Suppose the initial operating conditions of the two identical alternators in parallel with KW and KVAR load being shared equally, thus operating in same power factor. Each machine supplies a load current I so that total output current is 2I.
If excitation of alternator No.1 increases, then E1 increases than E2. This difference sets up a circulating current Ic = E1 - E2 / 2Zs which is confined to the local path through the stator and the busbars.
This current is superimposed on the original current. The Ic is added as a vector to the machine No.1 current I and subtracted from machine No.2 current I.
Now the two machines deliver I1 and I2 current at respective power factors cosø1 and cosø2. The cosø1 reduces and cosø2 increases.
So, the effect of KW loading is negligible but KVAR1 & current supplied by machine No.1 increases and KVAR2 & current supplied by machine No.2 decreases.
No comments:
Post a Comment