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Bus Pr
Bus Protection
the B90 is still measuring the current, a simple overcurrent function,
can be used to determine the fault exists, and send a direct transfer
trip signal to the circuit breaker on the other end of the transmission
line. Without the use of a dynamic bus replica, this fault would
cause an operation of the bus protection for what is essentially an
external fault.
Bus side CTS
Bus side CTs provide another illustration of the use of a dynamic
bus replica. Similar situation occurs for bus-side CTs. A fault
between the circuit breaker and the CT is in a blind spot of the
bus protection. To clear the fault the busbar must be tripped, but
the differential zone will not see this fault. Similar to the end-zone
fault, this situation requires using breaker position as a connection
status for the associated current. The fault is cleared sequentially.
First, protection of the circuit, fed from the CT, responds to the fault
and opens the breaker. When the breaker opens, the CT current
is removed from the differential zone by the dynamic bus replica.
As a result, the zone expands to the bus-side pole of the opened
breaker, the fault becomes internal, and the bus protection clears
the busbar.
Flexible input and output options
Traditional busbar protection and control schemes typically use a
lockout relay to open the connected circuit breakers when a bus
fault is detected. For simple busbars, this is the most effective
way to open the circuit breakers. GE Multilin relays can replace the
separate lockout relay with mechanically latched output contacts.
Once asserted, these contacts latch closed until manually reset via
contact input, pushbutton control from the relay HMI, or SCADA
For applications where the bus protection relay will be used for
control and status information, or the relay is protecting a complex
busbar where the status of circuit breakers and isolator switches
is vital, the number of inputs and outputs is quite large. Taking a
double busbar example with 5 feeders and a tie breaker, the relay
requires 12 output contacts (trip and close for each circuit breaker),
and 16 to 32 contact inputs (1 or 2 status inputs for each circuit
breaker and isolator switch). This many inputs and outputs may be
beyond the physical limits of an individual relay. For this reason, GE
Multilin provides an additional B90 to add a combination of up to
96 additional inputs and 84 additional outputs for a bus protection
system. The relays can communicate via Direct I/O communications
to pass digital input status and control output contacts. Direct I/O
is a robust communications protocol that uses copper or fiber optic
communications. The protocol is very reliable, and includes 32-bit
CRC error checking, and may integrate up to 16 different relays on
one communications circuit.
End Zone Fault - Line side CTs
End Zone Fault - Bus side CTs