WO2002054564A1

WO2002054564A1 - High efficiency ac motor

Info

Publication number: WO2002054564A1
Application number: PCT/KR2001/002207
Authority: WO
Inventors: Young-Gi Chun
Original assignee: Young-Gi Chun
Priority date: 2001-01-04
Filing date: 2001-12-19
Publication date: 2002-07-11

Abstract

There is provided a highly-efficient alternating current (AC) motor which improves efficiency and power factor to minimize power consumption. The highly-efficient AC motor includes a stator, a rotator having a secondary circuit for inducing current using the rotating magnetic field and generating torque, and an induction windig, which is inserted into the stator, insulated from the operation winding, and interlinked with the operation winding and the secondary circuit to induce electromotive force. The highly-efficient AC motor further includes a capacitor, which is connected to an output node of the induction winding to constitute a circuit for charging and discharging current due to induced electromotive force. The induction winding absorbs internal loss of the AC motor and performs a generative operation during the operation of the AC motor to minimize loss and greatly improve power factor. The electromotive force of the induction winding can be used for output of the AC motor or used to supply any additional load with power. Thus, power consumption caused by the AC motor is minimized to save energy considerably. Also, a rise in the temperature of the AC motor is inhibited, thus prolonging the life of the AC motor.

Description

HIGH EFFICIENCY AC MOTOR

Technical Field

The present invention relates to an alternating current (AC) motor including a single or three-phase induction motor, and more particularly, to a highly efficient AC motor having a considerably improved load efficiency and power factor.

Background Art A motor converts input electric energy into rotary or rectilinear mechanical energy and outputs the converted energy. However, not all of the input energy gets converted, and more than an expected amount of loss occurs depending on efficiency and power factor.

Induction motors are mainly used in general electric home appliances and industrial machines. Induction motors are operated at an efficiency of about 80 - 90% under full load. However, slip increases with an increase in load while efficiency sharply drops for a light load that is less than a rated load. In particular, efficiency is lower in induction motors having small capacity. About 60% of the power consumption in most countries as well as Korea is due to motors. A research report by U.S. Electric Power Research Institute (EPRI) shows that about 70% of industrial induction motors operate under less than 60% of rated load. Most motors including induction motors operate at a lower efficiency than the standard efficiency, and thus a large amount of power is wasted. Thus, a highly efficient induction motor is important to economize domestic energy.

Energy loss in motors is classified as electrical loss and mechanical loss. Losses may also be classified as load loss, no-load loss, and fixed loss. Here, load loss varies depending on the load, no-load loss occurs in a no-load operation, and fixed loss occurs regardless of the magnitude of load. Copper loss and iron loss are representative losses for electric loss. Copper loss occurs due to conductor resistance of a winding inserted into a stator or a rotator, where the energy of P=I²R(W) in a conductor that has resistance R (Ω) is changed into heat and lost if current 1(A) flows in the conductor. This copper loss as well as direct energy (power) loss causes breakdown of machines, such as breaking of insulation or shortening of the life of machines by heating the machines. Iron loss means power loss due to magnetic hysteresis in iron cores of the stator and rotator and due to eddy current brake induced in the iron cores and is also dissipated in the form of heat. Also, there is stray load loss, which occurs due to an increase in iron loss caused by leakage of magnetic flux, and mechanical loss, which occurs due to friction between a shaft and bearings and friction between air and a cooling fan. The conventional method of achieving high efficiency emphasizes the minimization of loss with respect to each part of equipment by optimizing design and the use of high-quality materials. In other words, to reduce copper loss, the copper amount in the winding and iron amount in the iron core are increased to reduce current density. A laminated core, made by forming a thin film of pure iron and silicon steel having weak electromotive force that are stacked in several thin films, is used to reduce iron loss. The optimization and insulation performance of gaps and slots between the stator and the rotator is improved to reduce stray load loss. Lastly, careful selection of a bearing, improvement of a lubricous structure thereof, and optimization of apparatuses such as a cooling fan reduce mechanical loss.

Optimum design of equipment and use of high-quality materials can substantially achieve an efficiency increase of 5 - 10%. However, the conventional method of achieving high efficiency can improve efficiency only to a certain limit. It also increases a user's initial investment cost because of an increase in the volume of equipment and an increase in the production cost of 40% or more.

