GE Industrial Solutions AKD-8 - Manual

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TYPE AKD-8
Low-Voltage Switchgear
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High Resistance Pulsing Ground Detection
System
GENERAL
Pulsing Current High Resistance Neutral Grounding
System
The following paragraphs describe a high resistance neutral
grounding system supplied with GE AKD-8 Low voltage
Switchgear. The system features an alarm system and utilizes
a pulsing current to locate the first ground fault. The system
has the following basic features:
1. Grounds the neutral of an ungrounded 3-phase power
system, utilizing the "high resistance" method. This
allows the system to operate as an "ungrounded" system
but eliminates the danger of high transient over-voltage
during certain types of ground faults.
2. Gives an immediate warning when the first ground fault
occurs.
3. Provides a method for quickly locating and removing the
fault before another fault develops on another phase,
thereby preventing circuit outages due to double line to
ground faults.
Reference: The high resistance grounding method is fully
described in IEEE Transactions on Industry and
EQUIPMENT DESCRIPTION AND
GROUNDING SYSTEM OPERATION
During normal conditions, with no ground fault on the
system, no voltage appears across the system and no voltage
appears across the grounding resistors. (Refer to Fig. 1).
When a ground fault occurs, the resistors limit the ground
current to a low value, adjustable between 0.9 and 3.6
amperes.
The voltage appearing across the resistors will be sensed by
the voltage coil of the meter relay. Auxiliary contacts
General Applications, Vol. IGA- 1 No. 5, Sept./Oct. 1965
under High Resistance Grounding.
Fault Locating
The success of operating a high resistance grounded system
relies heavily on a dependable method of searching out the
ground fault location to allow the faulty system member to be
removed with the least delay.
The two important innovations introduced in this equipment
to take the uncertainty out of signal tracing include:
1. Use of repeating, cyclic, switching sequence by which the
tracer current can be rhythmically switched to a slightly
higher value. This gives unique character to the tracer
signal by which it can be distinguished from steady state
background noise.
2. Use of an extremely sensitive ground-fault-current
sensing transformer such that extraneous noise will be
ignored and only the current-carrying member which
passes through the window will be registered on the
meter.
of the meter relay, operated by the voltage coil, may be used
for remote indications and annunciation.
A green indicating light on the equipment indicates that
control voltage is available and that the system is normal.
When a fault develops, a red indicating light on the
equipment will remain lighted until the ground fault is
removed. If no remote annunciator is available to notify the
operator, an audible signal may be added to the equipment as
an option. A rotating red signal beacon may be used in noisy
or remote installations.
GEI-72116 Installation/Operation Instructions