Parallel Operation of Single-phase Transformer

Parallel Operation of Single-phase Transformer

For presenting a load in excess of the ranking of an current transformer, a 2d transformer is also linked in parallel with it. 

It’s obvious that main windings are linked to the deliver bus bars and secondary windings are related to the burden bus-bars. In connecting two or greater than two transformers in parallel, it’s main that their terminals of identical polarities are joined to the identical bus-bars. If this is not accomplished, the two e.M.Fs. 

Caused within the secondaries which are paralleled with unsuitable polarities, will act together within the regional secondary circuit even when offering no load and will for that reason produce the an identical of a dead brief-circuit.

There are unique exact stipulations which have to be convinced as a way to restrict any local circulating currents and to make sure that the transformers share the customary load in percentage to their kVA rankings. The conditions are :

1. Major windings of the transformers should be suitable for the deliver process voltage and frequency.
2. The transformers should be properly linked in regards to polarity.
3. The voltage rankings of each primaries and secondaries must be identical. In different phrases, the transformers must have the same flip ratio i.E. Transformation ratio.
4. The percent impedances must be equal in magnitude and have the same X/R ratio in an effort to prevent circulating currents and operation at exclusive vigour causes.
5. the must be famous that the impedances of two transformers may just vary in magnitude and in exceptional (i.E. Ratio of identical resistance to reactance). 

It’s necessary to differentiate between the percentage and numerical worth of an impedance. 

For example, recall two transformers having ratings in the ratio 1 : 2. It is apparent that to carry double the present, the latter have to have half the impedance of the former for the equal legislation. 

For parallel operation, the legislation must be the same, this condition being enforced by way of the very fact of their being linked in parallel.

It means that the currents carried via the two transformers are proportional to their ratings offered their numerical impedances are inversely proportional to these rankings and their percent impedances are same. 

If the high-quality of the 2 percentage impedances is exclusive (i.E. Ratio of pe

rcentage resistance to reactance is distinctive), then this will outcome in divergence of phase attitude of the two currents, with the effect that one transformer might be running with a better and the other with a decrease energy factor than that of the mixed load.

(a) Case 1. Ideal Case

(b) Case 2. Equal Voltage Ratios

(c) Case 3. Unequal Voltage Ratios