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Answer Posted / abhi
Hopkinson's test is another useful method of testing the efficiency of a dc machine. It is a full load test and it requires two identical machines which are coupled to each other. One of these two machines is operated as a generator to supply the mechanical power to the motor and the other is operated as a motor to drive the generator. For this process of back to back driving the motor and the generator, Hopkinson's test is also called back-to-back test or regenerative test.
If there are no losses in the machine, then no external power supply would have needed. But due to the drop in the generator output voltage we need an extra voltage source to supply the proper input voltage to the motor. Hence, the power drawn from the external supply is therefore used to overcome the internal losses of the motor-generator set.
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Dear all, I just want to ask an expert on this forum for some insights. For the magnetic balance test, when applied voltage on a Delta-Star transformer e.g. Dyn11, the following relationships apply for HV side: 1. H1-H2 = H2-H3 H3-H1 2. H2-H3 = H3-H1 H1-H2 3. H3-H1 = H1-H2 H2-H3 For the LV side also: 4. X1-X0 = X2-X0 X3-X0 5. X2-X0 = X3-X0 X1-X0 6. X3-X0 = X1-X0 X2-X0 Is there a similar pattern for Y-d, Y-Y, D-d? And how about Y-z, D-z, Z-y transformers? I've tested a YNzn5 transformer and for LV side I don't see the pattern. In this particular case I got for LV side the following (see values below): H1-H0 H2-H0 H3-H0 X0-X1 X0-X2 X0-X3 128.0 119.9 7.2 29.2 13.3 15.8 70.7 128.4 59.2 23.4 22.0 3.6 7.2 120.1 128.1 13.4 29.3 15.8 What is the relationship here for LV? For row 1 I see the relationship, for row 3 I also see but it's shifted, but for row 2 I don't see such relationship. Any suggestions, answers, someone?
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