Discharge Time Lag Research Articles

Influence of frequency on the partial discharge characteristics of biaxially oriented polypropylene film under nanosecond pulse voltage

Partial discharge (PD) is one of the key factors leading to premature insulation failure of film capacitors used in pulse power devices. To study the effect of frequency on the PD characteristics of biaxially oriented polypropylene (BOPP) film, a sphere-plate electrode was used to simulate defects of the air gap between the film layers. PD experiments of the BOPP film were carried out under 1, 10, 100, 500 Hz, and 1 kHz with a rising edge of 65 ns and a pulse width of 300 ns. The results show that the repetitive partial discharge inception voltage (RPDIV), the number of discharges, the rising stage discharge (RSD) amplitude, and the falling stage discharge (FSD) time-lag, all show an increase and then decrease with increasing pulse frequencies and reach a maximum value at a pulse frequency of 100 Hz. Moreover, the FSD discharge amplitude and the RSD discharge time-lag increase with an increasing pulse frequency. From the perspective of initial electron generation, the quantitative mathematical relationship between PD characteristics (RPDIV, PD amplitude, PD number, and PD time-lag) and frequency was established based on the Fowler–Nordheim field emission effect for the first time, which can reflect the influence of frequency on the memory effect and the development process of PD. The results can provide an experimental basis and a mechanistic explanation for the evaluation of PD characteristics for film capacitors under nanosecond pulse voltage.

Influence of Pressure on the PD and Induced Aging Behavior of Polyimide Insulation Under Repetitive Pulse Voltage

Reduction of air pressure can influence insulation material’s behavior with respect to resisting partial discharge (PD) generation and its induced aging process. This may bring threat to the insulation reliability of medium frequency transformers working under low pressure condition, considering they are exposed to high probability of PD inception caused by PWM voltage. Aiming at investigating the performance of insulation of medium frequency transformer being operated in an environment with a decreasing pressure, this paper introduces a test system that can conduct partial discharge and endurance lifetime tests under repetitive pulse voltage and controlled pressure. Using this test system and focusing on polyimide film, which is one of the main insulation materials used by medium frequency transformers, partial discharge and endurance lifetime tests are conducted under different pressures. The results show that partial discharge inception voltage decreases with decreasing pressure. However, the changing of partial discharge magnitude, time lag and its induced insulation lifetime do not change monotonously. Surface of the failed insulation samples show that the erosion area caused by partial discharge is larger under lower pressure. The mechanisms behind the changing of partial discharge time lag, discharge magnitude, endurance lifetime, along with the discharge eroded area with pressure are discussed in detail.

Partial Discharge Characteristics of Biaxially Oriented Polypropylene Film Under Nanosecond Pulse Voltage With High Rise Rate

Film capacitors are used as the key energy storage device for high-power pulse generators, and partial discharge (PD) is an important factor leading to insulation degradation and the failure of film capacitors. To accurately evaluate the effect of the rise rate on PD under nanosecond pulse voltage, experiments on the PD characteristics of biaxially oriented polypropylene (BOPP) films under high rise rate (18.3–140 V/ns) nanosecond pulse voltages were carried out. The PDs were mostly concentrated in the rising and falling phases of the nanosecond pulse. Moreover, the repetitive PD inception voltage (RPDIV) first increased and then remained unchanged as the rise time increased, and the PD amplitude and the number of discharges in the rising phase of the nanosecond pulse increased as the rise rate increased, while the discharge time lag decreased gradually. The PD amplitude, the number of discharges, and the discharge time lag in the falling phase of the nanosecond pulse all increased as the rise rate increased. In addition, when the rise rate was less than 50 V/ns, the PD statistical characteristics changed rapidly as the rise rate increased, and when the rise rate was greater than 50 V/ns, the PD statistical characteristics gradually changed more slowly as the rise rate increased.

