Improving efficiency in electric motors

In this look at techniques to reduce losses in induction electric motors to meet the level of efficiency IE4 (IEC 60034-30), this article discusses the rules, guidelines and the best practices to reduce losses in induction electric motors. It also examines new technologies for electric motors to improve efficiency, highlighting their advantages and disadvantages, especially those designed for variable speed drives. Several technologies of motors are available in the market, since the most affordable in terms of cost up to the most efficient or compact one. Besides that, motors have to be able to meet many specific application requirements, like speed range, installation, safety, reliability, low level of noise and vibration, long life, maintenance etc. Nevertheless, despite of all motor technologies, induction motors remain the most used in the market, especially when variable speed is not necessary. Nevertheless, modern ac motor drives use induction motors with field-oriented control for variable-speed operation. In this scenario, in order the increase the overall efficiency, super premium efficient IE4 induction motors are used. Alternatively, permanent magnet synchronous motor higher efficient than IE4 could also be used, since both induction and PM motors need power electronics to control their speed. This paper presents and discusses the influence of each individual loss on the efficiency of induction motors and proposes means to mitigate them in order to reach the level of efficiency IE4 (IEC 60034-30). General rules, guidelines and best practices to reduce all kinds of losses in induction electric motors are presented. Even though an induction motor is already built, it is still possible to increase the efficiency in a Variable Speed Drive (VSD) application especially at low speed by controlling properly the magnetic flux (Voltage/frequency ratio) in order to maintain the total losses in a minimum value. This is known as ‘Optimal Flux’. Comparisons of different technologies against the induction motors are always difficult, and different applications can lead to different motor drive selection. There are cases where the choice of a particular motor drive system can be affected not only by performance or cost, but by other factors as maintenance issues (like easiness of assembly and disassembly of the motors), robustness against high-speed forces, acoustic noise, vibration, etc. Comparison analysis of performance must be done considering the speed range operation and speed limits to be reached, not only the performance of the induction motor operating from the mains or by a frequency inverter at fixed speed. IE4 Efficiency level The 1st edition of IEC 60034-30 defined the limits for IE1, IE2 and IE3 efficiency levels. Presently, the IE4 Super Premium Efficiency Class limits are being defined in the Committee Draft (CD) of IEC 60034-30, 2nd Ed. along with IE1, IE2 and IE3 classes. Nevertheless, changes in the efficiency level IE4 can still occur in the final version of IEC 60034-30 2nd Ed. This standard will define efficiency levels for motors from 0.12 to 800 kW, in 2, 4, 6 and 8 poles (for mains supply, fixed-speed motors) and also for variable-speed motors.

Comparing to the efficiency level IE3, the efficiency level IE4 motors have less losses ranging from 10% to 24%. So, the main question arising is: what should a motor manufacturer do to meet IE4 efficiency level requirements for induction motors maintaining the power/frame ratio? Or, in the other way, how to increase the induction motor efficiency with a minimum cost increasing?

Efficiency over speed range

Significant energy savings can be achieved through the use of variable-speed drives (VSDs). Although induction motors can presently have IE4 efficiency class, when they are fed by frequency converters they present a significant decrease in their efficiency, even for constant torque applications. Sometimes they also need to be over dimensioned, or use forced ventilation. In this case PM motors can contribute to increase the process efficiency, because they have higher efficiencies than induction motors at low speeds, and do not need over dimensioning nor forced ventilation. Figure 1 below illustrates this behavior. In this example, IE2, IE3 and IE4 induction motor efficiencies are plotted along with a PM motor efficiency, for variable-speed, constant torque. It shows that PM motor has superior efficiency than induction motors, especially at the lower speeds.

Figure 1. Efficiency over a 4:1 speed range with constant torque for three motors: a PM synchronous

motor and three induction motors (W22 IE2, IE3 and IE4), all rated 30 kW at nominal speed.

Optimal Flux

It is possible to increase the efficiency of induction motors for constant torque as speed decreases.

The fundamental theory of the electric machines shows that the torque provided by the induction

motor is directly proportional to the product between the magnetic flux and the electric current.

