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Figure 6.18 An ideal transformer
An ideal transformer is one which has no core loss, no winding losses, no
resistance of its windings, no winding leakage reactances, and no voltage
drop in the windings. The efficiency will be 100 per cent and voltage
regulation will be zero. Such ideal conditions are not possible to achieve.
6.12 TRANSFORMER TESTS
The performance of a transformer in terms of its voltage regulation (i.e.,
percentage change in voltage from full-load to no-load) and efficiency under
various loading conditions can be calculated using the approximate
equivalent circuit explained earlier. However, the circuit parameters like R e
and X , R and X have to be known. These parameters and the losses in the
c
e
m
transformer can be determined by performing two tests, viz the open-circuit
test or the no-load test, and the short-circuit test. These tests are explained as
follows.
6.12.1 Open-circuit Test or No-load Test
In this test the transformer primary winding is supplied with its rated voltage
keeping the secondary winding unconnected to the load, i.e., with no-load on
the secondary. Normally, the supply is given to the low-voltage winding. The
high-voltage winding is kept open. Three measuring instruments, viz a
