IEEE Std 421.2-2014 pdf download – IEEE Guide for ldentification, Testing, and Evaluation of the Dynamic Performance of Excitation Control Systems.
4. Dynamic performance classification 4.1 Overall The subclauses below describe methods for tuning and testing excitation system functions as applied to synchronous generators. The techniques and discussions apply directly to analog electronic proportional style controls with feedback from various measured signals and measured with external testing and recording instruments. Actual excitation system equipment and test equipment, however, have evolved from magnetic and rotating devices, through analog electronic implementations to digital control implementations. Both the controls and the test equipment details must be understood and the techniques described below adapted appropriately to achieve the desired tuning goals. Additionally, modern controls may have multiple modes of operation where gains or feedback signals are changed to allow better performance depending on unit conditions such as start-up, on-line at full load, or shut-down. As a result, tests performed in one operating condition, e.g., off-line, may not capture the control gains and time constants which are in service under load. A thorough review of the control gains and time constants settings as well as logic, which may alter these parameters, must be performed prior to embarking on a testing and tuning program. 4.2 Large signal performance Large signal performance is the response of an excitation control system, excitation system, or elements of an excitation system to signals that are large enough that nonlinearities must be included in the analysis of the response to obtain accurate results. The purpose of large signal performance criteria is to provide a means of evaluating excitation system performance for severe transients that may include large variations in synchronous machine stator voltages,synchronous machine stator currents, and induced synchronous machine field currents; that is, for transients affecting power system transient stability. To assess the ability of the excitation system to improve synchronous machine performance, the criteria must reflect the effects of operation under realistic power system disturbances. With respect to performance testing, it is often impractical to adequately duplicate all of these effects. In cases where tests can only be made on individual components and only at partial load or open circuit, analytical means may be used to predict performance under actual operating conditions. Criteria used to assess the large signal performance include quantities such as dynamic responses, ceiling currents and voltages, voltage response times, and nominal responses derived from dynamic responses (see IEEE Std 421.1™). 4.3 Small signal performance Small signal performance is the response of an excitation control system, excitation system, or elements of an excitation system to signals that are small enough that nonlinearities can be disregarded in the analysis of the response, and operation can be considered to be linear. Small signal performance of an excitation control system or its components can be assessed from dynamic responses, frequency responses, or by eigenvalue analysis. (See IEEE Std 421.5, Committee Report, 1973 [B6], IEEE Tutorial Course [B23], Kundur [B29], Kundur, et al. [B30], for examples.)