3 Phase Motor Voltage Unbalance

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dontheo

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The Great State of Texas
I have two submersible motors and pumps (375 ft) that supports our local water supply. We have just had them replaced and added a Symcom 777 "motor saver" to each. Once the Symcom 777 was connected to the motors, it started seeing faults on the motors for voltage unbalance and shut the motors off. We had the energy provider come out and they claim to be within Federal specifications and even monitored the situation for a week.


It seems like during heavy electrical usage times we are having the problem. I would expect some unbalance durng this time due to heavy residential usage of electricity but ours well exceeded the motors rating. The installer got the motor manufactuerer to increase the motors ratings and has offered to extend his three year warranty. I believe the unbalance is around 9% and the set the limit on the motor saver above this.


To me, this is nuts. I don't care about the warranty, I am looking at total motor life and the damage done by the heat which is accelerated by the depth of the motor. To pull the motor alone takes an act of congress, literally.


I have searched the web for other things to look for. We got about 12 years from the other motors and only replcaded them for efficiency and gallons per minute. If the electric provider claims they have done everything they can, where do I start? There are no single phase motors running in the plant either. They also claim that at install they were getting only a 3% varriance.


I am totally lost on where to start. I am thinking of bringing in an independent electrician. My one concern is that anyone who is familiar with water utilities are all part of this one big happy family which is small and all tend to know and protect one another. I just need to have it fixed, if possible and would love o know where to look for trouble locations.


Thanks in advance
 
dontheo said:
] I just need to have it fixed, if possible and would love o know where to look for trouble locations.
Click to expand...

POCO will usually just monitor the voltages at the service point. It may be worth your while to monitor the voltages at the feed point to the Sycoms. You may have something in your wiring which causes an increased voltage drop in between somewhere, such as a poor connection or undersized wire. The difference in Voltage Drop combined with a variation in the same direction at the service point may add up to something outside the tolerance set in the Sycom.
Or a current imbalance in the motors could be causing a similar effect.
I would probably do a current measurement, if you have not done so, before going to anything more complicated.
If there is a high resistance on just one phase, motor starting currents would be most likely to cause the trip.

Any voltage drop in the wiring down the well is not going to be visible to the Sycom and so could not cause it to trip.
For the volt imbalance at the Sycom to be greater than the voltage imbalance at the service means either a difference in the current or a difference in the resistance between phase lines.
 
Last edited:
dontheo said:
I have two submersible motors and pumps (375 ft) that supports our local water supply. We have just had them replaced and added a Symcom 777 "motor saver" to each. Once the Symcom 777 was connected to the motors, it started seeing faults on the motors for voltage unbalance and shut the motors off. We had the energy provider come out and they claim to be within Federal specifications and even monitored the situation for a week.


It seems like during heavy electrical usage times we are having the problem. I would expect some unbalance durng this time due to heavy residential usage of electricity but ours well exceeded the motors rating. The installer got the motor manufactuerer to increase the motors ratings and has offered to extend his three year warranty. I believe the unbalance is around 9% and the set the limit on the motor saver above this.


To me, this is nuts. I don't care about the warranty, I am looking at total motor life and the damage done by the heat which is accelerated by the depth of the motor. To pull the motor alone takes an act of congress, literally.


I have searched the web for other things to look for. We got about 12 years from the other motors and only replcaded them for efficiency and gallons per minute. If the electric provider claims they have done everything they can, where do I start? There are no single phase motors running in the plant either. They also claim that at install they were getting only a 3% varriance.


I am totally lost on where to start. I am thinking of bringing in an independent electrician. My one concern is that anyone who is familiar with water utilities are all part of this one big happy family which is small and all tend to know and protect one another. I just need to have it fixed, if possible and would love o know where to look for trouble locations.


Thanks in advance
Click to expand...

Submersible pumps are special construction motors with long ans skinny rotors and stators. The windings impedance have a much larger phase-to-phase imbalance than ordinary motors. Trying to protect those against imbalance will not be beneficial and somewhat futile and I would over-ride the V or I imbalance in the relay or open it up wide.

If you have voltage imbalance on the incoming side - and it can vary, dependent on the system loading - then you may try to rotate the phases and see how you can minimize the imbalance by moving the higher voltage phases to different positions, keeping the rotation the same of course.
 
Monday I will have the electrician check the plant side of things. The Syncom does let me monitor and log all information including pump starts and stops.

Does this sound crazy ? I know when the power company peak times are, and this seems to cause the greater imbalance and thus trip the motor saver. They also charge more for their electricity during those hours plus penalties for higher users like us.

If I could monitor tank water level in real time, and not just trip switches to activate the pumps, then we could let the water level in the tank decrease below the normal set point and say, go back to operations after the high electrical usage period is over. This assuming I could sustain the water level at a safe point.

I would then save on electricity and run the pumps when there was not such a high demand. This would cause less of an unbalance. Maybe even increase gpm if the motor can run faster without such a huge unbalance? Just thinking out loud because there are so many variables.

Of course we could do what the power company does and charge more during peak hours. Just kidding. Lol
 
Laszio:

I think that you need to add the variable of range into that equation. Being old school, or maybe just old, I favor a 300 mag. Anything over 200 yards is going to be pushing it further complicated by the elevation of the mouse. Is this from a cold barrel or do I get a few warm ups? Lol
 
dontheo,
I have had the EXACT same experience with Symcom 777 relays on submersible irrigation pumps that are in quasi-residential areas. In my case they were wells at wineries in the Napa Valley. The wells were there for years, but in the 1990s when wine prices collapsed and real estate skyrocketed, a number of smaller growers sold off their vineyards to developers. Only AFTER the resi developments came in did the 777s start becoming a problem. One theory of mine is that the utility can't really keep up with the rapid changes in demand from all the different single phase AC services, because they have no control on who is home with the AC on and who isn't. But the 777 is monitoring VOLTAGE, not current imbalance, so even though the pump is not called on to run, if the voltage imbalance occurs it trips anyway and you can't make it automatically reset. The grower I was working for finally gave up and we removed all of the 777s and replaced them with Solid State Overload Relays that had adjustable phase CURRENT imbalance protection, the problem went away. By doing that, it is only monitoring for the imbalance WHILE the motor is actually running, and since he ran the drip system at night to conserve water, there were no more serious imbalance issues.
 
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