Στην παρούσα εργασία ασχοληθήκαμε με τα ηλεκτροτεχνικά υγρά, τόσο θεωρητικά όσο και πειραματικά. Σε θεωρητικό επίπεδο περιγράφουμε το ρόλο των μονωτικών λαδιών, τις χρήσεις τους, τις ιδιότητές τους και τους παράγοντες που τα επηρεάζουν. Σε πειραματικό επίπεδο, πραγματοποιούμε πλήθος μετρήσεων με στόχο την εξακρίβωση και την εξαγωγή συμπερασμάτων από την εφαρμογή γραμμικώς αυξανόμενης a.c. τάσης πάνω σε δύο διαφορετικά είδη μονωτικών λαδιών. / As networks of High Voltage Alternate Power can be characterized those who function in voltage higher than 1000V. Therefore, the electrological equipment which is going to be settled and function in alternate power voltage higher than 1KV is characterized as a High Voltage Equipment. The insulation of the equipment and that of the high voltage establishments is indispensable in order to maintain the potential difference between the under high voltage conductible parts. Alongside its main destination, insulation may have other roles too such as the mechanic support of the wire way, the exchange of temperature e.c.t. In the present project we dealt with the electro – technical liquids in theoretical and also in experimental level. According to the theoretical level, we described the role of the insulating oils, their uses, their attributes and the factors that affect them. According to the experimental level we accomplished a number of measurements, having as intension the verification and the deduction of conclusions coming from the application of the linearly ongoing a.c. voltage on two different kinds of insulating oils. From the aforementioned measurements we noticed the impact that the length of the gap, the temperature, even the combination of the two different insulating oils have on the tendency in breaking not only quantitavely (change of size) but also qualitatively (change of statistical attributes). For carrying out the experimental procedure we utilized the device of the High Voltages Laboratory’s electrological equipment. All measurements and also the selection of the appropriate testing prescription were done by this device, taking each time the necessary safeguards for us and for the lab’s facilities. Finally, the results were gathered in billboards and were farther analyzed according to indispensable diagrams for the deduction of conclusions. In this point is very important to mention that on those billboards is indicated the average value which refers to the tendency in breaking and that of typical variations, just for practical reasons.