1 April 2007
Raising the standard for electric motor efficiency
Microprocessing the phase lag: Waste not, want not technology
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By John Hurst
Electric motors consume approximately 63% of the electricity used in U.S. manufacturing. They are the main motive force in our commercial buildings, industrial facilities, and appliances.
Everyone knows reducing energy consumption has become a priority for the U.S. Businesses are seeking practical solutions to help them save energy, including new electric motor efficiency technologies.
Some of these technologies will set new standards for motor efficiency, benefiting both the environment and U.S. industrial competitiveness. Motors are quite efficient at converting energy into work when they are heavily loaded.
However, they become very inefficient when they are lightly loaded. A new-patented technology has come to pass that improves the efficiency of AC induction motors when they are lightly loaded.
Incorporated into a soft start, potential applications for the technology include such key points in the automation schema as escalators, stamping presses, grinders, crushers, granulators, conveyors, saws, and others.
Any motor that is lightly loaded or variably loaded (and therefore sometimes lightly loaded) is operating inefficiently and is therefore a potential application for this technology.
Tests by utilities, OEMs, and end users have verified energy savings of 15-35% in appropriate applications.
Options for increasing motor efficiency
One easy method to reduce motor energy consumption is the power switch.
There is no denying that the best way to save energy is to shut off the machine, but it is not always possible. Replacing standard motors with high efficiency motors is another solution.
Although high efficiency motors are 4-6% more efficient than standard motors when they are both heavily loaded, even high efficiency motors become very inefficient when they are lightly loaded.
Installing a variable frequency drive (VFD) is another solution. By equipping the machine with a VFD, it will slow down or stop when it is lightly loaded and will speed up again when load increases.
By slowing or stopping the electric motor, energy use falls, and VFDs have many excellent applications. However, there are times when slowing the motor is not possible and other applications in which VFDs are too expensive to be economical based solely on energy savings.
This new solution provides a practical solution for many applications. In contrast to a VFD, our energy saving soft start keeps the motor running at full RPM and reduces the power used by the motor when it is lightly loaded-much like cruise control for a car.
Furthermore, this patented energy saving technology works in conjunction with high efficiency motors, since it makes them more efficient in the same way it operates on standard efficiency motors-improving their efficiency at low loads.
Utility efficiency incentive
Many utility companies are offering incentives for customers to reduce their energy consumption through new energy efficiency technologies. Standard soft starts do not qualify for utility rebates because they simply reduce the inrush current to the motor during startup.
Although some manufacturers have promoted this as "energy savings," the amount of energy saved is not significant.
In contrast, this soft start does qualify for utility rebates in appropriate applications because it saves energy while the motor is at normal operating speed.
In fact, Southern California Edison and Matrix Energy Services, Inc. recently launched the Escalator Power Genius Program. Through this program, Southern California Edison will purchase a contracted number of Power Efficiency Corporation's energy saving controllers.
Matrix will facilitate installation of the units on commercial escalators throughout Southern California Edison's territory. Customers willing to participate in the program receive free controller units on a first-come-first-serve basis but are required to pay for the installation.
New technologies, goods
Later this year, a digital version of this energy saving soft start will come out. The new version product can replace existing starters and soft starts on new equipment or can retrofit into existing motor control centers.
The new product will be smaller and will integrate with virtually any automation system, through a PLC or other control network architecture, and report the amount of energy savings.
Also on the horizon is an efficiency device for single-phase AC motors, such as those in refrigerators, residential air conditioning, and shop tools.
How power efficiency
In general, AC induction motors operate most efficiently at around 75% of full rated load.
At roughly 40% of full load, a motor's efficiency begins to decrease, and at even lower loads the efficiency drops off precipitously.
Numerous motors operate at light loads. According to a Department of Energy study, 44% of motors in industrial facilities operate at 40% or less of full load and are thus, operating inefficiently.
As a rule of thumb, the larger the motor, the flatter this curve is, and the lower the load percentage has to drop before the efficiency starts to drop.
The technology in Power Efficiency's energy saving soft start attacks the energy wasted when motors are lightly loaded-to the left of the dotted line on out efficiency curve. There is no opportunity for savings when the motor is heavily loaded and operating efficiently.
The soft-start technology constantly monitors the voltage and current going to the motor. When the voltage and current sine waves diverge, greatly-when the phase-lag increases-the motor is lightly loaded and operating inefficiently.
