Low-voltage Motor Research Articles

Effect of repetitive square voltage frequency on partial discharge features

The inverter-fed motor is a key component of environmental-friendly hybrid cars, high-speed trains, and other industrial applications. After the widespread use of inverter-fed motors, the repetitive impulse surges from inverters were found to cause new insulation problems in inverter-fed motors that were linked to premature insulation failure. The partial discharge (PD) induced by the overvoltage inner stator windings was found to be the root cause of insulation reliability problems. To mitigate this problem, PD detection and life testing at repetitive square voltages should be performed on new types of insulation models and entire motor insulation systems. The obtained partial discharge inception voltage (PDIV) and lifetime of insulation in the tests can be used to evaluate the insulation status of inverter-fed motor insulation systems and thus to improve the insulation designs. At AC voltage conditions, the voltage frequency can significantly affect PD activity. At repetitive square voltage with rapid rise time, the influence of the square voltage frequency on PD activity should be investigated (1) to suggest values for the repetitive square voltage frequency selection for the PDIV and lifetime tests, and (2) to increase the signal-to-noise ratio when extracting PD pulses from strong disturbances generated by the operating switch of impulse generators. Therefore, the main purpose of this paper was to investigate the effects of repetitive square voltage frequency on PD events. Insulation models of both Type I (low-voltage inverter-fed motor) and Type II (high-voltage inverter-fed motor) were used to obtain single-PD and multi-PD statistical features, respectively. Experimental results indicated that higher frequencies caused less PD events with lower PD magnitudes and shorter delay times in one square voltage cycle. This phenomenon was attributed to the different surface charge decay ratios and the initial electron emission probabilities resulting from different square voltage frequencies. Finally, a number of considerations for PD measurements on inverter-fed motors were provided to improve the sensitivity of the PD test system and to obtain high objective insulation lifetime test results, which are used to assess the insulation status of inverter-fed motors.

Industrial motors and drives markets

The global markets for low voltage motors and drives, with a combined value of nearly $30 billion according to the latest data from IMS Research, experienced a year of tempered growth in 2012. Total market revenues grew by about 5% last year, but are projected to grow at more than double that rate this year.

Considerations in Applying Arc-Resistant Low Voltage Motor Control Centers in Refining Environments

Arc-resistant equipment is becoming increasingly common in North America and in the petrochemical industry. Traditionally, low voltage motor control centers (LVMCCs) designed to National Electrical Manufacturers Association (NEMA) standards have not been addressed in arc resistant testing guides. This paper describes how arc resistant principles can be applied to the LVMCC, which is constructed according to Underwriters Laboratory 845 (i.e., the NEMA ICS 18 600V class of equipment). A brief overview and history of applicable arc resistant testing guides, specific considerations for adapting internal arcing fault test procedures to LVMCCs, and considerations for specifying and installing arc-resistant LVMCCs in a refining environment are discussed.

A Novel Type of Solid-State Soft-Starter

Among the modern industry, soft-starter has taken an important role in large-capacity motor systems. But all kinds of using soft-starters have some shortcomings, their application is restricted because of that. This article describes a type of solid-state soft-starter with a novel structure, in which a rectifier bridge structure is used in stead of the traditional antiparallel structure. Its same points and differentia are analyzed comparing with the traditional soft-starters. The new soft-starter overcomes some traditional shortcomings. It can be used for both low voltage and high voltage motor starting. Especially, when applied to a high-voltage motor starting, it has the advantage of simple structure and high reliability. This kind of soft-starters can be used in broad application prospects.

