Typical SRSE Test Data

Introduction

The data in these charts should be used as a guide only. Acceptable generator operation is possible with readings at plus or minus 25% of the given values for some items.

120-240V VOLT GENERATOR

A. Voltage droop transformer.

B. Voltage droop control switch.

C. Saturable reactor.

D. Full wave rectifier.

E. Stator.

F. Rotating field.

H. Voltage level resistor.

J. Voltage level rheostat.

M. Voltage change terminal block.

N. Power rectifier.

P. Heat sink.

Q. Voltage control choke.

R. Exciter reactor.

S. Trimmer resisitor.

T. Trimmer choke.

U. Relay N.C.

240-480V VOLT GENERATOR

A. Voltage droop transformer.

B. Voltage droop control switch.

C. Saturable reactor.

D. Full wave rectifier.

E. Stator.

F. Rotating field.

H. Voltage level resistor.

J. Voltage level rheostat.

M. Voltage change terminal block.

N. Power rectifier.

P. Heat sink.

Q. Voltage control choke.

R. Exciter reactor.

S. Trimmer resisitor.

T. Trimmer choke.

U. Relay N.C.

30 kW Generators

120-240V, 180/90 amperes, 60 cycle, 3 phase, 1800 rpm

120/208V, 104 amperes, 60 cycle, 3 phase, 1800 rpm

240-480V, 90-45 amperes, 60 cycle, 3 phase, 1800 rpm

300-600V, 145.2/72.6 amperes, 60 cycle, 3 phase, 1800 rpm

40 kW Generators

120-240V, 240/120 amperes, 60 cycle, 3 phase, 1800 rpm

120/208V, 139 amperes, 60 cycle, 3 phase, 1800 rpm

240-480V, 120/60 amperes, 60 cycle, 3 phase, 1800 rpm

300-600 V, 96.2/48.1 amperes, 60 cycle, 3 phase, 1800 rpm

60 kW Generators

120-240 V, 360/180 amperes, 60 cycle, 3 phase, 1800 rpm

120/208 V, 208 amperes, 60 cycle, 3 phase, 1800 rpm

240-480 V, 180/90 amperes, 60 cycle, 3 phase, 1800 rpm

75 kW Generators

120-240 V, 450/225 amperes, 60 cycle, 3 phase, 1800 rpm

120/208V, 260 amperes, 60 cycle, 3 phase, 1800 rpm

240-480 V, 226/113 amperes, 60 cycle, 3 phase, 1800 rpm

100 kW Generators

120/208 V, 347 amperes, 60 cycle, 3 phase, 1800 rpm

240/480 V, 300/150 amperes, 60 cycle, 3 phase, 1800 rpm

300-600 V, 240/120 amperes, 60 cycle, 3 phase, 1800 rpm

150 kW Generators

120/208 V, 521 amperes, 60 cycle, 3 phase, 1200 rpm

240-480 V, 450/225 amperes, 60 cycle, 3 phase, 1200 rpm

200 kW Generators

120/208 V, 695 amperes, 60 cycle, 3 phase, 1800 rpm

240-480 V, 602/301 amperes, 60 cycle, 3 phase, 1800 rpm

300-600 V, 480/240 amperes, 60 cycle, 3 phase, 1800 rpm

2400 V, 60.2 amperes, 60 cycle, 3 phase, 1800 rpm

250 kW Generators

120/208 V, 868 amperes, 60 cycle, 3 phase, 1200 rpm

240/480 V, 752/376 amperes, 60 cycle, 3 phase, 1200 rpm

300-600 V, 600/300 amperes, 60 cycle, 3 phase, 1200 rpm

2400 V, 75 amperes, 60 cycle, 3 phase, 1200 rpm

350 kW Generators

240-480 V, 1054/527 amperes, 60 cycle, 3 phase, 1200 rpm

300-600 V, 844/422 amperes, 60 cycle, 3 phase, 1200 rpm

2400 V, 150.4 amperes, 60 cycle, 3 phase, 1200 rpm

500 kW Generators

240-480 V, 1504/752 amperes, 60 cycle, 3 phase, 1200 rpm

300-600 V, 1210/605 amperes, 60 cycle, 3 phase, 1200 rpm

2400 V, 150.4 amperes, 60 cycle, 3 phase, 1200 rpm

Troubleshooting Guide

General

Before attempting major adjustments or repairs on the SRSE Generator, the serviceman should have a thorough understanding of the operating principles of the generator, the applicable wiring diagrams, and he should verify the reported operating trouble.

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DO NOT remove or install exciter cover with generator operating. When the engine-generator is running, the aluminum heat sink is electrically charged. Serious injury may result from personal contact with the heat sink. The power rectifiers may be damaged if a metal contact is made between the aluminum heat sink and the generator frame. Voltages up to 240V are present on the static exciter terminal board.

