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Bypass an off neutral regulator 1
- Thread starter stevenal
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Investigation is ongoing, but it appears the single phase regulator was bypassed and disconnected during an outage. When going back, power was needed to run it to neutral; so dispatcher said to close one blade. Lineman missed the "one" and closed both sides.
IMHO, you were lucky if the jumper is the only damage. Many years ago, my coop destroyed a regulator bank during the installation process. The story I got was that the installation was interrupted for some time due to weather. When work resumed, the control circuitry was turned on and some number of the (bypassed) regulators moved from neutral. All personnel concerned survived - the regulators did not, at the time the damage was thought to be a total loss. I understand that I missed a rather spectacular noise, light and finger pointing show.
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Bad! Very, very bad! Just don't do it...
Theory I've heard is that circulating current is more or less directly proportional to the # of taps by which the reg is offset from neutral; anecdotally, even on a single tap offset, the circulating current is reported to be so considerable as to be, as one lineman so eloquently put it, "ugly," to the point that my utility's standing instructions stipulate that the last resort to switching an off-neutral-tap regulator into service is to take an interruption on the line, open the bypass sw and close the reg isolating switches off pot, then return line to service.
Don't know if this helps or not...
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
Theory I've heard is that circulating current is more or less directly proportional to the # of taps by which the reg is offset from neutral; anecdotally, even on a single tap offset, the circulating current is reported to be so considerable as to be, as one lineman so eloquently put it, "ugly," to the point that my utility's standing instructions stipulate that the last resort to switching an off-neutral-tap regulator into service is to take an interruption on the line, open the bypass sw and close the reg isolating switches off pot, then return line to service.
Don't know if this helps or not...
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
davidbeach
Electrical
Anywhere other than neutral what you've got is a transformer with a turn-to-turn fault, the bypass being the "fault" path. The faulted turn(s) carry a very high current because there are few turns trying their darndest to do their part of the Amp-Turn balance; very few turns requires lots and lots of amps.
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- #7
So the plan was to energize from the (normal) load side. Operator insists he needed to bypass to do this. I don't see why locking it off wouldn't suffice. Then it could be run to neutral if need be, and never bypassed. Do you agree? And what size inverter would you need to power the motor from a truck battery?
Hmmm...I may have mis-read the OP...
Here's what I understand:
To switch a properly working in-service voltage regulator out of service without interrupting the supply to the downstream customers [although their voltage may not be all that great]:
1] Place the voltage regulator on manual control.
2] Drive to neutral tap.
Then, and not until then:
3] Close the bypass switch around the regulator, mostly unloading it [current divides inversely as impedance].
4] Open the load side disconnect switch, completely unloading the regulator.
5] Open the source side disconnect switch, removing the regulator from potential.
Return to service is the reverse sequence.
How in the situation being considered the taps would have moved during the out of service period is a mystery I'd want to get to the bottom of...
If the tap drive motor isn't working but the taps can still be cranked manually and your safety rules don't prohibit it, the same procedure can be followed but with the apprentice doing the grunt-work of cranking the taps.
If the taps are actually broken, you're euchred, and the only choice is to dump the feeder while switching the reg o/s - and unless lunacy runs rampant a defective regulator will never get switched INTO service...
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
Here's what I understand:
To switch a properly working in-service voltage regulator out of service without interrupting the supply to the downstream customers [although their voltage may not be all that great]:
1] Place the voltage regulator on manual control.
2] Drive to neutral tap.
Then, and not until then:
3] Close the bypass switch around the regulator, mostly unloading it [current divides inversely as impedance].
4] Open the load side disconnect switch, completely unloading the regulator.
5] Open the source side disconnect switch, removing the regulator from potential.
Return to service is the reverse sequence.
How in the situation being considered the taps would have moved during the out of service period is a mystery I'd want to get to the bottom of...
If the tap drive motor isn't working but the taps can still be cranked manually and your safety rules don't prohibit it, the same procedure can be followed but with the apprentice doing the grunt-work of cranking the taps.
If the taps are actually broken, you're euchred, and the only choice is to dump the feeder while switching the reg o/s - and unless lunacy runs rampant a defective regulator will never get switched INTO service...
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
Well, they can easily be moved if the line side blades/switches are closed from a powered bus. Also to add one step to crshears well detailed routine, I also turn the control power off after running it to neutral and verifying the position indicator and neutral light prior to bypassing. One vendor had a series of control panels that would occasionally decide to step in the manual mode. Needless to say catastrophic for a few end users. The mfg. made users aware and sent out labels to be placed on the front of the panel.
If I intend for it not to step, I do not want the control panel powered from any source.
Another option for a distribution feeder regulator is to simply tie to another circuit or substation and trip the breaker on the circuit with the inop regulator(assuming there is a breaker in front of it) and isolate it for service. For this I will usually cut the controls off on whatever step they are on.
Alan
If I intend for it not to step, I do not want the control panel powered from any source.
Another option for a distribution feeder regulator is to simply tie to another circuit or substation and trip the breaker on the circuit with the inop regulator(assuming there is a breaker in front of it) and isolate it for service. For this I will usually cut the controls off on whatever step they are on.
Alan
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- #11
So the regulator was operating normally on 2R when the outage occurred. Regulator was disconnected, both line and load sides; and locked off. Note that due to the outage, regulator was not run to neutral at this time. Switching occurred to pick up customers while line repairs were being made. Incident occurred when switching back to normal configuration following repairs. Bypass blade was closed to energize one span to an open cutout on the normal source side where the phasing was checked. Phasing checked good and the order was to close one blade on regulator to restore motor power so it could be run to neutral. Both blades were closed instead.
Clearer now?
Clearer now?
If I am understanding correctly, there appears to have need no reason to close the bypass at all. Line and load side switches could have been closed and then the breaker if at a substation. Sounds like it may be a single phase line and regulator down line from the station except that there seemed to be the need to check phasing. Even with the latter, still curious why the bypass needed to be closed. The regulator control would have been powered with just the line side energized.
Seems in either case a missed step was not to open the bypass immediately after verifying phasing and before closing anything else.....does that make sense with what you are seeing/hearing from the field folks?
Why not close the cutout and the line side regulator switch (no bypass or load side closed) and run it to neutral? Then it would have not been an issue to bypass.
Alan
Seems in either case a missed step was not to open the bypass immediately after verifying phasing and before closing anything else.....does that make sense with what you are seeing/hearing from the field folks?
Why not close the cutout and the line side regulator switch (no bypass or load side closed) and run it to neutral? Then it would have not been an issue to bypass.
Alan
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- #13
The single phase regulator is on a single phase tap off of a three phase system. I suspect that enough time had passed since the alternate feed had been used that it was prudent to recheck phasing prior to paralleling; eliminating the possibility that one of the taps had been moved to another phase some time in the past. Can't fault this decision, but I question the decision to close the bypass.
If regulator had been run to neutral, there would be no need to bypass. Just close in the other side and continue on.
If regulator had been run to neutral, there would be no need to bypass. Just close in the other side and continue on.
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- #15
It's an older installation with three individual disconnects. We have an S&C XL on a newer installation, but don't see how this would have changed the outcome. All blades are temporarily closed during the transition, so you still have a fault.
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