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Electric drive

Energy efficiency of electric drive. A complex approach

"Round table" within the framework of PTA-2011

Almost half of all electricity produced in the world is consumed by electric motors. And KM’s interest in the topic of energy efficiency of drive technology is understandable. In September, as part of the PTA exhibition, we held a round table dedicated to this problem. Today we publish the first part of the discussion.

Energy efficient engines - myths and reality

I would like to debunk some popular myths created by “successful managers” who sell motors with increased efficiency or energy-efficient motors (EEM).

What are energy-efficient motors? These are machines whose efficiency is 1–10% higher than that of standard motors. Moreover, if we are talking about large engines, the difference is 1–2%, and in motors low power it can reach 7–10%.

High efficiency in engines is achieved due to:

Increasing the mass of active materials - copper and steel;
- use of thinner and high-quality electrical steel;
- using copper instead of aluminum as a material for rotor windings;
- reducing the air gap between the rotor and stator using high-precision technological equipment;
- optimization of the tooth-slot zone of magnetic cores and winding design;
- use of high quality bearings;
- special fan design.

According to statistics, the cost of the engine itself is less than 2% of the total life cycle costs (assuming 4000 hours of operation annually for 10 years). About 97% is spent on electricity. About a percent is spent on installation and maintenance.

As can be seen from the diagram, for more than ten years in Europe there has been a systematic replacement of low-efficiency engines with motors with increased efficiency. From the middle of this year, the EU has banned the use of new motors of classes below IE2.

Advantages and disadvantages of EED

In general, the transition to the use of EED allows:

Increase engine efficiency by 1–10%;
- increase the reliability of its operation;
- reduce downtime and maintenance costs;
- increase engine resistance to thermal loads;
- improve overload capacity;
- increase the engine’s resistance to various violations of operating conditions: low and high voltage, waveform distortion (harmonics), phase imbalance, etc.;
- increase power factor;
- reduce noise level.

Machines with increased efficiency compared to conventional ones have a 10–30% higher cost and slightly greater weight. Energy efficient motors have compared to conventional engines less slip (resulting in a slightly higher rotation speed) and a higher starting current.

In some cases, using an energy-efficient motor is not advisable:

If the engine is operated for a short time (less than 1–2 thousand hours/year), the introduction of an energy-efficient engine may not make a significant contribution to energy saving;
- if the engine is operated in modes with frequent starting, the saved electrical energy may be consumed due to a higher starting current;
- If the motor is operated under partial load (eg pumps) but for a long period of time, the energy savings resulting from the introduction of an energy efficient motor may be negligible compared to the potential of a variable speed drive;
- each additional percent of efficiency requires an increase in the mass of active materials by 3–6%. In this case, the moment of inertia of the rotor increases by 20–50%. Therefore, highly efficient engines are inferior to conventional engines in terms of dynamic performance, unless this requirement is specifically taken into account during their development.

Practice and calculations show that the costs are recouped due to the saved electricity when operating in S1 mode in a year and a half (with an annual operating time of 7000 hours).

Energy efficiency and reliability of an electric machine are inextricably linked. The downside of energy efficiency is waste. It is losses that are one of the prevailing factors determining the duration of engine operation. Let's take just one aspect of this problem - the thermal effect on the motor windings. The bulk of electrical energy that is not converted into work is lost in the form of heat. When considering the reliability of winding insulation, you need to know the “Eight Degree Rule” (in fact, for different insulation classes we are talking about 8 – 13 °C): excess operating temperature engine by the above amount reduces its life expectancy by 2 times. Example from practice. In the carriages of the Moscow monorail, as a result of engineering miscalculations, the first experimental engines with class H insulation (180 °C) were forced to operate at a temperature of 215–220 °C. In this mode they were enough for only a few months of operation.

Engines that have increased efficiency heat up less, which means they last longer. Energy efficient motors are motors with increased reliability.

Repair or purchase

Another one important problem arising during the operation of electric motors - a decrease in efficiency after major repairs. Market repair work approximately three times the production capacity of new engines. To remove the old winding, in most cases, thermal effects are applied to the stator along with the frame. This operation significantly worsens the properties of electrical steel and increases its magnetic losses. Research has shown that when major renovation Efficiency decreases by 0.5–2%, and sometimes up to 4–5%. Accordingly, these losses begin to additionally heat the engine, which is very bad. In practice there are two options right actions. A cost-effective way is to purchase a new energy-efficient engine. The second option is high-quality repair of a burnt out motor. This should not be done in a regular workshop, but in a specialized enterprise.

