IR drop lag the terminal voltage by angle

In this

example, the armature IZ drop is more nearly in phase

The armature current of an ac generator varies

with the terminal voltage and the generated voltage.

approximately as a sine wave. The continuously

Hence, the terminal voltage is approximately equal to

varying current in the generator armature is

the generated voltage, less the armature IZ drop.

Because the IZ drop is much greater than the IR drop,

accompanied by an IXL voltage drop in addition to the

IR drop. Armature reactance in an ac generator may be

the terminal voltage is reduced that much more. The

from 30 to 50 times the value of armature resistance

volt age vectors for a leading power-factor load are

because of the relatively large inductance of the coils

shown in figure 3-30, view C. The load current and IR

compared with their resistance.

drop lead the terminal voltage by angle

This

condition results in an increase in terminal voltage

A simplified series equivalent circuit of one phase

above the value of EG. The total available voltage of

of an ac generator is shown in figure 3-30. The voltage

the ac generator phase is the combined effect of EC

generated in the phase winding is equal to the vector sum

(rotational y induced) and the self-induced voltage (not

of the terminal voltage for the phase and the internal

shown in the vectors). The self-induced voltage, as in

voltage loss in the armature resistance, R, and the

any ac circuit, is caused by the varying field

armature reactance, XL, associated with that phase. The

(accompanying the varying armature current) linking

voltage vectors for a unity power-factor load are shown

the armature conductors. The self-induced voltage

in figure 3-30, view A. The armature IR drop is in phase

always lags the current by 90; hence, when I leads ET,

with the current, I, and the terminal voltage, ET.

the self-induced voltage aids EG, and ET increases.

Because the armature IXL drop is 90 out of phase with

the current, the terminal voltage is approximate] y equal

to the generated voltage, less the IR drop in the armature.

The voltage vectors for a lagging power-factor load

When an ac generator supplies no load, the dc field

are shown in figure 3-30, view B. The load current and

flux is distributed uniformly across the air gap. When