Depolarization Current Measurements Research Articles

Effect of Nanofillers on the Polarization and Depolarization Current Characteristics of New LLDPE-NR Compound for High Voltage Application

Polymeric nanocomposites in which the nanosize fillers are evenly distributed in the polymer material attract attention as an insulating material due to their ability to enhance the materials performance properties of electrical and mechanical. For high voltage (HV) insulation application, one of the targets is to obtain new insulators with improved dielectric properties. This paper presents the outcome of an experimental study to determine the conductivity level of the linear low-density polyethylene- (LLDPE-)natural rubber (NR) compound, filled with different amount of SiO2and TiO2nanofiller by using the polarization and depolarization current (PDC) measurement technique. linear low-density polyethylene (LLDPE) and natural rubber (NR) with the ratio composition of 80 : 20 are selected as a base polymer. The experiment was conducted to find PDC pattern and conductivity variations of each of the LLDPE-NR/SiO2and LLDPE-NR/TiO2samples. The results show that the addition of SiO2filler exhibited less conductivity compared to TiO2filler with certain percentage. From the study, it can be concluded that LLDPE-NR/SiO2is a better insulator compared with LLDPE-NR/TiO2.

Evaluation of thermal stability of electro-optic polymer by thermally stimulated depolarization current measurement

The thermal relaxation process of electro-optic (EO) polymers, Disperse Red 1 (DR1)/poly(methyl methacrylate) (PMMA) guest/host polymer and side-chain copolymer DR1–PMMA (PMMA-co-DR1), was studied using thermally stimulated depolarization current (TSDC) measurement. For the guest/host polymer, two TSDC peaks were identified at temperatures of −50 °C (β-peak) and around 100 °C (α-peak) due to dipolar depolarization. It was also suggested that the α-peak is ascribed to disordering of guest DR1 molecules together with randomization of the main body of the PMMA. For the side-chain copolymer, a simple relaxation process of the side-chain DR1 was observed in contrast with the guest/host polymer. Analyzing the TSDC, we estimated the activation energy and relaxation times, and discussed the relaxation mechanisms. Results showed that the TSDC method is available for evaluating the thermal stability of EO polymer.

Faults identification of biodegradable oil-filled transformers based on polarization and depolarization current measurement (PDC) method

Polarization and depolarization current (PDC) measurements of insulation oil alone can be used for faults identification. From measurement of healthy oil conditions at different moisture levels and after faults, fault identification can be achieved by comparing the PDC pattern of an oil sample against the PDC fingerprints. Furthermore, a graph plot establishes a relationship between oil sample conductivity and moisture level as well as between oil sample's measured capacitance and moisture level. These curves can be used to evaluate the oil moisture conditions and the fault type. This paper seeks to find the PDC pattern of the biodegradable oil (Envirotemp ® FR3™) at different moisture levels and after being subjected to different types of fault: partial discharge, arcing, and overheating. The experiment was carried out in the laboratory to obtain the PDC patterns generated by the oil. Changes in the PDC pattern of biodegradable oil from its fingerprint due to the increased moisture level in the oil or because of faults that occurred to the oil sample were identified. These can help in predicting the biodegradable oil-filled transformer's condition and can give some indication of the maintenance work that should be taken on the transformer.

Role of Collagen and Inorganic Components in Electrical Polarizability of Bone

ABSTRACTHydroxyapatite (HA) has polarization capability and is able to accumulate electrical storage in bone. Experiments were conducted to measure the polarization capability of rabbit femurs. After preparing and polarizing bone samples using 2% KOH treatment (denoted 2% koh), 2% KOH and baking (2% koh+bake) and decalcification (decalcification) as well as untreated bone (untreated), stored charges were quantitatively determined using thermally stimulated depolarization current (TSDC) measurements. In TSDC spectra, untreated and 2% koh samples showed peaks at 100 and 500°C, while 2% koh+bake showed one peak at 580°C and decalcification one peak around 100°C. These evidences indicated that collagen and inorganic components play a major role in polarization of the bone at different temperature conditions.

Effect of Switching Method in Polarization and Depolarization Current (PDC) Measurement Technique

Switching method in Polarization and Depolarization Current (PDC) measurement technique is an appealing area to look at, especially in terms of its behavior over time based monitoring. Previous researches on this technique did not deliberate the effect of switching method in its measurement analysis. Most of the researchers use a conventional HV relay that acts as a switching component. This paper studies the behavior of PDC measurement results and its relationship between the types of switching methods used. It is due to the research hypothesis where different switching method produces distinctive PDC measurement results. Determination of which optimal method that suit with this technique can be made by comparing PDC measurement results; the result which analogous to the reference is considered as the finest method. Two different switching methods were applied in this research, which are HV relays and series-connected of 600V, 30A, Insulated Gate Bipolar Transistor (IGBT).

