A 3-phase, 20 MVA, 1IkV, star-connected generator is protected by the current balancing system of protection. If the ratio of the current transformer is 1,200/5, the minimum operating current of the relay is 0.75 ampere and the neutral point earthing resistance is 6 ohms, calculate, the percentage of each phase of the stator winding which is unprotected against earth faults when the machine is operating at normal voltage. Show quantitatively. the effect of varying neutral earthing resistance [say R = 3 ohm and 12 ohm].

A 3-phase, 20 MVA, 1IkV, star-connected generator is protected by the current balancing system of protection. If the ratio of the current transformer is 1,200/5, the minimum operating current of the relay is 0.75 ampere and the neutral point earthing resistance is 6 ohms, calculate, the percentage of each phase of the stator winding which is unprotected against earth faults when the machine is operating at normal voltage. Show quantitatively. the effect of varying neutral earthing resistance [say R = 3 ohm and 12 ohm].

Power System Analysis and Design (MindTap Course List)

6th Edition

ISBN:9781305632134

Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Chapter11: Transient Stability

Section: Chapter Questions

Problem 11.1P

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