45KVA portable transformer

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PowerdT

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Electrical Engineer
There is a 45KVA, 480V-208Y/120V step down transformer that will be used at military
port.

The primary power available at the shore is 480V, 3P, 3W with no ground.

How would you ground transformer? And the transformer is mobile
 
wording is the key
when you say "no ground"... do you mean no grounded conductor or no equipment grounding conductor ??
 
Is the 480 system ungrounded? With a Wye secondary that would be grounded but with no EGC on the primary a ground fault on the one leg of the 480 will do nothing which could be dangerous if the 480 is from a grounded system.
 
Is the 480 system ungrounded? With a Wye secondary that would be grounded but with no EGC on the primary a ground fault on the one leg of the 480 will do nothing which could be dangerous if the 480 is from a grounded system.
yes the 480V system is ungrounded
 
If your primary is 480V ungrounded system with only 3Wire and you need to step down the transformer to 208V, how do you wire it?
 
If your primary is 480V ungrounded system with only 3Wire and you need to step down the transformer to 208V, how do you wire it?
There is no code compliant way without an EGC on the primary side. Even ungrounded systems require EGCs. The only difference in the grounding and bonding requirements between grounded and ungrounded systems, is that an ungrounded system does not have a main or system bonding jumper.
Also not sure how you will get the required grounding electrode connection on the secondary for a portable system.
 
There is no code compliant way without an EGC on the primary side. Even ungrounded systems require EGCs. The only difference in the grounding and bonding requirements between grounded and ungrounded systems, is that an ungrounded system does not have a main or system bonding jumper.
Also not sure how you will get the required grounding electrode connection on the secondary for a portable system.
Navy standard shore power is 480V, 3P, 3W, ungrounded system and those MIL standard shore power cables carry only 3W so I guess there is no way to use this shore power to step down the voltage using the shore power
 
Navy standard shore power is 480V, 3P, 3W, ungrounded system and those MIL standard shore power cables carry only 3W so I guess there is no way to use this shore power to step down the voltage using the shore power
3pole, 3 wire does not mean that it can't have an EGC.
 
3pole, 3 wire does not mean that it can't have an EGC.
Right. For example, grounded 3P4W means three phase conductors and a neutral, which is a grounded conductor. The EGC is a grounding conductor and isn't one of the 4W.
 
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