Partial Discharge Behavior Research Articles

Effects of High Magnetic Field on Partial Discharge and Flashover Behavior of Epoxy Resin

High-field magnets use epoxy resin as the insulation for superconducting coil terminals. Surface flashover on the interface between the gas and solid insulation will cause insulation failure. In this paper, effects of high magnetic field on surface partial discharge and surface flashover of the epoxy resin are investigated. Experimental results show that high magnetic field causes the decrease of relative permittivity and further changes the electric field distribution along the surface of epoxy resin. Surface partial discharge behavior is directed by both the decrease of surface electric field at the interface and the decrease of breakdown voltage of air gap in high magnetic field. Lorentz force begins to play a role during the extension of electron avalanche by changing the migration of charge carriers and weakening the equivalent effect of the normal electric field near the triple junction. Opposite trends are observed with the increase of magnetic flux density when the direction of Lorentz force is parallel or perpendicular to the surface of epoxy resin.

Critical study of partial discharge inception in voids: statistical behavior to stochastic nature

Although many studies have been done and advanced progress has been made in understanding partial discharge (PD) behavior in the void, this is not the case firinception of PD, especially its stochastic nature. The statistical behaviors of PD inception voltage (PDIV) and inception time delay (PDTD) inside the void were investigated in this study through repeated tests to observe the stochastic nature of PD inception. The results show that the PDIV and PDTD of the void are highly dispersed and obey Weibull and exponential distributions, respectively. The significant dispersion of PDIV can be attributed to the statistical time delay of PD inception. The lengthy inception delay is attributable to a lack of free electrons. The exponential distribution of PDTD indicates that free-electron generation is completely random; further, the stochastic nature of void PD inception is determined by the supply of free electrons. The test method (voltage rise rate, test time, and test time interval), void parameters (size, material, and surface condition), and background radiation determine PD inception by affecting the volume ionization or surface-emission process providing free electrons. Enhanced background ionization or significant increase in test voltage and test time allow for the effective detection of void defects during PD tests. This work contributes to an empirical understanding of the physical process of PD inception in voids and improving existing PD testing technologies.

Partial Discharge Investigation under Low Air Pressure and Variable Frequency for More-electric-aircraft

More-electric-aircrafts (MEAs) are heading towards larger power, higher voltage, and more optimum architectures, it is extremely important to understand partial discharge (PD) behaviors under the challenging aeronautical power systems. PD under the pressure of 1–101 kPa and frequency of 50–1000 Hz is studied to emulate the practical situation with the consideration of insulation defects from electric machine windings. The high frequency current transformer (HFCT) is specifically employed to pick up partial discharge signals. Experimental results indicate that PD inception voltage (PDIV) decreases almost linearly with air pressure. As to the discharge amplitude, it increases first and then decreases as air pressure dropping. The highest discharge repetition rate and the number of discharges appear at 30 kPa. High frequency doubles the number of discharges without affecting PD amplitude. Low air pressure causes the phase shift and phase width of the phase-resolved partial discharge (PRPD) to increase, and the trend also is accelerated by high frequency. This experimental approach is beneficial to provide prerequisite knowledge in characterizing PD and assessing its potential adverse impact on the aeronautical power system and consequently contribute to optimizing the insulation design for MEA.

Effect of O2 on AC Partial Discharge and Decomposition Behavior of C4F7N/CO2/O2 Gas Mixture

This paper focus on the influence of oxygen on the partial discharge (PD) and decomposition characteristics of C4F7N/CO2/O2 gas mixture as eco-friendly gas insulating medium. The PD characteristic parameters and phase resolved partial discharge (PRPD) patterns of C4F7N/CO2/O2 gas mixture are, respectively, extracted and constructed. The influences of oxygen content and applied voltage on the PD and decomposition characteristics of C4F7N/CO2/O2 gas mixture are investigated based on gas chromatography-mass spectrometry (GC-MS). We find that the addition of 2-4% O2 to C4F7N/CO2 gas mixture can significantly inhibit the negative half-cycle PDs and the generation of most by-products (CF4, C2F6, C3F6, CO, C2F6O3, CF3CN, C2F5CN, C2N2). With the oxygen content higher than 6%, the accumulation discharge magnitude and discharge repetition rates of C4F7N/CO2/O2 gas mixture increase sharply, accompanying the intensification of decomposition and deterioration of insulation strength. There is a positive correlation between the mean discharge magnitude and gas mixture decomposition intensity. To avoid the serious impact of PD fault on gas insulated equipment (GIE), the optimal oxygen addition in C4F7N/CO2/O2 gas mixture should not exceed 6%.

