A variable speed drive (VSD) or variable frequency drive (VFD) is a device used to regulate the speed and output torque of electrical motors. By varying the frequency and voltage of the power supply, the motor speed can be adjusted to better suit the specific requirements of the application.
VSDs offer a wide range of benefits including reducing energy consumption, improving process controls, reducing machinery wear and tear, reducing machinery noise and vibration and more.
VFDs are used in a wide range of commercial and industrial applications ranging from small appliances to large industrial compressors, fans and pumps. They are used in heating, ventilation and air conditioning (HVAC) systems, as well as fluid pumping systems in mining, water treatment, manufacturing, power generation and a range of other industries. They can be used to provide control systems for positive displacement pumps, gear pumps, reciprocating pumps, conveyors, extruders, extruder knife-cutters, mixers, reciprocating compressors, cooling fans, airflow systems and much more.
Here are three of the most common applications for VSDs.
Most commercial or industrial fans are designed to operate at a single speed and are therefore either turned on or off. That means that controlling the operation of a fan without a VSD involves continuously switching it on and off. However, bringing a fan up to operating speed from stationary requires significant power and places a lot of strain on the system. This increases energy usage and can significantly decrease the lifespan of the motor.
While dampers are often used to regulate the output of fans, reducing the speed of the fan is much more efficient. A VSD can vary the speed of a fan motor to match load requirements and reduce the current drawn during peak demand periods. Because the power a fan draws is proportional to the cube of its speed, reducing the speed can save a large amount of energy. Reducing fan speed can also reduce noise and vibration in the fan system, which can be a major benefit for fans in residential or office buildings or manufacturing facilities where noise and vibration can be a major problem.
- Pumping Systems
Pumps are one of the most common applications for variable speed drive systems. VSDs are essential for limiting the life cycle costs of a pumping system, as a VSD can reduce energy costs, maintenance costs and extend the lifespan of the machine.
A VSD can reduce maintenance and repair costs in pumping systems in a number of ways. Gradually ramping up pumping acceleration can reduce water hammer effects caused by rapid changes in flow rate and pressure.
Use of a VSD can also reduce the risk of cavitation. Cavitation is the rapid creation and subsequent collapse of air bubbles in a fluid. The force of cavitation can be strong enough to damage the pump’s internal metal components or seals. With a VSD, you can monitor and control the pressure in the incoming pipeline and reduce the risk of cavitation.
Using a VSD also allows you more flexibility in your choice of pump. Since it can be difficult to precisely estimate your system parameters in advance, you can end up including larger safety margins than necessary. This can lead to higher operational costs if the flow and head end up being lower than expected. With a VSD you can run the pump at lower speeds, thereby reducing operating costs to only what’s necessary to adequately power the system.
- Air Compressors
Variable speed drives are often used in air compressors to alter the power to the motor and, thereby controlling the output of the compressor. A standard air compressor uses a direct electrical current to power the motor. Regardless of the compressor usage, the motor runs at a continuous speed, which leads to a lot of wasted energy and unnecessary motor load.
With a VSD, the frequency of the electricity powering the motor can be controlled according to the requirements of the compressor. This means that the motor can be slowed to generate only the necessary amount of power to run the compressor. In this way, a VFD can be used to reduce power consumption, generating significant energy efficiencies and saving money on power bills.
VSDs can also be programmed to monitor pressure, motor heat, and other factors that affect motor functionality. The VSD can monitor the motor performance and make automatic adjustments to ensure the motor remains within optimal operating parameters. This helps to minimise strain and unnecessary load on the motor, reducing wear and tear and downtime and lowering repair and maintenance costs.
These applications are just the tip of the iceberg when it comes to VSD usage. While a VSD is a costly, and in some cases, complex system, the savings it delivers in terms of energy efficiency and reduction in repairs and maintenance mean that the system will pay for itself over time.