Partial Discharge Inception Voltage Measurement Research Articles

Experimental Study on Partial Discharge Inception Voltage of Pressboard-Enclosed Void at Different Frequencies From the Perspective of the First Partial Discharge Time Lag

Partial discharge inception voltage (PDIV) at different frequencies is of great interest for PD tests conducted at nonpower frequency. However, in the existing literature, there is no agreement on PDIV characteristics with respect to frequency. There is a lack of comprehensive analysis of frequency-dependent PDIV characteristics either. In this article, the PDIV of a cylindrical void at different frequencies (from 0.5 to 300 Hz) is investigated from the perspective of the first PD time lag. First, an appropriate time interval between consecutive measurements is experimentally determined. Then, PDIV measurements at different frequencies are conducted by increasing voltage at a fixed ramp rate. Furthermore, the PDIVs defined by peak voltage and instantaneous voltage are compared. After that, a bipolar square wave is applied to measure the first PD time lag. Finally, based on the first PD time-lag distribution with respect to voltage at different frequencies, the cumulative probability of the first PD under sinusoidal voltage is computed and analyzed. The results suggest that the first PD time lag has a significant influence on the measured PDIV at frequencies above 10 Hz. This is because the mean time lag is nearly half the time period of half voltage cycle at low voltages. Thus, high voltages (HVs) are needed to obtain a high probability of the first PD, i.e., a large measured PDIV.

Investigation on thermally aged natural ester oil for real‐time monitoring and analysis of transformer insulation

Thermal aging of natural ester oil shows drastic reduction in partial discharge inception voltage (PDIV) and a significant variation is observed only above a certain aging time, under AC, DC, high frequency AC voltages and with harmonic voltages with different total harmonic distortion. Weibull distribution studies on PDIV measurements indicate a reduction in scale parameter (α) with increase in thermal aging temperature. A characteristic reduction in breakdown voltage was observed with the thermally aged ester oil, under AC, DC and standard lightning impulse voltage. The breakdown voltage variation with aged ester oil follows normal distribution. Ultraviolet (UV) analysis of ester oil thermally aged at 160°C has revealed a regular shift of the derived absorbance parameter to longer wavelengths. The interfacial tension and turbidity exhibits an inverse relationship with the thermally aged ester oil. Gas chromatography/mass spectrometric analysis of the thermally aged ester oil predicted the formation of more carboxylic acids and ketones with aging duration. The steady-state fluorescence on thermally aged ester oil exhibits a shift in its emission profile, which is in tandem with the UV absorption spectroscopic analysis. Fluorescence analysis can be adopted as a real-time monitoring tool in transformers, to understand the condition of liquid insulation. The viscosity dependence on the wavelength of derivative absorption maxima follows a direct relationship with the thermally aged natural ester oil.

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.

Use of partial discharge inception voltage measurements to design a gaseous helium cooled high temperature superconducting power cable

The occurrence of partial discharge is one of the challenges that limit the design options and voltage ratings of gaseous helium cooled high temperature superconducting (HTS) cables. The measurements of partial discharge inception voltage (PDIV) at cryogenic temperatures on several model cables were used in the optimization of the dielectric design of a 30 m long HTS power cable, which was successfully fabricated and tested at DC currents up to 6 kA and voltage of 3.5 kV RMS. Details of the PDIV measurements are described.

Effect of repetitive impulsive voltage duty cycle on partial discharge features and insulation endurance of enameled wires for inverter-fed low voltage machines

Dealing with electrical rotating machines fed by voltage converters, understanding the effect of impulsive voltage parameters on partial discharge features is of great importance to select appropriate impulsive voltage to perform partial discharge inception voltage measurements. Similarly, the dependence of insulation endurance on voltage parameters might help to develop qualification tests providing more accurate evaluation of insulation performance. The effect of voltage duty cycle on partial discharge characteristics and endurance of inverter-fed motor insulation were investigated through a large number of tests performed on single-contact crossed enameled wires under bipolar repetitive impulse wave voltages. The partial discharge pattern, magnitude, repetition rate show that short impulsive voltage duration (i.e. small duty cycles), can induce asymmetric PD patterns and reduce the probability of PD inception at the falling flanks of impulsive voltages. Moreover, the endurance tests indicate that the duty cycle of the repetitive square wave voltage can affect the insulation endurance significantly. Repetitive square wave voltages with small duty cycles tend to overestimate endurance. Accordingly, when performing partial discharge inception voltage and endurance tests on insulation of inverter-fed motors, the influence of duty cycle should be carefully considered.

