Each pump required motor capacity is not the same, in order to make the motor in use the most efficient, must be based on the load of different nature to choose the appropriate motor capacity and type. Such as the motor capacity is too large, although you can start, but can not play the best role of the motor, not only resulted in investment waste, but also efficiency and power factor are not high, so that a lot of energy waste. Motor capacity is too small, it will be difficult to start, or barely start up, the working current will exceed the rated current of the motor, causing the motor windings overheating and even burned. Select the motor capacity, but also take into account the size of the power supply transformer capacity. In general, the largest single direct-phase asynchronous single-phase (or three-phase) motor capacity, power supply transformer should not exceed the capacity of 1 / For continuously running motors, such as motors for pumps and fans, the efficiency is maximized when the motor is operated at a load factor of about 70% from the energy saving point of view. For agricultural motors, the average load rate of operation, the highest efficiency. Therefore, the average load of agricultural motors, motor rated capacity of 65% or more. That can be considered the choice of motor capacity is reasonable. For short-running motors, for example motors fitted with motorized gates, can be allowed to operate at an excessively high rated power, depending on whether the torque of the motor can meet the load torque requirements.