Repetitive Impulse Voltage Research Articles

A Novel Approach to Partial Discharge Detection Under Repetitive Unipolar Impulsive Voltage

Partial discharge (PD) detection is an important method to verify the reliability of the insulation structure of high voltage power electronics devices. Although there are many researches on PD detection inside power modules, they mainly focus on traditional electrical detection methods and 50 Hz working conditions, which do not meet the repetitive unipolar impulsive voltage conditions of power modules, and traditional methods cannot solve the electromagnetic interference (EMI) problem under working conditions. This paper proposes a novel approach to PD detection in power modules. This approach designs an optic fiber sensing (OFS) system based on optic theory, and conducts the detailed mathematical theoretical deduction. In addition, A partial discharge inception voltage (PDIV) signal processing method based on PD acoustic signal is proposed. Finally, the proposed approach is applied to a power module. The PD signal and PDIV is successfully captured without EMI interference and new insulation problems.

Space Charge Characteristics at the XLPE/EPDM Interface Under DC Voltage Superimposed by a Repetitive Impulse Voltage

Space Charge Characteristics at the XLPE/EPDM Interface Under DC Voltage Superimposed by a Repetitive Impulse Voltage

Design of a Rectangular Wave High Voltage Generator for the Evaluation of Inverter-Fed Motor Insulation

The urgent need for the safer operation of inverter-fed motors is leading research to the qualification tests under high frequency rectangular wave voltages. Consequently, the generation of rectangular wave voltages with adjustable parameters has become a major concern for manufacturers and researchers. This paper presents a design of high frequency and high voltage pulse generator able to provide unipolar or bipolar pulses up to 20 kV peak-to-peak with variable rise and fall time that can be tuned down to 40 ns. Such a generator is performant enough for testing a large part of motors following standards and with more stressful conditions for research of new winding technologies. Resorting to high voltage push-pull solid-state switches and dielectrics liquid & air-cooling technique, the tested capacitance load can reach up to 3000 pF. Also, the over-current protection circuit is carefully designed and verified by using real-time logic control hardware. The proposed generator has been successfully used for endurance tests and partial discharge inception voltage (PDIV) detection at repetitive impulsive voltages for capacitive, inductive insulation structures and windings during the qualification evaluation of inverter-fed motors.

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.

A Novel Embedded Sensor for Partial Discharge Detection in Inverter-Fed Machines

This article presents a novel ring-shaped hybrid fractal antenna for detection of partial discharge (PD) in inverter-fed machines. PD is known as a source of degradation and lifetime reduction in the machines winding insulation. PD activity is becoming a major concern in high performance drives, especially due to the increased use of repetitive impulse voltage with short rise-time (high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dt</i> ) from pulsewidth modulation-controlled inverters. The proposed hybrid fractal antenna is designed and experimentally demonstrated to show a high sensitivity in the ultrahigh-frequency bandwidth of interest for PD detection as well as an ability to discriminate PD signals from other sources of high-frequency disturbances. Additionally, the proposed PD sensing solution features a unique ring-shape geometry that facilitates its physical integration into a live machine, making it suitable as a noninvasive solution for online condition monitoring and PD detection of any inverter-fed electrical machine.

Effect of Repetitive Impulse Waveform Characteristics on Partial Discharges in Type II Turn-to-Turn Insulation

In this article, the effect of repetitive square wave impulse voltage, switching frequency, rise time, and overshoot (OS), on partial discharges (PDs) within Type II turn-to-turn insulation is reported. Two types of samples are used in this study: a back-to-back turn insulation sample and a single cavity layered insulation. This work aims to analyze the influence of the square wave impulse voltage parameters on the characteristics of PDs during aging while relating their effect on the life of turn insulation. The experimental setup used in this study separates the effect of the waveform rise time from the OS and highlights the role of the OS rather than the jump voltage in aging. The results, within the range of parameters considered in the study, indicate that the number and magnitude of PDs are lower at a higher switching frequency while shorter rise time triggers fewer discharges of larger magnitudes. It is also found that PDs, both occurrences and magnitudes, are in favor of waveforms of higher OSs even when the waveforms have a similar jump voltage. This highlights the role of the OS, rather than the jump voltage, as a main and additional factor affecting the life of turn insulation which is contrary to what has been described in the International Electrotechnical Commission (IEC) 60034-18-42. Based on the average magnitude of PDs per unit time, the results show, in the reported range of parameters, that the switching frequency and OS of the voltage waveform are among the main parameters affecting turn insulation life, whereas the effect of the rise time is found to be minimal.

