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Discussion Starter · #1 ·
I have a customer who had me connect a rotary PC for a lake fountain pump. The idler motor runs/works fine until I start fountain pump. It strains/revs up idler motor and after about 3-4 seconds it trips OL for fountain pump. The pump motor never even turned and I measured roughly 125 amps on one leg that I managed to clamp during testing. Unfortunately I didn't get any voltage readings during that time, but did get these readings on IM without any load-
L1 to grnd=120
L2 to grnd=120
L3 to grnd=208-(which is expected according to manufacturer)
I don't recall but I remember line to line readings not being very balanced.
The motor and cable megged great even submersed. I will note that prior to me being called, someone else (non EC) attempted to connect this setup but couldn't figure it out after several attempts. I'm wondering if that caused something with idler motor? The fountain rep ended up concluding, with OEM's engineers, that the voltage was too high and are sending me buck boost xfrmrs to install. Thoughts?

Also, the BB trannys (2) are rated 500va, stepping down from roughly 245v to 208. I not too good at motors and transformers but that seems too small to fit anywhere in any of the circuitry. The idler motor is 20HP and the pump motor is 10hp. These were spec'd/sized from fountain manufacturer's engineers. Thoughts? BTW, sorry for long post.
 

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Does the pump motor have a starter? If it does, make sure that the control wiring is connected to L1 and L2. Do not connect any control wiring to the manufactured phase.
Bingo! First order of business.

Also, make sure whoever messed with that pump didn't accidentally connect it for High voltage (460V). It would start, it would just have no torque and trip out once it started moving water.
 

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Discussion Starter · #7 ·
It sounds like the pump motor may be mechanically locked up. I didn't do the math but a buck boost only has to be sized for the buck/boost, 37 volts in your case as part of the VA calculation.
That's was my thought as well. The fact it merged good and that it would run, or try to, for a few seconds lead me to believe it was bound up. As for BB, wouldn't the entire load travel through it? I don't have diagram handy.
 

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That's was my thought as well. The fact it merged good and that it would run, or try to, for a few seconds lead me to believe it was bound up. As for BB, wouldn't the entire load travel through it? I don't have diagram handy.
In your first post you said "The pump motor never even turned". Here you are saying it tried to run for a few seconds. Important info to be clear for troubleshooting. If the pump is actually turning for a few seconds I would look into wendons suggestion. I also thought this was a working installation that failed but after reading the OP again it seems more like a new installation that has never worked.

The entire load does travel through the BB, and they take that into consideration, but it is only changing the voltage within itself, like 32 volts times current. Sort of like selecting the wattage of a series resistor. The lower the resistance (or voltage change), the lower the wattage has to be.
 

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Discussion Starter · #9 ·
8V71 said:
In your first post you said "The pump motor never even turned". Here you are saying it tried to run for a few seconds. Important info to be clear for troubleshooting. If the pump is actually turning for a few seconds I would look into wendons suggestion. I also thought this was a working installation that failed but after reading the OP again it seems more like a new installation that has never been working. The entire load does travel through the BB, and they take that into consideration, but it is only changing the voltage within itself, like 32 volts. Sort of like selecting the wattage of a series resistor. The lower the resistance, the lower the wattage has to be.
Correct, the pump motor never turned. What I meant by trying to run is that the starter remained closed for a few seconds prior to tripping. To me that seemed to be more of a mechanical problem rather than a short circuit or grnd fault which would/should trip instant and ahead of starter. As for BB, that makes sense what your saying, it just seems wrong tying a 50+ amp circuit into those tiny lead wires! but then again, it seems all transformers have small wires within.
 

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Discussion Starter · #13 ·
Get phase-phase voltage readings as it starts. Logging or min/max meter if possible.

What is the service situation, how far from the panel, size of feeders?
Feeder is less than 50' from idler motor and is #6's which I believe may be undersized according to manufacturer. I do know the idler motor was drawing around 25 amps on each leg while running.
 

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motors and controls.........
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A couple of thoughts here;

1) If this is a basic submersible pump (like a well pump), the motor will not like receiving its power from a phase converter. These are pretty 'high strung' motors and they have very little tolerance for voltage imbalance. I'd also megger the motor.

2) Depending of what type of pump it is, it might not start in reverse. Try swapping two of the motor leads and see if it'll start in the opposite direction.

3) Check the capacitors in the phase converter. There are usually a bunch of them in parallel, if one or more has become disconnected, the no-load voltage will be ok, but not ok under load. Test them for actual µfd vs. nameplate.

4) The B/Bs will seem grossly undersized. The load current goes through the secondary, not the primary. They usually come with either 12/24 or 16/32 secondaries. As a general rule, if the secondary current is more than the load, they'll be ok.

In your case (10HP motor at 208 volts; likely around 26 - 30 amps)
500/32=15.6 amps; too small
500/24=20.8 amps; too small
500/16=31.25 amps; ok
500/12=41.7 amps;ok.

Depending on the transformers supplied, you can buck off either 12 or 16 volts, but not 24 or 32.

Use only two B/Bs, if 3 are connected in a closed ∆, they will try to balance voltage, but due to their small size, they cannot. So at least one of them (more likely two) will burn up.

P.S. #6s are too small. The rated single phase current to the converter will be around 100 amps. The actual current with a 10HP load will be more like 50 or less.
 

