closed wye delta to wye wye keeping rotation

[Arc Blast]

So I had an outage I show up and find a bad transformer
In a wye delta bank the other two pots are covered in oil. I opt to just change out the bank. Company policy requires any new banks going up to be wye wye whenever possible. So I am unable to check rotation and going to the wye wye bank. Is there a way to make sure you get the rotation right every time in this case using vectors or other means or suggestions.

[Trouble1]

You may have been able to get rotation with one transformer out, especially if the motors were still spinning. On delta secondaries you can still get rotation, if wye secondaries then the motors will have to be running still to get rotation. I read that somewhere, but never actually tried it.

The only foolproof way I know of is to shut off all three phase breakers and leave one breaker on that controls something that will not be damaged by reverse rotation and then go check that piece of equipment. It will have an arrow somewhere or air will be sucking instead of blowing, or if it's an elevator/lift it will not work. That's how I do it. Also it's good to have the electrician there because he can pick what equipment to check.

If there is absolutely nobody around to help in the building, then we leave them off until a maintenance guy or electrician shows up.

[Pootnaigle]

Umm yes they make a rotation testor that will indicate rotation when hooked to the load also its hard to read because it has some lites that dont show up well in daylight

[urban1095]

So I had an outage I show up and find a bad transformer
In a wye delta bank the other two pots are covered in oil. I opt to just change out the bank. Company policy requires any new banks going up to be wye wye whenever possible. So I am unable to check rotation and going to the wye wye bank. Is there a way to make sure you get the rotation right every time in this case using vectors or other means or suggestions.

We always check rotation with a rotation meter, and usually mark it in meter can. You could run it open delta to get rotation. What's the big deal about delta sec.?

[Electriceel]

All new construction we are to get rotation and leave it in meter sockets, CT cabinets of each customer on that bank.
Wye secondaries only for new customers.

Not sure why the utility would up and change existing customers secondary voltages, their could be some issues with customers old equipment and motor starters.

[Arc Blast]

Our coops main customers are all farms with big irrigation pumps we require them to use motor savers so if the voltage runs excessively high or low or if you lose a phase it shuts the motor off to keep them from burning up. Were changing them out I guess because the wye wye banks are supposedly more efficient. Also the customers equipment doesn't see the phase to ground voltages of the banks. The 240 volt or the 277. I dealt with this situation again today and I think I have it figured. All our x formers are subtractive polarity. If the h1 are the energized bushings on the wye delta bank then the service leg moves to the can with the x1Bushing that is directly below the h1. So all your service legs move counterclockwise on the wye wye bank to keep rotation. This worked for me today. So in theory if your h2s were the energized bushings on the wye delta your service legs would move to the tubs clockwise on your wye wye banks. I am certain its just a matter of time till I get a chance to test this theory.

[rob8210]

I have not built a new bank with delta secondary voltage in many years. The utilities here want to supply a neutral to the customer, its up to the customer whether or not he uses it. I do remember a commercial plaza feed from a 600v delta secondary bank that was a constant trouble call, grounds on the secondaries blowing fuses. Problem was there were 10 or 12 customers off this bank. Made for interesting trouble shooting!

[Darkenedforest]

It seems to me in theory the rotation shouldn't change if all other factors are the same.

Your primary is rotating in one particular direction. Call it clockwise ABC. In a particular moment in time if A has a phase angle of 0 then secondary a should also have a phase angle of 0 (or 30° angular displacement in the case of wye delta, but for the sake of the explanation that doesn't matter because it's still proportional). Now as the angle of each phase changes B is then next to reach an angle of 0 and that causes a phase angle of 0 to be induce on your secondary coil b. Finally C reaches angle 0, thus inducing a phase angle of 0 on c. A coil is a coil whether it's x1 to x2, x1 to x3, or x1 to x75. So it follows that if the primary is rotating the same in each scenerio then it would be inducing that rotation onto the secondaries abc of each bank the same.

As to the polarity, that should not affect the rotation. Polarity tells you the direction the secondary coil is wound relative to the primary coil but that coil will still be at a particular phase angle relative to the primary coil. So abc should be the same as ABC, the current will just be flowing in the opposite direction.

Of course it's entirely possible I am completely wrong.

[trigger]

We have always had the habit of writing the phasing in the meter ses ABC and a arrow with direction of CW or CCW. All sec color taped or older apps taped 1-2 or 3 tape marks with black or gray tape

[Old Line Dog]

So I had an outage I show up and find a bad transformer
In a wye delta bank the other two pots are covered in oil.

Is the Oil on the other 2 transformers from the blown one? Which one Blew on the closed Delta? One of the wing pots or the main pot? Why did you opt to change all 3 Transformers?