New solutions from ABB

ABB pays great attention to the energy efficiency of motors. We produce motors of classes IE2 and IE3 in both aluminum and cast iron housings.

ABB has been selling IE3 class motors since the beginning of this year. They are in demand among machine builders and industrial enterprises focused on energy-efficient technologies. They are good where required Full time job engine with a load close to the rated load.

In the fourth quarter, ABB launches the M3BP series with axis height 280–355 with energy efficiency class IE4 (SUPER PREMIUM EFFICIENCY). The M3BP series is the pinnacle of design and technological developments ABB company in the field of electrical engineering. Combining high efficiency, reliability and long service life, the M3BP series motors are the most optimal and versatile offering for most sectors and applications of modern industry.

An important issue is the operation of the motor as part of a variable frequency drive. We firmly occupy a place among the top three global manufacturers of electric drive technology. An important advantage ABB offers the possibility of joint testing of motors with frequency converters.

When powering a motor from a frequency converter, it is very important to pay attention to issues such as insulation strength, the use of insulated bearings and forced cooling of the motor.

The CMEA members decided to increase the engine power by 1–2 stages without changing the size, i.e., in fact, maintaining the same engine volume. We are talking about the introduction of the CMEA linkage instead of the CENELEC linkage in force in Europe when introducing the 4A series. The next negative step in the context of ensuring energy efficiency was the reduction in the blank diameters of the AIR series compared to the 4A series. Then, probably, it was correct, it was necessary to save electrical materials, but today we are faced with the problem that efficiency corresponding to class IE2 or even IE3 must be “driven” into the CMEA linkage. Our careful studies have shown that the blank diameters junior cars CMEA linkage is not enough to ensure class IE3. And if Russia acts in line with the European Commission and focuses on IEC 60034-30 standards, even with a lag of two or three years, then when it comes to the highest energy efficiency class IE3, it will turn out that a colossal number of machines - from 90 to 132nd height - it simply cannot provide them. We will have to break the link; everything that has been done for thirty years will have to be changed. This is a real time bomb. It’s good that from size 160 and above there is no such danger. Despite the increased power (or reduced volume with CENELEC power), we can still achieve energy efficiency class IE3. I note that if for medium-sized European manufacturers the cost of IE3 class engines compared to IE1 increases by 30–40%, then for Russian coupling the cost of machines increases significantly more. We are limited by the diameter, which means we are forced to excessively increase the active length of the machine

About materials and price of AED

We have to think about the price of electric cars. Copper is rising in price much faster than steel. Therefore, we propose, where possible, to use so-called steel motors (with a smaller groove area), i.e. we save copper.

By the way, for the same reasons, NIPTIEM is not a supporter of permanent magnet motors, since magnets will become more and more expensive than copper. Although, in equal volumes, a permanent magnet motor provides greater efficiency than an asynchronous motor.

In the September issue of KM there was an article about SEW Eurodrive motors built using Line Start Permanent Magnet technology, as conceived by the creators, combining the advantages of synchronous and asynchronous machines. These are essentially permanent magnet machines and the squirrel cage rotor is used at start-up, accelerating the machine to sub-synchronous speed. Such engines upper class energy efficient and quite compact. It seems to me that they will not be widely used, because permanent magnets are very much in demand in industries other than general industry, and, according to expert estimates, in the future they will mainly be used to produce special equipment, for which no expense will be spared.

The first Russian EEDs from RUSELPROM

The 7AVE series is positioned as the first full-scale energy efficient RF series with dimensions from 112 to 315. In fact, all of it has been developed. Dimension 160 is fully implemented. Sizes 180 and 200 are being introduced. Starting with size 250, about ten standard sizes of machines currently produced in the 5A series, if we recalculate the efficiency by the measured additional losses, correspond to class IE2; two standard sizes – class IE3. In the 7AVE series, the mentioned standard sizes will be more economical.

Let me note that Russian scientists are faced with a very difficult and fascinating task of optimally constructing a series asynchronous machines, which contains several links (Russian and European, increased power) 13 dimensions, three energy efficiency classes, numerous modifications, that is, a global multi-object optimization problem.

