Electrostatic Precipitators (ESPs) are one of the most commonly used air-cleaning devices. It is essential to study different configurations of collecting and discharging electrodes which leads to improving the performance of ESPs. Many studies are running projects on improving the existing models in many approaches. One area of improvement is the shape of the electrodes. This paper aims to investigate the wavy configuration of collecting electrodes with different sizes of corona electrodes in a single-stage ESP. The range of different corona radius sizes (0.07-0.6 mm) in wavy plates (WPs) are used and compared to flat plates (FPs) using the COMSOL Multiphysics simulation tool. The consequences of this work show the influence of changing the corona radius size on the electric potential distribution, fluid flow velocity distribution, electric field strength, current density distribution, space charge density distribution, and particle collection efficiency when wavy collecting electrodes are used.
In order to study the insulation state of the cable joint with dampness, and to accurately evaluate the dampness of the cable joint, this paper measured the time-frequency domain dielectric constant of the XLPE cable joint using the PDC (polarized depolarized current, PDC) method. And the K-means algorithm is adopted to analyze it. The classification and state interval division are carried out, and the damp process of the cable joint is divided into four stages. Then, the damp and aging insulation state evaluation model of the cable joint is established according to the dynamic Bayesian network, and the network parameters are determined to compare comprehensive judgment is made on the degree of dampness of cable joints. Finally, the 2-CV cross-validation of the proposed damp and aging evaluation model is carried out, and the accuracy rate is as high as 90.065%, which shows that the model has good resolution and effectiveness in evaluating the dampness of cable joints.
Partial discharges (PD) measurements provide an estimation of the severity of the insulation degradation; additionally, it is used as a unit of standardization. Up to now, only the IEC 62478 briefly mentions partial discharge measurements using electromagnetic sensors in gas-insulated substations (GIS). The IEC60270 standard provides a method for PD charge measurement when the test object approximates to a lumped element; PD in SF 6 are in the range of nanosecond, and given the GIS length, it behaves as a transmission line. This work compares different sensors (commercially available and developed by the authors) used for measuring PD charge magnitude in GIS. The sensors’ sensitivity, time resolution, and charge estimation accuracy are tested in a full-scale 420 kV GIS. A nanosecond rise time pulse was connected to the GIS through a transition cone to provide a good PD representation. The pulse was measured by electric and magnetic sensors installed in mounting holes located in different sections of the GIS, and a directional coupler was used as a reference to the injected pulse. This work demonstrates that the charge magnitude can be extracted using different sensors, harmonizing the reading from different measuring systems. The results show the possibility of a standardized method for on-line PD measurements and routine and after-installation tests.
In DC gas-insulated switchgear (DC-GIS), temperature of high-voltage busbar rises due to Joule heat, and a temperature gradient is generated in an insulating spacer. The effect of temperature gradient on charge accumulation of the spacer needs to be clarified. In this study, surface charge distribution on a disk-type downsized epoxy spacer is measured under temperature gradient and compared with the measured results under uniform temperatures. The experiments are carried out in 0.1 MPa-abs SF6 under three temperature conditions: (a) 40°C and (b) 70°C without temperature gradient, and (c) with temperature gradient, 70°C at the center and 40°C at the edge of the spacer. Surface charge density distribution on the spacer is obtained by an inverse calculation from measured surface potential using an electrostatic probe. As a result, positive charge density near the high-voltage electrode is larger when the electrode is at 70°C than when it is at 40°C, while the positive charge density away from the central electrode is larger under (C) than (a) and (b). This result indicates that charge injection from the high-temperature electrode is more significant than that from the low-temperature electrode, and charge accumulation from high-temperature electrode propagates dominantly.
In order to establish a space charge measurement method for a full-size HVDC cable joint, a two-dimensional space charge measurement of a reduced joint model was attempted. A prototype of a high sensitivity PEA scanning cell using a polymer acoustic coupler combined with a 16-channel piezoelectric sensor array has been created, and applied to a scaled joint model. A pulse voltage was applied to the shield layer of the joint maintaining the cable screen at ground potential. Deconvolution was applied to 16 waveforms to create a 2D image representing the charge distribution. The measurement result was subjected to a compensation taking the result of finite element field analysis into account. An internal charge distribution including an interfacial charge was successfully indicated as a 2D cross-sectional profile.
