Variable Speed Drives (VSDs)

Advantages of using a Variable Speed Drive (VSD)

VSD Benefits

Variable Speed Drives are probably the best method for controlling motor speed in response to varying process demands. These small decreases in the speed of pumps and fans or the pressure of pumps could lead to large decreases in energy use (and thus electricity costs).

Since motors consume lots of energy, the importance of the control of motor load demands increases as energy supply becomes more expensive and ever more strained. One of the biggest advantages of using a VSD is the energy cost savings associated with speed control (more efficient operation), with energy savings of 25 - 70% that can be realised by using VSDs.

Motor speeds can be revved up, slowed down, sustained indefinitely, or brought to sudden halts, with speed levels delivered as-needed rather than at uniform, arbitrary rates. By ramping up the motor speed slowly, VSDs also help save energy by reducing the in-rush current and mechanical issues associated with starting motors. A VSD also saves you money by extending the life of your motor. VSDs decrease the fluid flow into an AC motor, which in turn decreases the pressure and friction on the valves and other machinery inside the motor. This will help reduce the wear and tear on your motor, thus extending the life of your equipment. A VSD can therefore save money by increasing the efficiency of AC motors and decreasing electricity use.

When you operate your motors at the most efficient speed for your application, fewer mistakes will occur and production levels will increase, while earning your company higher revenues. The initial cost of a motor or VSD is generally only a fraction of the cost of operating the motor for its lifetime. A VSD usually pays for itself in a matter of months or just a few years.

Modern VSD benefits include power-factor correction and low power consumption, along with full-speed control and not just start/stop control. Other benefits include dynamic braking, PID control, built-in I/O and logic, circulatory control mode, multi-motor control, communication interfaces etc.

Below is a list of the top 9 benefits of using a VSD:

• Controlled Starting Current and Acceleration
• Energy Cost Savings
• Elimination of Expensive Mechanical Drive Components
• Increased Motor Longevity
• Adjustable Operating Speed
• Limits and Adjusts Torque
• Controlled Stopping
• Reverse Operation
• Reduced Power Line Disturbances

Further to this VSDs allows for an increased number of motor starts per hour and protects motors against possible low/high voltage/current supply, short-circuits, lost phases (in/out) and 3-phase imbalances.

For a more detailed explanation on this, please see our blog post: Advantages of using a Variable Speed Drive (VSD)

Other VSD Use Cases

Other than the noted benefits of using a VSD, VSDs are also often used as Single-Phase to 3-Phase Converters and customised to offer Solar Powered VSD products, referred to as Solar Drives. If you have a 3-Phase motor/device and do not have ready access to 3-Phase power, VSDs offer a workaround to get your equipment properly powered.

For more details on using VSDs as converters, please see our blog post: Single-Phase To 3-Phase Converters

Solar Drives are essentially designed to make use of this free power from the sun, as well as combining it with the benefits of using a VSD.

For a more detailed comparison between VSDs and Solar Drives (for Water Pumps), please see our blog post: Solar Drive vs Variable Speed Drive

For more details on using Solar Powered VSDs, please see our Solar Drives (for Water Pumps) product page: Solar Drives

Advantages of VSDs vs Soft Starters

VSDs provide all the Soft Starter benefits and more. Compared to Soft Starters, Variable Speed Drives (VSDs) offer much more flexibility in terms of features and settings and, depending on the application, much bigger cost savings, especially where speed control is required.

Not only do VSDs provide an extremely smooth and controlled start, but they also efficiently control motors to nearly any desired level of speed, torque, or position, including over-speed and full torque at zero speed. Special applications and safety features are also included, providing even greater benefit. In most cases, variable speed control greatly improves processes and yields impressive energy savings.

The biggest advantage of a Soft Starter over a VSD is however the lower initial cost of the product. If matching of the speed of the process is not required, then the initial cost of the product becomes a bigger factor, which might make a Soft Starter a more optimal choice. If the process can be optimised or additional costs can be saved on electricity by matching the process speed, or by reducing maintenance costs of the overall system (extending system lifetime), then a VSD will most likely be the optimal choice.

For a more detailed comparison on this, please see our blog post: Choosing between a VSD and a Soft Starter

For more details on using Soft Starters, please see our product page: Soft Starters

How do Variable Speed Drives (VSDs) Work?

Variable Speed Drives Working Principle

Variable Speed Drives connect to standard AC induction motors with control capabilities for adjusting speed, torque, and horsepower. Modern VSDs contain three key components which can be used to describe its basic working principle:

1. Rectifier: The first step in this process is to convert the AC supply voltage into DC using a rectifier.
2. DC Filter (DC Link or DC Bus): The DC circuit contains the capacitor and inductor used for filtering (smoothing) the DC power output from the previous step which contains voltage ripples.
3. Inverter: The basic working principle of an inverter is switching the DC on and off so rapidly that the motor receives a pulsating voltage similar to AC. This conversion is typically achieved using power electronic devices such as IGBT power transistors using a technique called Pulse Width Modulation (PWM). The output voltage is turned on and off at a high frequency, with the duration of on-time, or width of the pulse, controlled to approximate a sinusoidal waveform. The switching rate is controlled to vary the frequency of the simulated AC that is applied to the motor.

With a standard AC across-the-line motor starter, line voltage and frequency are applied to the motor and the speed is solely dependent on the number of motor stator poles. In comparison, a VSD delivers a varying voltage and frequency to the motor, which determines its speed. The higher the frequency supplied to the motor, the faster it will run. Power applied to the motor through the VSD can make the motor working speed lower than the nameplate base speed or increase the speed to synchronous speed and higher.

For a more detailed explanation on this, please see our blog post: How do Variable Speed Drives (VSDs) Work?

Or see this article from science direct https://www.sciencedirect.com

Spares

TCGC offers the following EMHEATER standard Spare Parts:

Keypad  |  Control Card  |  Power Card  |  IGBT Model  |  Fan  |  Capacitor  |  Rectifier  |  Fan Board  |  Keypad Extender

Accessories

TCGC offers the following additional items to be used for EMHEATER products:

Dynamic Braking Systems | Aluminium Housed Braking Resistors | DC Chokes/Reactors | AC Chokes/Reactors | AC EMC/EMI Filters (Noise Filters) | Sine Wave Filters | Enclosures | Custom Built Panels | Remote Monitoring and Control Devices

Get Your Variable Speed Drives

Please feel free to Contact Us for your Variable Speed Drives needs, we also stock spares and accessories.