Melting and Generation of Micro-Protrusions on Cathode Surface During Spark Conditioning Process in Vacuum

Spark conditioning is an effective method to increase the dielectric strength in vacuum by melting and removing micro-protrusions on the cathode surface. We aim to optimize the conditioning effect in vacuum for the application of vacuum circuit breakers (VCBs) to higher voltage levels. To obtain high breakdown (BD) voltage, the control of BD charge in the conditioning process is required. When a BD occurs, we have suggested that micro-protrusions can be generated on the cathode surface by particles from the anode. For the suitable control of BD charge, the meltability of generated micro-protrusions and their size are important. In this article, we focus on the generation of micro-protrusions on the cathode surface in conditioning process. First, we conduct spark conditioning by repetitive impulse voltages of rod–plane electrodes made of OFHC Cu in a vacuum chamber with different BD charges. Later, we observe the surface of rod cathode with a digital microscope in order to count the number of visible protrusions and measure their radii. By considering the meltability of micro-protrusions, we quantitatively reveal the existence of residual protrusions that cannot be completely melted by BD. Next, we estimate the maximum size of generated micro-protrusions by BD charge. In consideration of the collision of ions into the anode accelerated by the anode sheath voltage, we estimate the meltable amount of anode material by the BD charge. We confirm that the radii of experimentally measured protrusions are close to the estimated ones. Moreover, we consider the difference in dielectric strength due to the difference in the initial surface condition of the electrodes. We clarify that the dielectric strength is improved by applying acid wash and heat treatment to the electrodes before conditioning, which can be optimized by the BD charge and the initial surface condition of the electrode.

Examination on Partial Discharge Characteristics and Frequency Acceleration Equivalence till Breakdown for Nanocomposite Enamel Wire

This paper presents partial discharge characteristics and film thickness wear till dielectric breakdown under bipolar repetitive impulse voltage application to twisted pair enamel wire added with nano-size boehmite to polyimide (PI) resin by comparing with a sample without the addition. The frequency acceleration equivalence of the life time and PD characteristics till breakdown is also examined. As a result, it was found that at frequencies 10 kHz to 30 kHz, a frequency acceleration equivalence held in terms of the total amount of PD charge at an applied voltage Va = 1.5 kV, while it did not at Va = 3.0 kV due to severer heat generated by PD. In addition, it was found that the coating thickness erosion of boehmite PI was less likely to be caused than that of neat PI under the same experimental conditions. Consequently, it is indicated that the total PD charge amount is closely related with the coating erosion speed.

Electrical aging characteristics of Aramid paper under nanosecond impulse and AC voltages for the stator slot of electric vehicle motors

Electric vehicles (EVs) have been helping to alleviate the pressure of the world energy crisis. However, the insulation of EV driving motors usually suffers from the electrical stress caused by partial discharge (PD) during the operation. Aramid paper in the stator can reduce the incidence of electrical degradation. In this context, PD characteristics, topography and chemical group changes of Aramid paper under AC and repetitive nanosecond impulse voltages were compared. The results illustrated that the increase of ambient temperature will promote the activity of PD under AC voltage. The PD magnitude under nanosecond impulse voltage is almost 100-fold that under AC voltage. PD caused by nanosecond impulse voltage leads to more severe destruction of chemical groups and higher roughness. This investigation offers an important reference for exploring the electrical aging of Aramid paper for the slot of the stator in EVs motor.