Unlike direct current (DC) motors, the phase of the current is delayed more than that of the voltage due to the induction load of a winding in AC motors that start and operate by AC power. A cosine value due to a phase difference between the voltage and current is called power factor, where the only effective power obtained by multiplying the input by the power factor contributes to the output. Thus, power loss increases with a low power factor, i.e., an increase in the phase difference between the voltage and current. There is a well-known method of connecting a phase capacitor to a power source in parallel to reduce power loss caused by a drop in power factor. However, since another load connected to a power line should be taken into account, it is difficult to accurately measure the capacity of the capacitor. Rather, another apparatus may have difficulty operating and thus caution is required.

Also, a method of optimizing operational conditions of a motor to economize power is disclosed in Korean Patent Registration No. 268136.

Here, an inverter controlling method is well-known, where the state of load is sensed and an input voltage is controlled so that necessary minimum power is supplied depending on current load using a semiconductor control rectifier diode. However, to control an inverter, the motor should be reconstructed, and an additional starting board is necessary: As a result, the user's investment cost is increased as previously described.

The present invention, which will be described later, is combined with the above-described prior art so that power conservation can be heightened to a higher degree.

A surge occurring when opening and closing one of several motors may affect another motor if several motors that are connected to the same power line operate at the same time in a factory. Thus, in this case, an additional apparatus is necessary to absorb the surge.

Disclosure of the Invention To solve the above problems, it is an object of the present invention to provide a highly-efficient AC motor that starts and operates by an AC power source like an induction motor, induces electromotive force due to mutual inductance with a stator circuit and an electromagnetic induction with a rotator circuit to absorb internal loss, and uses electromotive force for the output of the motor or uses electromotive force as an additional power source in order to improve efficiency and power factor thereof.

It is another object of the present invention to provide a highly efficient AC motor that is capable of decreasing power loss and increasing stable power flow when operating two or more AC motors. To achieve the above objects, there is provided a highly-efficient alternating current (AC) motor including: a stator into which an operation winding being connected to an AC power source to form a rotating magnetic field is inserted; a rotator having a secondary circuit for inducing current using the rotating magnetic field and generating torque; and an induction winding, which is inserted into the stator, insulated from the operation winding, and interlinked with the operation winding and the secondary circuit to induce electromotive force. Preferably, the highly-efficient AC motor further includes a capacitor, which is connected to an output node of the induction winding to constitute a circuit for charging and discharging current due to induced electromotive force.

According to the present invention, when the AC motor operates, i.e., if the operation winding is excited to form a rotating magnetic field in the stator, the induction winding induces electromotive force through the mutual inductance with the operation winding and simultaneously electromotive force through the electronic inductance with the secondary circuit of the rotator.

For reference, magnetic flux distributed in an air gap between the stator and the rotator is a sine wave corresponding to a frequency of input power source. Thus, the electromotive force induced in the induction winding interlinked with the magnetic flux has the same frequency as the input power source. The magnetic flux interlinked with the induction winding is substantially required for load operation and contains all flux including leakage flux and the like. As a result, like a generator, the AC motor according to the present invention serves to absorb power loss that does not contribute to output thereof during its operation so as to regenerate the power loss.

The generated power can be used for the output of the AC motor so as to effectively cope with changes in load and used as power source for other loads.

Brief Description of the Drawings

FIG. 1 is a cross-sectional view of the internal structure of a cage-type induction motor according to the present invention; FIG. 2 is an arrangement plan of windings of a three-phase tetrapolar cage-type induction motor according to a first embodiment of the present invention;

FIG. 3 is a circuit diagram of the three-phase tetrapolar cage-type induction motor according to the first embodiment of the present invention;

FIG. 4 is a circuit diagram of the connection of an induction winding and a capacitor of a three-phase tetrapolar cage-type induction motor according to a second embodiment of the present invention;

FIG. 5 is an arrangement plan of a winding of a single-phase tetrapolar condenser shunt type induction motor according to a third embodiment of the present invention;

FIG. 6 is a circuit diagram showing how power for operating the three-phase tetrapolar cage-type induction motor according to the first embodiment is transmitted by connecting the three-phase tetrapolar induction motor according to the second embodiment to a power source to operate and use power of an induction winding thereof;

FIG. 7 is a graph comparing power consumption with respect to load for the three-phase tetrapolar cage-type induction motor according to the first embodiment of the present invention and the prior art; FIG. 8 is a graph comparing input current with respect to load for the three-phase tetrapolar cage-type induction motor according to the first embodiment of the present invention and the prior art;

FIG. 9 is a graph comparing power factor with respect to load for the three-phase tetrapolar cage-type induction motor according to the first embodiment of the present invention and the prior art;

FIG. 10 is a graph comparing reactive power with respect to load of the three-phase tetrapolar cage-type induction motor according to the present invention and the prior art; and

FIG. 1 1 is a graph comparing temperature in no-load operation for the single-phase condenser shunt type induction motor according to the third embodiment of the present invention and the prior art.

