Operations & Management
How to improve energy management
March 13, 2012 by Frank Koditek Belden
Industry accounts for more than 40 percent of worldwide energy consumption. Of this, more than 65 percent of industrial power demand comes from electric motor-driven systems. Therefore, reducing the energy use of motor-driven systems represents a significant opportunity for industrial energy savings.
Variable frequency drives – the low-hanging fruit
Reducing energy consumption in motor-driven systems by using variable frequency drives (VFDs) for motor control is most likely the “low-hanging fruit” for industrial energy conservation. Briefly, VFDs control the rotational speed of an AC electric motor by controlling the frequency of electrical power supplied to the motor. Although they have been out for a decade, they are gaining increased popularity as industry looks for ways to control costs.
Older motor controls just weren’t precise enough to support variable speeds; thus, industrial designs were in place that assumed a constant speed. If, for example, it was necessary to control the flow of fluid or air, a valve would need to be actuated to adjust the flow. Types of equipment that benefit from having motor control capability for meeting variations in demands (such as temperature, pressure or force) include fans, conveyor belts and lathes.
Consider the possibilities for significant energy savings: At half maximum speed using a pulse width modulation (PWM) VFD, a motor consumes roughly one quarter of the energy required to run at full speed. In addition, VFDs reduce wear-and-tear, resulting in lower maintenance costs and longer motor life. It is possible to recover the cost of the VFD within a very short timeframe in many applications.
VFDs also have the capability to reduce scrap because they can control motor speeds to within 0.1 percent tolerance. More precise control of the process yields less variation in the finished product and reduces material usage and scrap.
A series of capacitors, diodes and an embedded computer chip allow the frequency drive to moderate speed while still delivering the full torque of power to the motor. The drive is not only able to vary the amount of frequency, but can also regulate the voltage that is being sent to the motor. It does this by delivering a full current to the motor.
When choosing components for a VFD system, it is important to carefully select the motor and drive components based on the operating requirements, which typically include the load, torque, speed and power required. Cabling requires no less thorough evaluation. The entire VFD system (drive, cable and motor) needs to be matched for a successful operation.
The tendency of some plants to cut corners on cabling when they install a VFD system is short-sighted and can be expensive. VFDs require purpose-built cables to address the unique sensitivities of a VFD system, which fall into four categories – noise emissions, voltage reflections, overvoltages and corona discharge. If inadequate cabling is installed, it is possible to damage the motor or the VFD, as well as suffer cable failures.
Intelligent automation devices save energy, reduce waste
Controlling motor speeds can contribute significantly to energy savings; however, the same intelligence through automation that allows motor speeds to be controlled successfully can be used in other industrial applications as well.
Industrial Ethernet has contributed greatly to helping industries become more efficient and reduce scrap, thus benefitting both the bottom line and the environment. Automating processes from activities such as regulating temperature, pressure, material flow and line speeds provides consistency, repeatability and efficiency. As manufacturing islands are networked by industrial Ethernet, monitoring and control becomes increasingly efficient, and can be managed remotely. Real-time sensing and alarms reduce scrap because of early warnings when lines or processes begin to deviate from the norm.
Automated systems controlled by industrial Ethernet reduce the amount of non-compliant product built, and thus reduce scrap. By monitoring equipment used in the manufacturing process, it is possible to note when machines are operating out of tolerance and provide servicing as required. Catching machine problems early reduces loss from premature machine failure. In addition, identifying problems early allows repairs to be made during scheduled service rather than through expensive, unplanned downtime when machines break down unexpectedly. With downtime costing manufacturers as much as $1,000 per minute – more if product scrap occurs due to delays – an automated early warning system can pay for itself the first time a shutdown is averted.
Automated systems, particularly the newer ones, have enhanced safety systems built in. Providing a safer manufacturing environment protects employees from injury, which, in addition to employee welfare, also reduces downtime and scrapped product.
Green manufacturing and manufacturing efficiency go together. Reducing energy costs and scrap are goals that serve both the planet and the manufacturer. This article has briefly outlined areas where little additional effort can bring about significant savings. It benefits manufacturers to perform audits of their manufacturing lines to determine where automation can provide lasting environmental and financial benefits.
Frank Koditek (firstname.lastname@example.org) has been with Belden for 28 years and has held various positions in engineering, manufacturing, sales and marketing. He is currently a product manager for industrial cables.
This article originally appeared in the March/April 2012 issue of Manufacturing AUTOMATION.