Influence of impulse corona discharge on discharge time lag of a surge arrester with a spark gap

ZnO surge arrester with a spark gap is used for reducing electrical failures in power distribution systems of Japan. The high responsiveness, the low residual voltage, and the stable operating voltage are required for the arresters. However, the discharge time lag generally occurs in a spark gap. In this study, measurements of V-t characteristics and observations of optical emissions from impulse corona discharges generated at a newly designed small step edge on an inclined plane of each electrode were carried out. The small step edge made the discharge time lag and the standard deviation small. Based on the results, we indicated that the impulse corona discharge improves the discharge time lag of the sparkover.

Influence of Rise Time and Fall Time on Surface Discharge Characteristics of PEEK Under Positive Repetitive Square Voltage

In this paper, the surface discharge current pulses of PEEK (polyether-ether-ketone) under positive repetitive square voltage are measured. The effects of voltage rise time and fall time on pulse parameters of discharge current, instantaneous voltage of discharge and time-lag of discharge are analyzed in detail. The results show that the amplitude of discharge current and the instantaneous voltage of discharge decrease, and the time-lag of discharge and the dispersion of time-lag increase with the increase of voltage rise time. With the increase of voltage fall time, the amplitude of discharge current decreases and the instantaneous voltage of discharge, the time-lag of discharge and the dispersion of time-lag increase. To analyze the influence mechanism of voltage rise time and fall time on surface discharge, the accumulation of surface charge under repetitive square voltage is regarded as a periodic process. Besides, the correlation between forward discharge and back discharge in the process of discharge is analyzed, and the development of discharge is analyzed by using the time-lag theory. Furthermore, the relationship between instantaneous discharge voltage and voltage slew rate is revealed, and the surface charge accumulation processes under different voltage rise times and fall times are compared to reveal the influence mechanism of rise time and fall time on the surface discharge under positive repetitive square voltage.

Contribution of free iron particles to PD characteristics in flowing transformer oil at DC voltages

Partial discharge (PD) characteristics of the transformer oil contaminated by metallic particles are relevant to particle movement. The motion characteristics of the particles will change when the oil flows, and hence, the PD characteristics differ from that in stationary oil. In this study, the PD characteristics were investigated at direct current voltages, and the particle trajectories were observed simultaneously. It was found that the number of discharges obviously decreased, but the discharge magnitude slightly increased as the oil flow speed increased. To explain the changes in the PD characteristics, a solid-liquid two-phase flow model was established to simulate the trajectories and the electric field distribution around particles. The experimental observations partially verified the simulated trajectories, which includes two stages, namely sedimentation and the subsequent oscillation-collision stage. With the increase of the flow speed, the sedimentation particles decreased, and the horizontal spacing between two adjacent particle-electrode collisions elongated. Therefore, the total collisions became infrequent, which reduced the number of discharges. Moreover, the higher the flow speed was, the slower the particle approached an electrode. Considering the discharge time lag, the distance between the particle and the electrode at the instant of the PD would increase, which increased the discharge magnitude.

Influence of surface charge decay on cavity PD frequency at DC voltage

In this study, two types of samples, i.e. a disc-shaped cavity embedded within solid dielectrics and the other on an electrode surface, were used to investigate partial discharge (PD) behaviours at DC voltage. It has been found that the discharge frequency of the sample with one metallic surface was much larger under a positive voltage than under a negative one, whereas it was not sensitive to voltage polarities for the sample with two insulating surfaces. In order to explain experimental results, a simulation model based on continuity equations was established to obtain PD sequences at DC voltage, in which surface charge decay and discharge time lag were taken into account. Simulation results showed that positive surface charges dissipated faster than the negative, and the discharge time lag kept almost unchanged at the same voltage amplitude. The discharge time interval consisted of field recovery time and discharge time lag, and the former was determined by surface charge decay rate. In terms of these, the effect of surface charge decay on discharge frequency was discussed. The research is helpful to clarify PD mechanism at DC voltage.

