EEE 576 Lecture 2
EEE 576 Lecture 2 EEE 576
Popular in Power System Dynamics
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This 2 page Class Notes was uploaded by Shammya Saha on Sunday January 24, 2016. The Class Notes belongs to EEE 576 at Arizona State University taught by Dr. Vittal in Fall 2015. Since its upload, it has received 36 views. For similar materials see Power System Dynamics in Electrical Engineering at Arizona State University.
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Date Created: 01/24/16
EEE 576 Lecture 2 Excitation Systems and AVR Excitation System Ceiling Voltage Maximum direct voltage that the excitation system is able to supply from its terminals under specified conditions. Excitation System Ceiling Current Maximum direct current that the excitation system is able to supply from its terminals for a specified time Excitation System Voltage Time Response The excitation system output expressed as a function of time under specified conditions. Excitation System Voltage Response Time The time in seconds for the excitation voltage to attain 95% of the difference between the ceiling voltage and rated load- field voltage under specified conditions. Rated load field voltage Rated load field voltage is the generator field voltage under rated continuous load conditions with field winding at 75°C for windings designed to operate at rating with a temp rise of 60°C or less 100°C for windings designed to operate at rating with a temp rise greater than 60°C High Initial-Response Excitation Systems An excitation system having a voltage response time of 0.1 sec or less. Excitation System Nominal Response (Excitation System Response Ratio) The rate of increase of the excitation system output voltage determined from the excitation system voltage response curve, divided by the rated field voltage. This rate if maintained constant, would develop the same voltage-time area as obtained from the actual curve over the first half-second interval. Control and Protective Functions A modern excitation control system performs several important functions including that of voltage regulation. These functions can be categorized as: - Control - Limiting - Protective AC and DC Regulators Main function is to maintain the generator station voltage. Other auxiliary control and protective functions act through the ac regulator to control the generator field voltage. DC regulator holds constant generator field voltage. Commonly referred to as manual control. Used fortestingand start-up and when acregulator is faulty. Inthis modefield voltageis regulated. To modify field voltage operator has to adjust set-points. In some excitation systems capabilities for automatic set-point tracking are provided. In this case the set-point continually tracks the generator excitation variation due to the ac regulator and minimizes the voltage and reactive power excursions if the ac regulator is removed abruptly from service. Load Compensation The AVR normally controls the generator stator terminal voltage. Sometimes, load compensation is used to control a voltage at a point within or external to the generator. To facilitate this, additional circuitry is built into the AVR loop. Usingtheimpedanceand measured armaturecurrent,avoltagedropis computedandadded or subtracted from the terminal voltage. Compensator regulates voltage at a point within the generator and provides voltage droop. This is to ensure proper sharing of reactive power between generators sharing a common step up transformer. Arrangement commonly used with hydro and cross-compounded thermal units. The compensator functions as a reactive-current compensator by creating an artificial coupling between the generators. In cases when the AVR reactance and resistance is negative, compensator regulates the voltage at a point beyond the generator terminals. Used to compensate for voltage drop across the step-up transformer, when two or more units connected through individual transformers.
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