lecture18 - EE 740 Professor Ali Keyhani Lecture #18 Short...

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Unformatted text preview: EE 740 Professor Ali Keyhani Lecture #18 Short Circuit Studies S h ort C ircu it S tu d ies 1) S hort circuit stud y as an en gineering tool: T he m ain objective of the short circuit study is to determ ine the interrupting capability required for circuit breakers at each sw itching location. F or this type of application, the m axim um currents the breaker m ay be exposed to during the three phase balanced faults on each side of the breaker need to be determ ined. F or protective relaying design it is necessary to determ ine voltages and currents for balanced and unbalanced faults at m any locations in the system . 2)Sh ort C ircuit P roblem F orm ulation: A ssu m ptions: 1) N orm ally, all shunt elem ents including loads and line charging are neglected. L oads m ay be represented w ith constant load im pedance m odels. 2) E ach generator is represented by a constant voltage behind its subtransient reactance. 3) A ll tap changing transform ers are assum ed to be at their nom inal tap settings. 4) B alanced transm ission lines are assum ed. F or a balanced three phase fault only the positive sequence netw ork is excited. F or an unbalanced fault, all three sequence netw orks m ay be excited. 5) T he negative and positive sequence netw orks are norm ally assum ed equal and coupling betw een adjacent circuits is taken into account in the zero sequence netw ork only. 3) All voltages behind the generator reactances are assumed equal in magnitude and phase angle (normally one per unit). Therefore no current is flowing in any portion of the network prior to the fault....
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This note was uploaded on 07/17/2008 for the course ECE 740 taught by Professor Keyhani during the Fall '07 term at Ohio State.

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lecture18 - EE 740 Professor Ali Keyhani Lecture #18 Short...

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