SIMULATION OF TRANSIENT STABILITY OF A LOCAL POWER PLANT DURING ISLAND AND PARALLEL CONNECTION WITH THE NETWORK Prof Srete NIKOLOVSKI, PhD; Prof Franjo JOVIC, PhD; Drazen TOMIC, BSc; Damir Sljivac, MSc srete@etfos.hr; franjo.jovic@etfos.hr; drazen.tomic@etfos.hr; sljivac@etfos.hr Faculty of Electrical Engineering, K. Trpimira 2B, 31000 Osijek, Croatia Abstract: In this paper, the transient stability of synchronous generator installed in "Termoelektrana - Toplana" Osijek power plant in island and parallel network operation is analyzed using TRANSMISSION 2000 ® software. By combining the mathematical models of synchronous machine, turbine, regulation and protection system, as well as the parts of surrounding transmission and distribution networks, the system analysis using determined criteria is enabled, with results presented graphically. 1. INTRODUCTION TRANSMISSION 2000 ® Transient Stability software was used for modeling and transient stability analysis of a 56.25 MVA generator in the combined heat and power plant "TE-TO" Osijek together with the surrounding transmission network. The software makes it possible to simulate transient stability by providing input data and creating synchronous machine and switching device models, depending on available data, then estimating which effects should be considered during the analysis. The computation is based on numerical calculation of differential equations, and the results are available as both tables and graphs. Analysis of dynamic behavior of control and protection systems, according to the theoretical considerations in this paper, will provide: 1. Analysis of dynamic behavior in island and parallel operation by simulating transients (i.e., single line to ground faults and load changes). 2. Observation of relevant operational values and variables: generator rotor speed, electrical and mechanical power, excitation voltage, generator voltage and frequency. Effects of the control system in both switched on and switched off states are considered and the influence on transient curves is shown. 2. THE MATHEMATICAL MODEL 2.1 Generator Model A turbogenerator model for modeling of synchronous machine in TE-TO Osijek, which consideres both transient and subtransient effects in generator is used. Fig. 1 3-phase sychronous machine scheme Mechanical behavior of synchronous generator is described by following swing equations: 2 H d/dt = T m -T e -K D (- 0 ) (1) d/dt= 0 (- 0 ) (2) Electric power is calculated from series and shunt component of armature voltage and current as: