Open Delta phase rotation

[Electromatic]

My town had a partial power outage a couple of weeks ago, and, after power was restored, one pump station had reverse rotation from the utility. Two other stations on the same poco (utility) circuit weren't affected. The station that was reversed is the only one of the three that is fed by an open delta transformer.

I don't have my head fully-around open delta systems. Is there some strange way that they can change rotation?
The poco lineman/troubleshooter was flummoxed, and the engineer was on vacation. [literally]

 

[ActionDave]

Interesting question. I'm just a wire pulling grunt so I will be open to any correction but, open delta or not, I don't see how rotation could spontaneously change just because the power went out. Something had to change, wires got swapped somewhere.

 

[hillbilly1]

Most likely the utility made a mistake-tap somewhere and flipped a phase. I repaired a feed from a padMount transformer that got knocked off its pad by a car. The lineman said they don’t mark the phase connections at the transformer, so I would have to check on my end. Luckily, they got it back right.

 

[don_resqcapt19]

The utility did some upgrade work many years ago on a circuit the fed one of our town's deep wells. That well had a shaft driven submersible pump. The utility got the rotation wrong and the reverse rotation spun the shaft apart dropping the pump down the shaft. It took the well company over a week to fish everything out and put it all back together. The utility did pick up the costs.

 

[ptonsparky]

The phase monitors we used prevented accidental reversal, if installed correctly.

 

[Joethemechanic]

The utility did some upgrade work many years ago on a circuit the fed one of our town's deep wells. That well had a shaft driven submersible pump. The utility got the rotation wrong and the reverse rotation spun the shaft apart dropping the pump down the shaft. It took the well company over a week to fish everything out and put it all back together. The utility did pick up the costs

Those are supposed to have a non-reverse rotation ratchet on them. Its a mechanical ratchet mechanism mounted on the tail end of the motor. But yeah they do fail, or get removed. From what I was told they are really there to prevent a column of water falling down the pipe and spinning the pumps backwards and over speeding the whole system. But normally if someone screws up phase order it will just trip the overloads when it goes full locked rotor current. I had nightmares fishing pumps out until an old timer from Gould's Pumps told me how to make a retrieval tool out of pipe and old leaf springs. It worked great, you have to drop it and the springs on the inside of the pipe lock on a coupler. Works better on a friction crane than a hydraulic crane because you can drop it faster. I had to build a trip mechanism to use it on a hydraulic, and it was a little scary.

 

[kwired]

From what I was told they are really there to prevent a column of water falling down the pipe and spinning the pumps backwards

Less of a problem on a municipal well during normal operations anyway as the pipe usually remains full of water even when not running. Could be a problem during maintenance operations where they end up opening the pipe and therefore have to let it drain back.

Field irrigation almost always drains back when not in use and could unthread an impeller from the shaft if you don't have a means of stopping shaft from spinning

 

[kwired]

My town had a partial power outage a couple of weeks ago, and, after power was restored, one pump station had reverse rotation from the utility. Two other stations on the same poco (utility) circuit weren't affected. The station that was reversed is the only one of the three that is fed by an open delta transformer.

I don't have my head fully-around open delta systems. Is there some strange way that they can change rotation?
The poco lineman/troubleshooter was flummoxed, and the engineer was on vacation. [literally]

The two phase conductors had to been swapped or even just one of them got moved to the other phase that wasn't connected to this before.

Open delta output fed by two phase conductors and the neutral on the primary still have a rotational relationship and changing any two around reverse the secondary phasing. Swapping an existing phase with the previously unused third phase conductor likely changes direction as well.

Whatever they did did not effect phasing of the entire town just whatever is downstream from the change. Any other three phase customers on same section of line likely saw reversal as well. Single phase customers wouldn't had any changes.

 

[Joethemechanic]

Less of a problem on a municipal well during normal operations anyway as the pipe usually remains full of water even when not running. Could be a problem during maintenance operations where they end up opening the pipe and therefore have to let it drain back.

Field irrigation almost always drains back when not in use and could unthread an impeller from the shaft if you don't have a means of stopping shaft from spinning

The relative torsional loading on the line couplers is still trying to tighten them because the torque produced by the pump acting as a turbine makes the pump the mechanical source and and the motor the load.

