Generator Fundamentals - Generac Power Systems 941-2 Service Manual

Figure 6. Electrical Units
OHM:
The OHM is the unit of RESISTANCE. In every circuit
there is a natural resistance or opposition to the flow
of electrons. When an EMF is applied to a complete
circuit, the electrons are forced to flow in a single
direction rather than their free or orbiting pattern. The
resistance of a conductor depends on (a) its physical
makeup, (b) its cross-sectional area, (c) its length,
and (d) its temperature. As the conductor's tempera-
ture increases, its resistance increases in direct pro-
portion. One (1) ohm of resistance will permit one (1)
ampere of current to flow when one (1) volt of electro-
motive force (EMF) is applied.
OHM'S LAW
A definite and exact relationship exists between
VOLTS, OHMS and AMPERES. The value of one can
be calculated when the value of the other two are
known. Ohm's Law states that in any circuit the current
will increase when voltage increases but resistance
remains the same, and current will decrease when
resistance Increases and voltage remains the same.
Figure 7.
If AMPERES is unknown while VOLTS and OHMS
are known, use the following formula:
AMPERES = VOLTS
If VOLTS is unknown while AMPERES and OHMS
are known, use the following formula:
VOLTS = AMPERES x OHMS
OHMS

GENERATOR FUNDAMENTALS

If OHMS is unknown but VOLTS and AMPERES are
known, use the following:
OHMS =
REACTANCE IN AC CIRCUITS
GENERAL:
When direct current (DC) is flowing, the only opposi-
tion to current flow that must be considered is resis-
tance (ohms). This is also true of alternating current
(AC) when only resistance type loads such as heating
and lamp elements are on the circuit. In such a case,
current will be in phase with voltage- that is, the cur-
rent sine wave will coincide in time with the voltage
sine wave.
However, two factors in AC circuits called INDUC-
TIVE and CAPACITIVE REACTANCE will prevent the
voltage and current sine waves from being in phase.
INDUCTIVE REACTANCE:
This condition exists when current lags behind volt-
age (Figure 8). As current flows in a circuit, magnetic
lines of force are created at right angles to the con-
ductor. The continuous changes in current value
(from positive to negative) cause these magnetic lines
to collapse and build up continuously.
The magnetic field around the conductor induces
electromotive forces that cause current to keep on
flowing while voltage drops. The result is a condition
in which voltage leads current. When a conductor is
formed into a coil, the magnetic lines of force are con-
centrated in the center of the coil. This increased den-
sity causes an increase in magnetically Induced EMF
without increasing current Thus, coils cause inductive
reactance.
Inductive reactance can also be caused by placing an
induction motor on the circuit which utilizes the cur-
rent's magnetic field for excitation.
Figure 8. Inductive Reactance
Section 1.1
VOLTS
AMPERES
Page 1.1-3