Operating Characteristics - GE CHC13D A Series Instructions Manual

GEK-1253E
From the above it is apparent that the cup unit (PFO) can detect single-phase-
to-ground faults as well as multiphase faults if the fault current is large enough.
When the CHCIIA relay is used as a fault detector, the cup unit should be set
so that the minimum phase-to-phase fault current exceeds
1.5
times the phase-to-
phase pickup. This will ensure pickup for all multiphase faults. If the minimum
single-phase fault current is sufficient to operate the unit for this setting, it
is not necessary to use the hinged-armature (GFD) unit. However, the GFD unit may
be used for single-phase-to-ground faults if desired.
The hinged-armature unit is connected in the current transformer-circuit to
receive three times the zero-sequence current. It should be set so that 3 10 for
minimum fault conditions exceeds 1.5 times the pickup of this unit.
An external reactor is included with the relay for connection across the GFD
operating circuit (see Figure
11).
The purpose of this reactor is to reduce the
dropout de
1
ay that may resu
1
t from the decay of energy in the CT core after the
primary current has been interrupted.
OPERATING CHARACTERISTICS
Table I lists the operating ranges for the cup (PFO) unit of CHC11A relay.
These ranges depend upon the type of fault experienced by the relay. See the
application section for details of why these pickup ranges vary with the type of
fault.
TYPE OF FAULT
PFD Pickup Range
Phase-to-Phase
Three Phase
Single Phase to Ground
TABLE
I
PICKUP RANGE OF CUP UNIT - AMPERES
1 -
4
2 - S 4 - 16 22 - SO
1 - 4
0.S15 -
3.76
1.415 -
5.65
2 - S
1.63 - 6.52
2.S3 - 11.3
4 -
16
3.26 -
13.0
5.66 - 22.6
20 -
SO
16.3 -
65.2
2S.3 - 113
The short-time-current-capability curve for the hinged-armature (GFD) unit is
shown in Figure 2.
The maximum pickup time/current characteristics of the cup unit plus auxiliary
telephone unit are shown in Figure 3. The pickup time is dependent on the pickup
setting of this unit. The maximum dropout time/current characteristic for the cup
unit plus auxiliary telephone unit is shown in Figure 4. This curve applies to all
pickup settings of this unit.
The maximum pickup and dropout time/current characteristics of the hinged-
armature unit plus the auxiliary telephone unU are shown in Figures 5 and 6,
respectively. These curves apply to all pickup settings of this unit.
Maximum pickup time is the total time required for the cup or hinged-armature
unit to close its contacts plus the time for a normally-open contact of the
auxiliary telephone unit to close. The maximum dropout time is the total time
required for the cup or hinged-armature unit to open its contacts plus the time
5