Partial discharge inception voltage in transformer natural ester liquid — Effect of the measurement method in the presence of moisture

The long term persistent occurrence of partial discharges (PD) may influence the long term stability of insulating liquid. Therefore, the Partial Discharge Inception Voltage (PDIV) is one of the important parameters of the condition of high voltage insulation systems. However, the PDIV is tested using different test methods and electrode configurations. The article aims to show the impact of test methods and electrode configuration on the PDIV measurement of natural ester based transformer oil in the presence of dissolved water.

Partial discharge inception voltage investigation of mineral oil: effect of electrode configurations and oil conditions

The aim of this paper is to describe the Partial Discharge Inception Voltage (PDIV) and Partial Discharge (PD) characteristic of mineral oil tested by various electrode configurations. Furthermore, mineral oil with different conditions was investigated under AC voltage. The PDIV and PD of the mineral oil, Nynas Nytro 4000x, with water content about 4 ppm was investigated by using various electrode configurations of needle - plane and needle - sphere electrodes under room temperature. The PDIV test circuit was set up according to IEC 60270. Then, two PDIV measurements were applied for the investigation. The first PDIV test procedure (IEC method) was performed in accordance with IEC 61294. The second PDIV test procedure so-called combined PDIV method was adapted from IEC standard. Moreover, the electric field distributions of the electrode systems were also calculated. According to the test results, PDIV depended clearly on the electric field stress of the electrode system and the test method. Compared with other electrode configurations, the 10 μm tip radius needle - 75 mm dia. plane electrode gave the highest electric field stress and inversely provided the lowest PDIV value tested by both test methods. The combined PDIV test method generated the PDIV, charge quantity, and charge repetition significantly lower than measuring by IEC method. To investigate the effect of oil conditions on PDIV and PD characteristics, the combined conditions of temperature and water content of the mineral oil were controlled as the parameters for investigation. It was found that the water content in the mineral oil influenced approximately on PDIV value when the oil temperature was at room temperature. However, at the oil temperature of 40-90 °C, the PDIV values of the mineral oil with water content 4, 20 and 40 ppm were relatively the same. From the PD pulse current test results, PD pulse current recorded at the PDIV value from both test methods was about 0.15-1.3 mA. Pulse duration was in the range of 0.7-9 μs and the rise time was between 40-570 ns.

The influence of the rotor on surge pd testing of low voltage AC motor stator windings

Partial discharge (PD) has been identified as one the main root causes of stator winding failures in low voltage (LV) random wound AC motors fed by PWM inverters. To ensure that PWM inverter-fed motors (type I) are PD-free under impulse excitation, the test procedure for acceptance testing of the stator insulation system was developed (IEC TS 60034-18-41). Although many successful cases of applying the TS have been reported, some concerns regarding the test procedure have been raised, and the TS is currently under revision. It is implied in the TS that the rotor has no impact on the surge PD test result, and testing is often performed without the rotor; however, it was observed that the surge PD test results can change with rotor insertion for some types of machines. The off-line surge PD test must be performed under conditions representative of actual operation (with the motor assembled) to guarantee absence of PD. Therefore, it is important to investigate the influence of the rotor, and to incorporate the findings in the test procedure, if necessary. In this paper, the influence of the rotor on the off-line surge PD test is investigated for AC machines, and it is shown that the PD inception voltage (PDIV) can change significantly depending on the rotor design. A detailed analysis is given along with experimental test results on a number of induction and permanent magnet (PM) synchronous motor samples with different rotor designs. Based on the observations made in this work, suggestions on the TS that can provide surge PDIV measurements under conditions closer to that of the actual operation with the rotor are given to help reduce the likelihood of false indications with off-line surge PD testing.

Ramp Rates Effect in Ramp Method for Partial Discharge Inception Voltage Measurement in Mineral Oil

Abstract IEC 61294 regulates about Partial Discharge Inception Voltage (PDIV) measurement procedure in liquid insulation using the ramp method with speed 1 kV/s. This PDIV test method is assumed to give the PDIV test results higher than it should be. This paper aims to study the feasibility of the using ramp rates lower than 1 kV/s on PDIV measurement in mineral oil. Experiments were performed using test circuit complied with IEC 60270 standard. The needle–plane electrode configuration with a gap distance of 50 mm was used. Tests were carried out with the mineral oil, Nynas 4000X, with moisture content less than 10 ppm. Test voltage with ramp rate 0.25 kV/s, 0.5 kV/s, 1 kV/s and 2 kV/s were applied to the test vessel to examine PDIV value respectively. In addition to PDIV level measurement, Partial Discharge (PD) activities were also measured for 1 minute at each PDIV level. Moreover, the combine test method which is combination of ramp method and step method was applied to the test electrode system. The test results show that the usage of lower ramp rate in ramp method for PDIV level measurement produced lower PDIV level. The PDIV levels and PD activities obtained in the test using the ramp rate of 0.25 kV/s and 0.5 kV/s decreased insignificantly compared to the test results acquired from the test with ramp rate 1 kV/s. Test result comparison illustrates that the combine method is the better alternative method compared with reducing ramp rate for PDIV measurement in mineral oil.

