기술분석과 주식수익 : 한국주식시장 실증 분석연구

용유림 한양대학교 대학원 2015 국내석사

V 벨트 풀리 드라이브의 결함에 대한 전기적 진단 방법 및 회전자 구조가 전동기 시험에 미치는 영향 분석

강태준 고려대학교 2017 국내박사

V-belt-pulley couplings are commonly used for speed reduction in induction motor driven industrial applications since they provide flexible transmission of power at low cost. However, they are susceptible to mechanical defects such as wear or crack that can lead to slippage or damage of the belt, which reduces the efficiency and lifetime of the system. There are many limitations to applying existing tests, which include visual inspection, thermal or mechanical monitoring, since they require visual or physical access to the motor and/or costly sensors/systems. Considering the large quantity of belt-pulley systems, the impact of economic loss incurred by low-efficiency operation and unplanned process outage can be significant. In this paper, electrical monitoring of belt-pulley coupling defects based on the analysis and trending of the stator current frequency spectrum under steady-state and startup conditions is presented. The proposed method is verified on 1) 6.6 kV motor driven pulpers, and on a 2) custom-built 380 V motor driven air compressor with speed reduction belt-pulleys under controlled fault conditions. It is shown that the proposed method can provide automated, remote, and safe detection of belt-pulley system defects based on current measurement available in the system for improving the system reliability and efficiency. In addition to the above topic, the effect of the rotor construction on motor tests, low voltage rotor test and surge PD test are analyzed and evaluated experimentally. The single-phase rotor rotation test(SPRT) is frequently used in the field for assessing the integrity of the rotor cage without motor disassembly. However, the inconvenience of the SPRT has triggered the advent of a portable low-voltage version of the test. This test has recently become common as it is convenient to use in an industrial environment. However, concerns on the reliability of the test have been raised due to frequent false test indications. The objective of this work is to provide an analysis and experimental evaluation of low-voltage rotor tests under controlled rotor fault conditions on 380-V and 6.6-kV motors. The results of the low-voltage test reveal that it cannot provide reliable diagnosis due to the low excitation flux level, particularly for motors with the closed rotor slot design. Partial discharge (PD) has been identified as one the main root causes of stator winding failures in low voltage (LV) random wound AC motors fed by PWM inverters. To ensure that PWM inverter-fed motors (type I) are PD-free under impulse excitation, the test procedure for acceptance testing of the stator insulation system was developed (IEC TS 60034-18-41). Although many successful cases of applying the TS have been reported, some concerns have been raised. It is implied in the TS that the rotor has no impact on the off-line surge PD test result, and testing is often performed without the rotor; however, it was observed that the test results can change with rotor insertion for some types of machines. The surge PD test must be performed under actual operation condition(with the motor assembled) to guarantee absence of PD. In this paper, the influence of the rotor on the surge PD test is investigated for AC machines, and it is shown that the PD inception voltage (PDIV) can change significantly depending on the rotor design. A detailed analysis is given along with experimental test results on a number of induction and permanent magnet (PM) synchronous motor samples with different rotor designs.

농형 유도 전동기 알루미늄 주조방식의 회전자 결함 진단에 대한 품질 검증 시험

정명 고려대학교 대학원 2018 국내석사

Recently, trend of squirrel cage induction motor manufacturing is shifting from fabricated copper bar rotors to aluminum die-cast rotors, thereby maintaining its competitiveness in the global market by reducing manufacturing costs. Porosity is inevitably introduced during the aluminum die-casting process, due to shrinking characteristics of aluminum. Such porosity may cause degradation in motor performance. In extreme cases, the porosity may cause fatal damages and it may lead to indirect harm to connected systems. In order to prevent this damage, many on-line and off-line tests have been developed and commercialized to detect porosity. However, most of the tests are focused on finding defects when the motor is operating in the field, and there is not much research on the method of diagnosing during the manufacturing process. Several new off-line tests for prognostics have also been proposed, but it is difficult to find porosity in the case of small or distributed porosity, or for shielded slot rotors. Those proposed methods also require direct contact between the test equipment and the motor, which means that safety issues during the tests are still being questioned. Although there is a method to diagnose porosity defects by using X-ray scanning, considering that porosity occurs randomly for each rotor, the test method for total inspection is in appropriate due to time and cost. In this paper, a new off-line test method that overcomes many of the weakness of the existing methods by sensitive detection of porosity in the rotor is proposed. The results of this method is compared with other existing methods to show that this method is more sensitive to minor or distributed porosity. The new method is validated and verified through finite element analysis simulation program and experiments on semi-open and closed slot aluminum die-cast rotors of 5.5 KW induction motors with and without porosity.

