Influences of Transient Electromagnetic Fields on Control Cables in a Gas-Insulated Substation Due to Switching Operations Saeed Shahabi Iran University of Science and Technology Shahabi_saeed@iust.ac.ir Ahmad Gholami Iran University of Science and Technology Gholami@iust.ac.ir Roshanak Heidary Iran University of Science and Research Heydari.roshanak@gmail.com Abstract- The transient electromagnetic fields during switching operation in gas-insulated substations (GIS) have rise times of nanoseconds. These fields leak into the external environment through the discontinuities of gas-insulated modules and affect on control cables and lead to induce transient voltage in cables which result in malfunctioning of equipment. Amplitudes of the electrical and magnetic fields could be a few tens of kilovolts per meter and a few hundreds of amperes per meter according to layout of gas-insulated substations, respectively.In this paper, the induced voltage in a control cable and induced current in its sheath in a gas-insulated substation with rated voltage of 245 kilovolts were calculated. Also, the effect of cable’s length and type of cable sheath grounding on the induced current will be calculated. Index Terms -- Gas-Insulated Substation, Restrike, Electromagnetic Field, Very Fast Transient Current, Very Fast Transient Overvoltage I. INTRODUCTION Gas insulated substations (GIS) have become a major component of the power networks and they have been used with considerable success over the past 40 years. Despite their excellent performance over so many years, GIS have their own problems. The important issues of concern are very fast transient overvoltages (VFTOs) and very fast transient currents (VFTCs) due to breakdown phenomena across the contacts of a breaker during switching operations. Very fast transients (VFTs) belong to the highest frequency range of transient in power systems [1]. These transient voltages and currents with a very short rise time in the range of 4 to 7 nanoseconds radiate electromagnetic fields (EMF) during its propagation through the GIS bus section as the related frequencies are in the range of a few megahertz to about a few hundreds of megahertz. The EMF leak into external environment and cause some stress on control circuitry and secondary equipment with inducing currents on the metallic sheath of cable, and then generate voltages on central conductor of cable via transfer impedance and by a mechanism of inductive coupling between the metallic sheath termination and the central conductor of control cable [2]. In this paper, the VFTC and its frequency spectrum at various locations in the GIS for switching operation is analyzed using computer simulation methods, mainly the ATP/EMTP, which has been successfully used for circuit breaker arc simulation. The configurations such as length of high voltage buses, terminal capacitance of equipment, and multiple branches of the bus section on the source/load side of the switch are considered for the study. The electrical field around bus conductor that carries VFTC is computed. The induced voltages in a control cable and induced currents in its sheath for both-end and one-end grounding of the cable sheath have been estimated. Also, the effects of cable’s length and distance of it from the high voltage bus on the induced current have been calculated. Fig.1: Single diagram of 245 kV gas-insulated substation II. VERY FAST TRANSIENT CURRENTS (VFTCS) The significant parameters that describe the VFTC and influence on the protection of GIS controls are amplitude and frequency components of VFTC [1]. Fig.1 shows the single- line diagram related to 230/66-kV Shiraz University gas- insulated substation. The incoming line of the GIS is UPEC 2011 ∙ 46th International Universities' Power Engineering Conference ∙ 5-8th September 2011 ∙ Soest ∙ Germany ISBN 978-3-8007-3402-3 © VDE VERLAG GMBH ∙ Berlin ∙ Offenbach