Synchronous Generator : Concepts -- 3 ( sai saikumar jn)

Synchronous Generator : Concepts

Synchronous Generator: BLONDELS TWO REACTION THEORY:

In case of cylindrical pole machines, the direct-axis and the quadrature axis mmfs act on the same magnetic circuits, hence they can be summed up as complexors. However, in a salient-pole machine, the two mmfs do not act on the same magnetic circuit. The direct axis component F_ad operates over a magnetic circuit identical with that of the field system, while the q-axis component F_aq is applied across the interpole space, producing a flux distribution different from that of F_ad or the Field mmf.

The Blondel's two reaction theory hence considers the results of the cross and direct-reaction components separately and if saturation is neglected, accounts for their different effects by assigning to each an appropriate value for armature-reaction "reactive" respectively X_aq and X_ad .

Considering the leakage reactance, the combined reactance values becomes

X_ad = X + X _ad and X _sq = X _aq

X_sq < X_sd as a given current component of the q-axis gives rise to a smaller flux due to the higher reluctance of the magnetic path.


Let l_q and I_d be the q and d-axis components of the current I in the armature reference to the phasor diagram in Figure. We get the following relationships

I_q= I cos (σ+θ) I_a = I cosφ

I_d = I sin (σ+ φ) I_r = I sinφ

And I = √(I_d² + I_q²)= = √(I_d² + I_r²)
 
where I_a and I_r are the active and reactive components of current I.

Voltage Regulation of synchronous generator:

voltage regulation of an alternator is defined as "the rise in voltage when full load is removed (field excitation and speed remaining unaltered) divided by the rated terminal voltage. Thus

% regulation =( E₀ – V ) / V x 100

In case of leading load pf the regulation is negative.

Parallel Operation of Synchronous Generators:

A stationary synchronous generator should not be connected to five bus bars because, stator induced e.mf. being zero, a short circuit will result. For proper paralleling of Generators the following three conditions must be satisfied :

1. The terminal voltage of the incoming generator must be same as bus-bar voltage.

2. The speed of the incoming generator must be such that its frequency (PN/120) equal bus-bar frequency.

3. The phase of the synchronous generator voltage must be identical with the phase of the bus voltage.

from ur's -- Bellapuri saikumar
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