T-305E User Manual Version 3.5 | 20
Operational procedure:
i.
Turn the
MODE
knob to the
DC
position.
ii.
Power on the T-305E, the green
STOP
button lights up.
iii.
Turn the voltage
ADJUST
knob to the zero position, which enables the
START
button.
iv.
Press the
START
button, which then lights-up and the green
STOP
light turns off. Inside
the instrument, the noise of the HV protective device can be heard
v.
Increase the voltage by slowly turning the
ADJUST
knob, the voltmeter shows the
voltage applied to the cable. When it reaches 75% of the test voltage, the rate of rise
should increase to roughly 2% per second avoiding undue stress to the cable.
vi.
If the cable fails the test, the voltage will collapse and the current will increase due to
the breakdown of the insulation. On a healthy cable, no breakdown will occur.
7.3
Power off the T-305E
After the test is finished, turn the
ADJUST
knob to zero to discharge the cable. The T-305E
can then be powered down.
Warning:
The power off procedure for DC Voltage Withstand Test is different from that for break-
down test. There is no discharge loop for this test, the energy on the cable can only be
discharged by the discharge rod. Therefore, the user MUST follow the correct discharge
procedure using the discharge rod as described in section 5.1.
8.
Pinpointing faults using the cyclic mode
This mode is used for pinpointing the fault position of the cable using the Kehui T-506
pinpointer or any similar device . In this mode, the T-305E will discharge to the cable at a
frequency determined by the TIME dial setting. The flow of current through the fault point
as it breaks down, generates periodic magnetic and acoustic signals, which can be picked up
by the T-506 pinpointer for precise location of the fault.
Figure 8.1 Pinpointer in use, with the resultant magnetic and acoustic waveforms