Diagnosis of Short-Circuit Faults in Stator Winding inside Low-Voltage Induction Motor Using Impulse Voltage Test

Short-circuit faults in windings due to the deterioration of insulation is one of the most common faults in motor drive systems. An easy and effective fault diagnosis method is urgently required to ensure a highly reliable operation. This paper proposes a novel method for the diagnosis of short-circuit faults in stator winding inside a low-voltage induction motor without removing the rotor, by performing an impulse voltage test. As the rotor does not need to be removed from the motor in the novel diagnosis method, the method can be applied for practical use. In this study, first, several impulse voltage tests are carried out on the stator windings of motors. Second, the values of two features that represent the characteristics corresponding to the condition of the motor are calculated, and it is found that the shape of the feature distribution does not depend on the rotor position but on the condition of the winding. Third, the distance between the feature distribution for the healthy motor and features obtained from a target motor is calculated. On the basis of this distance, the quality of stator winding inside the induction motor is determined. The effectiveness of the proposed diagnosis method is verified by performing experiments that involve several motors with healthy and faulty windings.

Enriched Efficiency with Cost effective Manufacturing Technique in 3.7 kW Submersible pump sets using DCR Technology

This paper describes the overall efficiency improvement in Submersible pump sets with reduced cost by increasing the efficiency of the submersible motor using die cast rotor (DCR) technology. The important parameters responsible for the submersible motor characteristics like Efficiency, Locked rotor Torque, Slip etc., are compared with the existing Copper Fabricated Rotor (CFR) and proposed DCR in a 5HP 3phase wet type water cooled induction motors in accordance with IS 9283. The overall performance, possible efficiency improvements in Submersible pump sets and cost comparisons between the existing CFR and DCR's are also practically verified and reported in accordance with IS 8034. It is estimated that about 30 % to 40 % of electrical energy produced in India is consumed by motorized pump sets employed in agricultural sector (1). Pumps and pumping systems use 60% of the new motors in the OEM supply chain. Any improvement in efficiency of motor would therefore result in increased efficiency of the system at end use. Low-voltage motors of up to 37.5 kW consume most of the energy size, which offer maximum potential for energy savings. Most of the energy is consumed by low-voltage motors of up to 37.5 kW size which offer maximum potential for energy savings. One of the ways to address the problem of energy shortage is to reduce demand mainly by increasing end use efficiency. As motors are the largest users of the electrical energy, even small efficiency improvements can produce very large savings across the country, Energy conservation measures taken by individual consumers in this direction will increase the comprehenses of the national economy and benefit the environment on a global scale. The total number of irrigation pump sets in India during the year 2001 was 12.5 million. In the year 2002-03 the Annual power consumption was 118,059 GWh by Agri-pump sets, based on this information, the number of pump- sets works out to 15.7412 Million. The demand is seen to be increasing year after year and also the resulting shortage of electrical energy. In the states of Andhra Pradesh and Gujarat, the agricultural sector alone accounts for 37.45 % and 40 % of total power consumption respectively (2,3). Based on the statistics, the total electricity consumption during the year 2002-03 was 562,572 GWh and the consumption by Agri-pump sets was 118,029 GWh, which works out to only 20.98%. By considering the average connected load of the pump as 6.5 kW per pump set and 1800 pumping hours annually, the total power consumption by agri-sector will be 184,172 GWh, and the percentage works out to 32.7%, which reasonably matches with the other studies. Numerous field studies have revealed that 90% of the agri-pump sets used in India are far inefficient and are wasting power worth of Crores of Rupees. Because there is no energy classification for pumps due to large variety of pumping systems.

Impedance and Emission Optimization of Low-Voltage DC Motors for EMC Compliance

This paper presents a method to automatically generate high-frequency (HF) generic electrical models for low-voltage dc motors. A software model generator creates an electrical circuit which reproduces both HF impedance and emission spectrum of any common dc motor within a frequency range from 150 kHz to 1 GHz. The impedance and emission spectrum are calculated from construction and material parameters like armature geometry and winding wire radius only; no measurements are required. This makes it possible to perform sensitivity analyses of motor construction parameters and minimize the motor's electromagnetic interference early in its design phase before samples and measurements are available.