이동형 전력수신코일안테나의 전달효율 향상을 위한 3코일 자기공진방식 무선전력전송시스템 연구

권해진 고려대학교 대학원 2018 국내석사

Recently, Wireless Power Transfer (WPT) technology has become commercially available for charging devices without wire. WPT technology can be classified into three major methods depending on the type of transfer or frequency. The first method is Inductive Coupling that has high efficiency for short distance charging applications such as mobile phone and smart watch wireless charging. The second is magnetic resonance, which has farther transfer distance and wide angular freedom compared to inductive coupling. There recently has been active research on magnetic resonance based wireless transfer for high transfer efficiency and on harmful effect on the human body. The last method is microwave radiation. This has the longest transfer distance, but its harmful to the human body. Magnetic resonance WPT method can transfer power efficiently in medium distance applications. One of the most important objectives in regards to magnetic resonance method WPT technology is to gain longer transfer distance compared to the traditional 2-coil transfer system. In multi-coil WPT system, multiplexing of transmitter can affect other transmitters. Because of the low transfer efficiency, control of resonance coil or impedance matching is required for maintaining transfer efficiency. In this paper, a method for switching of resonance coil antennas is proposed for maintaining efficiency and transfer distance, where a toggle switch is used for switching method. Experimental results show that proposed system maintains efficiency under multiplexing of transmitter.

회전자의 비이상성을 고려한 유한요소 해석 기반 유도전동기 특성 예측기법의 신뢰성 향상

윤장호 고려대학교 2019 국내박사

Efficiency regulation policies are being strengthened to improve energy efficiency for industrial motors, which account for about 46% of global power consumption. Improvement of the starting characteristics is also required to stabilize motors and power systems. The rotors of squirrel-cage induction motor occupying most of the industrial motors, can be classified into fabricated cooper bar rotors and die cast rotors. Since fabricated cooper bar rotors are mainly applied to medium- and high-voltage motors, it is very important to comply with limited delivery deadlines while satisfying the customer’s requirements for the starting performance. Low-voltage motors with die cast rotors are necessary to secure price competitiveness through design optimization while meeting the starting and efficiency characteristics in international standards. It is essential to accurately estimate the rotor design parameters that have a significant impact on the performance to meet the specified characteristics. However, the equivalent circuit or finite elements analysis (FEA) methods commonly used to predict characteristics are inaccurate or require a long computation time. Fabricated cooper bar rotors have a complicated rotor structure and the fill factor (FF) of die cast rotors is not perfect, but there has been little research on the influence of the rotor structure and FF on motor performance. In this paper, a simplified method based on the 2- and 3-dimensional (2D/3D) FE models is proposed to predict the starting performance for fabricated copper bar rotors. The effects of the radial cooling ducts, end region, skin effects, and magnetic saturation on the rotor parameters are considered using the single slot pitch 3D FEA to accurately predict the starting performance. The rotor slot design is modified with the single slot pitch 2D FEA to meet the required starting performance. The validity of the proposed method is tested on two 6.6 kV, 522 kW induction motors. The results indicate that the proposed method can accurately and quickly predict the starting characteristics based on rotor slot modifications. For aluminum die cast rotors, the effects of die cast rotor FF on the rotor parameters is investigated based on the FF and porosity distributions analysis in the actual rotor. A simplified 3D FEA model with the FF and porosity distribution in bars and end rings is proposed to predict the starting performance. A 2D and 3D FEA method that considers the porosity distribution and level is presented for reliable prediction of motor efficiency. It is tested on a 440 V, 8 poles, 15 kW induction motor with 93% and 67% FF rotors to verify the reliability of the proposed method. The results show that die cast rotor FF has a very large impact on the starting torque and motor efficiency, and that the proposed method can accurately predict the operating characteristics for design optimization.

