Analysis of Synchronous Generators’ Local Mode Eigenvalues in Modern Power Systems

Abstract

New energy sources, storage facilities, power electronics devices, advanced and complex control concepts, economic operating doctrines, and cost-optimized construction and production of machines and equipment in power systems adversely affect small-signal stability associated with local oscillations. The objective of the article is to analyze local oscillations and the causes that affect them in order to reduce their negative impact. There are no recognized analyses of the oscillations of modern operating synchronous generators exposed to new conditions in power systems. The basic idea is to perform a numerical analysis of local oscillations of a large number of synchronous generators in the power system. The paper represents the local mode data obtained from a systematic analysis of synchronous generators in the Slovenian power system. Analyzed were 74 synchronous generators of the Slovenian power system, plus many additional synchronous generators for which data were accessible in references. The mathematical models convenient for the study of local oscillations are described first in the paper. Next, the influences of transmission lines, size of the synchronous generators, operating conditions, and control systems were investigated. The paper’s merit is the applicable rules that have been defined to help power plant operators avoid stability-problematic situations. Consequently, boundaries were estimated of the eigenvalues of local modes. Finally, experiments were performed with a laboratory-size synchronous generator to assess the regularity of the numerically obtained conclusions. The obtained results enable the prediction of local oscillations’ frequencies and dampings and will be useful in PSS planning.

Dynamic Stability Analysis of Isolated Power System

“…Generator temporary droop, r = 1.5; Turbine regulator temporary time constant, T r = 10 s. The generator's standard frequency controller parameters were set as follows: Gain K = 250 MW/Hz, dead-band = 200 mHz, droop r = 2.5, turbine regulator time constant Tr = 15 s and ramp = 100 MW/s. The simulation results are shown in Figures 17 and 18 When using the temporary parameters of the unit operating in the generator mode, a smaller frequency increase is seen; in addition, the amplitude of the active power oscillations of the HVDC BtB converter decreases from 10 MW to ~5 MW [20,22,32,[35][36][37][38].…”

“…When two SC units operate and one of them disconnects, a faster dynamic process is observed after the disturbance, i.e., the isolated EPS stabilizes in a shorter period of time, but no significant improvement occurs. It is better to use two units operating in SC mode if possible [20,22,32,[35][36][37][38].…”

“…After synchronizing the unit operating in SC mode with the isolated EPS, at the initial point in time, the SC generates electricity to the isolated EPS at about 3 MW (duration 1 s); due to the additional functions required to prepare the unit to operate in SC, demand starts to grow linearly until it reaches a load of (−50 MW), and the length of the process is 10 s. When a load of (−50 MW) is reached, demand spasmodically decreases to (−10 MW) and stabilizes, and the unit can operate indefinitely with a constant demand of (−10 MW). A graphic representation of this process is given in Figure 20a [20,22,32,[35][36][37][38].…”