500 kVA step up transformer

I'm working on an application that will require a 480v delta to 2400v delta step up transformer. Are there any special issues I should consider given there is no grounded
conductor (neutral) on either the primary (480 v) or secondary (2400v) side of the transformer? Are these transformers commonly available?
Dave
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Dave wrote:

You might consider a zig zag transformer to establish a functional false neutral that provides some relief from voltage build up caused by arcing faults. An old audio tape from the Joe McPartland era discusses what happens when an ungrounded delta 480 volt system encounters an arcing ground fault. In one such case the build up of voltages became so high that all the transformers supplying two industrial plants were ruined by insulation punctures when an arcing ground fault caused the voltage to build up to several thousand volts. A zig zag transformer is the common cure for this type of installation. Several years ago I ran into a zig zag at the metering station on the Trans Alaska Pipeline near the Petro Star Refinery in Valdez, Alaska. It allowed a rather long run of three wires for a delta connection in place of four wires.
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Dave wrote:

when in need of HV power transformers i first look to Peter Dahl http://www.pwdahl.com /
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| I'm working on an application that will require a 480v delta to 2400v delta | step up transformer. | Are there any special issues I should consider given there is no grounded | conductor (neutral) on either the primary (480 v) or secondary (2400v) side | of the transformer? Are these transformers commonly available?
What reason would preclude the use of a transformer with a WYE secondary that ran at 1386/2400 volts with the neutral point grounded? Otherwise I like Gerald's suggestion of a zig-zag transformer.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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snipped-for-privacy@ipal.net wrote:

Phil is right. As long as you are not connecting this transformer in parallel with a unit that is Delta connected, you should not have a problem using a transformer that has a voltage rating of 480 Delta - 2400Y/1386. Also, you need to take into consideration the equipment to which the 2400Y/1386 secondary will be connected. Are there any special requirements from the manufacturer of the equipment? Is it a motor? If so, you shouldn't have any problems. If the equipment includes electronics and controls, you really should check with the manufacturer of the equipment.
We occasionally get asked for distribution transformers with a Delta secondary vector. Because we get so few calls for that configuration (not the small dry types but oil filled pad mounts, etc.), we only stock units with a Wye secondary vector. Typically, the equipment connected does not "know" whether it is connected to a Delta or a Wye transformer. The phase-to-phase voltage is the same in either case.
Using a zig-zag transformer to derive a neutral is a possible solution but one that I think would be an unnecessary cost.
Steve Lockridge Manager Alfa Transformer
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|

So what's the difference to the load between a wye connected with the neutral lifted and a delta? Seems like with just the three conductors coming off, it can't make a difference to the load.
Mind you, if you have another connection to the primary or something, then a delta or wye connection will introduce a different phase shift from the primary voltage, but other than that, can't see what the difference would be to the load.
Or am I having a 'senior moment' and overlooking something?
daestrom
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wrote:
| So what's the difference to the load between a wye connected with the | neutral lifted and a delta? Seems like with just the three conductors | coming off, it can't make a difference to the load. | | Mind you, if you have another connection to the primary or something, then a | delta or wye connection will introduce a different phase shift from the | primary voltage, but other than that, can't see what the difference would be | to the load. | | Or am I having a 'senior moment' and overlooking something?
I don't know if this is a factor in the OP's situation, but I would think that if it is, he should know about it. If the motor and control system will have a high level of harmonics, this could put a lot of current on the neutral point in the WYE secondary. But, this is also why there are transformers specifically made to deal with this. And this is only an issue with the transformer itself. A WYE secondary should otherwise supply voltage just as good as that of a DELTA secondary (other that for the phase difference if there is some interconnection elsewhere).
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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