Some of the difficulties encountered in testing large transformers are:
- For carrying out tests for large transformer huge amount of energy is wasted
- For carrying out direct tests by loading the transformer large amount of load is to be available at the test center
Therefore the performance characteristics of the transformer can be computed from the equivalent circuit parameters which in tern may be obtained by carrying out simple tests on the transformer.
Some of the tests that are conducted on transformers are:
Polarity test on the transformer helps to determine the same instantaneous polarity of the transformer. The relative polarities of the primary and secondary terminals at any instant must be known for connecting the windings of the same transformer in parallel
Open Circuit Test:
This test isalso called as no load test. This test helps to determine the core losses in the transformer.
Short Circuit Test:
Short Circuit test of a transformer helps to determine the full load copper losses for a given transformer.
These open circuit and short circuit tests are carried out not by directly loading on the transformer. Core Losses and Copper Losses can be determined from the open circuit and short circuit tests respectively. Therefore by carrying out these two indirect tests efficiency at different loads and regulation of the transformer can be determined for different power factors.
This is also called back to back test. In open circuit and short circuit tests no information is obtained about the temperature rise. In sumpner's test, two identical transformers are load to the full power like regenerative test in dc machines, transformers draw only the power required to supply iron and copper losses of the transformers.