Power Frequency Test Research Articles

Research on Traveling Wave Detection Performance Based on Optical Voltage Transformer

Traditional transformers cannot effectively transmit high-frequency traveling wave signals, which leads to the fact that traditional voltage transformers cannot fully reflect the panoramic information of fault traveling waves and ensure fault location accuracy. This paper mainly analyzes the working principle of optical voltage transformers. The Jones matrix models the optical path system and its optical components, and the output model of the optical path system is obtained. The principle of photoelectric signal conversion is analyzed. The test principle, experimental method, and data results are studied and analyzed by power frequency, withstand voltage, lightning impulse, and arc tests. The transmission effect of fault traveling wave signal is verified, which provides the theoretical and experimental basis for the fault location of the distribution network.

The Possibility of Insulation Level Reduction on 110 kV Overhead Line with Built-in Post Insulators Using Line Surge Arresters

Installation of line surge arresters (LSA) on overhead lines is normally accomplished with aim of line performance improvement. Co-ordination insulation procedure carried out during the line design in most cases doesn't take into account a suppression of overvoltages by using any overvoltage limiting devices. The decision supported by poor line performance to install LSA is usually made later. The reduction of overvoltage level depends mainly on the number of LSA installed, but in any case it is considerable. It means that insulation regarding dielectric strength might this way be over dimensioned. This fact could be considered for reduction of phase-to-ground and phase-to-phase distances, which lead to greater level of line compaction. This is of the most importance for lines with post insulators, since shorter insulators could be used and consequently narrower right of way achieved. Our target was to investigate the possibility of reducing lightning overvoltages by using LSA’s attached parallel to the insulators. For the analyses purpose we implemented a mathematical model of a single-system 110 kV compact overhead line. The Sigma Slp software was used for computer simulations. The line was investigated from the perspective of lightning over-voltages as they are the factors the most severely stressing the insulation. We focused to lightning strikes at a tower top for the case of single-phase (C) LSA installation configuration. The main influencing parameters were varied such as lightning current, surge shape and tower earthing resistance according to their most probable values to obtain overvoltage properties. We concluded, that adoption of LSA’s does not only reduce the overvoltage amplitude in that phase but also changes its shape, which has to be taken into account for test impulses generation. The physical model of wooden pole with composite line post insulators was built for testing in high-voltage laboratory. Power frequency and impulse tests were performed on insulators (phase-to-ground) and between phase conductors (phase-to-phase) in dry and wet conditions when necessary. Besides standard also non-standard impulse shape tests were accomplished to obtain withstand voltages for different arching distances. Based on our comparison with the simulation results we concluded that - speaking in terms of lightning overvoltages - it is possible to use insulators for the insulation level Um = 72,5 kV (140/325 kV), if LSA’s in phases A, B and C would be installed. To verify the conclusion in all other respects, further analyses are needed.

Breakdown Characteristics of Long Air Gap at Different Frequency Based on Series Resonance

In today’s rapid economic development, with the development of science and technology, higher requirements have been put forward in the economic operation of the system. This requires various departments to make more reasonable use of existing energy and equipment, and to ensure quality. Meet all aspects of supply with more energy-saving and more economical operation methods. Therefore, more and more attention has been paid to the research on the method of predicting the breakdown voltage of the air gap. Although domestic and foreign scholars have used power frequency test transformers to carry out a large number of long air gap experimental researches, the research on the breakdown voltage of long air gaps based on the principle of vector machines is still blank. In this paper, a vector machine test device is used to study the breakdown discharge characteristics of a long air gap at two frequencies of 229Hz and 68Hz. Comparing the test phenomena at different frequencies, it is found that the initial discharge voltage of the streamer corona is lower when the frequency is 229Hz, and the discharge phenomenon before breakdown is more intense, and the quality factor will be significantly reduced due to the violent discharge. At the same time, under the same test conditions, the breakdown voltage at 229Hz is lower than that at 68Hz, and as the air gap increases, the difference between the two is greater. The experimental results show that the breakdown voltage of the long air gap based on the vector machine is different when the frequency is different, and the safety distance of the field withstand voltage test should be evaluated according to the experimental data under the vector machine condition to ensure the safety of the test.

