WEB EXCLUSIVE: Improving motor efficiency in the plastics industry

U.S. plastics manufacturing companies are in a position to increase their competitiveness, productivity, and profits by using energy-efficient technologies in their industrial processes and equipment.

Plastic product manufacturing is an energy-intensive industry that drives massive production, consuming an abundance of electricity. In fact, this $6 billion industry consumes approximately 6% of all the energy used by U.S. industries. The U.S. Dept. of Energy (DOE) estimates that reducing the plastics industry's energy use by even 1% by 2010 could shave at least $100 million from its total annual energy costs.

Rising energy prices are becoming a major concern for all involved in the plastics industry, especially small- and medium-sized companies that have little wiggle room when trying to balance operating expenses against profitability. Adopting energy-efficient technologies offers the opportunity to cut costs and improve productivity and competitiveness, while improving the environment and reducing emissions that cause climate change.

Improving motor efficiency on plastic manufacturing equipment can provide a significant amount of energy savings to help meet the industry’s energy-reduction goals. For example, case studies completed on granulators at Graham Packaging Co. LP (York, PA) and Berry Plastics (Anaheim, CA) showed 37% and 44% savings, respectively.

Energy efficiency technologies for electric motors are a practical solution for variable-load equipment such as granulators. Before implementing electric motor energy efficiency technologies, it is important to understand electric motor efficiency in order to find the best possible and most appropriate solutions for certain equipment.

Why is it so important to improve the efficiency of motors?

Electric motors play a significant role in our energy problems. They are the true workhorses of our industrial and commercial facilities, consuming roughly a quarter of all electricity produced in the U.S. and more than 60% of all electricity used in industrial facilities. But a recent DOE study determined that 44% of industrial motors operate consistently at less than 40% of full load.

The key to saving energy on electric motor operations is to implement energy management practices or apply energy efficiency technologies. “The cheapest and most available source of new energy is the energy we waste. That’s why we at DOE are always looking for ways to promote energy savings,” says Samuel Bodman, Energy Secretary.

What makes a motor inefficient?

There are essentially five contributors to power losses in an AC induction motor: friction, windage, sound, copper, and iron loss. The first three, friction, windage, and sound, are mechanical losses, are fairly constant, and generally represent a very small fraction of the total wasted or lost power.

The copper loss is basically the energy lost to heat in the windings and is a function of the load. The iron loss is the energy lost due to eddy currents and hysteresis effects in the magnetic iron cores of the stator and rotor, and is a function of the voltage at the motor terminals; it is independent of the load. A motor is operating most efficiently when the iron loss and the copper loss are equal, which occurs when the motor is driving approximately 75-90% of the full rated load. As the load increases, the copper loss dominates. When the load is very low, the iron loss dominates, representing most of the energy loss.

What are the benefits of saving energy?

1. Reduced electricity costs
In 2005, the nation’s energy bill totaled $296 billion. According to the DOE, a typical industrial facility can realize savings of as much as 18% in motor systems. Investing in energy efficiency technologies will help bring electricity costs down and will reduce the number of new power plants needed. Companies affected by rising electricity costs would see an increase in their bottom line as energy efficiency improves.

2. Utility rebates
• Many utilities offer rebates to customers on energy-efficient technologies and equipment installed in their facilities. Utility rebate and incentive programs are designed to facilitate the implementation of energy efficiency improvements. This encourages electricity customers to use energy-saving technologies to cut energy usage, which will help lower the demand for electricity and will also reduce the number of new power plants needed.

3. Reduced carbon emissions
With increasing concern about greenhouse gases and climate change, we need to take responsibility and realize that carbon dioxide emissions are polluting our environment and causing the effects of global warming. When we use less energy, the result is less pollution. Reducing carbon emissions through the use of energy efficiency technologies can make a substantial impact on our environmental challenges.

What can we glean from the above? First, there are quite a few motors in the field that are operating well below optimum efficiency, wasting a considerable amount of energy in the process. Second, there are a number of valid reasons for reducing the amount of energy consumption, and reducing wasted energy is basically the low-hanging fruit.

Increasing the efficiency of a motor

As we have shown above, the efficiency of a motor is simply the ratio of the power out (useful work performed) to the power in (electrical power delivered to the motor terminals). Thus the only ways to increase the efficiency of a motor are to reduce the losses or to use more of the input power to do useful work.

While it is certainly possible to reduce the mechanical losses in a motor (better lubricants and bearing systems, streamlined motor designs to reduce windage, reduction of vibration noise), since these losses represent only a tiny fraction of the total losses, it is difficult to do so cost effectively. These are, however, some of the techniques used to produce NEMA Premium Efficiency motors (which helps explain the usually significant cost difference between Premium and Standard Efficiency motors).

