By: Mhy Pro-Power Services Sdn Bhd (772150-W)  29-12-2011
Keywords: DV POWER - TESTING EQUIPMENT, Transformer Switchgear,

After a DC current test, such as a winding resistance measurement, the magnetic core of a power or instrument transformer may be magnetized (remanent magnetism). Also, when disconnecting a transformer from service, some amount of magnetic flux trapped in the core could be present.
The remanent magnetism can cause various problems such as erroneous diagnostic electrical measurements on a transformer, or an inrush current at start-up of power transformer, or incorrect operation of protective relays due to magnetized CT cores.
To eliminate this source of potential problems, demagnetization should be performed.
When suspecting remanent magnetism, or when various test results, like FRA or magnetization/excitation current, show possible remanency use the DEM60 to perform fully automatic demagnetization.
Demagnetizing magnetic core of a transformer requires alternating current applied with decreasing magnitude down to zero. The DEM60 provides this alternating current by internally changing the polarity of a controlled DC current. During the demagnetization process the instrument supplies current at decreasing magnitude for each step, following a proprietary developed program.

Keywords: DV POWER - TESTING EQUIPMENT, Transformer Switchgear,

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