The need for distribution transformers in Macedonian Power System

In the Macedonian Power System currently are approximately 6000 distribution transformers in exploitation for more than five years. Since their exploitation up to now the makeup of the load served by a transformer change. The numbers energy saving devices, equipment based on power electronics, has drastically increasing, series connected FACTS controllers are more in demand. Extensive use of all this equipment can produce nonsinusoidal currents, tat can have significant effects on the distribution transformers in the Macedonian Power System. The state owned Public Enterprise Electric Power Company of Macedonia (ESM) has to be concerned about the steady increasing harmonic loads, and might consider performing tests, like the heat rise test explained in this paper, where is determined the need for derating of the existing transformers. According, IEEE C57.110 (Ref. 1), the heat rise test was perform on the 630 kVA oil exploiting distribution transformer, which load is transformer factory (welding machines, AC/DC motors, converters, ...). The temperature rise test under harmonic excitation was observed and documented. Based on the temperature rise test results, compare with calculation performed according the methodology developed in a (Ref. 1), the needs for derating the existing transformer was determined.