Specifications

December 2008 Page 14–3
Chapter 14. Protective Relay Interface (PRI/PRS) Module
14
occurs within 1ms. The redundant path is mapped
via the channel assignments page of FCS (see Fig.
14-2). On the channel map the modules are
labeled:
• PRI-R - addressed point-to-point with
redundant path
14.2.1.3 Multi-Drop Linear Chain
With the PRI Multi-Drop feature, a specific trip
input from any node in a system is presented as
the same trip output at every other PRI mapped to
the sending PRI module. This reduces the number
and complexity of FOCUS systems with PRI or
PRS modules applied to multi-terminal pilot
relaying or direct transfer trip applications. An
unlimited number of PRI or PRS modules can be
mapped in the chain. Each Multi-drop PRI will
add approximately 0.5ms of trip delay.
A Multi-drop linear chain (MDLC) is the option
applied when it is not physically possible to have
a redundant path and the Multi-drop feature is
desired (as shown in Fig. 14-3).
The types of PRI/MDLC modules are:
• PRI-ME - Multi-drop End Unit, the PRI
module at each end of the linear chain is
configured as an "End Unit".
• PRI-MM - Multi-drop Middle Unit, all PRI
modules in between the two "End Units"
are configured as a "Middle Unit".
Aminor alarm will be set when either channel A
or channel B has a problem.
14.2.1.4 Multi-Drop Redundant Path
The PRI Multi-Drop Redundant Path feature
(MDRP) provides a redundant path for the infor-
mation. When the PRI module is configured this
way a break in the network will not affect PRI
performance. The MDRP is pre-configured with a
redundant path (channel B) around the unused
side of the network to complete a PRI loop (see
Fig. 14-4). With this feature the PRI module
always monitors both channel A (primary) and
channel B (redundant). This ensures network
integrity when a channel is interrupted.
If either channel A or channel B is not good, the
PRI module automatically switches to the
alternate channel providing it is error-free. This
will set a minor alarm and the status LED will
blink steadily until the problem is fixed.
The types of PRI/MDRP modules are:
• PRI-MG - Multi-drop Gap Unit, only one
module on either of the ends must be the
"Gap Unit". The Gap Unit monitors
channel A of the main module unless a
Figure 14–2.
Addressed Point-to-Point PRI Modules with
redundant path
FOCUS
Mapped in FCS
Substation #2
Substation #1
Substation #3
PRI Module
Timeslot 4
PRI Module
Timeslot 4
PRI redundant
Pass-through
FOCUS
FOCUS
Fiber lines
Mapped in FCS
Mapped in FCS
Mapped in FCS