Electrical and Instrumentation Engineering: Unit III: AC Rotating Machines
Voltage Regulation of an Alternator
AC Rotating Machines
The voltage regulation of an alternator is defined as, the increase in terminal voltage when full-load is thrown off, assuming field current and speed remains the same.
VOLTAGE REGULATION
The
voltage regulation of an alternator is defined as, the increase in terminal
voltage when full-load is thrown off, assuming field current and speed remains
the same.
The
percentage regulation is defined as the ratio of change in terminal voltage
from full load to no load to rated terminal voltage.
Percentage
regulation = 
where,
E0 = N0 load terminal voltage
V
= Full load rated terminal voltage.
Voltage
characteristics of an alternator as shown in Figure 3.51.
To
determine the regulation of an alternator, open circuit and short circuit tests
are performed, which give open circuit characteristic and short circuit
characteristic.
Open Circuit Test:
The
machine is run on no load and the induced e.m.f/phase is measured corresponding
to various values of field current and the curve is drawn between induced e.m.f
per phase E and field current If as shown in Figure 4.45. The curve
so drawn is known as open circuit characteristics (O.C.C).
Short Circuit Test:
In
short circuit test, the armature winding short-circuited through a low
resistance ammeter. During this test, the speed is kept constant and
short-circuit current is measured corresponding to value of field current. The
field current is increased to give short circuit current above twice the full
load current.
The
short circuit characteristic is drawn by plotting a curve between short circuit
current Isc and field current If
If
OA is the normal field current, AB gives short circuit current Isc
corresponding to field current OA and AC gives induced e.m.f/phase, for the
same excitation. Since on short circuit for excitation OA, the whole of the
induced e.m.f. AC is utilized to create a short circuit current Isc
given by AB.
Hence
synchronous impedance:
ZS
= AC (in volts) / AB (in amps) ohms
Electrical and Instrumentation Engineering: Unit III: AC Rotating Machines : Tag: : AC Rotating Machines - Voltage Regulation of an Alternator
Electrical and Instrumentation Engineering: Unit III: AC Rotating Machines
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Electrical and Instrumentation Engineering
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