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Old 02-22-2012, 07:58 PM   #1
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Default 480v high leg(?) delta

How will this type of 480 three phase affect a motor? Will the high leg toast the winding it is attached yo?
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Old 02-22-2012, 08:00 PM   #2
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I meant "to".
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Old 02-22-2012, 08:09 PM   #3
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no .
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Old 02-22-2012, 08:30 PM   #4
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what transformers are you using to get 480v high leg delta?
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Old 02-22-2012, 08:36 PM   #5
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Never heard of it.

Open leg (Open Delta) maybe?

Please describe the context of this, where are you getting the idea that you have "480V High Leg Delta"?
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Old 02-22-2012, 08:38 PM   #6
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It is a service a customer had put in for an electric submersible pump. There are two transformers on the pole, each putting out 240ish volts to two legs and tied in together somehow to make up a third leg at about 480v.
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Old 02-22-2012, 08:39 PM   #7
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It is just a guess at what the voltage is actually called, please forgive my ignorance.
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Old 02-22-2012, 08:42 PM   #8
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460 between phases
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Old 02-22-2012, 08:47 PM   #9
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Hmmm... a quick Google search brings up some references in DIY sites where some people apparently refer to 480/277 as "High Leg", but that would NOT be a Delta service, that is Wye. So it is for DIY sites I guess. No big surprise.

There is such a thing as 240/120V 3 phase 4 wire service which is often called "High Leg", "Stinger Leg" or Red Leg" delta. In that arrangement it is a Delta transformer in which one of the 3 delta windings, usually A-C, is center tapped and grounded for a neutral so that you have 240V Line to Line from A to C and 120V between either end and neutral. The "High Leg" name comes from the fact that the phase to ground voltage on the remaining leg, i.e. B phase, has no reference to ground and so will float at around 80% of the L-L voltage, i.e. 215V on a 240V service. If you try to connect a single pole breaker to it, you get "stung".

480/277V is totally different. It's a true Wye service where any phase to neutral is going to be 277V.
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Old 02-22-2012, 08:50 PM   #10
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480 open delta? Yuk. Didn't even know it was done.
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Old 02-22-2012, 08:56 PM   #11
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480 open delta, thank you.
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Old 02-22-2012, 08:58 PM   #12
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Is there any reason this type of voltage would affect the performance of longevity of a motor?
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Old 02-22-2012, 08:58 PM   #13
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Quote:
Originally Posted by jeremievc View Post
It is a service a customer had put in for an electric submersible pump. There are two transformers on the pole, each putting out 240ish volts to two legs and tied in together somehow to make up a third leg at about 480v.
Sounds like an Open Delta. You are probably measuring 240V line to ground, which is erroneous. The two transformers are making up a 480V delta service with an open jaw. It's less efficient so the transformers have to be over sized to avoid a serious imbalance, but it saves on the cost of the 3rd transformer and more importantly on far flung sites, that 3rd wire on the primary side for the utility.

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Old 02-22-2012, 09:03 PM   #14
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Quote:
Originally Posted by jeremievc View Post
Is there any reason this type of voltage would affect the performance of longevity of a motor?
Yes, the voltage is often not balanced very well and I'm suprised an ESP would allow it. Has the owner checked with the pump supplier? Some of them, such as Franklin, will void the warranty if there is more than a 2% phase voltage imbalance. But he may not have a choice anyway, the cost of that third wire might be ridiculously prohibitive, as in 10's of thousands of dollars.
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Old 02-23-2012, 01:11 AM   #15
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Think of it as a 120/240 3 4 wire open delta, but operating at double the voltage.

I've seen two of these so far, both supplying 3 motors in remote locations.
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Old 02-25-2012, 01:20 AM   #16
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seen plenty of 120/240 open deltas but never a 240/480 open delta. now I know they are out there somewhere.
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Old 02-25-2012, 02:24 AM   #17
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It was my first time seeing it. This was about a two mile run made specifically for an ESP set in a wet well that is fed by a natural water source. The property owner is quite wealthy and has a system of piping and valves supplying various ponds and water features on his property. Really something to behold quite frankly.
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Old 02-25-2012, 06:58 AM   #18
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Quote:
Originally Posted by jeremievc View Post
How will this type of 480 three phase affect a motor? Will the high leg toast the winding it is attached yo?
If you are getting 460 phase to phase, how would that be a problem for the motor?
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Old 02-25-2012, 02:37 PM   #19
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If you are getting 460 phase to phase, how would that be a problem for the motor?
A 3 motor cares about phase to phase voltage. Nothing else. It doesn't care about any voltage to ground.....well, within reason.......

If the supply is a grounded delta, 3 wire or four, it doesn't matter at all which lead is connected to the grounded phase or the high leg.
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Old 02-25-2012, 03:07 PM   #20
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A 3 motor cares about phase to phase voltage. Nothing else. ....
But motors do care about voltage BALANCE, because unbalanced voltage creates negative sequence currents that cause counter rotating torque in the rotor which acts against the normal torque. That means that for any given amount of power, the motor is going to heat up more rapidly and it's entirely possible to burn up a motor without ever exceeding the FLC, so the overload relays don't protect it. That's why a lot of ESP (Electric Submersible Pump) mfrs don't allow more than a 2% voltage imbalance, they don't have any "fudge factor" designed into their motors (because of size and weight that would entail).

Open Delta power systems are inherently unbalanced, but the amount varies with loading on the transformers. If the utility over sized the transformers enough it may be OK enough for that ESP, but I almost NEVER see that happen.

So jeremievc,
If you want to look out for your customer, take a voltage reading under load and if there is more than a 2% imbalance, let him know that if the pump motor smokes, the ESP mfr may not honor their warranty. Many of them are like that, Franklin, the largest, is one of them.
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