Lightning Protection of the Explosion Airflow Arc-Quenching Gap for 110 kV Transmission Lines

With the increase in the voltage level and number of transmission lines, the probability of lightning strikes on transmission lines is significantly increased, while lightning breakage accidents occur frequently. Therefore, an explosion airflow arc-quenching gap for 110 kV transmission lines was developed based on the idea of rapid extinction. A mathematical model of the detonation wave based on the CJ (Chapman–Jouget) detonation wave theory was developed to calculate the detonation air pressure and analyze its influencing factors. ANSYS software and the magnetohydrodynamic (MHD) model were used to simulate the process of detonation airflow coupled with an arc, and the simulation results indicated that the power frequency arc was evidently suppressed with the influence of airflow, which can effectively prevent arcing. A combined impulse and power frequency test and arc-quenching tests were performed to verify the effectiveness of the arc-quenching gap. The results of the combined test indicated that the arc burn time was 0.1 ms and that no power frequency continuous current was displayed. The results ensured the accuracy of the simulation model. The results of the arc-quenching tests proved that the explosion airflow can extinguish a power frequency arc with an amplitude of 40 kA in half of a power frequency arc cycle.

The Preliminary Design of Large-Scale High-Intensity DC and Power Frequency Magnetic Field Immunity Test Platform

The electromagnetic interference caused by the strong stray magnetic field generated by a tokamak device and its coil power supply will greatly threaten the reliable operation of electrical and electronic devices nearby, and a magnetic field immunity test is the most commonly used method to qualify the sensitive equipment and ensure the reliability of the system. Thus, building a high-intensity magnetic field immunity test platform is essential for the stable operation of a large tokamak device in the future. This article presents the preliminary design of a large-scale high-intensity magnetic field immunity test platform, including dc static test platform, dc transient test platform, and power frequency test platform. Referring to the actual magnetic field environment around the International Thermonuclear Experimental Reactor (ITER) tokamak device and its magnet power supply, the design parameters of the subplatforms are determined. Then the scheme design of the subplatforms and the integration design of the whole platform are briefly introduced. As a part of the large-scale superconductor rest facility (LSTF) in Chinese Academy of Science, Institute of Plasma Physics (ASIPP), the design takes full advantages of the other devices planned in the facility. This test platform will be the largest in the world and enable the test of various equipment under different magnetic field environments, and more importantly, play an important role in the reliable operation of China Fusion Engineering Test Reactor (CFETR) and future large tokamak devices.

Development and test of a 220 kV/1.5 kA resistive type superconducting fault current limiter

Within a collaboration of Jiangsu Zhongtian and Beijing Jiaotong University, one phase of 220 kV/1.5 kA resistive type superconducting fault current limiter (SFCL) has been developed for testing. The current limiting unit of the SFCL consists of 8 series connected modules, and each of the module is composed of 16 parallel connected bifilar coils. The used high temperature superconductor (HTS) is the 12 mm wide steel-stabilized YBCO conductor supplied by Shanghai Superconductor. The current limiting unit is assembled in a cryostat with liquid nitrogen. The device has been successfully subjected to steady-state tests, fault current limiting tests and insulation tests. According to the testing results, the SFCL passed 22 current limiting tests at various prospective fault currents between 10 and 63 kArms for a fault duration of 100 ms, and the maximum limiting resistance could be as high as 3.5 Ω. The power frequency test at 360 kVrms for 1 min and lightning impulse test at 850 kV(1.2 µs/50 µs) have been carried out according to the Chinese national standard GB 1094.3.

Insulation Design and Simulation for Three-Phase Concentric High-Temperature Superconducting Cable Under 10-kV Power System

Compared with conventional cables, the high-temperature superconducting cables have advantages in a small volume, large capacity, high current density, low losses, and environmental friendship, which brings a new power electricity transmission method for the future power grid. With the development of the important researches in high-temperature superconducting materials, many projects with superconducting cables have been applied in the power system. This paper introduced a main insulation design for three-phase concentric high-temperature superconducting cable under 10-kV power system. AC puncturing test under power frequency and lighting puncture test have been achieved.

Analysis and Optimization of Electric Field Distribution in 1200kV SF6 Insulated Power Frequency Test Transformer

With the fast development of HV and EHV underground substations in large cities, the demand and technical challenge of field insulation test for HV and EHV power transmission equipment is increasing fast also. As the traditional field insulation test equipment, oil-immersed cascaded power frequency test transformer is very difficult to face the challenges because of its large size and weight. SF6 insulated test transformer, as the new site test equipment, also needs to be designed smaller in size. As a result of the size reduction, it will increase the risk of breakdown and partial discharge. This paper introduces the electric field analysis and design optimization of a newly designed 1200kV SF6 insulated test transformer. The finite element analysis software INFOLYTICA is adopted for the electric field simulation. The simulation results demonstrated its main design of size and insulation. In some particular regions where the electric field is significantly uneven distributed, optimization design is provided.

Breakdown characteristics of CF3I-N2 gas mixtures in a needle-plate geometry

The breakdown voltages in a needle-plate geometry have been measured by 50 Hz power frequency tests for the CF3I-N2 gas mixtures (5–30% CF3I) over the gas pressure from 0.1 to 0.3 MPa. The influence of different conditions on the breakdown performance is investigated. The synergistic effect of CF3I-N2 gas mixtures is verified from the respect of breakdown voltage. Moreover, the behavior of the gas mixtures in highly divergent fields is characterized by a pressure range of corona stabilization, which can explain the relation of the breakdown strength to gas pressure and mixing ratio. A comparison to the theoretical breakdown voltages in uniform electric field shows that the breakdown strength reduces with the rising non-uniform coefficient of electric field at relatively short gap distance. Furthermore, the sensitivity of the insulating ability to divergent field is weakened by the increasing CF3I ratio.

Partial discharge characterization of cross-linked polyethylene medium voltage power cable termination defects at very low frequency (0.1 Hz) and power frequency test voltages

Most power cable faults begin as defects in the cable accessories: terminations, joints, and junctions. Poor workmanship is a common cause of the accessory faults [1], [2]. A contributing problem is that power cable accessories are sometimes conveniently assembled manually on site by subcontractors rather than by the cable or accessory manufacturers, thereby increasing the risk on compromising quality.

Study on Static and Dynamic Voltage Distribution Characteristics and Voltage Sharing Design of a 126-kV Modular Triple-Break Vacuum Circuit Breaker

The static and dynamic voltage distribution characteristics and voltage sharing design of a 126-kV modular triple-break vacuum circuit breaker (VCB) was discussed in this paper. The finite-element method and power frequency tests were used to calculate and verify the static voltage distribution ratios and distributed capacitance parameters of multi-break VCBs, respectively. A model combining the post arc current model and equivalent capacitance model was proposed for simulations of dynamic transient recovery voltage (TRV) distribution characteristics of the triple-break VCB. The simulation results indicated that besides the stray capacitances, the TRV sharing design should take the influence of residual charge (RC) into account, and the influence of RC on the TRV distribution is relevant to the differences of RC parameters among the series interrupters. Therefore, the appropriate value of grading capacitors should meet the requirement of the worst case. Based on the investigation of this paper, a 126 kV U-shaped triple-break VCB prototype with 1000 pF grading capacitors has been produced, and the successful large current breaking tests indicate the good breaking capacity and suitable voltage sharing design of the triple-break VCB.

