Excitation Control for a Synchronous Generator

The objective of this project is to develop a static exciter for a generator used in the BEL power Lab at the University of Idaho Campus. The exciter should support a continuous operating mode and a three to four second burst for fault correction and testing. The exciter will consist of three main modules: a rectifier, a converter and a controller.

Exciter Overview
An exciter is a control system that adjusts the magnetic field of a generator. It is capable of monitoring the AC output of a generator and feeding a DC current back into the generator's field. The exciter uses system measurements and control logic to determine if the generator’s AC output is deviating from its desired rating. If a deviation is found, the exciter readjusts the DC current being fed into the field. This process ensures that the generator's output remains stable and at the desired value.

Depending on how the generator is connected to the system it may either control the bus voltage or it may inject reactive power into the system. It is common for modern exciters to be able take system measurements and regulate either the reactive power or voltage output of the generator based on a user dictated regulation mode.

There are two types of exciters, static and rotating. A static exciter is physically independent of a generator and requires a power source (can be the generator's output or some other external source). A Modern static exciter uses a rectifier and controller to convert the AC source into a DC output for the field. The static exciter contains no moving parts and receives its name from the stationary nature of the system. The second type of exciter is the rotating exciter. The rotating exciter uses a DC machine that is connected to the rotor shaft to generate a DC voltage that can be amplified or attenuated for use in the field. The rotating exciter receives its name due to the fact that is has components in motion by rotating.



Generator Overview
Synchronous generators have an additional coil on the rotor that will help pull the rotor and generator into synchronization. Also they only produce torque when the rotor is not turning at synchronous speed. The amount of current depends on the frequency difference between the stator and the rotor.

Problem Definition
In this project it is desired that Three Phase either design, assemble or purchase a static exciter. The Exciter must be capable of fast field forcing to temporarily increase the generator's AC output voltage during voltage sags caused by simulated faults. The exciter should also provide closed loop regulation of the generator's AC output voltage during normal operating conditions.

Project Objective
To create a more realistic testing system. In industry generators are required to have an excitation control system. In order to have meaningful simulations our testing system needs to behave like an industrial generator. In addition, the exciter will give "real world" results when using the generator and doing fault simulations. This will enhance the educational value of the system in upper division classes and labs.

Fall Semester
Three Phase is expected to assemble or purchase a working exciter. The team will then familiarize themselves with the generator and model power system so that they can test the exciter.

Spring Semester
Three Phase will program the exciter to perform the duties required by the client. The team will develop and execute tests to confirm that the programming satisfies the clients needs.

Deliverable

 * RTDS Simulation of Generator and Exciter
 * Operates Manual for Exciter
 * Report(training guide format) on the system (includes generator and exciter)

Selected Exciter Benefits


Build
The First option Three Phase could have used for this project would have been to design each of the main components. This option would have had Three Phase building an exciter from scratch. The option was given some consideration; however, it was decided that there was too much work involved for the time permitted. Three Phase confirmed this assumption when they obtained the portfolio for a similar rectifier and controller that performed closed loop regulation only, a 1996 design project. <>

Assemble
The second option Three Phase could have used for this project would have been to purchase the main components and complete the necessary assembly and programming. After the "Build" option was eliminated Three Phase gave this option some consideration. However, the client recommended that this option was only to be explored if the "Buy" option could not satisfy the desired specifications and budget.

Buy
The "Buy" option is to purchase an exciter as an individual unit. This option requires Three Phase to develop a list of required specifications and locate a product that will meet all of the specs. If the exciter meets all of the specs and is under the budget cap Three Phase will need to purchase and install the exciter. Installing the exciter will include programming the exciter to perform the functions desired by the client.

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