GE Industrial Solutions AKD-8 - Manual (Page 2)

EQUIPMENT DESCRIPTION AND
GROUNDING SYSTEM OPERATION
(CONT.)
To trace the ground fault, the operator turns the selector
switch to the "pulse" position. This initiates cycle timing
alternately energizing and deenergizing a shorting contactor
at the secondary resistor, resulting in a rhythmic fluctuation
in the magnitude of the ground current.
An optional current transformer and ammeter at the panel
will allow the operator to determine the current fluctuations
on the system. A portable hook-on detector is then used to
trace the fluctuations in ground current through the system to
the point of fault. After the ground point has been located
and removed from the system, the operator then resets the
selector switch to deenergize pulse cycle timing circuits, and
depresses a reset button to reset indicating lights and
annunciators.
Taps are provided on the resistor to adjust the magnitude of
the ground current in the range of 0.9 to 7.3A., depending on
the size of the system, so that the current through the resistor
to a ground fault will be slightly , greater than the system's
natural capacitance charging current.
The capacitance charging current of most 480 volt systems is
below one ampere, so that the resistor is usually set at 0.9
ampere, with an increase to 3.6 ampere during pulsing. For
unusually large systems, taps are available for an initial
ground current of 3.6 amps with pulsing to 7.3 amperes.
Refer to Fig. 2 for typical system circuit elementary.
CONTROL
TRANSFORMER
Figure 1. Basic System Operation
2
EQUIPMENT DESCRIPTION AND