# Do I have a bad transformer?



## Polishavenger (Dec 25, 2012)

Howdy all.  I have a Gorton mill I'm trying to power.  It has a 440V-only spindle motor, as well as a down-feed motor, cross-feed motor and coolant pump motor.  It has all the original electrical panel and power supply hookup with fuses.  I'm running my 220V shop supply to a Phase Craft RPC control box which starts (and channels the three phase power from) a 1725 rpm 5hp motor.  The three phase generated measures about 256V from L1 to L2, L2 to L3 and L3 to L1.  I run this through a fused disconnect box (Cutler Hammer, I believe), then on to the X1, X2 and X3 of a Square D transformer (model 6T5F).
This is a link to a little schematic.
http://static.schneider-electric.us...d General Purpose-Resin Encapsulated/3544.pdf
According to what I'm looking at, H2, H4, and H5 used as outputs should give me 456V.  Measuring in the same manner as I used for my 230V lines, I'm getting 256V, 256V and about 500V.  Is there something I'm missing, or is this transformer shot?
Thanks for any help you might be.....I'm pretty new to this electrical stuff.
-Mark


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## rdhem2 (Dec 25, 2012)

Check your tap connections and insure you are reading H to H to H.  You obviously have a delta conn so read deenergized with an ohm meter the three coils making up the connection.  You should have equal continuity across all three coils.  A varience of more then 5% to 10% indicates a bad winding.  I am being generious here as I do not know what quality of ohm meter you have.  The better the meter the smaller the difference should be.   :thinking:


:holdphone:
12/26/12 edit---I finally looked at the schematic you supplied.  Your xfmr is an open delta connection, meaning it only uses two windings to produce three phase.  You should check your incoming voltage under load not open voltage present as it will probably drop when you power up your machine.  In so saying I would use the 480v setting right off then check it under full load.  Change the taps if necessary then.  Better a few too many little volts then not enough.  10% from rated voltage is the industry norm from the power company so that is 48 volts on your end.  Good luck.


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## Polishavenger (Dec 27, 2012)

After borrowing a friend's Fluke meter to check the ohms, I decided that I would start from the beginning, which I thought that I'd already done.  Obviously, I was wrong.  The breaker box between my RPC control and the transformer had a brand new fuse go bad, thereby causing my problem.  I bridged the fuse and, lo and behold, everything's perfect!  Voltage, under load, at the milling machine reads 430-440-450 now.  That close enough?  Should I aim for the higher voltage still?  Thanks for your input!
-Mark


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## mattinker (Dec 27, 2012)

Hi,

it looks like you've got a transformer problem, between H2 and H4, H2and H5, and H4 and H5 you should have your 456volts (approximately, the voltages will vary, time of day etc,). You could also try testing H6 and H2 , H2 and H7 and  H7 and H6, to confirm the differences, if the H2,H6 and H7 combination works and isn't too far from 440volts, it would be OK. I am sceptical as it looks like you're getting your input voltage on two of the pairs. 

By the way, small digital multimeter cost about €6 (maybe $8US?) worth the investment, much less costly than a fluke if one gets it wrong!

Regards, Matthew


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## Polishavenger (Dec 27, 2012)

Matthew, my cheapo meters were giving me numbers that I couldn't help thinking weren't where they should be...I needed to defer to a higher power.

Today 2-4-5 gives me 460-453-464 at the mill before turning on the spindle or feed motors.

At the transformer with 2-4-5 I get 463-455-466
                          with 2-6-7 I get 438-430-441
                          with 1-2-3 I get 485-477-489

-Mark


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## mattinker (Dec 27, 2012)

Polishavenger said:


> Matthew, my cheapo meters were giving me numbers that I couldn't help thinking weren't where they should be...I needed to defer to a higher power.
> 
> Today 2-4-5 gives me 460-453-464 at the mill before turning on the spindle or feed motors.
> 
> ...


Mark,

point taken about your cheepo meters! 

So your getting something similar on each pair of phases. no longer "256V, 256V and about 500V" I would have thought this would indicate that your transformer is functioning normally. To be quite honest I couldn't tell you how critical it is, but I wouldn't think that a difference of eleven volts is going to change much! I would have thought that you would find a five or six volt difference at the in-put of your of your transformer. My three phase mains is supposed to be 380volts, at the moment, it's around 400volts. I use 440volt UK equipment on my "380" supply. Your biggest difference of 2.5%, *I will not be held responsible*, but I personally would try it,on the 2-6-7 I can't see what it could do beyond running one set of windings a little hotter than the rest!

Try it at your own risk, but I really can't see it not working! Let me know how you get on.

Regards, Matthew


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## Polishavenger (Dec 27, 2012)

I think I'm gonna stick with the 5% overage that I'm getting currently...the mill seems happy enough for my taste.
Thanks for the help guys.
-Mark


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