Authored by: Alicia Valero Masa, Jean-Claude Maun, Stefan Werben
ABSTRACT
High Impedance Fault (HIF) detection is increasingly a concern of distribution network protection engineers. Practical methods to deal with HIFs are in great demand in the USA, where HIFs are not detected by conventional protection devices. The lack of a globally accepted description of HIFs is a difficulty for HIF detection. In the effort to understand and explain HIFs, we have carried out a theoretical study, simulations, laboratory tests, and studied field recordings. To study the influence of factors affecting HIFs, we have developed an Alternative Transients Program (ATP) simulation model and designed laboratory tests. HIF field recordings provided by Iberdrola Distribución Eléctrica S.A.U. validate the findings. In this paper, we present a HIF characterization to improve HIF detection. This accurate characterization of HIFs allows us to develop a pattern recognition method to detect HIFs.
INTRODUCTION
Power system protection must cope with new requirements of clients. Nowadays, methods to deal with faults that are not detectable by conventional devices are in great demand. High Impedance Faults (HIFs) are one of those faults. Although important improvements have been made in the last two decades [2] [6] [7], HIF detection is still a challenge for protection engineers. This paper presents a procedure to characterize and detect HIFs.
Power system protection must cope with new requirements of clients. Nowadays, methods to deal with faults that are not detectable by conventional devices are in great demand. High Impedance Faults (HIFs) are one of those faults. Although important improvements have been made in the last two decades [2] [6] [7], HIF detection is still a challenge for protection engineers. This paper presents a procedure to characterize and detect HIFs.
A HIF occurs when an energized conductor makes an undesired contact with a quasi-insulating object, such as a tree or the ground. This contact restricts the flow of the fault current to a very low level, from a few mA up to 75A [3]. The HIF current may be undetectable by conventional overcurrent devices. A practical and effective solution for HIF detection is required, as HIFs represent a public security hazard and risk of fire. The difficulty of detecting HIFs depends on some network aspects, such as the neutral grounding system and the load connectivity. The typical network configuration in the USA illustrates the worst potential situation: multiple solidly grounded systems supplying loads by single-phase transformers [8]. In these networks the neutral current under normal conditions may be higher than the current caused by HIFs, so overcurrent protection relays are not suitable for detecting HIFs.
CONCLUSION
HIF detection is still a challenge for protection engineers. An effective solution is required due to the public and property security hazard involved in HIFs. The difficulty of HIF detection depends on the configuration of the power distribution network. The typical configuration in USA is especially unfavorable due to two practices: the use of multiple grounding and the installation of single-phase distribution transformers. These practices result in neutral protection devices with low sensitivity, which are inadequate to measure HIF currents. This paper presents a proposal to develop a functional HIF detection algorithm based on a comprehensive study of the characteristics of such faults.
HIF detection is still a challenge for protection engineers. An effective solution is required due to the public and property security hazard involved in HIFs. The difficulty of HIF detection depends on the configuration of the power distribution network. The typical configuration in USA is especially unfavorable due to two practices: the use of multiple grounding and the installation of single-phase distribution transformers. These practices result in neutral protection devices with low sensitivity, which are inadequate to measure HIF currents. This paper presents a proposal to develop a functional HIF detection algorithm based on a comprehensive study of the characteristics of such faults.
Understanding and characterizing HIFs is the first challenge. A complete study consisting of simulations, laboratory tests and analysis of field recordings enables us to faithfully describe HIFs. Once a reliable and accurate characterization is obtained, recognizing HIFs is possible. At the present we are working in the search of indicators of HIFs.Those indicators are quantitative or qualitative variables that reveal the present of distinguishing characteristics of HIF in the current, such as the dynamic behavior and the randomness.
Nevertheless, HIF detection involves not only identifying the fault but also distinguishing between HIFs and critical loads. For that reason, the HIF detection research will not be accomplished until obtaining and processing a critical load database and determining a differentiation criterion. The faithful description of HIFs is the basis of our research towards a reliable HIF detection method.
Comments
Post a Comment