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Type HCB-1 Pilot Wire Relay System
(I
is the phase A negative sequence current):
A2
0.2T
=
–
.2I
+
A1
0.2T
I
=
---------- -
=
I
A1
A2
5.2
But:
I
=
I
=
I
S
A1
A2
= 3I
A1
(
) 3 ( )
0.2T
So:
(
×
)
0.2T 3
I S
=
3I A1
=
------------------------ -
5.2
For T = 4
I
= 0.5
S
4.2. NOMINAL PICKUP (All Relays)
The nominal pickup, I
nom
I
=
KI
nom
S
Where
I
= total internal fault current
nom
K
= number of relays (2 or 3)
I
= single-relay pickup with pilot
S
wire disconnected (see above)
4.9 I
.46I
+
A2
A0
=
I
A0
+
I
A0
=
0.12T (A-G Fault)
Equ. (6)
, is defined as
Equ. (7)
Figure 4. Simplified External Schematic of the HCB-1 Relay System
For example, in the previous example or a phase-A-
ground fault, the single-relay pickup was determined
as I
= 0.5 ampere for 4CH taps with the pilot-wire
S
open. For a two-terminal line, the nominal pickup for
a phase-A-to-ground fault (4CH taps) is:
(
)
I
A to G
=
0.5
=
nom
4.3.
MINIMUM TRIP (All Relays)
With equal inputs to all relays and zero pilot-wire
shunt capacitance, the relays will operate at their
nominal pickup point. The minimum trip points will
vary somewhat from nominal value, depending on
the pilot-wire constants and the magnitude and
phase angle of the various relay input currents. For
example, Figure 6 shows the relay operating points
for a two-terminal line, assuming input current one
relay only.
An example of the characteristics with various cur-
rent distributions shown in Figure 6. The filter output
voltage, V
, of each relay, as defined by equation (1)
F
must be in phase or 180 degrees out-of-phase, in
order for Figure 7 to apply.
4.4.
INSULATING TRANSFORMER
Unless otherwise noted, all characteristics presented
include an insulating transformer with each relay.
Two ratios are available: 4/1 and 6/1. The high volt-
age side (H1-H4 Terminals) is connected to the pilot-
wires.
41-971.3M
×
0.5 2
=
1.0 ampere
Sub 4
183A61
7
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