유도 전동기 고정자 코어와 회전자 고장진단의 신뢰성 향상을 위한 전기적 진단 방법

양찬승 고려대학교 대학원 2019 국내박사

The purpose of this paper is to propose a diagnostic method to improve the reliability of stator core failure and rotor fault diagnosis in 3-phase induction motor. In particular, this paper focuses on 'on-line’ electrical monitoring. The methods currently available for core quality assessment are inconvenient since they require an outage and the machine to be disassembled or operated under no-load conditions. Off-line(standstill) monitoring requires not only interruption of the tested motor but also an interruption of the overall process related to the motor. Particularly in the steady-state test, the test is the industry's favorite test because it has the great advantage that it does not need to interrupt the motor in operation. In this paper, two main topics are covered. The first topic deals with stator core faults. Localized heating caused by damage to the laminations or inter-laminar insulation of the stator core increases the core losses and can lead to machine failure. Therefore, it is important to monitor the quality of the stator core for a reliable and efficient operation of the machine. In this paper, a new method of on-line monitoring the quality of the stator core without motor disassembly is proposed. For a reliable diagnosis of core failure, it is necessary to distinguish from the failure of high-resistance electrical connection, which is an obstacle to the diagnosis. It is aimed to distinguish stator inter-laminar core faults from failures of high-resistance electrical connection. The main concept is to use the magnitude and angle information of the stator currents (negative sequence currents) to diagnose them at motor operation. An experimental study on a 5.5kW induction motor verifies that local inter-laminar core faults can be detected. The proposed technique is expected to provide a simple solution for frequent stator-core quality assessment. The second topic deals with rotor fault diagnosis. Generally, motor current signature analysis(MCSA) is used for detection of rotor fault. However, It is necessary to distinguish the components generated by the rotor axial air duct structure, which can cause steady-state current or vibration spectrum analysis based fault detection techniques to fail. If the number of axial air ducts and that of poles are identical, frequency components that overlap with that of rotor faults can be produced for healthy motors. False positive rotor fault indication due to axial ducts is a common problem in the field that results in unnecessary maintenance cost. However, there is currently no known test method available for distinguishing rotor faults and false indications due to axial ducts other than offline rotor inspection or testing. In this paper, the wavelet-based detection method of broken bars using the start-up transient analysis is investigated in this paper. And the feasibility of using the rotor fault frequency component produced by the space harmonic waves is evaluated as a solution for the first time. Considering that there is no magnetic asymmetry under high slip conditions due to limited flux penetration into the rotor yoke, both detection methods are proposed. Both methods are verified on custom-built lab motors and 6.6-kV motors misdiagnosed with broken bars via MCSA(50/60Hz).

