Single-pole operation:
(1-pole operation), each individual pole of the circuit breaker is operated by its own operating mechanism.
This makes single-phase as well as three-phase auto-reclosing possible.
Three-pole operation:
(ganged operation) all three poles are operated by a common operating mechanism.
The three poles are mechanically linked together for three-phase auto-reclosing. (Two-pole operation applies only for special applications, i.e. railway systems.)
Pre-Insertion Resistors (PIR):
Pre-insertion resistors (closing resistors) are used to limit over-voltages in the network during switching operations. (450 Ohms)
The pre-insertion resistors are only used during closing and consist of resistor blocks that are connected in parallel with the breaking chamber.
The resistor blocks will close the circuit approximately 8-12 ms before the arcing contacts.
Pre-insertion resistors are mainly used at higher system voltages (≥362 kV).
Pre-insertion resistors should not be mixed up with opening resistors, which are used for reducing (damping) the TRV during the opening.
Opening resistors are mainly used on older types of circuit breakers, e.g. air-blast circuit breakers.
Rated operating sequence:
The rated operating sequence (also known as a standard operating duty or standard duty cycle) is the specified operating sequence, which the circuit breaker shall be able to perform at specified ratings. (O-0.3 s-CO-3min-CO)
Mechanical endurance class:
There are two different mechanical endurance classes:
Class M1: Circuit breaker with normal mechanical endurance (2 000 operations).
Class M2: Frequently operated circuit-breaker for special service requirements (10 000 operations).
A circuit breaker intended for Class M2 can of course also be used for Class M1.
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