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Appendix
5.1.2 Fault Localization
In order to find out the reason for high gas values, further tests have to be
performed for the transformer. Common test methods are:
• Winding resistance measurement
• On-Load Tap Changer (OLTC) test
• Turns ratio measurement
• Excitation current measurement
• Measurement of leakage reactance
• Capacitance and Dissipation factor measurement
5.1.3 Winding Resistance Measurement and On-Load Tap
Changer Test
Winding resistances are tested in the field to check for loose connections,
broken strands and high contact resistance in tap changers. Additionally, the
dynamic resistance measurement enables an analysis of the transient switching
operation of the diverter switch.
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