How Back to Back test is Performed on 3 Phase Transformer
Q. Explain how back to back test is performed on 3 phase transformer.
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| Back to back test on 3- phase transformer |
Back to back test as seen for the single phase transformers is also applicable in plus transformers. It is a regenerative test, requires less time, less energy consumption for performing the test as well as no huge loading arrangement is necessary. A variety of connections are available for conducting back to back test mostly to check temperature size of 3-Phase transformers.
Following is the circuit diagram for back to back test in which only one transformer is needed (Δ-Δ). The Δ connected L.V. winding is supplied with a 3 – phase 50HZ AC supply. The secondary’s are connected in open delta and fed from a low voltage auto transformer. The auto transformer is so adjusted that full load current circuits in the windings. This voltage indicated in open delta circuit = 3 x F.L. current x impendence per phase as referred to H.V. side.
Sum of two wattmeter W1 + W2 is equal to core losses. Wattmeter W3 gives total copper losses. From these readings efficiency can be worked out. Conducting the test for a longer period will indicate temperature rise which can be measured by some means.