NEMA PDS S1-2018

Guide to IEC 61800-9-2—Determining Loss of Power Drive Systems (PDSs) in Extended Products

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DISCLAIMER

The Standards or guidelines presented in a NEMA Standards publication are considered technically sound at the time they are approved for publication. They are not a substitute for a product seller’s or user’s own judgment with respect to the particular product referenced in the Standard or guideline, and NEMA does not undertake to guarantee the performance of any individual manufacturer’s products by virtue of this Standard or guide. Thus, NEMA expressly disclaims any responsibility for damages arising from the use, application, or reliance by others on the information contained in these Standards or guidelines.

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User Guide for the Energy Efficiency Determination of Extended Motor Products Using Variable Speed Drives

An extended motor product is a system that involves an electric motor paired with another component or components to deliver work. Examples of extended motor products include commercial and industrial pump, fan and compressor products, among others, which all use motors in combination with other components. In particular, extended motor products are increasingly subject to energy efficiency regulation whereby both the minimum energy efficiency of the motor itself is regulated along with the minimum energy efficiency of the product (e.g., pump or fan) containing the motor. This may not always be the best or most economical approach to achieving energy savings, particularly where extended motor products use variable speed drives. A motor not subject to efficiency regulation paired with a variable speed drive is capable in many extended motor products of achieving greater energy savings than an extended motor product not using a variable speed drive with a motor subject to minimum efficiency regulation. This user guide gives a quick overview on how to use the power loss data of power drive systems calculations from IEC Standard 61800-9-2 to make energy efficiency determinations of extended motor products when considering energy regulations for those systems.

System versus Component Evaluation

The energy efficiency regulation of extended motor products allows additional energy saving compared to the component regulation predominantly used today. In the case of an extended motor product without a variable speed drive, an end user is motivated to use the most efficient motor with the highest IE (international efficiency) class. By contrast, in the latter case using a variable speed drive may save significantly more energy than using a more efficient motor than the base case. This is particularly true if the motor is frequently used in part-load operation and if high starting torque is required.

Additionally, static “rebound” effects may occur. For instance, if a line-fed motor is replaced by a more efficient successor which has a lower slip in an otherwise unchanged hydraulic system, power consumption will increase due to the lower slip, consuming more energy in application than the paper-based savings estimates predicted by switching to the higher IE class motor. Dynamic rebound effects will also occur if a motor is frequently accelerated and slowed down. In this case, a lower inertia will save more energy than lower energy losses at the rated operating point which may rarely be seen in a dynamic application. Cases of lower inertia are not taken into account in the IE class determination of a motor. Thus it can be seen that application-specific dynamics can greatly influence the actual energy-savings potential of a motor-drive system, and the motor-drive system must be carefully selected as a result.

These are only some among numerous other examples of these effects, highlighting the importance of a system-level evaluation and the consideration of the end user application in order to achieve the estimated approximately 322 TWh of annual electricity savings by 2030 according to the International Energy Agency. At a demand level of 22000 TWh, this equals about 1.5 %, giving rise to corresponding savings of 206 Mt of CO2 emissions1.

Extended Motor Product Evaluation Based On IEC 61800-9-2

IEC 61800-9-2 and the next edition of IEC 60034-2-3 require manufacturers of frequency converters (CDM), motors and power drive systems (PDS) to provide power loss data of their products in standardized operating points. These standardized operating points are the superposition of the most relevant operating points of standardized applications for extended motor products. Some examples are illustrated below in Figure 1:

1OECD / IEA Working Paper. See page 15 of 132, https://www.oecd-ilibrary.org/energy-efficiency-policy-opportunities-for-electric-motor-driven-systems_5kgg52gb9gjd.pdf?itemId=%2Fcontent%2Fpaper%2F5kgg52gb9gjd-en&mimeType=pdf

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Figure 1: Standardized operating points

The power losses in any intermediate operating point can be calculated by linear interpolation or extrapolation. This loss data of the PDS can be used as input for the calculation of the energy efficiency of any extended motor product.

According to IEC 61800-9-2, the power loss data of a PDS is published as a relative value (ex. x.x %) at each standardized operating point. In order to calculate the absolute power losses in Watts, the published data has to be multiplied by the rated output power of the PDS.