Experimental analysis of the feasibility of CF3I/CO2 substituting SF6 as insulation medium using needle-plate electrodes

CF 3 I gas has low greenhouse effect and good insulation properties, so it can replace SF 6 gas that has high greenhouse effect. In this study, the partial discharge inception voltage (PDIV) of CF 3 I/CO 2 mixed gas is measured by power frequency test under different gas pressures, mixing ratios, and gap distances. The influence of these conditions on the partial discharge performance of CF 3 I/CO 2 mixed gas is investigated. The PDIV of the CF 3 I/CO 2 mixed gas is also comparatively analyzed with that of SF 6 /CO 2 mixed gas. The results show that the PDIV of the CF 3 I/CO 2 mixed gas is 1-1.2 times higher than that of SF 6 /CO 2 mixed gas,when the mixture ratio is between 10-30% and the gas pressure is between 0.1-0.3 MPa, which means the insulating ability of the CF 3 I/CO 2 mixed gas is better than that of the SF 6 /CO 2 mixed gas. By contrast, the PDIV of these two mixed gases exhibit similar variation trend with gas pressure when the mixing ratio is more than 20%. There is positive synergistic effect on the PDIV of CF 3 I and CO 2 . These results indicate that CF 3 I/CO 2 (20 to 30%) mixed gas may be used to replace SF 6 gas for gas-insulated equipment applications.

Electrical insulation of high voltage inductor with co-axial electrode at floating voltage

Inductive fault current limiters (FCLs) have several advantages, such as significant current limitation, immediate triggering and relatively low losses. Despite these advantages, saturated core FCLs have not been commercialized due to its large size and associated high costs. A major remaining challenge is to reduce the footprint of the device. In this paper, a solution to reduce the overall footprint is proposed and discussed. In arrangements of windings on a core in reactors such as FCLs, the core is conventionally grounded. The electrical insulation distance between high voltage winding and core can be reduced if the core is left at floating potential. This paper shows the results of the investigation carried out on the insulation of such a coil-core assembly. Two experiments were conducted. In the first, the behavior of the apparatus under high voltage conditions was assessed by performing power frequency and lightning impulse tests. In the second experiment, a low voltage test was conducted during which voltages of different frequencies and pulses with varying rise times were applied. A finite element simulation was also carried out for comparison and further investigation.

Effects of SiO2 and TiO2 Nano Fillers in Enhancing the Insulation Breakdown Strength of Epoxy Nano Composite Dielectric under Divergent Electric Fields

The proper mixing of nanoscale fillers in conventional dielectric materials leads to an enhancement in the breakdown strength and voltage endurance. In this study experimental investigations are carried out to compare the breakdown characteristics of epoxy nano-composites with that of a base epoxy resin under the influence of divergent electric fields so as to obtain inferences on its breakdown performances. This would in turn enable providing solutions to acquire more effective electrical insulation systems and explore the prospect of tapping the merits of utilizing the rapid strides made in field of fabrication of nano-dielectrics. The main objective is such studies are to enhance the electrical properties of the epoxy dielectric by employing nano-fillers such as SiO2, TiO2 etc. This research envisages the use of epoxy resin mixed with nano-fillers for ascertaining the ability of the nano-composite to be utilized as a dielectric/ insulator in power apparatus. The epoxy resin is mixed with appropriate proportion of SiO2 and TiO2 and experimentation is carried out under the influence of divergent electric fields. Classical breakdown voltage withstand tests such as AC power frequency, DC voltage, lightning impulse and switching impulse test is carried out on epoxy dielectrics (with and without nano-fillers) and the results are compared. In addition, a non-classical breakdown voltage test (high frequency high voltage) is also devised to analyze and ascertain the breakdown characteristics due to varying frequencies so as to investigate the possibility of utilizing such nano-composites in applications related to high speed switching devices.

