Voltage Variation Performance Indices in Distribution Network

Costs of power quality disturbances (interruptions, voltage sags, harmonics, surges etc.) are very significant and have the highest impact on industry. In order to minimize those costs, it is necessary to analyze the electrical system and then try to determine possible future problems. Only after that, it is possible to improve the system in the right way. HEP d.d. – (Croatian electricity company) Corporative development and strategy division and the Faculty of Electrical Engineering in Osijek were partners in the EU project Leonardo Power Quality Initiative (LPQI). Activities carried out within that project include measuring, analyzing and statistical data processing of power quality indices. This paper presents the result of online power quality indices monitoring at HEP DSO in the transformer station TS 110/35 kV at the secondary side on one of the two transformers which mainly supply the urban cable network in the city of Osijek. Power quality indices were measured with a permanently built-in three-phase power quality network analyzer Qualitrol QWave Power CO. Data were collected offsite with a modem via analog telephone line, and stored in MS SQL database. Voltage events were classified according to the EN 50160 and IEEE 1159:1995, and RMS variation performance indices were calculated. Electrical appliances become more complex due to complicated functions and mutual interactions. There are many advantages of automated manufactory systems and variable speed drives in industry, as well as information systems and fluorescent lights at the public and domestic consumers. Therefore, development of these systems and equipment is very fast and their usage is growing. Most of nowadays electrical equipment is more sensitive to deviations from sinusoidal supply voltage. At the same time, the same or other equipment causes modifications to the characteristics of the supply voltage [1, 2].