ABB HCB-1 - Page 10

41-971.3M Type HCB-1 Pilot Wire Relay System
10
Sub 1
619591
Figure 7:
Typical Operating Characteristics of the HCB-1 Relay System — Maximum Restraint Tap, with 4/1
Insulating Transformers and 2000-Ohm Pilot-wire. VF of Near and Far Relays in Phase or 180° Out-of-Phase.
R
NC
(I), R
NC
(II) – current transformer ratio at Sta-
tion I and II respectively.
5.2.1. Phase Fault Sensitivity (R1 and Taps)
The phase fault pickup is determined by the B, C and
T taps. In order to operate on the minimum 3-phase
fault current, the T tap should be set for not more
than:
Equ. (8)
In order to prevent operation on load current if the
pilot-wires become open circuited, the T tap should
be set for not less than:
Equ. (9)
The available taps are:
T: 4, 5, 6, 7, 8, 10, 12
Where sufficient fault current is available, it is recom-
mended that the relays be set as follows:
TI
L
tap C() T
;0.5
I
3
P
tap B()
==
TI
L
tap C() T
;
I
L
2
----
tap B()
==