Check Sensing Leads/Power Windings - Guardian 4700 Repair Manual

Section 7
DIAGNOSTIC TESTS
b. Connect one meter test lead to Stator Wire No.
2, the other test lead to Stator lead No. 11. The
meter should read "Infinity".
c. Connect one VOM test lead to Stator lead No. 2
the other test lead to Stator lead No. 33.
"Infinity" should be indicated.
d. Connect one VOM test lead to Stator lead No. 2
and connect the other test lead to Stator lead
No. 66. "Infinity" should be indicated.
RESULTS:
1. If the Stator excitation (DPE) windings are open or shorted,
replace the Stator assembly.
2. If the excitation windings are good, perform "Insulation
Resistance Test", page 11.
TEST 8- CHECK SENSING LEADS / POWER
WINDINGS
DISCUSSION:
The Voltage Regulator "regulates" excitation current
flow to the Rotor by electronically comparing sensing
voltage to a pre-set reference voltage. The sensing
voltage is delivered to the Regulator via Wires 11S
and 22S.
If an open circuit exists in sensing leads 11S or 22S,
the normal reaction of an unprotected Regulator
would be to Increase the excitation current to the
Rotor in an effort to increase the actual AC output
voltage. This would result in a "full field" condition and
an extremely high AC output voltage.
To protect the system against such a high AC output
voltage, the Voltage Regulator will shut down if sens-
ing voltage signals are lost.
If the regulator shuts down, the generator's AC output
voltage will decrease to a value that is commensurate
with the Rotor's residual magnetism (about 5-12 VAC).
PROCEDURE:
Gain access to the generator control panel interior.
Test the Stator power windings, as follows:
1. From main breaker, disconnect Wires 11 P and 33.
2. Also disconnect Wires 22P and 44 from the ground ter-
minal.
3. Disconnect Wires 11S and 22S from the Voltage Regulator.
4. Set a VOM to its "Rx1" scale and zero the meter.
5. Connect the meter test leads across Stator leads 11P and 22P.
Normal power winding resistance should be read.
Page 34
6. Connect the meter test leads across Stator leads 33 and 44.
Normal power winding resistance should be read.
7. Connect the meter test leads across Stator leads 11S and 22S.
Normal Power Winding resistance should be read.
AC POWER WINDING RESISTANCE (Ohms at 20° C.)
ACROSS WIRES:
11P & 22P
11S & 22S
33 & 44
8. Now, set the VOM to its "Rx1 K" or "Rx10,000" scale and zero
the meter.
9. Connect the meter test leads across Stator lead 11P and frame
ground. "Infinity" should be read.
10. Connect the meter test leads across Stator lead 33 and frame
ground. The reading should be "infinity".
11. Connect the meter test leads across Stator leads Wire 11P
and Wire 33. The reading should be "infinity."
12. Connect the meter test leads across Stator leads Wire 11P
and Wire 66. The reading should be "infinity."
13. Connect the meter test leads across Stator leads Wire 33 and
Wire 66. The reading should be "infinity."
RESULTS:
1. If the Stator passes all steps except Step 7, repair, re-connect
or replace Sensing leads 11S and 22S.
2. Replace the Stator if it's power windings fail the test. (Note
Result No. 1).
3. If the Power Windings test good, perform the "Insulation
Resistance Test" on Page 11.
11S 22S
33 44
11P
22P
A. Schematic
Figure 7-6. – Stator Power Winding Leads
OHMS
Ω − 0.542Ω
0.468
Ω − 0.542Ω
0.468
Ω − 0.542Ω
0.468
11S
22S
11P
33
44
22P
B. Pictorial