Effect of Cavity Position, Size and Geometry on Partial Discharge Behaviour inside 18/30 kV XLPE Cables

Effect of Cavity Position, Size and Geometry on Partial Discharge Behaviour inside 18/30 kV XLPE Cables

Effect of Cavity Position, Size and Geometry on Partial Discharge Behaviour inside 18/30 kV XLPE Cables

Effect of Cavity Position, Size and Geometry on Partial Discharge Behaviour inside 18/30 kV XLPE Cables

Temperature‐dependent partial discharge characteristics of high temperature materials at DC voltage for hybrid propulsion systems

The safe and reliable operation of insulation material used in key high voltage components under extreme environmental conditions represents the major concerns for manufacturers and operators of More Electric Aircrafts (MEA). Surface discharge occurring in high current carrying components in DC power system diminishes the insulation material’s performance and life, especially at high-temperature conditions. Here, the surface discharge behaviour of two commonly used high-temperature insulation materials, ethylene-tetrafluoroethylene (ETFE) and polyetheretherketone (PEEK) is studied at different temperatures under ramp and DC voltages. Extracted partial discharge (PD) features are presented and the impact of voltage polarity on surface discharge propagation is discussed. Our studies reveal that, while both materials exhibit non-linear PD behaviour with respect to their electrical conductivity, ETFE generally shows PDs with higher intensity at high temperature above 100°C with a higher possibility of surface discharge due to its lower permittivity. Overall, the PD mechanism in high-temperature, DC voltage applications is explored, and a basis for the selection of high-temperature PD suppressing materials is developed.

Partial Discharge Analysis and Simulation Using the Consecutive Pulses Correlation Method

The behaviour of partial discharge as consequences of an alternating current (AC) is already well defined. AC partial discharges have completely different behaviour, background physics and parameters than partial discharges (PD) under direct current (DC) stress. This paper focuses on the most used and promising evaluation method of the PD DC stress—pulse sequence analysis (PSA). The first step is understanding and verifying the mechanisms and principles of this method. It is provided by well-known fundamentals of AC PD and by comparison with the other diagnostic and fault-locating methods such as phase-resolved partial discharge (PRPD) and pulse diagrams. The paper shows the PSA simulations and PD analyses performed at AC and partly at DC test conditions on typical PD test arrangements such as corona, surface and internal discharges. It is shown that the simulations performed, compared and validated with data obtained from measurements on different PD arrangements are a good match. This fact opens the way for the PD source recognition in DC, especially the time-resolved pulse sequence analysis described in detail in the paper.

Study of Oil/Pressboard Creeping Discharges under Divergent AC Voltage—Part 1: Fundamental Phenomena and Influencing Factors

This paper presents an experimental study of the fundamental phenomena of progressive creeping discharge as well as the influences of pressboard ageing and voltage amplitude under divergent AC voltages. A ramp-stress test is used to determine the partial discharge inception voltage (PDIV) and the flashover voltage of oil/pressboard interface versus pressboard ageing. Constant-stress tests are carried out to investigate the partial discharge (PD) behaviors, the pressboard surface temperature, and the oil-dissolved gases of progressive creeping discharges. It is found that the pressboard ageing affects only the interface PDIV. The progressive creeping discharges concentrate at the triple-junction and comprises probably oil corona discharges and surface discharges in pressboard dimples. If no pressboard damage is present, the progressive discharges exhibit in general a constant PD pattern but a diminishing intensity, and nevertheless can be sustained for the severely-aged pressboards under strong voltages. The underlying causes are correlated with the competing effects of pressboard ageing on interface moisture and the triple-junction field intensification. Gas analyses indicate the hydrogen is the principal faulty gas and the Duval's Triangle diagnoses the progressive creeping discharges as either low-energy or high-energy discharge fault. No pressboard overheating is observed during the discharges.

An investigation on discharge fault in buffer layer of 220 kV XLPE AC cable

Discharge failure mechanism of the cable buffer layer is investigated in this paper by the analysis of causes and characteristics of partial discharge (PD) behaviours in the case of failure. The obtained results show that both the volume resistivity and the surface resistance of the buffer layer increase as the relative humidity is elevated. It is found that the electric field distribution inside the buffer layer is distorted when there is poor contact condition and aggravated with the increase of the volume resistivity by the finite element analysis. PD behaviours analysis shows that the PD intensity is closely related to the contact state of the buffer layer, and hence the latter can be reflected by statistical parameters like the maximum pulse amplitude and the average equivalent frequency. The conclusions indicate that the electric field distortion is caused by the variation of the contact state of the buffer layer and the deterioration, which is responsible for the occurrence of PD. Therefore, the PD detection for the suspected faulty cables provides an effective method for the state evaluation of the buffer layer.

