Question

Explain following techniques related to energy conservation in transmission and distribution system. (i) By balancing phase currents (ii) Variable technical losses (I2R losses).

Answer 1

(i) Balancing Phase currents: Proper (healthy balanced) three phase loads always draw equal currents in all lines but single phase loads in the 3 phase 4 wire system or loads connected between two phase lines lead to unequal currents in the lines. This leads to circulating currents in transformers/ neutral conductors due to which losses increase. Hence balancing of such feeder currents is needed to reduce the feeder copper losses. As a result of unequal loads on individual lines, sequence components in them cause overheating of transformers, cables, conductors, motors. These increase losses and resulting in motor malfunctioning under unbalanced voltage conditions.  Due to unequal loading on the single phase lines of a 3 phase, 4 wire supply system the voltage drops in lines are different that create unequal (non-rated) phase and line voltages at the load leading to unhealthy effects on the loads. Large ovens/furnaces of the single phase and two phase types are such loads. Hence it becomes necessary to equate/balance the three phase/line currents at the supply terminals. For furnaces the Scott connection transformers are employed to derive the two phase supply from the three phases which transforms the two phase load equally over the three phases. Unequal loading is also created due to unequal lengths of feeders of the three phases. Hence it is necessary to obtain current balance to the maximum.

(ii) Variable technical losses (I2R losses) 

Techniques of Reducing Technical Losses: 1) Find out the weakest area of more technical loss in the distribution system. 2) Locate distribution transformer near to the load centre. 3) Use proper capacity distribution transformer. 4) Use energy efficient transformers. 5) Use shunt capacitors for reactive power management. 6) Use HVDC system for long distance bulk power transmission. 7) Use ACSR or bundled conductors instead of solid conductors. 8) Reduce overloads on distribution transformer. 9) Use reactive power compensation techniques. 10) Use power factor controlling devices or techniques. 11) Minimize I2R losses. 12) Balance the load currents. 13) Regulate the system voltages.