Fig. shows two alternators with identical speed / load characteristics connected in parallel. The circulating current under no-load condition is

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PGCIL DT Electrical 22 Aug 2021 Official Paper (SR I)

Answer 1

Two identical alternators have impedances Z1 and Z2 connected in parallel produces, E1 & E2 as their individual induced emf’s.
If no load is connected between the alternators, the circulating current will flow in the circuit as given by $\frac{E_{1} - E_{2}}{Z_{1} + Z_{2}}$
Here, impedances are different also it should be noted that E1 & E2 are in phase relative to the external circuit but are in direct phase opposition in the local circuit, when it is in parallel.

F6 Uday 28-9-2020 Swati D1