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DO NOT attempt to measure line voltage or line current on generators rated above 600 volts with direct reading test metering equipment. Potential and current transformers rated for applicable voltages must be used, even though test instruments have high voltage scales. DO NOT rely on test instrument insulation alone when working on power circuits above 600 volts.

Successful troubleshooting can be accomplished in a minimum of time if you:

1. Recognize the apparent operational trouble.

2. Diagnose the trouble from the wiring diagram and troubleshooting guide.

3. Verify the diagnosed trouble by checking with appropriate test instruments.

4. Correct the trouble by adjustment or by replacing or repairing the defective components.

Keep these fundamentals in mind:

1. A generator is an energy converter. It can not deliver more power than the engine driving it.

2. A generator is essentially a constant speed device. Driving speeds 5 to 10 percent above or below rated speed can cause large variations in terminal voltage.

3. Electric motors are energy converters. Their power consumption depends on the load they drive. Automatically, they absorb more power if the connected load demands it. Power is a product of voltage and current. If the motor voltage is lower than normal, current input will increase proportionately.

4. Generator heating is the result of line current. The higher the line current the greater the heat.

5. Line currents do not necessarily indicate the power load on a generator because of the power factor of the load. Likewise, line amperes will not necessarily be equal to the sum of the nameplate amperes of the connected loads since load components, such as motors, may not be fully loaded.

6. When load testing a generator with a resistance load bank or a water barrel, load amperes for rated kilowatts at rated volts are determined by multiplying nameplate amperes by nameplate power factor; for example, a generator rated 240 volts, 100 amperes, 0.8 power factor will be fully loaded by a resistance bank or water barrel when delivering 240 volts and 80 amperes.

7. Current will flow only through clean, solid connections. Vibration can and does loosen switchboard fasteners. Use depreciates switches and circuit breakers.

8. Electrical test (and panel) instruments are not precisely accurate. A 5 percent difference in readings between two instruments is common. Multi-scale instruments can exhibit a 5 percent difference between scales. Where uniform adjustments are necessary (as in parallel operation), use the same instrument for all voltage adjustments.

9. Temperature has a notable effect on electrical equipment. Resistance measurements made on a cold unit will be lower than the same measurement made at elevated temperatures. Ohmmeters in general are quite inaccurate. Variations of up to 10 percent of published resistances can be expected if the total error of instrument method, temperature, and piece part tolerance happen to add in one direction.

10. Governor adjustments should never be hurried. Allow time for a governor to respond to slight adjustments.

11. A large percentage of reported electrical faults are the result of undetected mechanical deficiencies. Take time to examine the entire installation carefully and methodically, and separate mechanical deficiencies from electrical deficiencies.

Wiring Diagrams

A. Voltage droop transformer.

B. Voltage droop control switch.

C. Saturable reactor.

D. Full wave rectifier.

E. Stator.

F. Rotating field.

H. Voltage level resistor.

J. Voltage level rheostat.

M. Voltage change terminal block.

N. Power rectifier.

P. Heat sink.

Q. Voltage control choke.

R. Exciter reactor.

S. Trimmer resistor.

T. Trimmer choke.

U. Relay N.C.

Test Instruments

Most electrical troubleshooting can be accomplished with a volt-ohm-milliammeter having scales of approximately the following values:

AC Volts ... 0-12, 1-100, 1-300

DC Volts ... 0-50, 1-150

Ohms ... x 1, x 10, x 100, x1000

DC Amps ... 0-3

For load testing power rectifiers and for flashing the generator field, a volt-amp tester with a heavy duty rheostat and a minimum of a 50 amp ammeter can be used.

If the generator revolving field amperes are to be measured, a DC ammeter with a 75 ampere shunt is required. The volt-amp tester listed above may be adequate.

When measuring values of generator AC line voltage and line amperes, a tong-type volt-ammeter with scales 0-600 volts and 0-600 amperes may be used.

It should be noted that some of these generators are rated higher than 600 amperes, but these are normally connected with two or more conductors per phase. To measure line current for these generators, measure the current in one conductor per phase and multiply the reading by the number of conductors per phase.

Direct reading tachometers are seldom accurate enough for precise speed settings. A 3 or 5 second integrating tachometer is a relatively precise indicator, providing the drive does not slip.

When precise frequency control is required, a direct comparison with utility power can be made using lamps. Do not attempt this check with generators over 500 volts. When the lamps stay of uniform brilliance (no variation), generator frequency is precisely equal to that of the utility line. Tachometers can be point calibrated by this arrangement at the synchronous engine speed, 900, 1200, or 1800 RPM at 60 cycles.

