Switched Reluctance Motors
Motor: Switched Reluctance vs. Premium Efficiency with ASD
A Super Premium Efficiency motor with a rotor that does not have magnets, rotor bars or windings. It is essentially a piece of shaped iron, offering improved efficiency because it can withstand forces from a magnetic field many times greater than those of current-carrying conductors.
Item ID: 433
Motors & Drives--Motors
A Super Premium Efficiency Switched Reluctance (SR) motor has a rotor with no magnets, rotor bars or windings. The rotor is essentially a piece of shaped iron, and the SR motor design exploits the fact that forces from a magnetic field on the rotor iron can be many times greater than those on the current carrying conductors. SR motors are rapidly moving from the servo and hybrid electric vehicle drive arenas to industrial applications.
SR motors are available in NEMA frame sizes so they can be specified when new process equipment is ordered or retrofitted onto existing equipment. Due to the need for an inverter or controller, the SR motor costs much more than a constant speed Premium Efficiency induction motor. However,SR motors have inherent variable speed capability so an equivalent replacement is a pulse-width modulated adjustable speed drive with a new Premium Efficiency inverter-duty motor. For variable flow applications, energy savings due to the variable speed capability of the PM motor greatly exceed savings due to the increased efficiency of the motor.
SR motors may be used with blowers and high-speed pumps; low-speed, high-torque applications including extruders and conveyors; refrigerant compressors; weaving looms; centrifuges; and pumps for reverse osmosis systems. As rotor losses for a SR motor are the same during start-up as at full-load, these motors allow repeated starting under full-load. Note that rotor produces no heat at stall, so prolonged operation at stall is also possible. Switching losses for SR motor inverters are also reduced to about half of those for an AC motor inverter.
One manufacturer provides SR motors in the 30 hp to 335 hp range with base speeds from 200 RPM to 10,000 RPM, depending on application requirements. These motors can be directly coupled to driven equipment without the need for gearboxes or belted power transmission equipment, saving on costs while improving energy efficiency.
Baseline Description: Premium Efficiency Motor with ASD
Baseline Energy Use: 4909 kWh per year per hp
A 100 hp switched reluctance motor has variable speed capability. The energy savings of this motor compared to a premium efficiency (PE) motor equipped with an ASD given a duty cycle of 50% time at full speed and load (1800 RPM) and 50% time at about 80% speed (1428 RPM) is calculated. The PE motor has an efficiency of 95.4% at full-load, dropping to 91.5% when an ASD efficiency of 96% is incorporated. The efficiency at roughly 50% input power for the PE motor is reduced to 94.3% (or 90.5% when the drive efficiency is taken into account). The switched reluctance motor efficiency is very flat, dropping from 93.5% at full load to 93.0% at the reduced load. Assume a duty cycle of 4,000 hours per year at each load point. The projected energy savings of 11,408 kWh/year is dependent upon the baseline motor efficiency (here we are assuming a Premium Efficiency motor) and the number of hours at each load point on the duty cycle. Savings are dependent upon the baseline motor size in hp, on the assumed ASD efficiency (96% is used for this analysis) and whether or not the baseline motor is already equipped with an ASD, and on annual operating hours. SR motor efficiency is extracted from "Switched Reluctance Drives 'A Complete Drive Solution'.
Manufacturer's Energy Savings Claims:
Currently no data available.
Best Estimate of Energy Savings:
"Typical" Savings: 2%
Energy Savings Reliability: 3 - Limited Assessment
Energy Use of Emerging Technology:
4,810.8 kWh per hp per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Potential number of units replaced by this technology:
The motors most likely to be a good application for switched reluctance motors is motors with a fluctuating load such that they either already have or would benefit from a variable speed drive (VSD). According to the US DOE's market assessment in 1998, the percentage of industrial motors with a fluctuating load is 19.3% of all industrial motors (Xenergy, 2002 App B). Estimating the total number of horsepower installed in such applications is challenging. What we can more easily estimate, which is ultimately the more important number, is the total energy used by motors with fluctuating loads. In this analysis, we only consider industrial motors. Assuming drop-in replacements are available for most NEMA-frame motors, and that the sizes available are 30 to 335 hp, using national numbers from the Market Assessment, we get a total energy use for fluctuating loads in those sizes of about 54,352 GWh/yr. According to the EIA, there is approximately 8.2% less energy used by industrial motors now (2011) than there were in 1998 when this survey was done. Adjusting for that, and taking 4% of that, since the Northwest has a population of 4% of the US, we get approximately 2000 GWh/yr being used by these motors in the Northwest. Dividing that by are baseline example energy use of 4909 kWh/yr/hp, we get an effective installed base of motors in the Northwest with a fluctuating load in the order of 406,400 hp.
Regional Technical Potential:
0.04 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Currently no data available.
Simple payback, new construction (years): N/A
Simple payback, retrofit (years): N/A
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.