Reducing the copper losses (also known as I2R losses, as the power lost to heat is proportional to the resistance of the conductor as well as the square of the current) can be achieved by using larger conductors (quite expensive with the price of copper today) or by reducing the current by switching to a higher mains voltage. This is usually not feasible since the mains voltage level is primarily fixed by the location.

Reducing the iron core losses is accomplished by use of different materials and construction techniques. The magnitude of the eddy currents is significantly reduced by use of a core that is made up of many thin layers laminated together rather than a single monolithic core. Hysteresis effects are reduced by choice of laminate material.

Taken together, all of these measures will certainly reduce the losses significantly. Whether they are cost effective is a different story. However, as noted above, efficiency can also be improved by ensuring that more of the input power is used to do real work. We also noted above that a motor operates most efficiently when the load on the motor is around 75-90% of the rated load for the motor. There are a number of ways to accomplish this.

The power switch: There is no better way to conserve energy than simply to shut off an idling motor. However, this is not always an option.

Right-sizing the motor: If the driven load is fairly constant, one can simply install a motor that is matched to that load. In fact, the DOE recommends replacing oversized motors with smaller motors sized for the load. However, there are many cases where this is not possible, because the motor is sized to accommodate a much larger peak load, however infrequently that load occurs.  Granulators are a perfect example of this—the motor is sized to accommodate the maximum throughput, which does not occur 100% of the time.

Variable-frequency drives: In certain applications, particularly those in which it is desirable to change the speed of the motor, VFDs can save energy. VFDs are commonly used in industry around the world where speed control is essential to the process and energy savings is secondary, but in applications where the motor can run at slower speeds, significant energy savings can be realized.

There are, however, some drawbacks to VFDs. They generally require more expensive, inverter-duty rated motors (or additional equipment) to ensure that the motor can operate properly and safely at reduced speeds. The standard NEMA Design B motors that are most common are not designed to operate at anything other than the standard supply frequencies of 50 or 60 Hz, and extended operation at lower speeds can cause the motors to overheat fairly rapidly. Many of the least expensive VFDs commercially available may require additional filtering (the reason they are inexpensive). In addition, by changing the speed of a process, it may require additional hardware and software and a more complex control algorithm to ensure the system will run safely and as designed.

Reduced-voltage motor controls:  Reduced voltage motor controls, such as the Motor Efficiency Controller (MEC) family of energy-saving motor controls from Power Efficiency Corp., constantly monitor the phase lag and reduce the voltage at the motor terminals to compensate. By reducing the voltage, the current is also reduced, particularly the magnetizing current that contributes the most to the losses in a lightly loaded motor. The MEC effectively matches the horsepower of the motor to the load on a real-time basis, consuming only the energy required to run the motor most efficiently at any given moment, while still producing the required torque to run the load. Installation and maintenance of an MEC is similar to a motor starter or a soft start. Cost of an MEC can be compared relatively to soft starts and VFDs.

Granulator case studies

In a recent case study at Berry Plastics in Anaheim, CA, 28 motor efficiency controls were installed in granulators ranging from 7.5-hp to twin 30-hp motor machines in its manufacturing facility. The granulators run continuously during the manufacturing process. The annual energy consumption will be reduced more than 195,000 kWh, resulting in a cost decrease of $17,600. This represents an energy savings exceeding 40%, a simple payback of less than two years, and an internal rate of return equal to 74%.

Berry’s electricity provider, Anaheim Public Utilities, reviewed the metering and analysis conducted during the case study and approved an attractive incentive for the project based on its Anaheim Advantage program designed for reducing industrial energy consumption. Check with your local power supplier for similar programs. Environmental benefits included a CO2 reduction exceeding 300,000 lb per year.

In another recent case study at Graham Packaging, a 50-hp MEC was installed on a granulator to reduce energy consumption, electricity costs, and the company’s environmental footprint. Results from tests showed an energy savings of more than 37%. Annual kWh saved was 18,792 and annual savings was $1597.

Conclusion

The plastics industry is an energy-intensive industry. Focusing on energy efficiency in large energy-consuming industry sectors and investing in new energy-efficient technologies will make a substantial impact on the environment and the economy. While meeting their carbon reduction goals, end users may realize that the benefits of using energy-efficient technologies for their business operations will be a positive shift toward increased profitability and productivity.

Author Christine Toledo ([email protected]) is marketing communications manager for Power Efficiency Corp. (Las Vegas, NV).