Notes on configuration

Rated current of the device I_rated

In crane operation, the motors are not operated continuously, but with variable load, at varying speeds, and with different ON durations. Under these conditions, it is sufficient when the rated current for the device I_rated is greater than the motor rated current. In intermittent duty with appropriate pauses in operation, the devices can carry twice the rated device current of I_rated greater than the rated motor current for 20 s. In intermittent duty with appropriate pauses in operation, the devices can carry twice the rated device current of I_rated for 20 s. This covers all the normal acceleration situations that occur with cranes. The SIMOTRAS HD devices can be operated continuously at the rated current for the device I_rated; the limit temperature for the thyristors will, however, be reached. Acceleration is not permitted from this operating state since the thyristors could be overloaded.

Rotor contactors

To ensure a reliable ramp-up from the closed-loop control characteristic to rated speed, it is recommended that 4 rotor contactors are used. Activation of the rotor contactors through contactor relays.

Permissible ON duration

Under unusual operating conditions, such as traversing with full load at extremely low speed for a long time, motors, resistors and SIMOTRAS HD must be dimensioned appropriately. When phase angle control is used, a higher stator current flows to achieve the necessary torque due to the reduced magnetization. The motors may become thermally overloaded, because the thermal power losses rise with the quadrant of the current. The resistors are overloaded when the closed-loop control characteristic is traversed for an extended period.

Rotor resistances

Since the speed is influenced with additional rotor resistors, the rotor performance is largely converted into heat in the external resistor. This ensures that excessive heating of the motor is avoided when traversing at low speed over long periods.

Emergency or safety limit switch

Due to the lack of stator contactors, the motor can no longer be galvanically isolated from the AC power controller, e.g. when an operational limit switch is actuated. If the controller is then not able to block the thyristors due to a device fault, this could result in an impermissible operating state.
It is therefore recommended that emergency or safety limit switches are used. These respond when the operational limit switch is passed and act on a line contactor or the crane switch.