"Q1) input bus B A circulatingCurrentLoad busii) A BC transformer I ab cprimary C c 1 1BA1 1 Transformer II CA c1 1 1B ba 1 1 1Phasor diagramPrimary(star)secondary (Delta) AAo30 Oo 300 B30 CB C Q2) Conditions i) PolarityAlways ensure that the polarity of the transformer connected in parallel is same to avoid aproblem of dead short circuitii) Voltage ratioThe voltage ratio of two phase transformer should be sustain equal in order to minimiselosses occurring in the transformer caused by load circulating currents. If the voltage used isunequal in ratio it results to circulating current in a closed circuit that is formed by secondaryof transformer even at no load condition.iii) Zero relative phase displacementThe relative phase displacement between the two transformers should always be zeroiv) Phase sequenceIt’s an important condition for a three phase transformer which will require a phase sequenceof two transformers to be the same or else it may cause on each phase pair a short circuitIn order to meet the above requirement:i) Ensure that theirs is equal per unit impedancesii) Ensure there is equal “resistance to reactance” ratioConsequences when not applied If any one of the transformers run out or is tripped due to fault, other transformers in the systemwill not share the load hence power supply may be interruptedQ3) S = S [1 +( I *Z )/(I * Z )]A FL CA FL eBS = 500[1 + 250/400]= 812.5 KVAUnit A = 250/812.5 * 100 = 30.77%Unit B = 400/812.5 * 100 = 49.23%b) let S = 400 KVA i.e transformer A is fully loaded . for the other transformer not to be overhead,A Z must be less than Z , which is due because I *Z = 300 and I * Z = 300 and I *Z = 200 KVAeA CB FL eA FL eA FL eB S = 400[1 + 300/200]= 1000 KVA Q5)-"