17 th INTERNATIONAL SYMPOSIUM on POWER ELECTRONICS - Ee 2013 NOVI SAD, SERBIA, October 30 th – November 1 st , 2013 1 Abstract: The paper summarizes development of coordinated reactive power-voltage controller and PLC based laboratory test rig for multi generator thermal power plant. Theoretical background and basic practical requirements are clearly stated. Following this, several examples are presented to illustrate some of identified advantages and drawbacks of developed test rig during the laboratory testing of CQVC controller which led to improvement both test rig and CQVC controller design. The paper presents full cycle of development of advanced controller, from laboratory test model of steam power plant to practical device. It demonstrates the necessity for and benefits of developing adequate test platform and opens the possibility of its use in further applications. I. INTRODUCTION The constancy of voltage is one of the major factors contributing to reliable power system operation and insuring good quality of power supply. Voltage control is closely related to reactive power control. In most cases it is fairly good assumption that real (P) and reactive (Q) power flows in transmission networks are independent since the P transfer is predominantly determined by the angle between sending and receiving end voltages while the Q transfer is predominantly determined by the difference in voltage magnitude between sending and receiving end voltages. The voltage magnitude at all buses in the network must be maintained within a certain range under varying loading conditions, ideally from no load to full load. Injection of too much Q induces high voltages in the system which may result in flashovers, equipment failures, safety issues, etc. Too little injection of Q, on the other hand, leads to low voltages in the network, danger of voltage collapse, equipment misoperation etc. In general, inadequate Q reserve may result in voltage instability and blackout. Coordination of voltage control involves adjusting reference values of local/primary voltage and reactive power controlling equipment in the plant in a manner to achieve wider area coordination in obtaining optimal voltage profile and reactive power flows. Applied to power system, coordination involves control according multi objective function which aggregates and weights different technical (voltage limits, voltage deviation limits, reactive power limits) and economical (voltage drop and line losses, prime mover’s energy costs) aspects. However with large penetration of distributed generators into, by recent time, exclusively passive, highly mashed distribution network the voltage control strategy in distribution network is changing to a certain degree. Certainly by coordinating different voltage and reactive power control local equipment such as distributed generators, on-load tap changers and substation capacitors, smaller voltage variations, better voltage profile could be achieved in real time. Furthermore, multi-objective function which incorporates loss minimization, reactive power pricing and availability from different sources (distributed generators, switched shunt capacitors), maximization of the reactive power reserve for emergency purposes at DG by exploiting cheaper mechanically switched feeder capacitor reactive power whenever available is also achievable, by distributed smart control. To fulfill reactive power distribution request among participating generators, coordinated Q-V controller (CQVC) needs to be installed at steam power plant (SPP) control level. This Q-V controller would coordinate the primary controllers, i.e., the AVRs, in order to provide optimal allocation of the reactive power generation among participating generators in the plant taking into account security and economical aspects. The major advantage of such CQVC is that it controls voltage of the plant busbar while maintaining equal Q distribution among participating plant generators regarding generators specific reactive capability under real operating conditions. As having very specific functions, this kind of controller is not available at open market since it is strongly related to utility structure. Each utility needs to develop it according to specific local requirements and limitations. As it controls total amount of MVAr delivered by the power plant it is necessary to ensure high degree of reliability. It can be achieved by long term testing process prior commissioning. ADVANTAGES AND APPLICATION CONSTRAINTS OF PLC BASED LABORATORY TEST RIG OF MULTI-GENERATOR STEAM POWER PLANT J. Dragosavac*, Ž. Janda*, T. Gajić*, J. Pavlović*, S. Dobričić*, B. Radojičić**, J. V. Milanović*** and D. Arnautović * *Electrical Engineering Institute “Nikola Tesla”, University of Belgrade, 11000 Belgrade, Serbia **Thermal Power Plants Nikola Tesla, Obrenovac, Serbia *** The University of Manchester, Manchester M13 9PL, UK Paper No. Sps-1.1, pp. 1-5