Motor Power Rating

Motor Power Rating:

Classes of Motor Duty in Electrical Drives : IS: 4722-1968 categorises various load time variations encountered in practice into eight standard Classes of Motor Duty in Electrical Drives: Continuous duty. Short time duty. Intermittent periodic duty. Intermittent periodic duty with starting. Intermittent periodic duty with starting and braking. Continuous duty with intermittent periodic loading. Continuous duty with starting and braking. Continuous duty with periodic speed changes. These Classes of Motor Duty in Electrical Drives are explained below. 1. Continuous Duty (Fig. 4.2(a)): It denotes the motor operation at a constant load torque for a duration long enough for the motor temperature to reach steady-state value. This duty is characterised by a constant motor …


Heating and Cooling Curves of Electrical Drives : An accurate prediction of Heating and Cooling Curves of Electrical Drives rise inside an electrical motor is very difficult owing to complex geometrical shapes and use of heterogeneous materials. Since conductivities of various materials do not differ by a large amount, a simple thermal model of the machine can be obtained by assuming machine to be a homogeneous body. Although inaccurate, such a model is good enough for a drive engineer whose job is only to select the motor rating for a given application ensuring that temperatures in various parts of motor body do …


Motor Rating Various Duty Cycles : From the point of view of calculation of motor rating various Motor Rating Various Duty Cycles can be broadly classified as: Continuous duty. Fluctuating loads. Short-time and intermittent duty. Continuous Duty: Maximum continuous power demand of the load is ascertained. A motor with next higher power rating from commercially available ratings is selected. Obviously, motor speed should also match load’s speed requirements. It is also necessary to check whether the motor can fulfil starting torque requirement and can continue to drive load in the face of normal disturbances in power supply system; the latter is generally assured by the transient and …


Selection of Motor Power Rating : The Selection of Motor Power Rating of a motor for a specific application must be carefully chosen to achieve economy with reliability. Use of a motor having insufficient rating, either fails to drive the load at its normal productive level or lowers the productivity and reliability through frequent damages and shut-downs due to overloading of the motor and power modulator. On the other hand, if power rating is decided liberally, the extra initial cost and extra loss of energy due to operation below rated power makes the choice uneconomical. Furthermore, induction and synchronous motors operate at a …


Updated: May 1, 2020 — 2:43 pm