What are Variable Speed Drives? The Ultimate Guide

A variable speed drive is an electronic device used in electrical and mechanical driving systems which allows the user to conveniently control the AC motor speed. It is also helpful for monitoring the generated torque by changing the motor input speed and voltage.

Variable speed drives are also able to control the operating speed of a motor constantly with extreme precision. They are mostly suited for industrial applications for controlling the rotational speed of the connected motor system.

Variable speed drives are also commonly used in large fans, air conditioners, and industrial fillers. Usually, variable speed drives are equipped with electric motors and a controller for regulating the speed of the motor.

Along with variable speed drives, a motor speed governor is also used, which helps in regulating the maximum speed that the motor can reach at any given time. This prevents the motor from over-revving, which can cause sufficient damage to it.

The purpose behind variable speed drives

Electrical motors play a crucial role in our everyday lives and are found in almost all appliances we use to carry out regular chores. These motors must be connected to an electrical input line to be able to operate and produce torque and speed corresponding to the amount of energy it consumes.

However, unless the energy input is constant and adequate for maintaining motor functions for longer periods of time, the motor cannot operate at optimum levels, wasting more energy in the process.

Variable speed drives can be conveniently installed on electrical motors that offer greater control over the speed or the torque of the motor, depending on the requirement of the load. Hence, variable speed drives are readily installed to AC motors as an essential component that significantly improves their performance.

Advantages of a variable speed drive

There are several advantages, such as:

• Convenient performance control: variable speed drives play a vital role in controlling the performance of AC motors for industrial and commercial applications. It makes easy applications like flow, acceleration, speed, pressure, temperature, torque, tension, and monitoring.
• Lower stress: Fixed speed loads are often subjected to higher torques that require greater energy consumption, as well as put the motor through greater mechanical and electrical stress. By ensuring that the motor moves in a specialized pattern, such as the S-curve pattern, the variable speed drive can help lower mechanical and electrical stress. It also contributes to smoothening deceleration and acceleration controls.
• Easier maintenance: As variable speed drives offer some protection against mechanical stress and ensure that the motor is protected from hazards during frequent acceleration and deceleration changes, it contributes to the general durability of the motor. It also reduces the necessity for regular maintenance and high repair costs.
• Energy-saving: One of the primary advantages of using a variable speed drive is the energy-saving options it brings along. Fixed speed loads often draw significantly higher amounts of electricity to perform, which can put the motor through electrical stress.
  However, the energy consumption can be brought down considerably using variable speed drives. For this, the motor application connected to the main power line is operated with a variable speed drive. Variable speed drives, therefore, offer a greater reduction in energy consumption compared to fixed speed loads.

Variable Speed Drive (VSD) vs Variable Frequency Drive (VFD)

Electrical motors can be primarily regulated using two types of controlling components - the Variable Speed Drive (VSD) and the Variable Frequency Drive (VFD). While the VSD is responsible for changing the speed of the electrical motor whenever necessary by altering the input voltage, VFDs can change the speed of the electrical motor by changing the voltage, as well as the frequency of the input current. So, unlike VSDs, which can be used for both AC and DC motors, VFDs can only work effectively with AC motors.

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