The paper presents a virtual laboratory for studying power quality events like three-phase voltage dips, which is used by students to learn and test their knowledge about the subject. The virtual laboratory is needed because in real life, in power quality domain, it is very difficult to generate power quality events in order to see the effects or to analyze their characteristics. The virtual laboratory is designed to give the students the possibility to learn first the theoretical aspects of the subject, then to apply the knowledge they accumulate to several signals, in order to get the characteristics of the event and in the end to test their obtained results with signals characteristics. There are two major advantages of using the virtual laboratory: first is that the students can see different events, with different characteristics, and in this way, they understand better the phenomenon; and the second is that a classical laboratory for studying three phase voltage dips is very expensive, the main elements (programmable voltage sources) having a very high cost.

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The electrical power transmission is realised in most of the cases by overhead power lines long of hundred of kilometres and operating at different high voltage levels. The load of these overhead power lines is widely varying depending both on the evolution of consumers (the consumers load curve) and on the operating conditions of the power system elements. For experimental analysis of the operating conditions of transmission overhead power lines, the equivalent diagram П, T or Γ, generally symmetrical, are used. The paper presents the particular operating conditions of the overhead power lines: no load and short circuit, which are important in practice, because to their associated phenomena. A 400 kV overhead power line is modelled using MatLab Simulink and the above-mentioned operating conditions are analyzed. The presented model is used in teaching activity during the power grids laboratory lessons for power engineering students of our university. The paper includes the conclusions related to the studies and the detailed results.