Then, in order to keep the torque constant, if the flux increases the current decreases (and vice-

versa). As the Joule losses are directly proportional to the squared current, these losses can be

considered as inversely proportional to the square of the magnetic flux. From the Faraday-Lenz law

of induction, one can easily demonstrate that the magnetic flux in the motor is directly proportional

to the ratio between the electromotive force (E) and the frequency (f). Considering the steady-state

model of equivalent circuit of the induction motor per-phase, it can be noted that at the base

frequency the voltage drop in the primary impedance has little significance, so that the flux can be

considered as proportional to the V/f (voltage/frequency) ratio. For lower speeds, the drop voltage in

the primary impedance has to be considered.

The main idea behind optimal flux is to make a balance between magnetic flux and current as motor

speed decreases in order to maintain the torque constant and the total losses at a minimum. As we

know, iron losses are greatly dependent on magnetic flux density and frequency. As frequency

decreases, iron losses also decreases. It means that magnetic flux density could be increased by

boosting the voltage in order to reduce current and thus Joule losses (I2R losses). As final result, the

torque remains constant and the Joule losses, that are the major losses, are greatly reduced. This

leads to an overall reduction of losses as speed decreases. A complete description of this method can

be found in [1]* and [2]*. Considering the optimal flux solution for an IE4 efficiency level motor, it is

possible to determine how the efficiency is affected by the speed reduction compared to the same

motor without optimal flux solution. Figure 2 shows an example for the 30 kW, 4 poles, 50 Hz IE4

induction motor compared to a PM motor.

Figure 2. Efficiency comparison between a 30 kW, 4 poles, 50 Hz IE4 induction motor without optimal

flux, with optimal flux and a PM motor for constant torque.

Techniques to reduce losses

Knowing exactly where the losses are located is the key to propose modifications in the design and

manufacturing process to reduce them. The losses to be considered are: pj1 – Joule losses in the

stator windings, pj2 – Joule losses in the rotor, pmech – mechanical losses (friction and ventilating

losses), pfe – iron losses, padd – additional losses and pharm – harmonics losses. For instance, the

percentage losses distribution for a WEG, IE4, W22, 30kW, 4-pole induction motor is: pj1 = 43.7%, pj2

= 20.4%, pmech = 3.53%, pfe = 26,7%, padd = 4.91% and pharm = 0,67%. Particularly for this motor, it is

clear that the most relevant losses are Joule losses and iron losses.

Obviously, the reduction of each individual loss tends to increase the cost of the motor. Besides that,

in some cases, to reduce mechanical losses, temperature rise can be increased. In other situations,

starting current, starting torque or power factor are also affected. So, the challenge for induction

motor designers and researchers is to reduce losses with a minimum cost increase and general motor

performance improvement, not only in terms of efficiency but also noise, vibration, temperature rise,

starting current and torque, and power factor among others.

Joule Losses in the stator winding These losses present usually the highest percentage among all losses. It is necessary to reduce the

resistance of the winding in order to reduce this kind of losses. This can be done by:

Enlarging the wire diameter maintaining the number of turns. This solution demands

improvements in the winding manufacturing process because, as fill factor is higher, it is quite

more difficult to insert the windings into the stator slots. In the case of a complete new stator

lamination design is necessary, stator slots can be enlarged. The price to be paid is a narrower

stator tooth or stator core that will increase magnetic flux density in these regions, increasing

magnetic losses. So, many simulations are necessary to reach the best design where the sum of

the losses is as low as possible. To avoid this very time-consuming task, the use of software with

optimization techniques is mandatory.

Enlarging the wire diameter reducing proportionally the number of turns. In this case, the fill

factor remains unchangeable and there will not be any problem with the manufacturing process.

But the magnetic flux will increase and, therefore, the iron losses. Besides that, other

performance parameters are affected and they have to be analyzed carefully.

Enlarging the stator length and the wire diameter, reducing the number of turns and keeping

the original stator slot size. This solution is efficient to reduce losses but increase the cost with

conductors and steel lamination. In some cases, there still is a limitation to design a longer stator,

which demands modifications in the mechanical design of the motor. The volume of the

conductors is augmented by the new package length and, consequently, the cost. Since the

magnetic flux density remains as original, the stator resistance decreases, reducing the Joule

losses, but the performance characteristics of the motor do not remain the same because the

magnetic flux was modified.

Just enlarging the stator length. In this case, cost with conductors and steel lamination is

increased too. The stator resistance becomes higher, increasing Joule losses, but it is

compensated by the reduction of iron losses due to the magnetic flux density reduction. The

performance characteristics of the motor remain the same because the magnetic flux was not

modified.

