Winding Insulation Research Articles

Online Detection and Classification of Interturn and Groundwall Insulation Aging Based on Broadband Common-Mode Impedance Spectrum

Online condition monitoring for stator insulation is important for reliable operation of electrical machines. Recent studies show that the method based on common-mode (CM) impedance spectrum is effective in online monitoring of the overall insulation ageing condition. However, it is difficult to detect the inter-turn ageing condition since the groundwall insulation ageing has the similar impact on the monitoring results. In this paper, the relationship between the change in the common-mode impedance spectrum and the stator winding insulation ageing is studied based on the per-turn-unit broadband CM stator winding model. The dataset of impedance spectrum for different insulation ageing conditions is built using this model. Multiple points in the impedance spectrum are used to detect the change in the inter-turn and groundwall insulation parameters separately. The online experiment results prove the validity of the proposed method. The proposed method can detect the insulation ageing condition with the error about 6%. There is no other method which can quantify the ageing degree of inter-turn insulation in the presence of groundwall insulation ageing. Compared with the black-box data-driven methods, the proposed method is based on a model with clear physical meaning, which makes the results more reliable.

Developments in an acoustic resonance test for the detection of manufacturing anomalies in hydroelectric generator stator windings

To meet the ever-increasing demand for electricity, Hydro-Québec (HQ) is seeking to simultaneously increase the power of its generating stations while improving its service quality. Thus, the company has tasked its research institute to investigate innovate methods to meet the aforementioned goals. Of interest in the current study is the development of an acoustic resonance test (ART) to improve the quality control (QC) in the manufacturing of hydroelectric generator stator windings. Since HQ and its suppliers are investigating new fabrication methods for stator windings to meet the required timelines and increased power requirements, QC is required to ensure the service quality of its new hydroelectric generators. Typical manufacturing anomalies found in stator windings are delamination and air pockets between insulation layers. Such anomalies can result in an acceleration in the degradation of the winding insulation, which reduces the service quality of hydroelectric generators. To benchmark the ART method, the results of the suspected locations of the anomalies along the stator windings were compared with an acoustic camera and the locations were dissected and inspected under microscope for validation. Ten different stator windings were tested and two metrics (variations in both force and frequency responses) were found to indicate the location of delamination sites in the stator windings and corroborated with the result of both the acoustic camera and the dissections.

Evaluation method for insulation degradation of power transformer windings based on incomplete internet of things sensing data

AbstractThis paper proposes a novel evaluation method to address the challenge of evaluating insulation degradation in power transformer windings based on incomplete online Internet of Things (IoT) sensing data. The method leverages the Wasserstein Slim Generative Adversarial Imputation Network with Gradient Penalty algorithm to fill the irregularly missing power transformer IoT perception data, including voltage, current, temperature, and partial discharge. Subsequently, electrical, thermal, and mechanical performance degradation damage indicators for transformer winding insulation are constructed using the filled and complete IoT perception data. By applying the tensor fusion algorithm, the characteristics of these degradation damage indicators are fused, leading to the development of a comprehensive degradation evaluation index for the winding insulation. The evaluation of the winding insulation degradation state is achieved through the minimum quantization error method. The proposed method is validated using the real‐world transformer IoT perception data, and the experimental results demonstrate its ability to accurately assess the degree of winding insulation degradation, regardless of the presence of random or continuous irregularities in IoT sensing data.

Double-ring high-frequency common-mode switching oscillation current sensor for inverter-fed machine winding insulation monitoring

Double-ring high-frequency common-mode switching oscillation current sensor for inverter-fed machine winding insulation monitoring

Comparative analysis of the characteristics of outlet short circuit and winding insulation fault of distribution transformer and its preventive measures

AbstractOutlet short circuit on the low‐voltage (LV) side and winding inter‐turn short circuit faults are hazardous to transformer operation. To investigate the formation mechanism of winding insulation faults of distribution transformer, ANSYS Maxwell was used to build a coupled magnetic field‐circuit model with the same structural dimension as the actual distribution transformer. An outlet short circuit and winding inter‐turn insulation faults were set by using the voltage‐controlled switch in the external circuit of the model. Subsequently, the differences in the electromagnetic characteristics and the electrodynamic force distributions of the windings under three operating conditions, namely, nominal load, three‐phase outlet short circuit on the LV side and inter‐turn insulation failure were studied, respectively. The results show that compared with the rated load, in the cases of outlet short circuit and inter‐turn insulation faults, the amplitude of winding current increases by 20 and 50 times, the magnetic field strength grows by 20 and 17 times, and the electrodynamic force rises by 400 and 230 times, respectively. Outlet short circuit fault is more likely to cause the winding instability and deformation, and inter‐turn short circuit fault can easily burn out winding insulation. Therefore, corresponding preventive measures were proposed.

