Different motor characteristics
Difficult to standardise protection
Protection applied ranges from
FUSES to RELAYS
Motor Protection
SYSTEM
Voltage Dips
Voltage Unbalance
Loss of supply
Faults
MOTOR CIRCUIT
Insulation failure
Open circuits
Short circuits
Overheating
LOAD
Overload
Locked rotor
Coupling faults
Bearing faults
The main types to be considered :-
Overtemperature
Thermal overload
Stall / Locked rotor
Phase unbalance and single phasing
Short Circuit
Earth Fault
Undercurrent
Protection must be able to :-
Operate for abnormal conditions
Protection must not :-
Affect normal motor operation
Considerations :-
Starting current
Starting time
Full load current
Stall withstand time (hot & cold)
Thermal withstand
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