Think of a bolt and nut in a vertical hole.
Looking from the top turning the bolt head (on top) you rotate clockwise to tighten. Bit still viewing from the top, if you put a wrench on the nut on the bottom from your perspective you are rotating counter clockwise to tighten

 

[hillbilly1]

The two phase conductors had to been swapped or even just one of them got moved to the other phase that wasn't connected to this before.

Open delta output fed by two phase conductors and the neutral on the primary still have a rotational relationship and changing any two around reverse the secondary phasing. Swapping an existing phase with the previously unused third phase conductor likely changes direction as well.

Whatever they did did not effect phasing of the entire town just whatever is downstream from the change. Any other three phase customers on same section of line likely saw reversal as well. Single phase customers wouldn't had any changes.

That’s what I’m thinking, could have been load balancing, and the lineman or engineer didn’t think about any open deltas on that line, because it was only two phases. They may have moved one to the third phase at the beginning of the line split.

 

[Jraef]

I once got called out to a lumber mill in Washington State that had the utility line swap rotation after a storm took down a primary. It affected the entire area, but of course only manifested in the industrial plants. It wrecked a bunch of their machinery, but the utility insurance covered the cost. They had zero phase monitoring installed up to that point, the plant was about 80 years old and it had never happened up to that point, so the concept of that happening had never occurred to anyone. I got the contract to come up with a system to make sure it didn't happen again. They wanted to go with a shunt trip on the main breaker tied to a phase monitor relay, to kill power to the entire mill if it happened again. I talked them out of that because they were also using the insurance money to optimize the plant by using a lot more VFDs, which don't care about rotation, and soft staters, which had phase rotation protection built-in. So we settled on only installing individual phase monitors on the few remaining machines that needed it.

 

[hillbilly1]

I once got called out to a lumber mill in Washington State that had the utility line swap rotation after a storm took down a primary. It affected the entire area, but of course only manifested in the industrial plants. It wrecked a bunch of their machinery, but the utility insurance covered the cost. They had zero phase monitoring installed up to that point, the plant was about 80 years old and it had never happened up to that point, so the concept of that happening had never occurred to anyone. I got the contract to come up with a system to make sure it didn't happen again. They wanted to go with a shunt trip on the main breaker tied to a phase monitor relay, to kill power to the entire mill if it happened again. I talked them out of that because they were also using the insurance money to optimize the plant by using a lot more VFDs, which don't care about rotation, and soft staters, which had phase rotation protection built-in. So we settled on only installing individual phase monitors on the few remaining machines that needed it.

I seen that done on an old high rise in downtown Atlanta, apparently to protect the chillers, but killed the whole building. I didn’t think that was a really good idea. Monitor went bad, and did exactly that!

 

[Joethemechanic]

Less of a problem on a municipal well during normal operations anyway as the pipe usually remains full of water even when not running. Could be a problem during maintenance operations where they end up opening the pipe and therefore have to let it drain back.

Field irrigation almost always drains back when not in use and could unthread an impeller from the shaft if you don't have a means of stopping shaft from spinning

The relative torsional loading on the line couplers is still trying to tighten them because the torque produced by the pump acting as a turbine makes the pump the mechanical source and and the motor the load.

Think of a bolt and nut in a vertical hole.
Looking from the top turning the bolt head (on top) you rotate clockwise to tighten. Bit still viewing from the top, if you put a wrench on the nut on the bottom from your perspective you are rotating counter clockwise to tighten

Thinking about this a bit, I could still see the possibility of it coming unscrewed. At some point when the water column had drained, the reverse rotation will start deaccelerating and because of the large rotating mass of the motor's rotor storing a bunch of energy especially if it overspeeds, then spinning rotor will again become the driver, and the impeller/impellers will be the driven again unscrewing everything'

Actually centrifugal pumps will still pump when driven backwards, just with crappy efficiency, reduced head and flow. I've come across that problem more than a few times, when someone got phases out of order somewhere electrically upstream. Lots of the operators in those places think that if rotation is reversed the pump will pump backwards so because it's pumping in the right direction they don't catch the problem