Polarization and Depolarization Current Measurement of Polymer Added with Nano-particles of Silicon Oxide For HV Insulation

Polymer nanocomposites materials have recently emerged as a dielectric and for electrical insulation. Polyethylene has long been used as extruded cable and HV insulation. Currently, this material has received significant attention because of its ability to enhance electrical insulation properties by addition of nano-filler. Polarization and Depolarization Current (PDC) measurement is an efficient and effective diagnostic technique based on time domain measurement for evaluating and condition monitoring of polymer nanocomopsite for HV insulation. Electrical conduction for polymer nanocomposites has been used widely as a tool to monitor the dielectric behaviour. This paper focuses on application of Polarization and Depolarization Current (PDC) testing method to evaluate and determine the performance of LLDPE nanocomposite for high voltage insulating material. The experiment was conducted to find PDC pattern of the material when added with nano-filler (silicon oxide) as well as to find its conductivity values at different percentage of nano- filler. PDC values and DC conductivity exhibits significant reduction with addition of nano-filler at different %wt of concentration. This was due to the decrease of initiation probability of short circuit treeing in the insulation. The PDC result shows that addition with certain percentage of nano-filler into the LLDPE based material could improve HV insulation properties of the material.

RVM versus PDC Methods for Insulations’ Conductivity and Moisture Content Monitoring

Degradation due to ageing is a major concern for the life span of high voltage insulation. In maintaining the insulation system’s performance, it is crucial to monitor the insulation condition as it contributes to the whole system’s efficiency and safety. Many diagnostic methods have been introduced, and in use for monitoring the condition of insulation. Measurement and analysis in either frequency or time domain. Condition-based monitoring (CBM) is in growing interest lately, compared to time-based monitoring due to the increasing population of aged insulators being utilized in existing power systems. Time-based monitoring has then been integrated with CBM. CBM’s ability to enhance reliability, improve safety and reduce hazard of a system has been recognized by many researchers and utilities. This paper presents the study and comparison of two time domain CBM techniques namely the polarization and depolarization current (PDC) measurement and return voltage measurement (RVM). Findings of previous researches on determining the insulator’s moisture content and conductivity by both methods were reviewed. Moisture content and conductivity affect the dielectric response of the insulation material. Thus, condition of the insulation system can be determined based on these two characteristics.

Surface charge induced enhanced crystallization on the piezoelectric sodium potassium niobate substrate

The present work demonstrates the influence of negatively charged surface on piezoelectric Li-modified sodium potassium niobate substrate in inducing the crystallization of KCl, NaCl and Na2SO4 ionic crystals from their respective aqueous solutions. The crystallization ability and morphology of the grown crystal were examined on unpoled, poled and poled as well heat-treated substrate surfaces. It has been observed that the crystallization process can be controlled by varying the surface charge density through the heat treatment of polarized substrate at different temperatures. Thermally stimulated depolarization current (TSDC) measurement suggested that the charge affecting the crystal growth and morphology is likely to be generated in the space charge region.

Induced polarized state in intentionally grown oxygen deficient KTaO3 thin films

Deliberately oxygen deficient potassium tantalate thin films were grown by RF magnetron sputtering on Si/SiO2/Ti/Pt substrates. Once they were structurally characterized, the effect of oxygen vacancies on their electric properties was addressed by measuring leakage currents, dielectric constant, electric polarization, and thermally stimulated depolarization currents. By using K2O rich KTaO3 targets and specific deposition conditions, KTaO3−δ oxygen deficient thin films with a K/Ta = 1 ratio were obtained. Room temperature X-ray diffraction patterns show that KTaO3−δ thin films are under a compressive strain of 2.3% relative to KTaO3 crystals. Leakage current results reveal the presence of a conductive mechanism, following the Poole-Frenkel formalism. Furthermore, dielectric, polarization, and depolarization current measurements yield the existence of a polarized state below Tpol ∼ 367 °C. A Cole-Cole dipolar relaxation was also ascertained apparently due to oxygen vacancies induced dipoles. After thermal annealing the films in an oxygen atmosphere at a temperature above Tpol, the aforementioned polarized state is suppressed, associated with a drastic oxygen vacancies reduction emerging from annealing process.

Drug Adsorption Property of Surfaces of Polarized Calcium Phosphate Powders

Calcium phosphate powders (hydroxyapatite, α-tricalcium phosphate, β-tricalcium phosphate, and tetracalcium phosphate) were electrically polarized by an applied dc voltage. Thermally stimulated depolarization current measurements confirmed that each calcium phosphate powder exhibited surface charges after polarization treatment. The surface adsorption of simvastatin on each powder was investigated. We observed a difference in adsorption between polarized and non-polarized powders. This difference in adsorption is due to the electrostatic force between the polarized surface and the open-ring form of simvastatin, which has a larger electrical polarity than its closed-ring form.