Troubleshooting Detailed Guide

I. No. AC Voltage

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To avoid the possibility of personal injury, refer to the warnings in the GENERAL section of the TROUBLESHOOTING GUIDE before proceeding with any of the following checks.

A. Faulty Voltmeter

1. Check voltage with a meter known to be accurate.

2. Check fuses and connections in switchgear voltmeter circuit.

B. No Excitation

1. See Fig. 1 and 1A. Check voltage build-up relay contacts (1). Contacts should be free to open. Contacts are always closed when the generator is stopped. When the generator is being started and the voltage reaches approximately 60 percent of generator rated voltage, the coil (2) is energized and the contacts open and are held open until the generator is shut down. As the generator voltage decreases, the coil is de-energized and the contacts close. On generators equipped with a DC voltage build-up relay, check the wires (3). If a wire is parted, it can be replaced with #22 stranded copper-tinned wire.

2a. See Fig. 2. Check power rectifiers (2) for open or short circuit. Typical value of forward resistance is 10-15 ohms; typical value of reverse resistance is 75,000 ohms or more. Resistance values listed are typical as measured with commercial ohmmeter. If testing results are questionable, see the topic, POWER RECTIFIERS.

FIG. 1. DC VOLTAGE BUILD-UP RELAY
1. Contacts. 2. Coil. 3. Wires. 4. Rectifier.

FIG. 1A. AC VOLTAGE BUILD-UP RELAY
1. Contacts. 2. Coil.

FIG. 2. CHECKING POWER RECTIFIERS
1. Power rectifier lead. 2. Power rectifiers.

2b. If one or more of the power rectifiers have been short circuited, it is possible that wires 15, 6 and 17 from the generator armature to the exciter terminal strip may have overheated. If the insulation is blistered, brittle or charred, the wires must be replaced. Use #12 wire for 30 kW-250 kW generators except as noted later. Use #10 wire for 350 kW and 500 kW generators and all 120 volt-240 volt generators. The new wires should be installed in the following manner:

(1) Remove the wire connecting the exciter terminal 15 to the generator armature. Cut it off near the armature and tape the end. Install the new wire from exciter terminal 15 to generator lead T7.

(2) Remove the wire connecting exciter terminal 16 to the generator armature. Cut it off near the armature and tape the end. Install the new wire from exciter terminal 16 to the voltage droop transformer terminal GEN-T8.

(3) Remove the wire connecting exciter terminal 17 to the generator armature. Cut it off near the armature and tape the end. Install the new wire from exciter terminal 17 to generator lead T9.

NOTE: For 120/208 volt four wire generators, wire 15 is connected to T1, wire 16 is connected to transformer terminal generator T8, and wire 17 is connected to generator lead T3. For 2400 volt four wire generators, it is necessary to have an electric motor shop install the new wires at the former connecting points in the generator armature winding.

NOTE: To prevent sneak circuits, it is necessary to isolate the rectifiers; open the circuit by disconnecting the power rectifier lead (1) at H₂ or H₃, depending on the electric set. Shorted rectifiers will usually weld contacts of voltage build-up relay. If a rectifier test shorted, always check the relay contacts.

C. Open or Short Circuit

1. See Fig. 3. Lift all the slip ring brushes (1) from their holders (2) and check the generator revolving field for continuity and resistance. Typical values of rotating field resistance are .7 to 1.7 ohms.

FIG. 3. CHECKING REVOLVING FIELD
1. Brush. 2. Holder.

2. See Fig. 4. Disconnect the load. Disconnect the regulator terminals 2 (A) and 10 (B) and the wire (C) to the heat sink. Check continuity of the generator coils and connections, including the primary of the voltage droop transformer.

FIG. 4. CHECKING GENERATOR COIL CONTINUITY
A. Terminal 2. B. Terminal 10. C. Wire.

D. Grounded Circuit

1. See Fig. 5 and 6. Disconnect the load lines (J). Disconnect wires from the generator to the regulator terminals 2 (A) and 10 (B) (required to isolate full wave rectifier). Install jumper wires (D) around each of the power rectifiers (F) [heat sink (E) to each H₂ or H₃ (C)]. If the generator neutral (K) is connected to the frame or ground, open this connection. Test the generator armature insulation with a magnet or vibrator-type insulation tester. Generators rated 600 volts or less should test 1.5 megohm or more, and 2400 volts or higher should test 3.25 megohms or more.

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NOTICE
The equipment required for ground testing utilizes voltages of 1000 plus twice rated voltage. It is very important to isolate the full wave rectifier and install jumper wires (D) around the power rectifiers before attempting to ground test. The high voltages associated with this test may cause permanent damage to full wave and power rectifiers.