A Method for Indentifying Broken Rotor Bar and Stator Winding Fault in a Low-voltage Squirrel-cage Induction Motor Using Radial Flux Sensor

In this paper, a method for detecting broken rotor bar and stator winding fault in a low voltage squirrel-case induction motor using an air-gap flux variation analysis is proposed to develop a simple and low cost diagnosis technique. To measure the leakage flux in radial direction, a radial flux sensor is designed as a search coil and installed between stator slots. The proposed method is able to identify two kinds of motor faults by calculating load condition of motors and monitoring abnormal signals those are related with motor faults. Experimental results obtained on 7.5kW three-phase squirrel-cage induction motors are discussed to verify the performance of the proposed method. Induction motors are widely used electrical machines, for their simplicity of construction and reliability. However, they are subject to failures those may be due to production processes or operating conditions. These unexpected failures cause severe damages in industrial processes. Motor reliability working group have announced that percentage failure in induction motors is typically: stator related (38%), rotor related (10%), bearing related (40%), and others (12%) (1). Recently, many researchers have studied diagnosis techniques to predict motor failures at their incipient stage and decide proper replacement time of induction motors. Most of them are focused on the failure prediction method using abnormal signals of failure patterns of motors from current and vibration signals (2)- (4). Although vibration and current analysis are the most powerful methods for diagnosing motor faults, their sensors are occasionally difficult to install where the environment of industrial field is in poor condition. In addition to this installation problem, there are many low priced low voltage induction motors in the field. Therefore, the diagnosis technique should be easy to install their sensors and low cost comparing to the price of motors. This paper proposes a method for detecting broken rotor bar and stator winding fault in a low voltage squirrel-cage induction motor using a radial flux sensor to develop a simple and low cost diagnosis technique. The sensor is designed as a search coil and installed between stator slots during motor production to measure the leakage flux in radial direction at the air-gap. The proposed method consists of a calculating load condition, finding abnormal signals and monitoring those signals related with motor faults to indentify two kinds of motor failures. To demonstrate the performance of the method, experimental results obtained on 7.5kW three-phase squirrel-cage induction motors are discussed.

Rapid Design of Low-Voltage Motor Protector Based on Axiomatic Theory

Facing the diversified demands and design complexity, a systematic design method for low-voltage motor protector is proposed based on axiomatic design theory, which integrates with design constraints and expert's knowledge. Zigzagging mapping between functional requirements and design parameters is obtained by the top-to-down decomposition according to the customer's needs, and the hierarchy of independent functions is also built. Systematic chart and mapping process are also analyzed in order to simplify the design process for different designers. Finally, a case of motor protector of LM5 series is illustrated to verify the method’s feasibility and effectiveness.

Arc-Resistant Equipment

Because of the recent focus on arc flash hazards, arc-resistant equipment is becoming increasingly common in industrial facilities throughout North America. This article addresses arc-resistant equipment as it applies to low-voltage motor control centers (LVMCCs) [National Electric Manufacturing Association (NEMA) 600 V LVMCC/International Electrotechnical Commission (IEC) 690 V LV control gear}. A brief overview and history of applicable internal arc fault testing guides (IEEE C37.20.7 and IEC/TR 61641) are included. Test procedures and their considerations as well as arc-resistant assessment criteria are reviewed. An examination of various methods to achieve an arc resistant rating (device-limited rating and duration rating) as well as considerations for implementing arc-resistant equipment are addressed.

Selective Coordination

The Underwriters Laboratories (UL) 845 standard for low-voltage (LV) motor control centers (MCCs) requires a short-circuit withstand rating on the bus for only three cycles. The LV power-circuit breakers are typically rated for up to 30 cycles short delay, which can be greater than the UL 845 short-circuit withstand test requirements. The trip settings on these LV power-circuit breakers may include short time delay that can result in the MCC-enduring fault currents for much more than the three cycles for which it is rated. In this article, it is proposed that MCC bus designed and tested for higher number of cycles of withstand can address the above potential issue by offering better coordination and safer power distribution design options.

