2. A 1200 kva ,3300v,50 hz, 3 phase star connected alternator has armature resistance of 0.25 per phase. A field current of 40 a produce a short circuit current of 200a and an open circuit emf of 1100v line to line. Find the voltage regulation on full load 0.8 p.F lagging
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armature ...
31 minutes ago · 2. A 1200 kva ,3300v,50 hz, 3 phase star connected alternator has armature resistance of 0.25 per phase. A field current of 40 a produce a short circuit current of 200a and an open circuit emf of 1100v line to line. Find the voltage regulation on full load 0.8 p.F lagging.
Similar to the case of DC generator, the behaviour of a Synchronous generator connected to an external load is different than that at no-load. In order to understand the performance of the Synchronous generator when it is loaded, consider the flux distributions in the machine when the armature also carries a current. Unlike in the DC machine in alternators the emf peak and the current peak will not occur in the same coil due to the effect of the power factor of the load. The current and the induced emf will be at their peaks in the same coil only for upf loads. For zero power factor lagging loads, the current reaches its peak in a coil which falls behind that coil wherein the induced emf is at its peak by 90 electrical degrees or half a pole-pitch. Likewise for zero power factor leading
loads, the current reaches its peak in a coil which is ahead of that coil wherein the induced emf is at its peak by 90 electrical degrees or half a pole-pitch. For simplicity, assume the resistance and leakage reactance of the stator windings to be negligible. Also assume the magnetic circuit to be linear i.e. the flux in the magnetic circuit is deemed to be proportional to the resultant ampere-turns – in other words the machine is operating in the linear portion of the magnetization characteristics. Thus the emf induced is the same as the terminal voltage, and the phase-angle between current and emf is determined only by the power factor (pf) of the external load connected to the synchronous generator. Armature Reaction:
Magnetic fluxes in alternators
There are three main fluxes associated with an alternator:
(i) Main useful flux linked with both field & armature winding.
(ii) Leakage flux linked only with armature winding.
(iii) Leakage flux linked only with field winding.