2
SEL Application Guide 2000-02
Date Code 20070803
SEL devices compatible with spread spectrum radios include the SEL-300 and SEL-400 series
relays and recloser controls, as well as the SEL-2100 Logic Processor and the SEL-2505 Remote
I/O Module.
R
ADIO
S
ELECTION
This application guide shows the settings and connections required to establish M
IRRORED
B
ITS
communications when using the FreeWave
®
Technologies, Inc. model FGR-115MB spread
spectrum transceiver.
One important consideration when choosing a radio for use with M
IRRORED
B
ITS
is how
effectively the brand emulates full-duplex communications. Radios are effectively half-duplex
devices, while M
IRRORED
B
ITS
requires that each relay constantly transmit and receive data.
FreeWave has worked with SEL to optimize the FGR-115MB to the
M
IRRORED
B
ITS
MB8
communications data structure. Those radios that do not adequately emulate full duplex can still
be used. However, two radios must be used per location (one dedicated to transmit data and the
other to receive data). Please test to ensure compatibility.
Also, radios with no built-in error detection work best with M
IRRORED
B
ITS
as they only add a
few milliseconds to the overall relay-to-relay communication data delay. Radio
resynchronization time can also momentarily delay a signal. Because speed is critical in pilot
protection schemes, be sure to check the radio specifications carefully for data delay and
resynchronization characteristics.
The FGR-115MB radio operates in a non-licensed 900 MHz frequency range. It has a point-to-
point range of up to 10 miles, based on an unobstructed line-of-sight.
S
ECURITY
M
IRRORED
B
ITS
repeatedly sends data in an encoded message. Each of eight data bits is sent
three times within each message. Received messages are checked for data bit consistency, parity,
framing, overrun, and timing. In addition, an addressing scheme is used so that only relays set as
pairs can communicate to one another.
The FGR-115MB radio also contains some features that improve security and minimize
interference. Each radio’s serial number is encoded into its transmission. Each radio has a “Call
Book” setting and will only accept messages from radio serial numbers listed in its call book
(e.g., the master radio would have the slave radio’s serial number listed in its call book, and vice
versa). In addition, the “FreqKey” setting allows the user to modify the frequency hopping
patterns of the transceivers to minimize interference with other radios or devices in the area; the
radio has 15 pseudo-random patterns to choose from.
M
ONITORING
R
ADIO
P
ERFORMANCE
The performance of the radios and channel can be monitored using a variety of methods. SEL
relays with M
IRRORED
B
ITS
constantly monitor the channel performance. Logic bits ROK
(instantaneous channel monitor), RBAD (ROK drop-out for a settable time), and CBAD
(long-term channel unavailability exceeding a settable threshold) can be used to trigger event
reports, create a sequential events recording, or alarm SCADA via output contact closure or
EIA-232 communications. In addition, the relays generate a detailed Communications Data Log,
which records the latest 255 channel failures, including a time and date stamp, cause of each
error, and outage duration. Refer to the instruction manual of the SEL device for more details on
each of these features.
