Application - ABB RELION REX640 Technical Manual

Section 4
Protection functions
4.10.6
1000
This module also protects the motor from consecutive start-ups. When the
LOCK_START output is active, T_RST_ENA shows the possible time for next restart.
The value of T_RST_ENA is calculated by the difference of Restart inhibit time and
the elapsed time from the instant LOCK_START is enabled.
When the ST_EMERG_ENA emergency start is set high, the value of the cumulative
start-up time counter is set to Cumulative time Lim - 60s · Emg start Red rate. This
disables LOCK_START and in turn makes the restart of the motor possible.
This module also calculates the total number of start-ups occurred, START_CNT. The
value can be reset from the Clear menu.
The old Number of motor start-ups occurred counter value (START_CNT) can be
taken into use by writing the value to the Ini start up counter parameter and resetting
the value via the Clear menu from WHMI or LHMI.
The calculated values of T_RST_ENA, T_ST_CNT and START_CNT are available in
the Monitored data view.
The activation of the BLK_LK_ST input signal deactivates the LOCK_START output.
The activation of the BLOCK input signal resets the cumulative start-up counter
module.

Application

When a motor is started, it draws a current well in excess of the motor's full-load rating
throughout the period it takes for the motor to run up to the rated speed. The motor
starting current decreases as the motor speed increases and the value of current
remains close to the rotor-locked value for most of the acceleration period.
The full-voltage starting or the direct-on-line starting method is used out of the many
methods used for starting the induction motor. If there is either an electrical or
mechanical constraint, this starting method is not suitable. The full-voltage starting
produces the highest starting torque. A high starting torque is generally required to
start a high-inertia load to limit the acceleration time. In this method, full voltage is
applied to the motor when the switch is in the "On" position. This method of starting
results in a large initial current surge, which is typically four to eight times that of the
full-load current drawn by the motor. If a star-delta starter is used, the value of the line
current will only be about one-third of the direct-on-line starting current.
1MRS759142 C
REX640
Technical Manual