Best mode for carrying out the Invention

The present invention may be applied to an existing cage-type induction motor, as shown in FIG. 1. It is unnecessary to change the structure of the existing cage-type induction motor. A cage-type induction motor shown in FIG. 1 is generally a fully enclosed structure. A frame 1 and brackets 2 and 3 at both sides encloses the cage-type induction motor. A stator 4 is positioned in the frame 1 , and a rotator 5 is positioned inward of the stator 4. A shaft 6 is put in the center of rotator 5. Bearings 7 and 8 are mounted on both brackets 2 and 3 to support the shaft 6 so that an air gap is formed between the rotator 5 and the stator 4 to allow the rotator 5 to rotate. An end of the shaft 6 protrudes through the bearing 7 on the front bracket 2 outward to be connected to load. The other end of the shaft 6 protrudes to a shorter extent through the bearing 8 on the rear bracket 3. A cooling fan 9 is connected to the shorter protruding end of the shaft 6. A fan cover 10 covers the cooling fan 9.

The stator 4 is composed of a laminated core having slots (not shown) opened to and spaced apart from the inner circumference of the laminated core. The stator 4 has an operation winding 1 1 for forming a rotating magnetic field in the slots and further has an additional induction winding 12 inserted into the slots to be abreast with the operation winding 1 1. The induction winding 12 is insulated from the operation winding 1 1 so as to form a separate electric circuit. It is preferable that the induction winding 12 has the same thickness and turn ratio as the operation winding 1 1.

The rotator 5 is a cage-type rotator having a cage-type winding (not shown) that is formed by casting aluminum into a laminated core. If the operation winding 11 is excited to form a rotating magnetic field, current is induced in a secondary circuit (the cage-type winding) of the cage-type rotator by the rotating magnetic field and torque occurs due to the rotating magnetic field and the current. As a result, the cage-type rotator rotates. Here, the induction winding 12 is interlinked with the rotating magnetic field formed by the operation winding 1 1 to induce electromotive force through the mutual inductance with the rotary magnetic field like a transformer. The induction winding 12 is also interlinked with secondary magnetic flux due to a current induced in the secondary circuit of the cage-type rotator so as to serve as a generator. Moreover, the induction winding 12 is also interlinked with leakage flux, which cannot be interlinked with the secondary circuit of the cage-type rotator.

Electromotive force of the induction winding 12 induced due to the mutual inductance and generative operations substantially decreases amount of input energy of a motor that is converted and output, thus absorbing loss. Electromotive force of the induction winding 12 may be used for increasing output of the motor or as additional power source for other loads. [First Embodiment] In this embodiment, a three-phase cage-type (or winding-type) induction motor is described. As shown in FIG. 2, an operation winding 11 and an induction winding 12 are respectively disposed in three-phase tetrapolar arrangement and are respectively connected in series star connection as shown in FIG. 3. A three-phase capacitor 13 is connected to a node of the induction winding 12.

Connection of windings may be any one of a Y (star) connection which is a three-phase connection and a Δ (delta) connection as shown. FIGS. 2 and 3 show the Y connection. However, the operation winding 11 and the induction winding 12 should have the same thickness and turn ratio and also be connected in the same manner so potential difference does not occur therebetween. The three-phase capacitor 13 has three capacitor elements CR, CS, and CT with the same Y connections. The capacitance of each of the capacitor elements is determined so that optimal phase lead conditions can be achieved in consideration of the reactance of the induction winding 12. Reference characters R, S, and T represent symbols for classifying three phases and subscripts attached to R, S, and T represent the order of windings in each phase.