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Discussion Starter · #15 ·
Ok went back out there today with fountain rep and here's what I happened-

He pulled it out of water, dismantled it and decoupled the motor from pump and motor worked. We spun the impeller by hand and it spun but not smoothly (not sure if that's normal). So we put back together and bump it and sure enough it worked. Finally get it out into water and now it would start pumping water but cut out about 2 seconds into it. The control panel has an integrated phase monitor device that was doing the cutting out. I'm not sure of the % tolerance it has as far as imbalance goes but obviously enough to trip it every time. I tried measuring the voltage phase to phase while running but was getting unreliable readings, which by the way, has me a bit frustrated with my Fluke 289, I used the Max/Min and would get a max of around 20 VAC, but would get around 225ish sluggishly when trying to manually read voltage. Is there a quick feature on that meter, to basically show real time readings instead of that awful delay? Surely the meters a nice instrument, I just haven't gotten used to it. Sorry to side track, basically the verdict I suggested was to possibly look into a VFD as a solution. This way we get the our 3 phase and also soft start capabilities. Am I on the right track? If so, you generally double the size of the VFD to compensate the phase loss....right? Any help is appreciated, as always.
 

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Bilge Rat
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If the control panel has a phase failure relay, and it's being fed by a phase converter, it will almost always trip under load. These relays are usually set at about 4% imbalance; a phase converter will almost always be more than that when its loaded.

Given that this is a submersible pump motor, I wouldn't run it on a phase converter at all. These motors are not very tolerant of anything other than reasonably balanced sine-wave power.

A VFD may very well be the best choice here. Yes, you'll need to double the VFD HP for single phase input, and be sure that the VFD will accept single phase. Most will, some won't.

Also, stay away from the cheap VFDs like you find on ebay. Generally speaking, with VFDs (and a lot of other equipment) you get what you pay for.

This won't be cheap, but it'll solve a lot of problems.

As far as soft-starting, a lot of VFDs can be programmed to ramp from zero to full speed anywhere from a fraction of a second to over an hour. Same thing with soft-stopping.

VFDs produce heat when they run, make sure to ventilate it properly.
 

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Discussion Starter · #18 ·
If the control panel has a phase failure relay, and it's being fed by a phase converter, it will almost always trip under load. These relays are usually set at about 4% imbalance; a phase converter will almost always be more than that when its loaded.

Given that this is a submersible pump motor, I wouldn't run it on a phase converter at all. These motors are not very tolerant of anything other than reasonably balanced sine-wave power.

A VFD may very well be the best choice here. Yes, you'll need to double the VFD HP for single phase input, and be sure that the VFD will accept single phase. Most will, some won't.

Also, stay away from the cheap VFDs like you find on ebay. Generally speaking, with VFDs (and a lot of other equipment) you get what you pay for.

This won't be cheap, but it'll solve a lot of problems.

As far as soft-starting, a lot of VFDs can be programmed to ramp from zero to full speed anywhere from a fraction of a second to over an hour. Same thing with soft-stopping.

VFDs produce heat when they run, make sure to ventilate it properly.
Great, thanks micro, I'll have to start sourcing & pricing that setup. Any recommendations for a lower end vfd that's suitable?
 

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A few of words of caution here.

1) Often, submersible pump mfrs will dictate a maximum acceleration time. This is because the pump bearings are dependent upon the water pressure as a lube and without it, the pump fries very fast. It will have a thrust bearing that lets it start, but within 2 seconds or so the pump must be at full speed or the damage starts. That shouldn't be a problem for the VFD to accomplish, but it just means you cannot leave them on the factory default settings.

2) Technically any VFD is capable of being run on single phase with proper de-rating, but what micromind is referring to is that some designers never anticipated doing that on larger drives and they didn't make the Phase Loss protection capable of being turned off. So to tell in advance, look at the manual BEFORE you buy it and make sure there is a parameter assigned to disabling the Phase Loss protection. If there isn't one, you will not be able to use that drive.

3) Some submersible pumps require Class 5 overload protection or you void the warranty (Franklin), most VFDs provide Class 10 and many are not adjustable. Double check that with the pump mfr. Frsanklin requires you to use their Subtrol unit to get the warranty, and I'm not sure if they are rated for use with a VFD or not, Franklin makes their own VFDs and are known to force people to only use their stuff.
 

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Discussion Starter · #20 ·
A few of words of caution here.

1) Often, submersible pump mfrs will dictate a maximum acceleration time. This is because the pump bearings are dependent upon the water pressure as a lube and without it, the pump fries very fast. It will have a thrust bearing that lets it start, but within 2 seconds or so the pump must be at full speed or the damage starts. That shouldn't be a problem for the VFD to accomplish, but it just means you cannot leave them on the factory default settings.

2) Technically any VFD is capable of being run on single phase with proper de-rating, but what micromind is referring to is that some designers never anticipated doing that on larger drives and they didn't make the Phase Loss protection capable of being turned off. So to tell in advance, look at the manual BEFORE you buy it and make sure there is a parameter assigned to disabling the Phase Loss protection. If there isn't one, you will not be able to use that drive.

3) Some submersible pumps require Class 5 overload protection or you void the warranty (Franklin), most VFDs provide Class 10 and many are not adjustable. Double check that with the pump mfr. Frsanklin requires you to use their Subtrol unit to get the warranty, and I'm not sure if they are rated for use with a VFD or not, Franklin makes their own VFDs and are known to force people to only use their stuff.
Good advice, this is a Franklin motor. I guess I can contact them first and see about getting vfd from them. Also, as micro mentioned, this will be outside, do you think a heating unit is absolutely necessary? If so, would it still be necessary if it ran 24/7?
 
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