12
Electronic Motor Protection Relays
Product characteristics
Over current. Overload
Considering the start-up time of a motor and based on 600% of the rated current, operating
time is set by 1sec unit ranging from 1 to 60 seconds to establish an overload characteristic
curve (Class 1~60). When a definite time characteristic is chosen, overcurrent is detected
from the set operating delay time (D-Time) regardless of the quantity of heat generated
from the motor. Then, Trip is generated when overcurrent continues, exceeding the
operating time (O-Time).
Stall/Locked Rotor
It is a function to prevent burning caused by locked rotor, startup failure and startup
delay. When the level of load current increases due to overheating and overcurrent during
operation or when the load torque exceeds the motor torque, such failure is detected to
break the related circuits.
Phase Fail/Phase Unbalance
When phase fail occurs, a motor may not start to operate and the motor under operation
will stop owing to the lack of torque or reverse phase current will continue to flow,
generating heat. DMPi calculates the unbalance of three-phase current and when it reaches
100%, it operates at 3sec as phase fail. It can be set for tripping at 5sec when the phase
unbalance in within 10~90%.
*Delay time may be set within the range of 0~200sec so that it does not function upon startup.
Reverse Phase
It is a function to prevent reversing of a motor. The phase difference of three-phase current
is compared for operation within 0.1~1.0sec when the phase sequence has changed.
Reverse phase is checked only upon motor startup.
Under Current Protection
This equipment is mainly used to monitor no-load status caused by the separation or
damage of the drive shaft of a motor, or to protect the idle rotation (no-load) status of
pump. It is possible to set up 30~70% of rated current. At the time of third second, it runs.
Ground Fault
Ground fault leakage current is detected to prevent ground faults arising from electric
leakage and secondary accidents (Phase faults and electric shock accidents). Current
sensitivity and operating time are set differently according to the grounded system or
purpose of protection. Current sensitivity can be set within the range of 30mA~3A and the
operating time within the range of 0.05~5.0sec.
* Delay time may be set within the range of 0~200sec so that it does not function upon startup,
and built-in ZCT is provided according to the Type.
Instance
It is a function to protect a motor from short-circuit current. It operates within 50ms when
fault current of more than 500~1500% is generated. Delay time may be set within the range
of 0~200sec so that it does not function upon startup.
<Inverse time characteristic>
<Definite time characteristic>
Protection functions