Trap level distribution dependence of lifetime for polyimide films under repetitive impulse voltage

In this paper, polyimide (PI) films were modified by using non-thermal plasma, which was generated by dielectric barrier discharge (DBD) in atmospheric air. Under repetitive impulse voltage, the lifetime of plasma treated PI films increases obviously, which reaches the maximum value of 16.8% higher than that of untreated PI films, obtained by 20 s’ treatment. For further understanding lifetime improvement mechanism, energy level distribution of both electron-type and hole-type traps was calculated based on isothermal surface potential decay (ISPD) measurement. It is found that energy level of both shallow and deep traps decrease after treatment, reaching the lowest value for the films treated for 20 s. Lower energy for shallow trap is beneficial to charge dissipation, so that local electrical field would be mitigated. Furthermore, lower energy for deep trap results in less amount of trapped surface charges. Thus, surface PD intensity would be suppressed, ending up with longer lifetime. Analysis of chemical bonding structure reveals that active groups rich in oxygen and nitrogen were introduced into the near-surface region of plasma treated sample, which are responsible for corresponding change of trap energy level distribution. However, in order to prolong lifetime effectively, plasma treating time must to be controlled in an appropriate range.

Accumulative effect of partial discharges at impulse voltage wave tail

This study describes a technique for evaluating partial discharges at fast impulse voltages. Fast transient voltages are increasingly present in power equipment and industrial environments due to the ubiquitous application of power electronics switching devices. Special attention should be paid to the dangers caused by the accumulative effect of repetitive impulse voltages on electrical insulation. This study describes a method of analysing partial discharges occurring during impulse voltage stimuli. A repetitive train of pulses is applied to a dielectric specimen and the accumulated PD pattern is obtained. This study focuses on the reverse discharges which occur during the tail part of the impulse voltage waveform acquired in time-resolved mode. Investigations of the partial discharges in the wave tail can potentially lead to greater degradation of the insulation due to the formation of longer, repetitive sequence occurring along the decaying impulse voltage tail. Experiments were performed which investigated the influence of rise time, fall time and peak voltage on discharge pattern reshaping, intensity and time to inception on the tail. In the future, such an approach might be further developed for diagnostic applications and for extended factory tests.

Gas desorption induced discharge in vacuum and its polarity effect

The objective of this paper is to propose mechanisms of gas desorption induced discharge and their polarity effect. Three electrode pair types were combined in the in-situ experimental apparatus with high vacuum; air-exposed cathode and anode, airexposed cathode and conditioned anode, conditioned cathode and air-exposed anode. Electrode pairs were subjected to repetitive impulse voltage breakdowns till conditioning saturation. The results showed two gas desorption induced discharge mechanisms; namely, pulsed current discharge (PCD) and pulsed current induced breakdown (PB). Many gas desorption induced discharge (PCD and PB) occurred in air-exposed cathode and anode pair and air-exposed cathode and conditioned anode pairs. While only a few discharges occurred in the conditioned cathode and air-exposed anode pair. The gas desorption induced discharge in vacuum showed a polarity effect; Only when the cathode electrode of the pair was the original air-exposed electrode, no matter the anode electrode was or not, gas desorption induced discharge (PCD and PB) could occur in the beginning stage of the conditioning. The physical evolution of gas desorption induced discharge is explained.

Temperature and electric field distributions along a form wound coil of an inverter-fed rotating machine with micro-varistor stress grading system

Temperature and electric field along the stress grading system of a form wound coil under repetitive impulse voltage are studied using 2D axisymmetric and 3D models in COMSOL¯ 5.3a. The validity of the 3D model is shown by comparing the results with the measured temperature profile along the stress grading system. The evaluation of both temperature and electric field shows that using a stress grading system based on a micro-varistor characteristic reduces the maximum temperature; however, with an increase in the electric field, which can be reduced to an acceptable level. An optimization on the initial conductivity of the micro-varistor characteristic confirms that desired electric field and temperature rise are achievable by selecting an optimized conductivity characteristic. 2D and 3D simulations show that a proposed stress grading system, which is a combination of an optimized stress grading tape conductivity and minimum conductive armor tape length, has a good temperature and electrical performances under repetitive impulse voltage.

