Five reasons to control your compressor with a variable frequency drive.

R ecent improvements to Variable Frequency Drive (VFD) feature sets mean they now offer more than just their well-known energy savings capability, particularly when paired with a motor/compressor system.

Here are five reasons why you might want to consider using a VFD in your compressor application:

1. Energy efficiency

The most obvious advantage of a VFD is the notable energy efficiency.

A typical compressor application setup uses a direct electrical supply to power a motor, which then runs the compressor. The motor runs at a continuous speed regardless of the requirements placed on it by the compressor because the power supply is constant. The compressor uses the energy output it needs from the motor; the rest is wasted. If the motor is controlled by a VFD, the frequency of the electricity powering the motor – and hence the speed of the motor – can be regulated according to the demands of the application. If less power is required from the motor at certain points in a process, then the drive adjusts the electrical frequency, slowing the motor. The aim is to ensure that the motor only generates enough energy to power the compressor and no more, eliminating energy wastage. Studies have shown that a 20% reduction in motor speed can lead to a 50% energy saving (source: GAMBICA).

Operators of compressor based systems such as refrigeration or pneumatic power supply applications, whatever the industry, can achieve energy efficiencies and cut costs by using variable speed drives to control their compressors.

Whilst energy savings are arguably the key factor behind investment in a VFD, there are a number of other advantages to take into account when considering building it into a system.

2. Advanced functionality

Drives are becoming more advanced, now offering exceptional feedback and monitoring capabilities. Sensors used to detect a wide range of variables, such as pressure, temperature or movement, can be fed into the drive control module to accurately determine the optimal output frequency and motor speed. If a given variable changes, the drive can be set-up to automatically adapt the frequency, altering the speed of the motor. Once the sensors indicate that the desired state has been achieved, the drive can then normalise its frequency.

A great example of this adaptation is temperature monitoring. A VFD can be set up to monitor motor temperature. To ensure it does not overheat, it can automatically lower the motor speed, send error signals or stop the motor altogether. The drive can also monitor compressor oil pressure, eliminating the need to do so manually.

This advanced functionality can improve the performance of your application, allowing you to add additional monitoring of variables as required.

3. Reduced component degradation

Optimising motor and compressor performance can reduce stress on the mechanical and electrical components of a system, limiting component failure resulting from wear. By reducing the speed at which a motor is running at certain points in the process, the individual components are placed under less mechanical stress. This change also reduces stress on other components such as cables and connectors further down the line.

4. System reliability

Many drives now offer safety features such as short circuit protection and safety torque off (STO) functionality. Selecting a drive with these features can eliminate the need for electrical components, such as motor circuit breakers and contactors, reducing the number of components and therefore costs. Reducing the number of electrical components also increases system reliability and reduces the risk of system downtime.

5. Lower starting currents

In comparison to a mains-powered motor with direct starting, a VFD can reduce the starting current by up to 80% without affecting the starting torque. By enabling lower starting currents, the energy grid is placed under less stress when motors are powered up, reducing the impact on other local grid energy consumers. The resulting lower energy frequency fluctuations also mean that failures of electrical equipment can be reduced.

Conclusion

As drives functionality is becoming more advanced, manufacturers are taking steps to actually simplify the usability and the commissioning process, to make the benefits of VFDs more accessible to a wider range of industrial manufacturers.

Complex settings and adjustments can be largely eliminated from the commissioning process. In most cases the commissioning can be safely and successfully performed by the manufacturer or a mechanic without the requirement for special electrical knowledge. Setting up the application to control the VFD is also easier to achieve than ever before. Simpler software tools and sophisticated databases containing pre-loaded information on a wide range of motors, compressors and other system components have made setting up a previously complex application much easier.

What’s more, just taking into account the easy-to-measure energy saving aspects, a VFD will typically pay for itself within eight months, removing the investment risk.

So, improvements and simplifications to the usability of variable frequency drives, paired with the benefits when used to power compressors, as well as the cost saving possibilities, make VFDs a credible and obvious addition to any compressor application.

- This article contributed by Matthew Dowd, Marketing Communications Manager, Automation Group EMEA, Parker Hannifin Corporation.

(More information is available at www.parker.com/electromechanical or contact: mitali.nair@parker.com)