Motor Insulation Systems Research Articles

Insulation life prediction of stacking multi-model fusion motors based on Conv1d-LSTM

Abstract The insulation system of the mine motor is key to ensuring its stable operation, which affects the efficiency of mine production and transportation and the benefit of enterprises. The prediction of motor insulation life can effectively prevent the deterioration of motor performance. Due to the complex underground environment, many factors affect the insulation of coal mine motors, which are not conducive to the selection of feature parameters. The insulation life prediction efficiency and accuracy of motors need to be improved. To solve this problem, this paper proposes a prediction method based on Conv1d (one-dimensional convolve) and LSTM (long short-term memory neural network), which integrates multiple models and the Stacking integrated algorithms. The operating data and environmental parameters of a coal mine motor under different conditions are analyzed. Three Conv1d-LSTM hybrid models with batch normalization, residual network, and dense number are used as the base learner, and the results are weighted by K-fold to verify the accuracy of the three models. The linear regression model is used as a meta-learner to prevent overfitting of the model and effectively improve the speed and accuracy of single network optimization. Compared with the traditional method, the results show that the optimization of the LSTM neural network by the multi-feature model has a higher accuracy in predicting the remaining life of motor insulation, which provides a new way for the prediction of motor insulation life.

Considerations regarding the impulse ignition test for level of protection “eb” and ignition test for protection levels “eb” and “ec” stator insulation systems of Ex-proof electric motors

According to the provisions of the 5th edition of the standard IEC 60079 – 7, equipment protection by increased safety “e”, for Level of protection “eb” and “ec” electrical machines, if the rated voltage exceeds 1 kV, type tests in explosive mixtures have to be carried out, in order to certify such an electrical machine. The purpose of this paper is to provide some considerations regarding the impulse ignition test for level of protection “eb” and ignition test for levels of protection “eb” and “ec” stator insulation systems of explosion proof electric motors and also to present a case study regarding such tests conducted in the specialized laboratory of INSEMEX Petrosani, on a stator insulation winding system of a 6 kV electric motor type of protection Ex eb IIC Gb, case study which will assist manufacturers in designing appropriate stator winding insulation systems for increased safety type of protection electric motors.

Effects of Partial Discharge Echo in Motor-insulation Systems of Transportation Power Devices

Effects of Partial Discharge Echo in Motor-insulation Systems of Transportation Power Devices

РЕЗУЛЬТАТЫ СРАВНИТЕЛЬНЫХ РЕСУРСНЫХ ИСПЫТАНИЙ СИСТЕМ ИЗОЛЯЦИИ КЛАССА НАГРЕВОСТОЙКОСТИ Н (180°С) ТЯГОВЫХ ДВИГАТЕЛЕЙ ЭЛЕКТРОВОЗОВ С ИСПОЛЬЗОВАНИЕМ ПОЛИЭФИРКЕТОНОВОЙ И ПОЛИИМИДНОЙ ПЛЕНОК

The operation of electric locomotive traction motors in conditions of constantly increasing temperature and humidity naturally leads to a decrease in the resistance of the body insulation of the coils of the main and auxiliary poles, which then leads to insulation breakdown and engine failure. In the general statistics on TED breakdowns, the percentage of failure due to low insulation resistance is up to 30%.
 Manufacturers of electrical insulation are constantly working to increase its reliability, using modern systems of polymer materials for this purpose. This article provides a brief description of the insulation systems of traction electric motors of heat resistance class H (180 °C) based on polyethyrketone and polyimide films. The main normative documents on the basis of which the assessment of insulation characteristics was carried out are indicated. Insulating tapes based on fiberglass and mica, mass-produced by ZEIM Elinar LLC, were used as objects of research. The methods are given, the equipment and the main results of resource tests of various insulation systems are indicated. According to the test results, it is shown that the system based on a polyester ketone film is in no way inferior in terms of heat resistance to a system based on a polyimide film.