Effect of Crystalline Morphology on Electrical Tree Growth Characteristics of High-Density and Low-Density Polyethylene Blend Insulation

The electrical tree initiation and propagation behaviors are a key issue for the polyethylene-based cable insulation. This paper focuses on the effect of crystalline morphology on electrical tree growth characteristics of high-density and low-density polyethylene (HDPE/LDPE) blend insulation. In this paper, the electrical tree growth characteristics of HDPE/LDPE blends with HDPE mass fractions of 0, 10, 15, 20 wt% are investigated under repetitive impulse voltage at 40, 60, 80 °C. It is found that with the rise of HDPE content from 0 to 15 wt%, the growth rate and accumulated damage of electrical tree decreases, with the morphology of electrical tree tending to bush tree. The increasing of voltage amplitude improves the energy of injected charge while the temperature rise leads to the relaxation of molecular chain, which both result in the promotion of collision ionization, thus increasing the density of electrical tree. Compared with branch tree, bush tree illustrates better inhibition of discharge tracks due to uniform electric field at the end of branches. The crystalline characteristics of HDPE/LDPE blends indicate that the crystallinity increases with the addition of HDPE, and the blend comprising 15 wt% HDPE in an LDPE matrix apparently reduces the average size of spherulites and improves the distribution of spherulites evenly. The upsurge of crystal-amorphous interface leads to the increase of deep trap energy level density and the decrease of carrier mobility. Carrier injection and migration at the interface between crystalline and amorphous regions are restrained, thus inhibiting the growth of electrical tree. It is concluded that the crystalline morphology modified by polymer blending has a significant effect on the electrical tree growth characteristics.

Design of Archimedes Spiral Antenna to Optimize for Partial Discharge Detection of Inverter Fed Motor Insulation

The partial discharge (PD) in inverter-fed motors generated from high frequency and short rise time impulsive voltage are more complex than traditional sinusoidal voltage operated motors due to the noise initiated from fast switching power electronics devices. Available PD sensors and related technology for DC and sinusoidal voltage cannot be used at repetitive impulsive voltage conditions. This work aims to report the design of antenna with optimized geometry and satisfied parameters to detect PD for impulsive voltage. The antenna is verified and the influence of both impulse voltage parameters and test configuration on PD features are discussed. The envelope detection technique after the filter in the frequency domain was proposed to reduce the complexity and cost of PD test hardware under impulsive voltages with fast rise times. The frequency domain energy of PD from motor insulation is mainly distributed in the range of 0.6-1.8 GHz. By increasing the amplitude and frequency of input impulsive voltage, the range of PD energy spectrum is enlarged to (1.5-1.8 GHz) and by decreasing input amplitude the PD signal strength decays abruptly. Moreover, the high-frequency distribution of PD energy attenuates more severely with the distance and the electromagnetic energy of PD decays nonlinearly with the increase of propagation distance. Therefore, under the premise of satisfying the safety test, selecting the test distance below 15 cm can ensure that the test results have a high signal-to-noise ratio and signal integrity. The experience reported in this study could provide suggestions for off-line PD measurements for inverter-fed motor insulation evaluations for manufacturers.

Electrical treeing in silicone gel under repetitive voltage impulses

Silicone gel is widely used to encapsulate power electronic modules. The weakness of the electrical insulation is surface discharges initiated at the gel-substrate-electrode triple junction and the subsequent formation of cavities; so called electrical trees. The propagation characteristics of cavities under high frequency and fast rise time voltages, which are typical waveforms formed in power electronic modules, have not been fully understood. Thus, in this research, the influence of frequency, rise time, and polarity on electrical treeing under repetitive voltage impulses are investigated. The results show that discharge tracks under positive impulses have filamentary shapes, and discharge tracks under negative impulses have spindle-shapes. The cavity length increases with the frequency and is especially long when the rise time is short under high frequency. This indicates the importance of understanding the cavity propagation characteristics under actual voltage waveforms in power electronics modules.

