5
Instruction Leaflet
IL019226EN
Effective October 2018
C-HRG technical information
and adjustment procedure
EATON
www.eaton.com
Ground fault
Ground fault detection
Any time a system is energized, a very small ground current will be
observed. When one phase becomes grounded, much more current
will flow to ground. The maximum amount of current that will flow to
ground during a ground fault is predetermined by the resistor taps in
a high resistance grounding system.
A small current called “the charging current” will flow toward the
unfaulted phases. Most of the ground current, however, must flow
through the grounding resistor, and an ammeter in this circuit will
read the amount of current.
By placing a current-sensing relay in series with the ammeter,
the current relay can be adjusted to pick up at a preset level, thus
indicating an abnormal condition.
An alternative detection scheme employs a voltmeter-relay
connected across grounding resistors. The voltage across the
resistors is proportional to the amount of ground current. The
voltmeter-relay’s pickup adjustment is preset to a desired level
to avoid nuisance tripping.
It will be helpful to periodically note the ammeter’s reading;
a trend toward higher values may indicate the need for
equipment maintenance and hence reduce the occurrence of
unplanned shutdowns.
Ground fault location
The current pulses can be noted with a clamp-on ammeter when
the ammeter is placed around the cables or the conduit feeding
the fault. See
.
ote:
N
When tracing along cables or conduits that are carrying a load, all three
phases must be within the ammeter’s jaws. If not, the pulsing current may
not be noticeable above the load, or the ammeter may be “pegged” by the
magnitude of the load current.
The operator tests each conduit or set of cables until the pulsing
current is noted. By moving the ammeter along the conduit, or
checking the conduit periodically along its length, the fault can be
traced to its origin. The fault may be located at the point where the
pulsing current drops off or stops. See
and
.
ote:
N
It may not be possible to precisely locate faults within a conduit. The
ground current may divide into many components, depending on the number
of cables per phase, number of conduits per feeder, and the number and
resistance of each ground point along the conduits. The resulting currents
may be too small to allow detection with the pulser or may take a path that
the ammeter cannot trace.
If little or no change in the pulsing current is noted along the entire
length of a conduit, then the fault may be in the connected load. If
the load is a panelboard, distribution switchboard, or motor control
center, repeat the process of checking all outgoing cable groups
and conduits to find the faulted feeder. If the fault is not found in an
outgoing feeder, the fault may be internal to that equipment.
An important note to keep in mind is that while the pulser can
greatly aid in locating a fault, there may be certain conditions under
which the pulses cannot be readily traced, and other test procedures
(megger, high-potential, and so on) may be needed.
Maintenance
SAFETY PRECAUTIONS:
ONLY PERSONS TRAINED AND EXPERIENCED IN THE
SERVICING OF ELECTRICAL DISTRIBUTION EQUIPMENT
SHOULD ATTEMPT TO SERVICE THIS EQUIPMENT.
DANGER
IF YOU ARE NOT QUALIFIED AND AUTHORIZED TO SERVICE THIS
EQUIPMENT, DO NOT DO SO.
YOU AND/OR OTHERS COULD BE KILLED OR OTHERWISE SERIOUSLY
INJURED, AND/OR PROPERTY DAMAGE COULD RESULT.
DANGER
HIGH VOLTAGE!
WILL CAUSE DEATH, BODILY INJURY, OR EQUIPMENT DAMAGE.
TURN OFF POWER AT THE SOURCE BEFORE WORKING INSIDE.
Before attempting any inspection or maintenance, open, tag, and
lock out the primary devices supplying this equipment. Verify that no
voltage is present in this equipment using calibrated testers that are
known to be operating correctly.
CAUTION
HIGH TEMPERATURES!
MAY CAUSE SERIOUS BURNS.
ALLOW RESISTOR ASSEMBLY TO COOL DOWN BEFORE SERVICING.
The resistor assembly is rated at up to 375 °C at full load. Approach
it with due caution, especially if a fault condition has occurred
recently. Even when it is hot enough to cause serious burn, the
resistor assembly may not appear hot!
Monthly
•
Ammeter readings: note ground current reading on ammeter
and record in test log. Compare with previous month’s reading
(Take readings at a time when most equipment is online. More
importantly, take readings when loads are similar in nature, and
environmental conditions are similar as well)
•
Test system: turn mode selector to “test” and hold long enough
for pulser to begin operating. Note pulse amplitude on test log
and compare to previous month’s readings
•
When under test mode, the ground fault relay should pick up and
the ground fault alarm should activate. Make sure the ground fault
relay is working properly
•
Inspect compartments: open control compartment door and
inspect for dirt accumulation, or any sign of component/wiring
degradation or overheating
•
Inspect vents: check that all vents are clean and unobstructed
•
Check lamps: note that all lamps are working and replace bulb
as required
•
Record findings: record any findings in test log (
) and
arrange for further maintenance if required