The operation winding 11 is connected to a three-phase power source directly or via a starting board (not shown). Here, the capacitor is repeatedly charged by electromotive force induced in the induction winding 12 and discharged. In discharging, the induction winding 12 serves as an assistant of the operation winding 12. As a result, the magnetic field between a stator and a rotator can be strengthened and torque can be improved. Also, the number of rotations can be increased with a reduction in slip. [Second Embodiment]

In this embodiment, a motor which also serves as a generator is described. An operation winding 1 1 and an induction winding 12 are connected as described in the first embodiment. However, a capacitor

13 is connected to the induction winding 12 via intermediate taps TR, TS, and TT, which are led from the induction winding 12 as shown in FIG. 4.

The intermediate taps TR, TS, and TT provide optimal operating conditions for maintaining and strengthening the performance and efficiency of the motor. Also, the intermediate taps TR, TS, and TT reduce a voltage drop due to the impedance of the capacitor 13 with respect to an output node of the induction winding 12 and flow much more current to an additional load connected to the output node.

The intermediate taps TR, TS, and TT need to be led from appropriate places in consideration of all operating conditions, such as the operational efficiency of the motor, capacitance of the capacitor 13, and load capacity, preferably, led from the points in which the induction winding has taken place for 1/3 of a distance from the output node. [Third Embodiment] In this embodiment, a condenser starting type single-phase tetrapolar induction motor is described. As shown in FIG. 5, an operation winding 21 and a starting winding 22 are spaced apart from each other at an electrical angle of 90°. An induction winding 23 is disposed in the same position (slot) as the operation winding 21. A power capacitor for low tension 24 is connected to both ends of the induction winding 23.

The operation winding 21 is directly connected to single-phase power lines L1 and L2. The starting winding 22 is connected to the single-phase power lines L1 and L2 via a starting capacitor 25 and a rotary speed switch 26. The rotary speed switch 26 is combined with a shaft of the motor to be rotated and operated and has a b-contact which is normally turned on but is turned off when the rotary speed switch 26 reaches predetermined rotative speed.

Though not shown, the capacitor 24 may selectively be connected to intermediate taps as in the previously-described second embodiment, based on how the electromotive force of the induction winding 23 is used.

[First Comparison Example]

A conventional three-phase tetrapolar cage-type induction motor operates to measure instantaneous power consumption, input current, power factor, and reactive power with respect to changes in load.

Tables 1 through 4 were created based on the measured result and graphs based on each characteristic shown in FIGS. 7 through 10.

The specification of the conventional three-phase tetrapolar cage-type induction motor used for the comparison example is seen below.

Maker : HYOSUNG INDUSTRIAL CO., LTD. Model : TE 160 L Rated Voltage : AC220/380V

Rated Current : 51 .8/31.2A Rated Output : 15kW (20HP) Number of Rotations of Full Load : 1720RPM

An oil pressure-type dynamometer and a three-phase power analyzer (Japanese HIOKI 3165) are equipment used for testing the shaft horsepower.

[First Test Example]

The three-phase tetrapolar cage-type induction motor used in the first comparison example was reconstructed to have the same winding thickness and turn ratio as the previously-described first embodiment.

Capacitors of 120 and 130 μF were connected to an output node of an induction winding. Next, instantaneous power consumption, input current, power factor, and reactive power were measured under the same conditions as the first comparison example. The measured result is shown with the first comparison example in tables 1 through 4 and

FIGS. 7 through 10.

[Table 1 ]

Load Power Consumption (W) | Rate (%) of Increase

[Table 2]

[Table 4]

In the first comparison example and the first test example, it can be seen that efficiency of a full load (load factor of 100%) increased from 85.5% to 93.5%. Instantaneous power consumption of a full load was about 14.05 - 14.25kW, which is a decrease of 5 - 7 % compared to conventional power consumption. In particular, the rate of decrease of power consumption increased as load became smaller, and thus power consumption of a light load greatly decreased. Also, power factor increased to over 15%, and thus reactive power loss greatly decreased. However, when a 120 μF-capacitor was used, power consumption under no-load slightly increased. The number of rotations increased from 1720 to 1764 RPM, and thus slip decreased.

In other words, in a highly efficient AC motor according to the present invention, internal loss is absorbed by an induction winding which is inserted apart from an operation winding. In other words, the improvement of electric and magnetic characteristics improves efficiency and power factor. Also, the electromotive force of the induction winding strengthens the capability of forming an internal magnetic field and thus output is improved. [Second Comparison Example]

A conventional single-phase tetrapolar capacitor start type induction motor was operated under no-load to check the temperature of each part of the induction motor with a thermograph. As a result, the motor was saturated one hour and 10 minutes after starting the motor, and the surface temperature of the motor was distributed in a range of 36 - 52^°C with an ambient temperature of 20°C at saturation.