Design of an Effective Antenna for Partial Discharge Detection in Insulation Systems of Inverter-fed Motors

Partial discharge (PD) measurements under repetitive impulse voltages are critical for the qualification of inverter-fed motor insulation systems. Severe electromagnetic interference due to high frequency switching from power electronic devices can cause the traditional PD detection techniques of sinusoidal voltage unfeasible. This article presents the design of an Archimedes spiral antenna that can work effectively for PD detection under fast rise time repetitive impulse voltages. The antenna structure is optimized by a media superstrate with a high dielectric constant over the radiant surface. Through the optimized design, both the gains of the antenna in the 0.5–1.5 GHz frequency range and the signal-to-noise ratio for PD detection are increased substantially. Modeling and experimental results prove that the gain of the antenna can reach 2.5 dB in the frequency range of 500–900 MHz and become higher than 7.0 dB in the frequency range of 900–2.0 GHz, with a voltage standing–wave ratio smaller than 1.4. This seems to be a significant achievement for PD detection under fast rise time impulse voltages.

Use of the high voltage source in order to verify the insulation systems of electric motors with the type of protection increased safety used in potentially explosive atmosphere

Evaluation of explosion-proof protected electrical equipment in scope of certification is extremely important considering the risk of explosion that has to be minimized in order to ensure life safety and health of workers and to prevent damaging of property and the environment, as well as free movement of goods when they meet the essential safety requirements at European level. The standards SR EN 60079-0 (Explosive atmospheres. Part 0: Equipment. General requirements) and one or more of the standards containing the specific requirements for the type(s) of protection applied to equipment (ex. SR EN 60079-7 for the type of protection increased safety “e”), are used to perform the assessment. Due to the fact that electric motors with type of protection Increased Safety, whose supply voltage exceeds 1000 V, presents a high risk of sparks occurring in windings, it is necessary to perform tests to verify that the insulation of the windings is adequate and does not lead to electric discharge (through electric springs or sparks) at winding levels.A very important test by which these aspects are verified is the overvoltage-ignition test, applicable to electric motors with increased safety protection type.

Steady-State Conduction Current Performance for Multilayer Polyimide/SiO2 Films.

The steady-state electrical conduction current for single and multilayer polyimide (PI) nanocomposite films was observed at the low and high electric field for different temperatures. Experimental data were fitted to conduction models to investigate the dominant conduction mechanism in these films. In most films, space charge limited current (SCLC) and Poole–Frenkel current displayed dominant conduction. At a high electric field, the ohmic conduction was replaced by current–voltage dependency. Higher conduction current was observed for nanocomposite films at a lower temperature, but it declined at a higher temperature. PI nanocomposite multilayer films showed a huge reduction in the conduction current at higher electric fields and temperatures. The conclusions derived in this study would provide the empirical basis and early breakdown phenomenon explanation when performing dielectric strength and partial discharge measurements of PI-based nanocomposite insulation systems of electric motors.

Fazi logički ekspertski sistem za procenu stanja izolacionog sistema statora VN motora

During operation, the electrical insulation system (EIS) of high-voltage motors is exposed to various factors that can accelerate its aging. Timely knowledge of the actual state of the EIS is of great help in allocating funds for service activities. The condition of the EIS of the HV motor can be assessed to some extent by performing available electrical tests. A major shortcoming is the lack of accuracy and the lack of well-defined criteria in the current standards. In that way, a potential error can bias the evaluation of recorded results. The paper proposes the use of a fuzzy logic expert system for assessing the condition of EIS stators of HV motors based on the results of electrical measurements. Also, the proposed fuzzy approach is fully discussed. The created expert system fully relies on the criteria defined in the IS32-Internal Standard of PE EPS.

