Restart after power outage

faehigkeit1 · Apr 1, 2008

Hello,
I have a small motor starter (1hp) that has to be restarted manually after we have a power outage. What could I use that would do this automatically after the power comes back on? It is a typical three wire start/stop 110vac control circuit.
Thanks for any ideas on this.
Dean

dmroeder · Apr 1, 2008

What is the application for the motor. Is it safe to just restart it?

TConnolly · Apr 1, 2008

If it is safe for it to automatically restart then I suggest you replace the 3 wire start/stop buttons with an ON/OFF selector switch - you may need a maintained position e-stop button that can be mashed in to quickly stop the motor if necessary - thats for you to evaluate.

msmassey · Apr 1, 2008

Well, you could add a timer that would be NC when timing and NO when timed out. Added it into the start circuit. The coil would be powered when the electrical power comes on for x seconds and then switch off and the normal start logic would work. - NON-PLC application

In a PLC application, you could do it similarly with a first scan bit when the PLC powers up or with a power on input into the I/O.

leitmotif · Apr 1, 2008

One thing to keep in mind regarding auto start in addition to safety considerations is the short term load on distribution gear after an outage. All the lights energize, heaters energize and motors turn on. This heavily loads and can overload distribution - not for long I admit but in some cases long enough to create problems.

Dan Bentler

mcafone · Apr 1, 2008

So this is a latching circuit that drops out when you lose power? Sounds like its doing exactly what it should. I wouldn't want to mess with that considering the possible safety issues unless it was some kind of sump pump type of application where having the motor stay off after a power loss would cause a catastrophic problem. Please explain further...

faehigkeit1 · Apr 1, 2008

This is a latching circuit that drops out during a power outage....and when the power comes back on we all run like mad men to push the start button again to get the pump running (I didn't design this thing) There are no real safety issues with the pump coming back on. The real safety issue is all the running

Thanks for all the replies, I think the off-delay timer might work out really well...
Dean

milldrone · Apr 1, 2008

faehigkeit1,

If I have an item that I need to auto run after a power failure then I use a three phase monitor to insure that there are three phases present.

Here is one unit that has served me well it's made by SSAC, now a division of ABB.
http://www.ssac.com/motorpro/plmdsmp.pdf

I'm sure there are others that will work for you also.

Lancie1 · Apr 1, 2008

There are no real safety issues with the pump coming back on.

Not now, that is one reason why the electically-held motor starter was invented. But if you make it automatic, there will always be some fool that didn't get the word. He will be up to his elbows in bare terminals trying to fix the pump when the power comes back on...At least put a warning sign on the motor starter: "This pump restarts automatically"

Kabir · Apr 1, 2008

I agree with the idea to turn the pump from 3-Wire to 2-Wire PLUS EM-STOP however as everyone else noted safety regarding auto start is VERY VERY IMPORTANT!!!....

You should really give some more reason as to why you would really want the auto start and see if we could come up with the BEST Alternative.

leitmotif · Apr 2, 2008

Lancie1 said:
Not now, that is one reason why the electically-held motor starter was invented. But if you make it automatic, there will always be some fool that didn't get the word. He will be up to his elbows in bare terminals trying to fix the pump when the power comes back on...At least put a warning sign on the motor starter: "This pump restarts automatically"

Lancie,
Warning sign is nice idea for those in vicinity to prevent startle when unit turns back on.
BUT it does not relieve the responsibility of mechanic or electrician trouble shooting the unit to open the disconnect and do lock out tag out to prevent their own injury.

Dan Bentler

Kent Hostetler · Apr 2, 2008

You will also have to worry about differentiate between "loss and restoration of normal power" and the reenergizing of a circuit breaker or disconnect after a lockout/tagout. You don't want to build something that just restarts because power was lost and is now restored.

Most motors at our plant are controlled by a PLC. The MCC buckets have Manual-OFF-Auto selectors on them which determines what controls the starting of the motors. Manual = Start/Stop buttons at the pump or fan motor. OFF = neither. Auto = the PLC controls the motor.

Both are overridden by the maintained (and lockable) push-pull E-Stop located at the motor.

As always, your Lockout/Tagout policy needs to be followed without question. This includes not relying on the push-pull E-stop button as the primary lockout method - that needs to be the breaker.

monkeyhead · Apr 2, 2008

I've always been taught that machines should not be restarted automatically after loss of power. But we also have some air compressors that are set up to automatically restart themselves. They are clearly labled.

In your case where the pump is something of a utility service and you are all scrambling to get it turned back on anyway, I see it as a situation more analagous to our air compressors than a machine that people are interacting with. Perhaps a time delay and buzzer before starting the pump along with the signs?

As for the fool being up to his elbows in terminals when the power comes back on... well, he fails because he should have locked out the power source before beginning work. Any other behavior is irresponsible and just plain stupid.

mcafone · Apr 2, 2008

Reverse timer circuit as previously mentioned

Once the safety issues are dealt with...

If you reverse the timer contacts to a delay-on configuration, you can avoid any issues with power up surges. Just set the timer for three seconds or so and use the normally open contacts to energise the motor starter coil.

TConnolly · Apr 2, 2008

monkeyhead said:
I've always been taught that machines should not be restarted automatically after loss of power. But we also have some air compressors that are set up to automatically restart themselves. They are clearly labled.

In your case where the pump is something of a utility service and you are all scrambling to get it turned back on anyway, I see it as a situation more analagous to our air compressors than a machine that people are interacting with. Perhaps a time delay and buzzer before starting the pump along with the signs?

Thats what we do for our compressors, cooling towers, and chillers - but they all have a PLC on them.

When power is restored the PLC first ascertains if it was running when the power went off. If it was then it performs a series of checks to make sure it's OK to restart (fluid levels OK, all phases present, an anti-short cycle check if a chiller, etc.) If everything is OK then the equipment restarts. The utility equipment over which we have control all have different time delays on restarting so we don't have a start up surge at the main gear. Some utility equipment is dependent on other utility eqipment, eg, chillers are depenednt on the cooling tower - which affects the start up delay times.

Restart after power outage

faehigkeit1

Member

dmroeder

Lifetime Supporting Member

TConnolly

Lifetime Supporting Member

msmassey

Member

leitmotif

Member

mcafone

Member

faehigkeit1

Member

milldrone

Member

Lancie1

Lifetime Supporting Member

Kabir

Member

leitmotif

Member

Kent Hostetler

Member

monkeyhead

Member

mcafone

Member

TConnolly

Lifetime Supporting Member

Similar Topics