Condition Assessment of Metal Oxide Surge Arrester Based on Multi-Layer SVM Classifier

Metal Oxide Surge Arrester (MOSA) does not require any ordinary maintenance. But MOSA is get affected from ageing due to the effect of discharging impulse currents, uneven heating and internal partial discharges. A leading cause of deterioration is ingress of moisture. The degradation of MOSA also correlated with the ageing level of the arrester. This is called degradation under surge. The ageing level with the degradation of MO surge arrester or the leakage current of the surge arrester is related to each other. The leakage current is directly proportional to the ageing level. If the ageing level is raise, the leakage current also will increase. So, various methods for determination of the condition of ZnO surge arrester by means of measurement of the arrester leakage current are discussed. A MSCM method, which is based on leakage current of the surge arrester presented. The measuring instrument Leakage Current Monitor is also discussed.

Lightning surge arresters are key components for the protection and reliability of power systems. During service, surge arresters are aged by deteriorating their properties. It is important to monitor conditions periodically in order to avoid failures of power apparatus. This study proposes an online-based condition monitoring method for surge arresters using principal component analysis (PCA), support vector machine (SVM) and thermal image processing of infrared images captured from 46 energized 33kV lightning surge arresters belonging to Ceylon Electricity Board (CEB). Field-energized aged arresters (18 samples), laboratory-tested aged arresters (27 samples) and a brand-new arrester were taken for the investigation. The main focus was to build a model to identify the healthiness of the lightning surge arresters based on their temperature profiles. Leakage current, insulation resistance and finite element method (FEM) based simulations were considered to validate the healthiness of the arresters. Using this model, it can be visualized whether the surge arrester condition is acceptable, only using a single thermal image of the arrester as an input. Even though, an arrester islocated in good condition region of the proposed model, the distance to the decision boundary indicates how close that arrester to be in unhealthy region.

Zinc oxide (ZnO) gapless surge arresters are used for lightning and overvoltage protection in electrical power system. The leakage current monitoring is one of the well known method for the ZnO surge arrester ageing level determination. However, the ZnO leakage current is known to be dependent on the ambient temperature. This paper aims to study the effects of temperature variation due to ambient conditions on the leakage current of ZnO surge arrester. The effect of a significant increment of leakage current with an increase in temperature may result in a wrong assesment of the ageing level of the arrester. The leakage current of three 120kV rated polymeric housed ZnO surge arresters were measured in a custom made thermally insulated enclosures at varying temperatures. Up to 20% increase in the leakage current was observed with a 20°C increment above the ambient temperature. For a typical variation of ambient temperature in Malaysia in the range of between 30°C and 40°C, the corresponding changes in the leakage current can be up to 11%. The temperature does significantly affect the leakage current measurements used for monitoring of zinc oxide surge arresters. This significant change in the leakage current due to ambient temperature variation can affect the decision in assessing the condition of surge arresters during routine monitoring.

Metal Oxide Surge Arresters (MOSA) are proven to be reliable protective devices for power distribution and electrical transmission system. MOSA are subjected to electrical ageing or degradation due to constant AC conduction or transient voltages. Leakage current measured from surge arresters are used to observe its degradation and the resistive leakage component is extracted from the total to determine the health of the surge arresters. If resistive current increases, life of the surge arresters decreases. Generally, leakage current is measured using current shunts or current transformers where it's necessary to measure the applied voltage which is very hard to measure in online condition. This paper develops an easy and accurate method to separate the resistive leakage current from the total leakage current without any voltage measurements by using a technique called Modified Phase Shifted Method (MPSM) and simulated in MATLAB which enables online monitoring system and easy to apply into a device.

External insulation pollution flashover causes serious damage to the security and stability of power grid. Pollution flashover prediction is prominent in the study on external insulation. Insulator leakage current is most widely used in the pollution flashover prediction. Wet contaminant is an important precondition for pollution insulation discharge. Wet process is affected by the atmospheric environment and the hygroscopicity together. This paper analyzed the moisture absorption of insoluble substances, and chose aluminium phosphate as the strongly hygroscopic material to join the composition of artificial contaminants. The discharge test of polluted insulation was performed in constant humidity condition. The test was performed respectively in the humidity of 55%, 60%, 65%, 70%, 75% and 80%. Some leakage current characteristics were investigated to point out the influence of hygroscopicity of insoluble substances on insulator leakage current, such as current amplitude, fundamental current amplitude, 3rd harmonic current amplitude and phase. Test results show that insulator leakage current is affected by insoluble substance hygroscopicity, and extent depends on atmospheric humidity and the amount of strongly hygroscopic material. As the amount of aluminium phosphate exceeds 20% and the humidity exceeds 70%, the leakage current characteristics of aluminium phosphate sample is much different from that of normal sample. The leakage current amplitude, fundamental current amplitude and 3rd harmonic current amplitude of aluminium phosphate sample is much larger than that of normal sample and the phase is smaller. The leakage current amplitude, fundamental current amplitude, 3rd harmonic current amplitude and phase can reflect the difference of the hygroscopicity of pollution layer. Among them, the phase between fundamental current and voltage is the most sensitive to the hygroscopicity of pollution layer. The strongly hygroscopic material will absorb more moisture under a certain humidity, the dissolution of electrolyte of pollution layer will be promoted, leakage current will increase and the atmospheric humidity of discharge will be reduced.