If the power loss data of the entire power drive system is not available, for example, if the PDS consists of a frequency converter and a motor from different manufacturers, the power loss data of the PDS can be calculated by adding the absolute loss values (in Watts) of the CDM and the motor at any operating point. For CDMs and motors, power losses are usually given at 90% speed instead of 100% speed shown in Figure 1. Nevertheless, this does not change the procedure for the power loss calculation of the PDS.

The absolute losses of the CDM can be calculated by multiplying the published relative data with the rated apparent output power of the CDM. Intermediate operating points can be calculated by linear interpolation and extrapolation.

The absolute losses of the motor can be calculated by multiplying the published relative data with the rated power of the motor. Losses in any intermediate operating point can be calculated either by linear interpolation or by a more sophisticated interpolation formula given in clause 7 of the next edition of IEC 60034-2-3.

At the operating point of rated speed and rated torque (100;100), the power losses of the motor have to be multiplied with an additional factor representing the ratio of the rated motor input voltage (ex. 400V) and the rated CDM fundamental output voltage (ex. 360V). If specific data of the CDM or the motor is not available, a ratio of 1.1 (400V/360V) is recommended for this factor.

In addition to power loss data, an IE class is assigned to CDMs and motors, and an IES class is assigned to a PDS. This information is not suitable for the energy efficiency determination of extended motor products.

Application Example

In order to quickly demonstrate the use of IEC 61800-9-2, the following example is given:

R e la t iv e to rq u e / %

R e la t iv e s p e e d / %5 0 1 0 0

1 0 0

5 0

2 5

P u m p s

H o is ts

W in d e rsC a le n d e rs

F a n s a n d B lo w e rsC o m p re s s o rs

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The operator of an industrial plant buys a CDM for manufacturer A with a rated output current of 30A. In addition, the operator buys a 22kw motor of the same voltage from manufacturer B with a rated power of 18.5kW. In the user documentation of the products, the operator finds the following information:

CDM Motor Frequency/torque producing current

Losses

Speed/torque

Losses

0/25 0.9% 0/25 1.55% 0/50 1.3% 0/50 2.1%

0/100 1.9% 0/100 3.6% 50/25 1.15% 50/25 1.8% 50/50 1.45% 50/50 2.5%

50/100 2.25% 50/100 3.88% 90/50 1.6% 90/50 2.95%

90/100 2.35% 90/100 4.14% The plant operator uses these components for a winder application, which runs at the operating point 0/100 for 20% of the time, at 50/50 for 50% of the time and at 90/50 for 30% of the time for one production cycle. First, the operator calculates the losses of the PDS at 0% speed and 100% torque:

𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃,0/100 = 1.9% ∙ √3 ∙ 400𝑉𝑉 ∙ 30𝐴𝐴 + 3.6% ∙ 18.5𝑘𝑘𝑘𝑘 = 1.13𝑘𝑘𝑘𝑘 In the same way, the operator calculates the losses at the operating point 50/50 to 0.81kW and at 90/50 to 0.93kW. Taking into account the mentioned duty cycle, the average losses over one production cycle result in:

𝑃𝑃𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎 = 1.13𝑘𝑘𝑘𝑘 ∙ 0.2 + 0.81𝑘𝑘𝑘𝑘 ∙ 0.5 + 0.93𝑘𝑘𝑘𝑘 ∙ 0.3 = 0.91𝑘𝑘𝑘𝑘 If the operating points are different from those specified in Figure 1 and the table above, the losses can be calculated in the same way by using a simple interpolation formula provided in 61800-9-2. ---------------------------------------------------------------------------------------------------------------------------

About CEMEP

CEMEP is the European Committee of Manufacturers of Electrical Machines and Power Electronics, representing an industry with a market value of € 6.3 billion and 130,000 employees. The members of CEMEP are the National Associations in Europe, representing manufacturers of electric motors, variable speed drives, and uninterruptible power supplies. This organization allows industry to co-ordinate actions at the European and International level, with the main topics being: market evolution, standardization, regulation, promotion, and connection with other products & professional groups. The National Electrical Manufacturers Association (NEMA) The National Electrical Manufacturers Association (NEMA) represents nearly 350 electrical equipment and medical imaging manufacturers that make safe, reliable, and efficient products and systems. Our combined industries account for 360,000 American jobs in more than 7,000 facilities covering every state.

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Our industry produces $106 billion shipments of electrical equipment and medical imaging technologies per year with $36 billion exports.

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