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Corona discharge is an inherent and unique phenomenon in the high voltage transmission lines. When an alternating current of high and very high potential difference is applied to the conductors whose spacing is large as compared to their diameter than the atmospheric air surrounding the wires is subjected to electro-statìc stresses.
Much more attention be given to this job as the reliability of service depends on proper methods of laying, attachment fittings i.e. cable joints, joint boxes, connection etc.
In this topic, you study the Difference between AC and DC Transmission.
The main types of insulators used for overhead lines are
Now the turning of this century has comprehensively switching on to the use of sulphur Hexafluoride (SF6) circuit breakers instead of OCB and ABCBs, etc.
Generator is the most important and costly equipment in power system. The cost is high because the alternator unit is accompanied by prime mover, excitation system, voltage regulator, cooling system etc. The protection system provided should therefore becomes elaborate and complex. As soon as the fault develops on an alternator, it should be immediately disconnected from the other generating plant to avoid the faulty machine from being fed by other sources. Following Table 1 shows abnormal conditions (faults) and protection schemes employed for the alternator.
Buchholz Relay is a gas actuated relay. It is connected to the conservator as shown in Fig. 1.
Fig. 1: Location of Buchholz Relay.
A resistance ‘R’ may be of metal or maybe liquid resistance (used 66 kV or above). Metal resistance is easy for maintenance but being slightly inductive the effect may create breakdown of insulation due to lightning.
Sudden rise in the voltage for a very short period on the power system is known as a voltage surge or transient voltage. When lightning strucks a line; the surge rushes along the line just as flood of water along a narrow valley.
Earthing screens and ground wires are suggested for protection against direct lightning strokes but they are unable to protect the equipment against travelling waves. The lightning arresters or surge diverters take care of the terminal equipments against such surges.