Guardian 4389 Repair Manual page 18

SECTION 1.4
TESTING, CLEANING AND DRYING
leads together. FOLLOW THE MEGGER MANUFAC-
TURER'S INSTRUCTIONS CAREFULLY.
Use a megger power setting of 500 volts. Connect
one megger test lead to the junction of all stator
leads, the other test lead to frame ground on the sta-
tor can. Read the number of megohms on the meter.
The MINIMUM acceptable megger reading for stators
may be calculated using the following formula:
MINIMUM INSULATION
__________________________
RESISTANCE =
(in "Megohms")
EXAMPLE: Generator is rated at 120 volts AC.
Divide "120" by "1000" to obtain "0.12". Then add
"1" to obtain "1.12" megohms. Minimum
Insulation resistance for a 120 VAC stator is 1.12
megohms.
If the stator insulation resistance is less than the cal-
culated minimum resistance, clean and dry the stator.
Then, repeat the test. If resistance is still low, replace
the stator.
Use the Megger to test for shorts between isolated
windings as outlined "Stator Insulation Tests".
Also test between parallel windings. See "Test
Between Windings" on next page.
TESTING ROTOR INSULATION:
Apply a voltage of 500 volts across the rotor positive
(+) slip ring (nearest the rotor bearing), and a clean
frame ground (i.e. the rotor shaft). DO NOT
EXCEED 500 VOLTS AND DO NOT APPLY VOLT-
AGE LONGER THAN 1 SECOND. FOLLOW THE
MEGGER MANUFACTURER'S INSTRUCTIONS
CAREFULLY.
ROTOR MINIMUM INSULATION RESISTANCE:
1.5 megohms
CAUTION: Before attempting to measure
!
Insulation resistance, first disconnect and
Isolate all leads of the winding to be tested.
Electronic components, diodes, surge protec-
tors, relays, voltage regulators, etc., can be
destroyed if subjected to high megger voltages.
Figure 1. One Type of Hi-Pot Tester
Page 16
GENERATOR RATED VOLTS
1000
HI-POT TESTER:
A "Hi-Pot" tester is shown in Figure 1. The model
shown is only one of many that are commercially
available. The tester shown is equipped with a volt-
age selector switch that permits the power supply
voltage to be selected. It also mounts a breakdown
lamp that will illuminate to indicate an insulation
breakdown during the test.
STATOR INSULATION RESISTANCE TEST
+1
GENERAL:
Units with air-cooled engines are equipped with (a)
dual stator AC power windings, (b) an excitation or
DPE winding, (c) a battery charge winding and (d) an
engine run winding. Insulation tests of the stator con-
sist of (a) testing all windings to ground, (b) testing
between isolated windings, and (c) testing between
parallel windings. Figure 2 is a pictorial representation
of the various stator leads on units with air-cooled
engine.
TESTING ALL STATOR WINDINGS TO GROUND:
1. Disconnect stator output leads 11 and 44 from the gen-
erator main line circuit breaker.
2. Remove stator output leads 22 and 33 from the neutral
connection and separate the two leads.
3. Disconnect C2 connector from the side of the control
panel. The C2 connector is the closest to the back
panel (see Figure 9, Section 6).
Figure 2. Stator Winding Leads
4. Connect the terminal ends of Wires 11, 22, 33 and 44
together. Make sure the wire ends are not touching any
part of the generator frame or any terminal.
5. Connect the red test probe of the Hi-Pot tester to the
joined terminal ends of stator leads 11, 22, 33 and 44.
Connect the black tester lead to a clean frame ground
on the stator can. With tester leads connected in this
manner, proceed as follows:
PART 1
GENERAL INFORMATION
2
6
11P
11S
22P
22S
44
55
66A
66
77