Guardian 4389 Repair Manual page 16

SECTION 1.4
TESTING, CLEANING AND DRYING
3. The design of some meters is based on the "current
flow" theory while others are based on the "electron
flow" theory.
a. The "current flow" theory assumes that
direct current flows from the positive (+) to
the negative (-).
b. The "electron flow" theory assumes that cur-
rent flows from negative (-) to positive (+).
NOTE: When testing generators, the "current
flow" theory is applied. That is, current is
assumed to flow from positive (+) to negative (-).
MEASURING AC FREQUENCY
The generator AC output frequency is proportional to
rotor speed. Generators equipped with a 2-pole rotor
must operate at 3600 rpm to supply a frequency of 60
Hertz. Units with 4-pole rotor must run at 1800 rpm to
deliver 60 Hertz.
Correct engine and rotor speed is maintained by an
engine speed governor. For models rated 60 Hertz,
the governor is generally set to maintain a no-load
frequency of about 62 Hertz with a corresponding out-
put voltage of about 124 volts AC line-to-neutral.
Engine speed and frequency at no-load are set slight-
ly high to prevent excessive rpm and frequency droop
under heavy electrical loading.
MEASURING CURRENT
To read the current flow, in AMPERES, a clamp-on
ammeter may be used. This type of meter indicates
current flow through a conductor by measuring the
strength of the magnetic field around that conductor.
The meter consists essentially of a current trans-
former with a split core and a rectifier type instrument
connected to the secondary. The primary of the cur-
rent transformer is the conductor through which the
current to be measured flows. The split core allows
the Instrument to be clamped around the conductor
without disconnecting it.
Figure 2. Clamp-On Ammeter
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PART 1
Figure 3. A Line-Splitter
Current flowing through a conductor may be mea-
sured safely and easily. A line-splitter can be used to
measure current in a cord without separating the con-
ductors.
NOTE: If the physical size of the conductor or
ammeter capacity does not permit all lines to be
measured simultaneously, measure current flow
in each individual line. Then, add the Individual
readings.
MEASURING RESISTANCE
The volt-ohm-milliammeter may be used to measure
the resistance in a circuit. Resistance values can be
very valuable when testing coils or windings, such as
the stator and rotor windings.
When testing stator windings, keep in mind that the
resistance of these windings is very low. Some
meters are not capable of reading such a low resis-
tance and will simply read CONTINUITY.
If proper procedures are used, the following condi-
tions can be detected using a VOM:
• A "short-to-ground" condition in any stator or rotor
winding.
• Shorting together of any two parallel stator wind-
ings.
• Shorting together of any two isolated stator wind-
ings.
• An open condition in any stator or rotor winding.
Component testing may require a specific resistance
value or a test for INFINITY or CONTINUITY. Infinity
is an OPEN condition between two electrical points,
which would read as no resistance on a VOM.
Continuity is a closed condition between two electrical
points, which would be indicated as very low resis-
tance or ZERO on a VOM.
ELECTRICAL UNITS
AMPERE:
The rate of electron flow in a circuit is represented by
the AMPERE. The ampere is the number of electrons
flowing past a given point at a given time. One
AMPERE is equal to just slightly more than six thou-
sand million billion electrons per second.
GENERAL INFORMATION