Enhancement and Comparison of Simple Types of Closed Networks
As distinct from radial electric power lines, in high voltage networks in most cases consumers are fed from two sides. The advantages in this arrangement are: greater reliability of electricity supply, better power quality, and smaller active power losses. However, the losses could be reduced more fully only when the network is a uniform loop or a uniform network fed at two sides by equal EMFs. If these conditions are not complied with, circulating current (or equalizing current when EMFs at two sides are not equal) arises, and the active losses increase proportionally to its square, whereas voltage losses — proportionally to its first degree. To reduce losses in such cases, these currents should be eliminated. Irrespective of their cause, a booster transformer is mostly used for this purpose. If a non-uniform loop includes voltage of one standard rating, the circulating current can be eliminated by cheaper means than with a booster transformer: by inserting an induction coil into the loop. When the loop contains two standard voltage ratings, two transformers or autotransformers are needed. In this case, to eliminate circulating current, not only an induction coil should be inserted into the loop but also the transformer turn ratio is to be appropriately adjusted. When during a day the loads change approximately proportionally, the reactance of the induction coil may remain constant; however the turn ratio of a transformer should be changed in either case — whether the loads vary proportionally or not. When the network is not a loop but has independent EMFs at two sides, two quantities must be calculated: the magnitude of EMF difference at the ends of a network, and the inductance of the coil.
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