No-Break System

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danilo

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Guys,

what system protection or device should be installed at the ATS for the no-break transistion of power from normal to emergency system..got a lot critical tenants here in the building that need continuous power even during preventive maintenance,however, as building engineer, i wont sacrifice our facilities to operate without proper maintenance and so i thought of doing an un-interrupted system to serve both the interest of building owner and our tenants.

thanks for your comments in advance.

Danilo
 
Re: No-Break System

There are closed transition transfer switches asvailable for that purpose. With this type of transfer switch the only time that the load is without out power is the time for the generator to pick up when there is a loss of utility power.
Don
 
Re: No-Break System

What you are describing is the need to place the utility power and the on-site backup power source (e.g., diesel generator) in parallel during the transition from one to the other. I have not worked with a design that performs that paralleling function at the ATS. What you should do is to talk with ATS manufacturers, and see what they recommend. You need to tell them exactly what components will need preventive maintenance, in order for them to help you determine at what point in your distribution system the paralleling needs to take place. Also, there is an NEC article that discussed placing on-site sources in parallel with the utility. I think it?s either 704 or 705 (I still haven?t unpacked my NEC books after my recent move).
 
Re: No-Break System

Converting the transfer switch to a closed transition style and modifying the generator controls to allow momentary paralleling of normal and emergency sources would minimize outages for maintenance. It might be possible to convert the existing switch with an in-phase monitor to do what you need. Several of the ATS manufacturer's have similar products (ASCO, Russell, GE Zenith) Check with the local rep for your transfer switch or research on-line.

If you go with momentary paralleling, the utility probably will have requirements for additional protection and controls to protect their system.

Good luck. I like your attitude toward maintenance!
 
Re: No-Break System

You've had several good replies. I'd like to point out an implication of a very often overlooked section of the code as it applies to paralleled supplies:
110.9 Interrupting Rating. Equipment intended to interrupt current at fault levels shall have an interrupting rating sufficient for the nominal circuit voltage and the current that is available at the line terminals of the equipment.

Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage sufficient for the current that must be interrupted.
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If your onsite generation is large enough, it will (not could) affect the required fault interrupting duty of your OCPDs. Under current wording it does not matter that the paralleling may only be momentary. In fact, since it defines the required fault rating as what "... is available at the line terminals of the equipment," even the service and parts of the ATS OCPDs that will never see the full calculated fault must have increased interrupting ratings.
 
Re: No-Break System

While all the above is true only good design with distribution bypasses and isolation bypass transfer switches that allow you to service the main distribution equipment will suffice. This along with good acceptance testing, ongoing infrared scanning, and monitoring your contractors will help in insuring a safe reliable facility (IN MOST CASES).

A good design that permits true service and testing of distribution equipment is a tough sell. There will always be some equipment that must remain on line and IR testing will have to suffice in these circumstances.
 
Re: No-Break System

Appreciate all your replies..thanks

yeah Charlie is right,im trying to synchronize the utility power and the on-site back-up power source during transition at the ATS.Im thinking if i can synch them in for a couple of seconds to have a no break power transition.

im tempted to follow what we did in other building i worked with before when we used a contactor type ATS to make this no-break transition happened.Unfortunately,after few times it operated, the system exploded due to locked contactors that almost killed our senior engineer.

i sense a challenge here to proceed with my grand plan as this will surely give our building a competitive advantage over other buildigs in our district, but i want to risk this out with some calculation..do you think im missing out something here?

Gracias!

Danilo
 
Re: No-Break System

If you go with momentary paralleling, the utility probably will have requirements for additional protection and controls to protect their system.
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You are absolutely correct on this point, we have requirements and, I assume, other electric utilities also have requirements for a make before break installation. :D
 
Re: No-Break System

danilo, also remember that a generator with a make before break ATS alone would work well for maintenance (i.e. planned outages), but for the unplanned outages, an UPS is needed if you really want no interruption to power while the generator fires up.
 
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