Specifications

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17
17.1 Description
The Pilot Wire Interface Module connects directly
to the HCB, HCB-1, or SPD relays. It monitors
the voltage and the current of the connected pilot
wire. The module is designed for use with either
Westinghouse/ABB HCB and HCB-1 relays or the
General Electric SPD relay.
Connecting this module (via the FOCUS system)
to the existing relay terminals removes the
necessity for the metallic pilot wire, isolating
transformers, neutralizing or drainage reactors, or
lightning arrester tubes or other devices required
to compensate or condition the metallic pilot
wires. It also replaces all of the pilot wire moni-
toring equipment and the dc auxiliary transfer trip
function.
Although the module occupies two physical
module slots in the FOCUS chassis, it requires
only one time slot, DS0. The current comparison
information and a single transfer trip function are
encoded in this time slot.
17.2 Application
17.2.1 General
To apply a FOCUS Pilot Wire Interface Module to
a pilot wire relay system, you simply disconnect
the existing circuitry at the pilot wire terminals of
the protective relay and connect those same relay
terminals to the pilot wire terminals on the
FOCUS rear interface module. We also
recommend that you perform a functional test on
the system to make sure that the overall relay
system is operating properly for both internal and
external faults (see the "Installation" and
"Acceptance Test" sections later in this chapter).
With both the HCB/HCB-1 and the SPD systems,
there usually is a test switch with a milliammeter
applied to the pilot wire terminals of the relay at
each line terminal. The purpose of this circuitry is
to perform a functional test on the relay system,
primarily when the system is first installed. This
helps determine if the system is wired properly. It
helps check out the system for wrong current
transformer and pilot wire connections. Although
not recommended, you may keep this circuitry in
service, if desired, as it is still useful for testing
connections after installation or maintenance.
Note, however, that the current readings obtained
when using the FOCUS HCB interface are not the
same as those obtained with a pilot wire.
17. Pilot Wire Interface (HCB/SPD) Module