After selecting the type of electric motor, depending on the working conditions, the scope of its use, the specifics of the mechanism, and so on, it is necessary to determine the important performance characteristics of the motor.
So, first of all you need to pay attention to power, starting and rated moments, rated current and voltage, type of operation mode, energy efficiency class and power factor. All these parameters are specified in the instructions or the description of the electric motor.
Before buying an electric motor, select its type. So, there is an electric DC motor, a synchronous motor and an asynchronous motor.
Asynchronous electric motors are divided into devices with a phase and short-circuited rotor. Mostly in life there are the latter, since they have a very simple design, are easy to use and maintain, have high reliability and relatively low cost.
The disadvantages of these motors are high starting current, a relatively small starting torque, high sensitivity to voltage drops in the network, the need to use a frequency converter for smooth adjustment of the shaft rotation speed. Also, these motors use reactive power from the network itself.
The use of an asynchronous motor with a phase rotor makes it possible to reduce the starting current and increase the starting torque. The use of such motors is very limited, since their design is very complex, which leads to an increase in their value. Such motors are used in drives of various mechanisms with very severe starting conditions.
Where speed regulation is required, for example, in elevators, a multi-speed asynchronous electric motor is used. So, where it is necessary to stop during the specified time and fix the shaft when the mains voltage is disconnected, for example, winches, metal machines, use an asynchronous electric motor with a special electromagnetic brake.
There is also an asynchronous electric motor with increased slip, required for operation in modes with pulsating load and intermittent modes.
Synchronous electric motor
The advantage of this motor is the ability to work with the power factor cos φ = 1. Also, in the overexcitation mode, this electric motor can transfer reactive power to the power grid, which leads to an increase in its power factor, a significant reduction in the loss and drop in the mains voltage. It is worth noting. That this type of electric motor is resistant to voltage drops.
The greatest moment of this motor is proportional to the voltage, the motor of the asynchronous type is the square of the voltage. Thus, when the voltage is lowered, this electric motor will retain the ability to withstand large overloads, forcing the excitation significantly increases the efficiency of using the motor when the voltage is lowered in the network.
Also, the efficiency of such an engine is higher than asynchronous, since it has a large air gap and permanent magnets. Also, the shaft of such a motor rotates at a constant speed even during a change in the moment of load on an existing shaft.
The disadvantages of a synchronous electric motor are the complexity of the design, a very high price, the presence of a pathogen and a rather complicated start. Thus, a synchronous electric motor is used with powers of more than 100 kW in various compressors, pumps, fans, and engine-generator devices.