영구자석 전동기의 균일 부분감자 진단

정지균 고려대학교 대학원 2023 국내석사

근래의 영구자석 전동기는 출력밀도와 효율을 높이기 위해 주로 희토류 자석을 사용하고 있다. 하지만 전동기용으로 주로 사용되는 희토류 자석의 하나인 네오디뮴 자석은 고온에서 잔류 자속밀도와 보자력이 낮아지는 특성을 가지고 있다. 이러한 특성을 고려하면 영구자석 전동기는 고온과 역방향 자계가 함께 가해지는 상황을 피해야 한다. 하지만 인버터 구동으로 인해 발생되는 고조파에 의한 영구자석 와류손, 고속운전을 위한 약계자 운전, 과부하 등에 의해 영구자석 전동기는 고온과 역방향 자계가 함께 발생하는 상황에 놓인다. 또한, 영구자석 전동기는 양의 q축전류와 음의 d축전류에 의해 운전되기 때문에 역방향 자계는 주로 영구자석의 회전방향의 뒷부분에 가해지게 된다. 따라서, 영구자석 전동기의 구조와 운전환경을 고려할 때 균일 부분 감자 현상은 고온과 역방향자계에 빈번하게 노출되는 영구자석 전동기에서 가장 쉽게 일어날 수 있는 감자 고장이다. 하지만 학계 및 산업계에서 해당 고장을 진단하는 방법은 보고된 바가 없다. 본 연구에서는 기존에 있는 영구자석 감자 진단방법을 균일 부분 감자된 영구자석 전동기에 실험해보고 균일 부분 감자진단에 가장 적절한 방법을 제안한다. 실험은 1.8KW급 380V 8극 12슬롯 표면 부착형 영구자석 동기전동기를 대상으로 수행되었고 회전자 분해 후 홀센서를 이용한 자속 측정, 역기전력과 같은 비활선 상태 진단방식과 전동기 전류 스펙트럼 분석 기법(MCSA), 진동 분석, 누설 자속, 공극 자속 측정과 같은 활선 상태 진단방식을 시행했다. 실험 결과를 바탕으로 정확성, 용이성을 고려할 때 공극 자속 측정 방식이 균일 부분 감자고장 진단에 가장 적절한 방식으로 판단된다. Recent permanent magnet electric machines mainly adapt rare-earth magnet to increase output density and efficiency. However, the neodymium magnet, one of the rare earth magnets mainly used for electric motors, has a characteristic that the residual flux density and the coercive force of magnet decrease at high temperature. Considering these characteristics, the permanent magnet motors should avoid the situation in which high temperature and reverse magnetic field are applied together. However, permanent magnet eddy current loss due to harmonics generated by inverter driving, field-weakening operation for high-speed operation, overload put permanent magnet motors in high temperature and reverse magnetic field are applied together. Also, since permanent magnet motors are operated with positive q axis current and negative d axis current, the reverse magnetic flux is mainly applied to the trailing edge of permanent magnets. For these reasons, uniform partial demagnetization is the most common case in all demagnetization faults. However, there are no method reported for diagnosing this demagnetization in academia and industry. In this study, the existing permanent magnet demagnetization diagnosis method is tested on a permanent magnet motor with uniform partial demagnetization and the most appropriate method for uniform partial demagnetization diagnosis is proposed. The experiment includes offline diagnosis method such as direct flux measurement, BEMF and online diagnosis method such as MCSA, vibration analysis, measurement of leakage and airgap flux. The experimental study on 1.8KW class 380V 8-pole 12-slot surface-attached permanent magnet synchronous motor shows that airgap flux measurement is the most appropriate method for uniform partial demagnetization diagnosis.

인버터를 이용한 교류 전동기의 영구 자석 감자 및 편심 진단

홍종만 고려대학교 대학원 2013 국내박사

A major root cause of demagnetization is ‘operating point effect’, which is a combined effect of temperature-dependency of the demagnetization curve and demagnetizing armature MMF. In addition, NdFeB magnets, which have become popular as they have enabled high power density PMSMs, have poor thermal characteristics, low corrosion resistance, and poor mechanical strength. Airgap eccentricity can be introduced during motor operation or due to imperfections in the manufacturing stage. It can be caused by stator core ovality, incorrect positioning of stator core, worn bearings, a bent shaft, asymmetric thermal expansion of the rotor, or by high level of static eccentricity. Demagnetization and eccentricity causes unbalanced magnetic pull which results in vibration, acoustic noise, bearing wear, and/or rotor deflection. Furthermore, dynamic eccentricity can increase resulting in stator-rotor rub, which can cause serious damage in the PM, core, or winding insulation. Therefore, condition monitoring of rotor problems such as demagnetization and eccentricity in ac motor is essential for guaranteeing high motor performance, efficiency, and reliability. Although there has been a lot of research activity recently on developing techniques for detecting demagnetization and eccentricity faults, there are many limitations to the offline and online methods currently used for detection of both rotor faults. Offline tests require motor or load disassembly, flux/ovality measurement, rotor rotation, or access to motor, and they cannot be perform frequently. Online tests are dependent to motor parameters, operating conditions, or mechanical problems. In this paper, an inverter-embedded technique for automated detection and classification of rotor faults of PMSM and IM is proposed as an alternative. The main concept is to use the inverter to perform a test when the motor is stopped. The motor is excited with a small ac field superimposed on varying levels of dc field, and the variation in the differential inductance pattern due to the change in the degree of magnetic saturation caused by demagnetization or eccentricity is observed for fault detection. Experimental studies on 7.5kW PMSM under demagnetization / eccentricity conditions, and 5.5kW IM under eccentricity conditions verify that demagnetization and eccentricity can be detected and classified. It is also shown that the proposed method achieved significant improve of sensitivity and reliability. The proposed method can be implemented in an inverter without additional hardware as a built-in diagnostics feature for testing rotor faults frequently whenever the motor is stopped. It is expected to be a suitable solution to reliability-critical applications with frequent stops such as EV or electrical traction/propulsion. The proposed method can also be developed as a portable off-line test equipment for quality assurance in manufacturing stage.