Enlarging the stator length has another positive consequence: the area for heat transfer from stator

surface to the frame becomes larger and, by this reason, the temperature rise decreases, demanding

less energy from the ventilating system. So, a new ventilating system can be designed with smaller

mechanical losses. As many other parameters are influenced by any electric or magnetic modification

in the stator and rotor, a software with optimization capabilities has to be run to evaluate all

possibilities simultaneously and select just some few options to be prototyped. In practice, the

adopted solution usually is a mix of enlarging the stator length, reducing the number of turns and

increasing the wire diameter.

Joule Losses in the rotor Joule losses in the rotor are not only a matter of rotor bars conductivity. Shape of rotor bars and

short-circuit rings is also relevant, although several shapes are already well established among

manufacturers and in the related technical literature. The question is not how to design properly the

rotor cage but how to fabricate it free from many interferences of the manufacturing process. In

order to reduce Joule losses of cast aluminum rotor cage, simulation software should be used to

analyze the quality of rotor slots and short-circuit rings filling and its correlation to the cast aluminum

process parameters.

Other important aspect to be considered to reduce Joule losses in the rotor is related to the

conductivity of the rotor bars and short-circuit rings, specifically about the advantages and

disadvantages of using cast copper or aluminum. In 2011, WEG conducted a study [3]* to ascertain

the feasibility of manufacturing squirrel cage low voltage induction motors using cast copper as a

substitute for the traditional aluminum, as an alternative to increase efficiency and reduce costs. A

case study accomplished with a 15 kW 4-pole IE3 motor showed that, in order for the use of die cast

copper cage, rather than the traditional die cast aluminum cage, to become economically

advantageous in industrial three phase induction motors, the quotation (price/kg) of the copper

must be no greater than 1.1 times the quotation of the aluminum.

Mechanical Losses One of the best practices to reduce the total losses in an electric motor is a good ventilation system

design, especially for 2 pole motors. Besides of that, incorporated ventilating system is the most

responsible for acoustic noise in 2- and 4-pole TEFC and ODP motors. Due to its high efficiency, an IE4

motor has inherently less demand for heating removal. So, the ventilating system can be optimized in

order to reduce mechanical losses and consequently acoustic noise. Some aspects to be considered

are:

Geometry of the fins: there is a good relationship between height of fins and width between two

adjacent fins. They have to be designed in order to provide the best thermal dissipation.

Numerical simulation software can help to evidence the best geometry. At the same time,

manufacturing process limitations such as painting difficulties and quality of the die cast iron

frame (or aluminum, if this is the case) have to be taken into account.

Position of the terminal box: it has to be designed to not interfere on the air flow over the frame

surface along the fins channels. The terminal box must be placed as close as possible to the drive

end shield allowing that the airflow reaches almost completely all frame surface, thus removing

heating more efficiently. Again, numerical simulation tools should be used to analyze the

behavior of the airflow. It is important to ensure that the airflow is turbulent in order to remove

heating more efficiently.

End shields: it is recommended that the drive end shield has fins to remove the heating

generated by the bearings friction or transferred from the interior of the motor to the exterior by

the shaft. The surface of the non-drive end shield, where the fan is mounted, must be very

smooth since the amount of air in that region is abundant and any sharp geometry increases the

noise.

Fan and end cover: not only efficiency has to be considered but also noise. Geometry and

number of blades, shape of the end cover to avoid vortices, axial distance between fan and end

shield surface, radial gap from fan and fan cover and distance between air inlet and fan have to

be carefully designed to reduce losses and avoid pressure deviation that causes passage noise.

Figure 3 shows improvements in the ventilating system of W22 platform in order to reduce losses

and noise.

Figure 3 – Design of fan and fan cover for WEG W22 platform.

Iron losses

Iron losses contribute with a large part of the total losses in an induction motor. It seems to be easy

to recognize that the simplest way to reduce iron losses in an induction motor is using higher quality,

lower losses silicon steel lamination (usually thinner lamination) than those currently used.

Unfortunately, this solution usually increases dramatically the cost of the motor. Reducing magnetic

flux density is another possible solution but, in this case, again, lamination cost increases by

increasing the amount of magnetic material, since the original motor performance must not be

affected. On the other hand, some initiatives can be taken without cost addition in order to reduce

iron losses:

Lamination stress relief thermal treatment to recover the magnetic properties along the border

of the stator teeth, especially for those narrower ones.

