A wireless system for monitoring leakage current in electrical substation equipment

In this paper, the design and the development of a remote system for continuous monitoring of leakage currents and ground currents in high voltage electrical substations are proposed. Based on wireless local area network technology, the system can be used to monitor continuously a variety of plants within the substation and has low power consumption with inbuilt overvoltage protection. It consists of a transmitter module equipped with a data acquisition (DAQ) system connected to leakage current and voltage sensors, and a receiver module connected to a remote controller for data processing and storage. The principle of operation and the characteristics of the various components of the system are described. Validation tests have been used to verify its performance in three different test situations: A) laboratory monitoring of the leakage current and voltage of a distribution surge arrester; B) laboratory measurement of the leakage current of an outdoor insulator; and C) field monitoring of the earth current and potential rise of high-voltage tower. The measured results are in close agreement with those recorded directly through a DAQ card with fiber-optic and coaxial cable connected systems. Data processing is carried out at the receiving end so that the monitored parameter is displayed continuously or at specified time intervals. The operation of the system has been tested and proved resilient under high-frequency interference signals such as those generated by corona and surface discharges

Statistical Study of Impulse Corona Inception Parameters on Line Conductors

Laboratory tests on corona on line conductors of cylindrical cross-section have provided charge measurements and surface field data for negative corona resulting from double-exponential and oscillatory impulses. The charge measurements show that minimum corona charge is injected for impulse front times intermediate between the standard lightning and switching impulse shapes. This result is associated with the interdependence of the corona charge and the statistical time lag of corona inception and with the time required to clear the corona space charge. Time lag effects are simulated by applying critical volume theory to line conductor geometry. The corona space-charge field reduction is quantified by the electric field measurements using a cylindrical field filter

A Survey on the Potential of CF3I Gas as an Alternative for SF6

Sulphur hexafluoride (SF6) has been widely used as an insulator in gas-insulated switchgear (GIS) applications. But due to the fact that it is a greenhouse gas, many researchers have been trying to find alternative solutions for it. Furthermore, SF6 produces highly toxic and corrosive substances when it is subjected to electrical discharges. Trifluoroiodomethane (CF3I) has recently been regarded as a candidate for replacing SF6. CF3I has been used as a fire suppressor and now many investigations have been carried out throughout the world to assess its capability in high voltage applications. This paper surveys this previous work and identifies some of the properties which are relevant to high voltage applications

Transient electromagnetic field radiated by grounding systems caused by lightning strike in a dissipative half-space

In this work, a method is proposed for the calculation of the electromagnetic field radiated by a grounding system in a semi-infinite dissipative medium subjected to a current excitation generated by the lightning strike. The assessment of the induced current distribution on the grounding system due to a transient excitation is obtained by solving Pocklington’s equation using the method of moments. A new method for the calculation of the transient electromagnetic field following the injection of a lightning current or short circuit is also developed. This method is based on the concept of the hertzian dipoles and the asymptotic expansion of a single dipole. A MATLAB computer program has been developed for the determination of the induced currents. The program is validated by comparing its results with those obtained with the commercial software NEC 4

Experimental investigation of high frequency and transient performance of earth rod systems

The high-frequency performance of vertical earth rods is important for designing earthing systems and lightning protection systems. In this work, experimental investigations on the high-frequency and impulse response of vertical earth rods with horizontal electrode enhancements are described. The rod electrode systems are installed at the Cardiff University outdoor earthing test facility and variable frequency tests were carried over the range 50 Hz–10 MHz. In addition, a low voltage impulse generator was used to inject impulse current of variable magnitude and shape into the electrode under test. The application of ‘4-point cross’ and ‘8-point star’ enhancements to single-rod electrodes have not only demonstrated the expected reduction of low frequency earth resistance but have also helped with a reduction in impedance at higher frequencies. Such enhancements may produce a greater overall benefit compared with extending the length of the rod only. Numerical simulations of the experimental setups agree quite well with test results over a low frequency range but more significant differences are seen at higher frequencies