motor drive system must be designed such that motive power is supplied in equal parts by the two motors to prevent overloading of either one of them or its mechanical transmission system. The speed of the two motors must necessarily be the same because they are coupled through the gear system. This can be achieved either with series connection of the two de motors or with parallel connection by means of a closed loop control system. Crusher drives: The motors used in crushers are of the slip ring type. Stalling considerations play a very important part in the design of these motors. Normally, the motors are designed to withstand locked rotor current during running without any external resistance introduced in the rotor circuit, for one minute. This is quite important, since very often the crushers tend to get jammed, when a big sized boulder gets trapped between the jaws of the crushers. Generally, the starting torque for such drives is limited to 160 per cent of the full load torque and the pull out torque is limited to 200 per cent to 250 per cent of the full load torque. The motors are also normally designed for IS per cent overload for 15 seconds and 20 per cent overload for 10 seconds taking into consideration the adverse loading conditions encountered in practice. Fan drives: The motors used are of the slip ring type with a speed variation, generally, between 1000 and 750 rpm. The cast iron grid resistance arc normally used for starting and controlling controller’s the speed of these drives. As the motors are located outdoor or in semi-outdoor locations totally enclosed motors of TEFC are employed.
motor drive system must be designed such that motive power is supplied in equal parts by the two motors to prevent overloading of either one of them or its mechanical transmission system. The speed of the two motors must necessarily be the same because they are coupled through the gear system. This can be achieved either with series connection of the two de motors or with parallel connection by means of a closed loop control system. Crusher drives: The motors used in crushers are of the slip ring type. Stalling considerations play a very important part in the design of these motors. Normally, the motors are designed to withstand locked rotor current during running without any external resistance introduced in the rotor circuit, for one minute. This is quite important, since very often the crushers tend to get jammed, when a big sized boulder gets trapped between the jaws of the crushers. Generally, the starting torque for such drives is limited to 160 per cent of the full load torque and the pull out torque is limited to 200 per cent to 250 per cent of the full load torque. The motors are also normally designed for IS per cent overload for 15 seconds and 20 per cent overload for 10 seconds taking into consideration the adverse loading conditions encountered in practice. Fan drives: The motors used are of the slip ring type with a speed variation, generally, between 1000 and 750 rpm. The cast iron grid resistance controller’s arc normally used for starting and controlling the speed of these drives. As the motors are located outdoor or in semi-outdoor locations totally enclosed motors of TEFC are employed.
IDA-QP8.docx