Measurement of Transformer Losses by 3 Wattmeter Method

look at this information http://www.osun.org/three+wattmeter+method-pdf.html

While 2 wattmeters is ok to do it, why you need 3 wattmeters? See the links for 2 wattameter connections to measure the loss: http://cr4.globalspec.com/thread/37060

If you want to use 3 wattmeters, remove the voltage coil connections from the middle phase and add one more wattmeter there. Connect the other ends (free ends) of the voltage coil of the 3 wattmeters together to neutral (if neutral is not available, leave it floating).

- MS

blondel's theorem