Insulation Condition Assessment in Inverter-Fed Motors Using the High-Frequency Common Mode Current: A Case Study

The use of the common mode current for stator winding insulation condition assessment has been extensively studied. Two main approaches have been followed. The first models the electric behavior of ground-wall insulation as an equivalent RC circuit; these methods have been successfully applied to high-voltage high-power machines. The second uses the high frequency of the common mode current which results from the voltage pulses applied by the inverter. This approach has mainly been studied for the case of low-voltage, inverter-fed machines, and has not yet reached the level of maturity of the first. One fact noticed after a literature review is that in most cases, the faults being detected were induced by connecting external elements between winding and stator magnetic core. This paper presents a case study on the use of the high-frequency common mode current to monitor the stator insulation condition. Insulation degradation occurred progressively with the machine operating normally; no exogenous elements were added. Signal processing able to detect the degradation at early stages will be discussed.

Low voltage winding insulation systems under the influence of high du/dt slew rate inverter voltage

Low voltage winding insulation systems under the influence of high du/dt slew rate inverter voltage

Principle of predicting the reduction of insulation properties of electric motor windings

The simplicity of the design of the asynchronous electric motors (AM) allows them to be widely used in industry. The AM fleet sometimes reaches 80% of the total load of the enterprise. According to statistics, more than 60% of AM failures are observed due to damage to the insulation of the AM stator winding. The reason is premature dynamic and thermal aging of the insulation, which leads to the failure of the conductive and grooved parts of the AM winding. As a result of a decrease in the dielectric properties of the insulation, damage occurs in the stator windings of AM, such as turn, phase-to-phase short circuits, which tend to develop into a short circuit. Short circuits in the stator windings of the AM are emergency and lead to a sudden disconnection of the AM from the power supply network by existing relay protection means, for example, current cut-off or thermal protection. Sudden, non-sanctioned disconnection of the electric motor from the power supply leads to the shutdown of technological equipment, damage to equipment, raw materials and economic losses. The aim of the work is to develop the principles of timely monitoring and prediction of the state of housing and interphrase insulation of stator windings of AM using the energy of capacitors with local compensation of reactive power. To achieve this goal, research was carried out at a laboratory institution with AM, in which branches of turns were made. The transient processes of capacitor discharge are considered and new methods for monitoring and predicting the residual insulation life are proposed. The new method is based on monitoring the condition of the insulation after each disconnection of the AM from the power supply, while using the energy that remains in the capacitors. The use of a change in the velocity characteristic of the constant discharge time of the capacitor made it possible to predict the residual service life of the AM. The personality of the study is that under the conditions of local compensation of reactive power, it is possible to use the energy remaining in the capacitors to diagnose and predict the state of insulation, as well as the change in the velocity characteristic of the capacitor discharge time constant, which is a criterion parameter for predicting the residual service life of the AM. The carried out studies confirmed the development of test diagnostics in conditions of reactive voltage compensation, which is a new direction in systems non-poisonous diagnostics, which requires continued research and applications in industry.

Gaussian Process Regression for an Accurate and Uncertainty-Aware Winding Insulation Degradation Prediction

Gaussian Process Regression for an Accurate and Uncertainty-Aware Winding Insulation Degradation Prediction

Motor Winding Insulation Degradation Under Repetitive Voltage Pulses

Motor Winding Insulation Degradation Under Repetitive Voltage Pulses

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.

Modified SVPWM technique for CMV reduction in asymmetrical dual three phase induction machine drive

Due to its advantages, the asymmetrical dual three-phase induction motor drive is a strong choice in high-power applications. However, the common-mode voltage produced by the voltage source inverters affects the winding insulation and damages the bearings. Common-mode voltage is also responsible for electromagnetic interference and leakage currents. This paper, therefore, analyses the common-mode voltage produced by the inverter supplying a dual three-phase induction motor drive and proposes a novel modified space vector decomposition-based Space Vector Pulse Width Modulation (SVPWM) technique for common mode reduction. The vector space decomposition-based space vector modulation technique offers excellent flexibility as it reduces the common-mode voltage (CMV) by exploiting the additional degree of freedom in a dual three-phase system. The common-mode voltage (CMV) can be reduced to one-sixth of the DC link voltage compared to the highest CMV, i.e. half of the DC-link voltage produced in conventional space vector modulation. The proposed method is also validated experimentally to demonstrate the effectiveness of the proposed scheme in terms of the amplitude of CMV, pulsations, and total harmonic distortion(THD) in current.

