Transformers with on-load tap changer and step voltage regulators are now mainly used for regulating the distribution network voltage. Therefore, several problems exist in the present system, i.e., the voltage control is in discrete steps and the response time is not enough satisfactory. In the meantime, power factor (p.f.) compensation relies on capacitors installed by electricity customers, which give another problems of unexpected over voltage during light load and increase of power losses.
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