The laser current transformer for EHV power transmission lines
Abstract
A current measuring device applicable to an extra-high voltage power transmission line higher than 500 kV is proposed with preliminary experimental results. It obtains the instantaneous magnetic field ajacent to a transmission wire by measuring the angle of Faraday rotation of a laser beam in a flint glass rod. The laser beam is transmitted and analyzed at a ground potential site, and in the energized part this device has neither insulated conductors nor active elements. An experimental laser current transformer yielded a sensitivity of 66 mV per 100 A and good linearity. Various sources of error and modifications are discussed.
Development of the laser current transformer for the extra-high-voltage power transmission lines
Abstract
Further developments and experiments of the laser current transformer for extra-high-voltage power transmission lines are described. A developmental model for reproduction of a large current waveform of extra-high-voltage is constructed by using a 6328-Å gas laser beam and a flint glass rod fixed on the top of 30-cm-diameter supporting insulators. It was tested at the Shiobara Laboratory of the Central Research Institute of the Electric Power Industry. Experiments under large current and/or high-voltage conditions of a 50-Hz continuous and impulse current basis reveal that the transformer will perform its functions satisfactorily in an extra-high-voltage line. A microwave current transformer (under development in Japan), which uses a Faraday rotation of a microwave instead of a laser beam for measuring a current of an extra-high-voltage wire, is compared with the laser current transformer.
Design and application of a compatible clamping fixture for current transformers auto-testing line
Abstract
This paper presents a compatible clamping fixture for metering current transformers auto-testing line. As the transfer carrier for metering current transformers, the fixture can be used with the transmission line and manipulator to achieve the fixation, transfer flow, grounding protection and other functions. With special design of the holding mechanism, transmission base and information carrier, the fixture obtains better reliability for fixation, grounding and safer transmission of the metering transformers.
A hybrid method for current transformer saturation detection and compensation in smart grid
Abstract
A new hybrid method for current transformer (CT) saturation detection and compensation is proposed to solve the problem that the large fault current can saturate the CT in smart grid. The proposed method uses the differential equation after digital filtering to detect the saturation start time and has a strong anti-noise capability. After the saturation start time is detected, the current integral is used to detect the saturation end time, so that the saturation interval is fully determined. Finally, the improved least square method is used to compensate for the distorted saturation current. It calculates the sine component and the DC attenuation component separately. Simulation studies under different saturation conditions are performed using PSCAD, and the simulation results demonstrate the effectiveness of the proposed method.
Leakage current and partial discharge characteristics of epoxy resin material of distribution current transformer in salt fog pollutant condition
Abstract
Outdoor Distribution Transformer is frequently used for 20 kV Medium Voltage Overhead Line. The main material for the isolator is the epoxy resin mixed with white cement (talk haichen). In outdoor use, resin epoxy material experiences isolation aging due to influences from various environment condition (pollutant and humidity). In this paper, results of partial discharge (PD) measurement testing of the epoxy resin material is presented. The ability of pollutant to absorb humidity very much affect PD maximum content. In wet condition (95% RH), the best white cement filler is 75% of the weight for 4.6 mS and 36 mS/cm conductivity, while for 24 mS/cm conductivity, the best white cement filler composition is 25% of the weight. The results of the epoxy resin material current leakage testing show that the increase in current leakage is very much affected by the environmental condition (humidity and pollutant). In wet condition (95% RH), the dry band phenomenon is seen in the surface leakage current increase fluctuation. The flash over condition frequently happens in 30 kV testing voltage for 36 mS/cm conductivity.
Overvoltage protection procedures for high frequency high voltage transformers
Abstract
Parasitic elements, as leakage inductance and winding capacitance are present in all transformers. If such elements will or won't play a significant role in the transformer's operation depends on the specific application. In high-voltage devices the both cited parameters tend to be more relevant, since the isolation asks for increasing the separation between primary and secondary, while the high secondary number of turns increases the capacitance. In power electronics applications, especially if the primary voltage has squared waveform, the high order harmonics can excite the resulting resonances, producing very high primary current and secondary voltage stresses. This behavior is more relevant when the transformer operates without load, what means, without damping. This paper explores the overvoltage phenomenon and proposes different protection strategies to avoid its manifestation, depending on the transformer parameters. Experimental results validate the proposed strategies.
Multiple partial discharge source discrimination in a high voltage transformer winding
Abstract
Partial discharge (PD) analysis is an important technique for diagnosis and online monitoring of transformer insulation systems. PD within transformer windings may be due to several causes such as manufacturing defects, degradation of the primary insulation or contamination of the oil. The degradation processes occurring in dielectric insulation components can lead to development of different types of PD source [1], [2]. Multiple PD sources induced by different defects can be simultaneously present within the transformer winding. Therefore, it is necessary to develop tools to separate measurement data from multiple PD sources in order to facilitate separate PD source identification and location to allow accurate condition assessment of the winding