Function Block - ABB 615 series Technical Manual

Section 4
Protection functions
4.10.2
4.10.3
4.10.4
750

Function block

GUID-CCCBE20D-0546-41DB-8C68-A32EFD28E9D1 V4 EN
Figure 375: Function block
Functionality
The motor start-up supervision function 66/51LRS is designed for protection against
excessive starting time and locked rotor conditions of the motor during starting. For the
good and reliable operation of the motor, the thermal stress during the motor starting is
maintained within the allowed limits.
The starting of the motor is supervised by monitoring the TRMS magnitude of all the
phase currents or by monitoring the status of the circuit breaker connected to the motor.
During the start-up period of the motor, 66/51LRS calculates the integral of the I²t value.
If the calculated value exceeds the set value, the trip signal is activated.
66/51LRS has the provision to check the locked rotor condition of the motor using the
speed switch, which means checking if the rotor is able to rotate or not. This feature trips
after a predefined operating time.
66/51LRS also protects the motor from an excessive number of start-ups. Upon exceeding
the specified number of start-ups within certain duration, 66/51LRS blocks further
pickups. The restart of the motor is also inhibited after each start and continues to be
inhibited for a set duration. When the lock of pickup of motor is enabled, 66/51LRS gives
the time remaining until the restart of the motor.
The function contains a blocking functionality. It is possible to block function outputs,
timer or the function itself, if desired.
Operation principle
The function can be enabled and disabled with the Operation setting. The corresponding
parameter values are "Enable" and "Disable".
The operation of 66/51LRS can be described with a module diagram. All the modules in
the diagram are explained in the next sections.
1MAC059074-MB A
615 series ANSI
Technical Manual