Variable Speed Drives Basics: What They Are & Why Your Equipment Needs one

Variable Speed Drives Basics: What They Are & Why Your Equipment Needs one

The speed and torque of a motor may be controlled using variable speed drives by adjusting the voltage and frequency of the motor’s input. Therefore, it is possible to attain a level of motor speed that is very closely matched to the output needs of the machine that the motor is operating. 

The regulation of the energy that is sent from the mains to the process is the primary purpose of a variable speed drive motor, often known as a VSD. Between the electrical supply and the motor is where you’ll find the variable speed drive.

The electric variable speed drives receive electricity from the electrical supply, and then the drive is responsible for regulating the amount of power that is supplied to the motor. In centrifugal load activities such as fans, variable speed drives may greatly reduce the amount of energy that is used. 

If, for instance, a fan is set to operate at just half of its typical speed, then the amount of horsepower required to power the device is cut by a factor of eight. In this essay, we will gain knowledge about how a variable speed drive works and the many uses it has.

What is Variable Speed Drive?

Alternately referred to as an adjustable speed drive, variable speed drive, adjustable frequency drive, inverter AC drive, and Microdrive, a variable frequency drive (VFD) is a type of motor controller that varies the voltage and frequency that is supplied to drive an electric motor. VFDs are also sometimes referred to as adjustable frequency drives. In most cases, the gadget is used in commercial buildings’ heating, ventilation, and air conditioning (HVAC) systems for the purpose of managing the speed of the motor, fan, and even the compressor. 

Drives with variable speeds and frequencies are used in a wide spectrum of applications, ranging from little home appliances to industrial-sized compressors. As a result of increasingly severe emission rules and the desire for enhanced dependability and better availability, a rising number of end users are exhibiting greater interest in electric drive systems. This is due to the fact that electric drive systems provide a number of advantages. 

Systems that use variable frequency drives (VFDs) have the potential to be more energy efficient than throttling control of fluid flow systems, such as those used in systems with pumps and damper control for fans. Despite this, the penetration of the worldwide market for VFDs in all of their applications is still quite low.

The Purpose of Using a Drive that has Variable Speeds

Listed down below are some of the most important applications for variable-speed drives:

  1. Imagine the variable frequency drive (VFD) as the dimmer on a light bulb. It gives you complete control over the brightness without requiring you to use the on/off button at any point in the process.
  1. Additionally, having one installed enables variable voltage and may or may not include a bypass switch. This means that in the event that the drive fails, all you have to do to turn off the component is flip a switch, and your HVAC system will continue to operate as it did before.
  1. The most important reason to use a variable frequency drive, or VFD, is to reduce the amount of energy wasted and the amount of wear and tear on the machine.
  1. Even with reduced energy needs, your heating, ventilation, and air conditioning system, along with any other equipment, will continue to operate normally.
  1. VFDs provide gentler stops and starts for moving components inside an assembly, which contributes to a reduction in the noise contamination caused by the assembly.
  1. The torque, direction, and speed of an AC induction motor may all be controlled by your variable frequency drive (VFD).
  1. When converting the frequency and voltage of a DC bus into the variable frequency and voltage of an AC output, the DC bus’s frequency and voltage are used as the starting point.
  1. Very compact variable frequency drives (VFDs) could include a single power pack protection component that doubles as an inverter and converter.
  1. Through the use of a control board, involved control circuitry is responsible for coordinating the turning on and turning off of power devices.
  1. The firing of the capacitors in the appropriate order is determined by the circuit boards.
  1. Either a Digital Signal Processor, sometimes known as DSP, or a microprocessor may fulfill all of the decision needs and internal logic requirements. Because of this, VFD is comparable to a computer’s power supply.
  1. Imagine a vehicle being driven by an unskilled person who is constantly slamming on the brakes and stepping on the throttle. A greater amount of wear and tear would be inflicted on the vehicle.
  1. Your heating, ventilation, and air conditioning (HVAC) systems may make a seamless transition between starting and switching off power devices when you use VFD. This results in an overall improvement in the unit’s lifetime as well as its durability.

Common Operation & Maintenance Instructions

The VFD maintenance schedule is broken down into three primary categories, which are as follows:

1.) Maintaining a Clean Condition of the VFD

2.) Maintaining a Moisture-Free VFD

3.) Maintaining a Secure Hold on Every Connection

The next paragraphs will go into more depth on these protective measures, as follows:

Keeping the VFD clean

  1. The vast majority of variable frequency drives are classified as NEMA 1 devices, which include side vents to provide airflow for cooling purposes. A great number of VFDs are also considered to be protected by the NEMA 12 standard, which mandates that their enclosures be airtight and dustproof. NEMA 1 VFDs are prone to dust contamination. If there is dust or debris collection on the VFD, there is a good chance that there will be insufficient airflow. As a direct consequence of this, the performance of the circulating fans and heat sinks is reduced.
  1. Dust on a gadget might potentially lead to malfunctions or even total failure of the item. This is due to the fact that dust has the propensity to soak up moisture. Compressed air may also be released by the variable frequency drive (VFD) in certain settings. You should be aware, on the other hand, that the air in a typical business building is full of moisture as well as particulate matter.
  1. You need to take advantage of dry, oil- and moisture-free air. In such cases, the procedure can be counterproductive rather than beneficial. If you want to avoid the possibility of an electrostatic discharge, you should choose an air supply that is both dedicated and specialized (ESD). It is possible to reduce the accumulation of static electricity by using a non-static producing spray or a reverse-operated ESD vacuum.

