Satisfy machine protection requirements
Have definite time characteristics: Current threshold and time based function.
LR97D Electronic Over Current Relay
LR97 D and LT47 electronic over current relays have been developed to satisfy machine protection requirements. These relays have definite time characteristics: Current threshold and time based function. They are particularly recommended for providing mechanical protection on machines with high resistive torque, high Inertia and with strong probability of jamming under steady state conditions. They can be used for motor protection in the case of long starting times or frequent starting. The LR97 D relay also incorporates two fixed time protection functions, one of 0.5 seconds against locked rotor and One of 3 seconds against phase failure. LR97 D and LT47 can be used to provide mechanical shock protection. In this case, setting the O-Time knob to Minimum will ensure tripping in 0.3 seconds.
LR97 D and LT47 relays are particularly suitable for the following machines:
Monitoring function for excessively long starting time on machines with a risk of difficult starting: Machines with high resistive torque, high inertia machines. Monitoring of machines during steady state operation: Overtorque detection function Machines with strong risk of jamming, machines with torque build-up over time, Mechanical failure monitoring, Faster detection of malfunctioning on machines where the motor is oversized in relation to its thermal protection I² T. Motor protection for specific applications: Machines with long starting times, Machines with high on-load factor: More than 30 to 50 starts/hour, Machine with fluctuating load from a steady state, where the thermal image of a thermal overload relay (thermal Memory) is unsuitable in relation to actual overheating of the motor. Examples of machines: Conveyors, crushers and mixers, Fans, pumps and compressors, Centrifuges and spin-dryers, Presses, shearing machines, saws, broaching machines, sanders and lifting hoists.