Presentation
LR97 D 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.
Applications
LT47 relay is particularly suitable for the following machines:
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- | 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 I2t.
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. |
Operation
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- | Because of their two separate time settings, LT47 relay can be
combined with the motor-starter function:
D-Time: starting time, O-Time: trip time during steady state.
The D-Time function is only available during the motor starting
phase. During this phase the overload detection function is
inhibited in order to allow starting. Under steady state
conditions, when the motor current is greater than the setting
current due to an overload or single-phasing, the red LED lights up
and the internal relay switches its
contact after a time preset by the O-Time knob.
The red LED stays on, indicating that the relay has tripped.
The relays are simple to set, in 5 easy steps:
Adjust the 3 knobs to maximum (Load, D-Time and O-Time),
Adjust the D-Time knob to the value corresponding to the motor
starting time.
When the motor reaches steady state, adjust the Load knob (turn the
knob counter-clockwise until the red LED starts to flicker).
Slowly turn the Load knob clockwise until the LED goes out.
Set the required tripping time, using the O-Time knob. |
| Status Signaling | Description |
To assist fast diagnostics, two LEDs (one green and one red) allow
Signaling of the operating status:
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LT47 Electronic Over Current Relays
| Relay setting range | Usable range (1) | Relay supply voltage | Reference | Weight | | A | A | | | kg | | LT47 relay with manual/electric reset | | 0.5…6 | 0.5…5 | a 200…240 V | LT47 06M7S | 0.192 | | a 100…120 V | LT47 06F7S | 0.192 | |
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