Exploring Three-Phase Systems and Synchronous Motors: A Low-Voltage and Low-Cost Experiment at the Sophomore Level

In order to meet changing curricular and societal needs, a three-phase system and synchronous motor laboratory experience for sophomore-level students in a wide variety of engineering majors was designed, implemented, and assessed. The experiment is unusual in its early placement in the curriculum, and in that it focuses primarily on basic understanding of balanced three-phase systems and synchronous motor operating principles. While a low-voltage three-phase system and subfractional-horsepower electric motors were used, experimental results proved to be reliable, accurate, and repeatable. Changes in student knowledge and confidence in the application of that knowledge was assessed and shown to have increased significantly in each case.

Insulation Deterioration Detection by Zero-Sequence Current Analysis for Induction Motors

Insulation tests for the stator coil, which decides the motor life, are carried out once several years in power and industrial plant. In the case of high voltage (HV) motors, insulation failure may adversely affect plant operation. Hence, maintenance activities, including insulation tests, research on insulation deterioration, and online Partial Discharge (PD) monitoring, are actively pursued for HV motors.On the other hand, the maintenance of low voltage (LV) motors is restricted to breakdown maintenance (BDM) because (1) a large number of LV motors are in operation in plants and (2) maintenance activities are relatively more expensive than those for HV motors. In this paper, the results of a study on insulation deterioration detection for LV motors are presented. For the deterioration detection, the deference in Zero-Sequence current waveforms between normal conditions and fault conditions is analyzed. This method helps in decreasing the maintenance cost and in online insulation diagnosis for LV motors.

Silica nanofilled varnish designed for electrical insulation of low voltage inverter-fed motors

The resistance to partial discharges of pure, microfilled and nanofilled Polyetherimide varnish for low voltage motors fed by inverters is presented. Micro and nano-sized Silica particles (1.5 % wt) are used as fillers. Experimental results of lifetime versus temperature (-55 to 180°C), frequency (5 to 15 kHz) and level of the applied square voltage (+/- 1 kV to +/- 3 kV) clearly demonstrate that nanofillers are more efficient than microfillers. The lifetime of nanofilled polyetherimide varnish is found to be up to thirty times higher than the standard one. Crucial properties for a varnish such as its electrical conductivity, its dc and ac dielectric strengths and its bonding strength are measured. Due to the presence of aggregates having a micrometric size, the microfilled varnish exhibits the worst characteristics, except for the ac dielectric strength which remains unchanged. These aggregates act as bridges for charge carriers, increasing the conduction current and reducing the resulting dc dielectric breakdown field. They also reduce the mechanical properties of the varnish.

Power-Factor Compensation for PWM CSR–CSI-Fed High-Power Drive System Using Flux Adjustment

This paper presents a novel power-factor (PF) control strategy for a high-power pulsewidth-modulated current-source rectifier-current-source inverter-fed motor drive system. The PF regulation is realized by adjusting the motor flux in the drive's field-oriented control scheme. The relationship between the motor flux and the drive's input reactive power is first investigated. Based on this analysis, a flux-adjustment PF regulation scheme is proposed. The proposed PF regulation method, together with a properly designed input line capacitor, can ensure a unity PF throughout the whole speed range (including flux-weakening range). Furthermore, unlike all the other PF compensation techniques, the proposed flux-adjustment approach does not require online modulation index control of the rectifier and the inverter, and therefore, offline selective harmonic elimination modulation can be implemented on both the rectifier and the inverter to minimize the line-side and motor-side waveform distortions. Medium-voltage simulation results and experimental results from a low-voltage 30-hp induction motor drive are provided to verify the effectiveness of the PF correction strategy.

Performance of a High-Speed Motor Drive System Using a Novel Multilevel Inverter Topology

The performance of a novel multilevel six-switch (SS) three-phase inverter drive is examined for low-voltage high-speed motor applications. The switching losses of hard-switched voltage-source-inverter topologies place limits on the maximum feasible switching frequency. When operating at higher fundamental frequencies, this results in low-frequency modulation ratios and either high load harmonic currents that cause excessive rotor heating or larger than desired output reactors with a large fundamental voltage drop. The multilevel inverter structure examined offers an increased number of output pulsewidth-modulated (PWM) voltage levels, higher frequency PWM output waveforms, reduced dead-time effects, and a significant reduction in harmonic content. These features reduce the total losses in the motor load when compared to the standard SS three-phase inverter. The harmonic reduction provided by the multilevel topology relative to the standard inverter is experimentally demonstrated with a 15-hp 18 000-r/min induction machine.

