Phase loss protection

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Ragin Cajun

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Upstate S.C.
Just came back from a new client meeting. A school in the boonies is being hammered by single plasing on the distribution line serving the school. As a result they are loosing motors. Obviously, they need phase loss protection. It's affecting not just three phase motors, but also the room AC units so individual protection is not the answer.

They want to simply trip the main and manually reset the breaker. I have no problem with that. They have radio communication with the school to central monitoring that will tell them to go and reset the main.

Fortunately they have a 1600A main at 480V with GFIC. So it already has a shunt trip on the main disconnect. Sometimes you lick out.

I plan on installing a phase loss sensor to monitor the incoming line and trip the main as needed. One of the TimeMark ice cube units.

However, my brain went into details and I see the need for a time delay before tripping to avoid nuisance trips.

Several questions for the forum:


1. How long a time delay? I was figuring on 3-5 seconds. Obviously I will use a pneumatic relay since I need to time out upon loss of power.

2. A concern is the source for trip power to the shunt trip. I will be getting with GE for a wiring diagram for the GFIC circuit. If the phase that's lost is on the leg I am getting the power to hit the shunt trip, will there be enough voltage to trip the shunt trip? There is a CPT to go from 480V to 120V.

Anybody run into this?

Thanks ahead of time,

RC
 
I'm not sure I would want to be tripping and resetting a 1600A breaker that often. Large breakers are only rated for a certain number of operations.

I'm also not sure if you can shut off power to an entire school while it is full of kids (if I understand this right). Sure there is emergency lighting, but doesn't everyone have to leave the school when the power goes out? They can't just sit in the school waiting for the battery lights to go dead.

Can the motor loads be grouped on a subpanel, and then just trip the sub panel and leave the lighting loads on?

Steve
 
Good points. They are aware of all that but I will be putting those and other considerations in writing

The motor loads are all over the facility. During the day there is someone who can reset the breaker. I also have concerns regarding closing the breaker as well. Unfortunately - of course, the breaker is shunt trip only, no electric close means.

The main breaker will not be required to trip that often. But when it does the savings in loss prevention are significant. The last single phase outage cost them $6000!


RC
 
I would think that properly sized overload relays (that are required by code) would take care of the 3 phase motors.
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Unless you are using electronic overloads with built in loss of phase protection, your three phase motors can be damaged by phase loss. Standard overloads are often not sensitive enough to protect the motors under phase loss conditions.
Don
 
Since a single event would cost $6000, could you covince them to put in an electrically operated breaker, that could be opened, and re-closed automatically using voltage sensing. Would be relatively easy to do. A timer could be provided so that it doesn't cycle open-closed, in case the power returns for just a few seconds, etc.

Wouldn't each time you open and close the breaker under load, weaken the device? Not sure if large breakers are switch duty rated or not.
 
Why shut down the whole school for phase loss?

Typically the Main gear has a feeder circuit for the MCC or to a large power panel that feeds the motor loads.

Buy a shunt trip kit for that feeder breaker, connect it to your phase loss relay and only kill the motor loads.

As for your concern about the lost phase being the one for the shunt trip...use a battery backed up ups...something as simple as a ups for a PC (computer) like they sell at WalMart could work...well...on that order anyway.

You can put in a lot of shunt trip kits for $6000.
 
Shoulda thought of this, too

You can install phase loss relays for a lot of individual motors for $6000.00.

Is this a fairly new school? All new schools in our area have sophisticated 'building automation controls' which can monitor phase loss, shut down critical loads and restart on restored power.
 
thinfool said:
Shoulda thought of this, too

You can install phase loss relays for a lot of individual motors for $6000.00.

Is this a fairly new school? All new schools in our area have sophisticated 'building automation controls' which can monitor phase loss, shut down critical loads and restart on restored power.
Click to expand...

This is what I am thinking. The Time Mark plug in phase loss relay could be installed in each motor starter. Beats shutting down everything.

edited to correct spelling.
 
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