The specification of the conventional single-phase tetrapolar capacitor start type induction motor that was used for this comparison example is seen below.

Maker : EUL Jl ELECTRICAL MACHINERY CO., LTD. Model : SSH-0154

Rated Voltage : Single-phase AC220, 60Hz Rated Current : 15.04A Rated Output : 1.5kw

[Second Test Example]

The single-phase tetrapolar capacitor start type induction motor used in the second comparison example was reconstructed under the same conditions as in the previously-described third embodiment. A 25μF-capacitor was connected to an induction winding and the temperature of each part of the motor was checked under the same conditions as the first comparison example. The results show that the surface temperature of the motor was distributed in a range of 36 - 46^°C. FIG. 1 1 is a graph showing the comparison of changes in temperature with respect to the central part of the motor having the highest temperature. In other words, the central part of the motor having the highest temperature is at about 6 ^°C lower than the central part of the conventional motor. As a result, in a highly efficient AC motor according to the present invention, an induction winding that is inserted apart from an operation winding improves efficiency and temperature characteristics. Thus, the life of the highly efficient AC motor is prolonged. [Third Test Example] As shown in FIG. 6, a general three-phase motor M2 was operated using the power of a motor M1 according to a third embodiment of the present invention. In other words, the front motor M1 has an operation winding 1 1 , an induction winding 12, and a capacitor 13. The capacitor 13 is connected to intermediate taps TR, TS, and TT of the induction winding 12. The operation winding 1 1 of the front motor M1 is directly connected to three-phase power lines R, S, and T, and the rear motor M2 is connected to output nodes of the induction winding 12 of the front motor M1.

As a result, torque of the front motor M1 is slightly decreased and efficiency and power factor improved.

Also, any one of the three-phase power lines R, S, and T was disconnected during the operation of the motors M1 and M2 to test a nonequilibrium two-phase operation. In this case, the front motor M1 operates as a normal three-phase power source. Also, stable three-phase power was output to the induction winding 12 of the front motor M1. As a result, the rear motor M2 stably operated.

During the operation of the motors M1 and M2, the power of the induction winding 12 of the rear motor M1 , which was the power source of the front motor M2, was switched on and off. Resultingly, the front motor M1 was not disturbed and continued operating stably.

Industrial Applicability

As described in the above embodiments, in a motor according to the present invention, internal loss is minimized to improve efficiency and power factor. In particular, unnecessary power consumption caused by operating an induction motor under a light load can be reduced considerably and the rise in temperature of the motor inhibited. As a result, the life of the motor is prolonged.

The motor of the present invention may be applied to an existing motor without reconstructing the existing motor, which reduces any causes for price increase. Thus, a low-priced, highly-efficient AC motor can be provided.

Moreover, the motor of the present invention can be used with an existing highly-efficient means to increase energy saved. In particular, energy costs are reduced in a factory where a plurality of motors operate.

Thus, the production cost is lowered, and a stable power operation is possible. As a result, productivity can be improved.

Claims

What is claimed is:

1. A highly-efficient alternating current (AC) motor comprising: a stator into which an operation winding being connected to an

AC power source to form a rotating magnetic field is inserted; a rotator having a secondary circuit for inducing current using the rotating magnetic field and generating torque; and an induction winding, which is inserted into the stator, insulated from the operation winding, and interlinked with the operation winding and the secondary circuit to induce electromotive force.

2. The highly-efficient AC motor of claim 1 , wherein the turn ratio of the operation winding and the induction winding is 1 :1.

3. The highly-efficient AC motor of claim 1 or 2, further comprising a capacitor, which is connected to an output node of the induction winding to constitute a circuit for charging and discharging current due to induced electromotive force.

4. The highly-efficient AC motor of claim 3, wherein the induction winding has intermediate taps which are led from the middle of the induction winding so that the capacitor is connected to one of the output node and the intermediate taps.

5. The highly-efficient AC motor of claim 4, wherein the intermediate taps are led from the points in which the induction winding has taken place for 1/3 of a distance from the output node.