Classification of severity of low-voltage motor coil arcing fault using statistical techniques

Developments spanning a major portion of the previous decade have witnessed the emergence of high/medium/low-voltage arcing fault as one of the more prominent issues confronting the power industry and associated researchers alike. Research over the past decade has been dedicated to the modelling, detection and/or monitoring of arcing faults at various voltage levels and power system apparatuses. The performance of statistical methodologies utilised to classify the severity of low-voltage arcing in a motor coil is presented and compared. The approaches revolve around the utilisation of statistical techniques such as spectral angle mapper, spectral information divergence and linear discriminant analysis to classify the severity of the motor coil arcing fault. Dedicated test-benches are utilised to simulate the arcing phenomenon of varying severity in a motor coil within laboratory environment. Hall-effect sensors in conjunction with the data acquisition module of LabVIEW provide an able means for data collection which is then subjected to offline analysis. The conceptual approach preceding the classification process revolves around the extraction of pre-decided features associated with the current signal gathered during the arcing process. These features are associated with the higher-order harmonic content of the current signal. Comparative analysis of the higher-order harmonic content in the arcing current as obtained from the test-bench and that from contemporary mathematical models for low-voltage arcing faults is presented to validate the choice of parameters for the spectral signature. The extracted features are utilised for classifying the severity of the motor coil arcing fault using the approaches mentioned above. The performance of the classification approaches has been evaluated based on the accuracy of classification, robustness and feasibility of implementation of the approach. The classification results seem very promising in terms of accuracy and feasibility of approach for real-time implementation.

Technique for evaluating the energy efficiency of modern low-voltage asynchronous motors

Requirements for and comparative characteristics of the techniques intended for determining losses and efficiency are considered. A comparative analysis of tests on asynchronous motors of the 5A lineup and a new energy-efficient lineup is described. Recommendations on choosing a technique to determine additional losses are given.

A novel method to diagnose PWM-fed induction motors

A novel method for measurement and interpretation of PD phenomena in inverter-fed motors is discussed in this paper. The interpretation of PD measurements is carried out resorting to the direct-quadrature (dq) transform of the three voltages at motor terminals at the instant a PD event occurs. New tools (the dq loci, dq Hq and dq Hn patterns) are proposed to infer PD activity in a statistical way, similar to that used under AC supply. The method has been validated through tests on motorettes. In addition, measurements on low-voltage inverter-fed motors subjected to repetitive surges till breakdown are reported to support the capability of the method to infer onsetting faults. Measurements are performed through a reliable and lightweight (thus suitable for, e.g., automotive or avionics applications) antenna coupler characterized by excellent signal-to-nose ratio.

유도전동기에 대한 역률 보상설비의 특성 해석

유도전동기의 자계는 전류의 방향에 따라 자화 및 감자되는 특성을 가지고 있다. 전동기의 자계를 형성하는데 필요한 자화전류는 유도성으로 무효전력의 대부분을 차지하고 있다. 무효전력은 유도전동기가 동작하는데 필요한 자계를 지속시키는 역할을 한다.BR 유도전동기의 역률은 낮은 편이므로 역률 보상이 필요하다. 유도전동기를 정격출력보다 낮은 부하로 운전할 경우 유효전력에 비해 무효성분의 비율증가로 역률이 낮아진다. 역률 보상장치의 용량은 전동기 정격에 맞도록 설치하기를 권고하고 있다. 그러나 부하의 운전상황에 따라 역률 보상용 커패시터 값은 수정하기가 어렵다.BR 본 논문에서는 저압 소용량 유도 전동기에 연결된 부하의 변화에 따라 전력 및 역률의 동작특성을 해석한 결과 기존에 제시된 낮은 역률 보상용 파라미터는 수정되어야 함을 확인하였다.