전기기기의 절연 상태 평가 기법 개선에 관한 연구

양진규 高麗大學校 大學院 2011 국내박사

The lifetime of the stator winding insulation is reduced when operated with PWM inverters, since insulation degradation is accelerated due to increased thermal and electrical stresses on the motor. Especially, turn insulation is a vulnerable component and its failure results in a large circulating current within the faulted loop, which causes overheating and can rapidly progress into groundwall insulation failure. Primary topic of this paper is a new approach for monitoring the condition of the stator insulation for failure-prone inverter-fed machines. The main concept of the proposed technique is to apply a DC and/or variable frequency AC test voltage to the stator insulation using the inverter, to perform standard off-line insulation tests whenever the motor is not operating. This allows the stator insulation to be tested more frequently compared to off-line tests performed once every 3-6 yrs. during periodic maintenance. Two methods for testing the insulation with minimal modifications to the inverter circuit are proposed and verified experimentally. The results show that the proposed technique provides a simple low cost solution for detecting stator insulation degradation at an early stage for reliable operation of inverter-fed machine systems, since the insulation condition can be monitored frequently. The surge test is the only method available for testing the integrity of turn insulation; however, it is a pass/fail test that only shows an indication provided that an arc is instigated between turns, and therefore does not have “monitoring” capability. In addition, there are concerns regarding the high voltage surge applied to the turn insulation as it is higher than what is applied during normal motor operation. The surge PD test measures the PD activity under surge excitation, and is used for evaluating PWM inverter-fed motors for existence of PD. In this paper, the surge PD test is evaluated as a predictive maintenance tool for turn insulation quality assessment. The IR, DC hipot, surge, PD, and surge PD tests are performed on random wound stator windings under accelerated thermal degradation for comparison. It will be shown that the PDIV and PD magnitude of the surge PD test provides an early indication of turn insulation degradation before any other insulation test under comparison. The result of this test shows that the surge PD test has a potential of providing early indications of turn insulation problems under lower voltage surge excitation. The proposed techniques not only help prevent forced outages and safety risks due to insulation breakdown, but also help perform maintenance in an efficient manner since individual motor maintenance can be prioritized and scheduled based on its present condition.

인버터 구동 전동기의 체결 불량 자동 진단

주정석 高麗大學校 大學院 2011 국내석사

High-resistance(R) connection in motor electrical circuit result in localized overheating and supply voltage unbalance, which leads to decreased efficiency, reliability and increased fire hazard in the electrical distribution system and motor. Therefore, it is important to monitor and correct High-R connection for reliable, efficient, and safe operation of the industrial facility. The main concept of the proposed method is to estimate winding resistance of motor using the inverter whenever the motor stopped. The parameters are estimated from the unipolar switched dc link voltage and stator current measurements avaiable in the inverter with the switched dc link voltage applied to the motor stator winding. An experimental study on a 3-phase 5.5KW induction motor performed under proposed technique. The proposed technique helps improve the reliability, efficiency, and safety of the motor system and industrial plant, and also allows maintenance to be performed in a more efficient manner without additional hardware requirements