A Voltage Threshold in Operating Condition of PWM Inverters and its Impact on Reliability of Insulation Systems in Electrified Transport Applications

There is a trend in industrial applications and electrified transport toward rising supply voltage and switching modulation frequencies in order to reach better efficiency and higher specific power of rotating machines. However, the aspect of insulation system design and reliability for the whole chain of the adjustable speed drive, including inverter, cable, and rotating machine, is often neglected. The major electric aging mechanism that can bring insulation to failure in short times is partial discharges (PDs), which can incept in insulation defects, being triggered by local electric stress. Understanding PD phenomenology in insulation fed by pulsewidth modulation (PWM) is, therefore, a must to ensure adequate life to the insulation chain. This article shows the existence of a peculiar PD behavior, associated with a threshold voltage below and above in which the PD regime may change significantly in terms of amplitude and repetition rate. Inverter behavior under PD is modeled as a function of the number of inverter levels, and the validity of the model is tested through PD and accelerated life testing. Good fitting to experimental results is obtained using the twisted pairs’ test objects, with striking evidence about the effects on life of operating below or above the threshold on insulation reliability.

High Temperature Insulation Materials for DC Cable Insulation—Part II: Partial Discharge Behavior at Elevated Altitudes

Utilizing hybrid electric propulsion systems in the next generation of aircrafts with elevated DC voltage level has raised the concern about the degradation of insulation subjected to partial discharge at high altitude and harsh environment. In this work, the surface discharge behavior of commonly used high-temperature insulation materials in aviation systems (FEP, ETFE, and PEEK) under positive and negative DC and ramp voltage was studied, including the pulse waveform, frequency spectrum, PD count and magnitude. Pressure changes as a significant factor influencing surface discharge phenomenon was thoroughly studied. Dust figure technique was employed after voltage ramping tests for both positive and negative polarities at low pressure to investigate the surface charge accumulation and surface discharge traces, and unveil the involved physical mechanisms at different stages of streamer propagation. The content of this paper provides a reference for surface discharge studies and evaluation of high temperature materials for medium voltage direct current power distribution in the future aviation systems.

Partial Discharge Features for Power Electronic Transformers Under High-Frequency Pulse Voltage

Power electronic transformers (PETs) are becoming popular in the modern dc distribution grid due to their high efficiency and flexibility. To increase the power density of PETs, high-switching frequency would be adopted for the power switches. However, this may eventually increase the risk of partial discharge (PD) as the internal insulation space is reduced. In order to investigate PD characteristics in PETs under high-frequency pulse voltage, an experimental platform was set up in the laboratory, in which a twisted pair of wires model was used to test the insulation failure between windings in PETs. The PD behaviors were thoroughly investigated in the frequency range of 50 Hz to 20 kHz by time-resolved PD (TRPD). The results reveal that at high frequency, both the initial discharge voltage and discharge repetition would increase, while the PD amplitude decreases. Moreover, the PD pulses mainly occur at the field strength inversion of the rising and falling edges, the discharge time width tends to increase at high frequency. By analyzing the discharge model under pulse voltage, the discharge amplitude decrease and discharge times increase due to the difference of charge accumulation field intensity and effective discharge time at different frequencies. Under high-frequency voltage, the number of PD and the proportion of discharge time is much higher than 50 Hz, which may be the main reason for high-frequency insulation failure prematurely. According to the insulation life model based on the total discharge amplitude, the insulation life of 20 kHz is slightly higher than 10 kHz. When designing HFT, 20 kHz should be elected as operation frequency rather than 10 kHz.

WITHDRAWN: Analysis of partial discharge patterns of natural ester oil and mineral oil used in power transformer

Abstract The liquid insulation used for power transformer over the years is petroleum based mineral oil because of it availability and good electrical, chemical insulation properties. However because of its poor biodegradability, low flash point and concern over environment nowadays mineral oil has been replaced with biodegradable oil. Natural ester oil is made from natural substances like soyabean, which are environment friendly, almost fire proof and have great electrical insulation properties. Partial discharge is considered to be one of the main reasons for degradation of insulations in power transformers. In this paper comparative study of experimental results of partial discharge patterns of mineral and natural ester oil are discussed. The experimental setup was designed as per IEC Standard. Power transformer insulation is modeled as pigtail specimen and tested for partial discharge behavior by applying stress more than inception voltage of mineral and natural ester oil. Phase resolved partial discharge pattern are used to analyze the results. It was found that Natural ester oil has better inception voltage compared to mineral oil and also number of partial discharge pulses and PD magnitudes are less compare to mineral oil.

Modeling of the Partial Discharge Process Between the Winding and the Stator of Low Voltage Machines for Traction Applications

The application of wide-band-gap-semiconductors in the power-electric circuit of future traction drives leads to an increased stress on the insulation system. This can cause partial discharge, which leads to a rapid breakdown of the insulation and must, therefore, be avoided. To enhance the durability of the insulation system and to fill up the air gaps between the enameled wires, impregnation material is applied. This leads to an increased partial discharge inception voltage between neighboring conductors as the discharge process only occurs in the remaining air enclosures. Due to the change of the electric field distribution, which is caused by the impregnation material, also the threshold voltage for partial discharge between the stator and the winding changes. While so-called twisted pairs are commonly applied to study the partial discharge behavior of the inter-turn insulation isolated from other effects, in this article a specimen that considers the phase-to-ground insulation is proposed.