When this happens, the device reduces the current and voltage appropriately, while always maintaining the motor at a constant (full) operating speed.
When the load on the motor increases, the device reads this condition and increases the power to the motor so it does not stall. Although the theory of making motors more efficient in this manner has been around for years, the process has been very difficult to perfect such that the system realizes the maximum savings over multiple applications and the motor still receives max power when it needs it.
This new and effective technology is all about algorithms and software, which optimize the operation. We are seeing savings of 15-40% of the energy consumed by an electric motor depending on the load and operation of the machine.
In a recent test by Nevada Power Company, the electric utility for Southern Nevada, on an escalator motor at a major casino on the Las Vegas Strip, the device reduced the average power consumption by 34%.
Other applications for this efficiency technology include compressors, conveyors, pumps, saws, mixers, shredders, and injection molding machines.
With energy prices soaring and environmental concerns becoming increasingly important, this technology may set the new standard for electric motor energy savings.
The patented energy saving technology and intelligent product features represent significant advancements in electric motor efficiency and provide a smart solution to conserving energy.
ABOUT THE AUTHOR
John Hurst (jhurst@powerefficiencycorp.com) is director of engineering at Power Efficiency Corporation in Las Vegas.
Managing industrial electricityTypically, in mills where large amounts of steam are required for the process, steam turbines are for co-generation of electricity. However, since the amount of co-generated power in most mills is insufficient to satisfy the mills total electric load, the mill purchases the balance of its requirements from the local electric utility as well as relying on them for backup service in case of generating equipment outages. Electricity rates charged to industrial and commercial customers vary widely across the U.S. A recent survey comparing the monthly cost of 10,000 kWh (a small commercial user's consumption) indicated a wide variation between the highest ($1,270) and lowest ($186) cost. This large variation is from the cost of the fuel used to generate the power by the providing utility. Access to extensive hydroelectric generation facilities tends to stabilize and reduce that area's electric costs, while urban area's rates have risen rapidly with the cost of fuel oil. Thus, a customer's incentive for requiring a power management solution depends heavily on his specific location and specific electric power economics. Real-time pricing contracts swing drastically based on supply and demand. What makes sense on the night shift may not apply to the day shift, for example. Weekend and summer rates may require a different operating procedure. Regardless of the specific charges assessed by the utility, customer service charges usually have two components: 1) An energy charge that costs so much per kilowatt-hour used during the billing period. This is usually subject to a sliding scale with the rate per kWh decreasing with increasing usage. The energy charge may also be broken down further with a fuel adjustment charge. The fuel adjustment charge is a convenient way for the utility to modify its rates with little or no regulatory delay in times of rapidly escalating fuel costs. 2) A demand charge at so much per kilowatt of demand, where demand is the highest kW load imposed on the tie line usually averaged over a 15-, 30-, or 60-minute interval during billing period (or the highest demand period established during the month). The theoretical basis of the demand charge is it pays the utility for the capital cost of generating equipment capability. Some service contracts contain a "ratchet" clause, which specifies once a customer establishes a monthly demand higher than the previous demand, the new demand charge is for a year or more even if ensuing monthly demands are reduced. Read more about this solution at: |
Standard soft start vs. digital energy-saving soft startSoft start motor PEC technology soft start motor |
Saving stepsApplication/ Average annual Savings Stamping press / 10 hp 23% 1,351 kWh |
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TERMINOLOGYSoft start: An electronic means of slowly starting vacuum motors to reduce initial inrush voltage spikes. It starts the motor at a lower voltage, slowly ramping up to operation voltage. There is no evidence that this extends a motor's life. AC induction motor is the simplest and most rugged electric motor; it consists of a wound stator and a rotor assembly. An AC induction motor is such because the alternating current flowing in its primary member (the stator) induces the electric current flowing in its secondary member (the rotor).The power supply connects only to the stator. The combined electromagnetic effects of the two currents produce the force to create rotation. Phase lag is the time delay with which one rhythmic activity follows another of the same frequency. OEM (original equipment manufacturer): The maker of equipment marketed by another vendor, usually under the name of the reseller. The OEM may make only certain components or complete devices, which a reseller can then configure with software and or hardware. Variable-speed drive (VSD) is an electronic device that controls the rotational speed of a piece of motor-driven equipment (e.g., a blower, compressor, fan, or pump). Speed control comes by adjusting the frequency of the voltage applied to the motor. This approach usually saves energy for variable-load applications. |
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