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Development of the DC superimposition bridge method for the measurement of high insulation resistance of medium voltage XLPE cables in operations
Author(s) -
Shinmoto Takashi,
Kimura Chiaki,
Yamamoto Ken,
Umeda Susumu
Publication year - 1996
Publication title -
electrical engineering in japan
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.136
H-Index - 28
eISSN - 1520-6416
pISSN - 0424-7760
DOI - 10.1002/eej.4391160507
Subject(s) - voltage , electrical engineering , resistor , ground , current (fluid) , high voltage , engineering , electromagnetic shielding , materials science
The method for measuring insulation resistance by superimposing the dc voltage has potential for detecting the deterioration of cable insulations. The deterioration of cable insulations can be detected by measuring current which flows through a grounded shielding wire. However, the earth current also flows from the cable sheath into the grounding wire as noise. Thus, to assess the deterioration properly, it is necessary to separate the earth current from the total current. On the other hand, to improve detection sensitivity, it is desirable to superimpose the highest possible dc voltage. In this case, provision must be made so that there are no adverse effects on the GPT. The authors, placing special emphasis on the method of measuring high insulation resistance by configuring the bridge, have conducted an investigation on how to detect the insulation deterioration with high accuracy and sensitivity without impairing the functions of the GPT. The following issues were investigated and the results are reported in this paper: (1) It is possible to measure insulation resistance as high as 100,000 MΩ by superimposing 50‐V dc through the GPT after cancelling the earth‐current and by configuring a bridge for determining insulation resistance from voltage ratio. (2) Even if 50‐V dc is superimposed through the GPT, it is possible to prevent the magnetic saturation of GPT if the current injected by such superimposition is limited (i.e., below max. 5 mA). (3) In lieu of a variable resistor, a variable dc voltage supply is employed in the bridge. The variable dc voltage supply requires no mechanically driven part, thus making it possible to realize a fully automatic monitoring system.