This article presents an online diagnostics method to predict critical conditions in ceramic insulators. For this purpose, a variety of experimental tests have been conducted on different kinds of ceramic insulators under different environmental conditions in order to analyze their leakage current. Fast Fourier transform analysis of leakage currents shows a strong correlation between the ratio of the third to fifth harmonic amplitude regarding occurrence of critical conditions and degree of insulator ageing. Therefore, the index of the third to fifth harmonic amplitude is utilized as the detection indicator of critical conditions in ceramic insulators. An increase in the index of the third to fifth harmonic amplitude to more than one represents a critical condition in the insulators and estimates a high probability of flashover occurrence. The obtained results have also shown the viability of the index in insulators monitoring procedures. Training the proposed index to a microprocessor powered device gives ability to the system for online diagnosis of ceramic insulator qualifications, detecting critical conditions, and predicting flashover occurrence.

To study the change rules of leakage current of long string insulators under high altitude condition, and using the current to characterize the insulators' running state and pollution level can be highly useful to prevent flashovers from happening. In this paper, waveforms the leakage current of long string insulators under high altitude condition are measured by artificial pollution tests and the amplitude-frequency characteristics of the leakage current are analyzed. The results show that with the increase of leakage current amplitude, the third harmonic content decreases, the current waveform became more sinusoidal, the phase difference between current and voltage reduces. Through the analysis of maximum leakage current of insulator strings in different salt deposit density (SDD), a linear relationship is found between the maximum leakage current and SDD, thus the insulator pollution level can be characterized with leakage current peak value. Through the analysis of leakage peak currents under different altitudes, it is found that the effects of altitude on the leakage current is the same with the influence of altitude on U50, leakage current peak becomes smaller with the increase of altitude, therefore the leakage current of different altitudes can be corrected by an index n which stands for the effect level of altitude drops on the flashover voltage.

Equipment in high voltage power systems can be protected effectively by metal oxide surge arresters. Basically two different types of surge arresters are used: surge arresters with air insulation using porcelain or polymeric housings (AIS surge arresters) and surge arresters with SF6-insulation using a metallic housing (GIS surge arresters). The probability of a failure of a GIS surge arrester shall be considerably less than for an air insulated surge arrester. Failures of GIS equipment always will result in major outages and costly corrective maintenance. Potential sources of surge arrester failures are the metal oxide (MO) resistor, insulating parts as fiber reinforced (FRP) rods and partitions and the metal enclosure. MO resistors are not allowed to show any aging and must have a high energy discharge capability. The FRP-rods must be free of partial discharges and must withstand high electrical strength. The metal enclosure must be made of high quality material as well as the manufacturing process shall be of high standard including sufficient testing and final certification. Required routine testing on the completely assembled surge arrester does not suffice rather all parts used must be routine tested in a proper way to avoid failing within the life time of more than 30 years. In case of a failure caused by overloading the destruction must be limited to the surge arrester.

A number of diagnostics are currently available to monitor the condition of metal oxide surge arresters. Very often a number of these diagnostics do not provide meaningful interpretation about the condition of arresters. The authors have experienced one such anomaly during their involvement with multipulse operating duty tests on distribution type metal oxide surge arresters. The return voltage method was found to be very sensitive and was compared to power loss measurement for such applications. The authors have recently conducted return voltage measurements on eight distribution class metal oxide arresters. The findings from this research are presented in this paper.