Water level management of lakes connected to regulated rivers: An integrated modeling and analytical methodology

Reservoir operations significantly alter the hydrological regime of the downstream river and river-connected lake, which has far-reaching impacts on the lake ecosystem. To facilitate the management of lakes connected to regulated rivers, the following information must be provided: (1) the response of lake water levels to reservoir operation schedules in the near future and (2) the importance of different rivers in terms of affecting the water levels in different lake regions of interest. We develop an integrated modeling and analytical methodology for the water level management of such lakes. The data-driven method is used to model the lake level as it has the potential of producing quick and accurate predictions. A new genetic algorithm-based synchronized search is proposed to optimize input variable time lags and data-driven model parameters simultaneously. The methodology also involves the orthogonal design and range analysis for extracting the influence of an individual river from that of all the rivers. The integrated methodology is applied to the second largest freshwater lake in China, the Dongting Lake. The results show that: (1) the antecedent lake levels are of crucial importance for the current lake level prediction; (2) the selected river discharge time lags reflect the spatial heterogeneity of the rivers’ impacts on lake level changes; (3) the predicted lake levels are in very good agreement with the observed data (RMSE ≤ 0.091 m; R2 ≥ 0.9986). This study demonstrates the practical potential of the integrated methodology, which can provide both the lake level responses to future dam releases and the relative contributions of different rivers to lake level changes.

Investigation of cavity PD physical processes at DC voltage by simulation

In order to reveal partial discharge (PD) physical processes at DC voltage, a model with regard to PD taking place within a cavity embedded in polyethylene is established, in which the charge fluid equations and the Poisson equation are employed to simulate streamer propagation and surface charge accumulation processes after it arrives at the gas–solid interface. Meanwhile, parameters such as discharge current and discharge time during a PD sequence are obtained by considering surface charge decay and discharge time lag variation in the discharge time interval. It is found from the simulation results that the electrons generated by the discharge accumulate on the upper surface of the cavity and the time taken to accumulate is less that 1 ns when a positive voltage is applied to the upper electrode. On the contrary, positive ions accumulate on the lower surface, and the time taken is about 90 ns. Besides, the density of positive ions is slightly higher than that of the electrons. During a PD sequence, the decay of surface charges resulting from previous discharge can be considered to be the key factor contributing to the occurrence of subsequent one, and electric field within the cavity mainly depends on negative surface charges just before the subsequent PD takes place, because of the lower decay rate of the negative charges than the positive ones. The discharge time interval can be divided into two parts: discharge time lag and discharge recovery time, which depend on the surface charge decay rate. As surface charge decay rate increases or the discharge time lag decreases, the discharge time interval decreases. Moreover, the discharge current is affected by discharge time lag and the surface charge decay rate. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Simulation of cavity PD sequences at DC voltage by considering surface charge decay

In this paper, the dynamic distribution of surface charges during partial discharge (PD) sequences was obtained at both polarities of direct current (DC) voltage, as well as at different levels of voltage. It is found that the decay rate of positive charges was higher than that of negative ones, and PD would take place with the existence of residual surface charges. Moreover, the curves to describe surface charges decaying discipline were obtained. Based on these, a simulation model about PD sequence at DC voltage was constructed by considering surface charge decay and discharge time lag. With the help of simulation model, microscopic physical processes, i.e. streamer development and surface charge accumulation, were obtained, as well as macroscopic parameters i.e. discharge current and discharge time. The accumulation of surface charges took a much shorter time at negative voltage than at the positive. Besides, discharge time interval at positive voltage was smaller than that at negative one, and it diminished as voltage increased, which were in accordance with the experimental results. In terms of the evolution of electric field within cavity, the effects of surface charge decay and discharge time lag on discharge time interval and PD magnitude were discussed. The exhaustive physical model is significant to clarify PD mechanism at DC voltage.

TiO<sub>2</sub> 또는 MgO 첨가에 따른 마이크로 유전격벽방전 셀의 방전특성 연구

For a higher definition discharge cell, the method of high speed addressing is necessary. In order to modify the surface charges, the liquefied TiO₂ or MgO powder is added on MgO layer in front glass and on the phosphor in rear glass in micro barrier discharge. Both the electro-optical properties and the discharge time lag characteristics are measured from 4 inch. test panel, such as the discharge voltage, current, luminance, luminous efficacy and discharge time lag. As the results, the statistic time lag is improved by about 40 %.