FIG. 5. CHECKING FOR GROUNDED CIRCUIT
A. Terminal 2. B. Terminal 10. C. H₂ or H₃. D. Jumper wires. E. Heat sink. F. Power rectifiers.

FIG. 6. CHECKING FOR GROUND CIRCUIT
G. Ohmmeter. H. Connection to generator frame. J. Load lines. K. Neutral. L. Generator terminal connection.

If an insulation tester is not available, the insulation resistance can be checked with the highest scale of an ohmmeter (G). This method of test will indicate low insulation resistance but does not place a high voltage "strain" on the insulation to show a possible failure.

II. AC Voltage Too Low

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To avoid the possibility of personal injury, refer to the warnings in the GENERAL section of the TROUBLESHOOTING GUIDE before proceeding with any of the following checks.

A. Incorrect Generator or Regulator Connections

1. Check the generator terminal connections against the high and low voltage connections shown on the generator nameplate.

FIG. 7. VOLTAGE CHANGE TERMINAL BLOCK
1. Terminal block.

2. See Fig. 7. On 120-240 volt generators, check that the regulator leads 21, 22 and 23 are connected to the high voltage side of the terminal block (1) when the 240 volt 3 phase connection is used. When the 120 volt 3 phase or 120/240 volt single phase connection is used, the regulator leads should be connected to the low voltage side of the terminal block (1).

3. See Fig. 8. Block the build-up relay contacts open, open the connections and check the continuity of the excitation circuit from terminals 15, 16 and 17 (1) through the exciter reactors (2) to output terminal 20 (3). Open the connections and check the continuity from terminals 19 and 20. Visually check for loose or broken connections.

4. See Fig. 9. Check residual voltage at generator line leads (1). This can be done at the line switch (2). If voltage fails to build up, residual magnetism in the rotating field may have been lost. Residual voltage (line to line) operating at high idle speed should be 1 to 2 percent of rated voltage. See the topic, FLASHING THE FIELD.

FIG. 8. CHECKING CONTINUITY OF EXCITATION CIRCUIT
1. Terminals 15, 16 and 17. 2. Exciter reactors. 3. Terminals 19 and 20.

FIG. 9. CHECKING RESIDUAL VOLTAGE
1. Generator line leads. 2. Line switch.

B. Faulty Voltmeter

1. Check voltage with a meter known to be accurate.

2. Check fuses and connections in switchgear voltmeter circuit.

C. Voltage Level Adjustment Too Low

1. See Fig. 10. Increase the setting of the voltage level control (1).

FIG. 10. VOLTAGE LEVEL ADJUSTMENT
1. Voltage level control.

D. Voltage Droop Adjustment Too High

1. See Fig. 11. If voltage under load is too low and open circuit voltage is correct, decrease the setting of the voltage droop control (1). Readjust the open circuit voltage if necessary.

FIG. 11. VOLTAGE DROOP ADJUSTMENT
1. Voltage droop control.

E. Engine Speed Too Low

1. Check the engine speed with an accurate tachometer or frequency meter. Adjust the governor as required.

2. If the engine low idle is too low, there may not be enough voltage generated to cause the relay contacts to open. Excessive current may, however, flow through the relay contacts and cause the flexible leads to melt or the contacts to weld. Also, the idle may be at a speed where the voltage generator is just enough to make the relay contacts chatter and arc. In this case the contacts will become pitted. Engine low idle must be high enough to cause the relay contacts to snap open.

F. Overload or Unbalanced Load

1. See Fig. 12. Check the ampere load on each phase against the generator rated amperes stamped on the nameplate. Reduce the load if overloading exists. Overload may be caused by excessive amperes in line leads. It can also be caused by high power factor. As the power factor increases from .8 to 1.0, line amperes must be reduced from rated toward 80 percent of rated to prevent kilowatt overload.

FIG. 12. CHECKING AMPERE LOAD ON EACH PHASE

2. If the load is not balanced on a three phase generator, a light load on phase 2 with heavy loads on phases 1 and 3 may result in low voltage on phases 1 and 3. The regulator sensing circuit is connected to phase 2 so the regulator will act to maintain rated voltage on this phase. The heavily loaded phases will show lower voltage. Reconnect some of the loads from phases 1 and 3 to phase 2 to effect better balance among the three phases. When generators are operated in parallel, phase 2 of each generator must be connected to the same load line, so all regulators will sense the same voltage.

G. Defective Brush or Poor Brush Seating

1. See Fig. 13. Brushes (2) must not bind in holders (1). Polish or turn slip rings (3) if necessary. If brushes are chipped, worn unevenly, worn to the minimum length specified in the brush chart or have loose wires, install new brushes.

