Equivalent fault loop in case of simultaneous failure of neutral and phase conductors for independently grounded poles.
Outdoor lighting installations are publicly accessible electrical pieces of equipment. Upon faults-to-ground, the appearance of dangerous potentials on the metal parts of such equipment exposes persons to shock hazards. This unsafe situation poses serious problems to utilities, or municipalities, or whoever operates the lighting installations. Owne...
Context in source publication
This paper presents a general overview of the principles of electric shock and the systems of protection used to prevent it in electrical installations. Although mainly built around the United Kingdom Regulations, its principles can be applied to any country. The paper first discusses electric shock and the effects of electric current on the human...
The work is dedicated to investigation of Hot Flow Anomaly (HFA), formed at the front of Earth’s bows hock. Using Interball-Tail data we estimated orientation of the current sheet that was a cause of the anomaly. From the ion energy-time spectrogram we divided the anomaly into several regions. The motional electric fields near the HFA were estimate...
In cases where the grounding system is buried in soils characterized by poor contact with the electrodes (e.g. karst and sandy terrains), the contact resistance frequently represents a dominant component of the total grounding resistance. In such cases, estimation of the grounding resistance by conventional formulas given in the literature is useless, because they do not take into account the contact resistance. An algorithm for estimating the total grounding resistance of complex grounding systems, with the contact resistance included, was developed and presented in this paper. The algorithm is applied to a grounding system of a typical 110 kV transmission line tower used in the Serbian transmission power system. Simple formulas by which the total grounding resistance of the analyzed grounding system can easily be calculated are also derived. The obtained results are validated using 3D FEM modeling and a practical method from the literature. It was shown that the total grounding resistances determined by the proposed algorithm deviate less than 4% from those obtained by FEM calculations. Since the proposed algorithm is general and can be applied to any grounding system, it represents a powerful tool for estimating the grounding resistance in an early stage of the design process.
Street lighting installations are publicly accessible electrical pieces of equipment out of the physical control of who operates/owns them. Street lighting systems are a typical case of low-voltage loads, distributed in a large area and collectively protected by the same protective device. In fault conditions, hazardous potentials may appear on the metal parts of such equipment, and expose persons to shock hazards. To reduce such risk, different solutions for the grounding are available. The Standard IEC 60364, and a current worldwide tendency, seem to encourage the use of Class II components, that is, equipment with double or reinforced insulation, for all the elements of the street light system (i.e. wiring systems, light fixtures, etc.). These authors examine possible technical alternatives in light of IEC standards, and propose to increase the safety of Class II metal poles by adopting a circuitry within lighting systems panelboards to monitor their double insulation-to-ground.
Street light systems are publicly accessible electrical pieces of equipment out of the physical control of who operates/owns them. Street lighting systems typically include low-voltage loads, distributed in a large area, and are collectively protected by the same device. Under fault conditions, hazardous potentials may appear on the metal enclosures of these systems, and expose people to shock hazards. To reduce the risk to an acceptable level, different solutions for the bonding and grounding are available. The Standard IEC 60364 and a current worldwide tendency seem to encourage the use of Class II equipment for the street light systems. Class II components, such as the wiring systems, the light fixtures, etc., have double or reinforced insulation. In this paper, these authors analyze technical alternatives to protect against indirect contact in light of the IEC standards. In order to elevate the level of safety offered by Class II metal poles, the adoption of special circuitry and bonding connections to continuously monitor the double insulation of metal poles is proposed.
The application of the residual current principle, as carried out by zero sequence current protective devices, is one of the most efficient ways to reduce the hazard of electric shock in case of the failure of equipment's basic insulation-to-ground. Highly sensitive, and regularly tested, residual current operated circuit-breakers without integral overcurrent protection devices (RCCBs) are rightfully recognized worldwide by standards and codes, as an effective means to protect persons against direct and indirect contact with energized parts by disconnecting the supply in a timely fashion. These devices are also referred to as ground fault circuit interrupters (GFCIs). The protective action of the RCCBs, though, can be nullified not only due to internal malfunctions of the device, but also due to particular ground-fault conditions. In these dangerous situations for persons, for example accidental direct contact with two parts at different potentials, the residual current flowing through the RCCB is below its residual operating value, and, therefore, it cannot trip. This hazardous circumstance exposes persons to dangerous touch voltages despite the presence of an efficient protective device, which cannot be blamed for not intervening. This paper seeks to clarify these particular fault conditions, occurring in the presence of healthy RCCBs.