Design of Experiments Predictive Models as a Tool for Lifespan Prediction and Comparison for Enameled Wires Used in Low-Voltage Inverter-Fed Motors

Since the development of power electronic components, which allowed the manufacturing of reliable and efficient inverters, variable speed drives using inductive motors have become more and more popular. The pulsewidth modulation (PWM) technique has proven to be a very effective method of rotational speed control. However, the fast-changing voltage pulses, with very steep slopes (in the order of a few kilovolt/microsecond), have brought new hazards for the electrical insulation system of such motors. Very high frequency harmonic components of PWM voltage will result in significant overvoltage due to an impedance mismatch between the cable and the motor. As an effect, the voltage seen by some parts of the insulation system may exceed the partial discharge inception voltage stating the localized partial discharges activity. The aim of this article is to investigate and analyze the aging process of the enameled wire exposed to different factors and to propose a method allowing them to predict their lifespans in given conditions. This study introduces a prediction based on the design of experiments method and the statistical Weibull distribution. Thanks to the model obtained with short multistress aging tests, it is possible to predict the results of significantly longer ones. Moreover, the adopted methodology is proposed that allows us to predict the scatter of the long tests based on the short-time results dispersion. The same approach is used to compare different products between each other and rank them. All model predictions are compared with the experimental data in order to prove the model accuracy.

Destruction of electrical insulating structures of electric motors during various drying techniques

The paper discusses the problem of drying electric motors in a humid environment. The study considers the influence of oven, current, electroosmotic, convective-electroosmotic drying methods on defect formation in electrical insulating materials of electric motors. Thermal oven drying destroys the insulation system of electric motors for an order of magnitude higher than other methods and has a lot of negative consequences. The electroosmotic and convective-electroosmotic drying processes do not have disadvantages of thermal drying methods, or these disadvantages are kept to a minimum. It is shown that electroosmotic and convective-electroosmotic drying result in a uniform distribution of moisture content in the volume of electrical insulating materials. This reduces the likelihood of dangerous stresses and subsequent cracking. Electroosmotic and convective-electroosmotic drying have little effect on defect formation processes in the insulation system of electric motors and, thus, almost do not reduce the service life of electric motors.

A Review on Different Aspects of Traction Motor Design for Railway Applications

This article presents a review in three parts on the current traction motor topologies available in the railway market. In the first part, essential aspects of the electromagnetic design of railway traction motors, e.g., motor sizing and rotor configurations, are discussed. Different topologies are compared considering the wide range of applications. The pros and cons of each topology in specific applications are highlighted based on the corresponding performance requirements. In the second part, different cooling configurations of traction motors common in railway are reviewed, focusing on the solutions based on air cooling. The third part presents a review of the available insulation systems for traction motors. Two primary insulation systems used in traction applications with thermal classes of H and N are discussed. The focus in this article is placed on the main applications in railway including light rail vehicles, metros, electric multiple units, high-speed trains, and locomotives. Additionally, trends in traction motors development in the coming years are reported separately for electromagnetic, cooling, and insulation designs.

The E-mobility Laboratory

A premises in Switzerland is proving to be the go-to place for evaluating and testing the insulation systems of drive-fed motors against the new generation of PWM drives

Partial discharge characteristics within motor insulatioi exposed to multi-level PWM waveforms

The frequent use of variable speed drives fed by pulse width modulated (PWM) inverters allow for a more efficient utilization of electric energy. The drawback is however that the stress imposed on motor winding insulation increases and partial discharges (PDs) may appear under such conditions, being considered the major contributor to the reduction of the insulation life time. This paper presents what influence the choice of PWM level and rise time has on the PD characteristics for two different motor insulations as well as introducing suitable high voltage generation test-set ups for these kinds of measurements. The two different test objects were twisted pair and a pig tail motor insulation test objects, the latter aimed for higher voltage levels. These test objects were fed from either two-, three-, four- or five level inverters of similar type, as often used in actual applications. Additionally a six level inverter was used for verification purposes. The twisted pair test objects were insulated by a polyamide-imide enamel, whereas the motor pig tail insulation objects were mica-epoxy based. To compare the performances, measurements of the PD characteristics are reported and observations concentrate on the importance of the voltage rise time, on the size of the voltage step in relation to the extinction voltages (PDEV). Specifically, the total number of PDs and their amplitude per cycle is obtained. The experimental results show that the total summed PD magnitude (exposure) drops considerably when applying the three- or higher level inverters. However the maximum PD magnitude is less dependent, which indicates that a change to a high level inverter alone may still not be sufficient condition for increasing motor insulation system life. In conclusion a combination of the PDEV level, rise time and PWM level must all together be considered in this complex design process.

