Exam 2 - Solution

# Exam 2 - Solution - Spring2011 Exam 2 Solutions 1(10 pt...

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ELEN 3441 – Fundamentals of Power Engineering Spring 2011 Page | 1 Exam 2 - Solutions 1. (10 pt.) During paralleling two synchronous generators, what are the two reasons for having the frequency of the oncoming generator being slightly higher than the system frequency? 1) Having a slightly higher frequency, it is possible to find a moment when instantaneous voltage of oncoming generator is exactly equal to the instantaneous voltage of the system; 2) Having a slightly higher frequency, the oncoming generator will start supplying small amount of real power to the system, while having a slightly lower frequency it would consume real power from the system. 2. (10 pt.) What are the interpoles in commutating machines? What purpose do they serve? Interpoles are small poles installed in DC machines midway between the main poles. Located directly over the conductors being commutated and connected in series with the armature, they produce weak flux proportional to the armature current (and therefore, to armature reaction) affecting only a few conductors undergoing commutation. The purpose of interpoles is to correct the neutral plane shift and the inductive kick in DC machines. 3. (10 pt.) Explain the technique of power factor correction while using a synchronous motor? By controlling the field current supplied to the motor, we control the internal generated voltage and (assuming a constant load) the motor’s power factor. PF of the over-excited synchronous motor is

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## This note was uploaded on 09/21/2011 for the course EE ee taught by Professor Ee during the Spring '10 term at Istanbul Technical University.

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Exam 2 - Solution - Spring2011 Exam 2 Solutions 1(10 pt...

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