Because electric motors in the United States are responsible for 64% of the energy used in the industrial sector, achieving the highest possible level of energy efficiency is critical to your bottom line. One of the most common ways to achieve that level is by using VFDs.
As common as they are in the industry, you can’t simply go to a hardware store and pick one off the shelf on a whim. If you’re considering using a VFD in your facility, Jim Montague provides some guidelines to consider.
- What are the torque demands of the loads or processes in your planned system? Will any of the loads be hard to start? VFDs have limited over-current capacity, so hard-to-start loads may require an over-sized unit to cover higher current demands.
- How many motors will the drive control? If it’s more than one, will they start sequentially or simultaneously? Calculate the total peak currents of all motor loads under the worst operating conditions your planned system will see. Size the VFD according to this maximum current requirement.
- Will your applications require a quick start or an emergency stop of the load? If so, high currents will be demanded of the VFD. Over-sizing the drive may be necessary.
- Is motor overheating a potential concern for any of your planned VFD applications? It may be, for reduced-speed, constant-torque applications.
- What range of motor sizes will your process or processes require the VFD to handle? Remember, smaller motors aren’t as efficient as larger ones, so improvements due to the VFD will likely be apparent. However, since large motors use much more power, even small increases in efficiency can produce appreciable savings over the life of the motor.
- Will the VFD system be operating in an environment containing volatiles, airborne particulates or high ambient temperatures? For volatiles, make sure all materials used are resistant to chemicals and are properly grounded. For particulates, ensure proper sealing. For high temperature, allow for needed cooling.
- Do you need equipment or drive protection features that will ensure continuity in processing? Be aware that you can have a drive that trips instantly in an over-current condition, or one that maintains constant motor torque and reduces motor speed to maintain current required.
- Do you want or need a lot of diagnostic capability in your unit? How critical is it to get a handle on load downtimes and be able to do a detailed fault analysis?
- Are power factor correction capacitors present on the motor loads your VFD system will have to handle? When these are switched, they typically generate power disturbances, and VFDs can be negatively impacted. Isolation transformers or line reactors may be necessary.
- Is it possible the power source for your planned system will occasionally be switched while the VFD is operating? This might happen, for example, when loads are switched to stand-by generators during a power outage. Some drives can handle a brief power outage, while others can’t.
Variable-speed drives are an excellent means of reducing the energy consumption of the motor-driven application they’re connected to. For example, power usage in pumps, fans and conveyors can be halved simply by reducing motor speed by 20 percent. Plus, the initial cost of a VSD can be recouped in energy savings within as little as six months.
Energy saving is a huge advantage to VSD users, and our clients have enjoyed significant reductions in their electricity bills since installing them. But what about the other major benefit – productivity?
Speed: By optimizing the speed of a process, a drive enables the user to maximize valuable production time and get the most out of their equipment.
Consistency: By accurately regulating speed in a motor-driven process, a consistent quality of end product can be achieved, meaning less wastage for the manufacturer and a satisfied customer base.
Reduced Maintenance: VSDs allow an electric motor to be brought up to speed gradually, which eliminates the mechanical shock associated with instant start-up. Sudden shock quickens the rate of normal wear and tear, which could lead to equipment failure and unscheduled downtime with obvious effects on productivity.
Yaskawa Electric makes a very good VFD and on their website is a calculator.
This collection of PC software support tools can be used for uploading and downloading drive parameters, calculating energy savings, or identifying how to reduce your operating costs and meet the harmonics compliance requirements.Yaskawa’s
Yaskawa’s Energy Savings Predictor software is available for free. It will enable you to accurately forecast your energy savings by using a VFD.