Briggs & Stratton 86262GS, Familiarization & Troubleshooting Manual

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Section 2 • Generator Components & Systems
Portable Generator Familiarization & Troubleshooting Guide
46
Each time the magnetic field around an (AC) conductor
collapses, a voltage (EMF) is induced into that conductor.This
induced voltage causes current to continue flowing as
voltage drops, forcing voltage to lead current.
If a conductor is formed into a coil, the magnetic lines of flux
are concentrated in the center of the coil.The greater
density of flux lines causes an increase in magnetically
induced voltage without increasing current flow. Coils,
therefore, cause inductive reactance.
Capacitive Reactance
Capacitive reactance is the condition that exists when
current is leading voltage. Capacitance may be defined as the
ability to oppose a change in voltage. It exists because some
electrical components can store electrical charges when
voltage is increased and discharge those electrical charges
when voltage drops.
Power Factor
The phrase “unity power factor” describes a circuit
where current and voltage are “in phase.” Such a circuit
would have a power factor of “1.” The
true power (in
watts) of a unity power factor circuit is the product of volts
times amperes.
When an “out-of-phase” condition exists, the product of
volts times amperes is the
apparent power (in watts)
rather than the true power.
Such a condition would exist when a reactance condition
occurs in a circuit.
To help explain the reason for apparent and true power
ratings of reactance circuits, mechanical work can be related
to electrical power. Figure 2.72 shows an airplane towing a
glider. If the airplane pulls the glider in position A, with the
tow cable at a 45° angle, more pulling force must be
exerted. In position B, no tow cable angle exists and force
and motion are in the same direction.
A situation similar to the airplane and glider exists in
reactance circuits because current either leads or lags
voltage.Thus, current and voltage never reach their
maximum values at the same time in a reactance circuit. If
we attempt to calculate watts with the volts times amperes
method, we will not obtain true power because when
voltage is at its peak, amperage is not.To determine true
power, the number of degrees that current (amperes) is
“out-of-phase” with voltage must be used as a correction
factor.
This correction factor is called the power factor in (AC)
circuits. It is the cosine of the phase angle (the cosine of any
angle is given in chart form in many math and electrical
books).The cosine of a 45° angle is 0.7077 so, stated
electrically, this is a power factor of 0.707.
Apparent Power is the term applied to the product of
voltage and current in an (AC) circuit. It is expressed in volt-
amperes (VA) or in kilovolt-amperes (KVA) or megavolt-
amperes (MVA) (Figure 2.73).
Figure 2.72 — Example of True vs. Apparent Power