2. See Fig. 14. Use a scale (2) to check spring (1). If spring tension is less than specified in the brush chart, install new springs.

FIG. 13. CHECKING SLIP RINGS AND BRUSHES
1. Holder. 2. Brushes. 3. Slip rings.

FIG. 14. CHECKING BRUSH SPRING PRESSURE
1. Spring. 2. Scale.

H. Open Power Rectifier

1. See Fig. 15. Check power rectifiers (2) for open circuits. Typical value of forward resistance would be 10-15 ohms; typical value of reverse resistance would be 75,000 ohms or more. Resistance values listed are typical as measured with commercial ohmmeter.

FIG. 15. CHECKING POWER RECTIFIERS
1. Power rectifier leads. 2. Power rectifiers.

NOTE: To prevent sneak circuits, it is necessary to isolate the rectifiers from the circuit by disconnecting the power rectifier leads (1) at H₂ or H₃.

a. With one power rectifier open, operation of the generator is apparently not affected. Actually, the voltage level will drop approximately 2 percent and the overload capacity and motor starting ability will be lower.

b. With two power rectifiers open, the voltage will decrease until the relay coil becomes ineffective, the contacts will arc and the generated voltage will hunt at a low level.

c. With three power rectifiers open, the excitation circuit would be open and line voltage would be zero.

I. Faulty (Open) Voltage Level Rheostat or Resistor

1. See Fig. 16 and 17. Isolate the voltage level rheostat from the circuit by disconnecting at terminal 5 (B). Check the operation of the rheostat with an ohmmeter (A). The resistance should vary evenly when the control is moved from 100 to 0. The maximum resistance should be within 10 percent of the value stamped on the rheostat. Check resistance value of the voltage level resistor (D). It should not be greater than 10 ohms or less than 4 ohms.

FIG. 16. CHECKING VOLTAGE LEVEL RHEOSTAT
A. Ohmmeter. B. Terminal 5. C. Voltage level rheostat terminals.

FIG. 17. CHECKING VOLTAGE LEVEL RESISTOR
A. Ohmmeter. B. Terminal 5. D. Voltage level resistor (fixed).

J. Incorrect Saturable Reactor Tap

1. See Fig. 18. Saturable reactor taps for statically regulated statically excited generators are listed in the following table. Terminal 10 is always connected to the B tap and terminal one is connected to the L, M, or H tap. If a tap lower than that listed is used, too much control winding current will be obtained, resulting in lower than normal generator voltage. Excessive control current over an extended period could damage the full wave rectifier. See III F.

FIG. 18. SATURABLE REACTOR TAPS

K. Compound Trimmer Resistance Too Low

1. If voltage with rated load is too low, open circuit voltage is correct and the voltage droop control is adjusted to minimum droop position, the compound trimmer resistance may be too low.

a. With the engine warm and operating at synchronous speed (1200 or 1800 RPM @ 60 cycles, 1000 or 1500 RPM @ 50 cycles) at no load, set the voltage level to 2 percent below rated voltage. Apply full load and adjust governor to bring engine up to synchronous speed. Adjust the trimmer resistance (with the engine stopped) until terminal voltage is rated. Remove load, measure terminal voltage. It will be 1 to 2 percent above rated.

III. AC Voltage Too High

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To avoid the possibility of personal injury, refer to the warnings in the GENERAL section of the TROUBLESHOOTING GUIDE before proceeding with any of the following checks.

A. Incorrect Generator or Regulator Connections

1. Check the generator terminal connections against the high and low voltage connections shown on the generator nameplate.

2. See Fig. 19. On 120-240 volt generators, check that the regulator leads 21, 22 and 23 are connected to the low voltage side of the terminal block (1) when the 120 volt 3 phase or the 120/240 volt single phase connection is used. The regulator leads must be connected to the high voltage side of the terminal block when the 240 volt 3 phase connection is used.

FIG. 19. VOLTAGE CHANGE TERMINAL BLOCK
1. Terminal block.

B. Faulty Voltmeter

1. Check voltage with a meter known to be accurate.

2. Check fuses and connections in the switch-gear voltmeter circuit.

C. Voltage Level Adjustment Too High

1. See Fig. 20. Decrease setting of voltage level control (1).

D. Voltage Droop Adjustment Too Low

1. See Fig. 21. If the electric set is operating with an isochronous governor, the generated voltage will overcompound from no load to full load. Normally this overcompounding is not harmful and is sometimes desireable to compensate for line drop. If it is required to eliminate the overcompounding, adjust the voltage droop control (1) to a higher setting. The droop control is much more effective with 0.8 power factor loads than with unity power fact or loads.

FIG. 20. VOLTAGE LEVEL ADJUSTMENT
1. Voltage level control.

