Technical information

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1SDC210033D0202

PTC

PR212/CI

Motor

Circuit-breaker

with magnetic

only trip unit

Thermal relay

Contactor

Motor

Circuit-breaker with

electronic trip unit

Ekip M-LRIU

Contactor

Conventional system Advanced protection system

The safety and reliability of the solution are important aspects that must be considered when

choosing and manufacturing the system for starting

(G4.3 and G4.4)

and monitoring motors.

Start-up is a particularly critical phase for the motor itself and for the installation powering it. Even

rated service needs to be adequately monitored and protected so as to deal with any faults that

might occur.

When it comes to direct starting, ABB SACE proposes two different solutions:

Q a conventional system with three poles a circuit-breaker equipped with a magnetic only trip

unit for protection against short-circuits, a thermal relay for protection against overloads and

phase failure or imbalance, and a contactor to operate the motor;

Q an advanced protection system which integrates all the protection and monitoring functions,

and a contactor for operating the motor, in the circuit-breaker itself.

Several different factors must be considered when choosing and coordinating the protection and

operating devices, e.g.:

Q the electrical speciﬁcations of the motor (type, power rating, efﬁciency, cos);

Q the starting type and diagram;

Q the fault current and voltage in the part of the network where the motor is installed.

Consult the QT7 Technical Application Paper: “The asynchronous three-phase motor: general infor-

mation and ABB’s offer for coordinating the protections” for further details.

The motor protection and operating devices must be chosen in accordance with the coordination

tables provided by ABB either through documentation “Coordination tables” or on the web site:

http://www.abbcontrol.fr/coordination_tables/.

Circuit-breakers for motors protection

Main characteristics