Photos courtesy of ABB LLC

Electric drive 02.10.2019 Gold medal for innovative eAutoPowr transmission and intelligent system e8WD received by the company John Deere from the German Agricultural Society (DLG). Another 39 products and solutions received silver awards.

Electric drive 30.09.2019 Sumitomo Heavy Industries has reached an agreement to acquire variable frequency drive manufacturer Invertek Drives. As reported in the release, this is the next step in the business development strategy, both in terms of increasing the portfolio and expanding global market coverage.

For about five years now, the NPO St. Petersburg Electrical Engineering Company (SPBEC) has been persistently collecting implemented innovations, developments, and innovations from enterprises, institutes, and research centers of the former Soviet Union.

Another innovation applicable in Russian realities is associated with the name of Dmitry Aleksandrovich Duyunov, who is engaged in problem of raising energy efficiency of asynchronous motors:

"In Russia, asynchronous motors, according to various estimates, account for from 47 to 53% of the consumption of all generated electricity. In industry, on average 60%, in cold water supply systems up to 80%. They carry out almost all technological processes related to movement and cover all spheres of human activity. Each apartment contains more asynchronous motors than there are residents. Previously, since there was no goal of saving energy resources, when designing equipment they tried to “play it safe” and used engines with power exceeding the calculated one. Energy saving in design faded into the background, and such a concept as energy efficiency was not so relevant. The Russian industry did not design or produce energy-efficient engines. The transition to a market economy changed the situation dramatically. Today, saving a unit of energy resources, for example, 1 ton of fuel in conventional terms, is half as expensive as extracting it.

Energy-efficient motors (EMs) are asynchronous motors with a squirrel-cage rotor, in which, due to an increase in the mass of active materials, their quality, as well as through special design techniques, it was possible to increase ( powerful engines) or 4-5% (small engines) rated efficiency with a slight increase in the price of the engine. This approach can be beneficial if the load varies little, speed control is not required and the motor is correctly selected. With the advent of motors with combined Slavyanka windings, it is possible to significantly improve their parameters without increasing their price. Due to improved mechanical characteristics and higher energy performance, it became possible not only to save from 30 to 50% of energy consumption with the same useful work, but also to create a variable drive with unique characteristics, which has no analogues in the world.

Unlike standard ones, electric motors with combined windings have a higher torque ratio, have efficiency and a power factor close to the rated one in a wide range of loads. This allows you to increase the average load on the engine to 0.8 and increase performance characteristics equipment served by the drive.

Compared to known methods for increasing the energy efficiency of an asynchronous drive, the novelty of our proposed approach lies in changing the fundamental design principle of classic motor windings. The scientific novelty lies in the fact that new principles have been formulated for the design of motor windings, as well as the selection of optimal ratios of the numbers of rotor and stator slots. On their basis, industrial designs and schemes of single-layer and double-layer combined windings have been developed, both for manual and automatic laying of windings on standard equipment. A number of Russian patents have been received for technical solutions.

The essence of the development follows from the fact that, depending on the connection diagram of a three-phase load to a three-phase network (star or triangle), two current systems can be obtained, forming an angle of 30 electrical degrees between the vectors. Accordingly, an electric motor that has not a three-phase winding, but a six-phase one, can be connected to a three-phase network. In this case, part of the winding must be connected to a star, and part to a triangle, and the resulting vectors of the poles of the same phases of the star and triangle must form an angle of 30 electrical degrees with each other. Combining two circuits in one winding makes it possible to improve the shape of the field in the operating gap of the engine and, as a result, significantly improve the main characteristics of the engine.

Compared to the known ones, a variable-frequency drive can be made on the basis of new motors with combined windings with an increased frequency of the supply voltage. This is achieved due to lower losses in the steel of the motor magnetic circuit. As a result, the cost of such a drive is significantly lower than when using standard motors, in particular, noise and vibration are significantly reduced.”

In energy-saving engines, due to an increase in the mass of active materials (iron and copper), the nominal values ​​of efficiency and cosj are increased. Energy-saving motors are used, for example, in the USA, and are effective when constant load. Feasibility of application energy saving engines should be assessed taking into account additional costs, since a small (up to 5%) increase in nominal efficiency and cosj is achieved by increasing the mass of iron by 30-35%, copper by 20-25%, aluminum by 10-15%, i.e. increase in engine cost by 30-40%.