New Normal Mode dv/dt Filter With a Built-In Resistor Failure Detection Circuit

Insulated gate bipolar transistors (IGBTs) will soon be replaced by wide band gap devices (SiC and GaN) as the choice for power semiconductor switch in voltage source inverters. These devices have extremely fast rise time and fall time compared with IGBT devices. The high dv/dt of pulse-width modulation outputs create excessive voltage stress in the insulation system of ac motors due to voltage reflection issues associated with motors at large distances from the drive. In many oil field applications, the distance between the motor and the variable frequency drive approaches 300 m. In walking rig applications, it is common to use multiple smaller sized conductors per phase, bunched together, to achieve the desired ampacity. This practice results in higher than usual value of the cable parasitic capacitance. Traditional dv/dt filters used for mitigating over-voltage at motor terminals have been found to be inadequate in reducing the over voltage at the motor terminals in such oil field installations. The damping resistor often experiences high voltage and gets damaged. A new dv/dt filter suitable for use with high power ac motors at distances nearing 300 m with a built-in resistor failure detection circuit is proposed here. Test results are given to demonstrate its efficacy.

An Algebraic Algorithm for Motor Voltage Waveform Prediction in Dual-LCI Drives With Interconnected DC-Links

Load-commutated inverters (LCI's) are often used to supply dual-three-phase synchronous motors in high-power variable-speed applications. A pair of LCIs is used in this arrangement to feed the two motor three-phase winding sets. In order to cope with inter-harmonic issues, a drive configuration with an interconnection of the two LCI dc-links has been proposed. In this paper, such a drive design is shown to produce an increased voltage stress on motor windings compared with traditional configurations. The problem is investigated in the paper by proposing an algebraic algorithm capable of predicting the steady-state voltage waveform applied to the motor terminals and arising between the star points of the two winding sets. Unlike conventional dynamic simulations, the proposed approach gives practically instantaneous results, making it possible to quickly investigate a wide number of possible operating conditions. Furthermore, it requires a limited knowledge of system parameters, which are often hardly available. Its reliability and accuracy are assessed by comparison with measurements on a test drive system and examples are given of the method application to the sizing of motor insulation system.

Lifetime model of the inverter-fed motors secondary insulation by using a design of experiments

Numerous parameters (environmental conditions, material and equipments design) affect the ageing (and consequently the lifetime) of the Electrical Insulation System (EIS) of motors supplied by static converters. In order to find a modeling of the lifetime of such materials, accelerated tests have to be considered. The problem is that if we consider all the relevant parameters, these tests become costly and take a lot of time. Consequently the topic of this study is to use a statistical method called: the ‘Design of Experiments’ (DoE) to obtain the lifetime modeling by only a ‘reasonable’ number of experiments. Only electrical and thermal parameters will be modified in this study (vibrations and thermal cycling are not taken into account). In this work, the ageing of the secondary insulation of a motor fed by an inverter is supposed to be originated from partial discharges. In this kind of machine, if a partial discharge activity begin to grow, the first insulation link of the EIS to be affected by these discharges will be the secondary one (i.e.: the impregnation varnish). Consequently, this study is focused only on this secondary insulation. The results obtained by using the DoE method show that it is possible to classify the different ageing parameters and to find their effects on the insulation lifetime. The interactions between all the parameters will also be shown by this method. Finally, a mathematical model of the insulation lifetime taking into account all the parameters and their interactions will be presented and discussed.

