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A pressure scaling law for the partial discharge inception voltage (PDIV) of wedge-shaped, dielectric-bounded gas gaps is derived and experimentally validated. The investigated prototypical electrode geometry is of relevance in a number of practical applications, such as contacting enameled wires in electric motors or transformers. The derived pressure scaling law is of particular interest for electric propulsion in aviation systems. The results show that the PDIV can be accurately parametrized from first principles as a function of the scaling parameter p ⋅ s / ε r , where p is the gas pressure, s is the thickness of the insulating coating and ɛ r its relative dielectric permittivity. Previously published empirical relationships between the PDIV and pressure are shown to be local approximations of the presented general scaling law. In particular, the often assumed linear relation of PDIV with pressure is shown to not be generally valid. [ABSTRACT FROM AUTHOR]

We investigated AC breakdown characteristics of ultra violet curable epoxy resin (UV‐EP) with nitrogen fine bubbles (FBs) in order to improve insulating properties of UV‐EP. As a result, it was found that self‐made FB generator mainly add FBs with a diameter between 60 and 150 nm to FB‐EP before curing. In addition, SEM images revealed that FB‐EP has FBs after curing. Bubble diameter in FB‐EP after curing was estimated between 55 and 140 nm due to resin shrinkage. Furthermore, partial discharge inception voltage and electric strength of FB‐EP with FB addition for 10 min were almost the same as No FB‐EP. [ABSTRACT FROM AUTHOR]

The partial discharge inception voltage (PDIV) of low-voltage induction motor turn-turn insulation analogy is investigated for variable relative humidity (RH) of the surrounding air (temperature and pressure are kept constant close to their ambient values). Three materials, perfluoralkoxy alkane, sealed and unsealed alumina (UA), are employed as the dielectric coating (insulation) of test samples. Each material's dielectric properties change differently with RH—of these, relative permittivity is regarded as the most crucial, as it was previously proven to be, along with the coating's thickness, the key factor in determining the PDIV in dry air conditions. To further vary the value of permittivity and thus provide larger data sets for the verification study, the frequency of the excitation voltage is also varied between 1 Hz and 50 kHz. The obtained experimental data are compared against the PDIV predictions obtained by a breakdown model based on the reduced thickness of the coating (ratio of the coating thickness to its relative permittivity). Satisfying agreement between the measured and predicted PDIV are obtained for the first two materials, whereas significant discrepancies are seen for the UA material. For this case, surface conductivity is introduced into the prediction model and much better fits to the experimental data are obtained for a suitable value of surface resistance. It is hence demonstrated that the model is able to satisfactorily predict the PDIV for three substantially different materials when the RH of the surrounding air is varied between 10 % – 80 % . [ABSTRACT FROM AUTHOR]

Rejuvenation of power cables addresses water trees, voids, or electrical trees. Partial discharge (PD) in joints or terminations are addressed by the sustained pressure rejuvenation process, which replaces all terminations and joints. In this study, partial discharge inception voltage (PDIV) is found to increase by 27% for each 0.1%w in crease in fluid concentration in field-aged rejuvenated cable samples. The mechanism of rejuvenation is discussed in which PD mechanism is prevented by plasticizing the dielectric, filling the voids, smoothing electrical stress, and sequestering free electrons in field-aged cables. [ABSTRACT FROM AUTHOR]

Kekuatan dielektrik minyak transformator nynas nitro murni dapat ditingkatkan dengan menambahkan berbagai partikel nano seperti nanoalumina (Al2O3). Penelitian ini bertujuan untuk melihat effek penambahan partikel nano alumina terhadap karakteristik tegangan tembus dan tegangan insepsi peluahan sebagian. Empat jenis minyak nynas dengan komposisi penambahan partikel nanoalumina sebesar 0.00%, 0.010%, 0.015% dan 0.020% diuji tegangan tembus dielektrik, tegangan insepsi peluahan sebagian (PDIV) pada suhu ruang dengan merujuk kepada standar pengujian IEC 60156. Hasil menunjukkan bahwa tegangan tembus minyak nanonynas meningkat sebesar 6% dan nilai tegangan insepsi dan peluahan sebagian lebih tinggi dibandingkan dengan minyak murni.

