Specifications

December 2008 Page 17–5
Chapter 17. Pilot Wire Interface (HCB/SPD) Module
17
Figure 17–9. HCB Rear Panel Interface.
The first setting decision you face is whether or
not you want to use the direct transfer trip feature.
This feature provides a direct transfer trip channel
with a separate output trip contact from the pilot
wire relay (see Figure 17-9). You can use this
feature for any function which requires a secure
channel, such as transformer protection or remote
breaker failure. If you use the direct transfer trip
function, the next decision you must make is
whether to apply an 8ms trip hold time to the
output. If you select the 8ms trip hold time, the
trip output contacts will remain closed for 8ms
after the module stops receiving the transfer trip
command. A 0ms trip hold time is the default. The
hold time is typically applied to transformer and
breaker failure applications, but never to a direc-
tional comparison pilot relay system. If you
decide to use DTT, keep in mind that the current
differential information is not sent when a DTT
command is sent.
The last three configuration decisions are related
to how you want the pilot wire relay to respond
when the channel fails or the direct transfer trip
command is received. These settings are for loss
of power to FOCUS control (LOPC), loss of the
channel control anywhere in between the pilot
wire modules (LOCC), and a received direct
transfer trip command control (DTTC).
In all three cases, you can either have the pilot
wire relay system block tripping or allow the pilot
wire relay to operate independently as a local,
non-directional overcurrent relay. If you choose to
have the relay system block tripping, you set all
three functions to BLK. If overcurrent tripping is
desired during these system conditions, set the
LOPC setting to OCT.
For both the LOCC and DTTC modes, you have
two choices for overcurrent tripping. They are: (1)
transmit pilot wire signal to the other end or (2)
send zero signal (no 60Hz) to the other end. In
both cases, the local relay will operate as an over-
current relay. The remote terminal relay response,
however, will vary depending on the setting.
If you choose to transmit the signal to the other
end, the remote relay will operate as a selective
tripping pilot wire relay system. If you choose not
to transmit the signal to the other end, the remote
terminal will operate as a non-directional overcur-
rent relay. For most applications, we recommend
that you allow the signal to be transmitted to the
remote terminal to avoid over-tripping of that
terminal. To do this, select "OCT/Tx Xmit Signal
to rcvr."
Figure 17–8. HCB Configuration Window for a
Module used in a Three-Terminal Application.