Investigation of self-adjusting cooling system for the autonomous underwater vehicle propulsion motor

Permanent magnet (PM) motors are widely employed in the autonomous underwater vehicle (AUV) propulsion because of their high efficiency and torque density. Since the AUV housings are sealed and narrow, motors are vulnerable to the risk of overheating, leading to dissolution of the winding insulation and demagnetization of the permanent magnets. In this study, a self-adjusting cooling scheme was proposed, which uses the hydrodynamic pressure to pump seawater into the cooling channel automatically. Firstly, the mathematical model of the flow field and heat transfer was established using equation derivations. Subsequently, to clarify the characteristics of the self-adjusting cooling system, the effect of the AUV speed on the thermal and fluid characteristics was investigated using computational fluid dynamics. Results show that the flow rate in the channel increases from 2 to 8.1 L/min as the AUV speed increases from 15 to 50 kn, resulting in the improvement of the heat transfer coefficient from 41 to 764 W/(m2∙K). Subsequently, the influences of inlet and outlet on the thermal characteristics were studied and found to be beneficial for improving the cooling performance. To investigate the spiral flow channels, the distribution coefficient kC and shape factor Rf were defined. Compared to the closed-cycle cooling system for the AUV propulsion motor, the proposed cooling system eliminated auxiliary devices such as pumps and heat exchangers, which makes it more compact and efficient for AUVs. However, introducing seawater into the AUV housing poses a risk of liquid leakage.

A Study on Quantities Driving Maintenance, Repair, and Overhaul for Hybrid-Electric Aeroengines

Abstract Hybrid-electric propulsion for commercial aircraft is currently a key industry interest. Consequently, publications on its design and performance estimation are manifold. However, models addressing characteristics of maintenance, repair, and overhaul (MRO) are virtually unavailable—even though direct maintenance costs (DMC) represent a significant part of direct operating costs (DOC) in commercial aviation. Detailed analysis of hybrid-electric aircraft propulsion degradation and maintenance scenarios must integrate both methods of sizing and design as well as operational factors for conventional and electric subsystems, as operator-specific utilization strongly influences MRO. Accordingly, a holistic engine analysis model is currently being developed using the example of an Airbus A320 aircraft, taking into account flight mission, engine performance, degradation, and MRO. This paper presents an implementation of hybridization into the gas turbine thermodynamic cycle calculation for parallel hybrid-electric (PHE) engine architectures with 2 and 5 MW electric motors, and the approach necessary for resizing hybridized gas turbine components. Turbomachinery loading throughout representative short-haul missions is analyzed for conventional and hybrid-electric configurations based on the V2500 high-bypass turbofan engine, whereby unknown or uncertain boundary conditions are considered in a probabilistic sensitivity study. As a result, MRO-driving quantities such as engine performance parameters, atmospheric conditions, and ingested aerosols can be compared. The findings suggest that DMC related to the gas turbine may be considerably lowered through hybridization, as it allows for reduced peak temperatures and more uniform gas turbine operation. However, these gains are at least partially offset by additional components' DMC. For electrical machines, bearings and the stator winding insulation are life-limiting, where the latter becomes increasingly dominant for higher power densities associated with high current densities and copper losses. Thermo-mechanical stresses are considered as driving mechanisms in power electronic systems degradation. Consequently, powerful lightweight machines must be balanced against tolerable thermal and electrical loads to achieve suitable service life.

Evaluation of a wind tunnel designed to investigate the response of evaporation to changes in the incoming long-wave radiation at a water surface

Abstract. To investigate the sensitivity of evaporation to changing long-wave radiation we developed a new experimental facility that locates a shallow water bath at the base of an insulated wind tunnel with evaporation measured using an accurate digital balance. The new facility has the unique ability to impose variations in the incoming long-wave radiation at the water surface whilst holding the air temperature, humidity and wind speed in the wind tunnel at fixed values. The underlying scientific aim is to isolate the effect of a change in the incoming long-wave radiation on both evaporation and surface temperature. In this paper, we describe the configuration and operation of the system and outline the experimental design and approach. We then evaluate the radiative and thermodynamic properties of the new system and show that the shallow water bath naturally adopts a steady-state temperature that closely approximates the thermodynamic wet-bulb temperature. We demonstrate that the long-wave radiation and evaporation are measured with sufficient precision to support the scientific aims.

Dynamic moisture diffusion in transformer winding insulation

Wind power production is intermittent due to varying wind conditions. This leads to frequent temperature changes in the wind farm transformers, which in turn affects the lifetime of the transformer winding insulation. To extend the lifetime through prediction of effects from dynamic loading, new models for degradation of insulation systems are needed. This article is laying the foundations of a model for dynamic moisture migration in the winding insulation of wind farm transformers. Relevant equations and approximations are presented and an experimental setup for laboratory testing of transformer insulation ageing related moisture migration under dynamic loading is described. The demonstration experiment clearly shows moisture migration through paper layers in a simple physical winding insulation model. As the ageing of cellulose is very moisture-dependent, the migration should clearly be included in models of ageing under dynamic load.

