Regulations look past motors to improve system efficiencies
Electric motor system efficiency and power electronics are impacting future energy saving opportunities as attention moves from motor efficiency to motor-driven system efficiency. In the U.S., the first move was to apply motor efficiency regulation. The next step is addressing the system.
Stage 1: Motor as a component
U.S. motor efficiency regulation began in 1992. At this time the motor already included efficiency data on each nameplate. The U.S. Congress drafted legislative language that included definitions of products to be included as well as referencing test methods and efficiency levels. The motor community began a journey into federal regulation that continues today.
In 2001, motor manufacturers created an efficiency level "reach" that raised the efficiency levels above the federal requirement (NEMA Table 12-12). In 2010, this new level was added to a second round of regulation bringing the markets greater savings to a select category of motors know as Subtype 1 and Subtype 2. These categories impacted approximately 40% of the units sold each year. In 2014, a third round of regulation was released that will take effect June 1, 2016. This latest round of regulation essentially covers all polyphase motors from 1 hp (0.75 kW) to 500 hp (375 kW). This latest round of regulation was carefully constructed to expand the scope of products to be covered while paying particular attention to unintended consequences that would defeat the energy saving goal of the rule. The motor community worked diligently with the energy advocates and the U.S. Dept. of Energy to create a regulation that took into account mechanical and electrical issues that would undermine the regulation if an efficiency level were to be increased to a point that triggered any or all of the following 10 consequences.
Avoid dampers, throttling
In the past, many motors ran without benefit of electronic speed control devices. Therefore, the control of the output volume of the pump, fan, or compressor had to be throttled by closing the valve, dampers, or vanes. Though this will adequately control the flow, this is by no means an efficient method. There are significant losses generated in the throttling mechanism and the motor’s efficiency drops significantly at the lower operating speeds.
Stage 2 energy savings will use energy savings (kWh) by employing power electronics within the power drive system to eliminate mechanical flow control devices. The European Union (EU) began looking at the system in EN 50598, which was published in December 2014. This was an excellent start in establishing a guideline for energy savings as it relates to the entire system.
This work is taking place today in an international standard Working Group (WG) 18 within the International Electrotechnical Commission (IEC). WG 18 is creating the international standard IEC 61800-9-1, 2, which establishes the needed methodology and necessary metrics. The work continues on establishing energy efficiency levels for entire systems.
Stage 2: Power drive system
The second stage is to create standards that quantify energy saving delivered by a power drive system. It becomes clear that the motor is a critical part of this system, but it only makes up a small percentage of the losses in the Stage 2 energy saving opportunity.
Stage 2 will leverage the motor, inverter, and controls system referred to here as the power drive system (PDS). Also, in consideration are the starters, torque transmission devices, and of course the load (pump, fan, compressor) which is now referred to as the extended product. While moving forward on this topic, it was discovered that it was necessary for a metric to move to losses versus efficiency. The reduction in losses as a result of process control through the use of a PDS delivers the reduction in kWh.
It is necessary to use loss reduction versus efficiency when considering total system energy savings. Considering an extreme case where the application requires a period of operation within its duty cycle at or near zero speed where the efficiency is 0% it becomes a little clearer that efficiency is no longer a meaningful metric.
The work that is now ongoing in NEMA’s WG 18 is to establish the losses generated at various operation points and determine the savings in energy as a result of using a PDS which includes the extended product. The system standard establishes a series of 8 points that can be used to evaluate the energy savings.
These points have been established to represent every possible application, but not all load points will be required for every application. For example, a variable torque application such as a centrifugal pump may only find three of the points relevant; PL (100,100), PL (100, 50), and PL (50, 25).
Reference losses of typical equipment in operation today are used as the basis for the loss reduction. These reference losses have been established for the CDM, motor, and PDS.
The CDM can now have IE levels established based on the loss reduction from a reference CDM which is defined in the standard. The motors already have IE levels established in 60034-30-1. The IE3 level established in 60034-30-1 is in harmony with premium levels in NEMA MG1, Table 12-12, regulated in the U.S. With this standard it will be necessary that the motor and inverter manufacturer provide the losses at all the required load points as requested by the system integrator who will be combining the entire system.
The standard also provides a methodology for calculating or testing for all the losses of the inverter and supporting CDM equipment. It has been determined that the motor losses at any load point can be extrapolated from 7 points that can be provided by the motor manufacturer.
This method for extrapolation will be covered in detail in IEC 61800-9-2 and in IEC 60034-30-2. Methods for testing or calculating the losses for the motor at these load points are covered in the motor standard 60034-2-3 still in progress.
Using the methodology covered in the future IEC standard 61800-9 series, the system integrator now has the tools to accurately predict minimum losses of the system. If the losses are equal to the losses of the reference PDS then the system is an IE1, but if the losses are 25% lower than the reference losses of the PDS then it is an IE2 PDS.
Even more important, the system integrator can now look at the extended product and compare the losses of the extended product versus the losses that would have occurred without a CDM by just throttling the load. The system integrator can then accurately establish the energy saving of the entire system. Considerably more energy savings can be achieved when evaluating the entire system rather than just the individual components.
Incorporating the PDS advantage in Stage 2 can increase the power saved by over six times the amount that could be saved by relying solely on the motor component efficiency.
– The authors all are members of the NEMA Motor Generator Section. They are: Rob Boteler of Nidec Motor Corp. (chairman NEMA Energy Management Committee), Bill Finley of Siemens, and Tim Schumann of SEW Eurodrive.