Generac Power Systems NP-40G - Manual (Page 7)

Section 1.1- GENERATOR FUNDAMENTALS
OHM:
The OHM Is the unit of RESISTANCE. In every circuit
there Is s 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 temper­
ature. As the conductor’s temperature Increases, Its re­
sistance Increases In direct proportion. One (1) ohm of
resistance will permit one (1) ampere of current to flow
when one (1) volt of electromotive force (EMF) Is applied.
Ohm’s Law
A definite and exact rela­
tionship exists between
VOLTS, OHMS and AMPERES.
The value of one can be calcu­
lated 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 resis­
tance remains the same, and
current will decrease when re­
sistance Increases and volt­
age remains the same.
i AMPS OHMS j
\(l) (R)y
If AMPERES Is unknown while VOLTS and OHMS are
known, use the following formula:
AMPERESs VOLTS
■ÖHMS"
If VOLTS is unknown while AMPERES and OHMS are
known, use the following formula:
VOLTS 3 AMPERES X OHMS
If OHMS Is unknown but VOLTS and
AMPERES are unknown, use the following:
The magnetic field around the conductor Induces elec­
tromotive 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 coll, the magnetic lines of force are concentrated In the
center of the coll. This Increased density causes an
Increase In magnetically Induced EMF without Increas­
ing current Thus, colls cause Inductive reactance.
Inductive reactance can also be caused by placing an
Inductlonmotoronthe circuit which utilizes the current’s
magnetic field for excitation.
OHMS: VOLTS
AMPERES
CAPACITIVE REACTANCE:
This condition occurs when current leads voltage (Fig­
ure 9). It might be thought of as the ability to oppose
change In voltage. Capacitance exists In a circuit when
certain devices are (a) capable of storing electrical
charges as voltage Increases and (b) discharging these
stored charges when the voltage decreases.
Reactance in AC Circuits
GENERAL:
When direct current (DC) Is flowing, the only opposi­
tion to current flow that must be considered is resistance
(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 current sine wave
will coincide In time with the voltage sine wave.
However, two factors In AC circuits called INDUCTIVE
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 offeree are created at right angles to the conductor.
The continuous changes In current value (from positive
to negative) cause these magnetic lines to collapse and
build up continuously.