FIG. 21. VOLTAGE DROOP ADJUSTMENT
1. Voltage droop control.

E. Engine Speed Too High

1. See Fig. 22. Check engine speed with an accurate tachometer (1) or frequency meter. Adjust governor as required.

F. Faulty Full Wave Rectifier

1. See Fig. 23. A faulty full wave rectifier (1), either open or shorted, will not furnish the required DC current to the control winding of the power reactor and will cause high AC generator voltage. The rectifier's forward and reverse resistance may be checked with an ohmmeter as illustrated. The reverse resistance should be at least ten times the forward resistance. Disconnect wires 2, 3, 4 and 5 to eliminate sneak circuits. Measure each rectifier leg for forward and reverse resistance.

FIG. 22. CHECKING ENGINE SPEED
1. Tachometer.

FIG. 23. CHECKING FULL WAVE RECTIFIER (Trimmer resistor removed for clearer illustration)
1. Rectifier.

G. Open Circuit in Regulator and Control Winding Circuit

1. See Fig. 24. Disconnect wires (A) from generator to regulator at terminals 16 (B) and 18 (C). Check continuity between the wires from the generator.

FIG. 24. CHECKING CONTINUITY
A. Wires from generator. B. Terminal 16. C. Terminal 18.

Fig. 25. CHECKING CONTINUITY OF SATURABLE REACTOR
A. Saturable reactor. B. Terminal 1. C. Terminal 10. D. Regulator wires.

2. See Fig. 25. Disconnect the regulator wires (D) at terminals 1 (B) and 10 (C) and check continuity of the saturable reactor (A).

3. See Fig. 26. Disconnect regulator wires at terminals 1 (A) and 2 (B) and check continuity of droop switch, secondary of droop transformer and full wave rectifier. Check all points of voltage droop switch, 0 through 9.

4. Disconnect the exciter reactor control winding circuit at terminals 3 and 4 and check continuity of voltage control choke and all three control windings on the reactors.

Fig. 26. CHECKING CONTINUITY
A. Terminal 1. B. Terminal 2.

5. Reconnect all wires removed.

H. Control Winding Polarity Reversed-Y windings on the control reactors (R)

1. See Fig. 27, 28 and 28A. Start the generator and, using a DC voltmeter with a scale reading of 7.5-10 volts, check to see that the control winding polarity at terminal 3 (B) is positive and 4 (A) is negative. Also observe the connections from the voltage control choke (Q) to the Y₂ end of the third reactor. Y₁ of the first reactor terminates at 4 on the rectifier.

FIG. 27. CHECKING CONTROL WINDING POLARITY
A. Terminal 4. B. Terminal 3. C. Trimmer choke.

FIG. 28. WIRING DIAGRAM (With DC build-up relay)

FIG. 28A. WIRING DIAGRAM (With AC build-up relay)

I. Incorrect Saturable Reactor Tap

1. Check the saturable reactor taps with the aid of the table given in II J. Reconnect to the proper taps if an incorrect connection has been made.

J. Leading Power Factor Load

1. A leading power factor load will furnish excitation to the generator, thus causing the generator voltage to rise. The regulator therefore acts to reduce the exciter output in an effort to maintain only enough excitation at the generator to produce the required voltage while supplying power to the connected load. If the load has a high leading power factor, there may be more excitation furnished to the generator than can be compensated for the regulator, and the AC voltage will rise.

2. Leading power factor can be caused by an excessive amount of capacitors connected to the load, a lightly loaded synchronous motor, or an induction motor being driven by its load.

3. Leading power factor can be corrected by disconnecting capacitors, adding load, reducing the excitation of synchronous motors, or arranging the control of induction motors so they do not generate back into the AC power source.

K. Faulty Voltage Build-up Relay

1. See Fig. 29. Visually check relay contacts (1), making sure the contacts are free to move and are not burned.

FIG. 29. VOLTAGE BUILD-UP RELAY
1. Contacts.

NOTE: There are two types of voltage build-up relays (See Fig. 1 and 1A). Both types have a coil and contacts. The DC relay incorporates a rectifier to change the AC voltage to DC voltage to energize the coil.

2. See Fig. 30. Check the continuity of the relay coil (2). To check the continuity of the DC relay coil and rectifier, first remove the wires from the two relay terminals nearest the coil. Check the resistance across the coil terminals. It should be about 4000 ohms.

To check the continuity of the AC coil, first remove the wire (3) and the wire from the other side of the coil. Check the continuity of the coil from the terminal on each side of the coil.