Effects of packing particles on the partial discharge behavior and the electrical characterization of oxygen PBRs

Packed-bed reactors (PBRs) hold great promise for environmental applications, but a deeper understanding of the behavior of plasma discharge within PBRs is required. To this end, a partial-discharge alternative equivalent circuit for PBRs was established in this work. Dielectric particles (glass beads or glass sand) were used to place focus on the effects of the particle size and shape on the partial discharge behavior of the oxygen PBRs. Some electrical characterizations were explored (e.g. the effective dielectric capacitance, partial discharge coefficient, and corrected burning voltage) that may differ from long-standing interpretations. The findings indicate that the suppressive effect of surface discharge on filament discharge is stronger with the decrease of the particle size. For partial discharge, the effective dielectric capacitance is always less than the dielectric capacitance. The corrected burning voltage and partial discharge tendency increase with the decrease of the particle size. As compared to an empty reactor, the average electric field in the PBR was found to be improved by 3–4 times, and the ozone energy efficiency and production were promoted by more than 20% and 15%, respectively. The plasma processing capacity can therefore be improved by choosing a relatively large size or a complex, irregularly-shaped packing material that is suitable for the discharge gap.

Understanding Partial Discharge Behavior from the Memory Effect Induced by Residual Charges: A Review

Residual charges produced in previous partial discharges (PDs) are considered as one aspect of memory effects that affect subsequent discharge behavior. In this paper, we review past studies about memory effects induced by residual charges during successive PDs. At first, surface charge dynamics for cavity and needle-to-dielectric discharges are presented. Subsequently, three methods used to unravel the memory effects are described, e.g. conditional distribution, pulse sequence analysis (PSA) and chopped PD (CPD). Then effects of residual charges on PD inception, discharge propagation and collective behavior are summarized. In addition, contributions of residual charges to the transitions between discharge modes and discharge patterns are presented. At last, some problems relevant to the memory effects are discussed, followed by suggestions for future work.

Partial Discharge of Polyurethane/ Organoclay Composite Coated on Aluminum Conductor Overhead Lines

Aluminum conductor have been used worldwide as the primary conductive materials for high voltage electrical transmission lines. The partial discharge behavior of the aluminum conductor have been obeserved during operation due to the transmission line's performance to serve electricity. The partial discharge of aluminum alloy coated by polyurethane/organoclay (PClay) composite material was studied. PClay composites were prepared by adding organoclay with different content in polyurethane as a matrix then coated on an aluminum conductor sample. A partial discharge test was conducted to obtain the behavior of partial discharge versus voltage. It was found that an escalation of organoclay content in the polyurethane reduce partial discharge appears.

Study of DC partial discharge on dielectric surfaces: Mechanism, patterns and similarities to AC

This paper presents the investigation on surface discharge behavior of various dielectric samples under DC. It sequentially develops the knowledge base for the study and analysis of the partial discharge (PD) defect with the goal of PD defect identification under DC. In order to facilitate this, the material properties of the dielectric are measured. Finite Element (FEM) simulation is used to obtain the preliminary estimates of the electric field and dielectric properties that concern partial discharge behavior. The DC-PD tests performed on the surface dielectric samples demonstrate a highly plausible behavior based on simulation results and other literature. It also displays a great degree of similarity towards the AC surface discharge behavior. The paper concludes by presenting novel partial discharge fingerprints for the surface PD defect that will aid in defect identification under HVDC.

Characterization of Defects Inside the Cable Dielectric With Partial Discharge Modeling

The continuous monitoring of power system devices is an important step toward keeping such capital assets safe. Partial discharge (PD)-based measurement tools provide a reliable and accurate condition assessment of power system insulations. It is very common that voids or cavities exist in every solid dielectric insulation medium. In this article, different voids are modeled and analyzed using an advanced finite element (FE)-based computational algorithm. The proposed approach can be used to measure PD in cavities and voids regardless of their shape and size. The frequentative scripting approach with finite element modeling (FEM) provides the results which satisfy all PD conditions. PD behavior has been studied and analyzed through PD statistical features obtained from the simulated PD signal. A comparative study between simulated and experimental results is also performed to validate the accuracy of the proposed modeling approach. To further improve the accuracy of the model, the influence and optimization of certain free parameters required for modeling has been carried out. The article shows how PD is greatly influenced by the shape and size of voids in dielectric insulators. The research realized in this article further provides the PD statistical features and its variation with respect to void shape and size. These features are utilized for the assessment of insulation quality. The variation in PD parameters with respect to voltage level is also presented and discussed.