Different faults may occur in three-phase electric engines and their supply circuits. These faults may cause the engine damage as well as the electric traumas of the personnel. Such faults are:
power loss;
overvoltage;
phase loss;
neutral line loss;
phase sequence faults;
voltage imbalance.

The electric engine protection from such vulnerabilities is provided by specific automatic switchers and protective relays. Also all the up-to-date electric engines control units have this protective function, these units are soft starters and frequency drives (frequency converters).

Automatic switchers and electric engine protective relays

Electric engine are protected by automatic switches from:
Short circuit ;
over current.

Relays provide protection from:
phase loss;
over- or under voltage ;
phase sequence faults.

Frequency converters

Frequency converters provide electric engine protection form:
short circuit to ground;
converter overheat;
over-torque of shaft

Soft starters
The main functions of the soft starters:
soft start
engine start with target inrush current
engine start with soft voltage increase
engine start with the “shift” initial torque
soft stop
engine soft stop with the specified rate
dynamic brake

Soft starters protect electric engines from:
Over current
phase loss
short circuit and overheat