Use silicon steel lamination with high magnetic permeability at 1.5 T, for instance, and usual cost.

Power factor is increased, reducing current and consequently Joule losses in the stator.

For a complete new stator design, it is important to search for the best stator slot/tooth width

ratio.

Usually, most of softwares used to calculate the motor performance, including iron losses, consider

the magnetic saturation (BH) curve of the steel lamination material obtained from the Epstein Frame

Test. This procedure is not accurate because the magnetic flux behavior in an Epstein Frame Test

sample is different from what really happens in a motor. Epstein Frame Test does not take into

account the rotational losses like those existing in the junction between stator teeth and yoke. Then,

the magnetic properties of the steel lamination should be taken from tests in a real motor and this

information should be used to calculate the performance of other similar motors. Nevertheless,

standard tests to determine iron losses in a motor are not very accurate, since the method used is

indirect. In order to evaluate properly the steel lamination properties, a three-phase electromagnetic

device was developed at WEG to be able to generate a magnetic flux that really represents the

magnetic flux of an electric motor. It can evaluate the magnetic losses generated in the stator, taking

into account the laminations geometry and the magnetic field rotating component. Unlike the Coil

Ring test, the mentioned device allows the evaluation of the total magnetic losses taking place in the

stator, which comprises those generated in the yoke and in the teeth. The test device was designed

to be placed in the rotor (Figure 4), once the intention was to evaluate the losses generated in the

stator core.

a) b)

Figure 4 - a) Full test system with the stator sample in position, b) Cut view of the test system showing

the test device placed in the rotor [4]*.

In the Epstein frame test, the magnetic losses were measured for four induction levels at 50 Hz. From

the results obtained with this method (Figure 5), it is possible to classify ‘A’ as the best supplier and

"B" as the worst supplier among the 3 evaluated ones. Magnetic losses of the supplier B at 1.7 T were

used as reference. The test performed with the electromagnetic device followed the same steps of

the Epstein frame test. However, different behavior was observed. The results obtained from the

three-phase electromagnetic device are presented in Figure 6. It can be realized that supplier ‘B’

remains the worst, but now supplier ‘C’ is the best, instead of supplier ‘A’. The results shown in the

graphs of figures 5 and 6 comprise the average losses found in these tests, showing the maximum

and minimum limits according to a Student t-distribution.

Figure 5 - Results obtained with the Epstein

frame test – 50Hz [4].

Figure 6 - Results obtained with the three-phase

electromagnetic device - 50Hz [4].

In the tests performed with actual electric motors running at no-load, the magnetic losses were

evaluated for nominal magnetic flux condition (380 V/50 Hz). The results confirmed the behavior as

for the electromagnetic device, with the supplier ‘C’ remaining as the best and the supplier "B" the

worst of the three investigated suppliers.

Additional losses Many times, additional losses are understood as iron losses. Although they occur mainly in the

ferromagnetic parts of the motor, they have actually a different nature. While iron losses are at

nominal frequency, additional losses are high frequency losses due to the pulsating magnetic flux. At

no-load, they are known as pulsating losses and, at load, as stray load losses.

Pulsating losses (at no-load): these losses occur essentially on the rotor surface as an eddy current

losses due to the magnetic flux variation in the stator teeth. By its turn, the magnetic flux variation in

the stator teeth is due to the relative slot opening between stator and rotor (reluctance variation)

and exists already at no load.

Stray load losses (at load): they occur mainly in the stator and rotor teeth, rotor surface and rotor

cage bars due to the space induction harmonics at load.

Other losses usually treated as additional losses are:

Stator slots skin effect:

Usually, losses due to the stator slots skin effect are neglected for low voltage motors. But it is

important to consider the skin effect when the number of stator winding turns is small, especially for

VFD application. Skin effect is caused by non-uniform induction distribution relatively to the leakage

magnetic flux along the stator slot. It can be understood as an increasing in the resistance of the

conductor, thus increasing the losses.

Harmonic losses:

These losses act as a load for the motor, like ventilating and friction losses. Each space induction

harmonic due to the winding current can be understood as a small motor with a positive or negative

torque related to the torque of the fundamental, depending on the rotation direction of the

harmonic. These losses are not large comparable with others, but cannot be neglected when each

small loss needs to be reduced. The way to reduce the harmonic losses is to design a winding as

sinusoidal as possible in order to eliminating the space induction harmonic content.

