Section 7

DIAGNOSTIC TESTS

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)

MODEL

OHMS

QP55 (4702/4703)

1.41Ω − 1.63Ω

QP65 (4704/4705)

1.59Ω − 1.84Ω

QP75 (4706/4707)

1.12Ω − 1.30Ω

*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

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 * QP55 (Model 4702/4703)

ACROSS WIRES:

OHMS

11P & 22P

0.28Ω − 0.32Ω

11S

& 22S

0.28Ω − 0.32Ω

33

& 44

0.28Ω − 0.32Ω

 

 

AC POWER WINDING RESISTANCE * QP65 (Model 4704/4705)

ACROSS WIRES:

OHMS

11P & 22P

0.209Ω − 0.242Ω

11S

& 22S

0.209Ω − 0.242Ω

33

& 44

0.209Ω − 0.242Ω

 

 

AC POWER WINDING RESISTANCE * QP75 (Model 4706/4707)

ACROSS WIRES:

OHMS

11P & 22P

0.157Ω − 0.182Ω

11S

& 22S

0.157Ω − 0.182Ω

33

& 44

0.157Ω − 0.182Ω

*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.

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Generac Power Systems 65, 55, 75 manual Test 8- Check Sensing Leads / Power Windings, 11S 22S, Model Ohms, Across Wires Ohms
Page 43 Page 45

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