March 21st, 2009
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1. Short-Circuited Line – If the line is short-circuited at the receiving end, i.e., Z = 0, then the transmitted and reflected waves arc given as: The unique characteristic of the short-circuit is that voltage across it is zero. When an incident voltage wave E arrives on short-circuit, the reflected voltage wave must be -E [...]
Written by John on March 21st, 2009 with no comments.
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If a travelling wave arrives at a point where the impedance suddenly changes the wave is partly transmitted and partly reflected. Loading points, line-cable junctions and even faults constitute such discontinuities. Independent waves meeting along a line will combine in accordance with their polarity to provide different voltage and current levels at the meeting point. [...]
Written by John on March 21st, 2009 with 2 comments.
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Consider a voltage wave travelling from the supply source end towards the far end, and the progressive charging of the line capacitances will account for the associated current wave. Assume that in a very small time δt the conditions of a current I and a voltage E are established along a length δx of the [...]
Written by John on March 21st, 2009 with no comments.
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A transmission line is a distributed parameter circuit and distinguishing feature of such a circuit is its ability to support traveling waves of voltage and current. A circuit with distributed parameters has a finite velocity of electromagnetic field propagation. In such a circuit the changes in voltage and current, owing to switching and lightning do [...]
Written by John on March 21st, 2009 with no comments.
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Valve type arresters incorporate non linear resistors and are extensively used on systems, operating at high voltages. Fig 12 (i) shows the various parts of a valve type arrester. It consists of two assemblies (i) series spark gaps and (ii) non-linear resistor discs in series. The non-linear elements are connected in series with the spark [...]
Written by John on March 21st, 2009 with 1 comment.
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This type of arrester is also called ‘protector tube’ and is commonly used on system operating at voltages up to 33kV. Fig 11(i) shows the essential parts of an expulsion type lightning arrester. It essentially consists of a rod gap AA’ in series with a second gap enclosed within the fiber tube. The gap in [...]
Written by John on March 21st, 2009 with no comments.
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Fig 10 shows the multigap arrester. It consists of a series of metallic (generally alloy of zinc) cylinders insulated from one another and separated by small intervals of air gaps. The first cylinder (i.e. A) in the series is connected to the line and the others to the ground through a series resistance. The series [...]
Written by John on March 21st, 2009 with no comments.
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Fig 9 shows the horn gap arrester. It consists of a horn shaped metal rods A and B separated by a small air gap. The horns are so constructed that distance between them gradually increases towards the top as shown. The horns are mounted on porcelain insulators. One end of horn is connected to the [...]
Written by John on March 21st, 2009 with 2 comments.
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It is a very simple type of diverter and consists of two 1.5 cm rods, which are bent at right angles with a gap in between as shown in Fig 8. One rod is connected to the line circuit and the other rod is connected to earth. The distance between gap and insulator (i.e. distance [...]
Written by John on March 21st, 2009 with 1 comment.
Read more articles on Lightning and Power System and Protection against lightning and Surge Over Voltages and Switchgear&Protection.
