OT: vertical turbine pump issues

lesmar96

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Off topic, but I thought someone might have some good experience.

One of our customers is a water treatment facility to provide fresh water to the the town. They have 2 vertical turbine pumps that pump water up the hill into the water tank. Voltage is 480 and FLA is 120A.

Last Sunday, they suddenly reported that turbine 2 is making a terrible noise inside at the control panel. It is on an old Saftronics AS6 soft start.

When I arrived, they had it off. We put it in hand and it would try to start. The lights in the plant would begin flickering and the wiring in the conduits would buzz like crazy. My amp meter was showing 300-400s on each leg, but the amperage was very far from stable. We went out by the pump and listened to it for a few seconds out there and it made a terrible electrical buzz but it also had a mechanical noise like the rotor would be dragging.

At first I thought maybe the pump was jammed and we had a stall. But you could spin the pump shaft freely. Then we got to looking and noticed that the pump shaft was no longer connected to the rotor of the motor. Its the hollow bore style with the anti-reverse balls device on the top. We took the top cover of the motor off and all 4 3/8" bolts that fastened the motor to the pump were all sheared off. Odd. But both the motor and pump spun freely.

We also expected that at this point the motor should run okay, but it wasn't. A computerized winding test told us that while the motor megged fine, it had a winding-winding short. Also I ohmed the soft start from L1-T1, L2-T2, L3-T3 and the ohm readings were very far from balanced.

When we craned the motor out, we decided to pull the pump as well because we had the hunch that the pump shaft might have busted. And sure enough, that is what had happened.

So it is kind of a puzzle to us, it had been running fine, but suddenly we have a broken pump shaft, 4 sheared bolts, motor windings shorted, and a bad soft start. The customer insists that all the check valves were working. We noticed that for some reason all the balls were missing in the anti-reverse device, which would have allowed it to spin excessively in the wrong direction.

the pump is coming in to our shop for inspection, but the customer wanted to scrap the motor so we do not get to evaluate it.

We haven't seen this before. We are unsure what was cause and what was effect. Any thoughts on this??
 
Rughly 15-20 years ago, there were issues with the AS6 firing circuits and cold solder joints failing. This was the early days of lead-free solder, and I saw plenty of issues in the field similar to what you are describing. The scr's would misfire enough to shake the snot out of the motor, control cabinet wiring and everything in proximity.

Retire the starter. It's lived long enough. Now that they have allowed it to break other equipment by ignoring the ongoing problem, the starter is the least expensive item left!
 
Hi, I worked for a large water utility out west for 10 years. (Las Vegas Valley Water District) We had almost all 5kv motors and many that were vertically mounted for wells. The anti-backspin keeps the pump shaft from unscrewing from the motor. In your case the steel balls could have been removed at some time. If the motor starts to spin backwards upon shutdown, then there's usually a problem with the foot valve on the pump downhole. Some of our wells were 700' plus deep and that's a lot of water to go whooshing down the pipe through the pump impeller. If your starter was stopping and starting rapidly this could've caused the destruction you described.
As far as a new starter, we used all RVAT starters, both for the 5kv and some 480 motors. They seemed to work well. Most of the 5 kv gear had a 269 or 469 GE Multilin motor protection relay. The 480 gear used all 269 relays. These would prevent what happened to your system. Most of the RVAT starters for the wells and some pump stations used timers and relays to transition to across the line run mode, however the 469 Multilin can do this for you and have the motor transition at optimum current from start to run. Maybe worth looking into something like this. I left there in 2010 so I'm sure there is better equipment out there now for these type of starters. Hope this helps.
 
A possibility is that something jammed an impeller, locked the motor, snapped the coupling, and the current pushed the starter over the edge. Another possibility is that the lack of the backspin preventer allowed the pump to rotate backward at high rpm. If the starter called for it to run while it was in backspin several times the normal torque and amps can result, raising heck as described.
 