Approximate dependences of efficiency (h) and cos j on rated power for conventional and energy-saving engines from Gould (USA) are shown in the figure.

Increasing the efficiency of energy-saving electric motors is achieved by the following design changes:

· cores are lengthened, assembled from individual plates of electrical steel with low losses. Such cores reduce magnetic induction, i.e. steel losses.

· losses in copper are reduced due to the maximum use of slots and the use of conductors of increased cross-section in the stator and rotor.

· additional losses are minimized by careful selection of the number and geometry of teeth and grooves.

· less heat is generated during operation, which makes it possible to reduce the power and size of the cooling fan, which leads to a decrease in fan losses and, consequently, a decrease in overall power losses.

Electric motors with increased efficiency reduce energy costs by reducing losses in the electric motor.

Tests carried out on three “energy saving” electric motors showed that at full load the savings achieved were: 3.3% for a 3 kW electric motor, 6% for a 7.5 kW electric motor and 4.5% for a 22 kW electric motor.

Savings at full load are approximately 0.45 kW, for an energy cost of $0.06/kW. h is $0.027/h. This is equivalent to 6% of the operating costs of the electric motor.

The list price for a regular 7.5 kW electric motor is US$171, while the high efficiency motor costs US$296 (a price premium of US$125). The table shows that the payback period for an increased efficiency motor, calculated on the basis of marginal costs, is approximately 5000 hours, which is equivalent to 6.8 months of operation of the motor at rated load. At lower loads the payback period will be slightly longer.

The higher the engine load and the closer its operating mode is to constant load, the higher the efficiency of using energy-saving engines.

The use and replacement of engines with energy-saving ones should be assessed taking into account all additional costs and their service life.

Modern three-phase energy-saving motors can significantly reduce energy costs due to a higher coefficient useful action. In other words, such engines are capable of generating a greater amount of mechanical energy from each kilowatt of electrical energy expended. More efficient energy consumption is achieved through individual reactive power compensation. At the same time, the design of energy-saving electric motors is different high reliability and long service life.

Universal three-phase energy-saving electric motor Besel 2SIE 80-2B version IMB14

Application of three-phase energy-saving motors

Three-phase energy-saving motors can be used in almost all industries. They differ from conventional three-phase motors only in their low energy consumption. In the context of constantly rising energy prices, energy-saving electric motors can become a truly profitable option for both small producers of goods and services and large industrial enterprises.

The money spent on purchasing a three-phase energy-saving motor will quickly return to you in the form of savings on the purchase of electricity. Our store offers you additional benefits by purchasing a high-quality three-phase energy-saving motor at a really low price. Replacing morally and physically obsolete electric motors with the latest high-tech energy-saving models is your next step to a new level of business profitability.

Energy saving motors

Smart solutions to save energy

Energy-saving Siemens motors are available in efficiency classes “EFF1” and “EFF2” according to CEMEP

• Number of poles 2 and 4
• Power range 1.1...90 kW
• 50 Hz version according to IEC 34-2
• EFF1 (High Efficiency Motors)
• EFF2 (Enhanced Efficiency Motors)

To reduce CO 2 emissions, engine manufacturers have committed to labeling engines according to efficiency classes.

EPACT – engines for the American market

Comprehensive range of EPACT motors with IEC dimensions

• Number of poles: 2,4 and 6
• Power range: 1 HP to 200 HP (0.75 kW to 150 kW)
• 60 Hz version in IEEE 112b

In accordance with the act of October 97 by EPACT, engine efficiency imported directly or otherwise into the United States must meet minimum values.

Benefits for the customer and the environment

Energy-saving motors with optimal efficiency consume less energy for the same output power. The increase in productivity is achieved through higher quality iron (cast iron, copper and aluminum) and technical improvements in every detail. Energy losses are reduced by 45%. The buyer receives huge cost savings by minimizing operating costs.

By using energy-saving motors, the damage caused by environment. The potential for energy savings is up to 20 TW per year, which is equivalent to the power of 8 thermal power plants and emissions of 11 million tons of carbon dioxide into the atmosphere.