Improvement on Address Discharge Characteristics for Overall Subfield Time Using Additional Scan Voltage in AC PDP

The address discharge time lags are investigated in each subfield time in AC PDP and shortened by changes in the amplitude of the additional scan voltage during total subfield time under the stable address voltage margin range. During the reset period, the reset discharge is produced by applying the high positive-going ramp voltage and the wall charge in a cell is generated. That wall charge plus the external address voltage induce the address discharge. In the first subfield time, the address discharge is fast produced than the other subfield times because the wall charge are much remained by the high positive-going ramp voltage during the reset period. Meanwhile, from the second to last subfield, the address discharge production time is gradually delayed due to the dissipation of the wall charge in a cell. In this study, the address discharge time lags are measured in each subfield time and the modified driving method to shorten the total address discharge time is proposed by applying the different additional scan voltages in each the subfield time.

Effect of gold nanorods in an MgO protective layer of AC plasma display panels.

We propose a modified MgO protective layer for alternating current plasma display panels. The modified MgO protective layer of the panel tested here has a structure that incorporates silica-coated Au nanorods (NRs), leading to localized surface plasmon resonance (LSPR) in the near-infrared (IR) region. The silica-coated Au NRs were synthesized by a simple chemical method and inserted into an MgO protective layer using an air-spray method. The operating voltage of the proposed structure was decreased by 10 V. The luminance and luminous efficacy of the test panel part with the silica-coated Au NRs both increased by about 15%. According to the measured results of the IR response time, the sustain discharge time lag was reduced. In addition, by inserting the silica-coated Au NRs into the MgO protective layer, a decrease of the IR emission proceeding from the plasma discharge was acquired. Finally, we investigated the LSPR effect of the silica-coated Au NRs in a simulation with a finite-difference time domain method.

Study on the Addressing Characteristics of an ac PDP With Sc-Doped MgO-Protecting Layer

In this paper, the addressing characteristics of an ac plasma display panel (PDP) with Sc-doped MgO-protecting layer are investigated. The characteristics of addressing voltage and temporal distribution of addressing discharge event in Sc-doped MgO panel are different from those in a conventional MgO panel. In particular, the characteristics depending on the operation temperature are changed drastically in Sc-doped MgO panel. The formative discharge time lag increases as the addressing pulse application time and operation temperature increase regardless of protecting layers. The statistical time lag shows the contrary trend compared to the formative discharge time lag except for the MgO when operated in room temperature. The variation of addressing voltage and temporal distribution of addressing discharge event in different protecting layers can be understood through the survey of previous research result on the exoelectron emission characteristics from protecting layers in an ac PDP. It is assumed that the emission of electrons from a protecting layer results in the decrease of wall voltage but increase of priming effect for the addressing discharge. Also, the possibility for the control of addressing characteristics is suggested by changing scan voltage level during address period.

Time-lag properties of corona streamer discharges between impulse sphere and dc needle electrodes under atmospheric air conditions

In this study of corona streamer discharges from an impulse generator using a dc power supply, the relationship of the discharge time-lag with the dc bias voltage between the sphere-to-needle electrodes under atmospheric conditions is investigated. Devices utilizing corona discharges have been used to purify air or water, destroy bacteria, and to remove undesirable substances, and in order to achieve fast response times and high power efficiencies in such devices, it is important to minimize the time-lag of the corona discharge. Our experimental results show that (a) the discharge path of a negatively biased needle electrode will be straighter than that of a positively biased needle and (b) the discharge threshold voltage in both the positive and the negative needle electrodes is nearly equal to 33 kV. By expressing the discharge voltage as a power function of time-lag, the extent of corona generation can be quantitatively specified using the exponent of this power function. The observed behavior of a corona streamer discharge between the negative spherical and the positive needle electrodes indicates that the largest power exponent is associated with the shortest time-lag, owing to the reduction in the statistical time-lag in the absence of a formative time-lag.

