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Delta-delta Transformer Voltage Problems

34592 Views 3 Replies 4 Participants Last post by  John Valdes
I Have A Three Phase Delta-delta 480vac To 240vac Transformer. This Transformers Has Me Concerned Due To The Voltage Readings To Ground. This Transformer Feeds A 3 Wire 240vac Panel.

When We Read Phase To Phase It Reads 240vac. I Measured Phase A To Ground And Read 10vac. Phase B To Ground Was 240vac, And Phase C To Ground Was 240vac. Phase A Increased To 120vac While Phase C Decreased To 120vac. We Used Two Meters And Witnessed Simultaneous Voltage Change On Those Two Phases.

These Connect Numerous Loads Which Do Not Seem To Be Effected By The Voltage Fluctuating. Once In Awhile The Machines Blows An Incoming Fuse, But Does Not Trip The Breaker.

I Know That This Is An Ungrounded Delta-delta Transformer. Do I Need To Ground One Phase Of The Secondary? Is It Possible That The Transformer Is Breaking Down?

P.s. We Are Only Using Single Phase 240vac Loads And Three Phase 240vac From This Panel I Mentioned Above.:(

Thanks For Suggestions
1 - 1 of 4 Posts
Reading voltages to ground do nothing but confuse people. However, you did realize the secondary was not grounded, which it should be. The XFMR needs to be grounded too.

What advantage does a delta to delta XFMR provide? Delta to wye is the way to go. Especially in an industrial environment. Many electronic devises such as AC drives do not operate well on delta derived sytems. Plus you get a true neutral.
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