Keeping the VFD dry

  1. Corrosion of the circuit board is a frequent kind of damage that may occur when the VFD is deployed in high-moisture environments. You have to check to see that the VFD does not have any drops of water falling across it. In addition, you should carry out routine checks to determine whether or not the VFD was put in moist environments.
  1. This is particularly valid for NEMA 1 enclosure fashions. In early iterations of the device, condensation was a significant source of annoyance. Condensation prevention was required to be included in all VFDs produced by their makers. In order to stop the drive from beginning, the software logic must first be activated.
  1. When it comes to the more current and complex models, the same level of security is seldom necessary. Regular heat cycles result in heat sinks, which stop condensation from occurring. If you believe that condensation is likely to occur, you should look into purchasing a space heater that has a thermostatic control and an enclosure that meets NEMA 12 standards.

Ensuring that all Connections Remain Seamless

  1. The majority of individuals either skip over an important step or do not carry it out in the proper manner, which is checking for weak connections. Before you even start to get the connections nice and snug, you have to make sure that the VFD is stored in a pristine environment. Poor connections may be caused by a variety of factors, including heat cycles and mechanical vibrations.
  1. The same is true for preventive maintenance techniques performed by amateurs. Re-torquing screws is not a good idea and should be avoided. In addition, you run the risk of causing unpredictable functioning or poor connections if you tighten screws that are already at their maximum level of tightness. Arcing is caused by improper connections, which may lead to voltage problems, the breakdown of fuses, and damage to protective components. Arcing can also harm protective components.
  1. Arcing at the output might potentially cause damage to the power components or issues caused by excessive current. The erratic functioning that results from loose control wires is a typical adverse effect. For instance, if the Start/Cease signal wire is loose, the VFD can stop working without the ability to regulate it. If the speed reference wire is not securely fastened, the drive speed may begin to oscillate, which might result in personal harm, damage to the machine, or even scrap.

Variable Speed Drives To Control Motors

A significant amount of money might be saved by controlling motors using variable speed drives, and the following are the concepts on how it’s done:

  • Powering electric motors consumes close to 70 percent of the total electrical energy that is used in industrial settings. These motors are the workhorses of the commercial world, powering anything from pumps that move fluids to fans that move air to compressors and conveyors, as well as any other kind of equipment that relies on rotational force to do its tasks.
  • These motors are the key to helping you minimize the amount of energy you consume and the CO2 emissions you produce. They are also the key to helping you create solutions that are more energy efficient for your customers. Pumps, fans, and compressors are often operated at a constant speed, and the manual opening and shutting of valves in the pipes are used to regulate the flow rate and the destination of the fluid.
  • Because of this, the process of starting up is often quite a labor demanding. For instance, it may take a single person up to an hour to start up a pumping station. When workers are required to travel great distances to isolated locations, more expenditures are incurred for their transportation. This procedure may be automated in certain facilities; however, the facilities typically have a low energy consumption rate.
  • There is another option that uses less energy and is more efficient. When these applications are run with variable speed drives, there is an immediate reduction in the amount of energy that is used, in addition to the long-term competitive benefits that this delivers. Any procedure that uses electric motors has the potential to reap significant financial savings as well as operational gains from the use of variable-speed drives. 
  • You should probably take a thorough look around your own operations and processes, regardless of how large or little they are, to determine the areas in which the focused usage of variable speed drives might assist you in obtaining quick financial payback and long-term benefits over your competitors.

To sum it up…

Utilizing an oscilloscope will allow you to create a map of the performance of your VFD. It is possible that you will need to compare it over time to look for fluctuations in the performance of the drive, the input power, and the output signal in the past. When compared to measurements taken in a configuration that has been optimized, these signals may suggest early warning indications of device failure. You may, for instance, assess problems with transformers, deteriorating capacitors, early warnings of motor insulation problems, or load and line reactor problems.

It is common knowledge that variable frequency drives (VFDs) play a significant part in the operation of a variety of motorized forms of equipment, devices, and systems, including HVAC systems. In addition, preventative maintenance guarantees that the gadget will continue to function faultlessly for the whole duration of its expected lifespan. Do you have any more inquiries about the maintenance and fixing of electric motors and variable frequency drives? For more elaboration of ideas and information pertaining to variable speed drivers, please see

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