Noise Rejection and Detection of Partial Discharges Under Repetitive Impulse Supply Voltage

Partial discharge (PD) detection is a fundamental tool for the design and diagnosis of insulation systems, particularly organic materials that must operate throughout their life without PD. While the methods for PD measurements under sinusoidal supply voltage are well-established, the same does not hold under repetitive-pulse voltage waveforms, such as those provided by inverters. Electromagnetic noise generated by electronic switch commutation in inverters can overlap with PD pulses, making it difficult to measure, separate from noise, and identify PD. This is particularly more cumbersome when fast rise-time switches are employed. To address these issues, this paper investigates methods to detect PD pulses on enameled wires under repetitive impulsive voltages with different rise times of 60, 500, and 1000 ns, proposing techniques which allow separation of PD from noise even when they overlap in time and frequency domains. This paper employs a time-domain approach using standard deviation curve acquired from a set of measurements to discriminate PD from repetitive commutation disturbance. These techniques can be implemented to achieve unsupervised noise rejection, which would be an important goal for both offline and online PD testing. The proposed approach is validated successfully through tests carried out on a low-voltage motor.

Design of an Archimedes spiral antenna for PD tests under repetitive impulsive voltages with fast rise times

Partial discharge inception voltage measurements under repetitive impulsive voltages play an essential role in evaluating the reliability of inverter-fed low voltage rotating machines. Using impulsive voltages, partial discharge (PD) signals and the disturbance induced by power electronics switches have often similar energy distribution in the frequency domain. Thus, PD test technologies used with sinusoidal voltages are no longer effective. Under repetitive impulsive voltages, ultra-high frequency detection is recommended to couple high-frequency spectral components from the PD and remove the low-frequency disturbance coming from power electronics. However, to obtain high signal to noise (S/N) ratio, the parameters of the antenna used for PD detection should be designed considering the PD and the disturbance energy distributions in the frequency domain. In this paper, we discuss the design and show the properties of an antenna with Archimedes plane spiral structure intended for PD detection under repetitive impulse voltages. The simulation shows that the antenna has low voltage standing wave ratio (<2) and improved directivity in the frequency range from 0.5 to 2 GHz. Moreover, PD tests performed using repetitive square waves with different rise times demonstrate that the designed antenna can receive PD signals efficiently with high S/N.

Review of accumulative failure of winding insulation subjected to repetitive impulse voltages

The premature failure phenomenon that occurs in solid insulation under the application of repetitive impulse voltages is known as the accumulative effect of impulse voltages on a solid dielectric. The accumulative failure of winding insulation is considered to be a core problem resulting from this phenomenon. The main problems include the accumulative failure of motor winding insulation under pulse-width modulation impulses and the accumulative failure of transformer winding insulation under the application of overvoltages, and these problems represent new challenges in the safe and stable operation of power grids. With regards to the above problems, this study reviews the results of recent research on the accumulative failure characteristics and mechanisms of winding insulation when subjected to repetitive impulse voltages. The challenges faced are discussed at the end of this study.

Development of an innovative repetitive impulse voltage generator [News from Japan

It is well recognized that our modern world would not be so developed without the advancement of power electronics. Almost all electrical and electronic machines use various power electronic technologies. Among many power electronic devices or systems, the contribution of a converter–inverter system is most significant. Here, converters are the devices that convert AC voltages to DC voltages, and inverters convert them in the opposite way. Electric power conversion devices that use both converters and inverters are often called “converters,” although they are usually called “inverters” in Japan. We can say that all electronic devices require converters. In addition, converters can significantly increase the efficiency of a driving system using electric motors. A typical example, Tokyo Metro Co. Ltd. and Mitsubishi Electric Corporation, both in Tokyo, announced that they achieved the reduction of electric power consumption of commuter subway trains by 38.6% by introducing SiC-based pulse-wave-modulation converters in 2012 [1].