CP TD1 Reference Manual V 1.44
88
6.2.4 Reactors
Similar to the auto-transformers, reactors also normally have only one winding.
Often the low-voltage ends of the three phases are connected outside the tank
to the Neutral. In this case we have 2 bushings per phase, which have to be
connected for the DF test. We can measure all combinations: phase to phase
and phase to tank (ground).
6.3 Transformer High-Voltage Bushing Tests
High-voltage bushings are generally used in power transformers, but also in
circuit breakers and in other electrical apparatus. Therefore, the test of bushings
is described in chapter 7 ”Capacitance and DF Measurement on High-Voltage
Bushings” on page 91.
6.4 Interpretation of Measurement Results
Initial tests on new transformers when it arrives from the manufacturer
determines the presence of manufacturing defects or transport damage, and
also provides "fingerprint" test values for future comparisons. Periodic tests
during the life cycle of the transformer can indicate that the insulation is aging
normally or rapidly.
6.4.1 Dissipation Factor Measurement
Environmental Conditions
As already mentioned in chapter 5 ”Capacitance and Dissipation Factor
Measurement” on page 39, 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 temperatures below freezing should be avoided, since the
measurement results are not reliable. If the water in the insulation is frozen to
ice, it may not be detected by DF testing.
Other factors like relative humidity and the general weather conditions should be
recorded in the test report for future reference.
To Next Page
Loading...
Need help?
General
