Check Sensing Leads/Power Windings - Guardian Quietpact 55 Repair Manual

S S e e c c t t i i o o n n 7 7
D D I I A A G G N N O O S S T T I I C C T T E E S S T T S S
PROCEDURE:
1. Disconnect Wire 2 from the Excitation Circuit Breaker.
2. Disconnect Wire 6 from the Voltage Regulator.
3. Set a VOM to its "Rx1" scale and zero the meter.
4. Connect the VOM test leads across the terminal ends of Wires
2 and 6. The VOM should indicate the resistance of the Stator
Excitation (DPE) Windings.
EXCITATION "DPE" WINDING RESISTANCE
(Measured Across Wires 2 & 6)
M M O O D D E E L L
QP55 (4702/4703)
QP65 (4704/4705)
QP75 (4706/4707)
* Resistance values In ohms at 20° C. (68° F.). Actual readings
may vary depending on ambient temperature. A tolerance of
plus or minus 5% is allowed.
5. Now, set the meter to its "Rx1 K" or "Rx10,000" scale and zero
the meter. Test for a "short-to-ground" condition as follows:
a. Connect one meter test lead to Stator lead No.
2, the other test lead to a clean frame ground.
b. The meter should read "Infinity". Any other read-
ing indicates a "short-to-ground" condition and
the Stator should be replaced.
6. Test for a short between windings as follows:
a. Meter should be set to its "Rx1 K" or "Rx10,000"
scale.
b. Connect one meter test lead to Stator Wire 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 13.
TEST 8- CHECK SENSING LEADS / POWER
WINDINGS
DISCUSSION:
The Voltage Regulator "regulates" excitation current
flow to the Rotor by electronically comparing sensing
Page 42
*
O O H H M M S S
Ω − 1.63Ω
1.41
Ω − 1.84Ω
1.59
Ω − 1.30Ω
1.12
voltage to a pre-set reference voltage. The sensing
voltage is delivered to the Voltage 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 terminal.
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.
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
A A C C R R O O S S S S W W I I R R E E S S : :
11P & 22P
11S & 22S
33 & 44
AC POWER WINDING RESISTANCE
A A C C R R O O S S S S W W I I R R E E S S : :
11P & 22P
11S & 22S
33 & 44
AC POWER WINDING RESISTANCE
A A C C R R O O S S S S W W I I R R E E S S : :
11P & 22P
11S & 22S
33 & 44
* Resistance values In ohms at 20° C. (68° F.). Actual readings
may vary depending on ambient temperature. A tolerance of
plus or minus 5% is allowed.
8. Now, set the VOM to its "Rx1 K" or "Rx10,000" scale and zero
the meter.
*
QP55 (Model 4702/4703)
O O H H M M S S
Ω − 0.32Ω
0.28
0.28Ω − 0.32Ω
0.28Ω − 0.32Ω
*
QP65 (Model 4704/4705)
O O H H M M S S
Ω − 0.242Ω
0.209
Ω − 0.242Ω
0.209
Ω − 0.242Ω
0.209
*
QP75 (Model 4706/4707)
O O H H M M S S
Ω − 0.182Ω
0.157
Ω − 0.182Ω
0.157
Ω − 0.182Ω
0.157