The performance of overhead transmission lines is measured by the number of lightning that reach a line component and cause a flashover. Lightning Condition in AC Line: The complete design that is achieved on PSCAD is shown in the figure below, Figure 4.1: - AC system designed in PSCAD software This lightning was strike between the two substations which can be seen in above figure When such a high voltage transient travels through the line, the peak voltage of 14.5 KV is observed ��7CoF��o��F��o��F��o��F��o��F��o��s��,f�}��3�se�a͵k��h�`���}*�� INTRODUCTIONPower transmission lines are the widest part of a power system from physical point of view and the lightning is the most important natural phenomenon to disturb their normal operation. Sometimes lightning creates hazard situations and in order to protect from lightning, there are several preventive measures taken into action. Lightning Arrester or surge suppressor is the protective device used in every electric substation (small or large) which protects the substation from lightning and other electrical transients. (8) (ii) An overhead line has inductance of 1.26 mH/km and capacitance of 0.009µF/km. line failures. The physical phenomenon of lightning shows that clouds acquire charge, or at least become polarised. Since the lower part of the cloud is negatively charged, the earth is positively charged by induction. Generally, lightning strikes mostly the top of a transmission tower (shield-wire) rather than the power transmission line (phase-conductor). When lightning current hits the top of a transmission tower, it flows to the bottom of the tower and out onto ground wire. Calculated lightning shielding failure withstand levels for 110 kV, 220 kV, 330 kV and 500 kV transmission lines are only 7 kA, 12 kA, 16 kA and 27 kA respectively. To browse Academia.edu and the wider internet faster and more securely, please take a few seconds to upgrade your browser. Lightning is a phenomenon in which negative electric charges generated in a thunderstorm discharge to the ground as a result of dielectric breakdown in the air. ��7EoJ�£�MћҦ�){S��t*����)� This voltage is transient in nature. Generally, lightning strikes mostly the top of a transmission tower (shield-wire) rather than the power transmission line (phase-conductor). Lightning Analysis in a High-voltage Transmission Environment Lightning is a leading cause of outages on power utility transmission and distribution systems and the single largest cause of pow-er outages in many lightning-prone regions in the world. The Lightning stroke is a natural phenomenon and the effect of it is really unpredictable. -�E�c�=�`i�BӖ�� �V2��lg��]��B ���t}����oqhw~2�>tџ�Kl���c�Ei��������ԌY�6��ɟ��0dum������_��7���nۥ��t�K{~V|\Go��yA�v��ylZ�p�Y]�ki��t-3�_������Ĭ.��(�-�=��@~ ?�S`]q}��Ղ�Hl�v�\�+r�d����`Gv`�X�X�X��G�#xM^�7� ��������_�/�x As we know that Lightning is one of the most natural and serious cause of over voltage .So, my this paper describes about the lightning phenomena, the way it is caused and in the manner it effects the power equipments, building frames, transmission In Tanzania, lightning strikes to power lines is a common phenomenon due to the fact that transmission and distribution systems are overhead in many places and spans-over thousands of kilometres. (1)–(8)) were used, while for the generation of random numbers uniformly distributed in the interval 0–1 Eqs. 3 Lightning return stroke models for electromagnetic field calculations + Show details-Hide details p. 101 –132 (32) Return stroke models are used in the calculation of lightning-induced over-voltages in power lines because the electric and magnetic field as a function of distance and height along the line is difficult, if not impossible, to obtain experimentally. H�\�͎�@��. When lightning current hits the top of a transmission tower, it flows to the bottom of the tower and out onto ground wire. �:er�[A��n����� s�9�h0�́� s�9��p�l�� O�!���MћҠ0( Principles of Power System " Protection Against Overvoltages 24.1 Voltage Surge 24.2 Causes of Overvoltages 24.3 Internal Causes of Overvoltages 24.4 Lightning 24.5 Mechanism of Lightning Discharge, 552 552 552 552 552 Principles of Power System Protection Against Overvoltages, High Voltage Engineering Practice and Theory, Senior Professor in Electrical Engineering. You can download the paper by clicking the button above. Shielding failures cannot be … It is the main reason that endangers the safety and reliability of transmission line system. Assume the surge impedance of the line is 350 ohm. Since the level of overvoltages induced by strokes to ground is too low for transmission-level overhead lines, lightning failures can be due to strokes to either a shield wire or a phase conductor. �:�NO2$�A���,n��o�];���p�qt�k�x�=�:�S��]6+]������]_�}��Ň�}��}w�e������qx��Us;��,�64qh��{��9������?���n�tM���kt���mߤ���|Kk�=���GWN�3b�[����ñ��lQ�c��t,��5��7.;����! This … The crest of the pulse can be calculated as: V = I × Z They have then briefly explained the possible types of lightning strike that may hit the Transmission Line and the resultant phenomena such as … mplgmg January 17, 2018 Lightning Phenomena is an electric discharge in the form of spark originated in the charge cloud. When a lightning strikes the top of a transmission line tower or shield wires, electromagnetic waves propagate through the tower back and forth, increasing the voltage across insulator strings. This natural phenomenon occurs due to the negative charge which located in the lower part of the cloud. Academia.edu no longer supports Internet Explorer. Before we discuss about lightning arrester it is important to learn some basics about the lightning phenomena. Lightning overvoltage is the major cause of the transmission line interruption in Malaysia. �Ҡ0( Effect of lightning strike on electrical lines A direct lightning strike on a conductor of a power line causes extremely high voltage pulses at the strike point, which are propagated as traveling waves in either direction from the point of strike. High voltage transmission lines are the one of the most common equipment which is prone to obtain lightning. This lightning stroke on the line conductor causes impulse voltage. In the United States alone, lightning is … Figure below shows such a cloud located above an overhead transmission line. Sorry, preview is currently unavailable. For example, operating data for 500 kV lines across five provinces within the China Southern Power Grid showed that, of the 62 total trip-outs registered during one year, 87% were linked to lightning. Lighting is a common phenomenon in transmission lines because of their tall height. transmission line during lightening. The electrostatic field across the conductor produces the condition of potential gradient. Mechanism of Lightning Stroke Lightning phenomenon is the discharge of the cloud to the ground. A transmission line having a grounding wire was considered, thus: for backflashover equations (Eqs. Estimate the voltage produced at the point of stroke on the transmission line. Lightning overvoltage is caused mainly by lightning discharging on transmission line towers, from strikes to shield-wire or to phase-conductor. Generally, lightning strikes mostly the top of a transmission tower (shield-wire) rather than the power transmission line (phase-conductor).
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