Some manufacturing rotor imperfections like lamination burrs and low contact resistance between

laminations can also increase additional surface losses. Low resistance between lamination and cage

bars increases inter-bar currents and consequently Joule losses. Bubbles or poor die casting rotor can

also increase losses. The perfect understanding of the nature, causes and consequences of such

imperfections is fundamental to improve the manufacturing process.

New technologies for super premium efficient motors

Switched reluctance motors

The switched reluctance motor has concentrated windings in the stator

and no aluminum cage nor permanent magnets in the rotor, but only

laminated steel with salient teeth. So there are no joule losses in the

rotor. An example of a 4-phase switched reluctance motor with eight

stator teeth and six rotor teeth is shown in Figure 7. The winding

inductance varies with rotor position; the reluctance torque is

proportional to the difference between the direct axis (maximum) and

quadrature axis (minimum) value of inductance (Ld and Lq,

respectively).

The switched reluctance motors present mechanical simplicity, robustness and reliability, however

they require sophisticated electronic control. With proper design for each application, efficiency and

power density are higher than induction motor of same power, but there is significant torque ripple.

Figure 7 – SRM - 8/6 four-phase motor

Consequently they usually have high vibration and acoustic noise [5]*, which has been limiting its

wide use.

Synchronous reluctance motors

The synchronous reluctance motor uses a conventional polyphase ac stator, and the rotor has no

aluminum cage nor permanent magnets, but flux barriers to create preferred paths for the armature

flux, thus creating different values of the d-axis and q-axis inductances. Contrary to the switched

reluctance motor, it can be more easily designed to give reduced levels of torque ripple and acoustic

noise [6]* and sinewave ac operation (rotating field). The motor performance is greatly dependent

on the geometry of the flux barriers in the rotor lamination [7]*. In order to have a performance

comparable to that of the induction motor, the synchronous reluctance motor must have a saliency

ratio (Ld/Lq) in the range 7-10 [8]*, which is achievable with a high anisotropic rotor design, e.g., the

axially laminated rotor (Figure 8), but they have a more complex manufacturing than the

conventional transversally-laminated motor (Figure 9).

Figure 18 - Axially-laminated

synchronous motor

Figure 9 - Transversally-laminated

synchronous motor

These motors have some characteristics that make them attractive: cost of active material is

comparable to that of induction motor and much lower than that of high energy permanent magnet

motors; easiness of rotor skewing; flux weakening capability, which is important for attaining high

speed ranges; suitability to large overloads [6]. On the other hand, power factor is poor and the

current is up to 40% higher compared to an equivalent induction motor. Efficiency is comparable to

that of induction motor.

Permanent magnet motors

PM motors offer the highest efficiency of all motors, with high power factor, due to the absence of

Joule losses in the rotor and the excitation flux of the permanent magnets, high torque-to-current

and torque-to-volume ratios, compactness, and fast dynamic response. Ferrite magnets are generally

used in low power applications where low cost is mandatory and NdFeB magnets in industrial motors

for a better performance.

Sinewave PM motors (or brushless ac motors) are synchronous motors, and usually make use of

similar stator windings as induction motors. Squarewave PM motors (or brushless dc motors) have

concentrated windings on the stator, and are often used in low power applications. Sinewave PM

motors are suitable for industrial applications due to the characteristics of low torque ripple and

acoustic noise, and high efficiency. There is a variety of rotor configurations for PM motors, and

which one is the best is a matter of the application requirements.

Surface-magnet motor

The permanent magnets are placed on the surface of the rotor. This facilitates manufacturing of the rotor, since the magnets can be put in place before magnetization, being magnetized all together at once in a special magnetizing fixture. This motor has poor field-weakening capability, so the speed range is very limited, the maximum speed usually not exceeding 2x base speed. Two examples of surface-PM motors are shown in Figure 10 and 11. High speed operation is limited by the strength of the magnets against centrifugal forces, unless special retention devices are used, for example, an external non-magnetic sleeve. These motors have no magnetic saliency, so there is no reluctance torque.

1.1.1 Interior-magnet motor

The permanent magnets are placed inside the rotor lamination. Several rotor topologies are possible,

some of them are shown in Figures 23, 24, 25 and 26.

