Space Charge Measurement System Research Articles

Study on Space Charge Characteristics in XLPE Under DC Voltage Superimposed by Impulse Voltage

In direct current (dc) transmission lines, power cables are susceptible to the invasion of switching overvoltage or lightning overvoltage. This causes the accumulation of space charge in the insulation due to the higher transient composite electric stress. Space charge is an important factor in dielectric breakdown, especially under high electric stress. However, until now, there are few reports on space charge characteristics under the composite stresses of dc voltage and impulse voltage. In this article, a modified pulsed electroacoustic space charge measurement system used for dc voltage superimposed by impulse voltage is developed by reasonably choosing resistor and capacitor elements in the measuring system. Then, space charge characteristics in cross-linked polyethylene (XLPE) are measured under dc voltage, impulse voltage, and dc voltage superimposed by impulse voltage. The test results show that hetero-charges dominated in the XLPE bulk under a positive dc voltage, whereas homo-charge injection occurred from the semiconductor (SC) electrode under a negative dc voltage. However, a continuous impulse voltage with high amplitude can cause a large degree of homo-charge injection from both electrodes. Moreover, greater homo-charge injection appeared under the negative impulse voltage than that under the positive impulse voltage. Under a dc voltage superimposed by an impulse voltage, the superposition of voltages with the same polarities facilitated homo-charges injection from both electrodes to a greater extent than did the superposition of voltages with opposite polarities. Furthermore, regardless of the polarity of the applied dc voltage, greater space charge accumulation appeared in XLPE when a negative impulse voltage is superimposed.

A Calibration Method for Acoustic Space Charge Measurements Using Multilayer Samples.

Nowadays, the use of several methods for the measurement of space charges in dielectrics has become more relevant. The availability of different space charge measurement methods brings the necessity of calibration and characterization of measurement equipment to reach standardized measurements. In this paper, a method is presented to apply known charges at built samples which can be used for acoustic and thermal methods to compare measured values with calibration purposes. Experimental tests for validation purposes were performed in flat samples by comparison of results between a single layer and multilayer samples. Moreover, this method can be used to measure the resolution and accuracy of space charge measurement systems.

Space Charge Accumulation Characteristics in Fluorinated Insulating Material under DC High Stress

Electron beam irradiated fluorinated materials, which are used for an OSR (Optical Solar Reflector) of spacecraft have been investigated using a space charge measurement system under DC high stress. It was found that a large amount of space charge accumulated in the electron beam irradiated ethylene-tetrafluoroethylene (ETFE) and fluorinated ethylene-propylene copolymer (FEP) under DC high stress, while it was not observed in non-irradiated them. In this report, a dependence of relaxation time after the irradiation on the space charge accumulation characteristics was also studied.

Space charge observation under periodic stresses — Part 1: The simplest system and corresponding phase identification

The simplest space charge measurement system is introduced for the direct space charge observation under arbitrary periodic stresses. An essential component of the system is the frequency allocation strategy for periodic stress fa and detection source fp. This strategy is based on the modified automatic equal phase shift (AEPS) principle, in which the relationship between fa and fp can be an integral multiple and a non-integral multiple. The phase detection in the range of 0°–360° can be completed during Na cycles of periodic stress with Np detected excitation to realize phase resolution Δ' = 2π/Np. Two different allocation strategies, namely, Na = 1 for the integral multiple between fa and fp and Na > 1 for the non-integral multiple between fa and fp, can be used to realize a high-phase resolution with consideration of the available frequency range for the detected source. Phase monitoring can be realized with the discrete voltage Va(i) of periodic stress at the detection phase and with the peak voltage Vg(i) of the raw signal representing the space charge density of the ground electrode. Phase delay is also introduced between the monitoring signal and real phase to avoid phase errors, especially at a high frequency and electric field. The detection phase of the space charge can be accurately identified through the monitoring signal via the data fitting or the Hilbert transform using the base wave component acquired with the Fourier transform. However, the data processing is complex for both methods. Thus, a simple and fast identification method is presented on the basis of the characteristic sequence of the AEPS principle. Finally, the feasibility and accuracy of the proposed system are successfully verified through the direct detection of the space charge within low-density polyethylene under several practical periodic stresses, namely, AC wave at 0.01 Hz, square wave at 1 kHz, and harmonic wave at 10 kHz.

Review of space charge measurement systems: acoustic, thermal and optical methods

In the last decade, remarkable developments have concerned the methods of space charge measurement in the field of insulation systems diagnostic. In particular, methods based on acoustic and thermal phenomena have been largely used. The present review provides a broad overview on the different techniques used describing, for each of them, the working principle, the main features and the most relevant applications. Further details are provided for the Pulsed Electro-Acoustic (PEA) method, as it seems to be the most used. This article provides more details on its historical evolution, showing evidence for its technological limits and taking into consideration the advantages and drawn from the different configurations of the measuring cell. A similar approach has been used for the group of thermal methods, whereas for the optical methods only the basic working principle and latest applications are reported.

