13.8kv Closed Transition in Hospital

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larrybartowski

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Has anyone ever paralleled 13.8kv utility feeders onto a common buss inside of main switchgear?

I have a main-tie-main lineup that will automatically (open transition) transfer to 1 utility source if the 2nd source is lost. Because of the critical loads involved, the customer wants to be able to go back to "normal" mode (2 utility sources) via a closed transition.

We will be installing sync-check relay's to ensure the sources are in phase, and we have the utilities permission to do this, but I wanted to get a second and third opinion.

Do you see any issues with this? How can expect the downstream loads to react to a closed transition? In theory I would expect there not to be a hiccup.
 
larrybartowski said:
Has anyone ever paralleled 13.8kv utility feeders onto a common buss inside of main switchgear?

I have a main-tie-main lineup that will automatically (open transition) transfer to 1 utility source if the 2nd source is lost. Because of the critical loads involved, the customer wants to be able to go back to "normal" mode (2 utility sources) via a closed transition.

We will be installing sync-check relay's to ensure the sources are in phase, and we have the utilities permission to do this, but I wanted to get a second and third opinion.

Do you see any issues with this? How can expect the downstream loads to react to a closed transition? In theory I would expect there not to be a hiccup.
Click to expand...

I see this type of a transfer frequently. One more consideration is how long the system will wait for sync before transfering back to normal using open transition.

I would not expect a hiccup either using closed transition.
 
texie said:
One thing to consider here is the impact this will have on the SCCR of the gear.
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This is a worthy point, although as long as it is only a momentary parallel make-before-break, the risk is understood and upgrades are not necessary. With that said, not sure about hospitals. Risk may not be worth it.

Regardless, the only equipment that should be considered to handle the transfer operation is the Beckwith M-4272.
 
You will want near identical phase angles as well as differential logic that can clear should a fault happen during transition. If both these feeders are coming from the same substation usually its doable. Different ones less so.
 
larrybartowski said:
Has anyone ever paralleled 13.8kv utility feeders onto a common buss inside of main switchgear?

I have a main-tie-main lineup that will automatically (open transition) transfer to 1 utility source if the 2nd source is lost. Because of the critical loads involved, the customer wants to be able to go back to "normal" mode (2 utility sources) via a closed transition.

We will be installing sync-check relay's to ensure the sources are in phase, and we have the utilities permission to do this, but I wanted to get a second and third opinion.

Do you see any issues with this? How can expect the downstream loads to react to a closed transition? In theory I would expect there not to be a hiccup.
Click to expand...

While this type of transfer scheme (M-T-M) whether open or closed transition, LV or MV, is not as common as the stand-alone contactor type transfer switch, they do exist and work well. Instead of re-inventing the wheel why not consider using a microprossor controller for the Brain such as the Eaton IQ Transfer controller or the GE-Zenith MX250 controller for controlling your breakers. These devices are really user frendly PLC's with I/O's, show the timer functions on the display and have the synch check feature built in. The MX250 has a safety feature where one of the paralleled breakers is shunt tripped to guard against Extended Parallel Time (EPT) should a failure occur. If this is a service entrance switchboard then the POCO may require installing a reverse power relay (32) for the same protection.
I suggest you do your homework before you finalize the design, this being a health care environment.

See pages 22-25 of this MX250 O&M manual:
https://www.gedigitalenergy.com/products/manuals/PowerQuality/71r2000.pdf

IQ Transfer Controller:
http://www.google.com/url?sa=t&rct=...3YGgBA&usg=AFQjCNEXVK1b3m_3VbtxsfIxd9oLt32R5g

Good Luck!
 
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