Figure 12 - Interior-

PM motor –

tangential magnets

Figure 13 - Interior-

PM motor – V-

shape magnets

Figure 14 - Interior-

PM motor – radial

magnets

Figure 15 - Multi-

layer PM motor

Flux-weakening capability is improved due to higher inductance, and these motors are more suitable

for a wider speed range than the surface PM motors. These motors have a magnetic saliency, so the

total torque has a reluctance torque component that can be added to the torque provided by the

magnets, through correct control strategies, like current angle advance.

PM motors with exterior rotor

Exterior-rotor PM motors have higher torque per volume ratio than interior rotor motors. The

magnets are placed on the internal surface of the rotor, and they are retained against centrifugal

forces by the rotor yoke. Assembly of the rotor is facilitated because the magnets can be put in place

before magnetization, as for the interior rotor surface PM motor. The windings can be distributed or

concentrated, the latter is generally used. Figures 16 and 17 show two examples of exterior-rotor

motors with 8 and 16 poles respectively.

The motor in Figure 16 can be used in customized fan applications with few kilowatts, where the

blades can be fixed directly on the external surface of the rotor. The motor in Figure 17 is well suited

Figure 10 - Surface-PM motor

with distributed windings

Figure 11 - Surface-PM motor with

concentrated windings

for high-torque low-speed applications, like direct-drive washing machines, elevators and cooling

towers.

Electronically commutated (EC) motors

EC motors are PM motors, generally for low-power variable-speed applications (residential and

commercial applications), in substitution for single-phase, low-efficient induction motors. The low

power allows the electronic control to be integrated to the motor, inside motor housing or attached

to the NDE end shield. These motors generally have concentrated windings and use ferrite magnets

on the rotor surface (Figure 11). They have higher efficiency than shaded-pole and split-capacitor

motors, and have an increasing demand in HVAC applications, where not only efficiency is desired,

but also easiness of assembly (no need for belts and pulleys), continuous speed control,

compactness, less weight and less acoustic noise.

Line-start PM motors

Line-start PM motors are hybrid induction/permanent-magnet motors which combine an

asynchronous start with a synchronous steady state operation. The stator windings are conventional

distributed windings, while the rotor is a special combination of squirrel cage and permanent

magnets buried beneath the squirrel cage. They can start and accelerate

directly from the mains without the need of electronic control, like a

conventional induction motor, and then be pulled into synchronism by

the permanent magnets.

After that the motor operates synchronously, without rotor currents.

With low copper losses at steady state (harmonic losses only), a better

efficiency (than induction motors) can be reached. But, since these

motors have no electronic control, they do not operate at maximum torque per ampere. For this

reason they have lower torque to volume ratio than the PM motors

discussed earlier. In general, line-start PM motors are limited to low-

inertia applications. If the load inertia is higher than the maximum

allowable inertia, the motor will start but will not synchronize.

Conclusions

This paper presented basic concepts of losses in induction motors and some rules to reduce them in

order to reach IEC IE4 efficiency level. New motor technologies like PM, Switched Reluctance and

Synchronous Reluctance motors were also presented, highlighting their main characteristics. Which

technology is the best, depends not only on the efficiency since other characteristics like cost, size

and weight, reliability, speed range, noise, vibration, easiness of maintenance and general

performance have to be also taken into consideration. Strictly in terms of efficiency, it is possible to

Figure 16 - Exterior-rotor PM motor with 8 poles Figure 17 - Exterior-rotor PM motor with 16 poles

Figure 18 - Line-Start PM

Motor

say that PM motors have the best performance because they do not have losses in the rotor and,

therefore, exhibit much better behavior at low frequencies for constant torque. Nevertheless,

induction motors, when properly designed and manufactured, can also reach IE4 efficiency levels.

Moreover, their performance can be improved at low frequencies with constant torque by applying

the Optimal Flux Solution.

Contact

Marek Lukaszczyk, WEG Electric Motors (UK) Ltd Tel: +44(0)1527 513800 Web: www.weg.net Email: wegsales@wegelectricmotors.co.uk Authors Sebastião L. Nau (slnau@weg.net), Daniel Schmitz (daniels1@weg.net). Research and Technological Innovation Department - WEG Motores Jaraguá do Sul - SC, Brazil

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