Depending on the size of pump, there can be either thre […]
Depending on the size of pump, there can be either three phase induction machines, or single phase induction machines.
The three phase variants will be squirrel cage due to their maintenance free nature, and mostly constant speed of operation. The same goes for single phase machines, but they will be more suitable for household pumps, in scale of few hundred watts to few kilowatts.
You may use DC machines, with shunt machine more suitable for constant speed application. I don’t believe you would require a very high starting torque, but if so, a combination of series-shunt arrangement can be used. In this case, apart from a reliable DC source (motor drives are easy solutions, both for AC and DC motors), and an arrangement to configure the motor as a series machine first (high starting torque configuration), and then convert the same machine into shunt (constant speed application).
The simplest of the motor, An induction motor called Squirrel cage motor.
Rotor could be either diecast or built with copper rods and fabricated.
Motors stator will be wound according to the designed speed (RPM) of the pump and its Horse power requirement.
The number of poles will be determined by the nearest synchronous speed of the pump requirement.
For a very large pumps even the rotor will be wound as the large motors demand is not very large to invest in a manufacturing technology that is cheap.
However Squirrel cage motors are less efficient than wound rotor motors as the former is standardised and are not individually designed for specific application and voltage and load condition.
Large Motors are usually three phase type. and in the event any failure of the windings it can be rewound easily quickly and relatively low cost.
Hence small domestic water pumps of 5 HP or less are generally Single phase and squirrel cage.