TELEPROTECTION SCHEME PRINCIPLES
Teleprotection schemes use signalling to convey a trip command to remote circuit breakers to isolate circuits.
Three types of teleprotection commands are commonly encountered:
In direct tripping applications (often described by the generic term: "intertripping"), teleprotection signals are sent
directly to a master trip device. Receipt of a command causes circuit breaker operation without any further
qualification. Communication must be reliable and secure because any signal detected at the receiving end
causes a trip of the circuit at that end. The communications system must be designed so that interference on the
communication circuit does not cause spurious trips. If a spurious trip occurs, the primary system might be
Permissive trip commands are monitored by a protection device. The circuit breaker is tripped when receipt of the
command coincides with a 'start' condition being detected by the protection at the receiving. Requirements for the
communications channel are less onerous than for direct tripping schemes, since receipt of an incorrect signal
must coincide with a 'start' of the receiving end protection for a trip operation to take place. Permissive tripping is
used to speed up tripping for faults occurring within a protected zone.
Chapter 17 - Electrical Teleprotection