20 Doctoral school of energy- and geo-technology January 15–20, 2007. Kuressaare, Estonia Modern Arrangement to Reduction of Voltage Perturbations R. Strzelecki Gdynia Maritime University, Department of Ships Automation rstrzele@am.gdynia.pl Abstract The contents of the paper encompasses general problems and the most important issues of power supply quality improvement in AC systems. In the context of above, consideration is given to evaluation of bilateral interactions of receivers with electrical power distribution system and methods of their reduction. Discussed are also the basis of operation of the most important compensation-filtration devices and their applications, that are joined to the system in parallel or in series. The main emphasis is placed on application of modern power electronic devices. Keywords Improvement of power quality, Custom power Mitigation methods, Power electronics, Introduction Rational decision relating to the power supply quality improvement (feeder voltage) can be made only as result of evaluation of different techno- economic aspects of possible actions and solutions [1]. This decision process, in simplified form is presented in the Figure 1. [2]. In addition it requires to answer for the following questions: • To what extend voltage disturbance in feeder influence work of power supply devices (in it different loads) of the feeder? • Which devices must be protected from power supply disturbances? • What is the reason of supply disturbances and how do these disturbances propagate? • What methods and technical solutions that mitigate voltage disturbances are available to apply? Fig. 1. The major aspects to find the best techno- economic solution The first and the second question result from different sensitivity of devices to supply disturbances [3]. Many contemporary devices, in respect to applied technical solution, are resistant to some of disturbances. For these devices, lower voltage quality in feeder is less important. In the electrical power system, first of all the „sensitive points” must be protected, where supply disturbances cause large economic loses or even may lead to a failure. The answers for the third and the fourth question refer to the choice of the points where the devices mitigating supply disturbances are joined and what type of the devices were used [4,5]. The disturbances may be mitigated by both reduction of the cause (source of the disturbances) and reduction of the effects in selected nodes (bus bars) of the electrical power system. In the first case, the quality of voltage in the whole system is improved. However, it usually requires the application of compensation-filtration device of relatively high rating power. In the second case improved is only the voltage quality for power receivers that are joined to the selected node. In this case adequate devices that mitigate voltage disturbances have lower rating power. It involves usually favorable relation cause-result and disturbances mitigation as their distance to the source increases. 1 Influence of Load on the Power Quality 1.1 Investigation Results Fig. 2. Single line diagram of a simple power distribution system (Z S1 =Z S2 =0.1+jω⋅3⋅10 -4 ) Fig. 3. Voltage sags caused by a starting an squirrel- cage induction motor (Load-1. Symmetrical R-L impedance: S=43 kVA, cosϕ=0.54; Load-2. Symmetrical ohmic resistance: P=15 kW; Load-3. Induction motor IM: S=16 kVA, cosϕ=0.8)