Low Voltage at Transformers

While the voltage applied to induction motor varies from the rated voltage, its performance is affected. Against permissible voltage variation of ± 6%, in practice, the supply voltage varies through more than 10% in several distribution systems. A decreased voltage in the case of an induction motor results in higher currents drawn for the similar output. For a voltage drop of 10%, the full load current drew through the induction motors increases through about 10% to 15%, the starting torque decreases through nearly 19% and the line loss in the distributor increases by about 20%. As the bulk load of rural areas and little scale industrial areas consists of induction motors, the line losses within the concerned distribution systems might even touch 20%.

The above situation is corrected through operating an "on-toad-tap changing" in the power transformer situated at high voltage substations, 66/11 kV and 33/11 kV substations and giving on the 11 kV feeders, a merge of switched capacitors and automatic voltage regulators. In addition, if the off- load tap changing gear is available, a "off load tap changing" in distribution transformers is adjusted prior to the commencement of agricultural load season. This is readjusted before the on-set of monsoons while the rural load is small.