Example: A30,5KVA,208V,60HZ,synchronous machine has negligible stator winding resistance and Xs =80 per phase at rating terminal voltage. The machine is first operated as generator in parallel with a 30,208V,60HZ power supply. Determine: a) The excitation voltage and the power angle when the machine is delivering rated kVA at 0.8 PF lagging. Draw the phasor diagram for this condition b) If the field excitation current is now increased by 20%,find the stator current ,power factor, and kVA supplied by the machine. Dr Audih 18

Example: A30,5KVA,208V,60HZ,synchronous machine has negligible stator winding resistance and Xs =80 per phase at rating terminal voltage. The machine is first operated as generator in parallel with a 30,208V,60HZ power supply. Determine: a) The excitation voltage and the power angle when the machine is delivering rated kVA at 0.8 PF lagging. Draw the phasor diagram for this condition b) If the field excitation current is now increased by 20%,find the stator current ,power factor, and kVA supplied by the machine. Dr Audih 18

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 11.26P

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Consider a three-phase generator rated 300MVA,23kV, supplying a system load of 240 MA and 0.9 power factor lagging at 230 kV through a 330MVA,23/230Y-kV step-up transformer with a leakage reactance of 0.11 per unit. (a) Neglecting the exciting current and choosing base values at the load of 100 MVL and 230 kV. Find the phasor currents IA,IB, and IC supplied to the load in per unit. (b) By choosing the load terminal voltage IA as reference, specify the proper base for the generator circuit and determine the generator voltage V as well as the phasor currents IA,IB, and IC, from the generator. (Note: Take into account the phase shift of the transformer.) (C) Find the generator terminal voltage in kV and the real power supplied by the generator in MW. (d) By omitting the transformer phase shift altogether, check to see whether you get the same magnitude of generator terminal voltage and real power delivered by the generator.
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An alternator having normal current of 100A is to be protected by unit protection using stabilizing resistor. The through faulty stability is estimated at fifteen times the full load current. Assuming that one of the transformers gets completely saturated, CT Ratio=100/1, CT winding resistance=0.051 ohms and total load burden=104 ohms. Calculate the required value of the stabilizing resistor and the stability ratio given also that the relay pick up