PGA-016A Littelfuse Inc, PGA-016A Datasheet - Page 47

• Manufacturer Part Number: PGA-016A
• Description: BULK / WATERTIGHT COVER FOR PGR-6200 / PGR-7200
• Manufacturer: Littelfuse Inc

Specifications of PGA-016A

• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

© 2009 Littelfuse
POWR-GARD
Ground Fault Protection
•
•
•
•
•
A protection relay for resistance grounded systems is used
to detect a ground fault and to monitor the neutral-to-ground
connection. It can be used to provide alarms or to trip the
faulted feeder from service during a ground fault. The relay
can provide a pulsing circuit that can be used to locate the
ground fault. The relay can also alarm or trip if the neutral-to-
ground path fails. For systems 5 kV and less, high-resistance
grounding can be used. High-resistance grounding typically
limits the resistor current to 10 A or less. By doing so, the
ground fault can remain on the system, given that the system
is rated for the voltage shift.
For systems 2.4 kV and higher, low-resistance grounding
systems can be used. Typically in those systems the ground
fault current is 25 A or above and is cleared within 10 s.
System Capacitive Charging Current
Although not physically connected to ground, electrical
conductors and the windings of all components are
capacitively connected to ground. Consequently, a small
current will flow to ground from each phase. This current
does not occur at any particular location; rather, it is
distributed throughout the system just as the capacitance to
ground is distributed throughout the system. For analysis,
it is convenient to consider the distributed capacitance as
lumped capacitance, as shown in Figure 8.
The only disadvantage of resistance grounding is that if the
resistor fails, the system will become ungrounded. Resistor
monitoring is recommended to protect against this.
Transient overvoltages can be eliminated by correctly
sizing the neutral grounding resistor (NGR) to provide an
adequate discharge path for the system capacitance.
Continuity of operation with one ground fault is allowable
in some applications when ground fault is
The NGR limits the available ground current. This
eliminates or minimizes point-of-fault damage (Arc Flash
Hazards) and controls the ground-fault voltage.
Pulsing can be used to locate ground faults when ground fault
is
to short out half of the resistance, causing the ground-fault
current to double (usually one cycle per second). A hand-held
zero-sequence meter is used to detect the fluctuating ground-
fault current, and locate the ground fault.
< −
GROUND
10 A. Pulsing is created by using a shorting contactor
NEUTRAL
•
POWR-GARD
®
Protection Relay Catalog
®
PHASE C
PHASE A
PHASE B
Protection Relays
FIGURE 7
< −
10 A.
45
Even if the distributed capacitance is not balanced, the
ammeter will read zero because all the current flowing
through the CT window must return through the CT window.
System charging current is the current that will flow into the
grounding connection when one phase of an ungrounded
system is faulted to ground. It can be measured as shown
below if appropriate precautions are taken:
•
•
A single-line diagram of a three-feeder, resistance-grounded
system with a fault on feeder 3 is shown in Figure 10.
•
•
If the fault occurs on the supply side of the CT, the sum
of the currents in the CT window is not zero.
Ammeter A will read the sum of the capacitive currents in
the unfaulted phases. This value is the charging current of
all the equipment on the load side of the CT.
A CT (A1 and A2) on unfaulted feeders will detect the
charging current of that feeder.
A CT (A3) on a faulted feeder will detect the sum of the
resistor current (I
unfaulted feeders.
l
R
R
A
A
) and the charging currents (I
A1
A2
A3
FIGURE 10
FIGURE 8
FIGURE 9
C
A
B
x
C
A
B
x
C
C
l
l
1
2
x
x
C
C
www.littelfuse.com/ProtectionRelays
x
x
C
C
I
I
A
A
+ I
1
+ I
+I
B
B
1
2
3
2
+ I
+ I
) of the
C
C
= 0
= 0
P