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Old 02-17-2015, 09:12 PM   #1
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Default Delta to wye

We have a 208 v wye service feeding a wye to delta transformer primary 208 secondary 550 delta the old motor is not starting and were getting a high inrush current. What am I missing? Any ideas?
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Old 02-17-2015, 09:15 PM   #2
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You could be missing a lot of things. Need more info.
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Old 02-17-2015, 09:19 PM   #3
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208 v 3 phase breaker feeding a custom wound transformer feeding out at 550 v delta three phase. The old delta 550 fed a disconnect which was killed and removed then fed from the new transformer output.is this what your looking for...
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Old 02-17-2015, 09:22 PM   #4
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Is it sized right? How big of motor? How big of service? What kind of motor is it? How is it started?
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Old 02-17-2015, 09:23 PM   #5
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200 amp 208 service feeding a 550 12 amp motor
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Old 02-17-2015, 09:26 PM   #6
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Elaborate.
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Old 02-17-2015, 09:28 PM   #7
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Main service 208 v wye feeding a custom wound transformer stepped up to 550 delta 12 amp rated motor
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Old 02-17-2015, 09:33 PM   #8
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What size is the transformer? How is the motor started? What style of motor is it? Is this a new setup or has it been running like this before it quit working?
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Old 02-17-2015, 10:15 PM   #9
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Does the motor move at all ?
Have you checked the starter system ?
Maybe not changing from start mode to run mode ?

Need more info ?
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Old 02-17-2015, 10:32 PM   #10
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Assuming (always a dangerous thing to do) that nothing other than the motor power source has changed: I would guess that the transformer is undersized.

What is the KVA rating of this transformer?

If this motor has a FLA of 12 amp and is started by an across the line starter, the transformer would need to be sized to handle a motor inrush of about 75 amps without an appreciable voltage drop.

If the voltage drop is more than 15 % on attempted starting, the motor may not start, the contactor will be damaged, and the motor life will be shortened.

A transformer supplying a single motor will almost always need to be oversized. If the motor is started by a VFD, the inrush will be considerably less, but the transformer would still need to have more capacity than the motor FLA.
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Old 02-18-2015, 12:41 AM   #11
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By the way, I hope you did NOT connect the X0 terminal on the 208Y side of that transformer... If you did, remove it immediately.

If your transformer is too small, you could be causing it to saturate with the starting current of the motor, which will cause a voltage drop, which reduces the starting torque of the motor and it can stall. But again, without DETAILS, as in NUMBERS on this equipment, we can only take stupid guesses.
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Old 02-18-2015, 06:13 AM   #12
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Quote:
Originally Posted by JRaef View Post
By the way, I hope you did NOT connect the X0 terminal on the 208Y side of that transformer... If you did, remove it immediately.

If your transformer is too small, you could be causing it to saturate with the starting current of the motor, which will cause a voltage drop, which reduces the starting torque of the motor and it can stall. But again, without DETAILS, as in NUMBERS on this equipment, we can only take stupid guesses.
Not only that but any phase angle imbalances or faults on the utility side will cause the transformer to act as a grounding transformer. It can either trip the OCPDs or burn up the unit.
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Old 02-18-2015, 06:25 AM   #13
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As was previously asked, did this setup every work properly?
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Old 02-18-2015, 07:04 AM   #14
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Yes set up worked on original power from utility
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Old 02-18-2015, 08:45 AM   #15
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Quote:
Originally Posted by fishinelectrician1 View Post
Yes set up worked on original power from utility
The utility furnished the 550V from their system or the utility installed the step up transformer?

In other words, did the system you are describing work as currently set up, or is this a new set up feeding a system that worked with a different set up and it's never worked with this setup?
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Old 02-18-2015, 08:47 AM   #16
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Are your voltages at the transformer correct? Are your voltages at your starter correct? Do you have a blown fuse or a bad breaker? What currents are you seeing? Does the motor spin freely by hand?
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Old 02-18-2015, 02:26 PM   #17
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I am starting to wounder if this guy is even an electrician.
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Old 02-18-2015, 04:57 PM   #18
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Yes I am was working not looking at the app
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Old 02-18-2015, 04:59 PM   #19
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Currently the outcome as of now I was sold an undersized transformer. Per an engineer at the factory.
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Old 02-18-2015, 05:13 PM   #20
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Nobody here magically knows your transformer KVA, type of motor starter, what the load driven by the motor is or even the horsepower of your motor. What kind of answer do you really expect?
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