Gábor Göcsei

Extra low frequency electric and magnetic fields during live-line maintenance

Nowadays different live-line maintenance methods are widely applied because of their economic and technical benefits. The different valid regulations are not always strict enough to guarantee the proper safety of the workers. In these regulations the criteria of the investigation is the shielding of the electric field. The proper way to shield electric field is wellknown: all the conductive clothing applied on high voltage live-line maintenance follow the principle of a Faraday cage. Although this principle seems theoretically easy, in practice many of conductive clothing cannot guarantee the proper electric shielding during the work. It is necessary to compare different conductive clothing to determine which construction is the most effective to protect the worker against electric field [1-4]. Another important thing is the proper shielding of extra low frequency magnetic field. Besides the electric field, this field is present during different live-line works as well. The long-term health effects of this magnetic field are still unexplained and there is not any effective practical way yet to shield it. Laboratory measurements and simulations are needed to investigate the magnetic field inside the different types of conductive clothing as a function of current flowing through the conductors near the live-line workers. The topic is practical and up-to-date: it is essential to minimize the risk on the workers during any type of work, especially during live-line maintenance. It is not acceptable to use any live-line methods without any effective shielding, if the loading current generates higher magnetic field than the limits of the valid regulations.

Shielding efficiency of conductive clothing during live-line maintenance

Nowadays live-line maintenance (LLM) is one of the most common methods to repair and maintain energized elements of the power grid. The main advantage of this technique that it represents a balance between technical and economic factors: no consumer disturbance is needed, there is not any service outage caused and losses can be kept as low as possible. Because of these reasons different live-line methods are becoming more and more popular on all voltage levels. Special techniques are available for low, middle and high voltage grids. On high voltage levels “barehand method” is widely applied worldwide. The main principle of this method is an enclosed metal surface around the worker acting as a Faraday cage. Inside an ideal Faraday-cage electric field is zero from outer source. The efficiency of a clothing mainly depends on the size of holes (so called “Faraday-holes”) on the surface. A proper face mesh can guarantee the safety of the live-line worker. Calculations, simulations and measurements in the High Voltage Laboratory of Budapest University of Technology and Economics have proved that poor, coarse or missing face shield decreases the efficiency by the increase of body current.

Health effects of magnetic fields during live-line maintenance

Based on the latest researches and guidelines of International Commission on Non-Ionizing Radiation Protection (ICNIRP) extra-low frequency (ELF) electric and magnetic fields have several short-term and long-term health effects. The short-term effects of these fields is detectable, but the long-term effects are mostly unknown - results of epidemiological investigations are available only. Basically electric fields are determined by the voltage of an equipment and magnetic fields are generated by currents flowing through the conductors. In case of high voltage (HV) live-line maintenance (LLM) both high voltage levels and high currents could endanger the safety of the worker. Electric fields can be easily shielded by a conductive clothing based on the principle of the Faraday-cage, but only properly designed and manufactured clothing can guarantee the required efficiency. This principle of shielding electric fields is not effective against magnetic fields. Results of calculations, simulations and measurements prove that in some cases induced magnetic fields in the body of the live-line worker exceed the current limits defined by ICNIRP. This risk caused by the miss of the proper protection against magnetic fields endangers the safety of the workers and is unacceptable for any period of time during any live-line method.

New challenges in live-line maintenance

In case of high voltage live-line maintenance (LLM), proper handling of issues related to electric fields is important because the high power is transmitted at high voltage levels. Conductive clothing are the most common protective equipment to shield extra low frequency (ELF) electric fields, acting as a Faraday-cage. Inspections have been executed at the High Voltage Laboratory of Budapest University of Technology and Economics regarding to the misses of the current international standards and regulations for the inspection of conductive clothing.

Adaptation of the application of portable protective air gap to the Hungarian live-line maintenance technology

The purpose of this paper is to examine the usability of portable protective air gaps in case of high voltage live-line maintenance in the Hungarian transmission network. After the examination of the characteristics of the network where the PPAG would be used, the operating range of the device has to be determined, then the gap distance has to be adjusted based on measurements with different voltage waveforms, different arrangements and regarding some other parameters affecting the sparkover characteristics. For these reasons measurements were performed in the High Voltage Laboratory (HVL) of Budapest University of Technology and Economics (BUTE); the results of the measurements were evaluated and are introduced in this paper.

Investigation of terrain effects on PPAG breakdown characteristics

The aim of this article is to present the operation and the potential benefits of the use of a portable protective air gap in the Hungarian transmission network. This equipment could extend the live work to those parts of the transmission grid, where the required clearances are currently not available according to the current national regulations. The article examines the usability of the device in the 400 kV transmission grid in Hungary and the effect of topography on the path of the selected power line.

Shielding of magnetic fields during high voltage live-line maintenance

In terms of electrical safety, electric shock prevention and arc protection are the two most common topics. In such special fields like live-line maintenance — especially at high voltage levels — some “invisible” sources of danger also occur. Long-term health effects of extra-low frequency electric and magnetic fields are mostly unknown, yet. One of the aims of electrical engineering is to keep even the occupational values of these fields below the limits during any time and type of live-line activities. Effective shielding of electric fields can be achieved by conductive clothing acting as Faraday-cages; this paper focuses on the critical points of high voltage LLM in terms of the protection against magnetic fields.

Arc protection during live-line maintenance on high voltage systems

Live-line maintenance (LLM) has special requirements for the equipment, which protects the LLM personnel from different kinds of hazards - especially in high voltage transmission systems. Conductive clothing provide protection for the primary effects of the high electric field acting as a Faraday cage. However, this kind of protection cannot guarantee the proper safety against all other possible threats. One of the potential hazards is the emitted energy of the power electric arc. Basically the extent of the emitted incident energy shall be calculated to estimate the risks related to the electric arc affecting the worker. The calculation needs a special method, which takes the consequences of the dimensional characteristic and other properties of the high-voltage network beside the characteristics of the high-current arc into account. This paper explains a method for the estimation of the emitted energy of an electric arc and a calculation method in the high-voltage system in the case of LLM in order to find out whether the existing protective materials are capable of providing proper protection for LLM personnel against the incident energy.

Failure analysis and inspection of long term behaviour of selected medium voltage equipment

In the service area of the Hungarian DSOs many of the failures of medium voltage devices are related to the lack of requirements regarding to the technical side of the procurement processes. The main aim of a research and development project executed by the High Voltage Laboratory of Budapest University of Technology and Economics was the inspection of current failure rates and typical ways of failures of composite insulators, cross-arms, surge arresters, concrete poles, conductor connectors (including live-line connectors), medium voltage fuses and rigid bird protective covers.

A new type of conductor car for high voltage live-line maintenance

Role of high voltage live-line maintenance is continuously increasing as the power market grows. Depending on the technology, various equipment is used worldwide, but the main principles of design and manufacturing have remained basically the same. To move along the conductors, so-called conductor cars are widely applied. Reparation and maintenance of conductors and their surroundings is safe and comfortable from this type of equipment: they are capable to roll on the conductors, but their applicability is usually limited to only one single section between two poles.