CP TD1 User Manual
40 OMICRON
• Short-circuit all bushing CTs.
• Do not perform high-voltage tests on transformers under vacuum.
• The test voltage should be chosen with respect to the rated voltage of the winding.
• All tests should be made with oil temperatures near 20 °C. Temperature corrections can be
calculated by using correction curves, but they depend a great deal on the insulation material, the
water content and many other parameters. This way the correction has limited accuracy.
5.1 Dissipation Factor Measurement
Environmental Conditions
Environmental factors can influence DF measurements greatly. Therefore it is important to record the
ambient conditions at the time of testing when comparing test results. The tests should be made with oil
temperatures near 20°C. Temperature corrections can be calculated, utilizing correction curves, but they
depend very much on the insulation material, the water content and a lot of other parameters. This way
the correction has limited accuracy. Testing at very low temperatures provides less accurate results and
should be avoided if possible.
Other factors like relative humidity and the general weather conditions should be recorded in the test
report for future reference.
It is always better to measure the values regularly and save them for comparison to tests in the past and
in the future. In this way, trends can be observed and the evaluation of results is of much higher quality.
5.2 Capacitance Measurement
The capacitance of the insulation gaps between the windings to each other and to ground depends
mainly on the geometry of the winding. Windings may be deformed after transport of the transformer or
nearby through faults with high currents. Changes in capacitance serve as an excellent indicator of
winding movement and structural problems (displaced wedging, buckling etc.). If a winding damage is
suspected then the capacitance measurement should be supplemented by a leakage reactance
measurement. A separate test can be done for each phase with this measurement technique. Therefore
this method is more sensitive to small changes in one phase.
To Next Page
Loading...
Need help?
General
