Variable Speed Drives
If you’re looking at ways to save energy – and let’s face it, who isn’t? – one of the most effective tools at your disposal is the Variable Speed Drive (VSD).
While some machinery needs to run at a fixed speed, many motor applications have different processes, needing different speeds.
Also known as Adjustable Speed Drives (ASDs), frequency converters, drives or inverters, VSDs are a highly effective way of using energy more efficiently – with associated benefits including helping you to hit environmental targets, cutting costs and increasing profit margins.
What are Variable Speed Drives?
VSDs have been on the market since the 1980s, providing a versatile alternative to a range of other systems designed to regulate machinery speed, from DC motors and hydraulic couplings to gears and pulleys.
What do Variable Speed Drives do?
Essentially, they control the electrical supply to an AC induction motor, adjusting the motor speed and torque to match the process requirements of the machine by converting an electrical supply into a variable frequency and voltage. Most are controlled automatically.
What different types of Variable Speed Drives are on the market?
A basic design of VSD would be used for applications such as controlling a fan or a pump. The smaller ones (under 15kW) can be built on to a motor, although in most cases VSDs are standalone devices, which are installed between the electrical mains supply and the motor unit.
The advanced versions, which can operate with several MW of power, are used for more precise speed and torque control. They can also be connected to a number of control functions as well as being linked to a computer network to provide useful up-to-the-minute operating data.
How do Variable Speed Drives work?
The most commonly used VSDs are those applied to AC induction motors. These comprise: a rectifier to change AC current to DC current; an intermediate circuit to condition the rectified DC supply; an inverter to convert the DC back to an AC supply of variable frequency and voltage; and finally a control unit to monitor the system and respond to external signals to ensure that the correct output is delivered.
How efficient are Variable Speed Drives?
Around 2-8% of energy may be lost through additional heat dissipation, making a VSD around 92-98% efficient. However, the benefits in energy savings from having variable speed and torque far outweigh any losses.
Any other benefits to Variable Speed Drives?
Although most companies will be looking at installing VSDs for their energy and money saving attributes, there are a range of other benefits, including:
Improved power factor
- More precise control of speed, pressure, flow and temperature
- Prolonged equipment life from soft starting and programmed acceleration or deceleration
- More control at high speed – and in some cases higher achievable speeds
- The possibility of linking with other process control systems
- Recovering electrical energy from braking for reuse
Anything else worth knowing?
As with any electrical equipment, VSDs should be kept dust free and in a dry, ventilated area to avoid damage from humidity or overheating.
The purchase and installation of VSDs are best carried out by a professional to ensure that your business reaps the maximum energy saving benefits. Choosing the wrong VSD or applying it incorrectly can reduce the potential savings.
It’s also a good idea to have your machinery checked first, before installing a VSD, to check that it is the correct size and is otherwise working efficiently, with no leaks or faulty parts. Also, some old motor models may not be suitable for VSDs.
Finally, your own staff should also be trained to operate the VSD, all operating paperwork should be kept safely for future reference and a programme of regular maintenance should be established so that energy savings can be maximised.
For more information, visit www.carbontrust.co.uk or contact our sales staff to chat through the benefits of VSDs.
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