Guardian 4721, Repair Manual

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VISUAL INSPECTION
When it becomes necessary to test or troubleshoot a
generator, it is a good practice to complete a thor-
ough visual inspection. Remove the access covers
and look closely for any obvious problems. Look for
the following:
• Burned or broken wires, broken wire connectors,
damaged mounting brackets, etc.
• Loose or frayed wiring insulation, loose or dirty con-
nections.
• Check that all wiring is well clear of rotating parts.
• Verify that the Generator properly connected for the
correct rated voltage. This is especially important
on new installations. See Section 1.2, "AC
Connection Systems".
• Look for foreign objects, loose nuts, bolts and other
fasteners.
• Clean the area around the Generator. Clear away
paper, leaves, snow, and other objects that might
blow against the generator and obstruct its air
openings.
MEASURING VOLTAGES
When troubleshooting and testing the generator set,
the technician will be required to measure both AC
and DC voltages. Measurement of voltage requires
that the user be thoroughly familiar with the meter
being used for such tests. Consult the instruction
manual for the meter being used.
When measuring voltage, it is best to connect the
meter test leads to the terminals being tested while
the generator is shut down or while power to those
terminals is turned off.
DANGER: POWER VOLTAGES GENERATED
BY THIS EQUIPMENT ARE EXTREMELY HIGH
AND DANGEROUS. USE EXTREME CARE
WHEN MEASURING POWER VOLTAGES
SUCH AS GENERATOR AC OUTPUT VOLT-
AGE. CONTACT WITH LIVE TERMINALS AND
CONDUCTORS MAY RESULT IN HARMFUL
AND POSSIBLY LETHAL ELECTRICAL
SHOCK. DO NOT ATTEMPT TO READ
POWER VOLTAGES WHILE STANDING ON
WET OR DAMP GROUND, OR WHILE HANDS
OR FEET ARE WET. STAY WELL CLEAR OF
HIGH VOLTAGE POWER TERMINALS. CON-
NECT METER TEST LEADS TO TERMINALS
AND LEADS WHILE THE GENERATOR IS
SHUT DOWN OR WHEN THE POWER SUP-
PLY TO SUCH LEADS AND TERMINALS IS
TURNED OFF. THE USE OF INSULATIVE
RUBBER MATS IS RECOMMENDED. TAKE
POWER VOLTAGE READINGS ONLY WHILE
STANDING ON SUCH INSULATIVE MATS.
MEASURING CURRENT
Alternating current (AC) can be measured with a
clamp-on ammeter. Most clamp-on ammeters will not
measure direct current (DC). Load current readings
should never exceed the generator’s data plate rating
for continuous operation. However, momentary
surges in load current may be encountered when
starting electric motors.
On 1-phase generators, the data plate generally lists
rated line-to-line and line-to-neutral current.
MEASURING RESISTANCE
The resistance (in ohms) of generator stator and rotor
windings can be measured using an ohmmeter or an
accurate volt-ohm-milliammeter (VOM).
The resistance of some windings is extremely low.
Some readings are so low that a meter capable of
reading in the "milliohms" range would be required.
Many meters will simply read CONTINUITY.
However, a standard volt-ohm-milliammeter (VOM)
may be used to test for continuity, or for a shorted or
grounded condition.
INSULATION RESISTANCE
The insulation resistance of stator and rotor windings
is a measurement of the integrity of the insulating
materials that separate the electrical windings from
the generator’s steel core. This resistance can
degrade over time or due to such contaminants as
dust, dirt, oil, grease and especially moisture. In
most cases, failures of stator and rotor windings is
due to a breakdown in the insulation. And, in many
cases, a low insulation resistance is caused by mois-
ture that collects while the generator is shut down.
When problems are caused by moisture buildup on
the windings, they can usually be corrected by dry-
ing the windings. Cleaning and drying the windings
can usually eliminate dirt and moisture built up in the
generator windings.
!
PART 1
GENERAL INFORMATION
SECTION 1.4
TESTING, CLEANING AND DRYING
Page 10