Single speed motor? I have seen one have a bad day when high speed was wired in the wrong direction.... ran great until high speed kick in
 
Rughly 15-20 years ago, there were issues with the AS6 firing circuits and cold solder joints failing. This was the early days of lead-free solder, and I saw plenty of issues in the field similar to what you are describing. The scr's would misfire enough to shake the snot out of the motor, control cabinet wiring and everything in proximity.

Retire the starter. It's lived long enough. Now that they have allowed it to break other equipment by ignoring the ongoing problem, the starter is the least expensive item left!

Yes, we did. We replaced the soft start, motor and pump.

Single speed motor? I have seen one have a bad day when high speed was wired in the wrong direction.... ran great until high speed kick in

Interesting thought, but this was a single speed.
 
Was the pump shaft broken or did it unscrew first and then break?
If the anti reverse bolts were not properly torqued they will loosen every time the pump stops and then eventually shear off.
A single phase or phase reversal can cause the motor to reverse rotation and with the anti reverse bolts in a weakened state they will shear off.
I don't know what soft start you installed but i would program the phase failure/reversal fault to require a manual reset.
I have seen hollow shaft vertical turbine motors that have not run for extended periods have the rotor slots rust and swell and cause shorted windings. Those pumps should have winding heaters if they are located outdoors.

This document give more information on the anti reverse coupling.
https://www.gepowerconversion.com/s... Installation Vertical High Thrust Motors.pdf.
 
it looks like you had a sudden phase reversal while it was running
I have seen pump shafts snap with a phase reversal
I can see the motor winding taking the hit with those stresses
Dose the soft start have a bypass contactor after it gets up to speed.
You may want to look at the supply
 
Was the pump shaft broken or did it unscrew first and then break?

we have not taken the pump apart yet, so we are not sure of the shaft damage inside the pump. The only way we know it is broken now is because we can spin the shaft and can see the impellers are not moving on the bottom end of the pump.

it looks like you had a sudden phase reversal while it was running

I thought of this too, but I wasn't sure if a dying soft start would have the capability to completely reverse a motor?
On the bypass contactor........this one does not have an external bypass contactor and i didn't take it apart or read the documentation enough to know if it had an internal one.
 
A Soft Start can never reverse the rotation / phase, most if not all are SCR's
on that size i would think they have a bypass contractor the power loss in the SCR's would be fairly high about 100 watt per phase or more
my thinking was somebody working on the feed lined switched the feed for some reason and the phase rotation was reversed it would only take a second or two then switched back when it became apparent. in my area they have switches on the primary to connect if the have to isolate sections
 
What Gary said first is the likely root cause; a failure in the gate circuit of the Soft Starter. Although rare, that used to happen on the old Saftronics, Benshaw and Motortronics analog soft starters because they all used a similar "thick film" gate firing logic board (a predecessor to microprocessor based firing circuits). When that went bad, the firing pattern of the SCRs would go haywire and cause the motor to "shake" violently back and forth. If left to do this for long, it would tear out the balls on the back spin ratchet, turned them to metal shavings in the grease / oil, then when they were gone, it starts to act on the shaft until that breaks. On the old Motortronics units that did this, the breaker or fuses would usually clear before the mechanical damage was severe because it would pull locked rotor current during the event. But on the Saftronics and Benshaw, which both used the same Zero Cross detection circuit developed by Saftronics in South Africa, the difference in how and when the SCRs fired would sometimes not create enough of a current surge to trip anything and continue on unabated for hours or days until something mechanical would break.

Bottom line, that old AS6 outlived it's usefulness.
 
thanks for all your feedback. it happened on a Sunday and no one was here, until they got a low water alarm from the water tank
 
They should have gotten an alarm when the pump failed and the 2nd Backup pump should have started automatically and they should have gotten an email
It sounds like a good time to talk to them about a system upgrade
 
They should have gotten an alarm when the pump failed and the 2nd Backup pump should have started automatically and they should have gotten an email
It sounds like a good time to talk to them about a system upgrade

Downhole pumps don't usually have a standby - it gets pretty cozy in the well.
 

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