Megger 651403, Instruction Manual

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AVTM6514J Rev. A (03/2003)
20
100 percent with a high resistance or an arcing fault, because the higher
impedance of these faults allows less current than a short circuit. Deflection for
voltage impulses below 15 kV is also lower than 100 percent as determined by a
proportionality law: 3 kV impulses produce a maximum (short circuit) reading
of 20 percent, 6 kV impulses produce 40 percent, etc.
b. A slight meter movement is produced with a capacitance as low as 0.1 µF in the
cable under test. Since this is the capacitance of the cable, slight meter
movements may occur when no fault is present.
Thus, as a general rule of thumb, the operator should ignore any meter deflections less
than 10 percent of full scale and interpret the results as a fault only when the deflection
is greater than 10 percent of full scale. As with most rules of thumb, ambiguities will
occur from time to time, and experience with the instrument will aid interpretation.
Increasing the output voltage to the next tap will usually resolve most questions.
SHUTDOWN PROCEDURE
1. When a test is complete, set the OUTPUT KILOVOLTS switch to ZERO START;
this disables the high-voltage output. Set the ON/OFF switch to OFF.
2. To disconnect the setup, manually ground the HV OUTPUT cable high-voltage
lead with a safety grounding stick and then apply safety ground jumpers.
F
WARNING
Never assume that the coaxial output cable or the cable under
test is completely discharged, even after following the above
procedures. Always use a safety grounding stick to ground any
conductive part of the circuit and then apply safety ground
jumpers before touching any connections.
3. Remove the test clips from the conductor and the shield.
F
WARNING
Leave the safety ground jumpers in place to drain any relaxation
charge for a period of at least four times as long as the test
voltage had been applied.