. 2 utility feeds and a generator, with the ability to change to two generators in the future.