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Transformer Testing Procedures

Transformer Testing Procedures

Transformer Testing Procedures

(OP)
I want to determine transformer efficiency. I have done an short circuit test to get the losses. Then I connected the transformer to a resistive load which was set to draw the full load rated current in the secondary. Using two wattmeters, I measured the primary watts and the secondary watts to determine efficiency. My problem is this - the difference between the wattmeters indicates the losses but this figure does not tie up with the losses I got when I performed the short circuit test. What am I doing wrong? Any help would be greatly appreciated.

RE: Transformer Testing Procedures

I don't know exactly what sort/size transformer you're trying to measure, or how you're carrying out your measurement but a short circuit test won't account for the no-load/magnetising losses.

RE: Transformer Testing Procedures

(OP)
Hi mgtrp, thankyou for your input. I am testing a 240:24 160VA torroidal transformer. To determine the total losses, I calculated the full load current (6.67 amps) then placed a short circuit across the secondary winding and applied an ac voltage until a current of 6.67 amps was recorded in the secondary circuit. I had placed a wattmeter in the primary circuit to measure the total losses (iron + copper). measure the iron losses (energy + magnetisation), I supplied the rated voltage to the primary with the secondary left open-circuit.  From (total losses - iron losses) I can determine the combined copper losses in both primary and secondary.  

RE: Transformer Testing Procedures

Measuring input and output power is not a very accurate way to determine losses.  If your measurements are each ±1% accuracy, then you could measure anywhere from 2% power gain to 2% loss if the transformer had no losses.
 

RE: Transformer Testing Procedures

Use the two Watt meters. Apply rated voltage. Read no-load losses at no load. Connect various loads of 25%, 50%, 75% 100% and any other percentage load at which you wish to calculate the efficiency.
 

Bill
--------------------
"Why not the best?"
Jimmy Carter

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