ZERO SPEED AND EMERGENCY BRAKING SYSTEM FOR ELECTRICAL OVERHEAD TRAVELLING CRANE

In this paper, zero speed is achieved in drive motor of an Electrical Overhead Travelling (EOT) crane by means of a dynamic braking system. There are two modes in the crane operation. The first one is running mode and another one is braking mode. In the zero speed braking, an induction motor is converted as a braking mechanism. The dynamic braking circuit is activated during the braking mode. In EOT crane, a thruster brake system is mostly used and it is an electro-mechanical device. The thruster brake is installed between the drive motor and gear box for controlling the load though the electric power is failed. The thruster brake is used to retard the rotating speed of motor shaft and to stop it at desired position. The Thruster brake and drive motor are energized simultaneously to run the crane/hoist is called the running mode and stop the crane/hoist by both are de-energized is called the braking mode. A small time difference (time clip) between the function of motor and thruster causes huge impact pulse on the gear box/shaft. This impact pulse may diminish the gear box/shaft progressively that cause load drop accident. For avoiding/minimizing the time clip, the drive motor is converted as a braking device during the braking mode. The drive motor will be turned to zero speed instead of deenergized