Effect of Test Method and Needle Plane Configuration on Partial Discharge Inception Voltage Measurement of Mineral Oil based on Weibull Analysis

Abstract The discussion of test method and electrode configuration for Partial Discharge Inception Voltage (PDIV) measurement is continuously developed because the PDIV can be used as indicator to determine condition of insulating liquid. However, many researchers investigate the PDIV using different test method and electrode configurations. This paper discusses the effect of test methods and needle to plane electrode configuration on the PDIV measurement of mineral oil as insulating liquid. The mineral oil that used in experiment test was Nynas Nitro 4000x with water content less than 10 ppm. In experiment, the test circuit was set up according to IEC 60270. The first test method that was carried out in this experiment according to IEC 61294 with ramp rate of test voltage 1 kV/s until PDIV occurred. Meanwhile, a Combine Method as the second test method was used as comparative PDIV test technique for this experiment. With this combine method, the test voltage was applied to the test object with rate 1 kV/s until 70% of the PDIV value obtained from the first test method. Then the test voltage was increased in steps with 1 kV/step with step duration of 1 minute until PDIV obtained with PD charge ≥ 100 pC. The rest time between consecutive tests was 5 minutes. The needle tip radii that used as high voltage electrode were 10 μm and 20 μm, meanwhile brass plane electrode with diameter 50 mm was used as the grounded electrode. In this paper, the electric field stress of the needle to plane electrode was calculated using Finite Element (FEM) simulation with input voltage 100 volt. The test result was analyzed using Weibull distribution to calculate the Cumulative Distribution Function (CDF) and Probability Density Function (PDF) of PDIV value. The calculation results show that the test results agree with Weibull distribution.

SEM and EDX analysis of The Electrode System for Partial Discharge Inception Voltage Measurement and Arcing Test of The Mineral Oil

The aim of this paper is to describe the Scanning Electron Microscope (SEM) and the Energy Dispersive X - Ray (EDX) test results of the original and tested electrodes used for Partial Discharge Inception Voltage (PDIV) measurement, as well as for the arcing test of mineral oil. The experimental investigations were performed with the mineral oil, Nynas 4000x, with the water content not more than 10 ppm under room temperature. For PDIV test, the tungsten needle electrodes with the tip radius of 10µm, 20µm, and 40µm respectively were used as the high voltage electrode while the brass plane electrode with 75 mm diameter was used as the grounded electrode with a gap distance of 50 mm. The test circuit was set up according to IEC 60270. The test procedure was performed in accordance with IEC 61294. For the arcing test, the tungsten rod electrodes with the tip diameter of 1 mm, and 2 mm with the curvature of 0.2 mm were used as the high voltage electrode while the brass plane electrode of 75 mm diameter as the grounded electrode with the gap distance of 0.3 mm and 0.8 mm respectively. The test experiment was modified from IEC 60156. The erosion of electrodes used for the mineral oil testing was examined by SEM techniques. SE images, BSE images and EDX spectrum of the original and tested electrodes were produced. The topography, the morphology, and the EDX spectra of the examined electrodes are analyzed. From the test results, there was no evidence to show the erosion of the electrodes after they were used for PDIV and arcing test. It can also be argued that the investigated tungsten needles, rods and brass plane electrodes can be used for PDIV testing and for arcing test without the problem of erosion. In addition, carbon was the main contamination created at the surface of the tested electrodes. The development of carbon was highly possible from the degradation of mineral oil.

PDIV characteristics of twisted-pair of magnet wires with repetitive impulse voltage

Reliability of inverter-fed motors depends upon partial discharge (PD) behavior of stator windings. A new measuring system of PD inception voltage (PDIV) was developed with repetitive impulses which simulate turn-to-turn voltage of the motors. Using the system, PDIV was measured repeatedly on twisted-pairs of magnet wires. With bipolar repetitive impulses PDIV fluctuated with large scatterings in early stage and converged to stable values, while such tendency was not observed with unipolar repetitive impulses. Pre-stress condition for stable PDIV measurement was discussed from a practical point of view.

Partial-discharge-inception testing on low-voltage motors

This is a review of one manufacturer's efforts toward testing National Electrical Manufacturers Association (NEMA) low-voltage motor insulation for compatibility with adjustable-speed drives (ASDs). Partial-discharge-inception-voltage (PDIV) measurements were selected as a tool to evaluate the future performance of the stator insulation system to resist deterioration by the drives. PDIV measurement is explained in terms of procedure and accuracy. Data are presented from tests made on motors from several prominent manufacturers.