3a. To check the operation of the contacts (4) of the DC relay, apply 120 volt AC to the center terminals on each side of the relay. The rectifier yellow leads are connected to these terminals. If the contacts are free and the coil shows 4000 to 5000 ohms, yet the relay will not operate, the relay rectifier is defective. If a stranded wire on a DC relay has parted, replace this wire with #22 stranded copper-tinned wire.

3b. To check the operation of the contacts (4) of the AC relay, apply 120 volt AC to the coil terminals. If a stranded wire on an AC relay has parted, replace this wire with #22 stranded copper-tinned wire.

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NOTICE
If the relay coil and/or contacts are defective, check the power rectifiers before attempting to operate the generator. A faulty relay may cause permanent damage to the rectifiers. When replacing a relay by installing an AC relay, observe the polarity markings on the relay contacts. An incorrectly connected relay can result in short circuiting the generator.

Fig. 30. CHECK CONTINUITY OF RELAY COIL
1. Ohmmeter. 2. Relay coil. 3. Wire. 4. Contacts.

4. This paragraph covers installation of the DC relay in place of the AC relay or in place of another DC relay.

FIG. 30A. PREPARING TO REMOVE FORMER RELAY
1. Relay upper left (plus) terminal; wire to exciter terminal 10. 2. Relay upper right (minus) terminal; wire to reactor. 3. Relay coil left terminal; wire to relay lower right (plus) terminal. 4. Relay coil right terminal; to rectifier yellow wire and terminal 8. 5. Relay lower left (minus) terminal; wire to reactor. 6. Relay lower right (plus) terminal; wire to terminal 12. A. Jumper wire between terminals 3 and 6.

FIG. 30B. RELAY
1. Relay upper left (plus) terminal; wire to exciter terminal 10. 2. Relay upper right (minus) terminal; wire to reactor. 3. Relay coil left terminal; wire to relay lower right (plus) terminal. 4. Relay coil right terminal; to rectifier yellow wire and terminal 8. 5. Relay lower left (minus) terminal; wire to reactor. 6. Relay lower right (plus) terminal; wire to terminal 12.

Before removing the former relay, and before disconnecting any wires, tag the wires attached to relay terminals (1), (2), (4), (5) and (6) as indicated in Figure 30A. The wire (A) attached to relay terminal (3) is a jumper wire between relay terminals (3) and (6), and can be removed later for installation on the new relay.

After tagging the wires, disconnect them from the relay, and remove the relay. Remove the jumper wire (A) between relay terminals (3) and (6); install the jumper wire between terminals (3) and (6) of the new relay, Figure 30B.

Install the new relay and attach the tagged wires to terminals (1), (2), (4), (5) and (6) as shown in Figure 30B.

5. Leave the cover off and start the generator. The relay should open as the generator builds up voltage.

L. Compound Trimmer Resistance Too High

1. See Fig. 31. If the voltage with rated load is too high and open circuit voltage is correct, the setting of the trimmer resistor (2) may be too high. Readjust, using the adjustable connector (1) as necessary, and readjust voltage level slightly if necessary. See II K. However, with a hydraulic governor set for isochronous operation, the voltage may overcompound. See III D.

FIG. 31. ADJUSTING TRIMMER RESISTOR
1. Adjustable connector. 2. Trimmer resistor.

2. See Fig. 32. Check for continuity through the trimmer circuit (X coils, choke, and resistors). Isolate this circuit at terminals 8 (A) and 11 (B) to prevent any sneak circuits.

FIG. 32. CHECKING TRIMMER CIRCUIT CONTINUITY
A. Terminal 8. B. Terminal 11.

M. Faulty (Shorted) Voltage Level Rheostat or Resistor

1. See Fig. 33. Isolate the voltage level rheostat (A) from the circuit by disconnecting at terminals 5 (B). Check the operation of the rheostat with an ohmmeter. The resistance should vary evenly when the control is moved from 100 to 0. The maximum resistance should be the value stamped on the rheostat. Isolate and measure the resistance of the voltage level resistor (C). It should also be stamped on the resistor. Check resistance value of the voltage level resistor (D). It should not be greater than 10 ohms nor less than 4 ohms. See the topic, FAULT CONDITION, paragraph I Step 1.

FIG. 33 VOLTAGE LEVEL RHEOSTAT AND RESISTOR
A. Voltage level rheostat. B. Terminal 5. C. Voltage level resistor (fixed).

IV. AC Voltage Fluctuates

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To avoid the possibility of personal injury, refer to the warnings in the GENERAL section of the TROUBLESHOOTING GUIDE before proceeding with any of the following checks.