Fundamental electrical properties of ceramic electrets

We used thermally stimulated depolarization current and potentiometer measurements to study the fundamental electrical properties, such as the surface potential, of polarized bioceramic hydroxyapatite. We demonstrate that, under certain conditions, the surface potential attributable to several overlapping electrets is given by the algebraic sum of the surface potentials of individual electrets. This can occur when the electrets are arranged in series and the components, found by resolving the polarization vector, determine the surface potential on the electrets. In addition, we prove that the surface potential is proportional to the surface charge density attributable to the electrets, and we further prove that the electrostatic shielding is caused by surrounding the electret with a conductor or a dielectric. Potentiometer measurements, obtained for different levels of shaved electret thickness, revealed that the electric field in the electret was not uniform and was stronger nearer the inner surface of the electret, as compared to the field in the bulk of the electret.

Influence of pentavalent dopant addition to polarization and bioactivity of hydroxyapatite

Influence of pentavalent tantalum doping in bulk hydroxyapatite (HAp) ceramics has been investigated for polarizability and bioactivity. Phase analysis from X-ray diffraction measurement indicates that increasing dopant concentration decreased the amount of HAp phase and increased β-TCP and/or α-TCP phases during sintering at 1250°C in a muffle furnace. Results from thermally stimulated depolarization current (TSDC) measurements showed that doping hindered charge storage ability in HAp ceramics, and doped samples stored fewer charge compared to pure HAp. However, doping enhanced wettability of HAp samples, which was improved further due to polarization. In vitro human osteoblast cell–material interaction study revealed an increase in bioactivity due to dopant addition and polarization compared to pure HAp. This increase in bioactivity was attributed to the increase in wettability due to surface charge and dopant addition.

Effect of humidity in charge formation and transport in LDPE

Abstract Charge distribution and transport have been investigated in LDPE films with different humidity content under electric fields up to 130 MV/m. Pulsed electroacoustic measurements showed that, as water content increases, positive charge packets formation in the anode is enhanced and they propagate toward the cathode with higher transit speeds. Fits of surface potential decay measurements showed that charges in dry samples are injected directly into the volume, but the presence of moisture generates new trap centers in the surface of the material. This new trap level causes a charge accumulation on the surface, that gradually passes into the bulk. The observed behavior in development and propagation of charge packets are explained according to these results. Thermally stimulated depolarization current measurements showed a non-distributed relaxation associated to the new trap levels on the surface of the wet samples.

Preparation and X-ray diffraction, dielectric, and Mössbauer characterization of Co1 − x Ni x Cr2O4 solid solutions

Co1 − x Ni x Cr2O (0 ≤ x ≤ 1) ceramic samples have been characterized by X-ray diffraction and relative dielectric permittivity ɛ(T), loss tangent tan δ(T) (0.1–200 kHz), and thermally stimulated depolarization current (TSDC) measurements in the range 100–350 K. The samples were shown to consist of spinel solid solutions with a cubic (0 < x ≤ 0.98) or tetragonal (0.99 ≤ x < 1) structure. Increasing the Ni content of the samples from 0 to 100 at % increases their tanδ and 1/ρ by three to four orders of magnitude. The ɛ(T), tan δ(T), and TSDC of the samples with 0.2 ≤ x ≤ 0.6 have anomalies at T 1 ∼ 220 K and T 2 ∼ 240 K, which point to a transition to a polar state below T 2. Samples containing 1–4 at % 57Fe as an impurity were characterized by Mossbauer spectroscopy in the range 54–330 K and were shown to be magnetically ordered at 78 K. We conclude that the solid solutions have ferroelectric properties with a Curie temperature T 2 and magnetoelectric multiferroic properties.

Simulation Panel on Conductivity for Polarization and Depolarization Current (PDC) Measurement of Offline Monitoring Using LabVIEW

Ageing is the major problem to the life span of high voltage insulation. Thus, continuous assessment method had gained an interest recently due to the economic concern. The measurement and evaluation of the dielectric response is one of the methods to diagnose transformer insulation condition. Dielectric diagnosis through polarization and depolarization current (PDC) measurement used dielectric response in time domain to assess the insulator. This paper presents the PDC data analysis system developed using LabVIEW software. The developed user-friendly system will enable user to run the recorded PDC data to evaluate the performance of the insulator in term of its conductivity and response function. The analysis result on PDC data recorded from field run using this system also been presented in this paper. Based on the obtained result, the system developed has been successfully helping user to do analysis on PDC data by giving the PDC pattern, conductivity value and response function of the insulator tested.

