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6.6 DC Fault Location with 3 Point Method
The purpose of the test is to find the location of the wire-to-ground
insulation fault. This test is applicable when the two wires of the pair have
different gauges and only one of them is leaky. The ratio of the good wire
insulation to the leaky wire insulation must be at least 1000. The passive
bridge of KMK 8 measures accurately even in the presence of disturbing
longitudinal AC voltages on the line.
For that measurement a third, auxiliary wire is required between KMK 8
and the far end. The resistance of auxiliary wire c has no effect on the
accuracy. The far endings of the tested pair should be joined to the wire c
manually or by means of the remote controllable loop-closing device
KLC 8.
The test arrangement:
The 3 Point method requires three part-measurements:
• Measurement 1. The generator Um is connected to wire A.
The result is MK1 (Practically always 0)
• Measurement 2. The bridge should be balanced when the
generator Um is connected to the ground. The result is MK2.
• Measurement 3. The bridge should be balanced when the
generator Um is connected to wire C. The result is MK3.
The Lx/L value is calculated out of MK1, MK2 and MK3
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