Electrical Energy Recovery From Unbalance Voltages

Overview

Generally voltages provided by Power Supply Companies to residential, commercial and industrial sites worldwide are never exactly balanced.In general, V1 is not equal to V2, is not equal to V3. This unbalance of voltages is further compounded by the relative large single phase loads such as lighting, heating etc.,drawing unequal currents from the transformers resulting in further increasing the unbalance between the three voltages, V1, V2, V3 which creates unnoticeable energy losses. 

Energy Loss Due To Unbalance

         An unbalance up to 1% is acceptable as it doesn’t affect the cable much. But above 1% it increases linearly and at 4% the de-rating will be nearly 20%. This implies that 20% of the current flowing in the cable will be unproductive and thus the copper losses in the cable will increase by 25% at 4% unbalance.

For motors, an unbalance of 5% will result in capacity reduction by 25%.That means, the motor current will ramp up to match the equipment torque requirements which will result in proportional copper losses in motor. The voltage unbalance of 3% increase the heating by 20% for an induction motor.

The resistance for negative sequence current is 1/6th of the positive sequence current which means a small unbalance in voltage waveform will give more current and thus losses. 

There is a technology available in the market where in the effects due to unbalance caused by negative sequence currents will be compensated with their patented passive filter units.

These enhancers will have a choke wrapped around a ferrite core. This is where the magnetic field will induce current into the wire, running through the coil. By using 50 or 60 cycles this coil has the means to induce the current. The current is then run through the capacitor and injected into the next phase at 180 degrees out of phase through magnetic coupling, this happens to each phase in each cycle. The net result is a reduction in power consumption of 7-15% depending on circuit and load parameters.

Power Quality Enhancer Circuit

These enhancers apart from compensating unbalances in voltage also acts as a passive power factor correction devices, surge suppressors and harmonic filters.  

Case Study:

Installed in a five star hotel where the energy consumption per month before and after were found as 12.3 and 11.1 lakh units after all normalisations.Nearly 7-9% savings in energy was observed due to combined benefits of unbalance compensation, power factor correction and harmonic reduction achieved by energy saving power quality enhancer.