Transformer Faults Classification Based on Polarization and Depolarization Current (PDC) Measurement Test Data on Mineral Oil Samples

Transformer is the main element of a power system. The insulation of transformer has to be maintained and do regular routine service in order to deliver power effectively. Recently dielectric measurement has been used for assessing the condition of oil/paper insulation. There are several nondestructive dielectric testing method for determining the conductivity and moisture content of insulation materials in a transformer. This research utilizes one of the dielectric methods which are Polarization and Depolarization Current (PDC) analysis in order to identify insulation condition of mineral oil. This paper presents the classifications of breakdown, overheating and partial discharge faults in mineral-oil insulated transformer by using PDC measurement data analysis. The classification is based on the data pattern and statistical analysis. The samples data was obtained from laboratory and from site testing. An analysis result shows that different type of faults will give different outcome to the PDC pattern and as well as statistical data. Based on the result, these three types of faults can be used to identify the insulation condition by using PDC measurement data analysis. Introduction

Effects of SiO&lt;sub&gt;2&lt;/sub&gt; and TiO&lt;sub&gt;2&lt;/sub&gt; Nanofillers on Conductivity Level of LLDPE-NR Nanocomposite HV Insulator

Polymeric nanocomposites have gained importance in the material properties to provide enhanced performances such as electrical and mechanical properties. One of the targets in this field is to obtain new materials with improved dielectric properties for High Voltage (HV) insulation application. In general, the good insulator must have low conductivity level. This paper presents the outcome of an experimental study to find the conductivity level of LLDPE-Natural Rubber (NR) compound filled with different amount of nanoparticles of SiO2 and TiO2 by using Polarization and Depolarization Current (PDC) measurement technique. PDC measurement is an efficient and effective insulator diagnostic technique based on time domain measurement to monitor the dielectric behaviour. The experiment was conducted to find PDC pattern and conductivity variations of each new sample. The results show that the addition of SiO2 filler exhibited in less conductivity compared to TiO2 filler with certain percentage. LLDPE-NR/ SiO2 can be a good insulator compared with LLDPE-NR/ TiO2.

Correlation of dielectric model parameters with experimental results based on PDC, RV and loss factor measurements for high voltage capacitors

To improve the reliability and quality of electric power systems, preventive diagnosis and regular maintenance of high voltage capacitors are required. Dielectric response measurements in both time domain and frequency domain are potential tools for assessing the condition of dielectric of high voltage capacitors. Modern measurements in time domain include polarisation and depolarisation current (PDC) and recovery voltage (RV) measurements, whereas frequency domain measurements include dielectric dissipation factor (DDF) measurements. To understand the physical behaviour due to the effect of moisture and aging, a detailed analysis of dielectric test results is required. In this paper, a detailed equivalent circuit model of the insulation system in high voltage capacitors has been given. The values of the parameter of the circuit model have been calculated from the dielectric test results. Correlation between the physical condition of the insulation and the equivalent model parameters are also presented in this paper.

Polyurethane–poly(2-hydroxyethyl methacrylate) semi-IPN–nanooxide composites

Two sets of hybrid polyurethane–poly(2-hydroxyethyl methacrylate) semi-interpenetrating polymer network–nanooxide composites with 0.25 or 3 wt% nanosilica or nanoalumina functionalised with OH, NH2 or CHCH2 groups were prepared. A combination of atomic force microscopy, infrared spectroscopy, thermally stimulated depolarisation current measurement, differential scanning calorimetry and creep rate spectroscopy analysis of the nanostructure and properties of the composites was performed. The pronounced dynamic heterogeneity and the strong impact of oxide additives, basically suppression of the dynamics and temperature-dependent increasing modulus of elasticity, were observed. The effects correlated with either interfacial interactions (for silica) or the nanostructure (for alumina). A low oxide content strongly affected the matrix due to the formation of an unusual cross-linked, via double covalent hybridisation of three components, structure of the nanocomposites.

Simplex-TSDC spectroscopy: An efficient tool to measure the relaxation time of the isothermal transient depolarization current in organic dielectrics

The temporal technique analysis by a simplex optimization method of isothermal transient depolarization current measurements (Simplex-TSDC) is presented for the study of the glass transition domain of different polymers. The advantage of the present method compared to the classical TSDC is that it gives direct results comparable to the experiment and allows a good estimate of the relaxation time close to the glass transition temperature in dielectric thin films. The present method also allows a direct determination of two relaxation times corresponding to a fast and a slow dynamics; and then confirms the heterogeneous character of the molecular relaxation dynamics.