Section 7
DIAGNOSTIC TESTS
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
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 equal to the Rotor's residual magnetism (about
PROCEDURE:
Gain access to the generator control panel interior. Test the Stator power windings, as follows:
1.From main breaker, disconnect Wires 11 and 44.
2.Also disconnect Wires 22 and 33 from the ground terminal.
3.Disconnect Wires 11 and 22 ( sensing leads) 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 11 and 22. 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 sensing leads 11 and 22. Normal Power Winding resistance should be read.
AC POWER WINDING RESISTANCE * QP75D
| ACROSS WIRES: | OHMS |
| 11 & 22 | 0.159W |
| 33 & 44 | 0.184W |
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*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.
9.Connect the meter test leads across Stator lead 11 and ground. “Infinity” should be read.
10.Connect the meter test leads across Stator lead 33 and ground. The reading should be “Infinity”.
11.Connect the meter test leads across Stator leads Wire 11 and Wire 33. The reading should be “Infinity”.
12.Connect the meter test leads across Stator leads Wire 11 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”.
14.Connect the meter test leads across Stator leads Wire 11 and Wire 2. The reading should be “Infinity”.
15.Connect the meter test leads across Stator leads Wire 33 and Wire 2. The reading should be “Infinity”.
RESULTS:
1.If the Stator passes all steps except Step 7, repair,
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 13.
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11 | 22 |
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| 33 | 44 |
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11 |
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| 33 | 44 | |||||
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Figure 7-5. – Stator Power Winding Leads
TEST 9- CHECK BRUSH LEADS
DISCUSSION:
In Test 4, if application of battery voltage to the Rotor did NOT result in an output of about
PROCEDURE:
1.Set a VOM to its “Rx1” scale and zero the meter.
2.Disconnect Wire 4 from the Voltage Regulator and from the Rotor brush terminal.
3.Connect the VOM test leads across each end of the wire. The meter should read “Continuity”.
4.Disconnect Wire 1 from the Rotor Brush Terminal. Connect
Page 41
