Repetitive Partial Discharge Inception Voltage 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.

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.

Characterization of PDIV, PDEV, and RPDIV in Insulated Wires Under Unipolar Repetitive Square Wave Excitations for Inverter-Fed Motors

The behaviour of partial discharge inception voltage (PDIV), partial discharge extinction voltage (PDEV) and repetitive partial discharge inception voltage (RPDIV) as a function of exposure/poling time under unipolar repetitive square wave excitations at atmospheric pressure (1013 mbar) is experimentally measured and investigated. The partial discharge (PD) tests are performed on two commercially available insulated wires: Glass fibre as Type II and Polyether Ether Ketone (PEEK) as Type I insulated wires used in inverter-fed motors. The impact of excitation polarity, pulse repetition frequency and rise time on the PD quantities (i.e., PDIV, PDEV and RPDIV) is studied as a function of stressing duration. In addition, the trend of RPDIV and PDIV dispersion levels are compared as a function of poling time under positive and negative unipolar excitations with two rise times (i.e., 80 and 800 ns) and two pulse repetition frequencies (i.e., 50 Hz and 2.5 kHz), relying on the shape/slope parameter of the Weibull distribution. The collected data shows that the electric field induced by the interface charge deposited by PD occurring during consecutive pulses and the space charge accumulation in the insulation bulk plays a decisive role in PD quantities’ variations under unipolar repetitive square wave excitations.

A Contribution to Thermal Ageing Assessment of Glass Fibre Insulated Wire Based on Partial Discharges Activity

This paper aims to evaluate a Type-II insulated wire (i.e., Glass fibre insulated wire) as a function of thermal ageing time based on partial discharges (PD) activity. Partial discharge inception voltage (PDIV), partial discharge extinction voltage (PDEV), and repetitive partial discharge inception voltage (RPDIV) measurements have been performed on both unaged and thermally aged specimens. Each specimen modelled the turn-to-turn insulation; hence it was made by a pair of Glass fibre wires wrapped in PTFE tape for a mechanical purpose. The PD tests have been carried out under positive and negative unipolar square waveform excitations using different rise times: 80, 400 and 800 ns. The trend of PD quantities vs exposure time demonstrates that the effect of space charge accumulation under unipolar excitation must be taken into account when unaged and thermally aged specimens are compared. Results revealed that although sometimes thermally aged samples might show a temporary superiority in the short run, unaged ones always present a better performance after space charge accumulation, as expected. Following the statistic postprocessing of the collected data, shape/slope parameters of the Weibull distribution relevant to PDIV can be used as an ageing indicator for Glass fibre insulated wire. Finally, the permittivity evaluation vs thermal and electrical stresses have been performed, relying on the measured capacitance of each specimen just after every PD test. Such analysis revealed that thermal ageing increases permittivity in the long run. However, electrical stress has different impacts on permittivity depending on the rise time, polarity, and magnitude of the applied voltage.

Influence of impulse voltage repetition frequency on RPDIV in partial vacuum

The reliability of low-voltage inverter-fed motors is highly dependent on the inception of partial discharges. The effect of impulsive waveform parameters must be investigated to predict the repetitive partial discharge inception voltage (RPDIV) and define test procedures that can indicate properly the behavior in service of the insulation system. This paper focuses on the RPDIV of magnet wires using twisted pairs subjected to repetitive unipolar impulsive voltage waveforms. The effects of supply frequency (5 to 200 kHz) at pressure levels that are typical for aircraft (20 to 100 kPa) is examined. Results show that RPDIV steadily decreases with frequency up to 100 kHz where it reaches a plateau. This behavior is explained as an effect of the oscillations that inevitably exist in the applied voltage waveform. Therefore, a conservative estimate of the RPDIV could be achieved by raising the supply frequency well above the operation frequency. In the experiments, the RPDIV is decreasing linearly with pressure. If this behavior could be confirmed for other insulation systems, the design of systems working at pressures typical of aircraft would result relatively easy.

Influence of Very Fast Voltage-Oscillation with Polarity Reversalon Partial Discharge Inception Probability for Twisted Enameled-Wires

This paper presents an experimental study on repetitive partial discharge inception probability of twisted enameled wires subjected to modified inverter-surges. In order to obtain the probability curves as a function of the voltage amplitude, we develop an automatic measurement system of partial discharge inception probability for the twisted enameled wires subjected to the repetitive pulses with step-by-step increasing in the voltage height. Very fast oscillated pulses with or without polarity-reversal and an impulse-like pulse without oscillation are used as the modified inverter-surges. In the test for the impulse-like voltage, repetitive partial discharge inception voltage (RPDIV) decreases with increasing the pulse width. On the other hand, RPDIV for the polarity-reversed pulse with a higher oscillation cycle is lower than that for the pulse with lower oscillation cycle. The difference of PD inception probability between the voltage waveforms will be discussed on the basis of charge dynamics on the wire surfaces. Index Terms: modified-inverter-surge, repetitive partial discharge, automatic measurement, polarity-reversed pulse, twisted-pair

Off-line PD testing of converter-fed wire-wound motors: when IEC TS 60034-18-41 may fail?

This paper reports and discusses qualification and type test procedures for random wound motors as specified in IEC Technical Specification 60034-18-41. Since laboratory tests dealing with off-line partial discharges measurements followed by life tests showed that motors qualified as good can fail in very short times, an extensive investigation on the causes of such discrepancy and, in particular, on the differences existing between the stresses applied during off-line tests and in service is described. In addition, the results of partial discharge measurements performed on crossed pairs are presented, highlighting how the differences in the applied voltage waveform can influence the Repetitive Partial Discharge Inception Voltage. Suggestions to improve the off-line test procedure and related equipment are eventually discussed.