A dielectric frequency response model to evaluate the moisture content within an oil impregnated paper condenser bushing

Increased moisture content within an oil-paper insulation system can significantly reduce its life expectancy, and for oil impregnated paper condenser type bushings, it is the most common cause of failure. Distinction between moisture contents using traditional power frequency tests of dissipation factor and capacitance can be difficult, particularly at ambient temperatures. Dielectric frequency response is becoming an established technique to measure the dissipation factor and capacitance of a bushing, but to date an accurate model to evaluate the condenser moisture content has not been presented using this technique. In this study, a dielectric frequency response bushing model is proposed and finite element method software is used to simulate the variation in dissipation factor and capacitance of a bushing with varying moisture content, as a function of frequency and temperature. The modelled results are compared with measurements reported in the literature and from the authors’ own field measurements, where a good agreement is demonstrated. It is shown that the distinction in dissipation factor between moisture contents at frequencies <0.1 Hz is in excess of ten times greater than at 50 Hz. The proposed model can be used by practitioners to evaluate moisture content within the condenser insulation and distinguish between moisture contents ranging from 0.2 to 4.0%.

Analysis of Surface Flashover of 33kV Pin Type Insulators due to Saline Pollution

Contamination-driven insulator failure is a problem that incessantly plagues distribution systems. Contamination levels can continue to grow unless abated by natural cleaning or if not taken measures to wash insulators at the distribution level in a preventative maintenance mode. In order to assess the pollution behavior, 33kV pin type insulator was selected as a sample insulator and been subjected for natural pollution at three selected localities (zone 1, 2 and 3) for considerable period. The naturally polluted insulators have been subjected for conductivity test and by which the equivalent salt deposit density (ESDD) is calculated. Subsequently, artificially contaminated insulators of different pollution severities were tested for power frequency and impulse test in the High Voltage Laboratory of University of Moratuwa. Finally, it is recommended that insulators in Zone 1 have to be treated after 8 months from the date of last treatment and those in Zone 2 & 3 to be treated after 18 months under preventive maintenance to get away from flashover. It is also recommended to review the required specific creepage distance (SCD) of insulators installed in non-polluted areas due to the fact that the current practice of insulators placement in most of the places are with SCD of 25mm/kV which is recommended for high polluted zones as per IEC regulation.

Insulation co-ordination for continuous operating voltages and temporary overvoltages

This paper presents an approach to the insulation co-ordination of electric-power installations in the scope of the continuous operating voltages and temporary overvoltages; this approach opens the possibility to calculate the necessary required withstand voltages of unit insulations for short-duration (1 min) power-frequency test voltage, with respect to continuous operating voltages and power-frequency temporary overvoltages and the necessary reliability of the operation of high-voltage power system installations.

A Consideration on Dielectric withstand test Method for Dead Tank Type High Voltage Circuit Breakers

The paper describes the necessity of adding several items on the existing standard dielectric withstand test for high voltage circuit breakers. These are supplementary chopped wave tests to check performance of ceramic grading capacitors, power frequency test to check the breakers' dielectric withstand capability with existence of metallic particles, and capacitor current switching tests after multiple interruptions of full short circuit current.

Experience with Field Testing of Consolidated Edison 49th Street 345 kV Gas Insulated Substation

Compact, gas insulated stations have many advantages over conventional stations, but pose a unique problem in the conduct of field acceptance tests. This paper describes a solution to the field test problem using metal enclosed test equipment. Power frequency tests at 500 kV, requiring 3350 KVA, and dc tests at 320 kV were successfully carried out in the indoor 49th Street switching station in New York City using this equipment.

The Effects of Pollution and Surface Discharges on the Impulse Strength of Line Insulation

The effect of surface discharges on the ability of polluted insulators to withstand lightning and switching surges has long been a matter of conjecture. This paper describes combined power frequency and impulse voltage tests on 66 kV and 132 kV insulator strings. The tests have shown that an appreciable lowering of both lightning and switching surge strength may occur in the presence of pollution layers. The worst lowering of impulse strength (about 50%) has been found in cases where drying of the pollution has reduced the leakage current almost to zero by the production of extensive dry bands on the insulator surface.