If you are an Electrical System Design engineer, you may require to choose an electric motor for industrial application purposes. When choosing a motor, there are several factors to take into account, including the application, electrical, operational, mechanical, and environmental concerns.
However, in this article, we would be focusing on the two most crucial factors for selecting a motor for industrial applications.
Selecting a motor based on Speed Variation
An AC motor must be able to change speed for numerous applications.
The simplest approach to changing the speed of an AC induction motor is to change the applied frequency using an AC drive.
Constant speed, variable speed, and position (or torque) control are the three basic uses for motors. Let us understand each one of them.
When used in a constant speed application, a motor frequently runs at a rough speed with little to no attention paid to ramps for acceleration and deceleration. Across-the-line on/off control is typically used to operate this kind of application.
The control circuit frequently comprises a manual motor controller or soft starter, an overload motor starter, and a branch circuit fusing with a contactor.
Constant speed applications can use both ac and dc motors.
AC motors are a good option as well. However, you can also use DC motors as it offers a hundred percent torque at zero speed.
Fans and centrifugal pumps are good examples of variable-speed applications.
With the right drivers, variable speed applications can be successfully used with both ac and dc motors.
A variable frequency drive (VFD) is a beneficial option for applications over 1 hp, such as fan and pumping applications, which results in increased efficiency. Brush wear is not a problem with ac induction motors.
Positional awareness may be increased depending on the drive type used to power the motor.
If the application calls for it, an encoder can be connected to the motor, and a drive can be defined to utilize the encoder feedback. As a result, this configuration can deliver servo-like speed.
Robots are the best example. Continuously checking the motor’s location as it moves allows for precise position control. A stepper motor with or without feedback or a servo motor with built-in feedback can be used for applications like placing a linear actuator.
A stepper’s purpose is to travel precisely and steadily to a position, then hold it. If correctly sized, an open-loop stepper system offers effective positional control. The stepper will take the appropriate number of steps even while feedback is absent unless it experiences a load interruption that exceeds its tolerance.
If the application’s speed and dynamics rise, open-loop stepper control system may not be able to meet system requirements. It calls for an upgrade to a servo motor system or a stepper with feedback.
A closed-loop system offers precise position control and accurate, fast motion profiles. In comparison to a stepper, a servo system will deliver more torque at high speeds, and they are also more effective in situations involving complex motion or high dynamic loads.
If want to go with a servo motor, it is important to match the inertia of the servo motor as closely as possible with a linear load. A mismatch of a 1:1 match is preferred. The reflected load inertia decreases by the square of the gear ratio, making geared speed reduction an excellent solution to inertia mismatch issues. However, gearbox inertia must be taken into account in the calculations.
Selecting a motor Depending on Various application loads
There are four different kinds of motor loads for industrial automation. We would be discussing each one of them with examples.
Constant torque and variable horsepower
Applications for variable horsepower and constant torque include gear-type pumps, conveyors, and cranes. Because the load doesn’t change in these applications, the torque remains constant.
Depending on the application, different horsepower requirements may apply. It makes ac and dc motors with constant speed a good option.
Constant horsepower and variable torque
Winders and unwinders used in paper mill are best illustration of a variable torque and constant horsepower application. Since the material speed doesn’t change, neither does the horsepower. But when the roll diameter grows, the burden does too. This is suitable use for servo motors or dc motors in small systems. Regenerative power should be taken into account while sizing the motor or picking the energy control strategy.
You can also use AC motors with speed feedback system and AC drives.
Variable Torque and Variable horsepower
Variable horsepower and torque are required by fans, centrifugal pumps, and agitators. The load output and necessary horsepower and torque both increase as the motor speed rises. With these kinds of loads, inverter duty ac motors with variable speed drives, the majority of the motor efficiency discussion start (VSDs).
Torque control or positional control
Applications like linear actuators, which must precisely move to numerous places, need precise positional or torque control. Feedback is frequently needed to confirm the correct motor position. The optimum motors for these applications are servo or stepper motors, although, for tight torque control in steel or paper lines as well as other comparable applications, a dc motor with feedback or an inverter-duty ac motor with an encoder is frequently utilized.
Industrial motors are available from a variety of manufacturers. The majority of industrial automation requirements can be satisfied by stepper, servo, ac, and dc motors; however, the best motor depends on the application. Users should collaborate closely with the motor and drive supplier to choose the best motor for the application, regardless of whether it is a constant speed, variable speed, or position control application.