This study presents the investigations on Partial Discharge (PD) behaviour of irregular‐shaped copper particle in oil with pressboard barrier placed in two positions under uniform field with different moisture contents. Frequency Domain Spectroscopy (FDS) was used to estimate percentage moisture in pressboard. Recovery Voltage Measurement was used to confirm obtained FDS results. PD characteristics like magnitude, number, discharge power, rise time and duration time of PD pulse were analysed. Electric field due to particle in oil with moisture content pressboard barrier was studied by simulations. Phase Resolved PD (PRPD) pattern for different moisture pressboard observed to have similar patterns with variation in PD inception voltage (PDIV), magnitude and number of discharges. It was observed that PD characteristics as a function of voltage, increases nearly quadratic rate with respect to percentage moisture in pressboard. Simulation results complimented experimentally measured PDIV values for particle in oil with moisture in pressboard. Filtering and conditioning of oil is mandatory practice in a new transformer before going to any high voltage (HV) applications. PRPD pattern and PD characteristics data obtained in this study has great practical significance to assess the condition of transformer insulation systems before proceeding for HV application to avoid any potential failure. [ABSTRACT FROM AUTHOR]

Ethylene propylene rubber (EPR) cable terminations have great potential in improving the operational reliability of electric multiple units, for their high elasticity and low loss. However, the breakdown of EPR cable terminations frequently occurred in northwestern China during winters. In this study, tests were conducted to investigate the effect of temperature (−40 to 20°C) on partial discharges (PDs) characteristics, characteristic transition temperature, and breakdown process of cable termination. In samples with no artificial defects, it was found that the average PD inception voltage (PDIV) decreased obviously by 45% when temperature reduced from 20°C to −40°C. Meanwhile, the PD amplitude increased rapidly with decreasing temperature. The symmetric phase resolved PD pattern also changed from 'turtle‐like' to 'wing‐like' shape with decreasing temperature. Differential scanning calorimetry results indicated that the decrease of mechanical mismatching between EPR and stress control tube (SCT) at low temperature led to decreasing PDIV. A physical model of electric field (EF) distribution within cracks on EPR/SCT interface inside the termination was designed. Distortion of the EF by simulation was consistent with the discharge channel in the test. These results showed that the decreasing temperature had significant influences on the PD initiation of EPR cable termination. [ABSTRACT FROM AUTHOR]

This experimental study aims to examine the partial discharge (PD) properties of palm oil and coconut oil (CO) based aluminum oxide (Al2O3) nanofluids with and without surfactants. The type of surfactant used in this study was sodium dodecyl sulfate (SDS). The volume concentrations range of Al2O3 dispersed in oil samples was varied from 0.001% to 0.05%. The ratio of surfactants to nanoparticles was set to 1:2. In total, two different types of refined, bleached and deodorized palm oil (RBDPO) and one type of CO were measured for PD. Mineral oil (MO) was also examined for comparison purpose. PDIV measurements for all samples were carried out based on rising voltage method whereby a needle-sphere electrode configuration with a gap distance of 50 mm was chosen in this study. Al2O3 improves the PDIVs of RBDPO, CO and MO whereby the highest improvements of PDIVs are 34%, 39.3% and 27%. The PD amplitude and repetition rate of RBDPO improve by 38% and 81% while for CO, it can increase up to 65% and 80% respectively. The improvement of PD amplitude and repetition rate for MO are 18% and 95%, regardless with and without SDS. Without SDS, the presence of Al2O3 could cause 26%, 75% and 65% reductions of the average emission of light signals for RBDPOA, RBDPOB and CO with the improvement of PD characteristics but both events do not correlate at the same volume concentration of Al2O3. On the other hand, the average emission of light signal levels of the oils increases with the introduction of SDS. The emission of light signal in MO does not correlate with the PD characteristics improvement either with or without SDS.

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. [ABSTRACT FROM AUTHOR]

This experimental study aims to examine the partial discharge (PD) properties of palm oil and coconut oil (CO) based aluminum oxide (Al2O3) nanofluids with and without surfactants. The type of surfactant used in this study was sodium dodecyl sulfate (SDS). The volume concentrations range of Al2O3 dispersed in oil samples was varied from 0.001% to 0.05%. The ratio of surfactants to nanoparticles was set to 1:2. In total, two different types of refined, bleached and deodorized palm oil (RBDPO) and one type of CO were measured for PD. Mineral oil (MO) was also examined for comparison purpose. PDIV measurements for all samples were carried out based on rising voltage method whereby a needle-sphere electrode configuration with a gap distance of 50 mm was chosen in this study. Al2O3 improves the PDIVs of RBDPO, CO and MO whereby the highest improvements of PDIVs are 34%, 39.3% and 27%. The PD amplitude and repetition rate of RBDPO improve by 38% and 81% while for CO, it can increase up to 65% and 80% respectively. The improvement of PD amplitude and repetition rate for MO are 18% and 95%, regardless with and without SDS. Without SDS, the presence of Al2O3 could cause 26%, 75% and 65% reductions of the average emission of light signals for RBDPOA, RBDPOB and CO with the improvement of PD characteristics but both events do not correlate at the same volume concentration of Al2O3. On the other hand, the average emission of light signal levels of the oils increases with the introduction of SDS. The emission of light signal in MO does not correlate with the PD characteristics improvement either with or without SDS. [ABSTRACT FROM AUTHOR]