The metal oxide varistors are used as voltage dependent switching devices to protect high voltage equipment and also low voltage electronic devices against transient overvoltages. The performance of a ZnO surge arrester (SA) is determined by the electrical and thermal properties of metal oxide elements, insulating materials used and design features of SA. The primary consideration in applying metal oxide SA is the thermal consideration of the environment. Ambient temperature and environmental conditions directly affect the performance of internal current drawn by and energy input to the metal oxide SA. The interaction between the polluted porcelain housing and the inner varistor columns due to capacitive coupling is responsible for the temperature rise of the varistor element. Metal oxide SAs are exposed to heavy thermal and electrical stresses if the porcelain housings of the units are polluted by industrial dusts, coastal salts, etc. The first part of this paper proposes an electrical model of SA that is computer simulated for leakage current investigation and the second part presents the effect of dry band on the performance of SA and damage due to this dry band. >

A surge arrester is modeled as a simplified electrical circuit in power frequency applied voltage that consists of a capacitance branch in parallel with a nonlinear resistor. Under applied harmonic voltage, the obtained resistive current of the simplified model exhibits some deficiency, especially in its harmonic contents. This paper presents a harmonic model for metal-oxide surge arresters that can be utilized to simulate their performances under applied harmonic voltage. It has three parallel RC branches to simulate fundamental, third and fifth harmonics contents of total leakage current. Proposed and conventional models have been simulated under different applied harmonic voltages to show the capability of the proposed model. Also, real voltage and leakage current signals, which have been measured experimentally from a 20 kV metal-oxide surge arrester, have been compared with simulation results. Results show that the proposed model can simulate the performance of metal-oxide surge arresters more accurately than the conventional ones under applied harmonic voltages.

As a metal oxide surge arrester (MOSA) ages, its resistive leakage current increases with accompanying increase in the third harmonic component which is therefore widely used as an indicator of ageing. Since the system voltage may contain harmonics, principally the third, researchers have developed a technique to account for the third harmonic component of capacitive current in deriving the resistive third harmonic current from the leakage current. However, the influence of voltage harmonics on the magnitude of the resistive current has not been considered which aspect is explored in this paper. It is shown that even nominal amounts of the third, fifth, seventh and eleventh system voltage harmonics have considerable influence on the third harmonic component of arrester resistive current. In fact the third harmonic resistive current of an aged MOSA under sinusoidal voltage is comparable to that obtained with an unaged MOSA subjected to harmonic contaminated voltage.

The prominent feature of the degradation of metal oxide surge arrester is an obvious increase of the resistive current, especially its fundamental and third harmonic, so it is very important to measure the resistive current. In this paper, a new method for the measurement of the resistive current is presented. At first, the time-domain equations of the resistive current, the capacitive current and the total leakage current on the applied voltage are deduced based on the equivalent model of MOA. According to the observed data and the fitted data of the total leakage current, the least square is then used to obtain the circuit parameters of the equivalent model. By substituting these circuit parameters into the relevant time-domain equations, both the resistive current and the capacitive current are obtained. In addition, the influence of the circuit parameters, harmonic voltage and current noise on the proposed method is also studied. The simulation results show that the proposed method can extract the resistive current exactly when the applied voltage and the total leakage current are ideal. The circuit parameters, harmonic voltage and current noise have little effect on the proposed method. Moreover, the proposed method can not only obtain the resistive current and the capacitive current at the same time, but give the circuit parameters of MOA as well.

Leakage current frequency components are frequently used as a tool for surface condition monitoring on polymeric insulation material and their pollution severity. Fast Fourier Transform (FFT) is one of the methods that are applied for the analysis, but it has some limitation in non-stationary signal. This paper presents analysis of leakage current on polymeric insulation material for high voltage application in frequency domain and time-frequency representation. Tracking and erosion test (Inclined Plane Test (IPT)) complying with BS EN 60587-2007 is conducted on polymeric insulation to select a set of different leakage current patterns from capacitive, resistive and discharge. Then, the leakage current patterns are analysed in frequency domain and time-frequency representation using Fast Fourier Transform and spectrogram technique, respectively. It is found that the surface condition of polymeric insulation material state can be classified accurately by using spectrogram compared to Fast Fourier Transform.

This paper provides an overview of how CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> cleaning works on energized electrical equipment. Contaminants can significantly reduce the dielectric strength of insulating materials in the electric equipment. These contaminants can cause increased levels of leakage current to pass over dielectric materials, leading to electrical breakdown due to surface tracking. Such conditions can result in flashovers, which can damage electrical equipment and cause unplanned service outages, as well as safety concerns. Experimental procedure to test the effectiveness of CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> cleaning in reducing leakage currents due to contamination is discussed. The CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> cleaning test results show that the cleaning process can be efficient and safe in cleaning exposed insulating surfaces. The analysis of leakage currents, measured during the cleaning process, indicate that there is a significant number of short duration discharges of leakage current. The number of discharges is reduced significantly as the magnitude of the leakage current increased. The leakage current observed during the process was measured in milliampereres during the short duration discharges, and never exceeded 34mA.