Investigation of magnetic field interference in distribution substations

Pao Yue-kong Library Electronic Theses Database

Investigation of magnetic field interference in distribution substations


Author: Lam, Yim-mou
Title: Investigation of magnetic field interference in distribution substations
Degree: M.Sc.
Year: 1996
Subject: Electric substations
Magnetic fields
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Pages: iii, 113 leaves : ill. ; 30 cm
Language: English
InnoPac Record:
Abstract: Magnetic field interference is a side product of the use of electricity. With increasing awareness of the people and the proliferation in the use of electronic equipment, complaints and concerns about magnetic field interference on the potential hazards on health are increasing. Due to scarcity of lands in Hong Kong, there are many high rise buildings. Distribution substations are usually situated inside the buildings for supply electricity. The areas in the vicinity of distribution substations are notoriously the most serious affected areas. An assessment to identify the dominant source of magnetic field interference in distribution substations was made. All heavy current apparatuses were assessed. Low voltage busbars and single core cables were identified to be the culprits of magnetic field interference from distribution substations. A site verification at a selected distribution substation showed the agreement of the above. Physical layouts of LV busbars and single core cables are changing in three dimensional coordinates throughout the routes. Three dimensional magnetic field calculations complicated the problems. Based on Maxwell's equations, a mathematical model and computer program were developed to estimate the magnetic fields from current carrying conductors with three dimensional coordinates. The developed computer program is a tool to estimate and analyze magnetic fields problems. Site verification confirmed that the mathematical model and developed computer program are acceptable and satisfactory for engineering purposes. By using the computer program, parameters affecting magnetic fields from current carrying conductors were investigated. The investigation results were used to solve the magnetic field interference problems from distribution substations. There are some measures to overcome magnetic field interference problems. Pretabricated busduct and single core cables of square formations for interconnecting the transformer and user's main switchboard will greatly reduce the magnetic field generated. Screening off the substation walls, ceiling and floors by metallic sheet, mesh or grid can further mitigate magnetic fields from distribution substations. Reallocation of layout and usage of affected areas according to the distribution of magnetic fields calculated by the computer program will alleviate the magnetic field interference. Magnetic shielding and compensators for equipment can relieve the interference to magnetic field sensitive electronic equipment. Engineers can use the results and insights provided in this thesis to formulate further mitigation measures for magnetic field interferences. The computer program is a useful tool to estimate magnetic fields and to tackle magnetic field interference problems. It can evaluate the effectiveness of mitigation measures and can also be used as a teaching aid to understand the three dimensional magnetic field calculations.

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