Determination of charge-trapping sites in saturated and aromatic polymers by quantum chemical calculation

We studied the trapping of positive and negative charges in the chemical structures of polymers under a high electric field using a space charge measurement system. Positive charges accumulated in low-density polyethylene (LDPE), whereas positive and negative charges accumulated in polyimide (Kapton) and also in ethylene tetrafluoroethylene (ETFE) subjected to electron beam irradiation. To determine the charge-trapping sites in the chemical structures, a quantum chemical calculation was carried out using Density Function Theory (DFT) with Gaussian 09. The relationship between the energy band and the isosurface of orbital electrons at various energy levels was obtained. A three-dimensional (3D) electrostatic potential distribution map was obtained for positively and negatively charged polymers to determine the relationship between a trapping site and the charge accumulation center in the 3D potential distribution map. Positive and negative charges in Kapton and ETFE films are trapped in trapping sites in chemical structures and the positive charges in an LDPE film are trapped in physical defects.

Space Charge Measurement System Using Sensor Array and Semiconductor Analog Switch

Real time space charge measurement systems are also required to observe the localized space charge distribution in insulating materials. Since the space charge behavior is generally transient, a real time measurement system will be also required in the two or three dimensional (2D or 3D) space charge measurement systems. A 2D sensor array PEA system has been developed. However, the number of sensors is limited by A/D converter channel, because the cost of A/D converter is expensive. So, an improved 2D space charge measurement system in lateral and thickness direction for transient space charge has been developed by using the sensor array and semiconductor analog switch unit in the PEA method.

Morphology Effects on Space Charge Characteristics of Low Density Polyethylene

Low density polyethylene (LDPE) film samples with different morphology were prepared by three kinds of annealing methods which were different in cooling rates in this study. A pulsed electro-acoustic (PEA) space charge measurement system was improved to solve the surface discharge problems for small samples applied with a high voltage. Negative direct current (DC) fields from 50 to above 220 kV/mm were applied to the samples. The influences of morphologies on space charge and space charge packet characteristics were measured by the improved high voltage withstand (HVW) PEA system. Mobility and trap depth of released charges were calculated by space charge decay. It was found that there is a different probability of space charge packet initiation under applied field from -60 to -100 kV/mm. Average velocity and mobility of the space charge packets were calculated by space charge packet dynamics. It was found that the lower cooling rate samples have higher crystallinity, more homo-charge accumulation, lower mobility and deeper trap depth. The mechanism of morphological effects on space charge phenomena have been presumed to give a plausible explanation for their inherent relationships. The morphology in the metal–dielectric interface and in the bulk is convincingly suggested to be responsible for the injection and propagation processes of space charge. A model of positive space charge initiation in LDPE samples was also suggested and analyzed. The mechanism of morphological effects and the charge injection model are well fit with the injection and propagation processes of space charge. The different effects of morphology in the metal–dielectric interface and in the bulk of polymers are stressed.

Morphology Effects on Space Charge Characteristics of Low Density Polyethylene

Low density polyethylene (LDPE) film samples with different morphology were prepared by three kinds of annealing methods which were different in cooling rates in this study. A pulsed electro-acoustic (PEA) space charge measurement system was improved to solve the surface discharge problems for small samples applied with a high voltage. Negative direct current (DC) fields from 50 to above 220 kV/mm were applied to the samples. The influences of morphologies on space charge and space charge packet characteristics were measured by the improved high voltage withstand (HVW) PEA system. Mobility and trap depth of released charges were calculated by space charge decay. It was found that there is a different probability of space charge packet initiation under applied field from -60 to -100 kV/mm. Average velocity and mobility of the space charge packets were calculated by space charge packet dynamics. It was found that the lower cooling rate samples have higher crystallinity, more homo-charge accumulation, lower mobility and deeper trap depth. The mechanism of morphological effects on space charge phenomena have been presumed to give a plausible explanation for their inherent relationships. The morphology in the metal–dielectric interface and in the bulk is convincingly suggested to be responsible for the injection and propagation processes of space charge. A model of positive space charge initiation in LDPE samples was also suggested and analyzed. The mechanism of morphological effects and the charge injection model are well fit with the injection and propagation processes of space charge. The different effects of morphology in the metal–dielectric interface and in the bulk of polymers are stressed.

