Welcome back dear Knowledge seekers. We will discuss one by one reasons that create situation for conducting this test.
This is one of the major test of transformer which is included in type test, routine test and field test of transformer. Type test is required for particular design of transformer by manufacturer for confirming product design in use. Routine test is required on every transformer for its construction healthiness and operational performance and field test is required on every transformer before putting into service and for regular maintenance purpose.
This test is useful to identify any damage of transformer winding which can be during time of manufacturing, transporting, erecting, commissioning or maintenance. Manufacturing needs different kind of work upon transformer so after it is required to check healthiness of winding. During transportation and erection-commissioning also there may be chance of winding damage as during transportation, transformer may subject to jerks and vibration. During erection-commissioning is also chance of winding damage as during these works transformer is lifted, put on foundation and manpower may make mistake while working with inside parts of transformer. Maintenance work is also the same case as erection-commissioning for requirement of the winding resistance test.
Detection of deterioration of tap changer contacts and problem in tap changer mechanism can be found by this test. For the transformer with tap changers, current injection path to the windings goes via tap changer so if deterioration is there, the resistance measurement will be abnormal and we will come to know about it. Now a days test kit senses the decrement in current injection during changing tap of transformer so if the current decrement is large, the test kit will stop it self and we will come to know about problem in tap changer mechanism while changing the tap.
Detection of open or loose connection of winding with bushing, shorting of phase, broken strands can be identified by this test. By measuring the resistance of each winding, we can assure that connections are properly connected and tight. Winding resistance measurement is useful for calculation of I2R loss and winding temperature rise test.