Influence of Inverter Voltage Switching on Windings of Asynchronous Motor

Focus on the stator winding insulation of asynchronous motor, the transition process of the pulse voltage output by the frequency converter was analyzed, the voltage equivalent mathematical models and simulation model of the stator winding, reactor and cable were established. For rolling mill in metallurgical industry, the different voltage slope was verified by using real high-power asynchronous motor and frequency converter for pulse voltage test. Aiming at the voltage oscillation caused by different cables length, the second order system fitting was used to analyze the voltage spectrum characteristics, and the reactor’s suppression effect for voltage oscillation was also verified.

Analysis of Inter-Turn Short Circuit Faults in Dual Three-Phase PMSM for Electromechanical Actuator

Dual three-phase permanent magnet synchronous machine (DTPM) is an attractive choice for electromechanical actuator owing to its advantages of double redundancy, high power density and high reliability. However, the winding insulation is susceptible to the high thermal and mechanical stress, which will lead to the inter-turn short circuit faults (ITSCF) and poses threat to the safety of the machine system. Moreover, the ITSCF of DTPM is not only limited to single-phase, but also occurs between adjacent phases. Therefore, in this paper, the characteristics of single-phase and phase-to-phase ITSCFs are investigated and compared while the short-circuit contact resistance is considered. Firstly, a general mathematical model for single-phase and phase-to-phase ITSCFs are established, and the expressions of short circuit current (SCC) and output torque are derived. Then, the characteristics of flux density, back-EMF, SCC, fault phase current and output torque of the different fault models are compared by finite element analysis. It is demonstrated that when the contact resistance is not zero ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R_f</i> ≠0), the amplitude of SCC and the third harmonic content of fault phase current are inversely proportional to the contact resistance and proportional to the number of short-circuit turns. In addition, the amplitude of SCC, torque ripple and braking torque caused by a phase-to-phase ITSCF will be larger than those of the single-phase ITSCF under the same fault conditions, especially when the contact resistance is small. Finally, an experimental prototype is made and tested to validate these analyses.

Three-Stage Duty Cycle-Based Deadbeat Predictive Torque Control for Three-Phase SPMSMs With CMV Reduction

Model Predictive Torque Control (MPTC) is highly regarded for its simple structure, rapid dynamic response, and optimized control performance when applied to actual motor driving systems. However, conventional MPTC techniques often lead to undesirable effects in three-phase inverter-based surface-mounted permanent magnet synchronous motors (SPMSMs), such as high electromagnetic torque, stator flux ripples, and significant current harmonic distortion. Notably, the generalized MPTC approach generates a substantial common mode voltage (CMV) that can cause damage to the motor bearing and winding insulation in SPMSMs. To address these issues, this paper proposes a three-stage duty cycle-based deadbeat predictive torque control (DCDPTC) technique for SPMSMs. The proposed technique leverages the volt-second equilibrium theorem by aligning the duty cycles with the predicted electromagnetic torque, stator flux, and their respective target values while accounting for extreme cases, accordingly electromagnetic torque and stator flux ripples as well as the total harmonic distortion (THD) of the stator current are minimized. In order to improve the system robustness, the duty cycle is limited to avoid the overmodulation. Furthermore, optimized switching sequences are meticulously arranged to ensure the CMV is lowered and the minimum number of switching transitions is maintained while utilizing a fixed switching frequency. The proposed technique is simplified. Its resultant performance is validated by experimental results.

Analysis and mitigation of the impact of electric vehicle charging on service disruption of distribution transformers

The transition to electric mobility could overload distribution transformers to unprecedented levels. Sustained overloads produce excessive heat within the transformer and hasten insulation deterioration. As EV deployment rises and the severity of overloads increases, the focus shifts from long-term effects that reduce transformer life to more immediate impacts that can disrupt normal functioning. The latter typically manifest as the blowing of protection fuse, the triggering of pressure relief device, or the breakdown of winding insulation, each of which could result in transformer outage. The transformer’s vulnerability can be monitored in terms of its apparent power flow, top-oil temperature and hottest-spot temperature. The IEEE C57.91 standard specifies the permissible range for these parameters, beyond which the transformer operation could get interrupted. A study to determine the range of EV penetration that can be accommodated by a distribution transformer without any discontinuity in its operation is presented in this paper. The non-linear nature of EV charging is incorporated in the analysis to account for the effect of higher-order harmonics on the transformer’s internal temperature. The effectiveness of a controlled charging strategy, which seeks to regulate transformer loading by minimizing its variance, in preventing service disruption is also validated in this simulation study.