Date Code 20010625
M
IRRORED
B
ITS
™ Communications
I-1
SEL-311L Instruction Manual
APPENDIX I: M
IRRORED
B
ITS
™ COMMUNICATIONS
O
VERVIEW
M
IRRORED
B
ITS
is a direct relay-to-relay communications protocol that allows protective relays
to exchange information quickly and securely, and with minimal expense. The information
exchanged can facilitate remote control, remote sensing, or communications-assisted protection
schemes such as POTT, DCB, etc. The SEL-311L Relay supports two M
IRRORED
B
ITS
channels,
differentiated by the channel specifiers A and B. Bits transmitted are called TMB1
x
through
TMB8
x
, where
x
is the channel specifier (e.g., A or B), and are controlled by the corresponding
SEL
OGIC
control equations. Bits received are called RMB1
x
through RMB8
x
and are usable as
inputs to any SEL
OGIC
control equations. Channel status bits are called ROK
x
, RBAD
x
, CBAD
x
and LBOK
x
and are also usable as inputs to any SEL
OGIC
control equations. Further channel
status information is available via the
COM
command.
Important:
Do not connect an unconfigured port to a M
IRRORED
B
ITS
device. Otherwise the
relay will appear to be locked up. Configure the port first, then connect the device.
O
PERATION
Message Transmission
All messages are transmitted without idle bits between characters. Idle bits are allowed between
messages.
•
At 4800 baud, one message is transmitted each 1/2-power system cycle.
•
At 9600 baud, one message is transmitted each 1/4-power system cycle.
•
At 19200 and 38400 baud, one message is transmitted each 1/8-power system cycle for
the SEL-321 and 1/4 power system cycle for the SEL-311L Relay.
Message Decoding and Integrity Checks
The relay will deassert a user-accessible flag per channel (hereafter called ROK
x
) upon failing
any of the following received-data checks:
•
Parity, framing, or overrun errors.
•
Receive data redundancy error.
•
Receive message identification error.
•
No message received in the time three messages have been sent.
While ROK
x
is not asserted, the relay will prevent new data from being transferred to the pickup
dropout security counters described later. Instead, the relay will send one of the following user
selectable values (hereafter called default values) to the security counter inputs:
•
1
•
0
•
The last valid value
The user will be allowed to select one of the default values for each RMB.
Summary of Contents for SEL-311L
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