Analysis of Weak and Strong Discharge Characteristics for Fast Address Discharge in Microplasma Cells

In this paper, the voltage level of the negative falling ramp in the reset waveform is lower, the accumulated wall charges during the ramp-up period are more erased between A-Y electrodes, thus, reducing the number of wall charges prior to address discharge. In particular, the measured Vt closed-curves and the weak and strong discharge characteristics corresponding IR emission profiles show that fewer wall charges prior to an address discharge induce a decrease in the statistical time lag during the address period. The discharge transient contours of simultaneous discharges are changed by the wall voltage states after reset discharge, thereby influencing the statistical discharge time lag of the address discharge for the stable drive, thereby resulting in stable and fast addressing.

Effect of the Driving Waveform With Negative-Going Ramp on the Address Discharge Characteristics of Plasma Display Panel With High-Gamma Cathode Material

The address discharge characteristics of the plasma display with a MgO single cathode layer and the one with a MgO-SrO double cathode layer were investigated. In particular, the conventional waveform with a positive-going ramp and the proposed waveform with a negative-going ramp were applied in order to demonstrate that the polarity of the scan electrode during the reset period affects the dynamic voltage margin and the address discharge time lag. It was confirmed that the total address discharge time lag of the plasma display with the MgO-SrO double cathode layer decreased by about 550 ns by applying the proposed waveform with the negative-going ramp.

7.2: Fast‐Addressing Waveform with Negative‐Going Ramp for High‐Xe PDP with High‐Gamma Cathode Materials

AbstractIn this paper, the address discharge characteristics of high‐Xe PDPs with high‐gamma cathode materials were investigated. It will be shown that the address discharge characteristics such as the dynamic voltage margin and the address discharge time lag of high‐Xe PDP with MgO‐SrO double cathode layer and one with MgCaO single cathode layer can be improved by inducing stable, continuous weak discharges during the reset period with a newly designed waveform. The deposition of pure MgO powder on high gamma cathode material has also proved to be effective in reducing the address discharge time lag of high‐Xe PDP.

Discharge Characteristics of Plasma Display Panels with SrCaO Protective Layer Manufactured Using “All-in-Vacuum” Process

Plasma display panels (PDPs) with a SrCaO protective layer of high secondary electron emission coefficient were manufactured using the “all-in-vacuum” process, whereby the protective layer deposition and panel sealing were performed continuously in high vacuum in order to keep the surface of the protective layer as clean as possible. The PDP with the SrCaO protective layer manufactured using the “all-in-vacuum” process (“all-in-vacuum” SrCaO-PDP) for Ne­20 vol% Xe exhibited a luminance 2.1 times larger, a luminous efficacy 1.7 times larger, and the same discharge time lag, compared with the PDP with the MgO protective layer manufactured using the conventional process (conventional MgO-PDP) for Ne­4 vol% Xe, which had almost the same discharge voltage. [doi:10.2320/matertrans.M2011181]

Biased scan of plasma display panel for data voltage reduction

This paper proposes a method of reducing the data voltage Vd of plasma display panels (PDPs). The proposed biased-scan method uses two separate ground systems: one for the sustain pulse generator (FGND) and the other for the data address and control systems (CHGND). A dc voltage bias, which is applied between CHGND and FGND during the address period, reduces Vd while preventing the undesired glow discharge induced by a scan pulse only. CHGND is connected to FGND for the first sustain pulse of each subfield, which reduces the time lag of address discharge, but it is separated from FGND for the other sustain pulses to increase the margin of the sustain voltage. The proposed method was tested on a 15% Xe 50-in. Full HD (1920×1080) single-scan PDP which had a sustain discharge gap of 110μm. Vd could be reduced by 20V (30%), and the power consumption of the Vd voltage source decreased by ∼25W (50%) from that of the conventional method.