Space charge measurement in LPDE films under temperature gradient and DC stress

Space charge profiles and field distributions in the cable bulk are strongly affected by high voltage direct current (HVDC) voltage especially with the cooperation of the temperature gradient across the cable insulation. In this paper, a modified space charge measurement system suitable for temperature gradient was designed to fulfill the temperature difference through changing the upper and lower electrodes' temperature. The effect of temperature gradient on the PEA measurement system was analyzed and the space charge waveform was recovered. Space charge profiles and field distributions in low density polyethylene (LDPE) films were measured under different temperature differences (ΔT=0-40°C), and dc stresses of 10, 30, 50, and 70 kV/mm, respectively. The results show that the increasing temperature difference as well as the applied stress results in a more enhanced field at the low temperature side of sample. Along with the poling time, the enhanced field is reduced due to the injection of homocharges from the electrode under high electrical stress.

プリント配線板用絶縁材料の劣化試験中における内部電荷挙動の観測

The internal charge behaviour of insulation layers of printed circuit boards is discussed. Internal charges due to ion impurities can move under adc electric field, and the internal electric field is determined by the charges. The charge behaviour is strongly influenced by temperature and humidity. We have newly developed an in-situ space charge measurement system that can measure the space charge profiles in an environmental chamber at 85°C and 85%. Larger levels of internal charge were observed at higher humidity, and the electric fields near the electrodes were increased. The in-situ space charge measurement system should contribute to the study of ageing phenomena of insulation layers of PCBs.

In-Situ Space Charge Measurement System for Space Environment Monitoring

An in-situ, internal space charge measurement system for dielectric materials under irradiation has been developed by using the pulsed electroacoustic (PEA) method. This system can observe space charge profiles in dielectric materials under irradiation, and was applied to an irradiation chamber at the Office National d'Etudes et de Recherches Mrospatiales, Centre de Toulouse (ONERA-CERT), supported by Centre National d'Etudes Spatiales (CNES). Space charge profiles in a several kinds of polymeric materials were clearly observed under and after electron beam irradiations. Negative charges accumulated at the position corresponding to the energy of the electron beam in all the specimens. The in-situ observation of the internal space charge behaviour can give valuable information for the investigation of charging and discharging phenomena and of ageing mechanisms of dielectric materials used in the space.

Innovative PEA space charge measurement systems for industrial applications

This article introduces new space charge measurement systems developed in Japan using the pulsed electroacoustics (PEA) method. The new methods include two types of 3-D systems, two types of transient systems for extremely high or low temperature, a small PEA unit for a portable system, and a mountable PEA unit that can be applied to another facility, such as a vacuum chamber. These new PEA systems should expand the applicable research field.

High repetition rate PEA system for in-situ space charge measurement during breakdown tests

In order to investigate transient space charge phenomena, it is essential that the space charge profile be observed at a high repetition rate. We have developed a new space charge measurement system using the pulsed electroacoustic (PEA) method, which can measure the space charge profiles every 10 /spl mu/s. It employs the most recent digitising oscilloscope model and a semiconductor switch. The effect of prestressing on impulse breakdown voltage of a low-density polyethylene sheet was investigated by using the new system. Experimental results suggest that positive charge injection was dominant immediately before the breakdown, and charge injection during the prestressing causes distortion of the electric field near the electrode, and enhances the subsequent charge injection due to the impulse voltage.

Portable space charge measurement system using the pulsed electrostatic method

The pulsed electroacoustic (PEA) method is used to measure space charge distributions in insulating materials. A high-resolution PEA measurement system and signal procedure has been discussed in previous papers. Since the signal procedure is necessary for high-resolution measurement, the system must include a computer. In this paper, a new PEA system without signal processing is introduced. In order to eliminate the inevitable signal distortion of the conventional PEA method, the new system employs a new voltage waveform generator, one that is different from the very narrow pulse generator used in conventional PEA systems. Using the new waveform, designed based on the impulse response of the measurement system; the output signal can show the space charge distribution directly, without the need to conduct deconvolution. Thus, space charge distributions can be measured on site, such as in a factory, with a portable oscilloscope. The spatial resolution of the space charge measurement of the system is 10 /spl mu/m, which is the same as that of conventional PEA systems. Such a portable PEA system can contribute to various industrial applications.

Three-dimensional space-charge measurement in a dielectric using the acoustic lens and PWP method

A three-dimensional space-charge measurement system using the acoustic lens and PWP method has been developed. The resolutions on the x-y plane and in the z direction of this system are about and m respectively. It takes about 3 s for each sample position and 130 min for positions on the x-y plane for a mm specimen. This speed is much higher than that of the three-dimensional space-charge measurement system using the PEA method. Although the resolutions of this system on the x-y plane and along the z direction are not high, the three-dimensional charge profile of an electron-beam-irradiated PMMA specimen is successfully constructed.