Reference-Trajectory-Optimized SVM for High-Power Current-Source Converters to Improve Harmonic Performance and Reduce Common-Mode Voltage

For medium-voltage high-power drives fed by current-source converters (CSCs), a transformerless configuration has benefits in both cost and volume. Removing the isolation transformer necessitates a common-mode choke to undertake the major portion of the drive's common-mode voltage (CMV) stress, which would otherwise cause premature failure of the motor insulation system. On the other hand, as device switching frequency in high-power CSCs is normally limited to a few hundred hertz, improving harmonic performance via modulation has always been a challenge. Selective harmonic elimination (SHE) is a preferred modulation scheme in such a system owing to its ability to eliminate several unwanted low-order harmonic currents. Alternatively, conventional space vector modulation (SVM) provides continuous modulation index adjustment capability, but its output current contains low-order harmonics with high magnitudes that may arouse harmful resonances in the system. Aiming at reducing CMV and improving harmonic performance at the same time, this paper proposes a new SVM-based modulation strategy for high-power CSCs using synthesized reference trajectory on the hexagon in the αβ plane. Along with the proposed strategy, two methods of reference trajectory optimization (RTO) are investigated. By introducing a coefficient to the duty-cycle function for RTO, the first method can remove an extra low-order harmonic component, or minimize the weighted total harmonic distortion. The second method, with a different approach of RTO, eliminates the unwanted low-order harmonics by combining the proposed SVM with the SHE. The proposed concepts are verified by both simulation and experimental results.

Testing and Simulation of Motor Insulation System under Some Artificial Environmental Conditions

This study deals with the effect of humidity and contamination of salt on insulation resistance and polarization index. It investigated experimentally and is also analyzed by using its equivalent circuit. Surface leakage and absorption currents were measured to interpret the quality of insulation winding of a motor. The result shows that in all conditions, the value of absorption current is constant during the testing, meanwhile due to effect of humidity and contamination the leakage current is much larger than normal conditioned motor. Data obtained from insulation resistance test are used to calculate the resistance to ground (RTG) and capacitance to ground (CTG). RTG and CTG are then used as value of components on equivalent circuit for simulation matter. The simulation result using equivalent circuit is reasonable agree with the experiment done.

The influence of repetitive square wave voltage parameters on enameled wire endurance

The dependence of endurance test results on repetitive square wave voltage waveform parameters is investigated in this paper focusing on crossed pair specimens made of polyamide-imide enameled wires. Endurance tests carried out on crossed pairs above partial discharge inception voltage using both sinusoidal and square wave voltages show that lifetimes can be influenced significantly by voltage waveform parameters (rise time and frequency). Partial discharge statistics, recorded from test beginning to breakdown, are used to explain the remarkable differences associated with voltage waveform parameters. According to this study, the influence of voltage waveform parameters should be carefully considered in order to obtain effective evaluation of inverter-fed motor insulation systems.

Microscopic degradation mechanism of polyimide film caused by surface discharge under bipolar continuous square impulse voltage

Polyimide (PI) film is an important type of insulating material used in inverter-fed motors. Partial discharge (PD) under a sequence of high-frequency square impulses is one of the key factors that lead to premature failures in insulation systems of inverter-fed motors. In order to explore the damage mechanism of PI film caused by discharge, an aging system of surface discharge under bipolar continuous square impulse voltage (BCSIV) is designed based on the ASTM 2275 01 standard and the electrical aging tests of PI film samples are performed above the partial discharge inception voltage (PDIV). The chemical bonds of PI polymer chains are analyzed through Fourier transform infrared spectroscopy (FTIR) and the dielectric properties of unaged and aged PI samples are investigated by LCR testers HIOKI 3532-50. Finally, the micro-morphology and micro-structure changes of PI film samples are observed through scanning electron microscopy (SEM). The results show that the physical and chemical effects of discharge cut off the chemical bonds of PI polymer chains. The fractures of ether bond (C—O—C) and imide ring (C—N—C) on the backbone of a PI polymer chain leads to the decrease of molecular weight, which results in the degradation of PI polymers and the generation of new chemical groups and materials, like carboxylic acid, ketone, aldehydes, etc. The variation of microscopic structure of PI polymers can change the orientation ability of polarizable units when the samples are under an AC electric field, which would cause the dielectric constant ε to increase and dielectric loss tan δ to decrease. The SEM images show that the degradation path of PI film is initiated from the surface and then gradually extends to the interior with continuous aging. The injection charge could result in the PI macromolecular chain degradation and increase the trap density in the PI polymer bulk.