A. Engine Speed Fluctuates

1. See Fig. 22. Fluctuation of voltage and speed at no load.

a. It is possible to isolate the engine governor from the exciter regulator, as a probable cause of instability, by disconnecting the excitation to the revolving field at terminals 19 and 20. Insulate the connections. With the revolving field disconnected, the engine may be operated without generating voltage. Check the speed with a constant reading tachometer and if speed fluctuation still exists, the engine governor is at fault. If speed fluctuation no longer exists, the exciter-regulator is at fault.

2. See Fig. 34. Fluctuation of voltage and speed at rated load.

a. To isolate the engine governor from the exciter-regulator as possible cause of instability, it is necessary to have a separate source of excitation equal to the ampere rating stamped on the generator nameplate. Disconnect the exciter reactors at terminals 15, 16, 17, 19 and 20 (1) and isolate the terminals. Excite the revolving field with a separate DC source (2) using a hand rheostat (3), of adequate rating, to control voltage manually. Make sure the positive side of the source connects to the outer slip ring brush. If speed fluctuation still exists, the engine governor is at fault. If speed fluctuation no longer exists, the static exciter regulator is at fault. Turn the hand rheostat to give minimum field current before disconnecting the separate DC source.

FIG. 34. CHECKING VOLTAGE AND SPEED FLUCTUATION
1. Terminals 15, 16, 17, 19 and 20. 2. Separate DC source. 3. Hand rheostat.

B. Load Fluctuates

1. Fluctuating voltage, caused by changes in load, is not a generator malfunction. The sequence of variation of different parts of the load should be checked from the viewpoint of reducing the number of simultaneous load changes.

C. Loose Connections

1. Check that all connections are tight. Loose connections may cause intermittent open circuits, resulting in voltage fluctuations.

D. Compound Trimmer Resistance Too High

1. AC voltage fluctuations above rated voltage.

a. See Fig. 32. Check for continuity through the trimmer circuit. Isolate circuit at terminals 8 (A) and 11 (B) to prevent sneak circuits.

b. See Fig. 31. Readjust trimmer resistor (2) and voltage level if necessary. See II K.

E. Compound Trimmer Resistance Too Low

1. AC voltage fluctuates below rated voltage.

a. With the engine operating at synchronous speed, at no load and full load (constant speed), the trimmer resistor should be adjusted to provide a 2 to 2 1/2 percent overcompounding at normal operating temperature from no load to full load. Undercompounding at constant speed may cause instability.

b. Readjust trimmer resistor and voltage level if necessary. See II K.

F. Faulty Voltage Build-Up Relay

1. See Fig. 29. Remove cover of relay and check operation of the relay contacts (1). Intermittently closing contacts will cause the voltage to fluctuate.

a. If the low idle speed of engine is too low, sufficient voltage will not be generated to actuate the voltage build-up relay contacts. Arcing contacts will cause the voltage to fluctuate and in time will destroy the contacts. Increase the low idle speed.

b. If it is desireable to operate engine at low idle speed lower than the standard factory setting, disconnect the revolving field from the exciter reactor at terminal 20. This will permit operating the engine without generating a voltage.

Flashing The Field

The operation of the SRSE Generator is dependent upon residual magnetism in the revolving field poles to induce a small voltage into the stator windings when the engine-generator is started. The voltage induced by the residual magnetism is approximately 1 to 2 percent of the rated voltage. This voltage is sufficient to permit voltage build-up to rated values.

It is possible for the revolving field poles to lose residual magnetism but the probability of this happening is not as great as the possibility of a self-excited shunt-wound rotating exciter losing its residual magnetism. If the field poles do lose their residual magnetism, it may be restored by exciting the revolving field windings with a DC voltage source. A storage battery of 6 volts or more is suitable.

Static Flashing

See Fig. 35. Before attempting to flash the revolving field with the engine stopped, remove the connection from Z2 to terminal 20 and the connection from terminal 11 to terminal 20. If these connections are not opened, permanent damage to the power rectifiers could result. After the exciter reactor circuit has been isolated, apply a DC voltage from a separate source (3) across the revolving field at terminals 19 and 20 (1). Terminal 20 is positive polarity and terminal 19 is negative. Polarity markings are shown on the terminal strip and must be observed correctly.

FIG. 35. FLASHING THE FIELD
1. Terminals 19 and 20. 2. Terminal 11. 3. Separate DC source. 4. Variable resistance.

To assure success, always use a variable resistance (4) in the circuit, increasing the current from 0 to 25-30 amps and then decreasing the current to zero.

Power Rectifiers

See Fig. 36. The power rectifiers used in the SRSE Generator are of the silicon diode type. Particular care must be exercised in the original installation, testing and replacement of the power rectifiers.

Power rectifiers are subject to failure due to:

1. Excess current

2. Excess voltage

3. Excess heat

4. Excess torque

FIG. 36. POWER RECTIFIERS

If a power rectifier fails, it will normally fail shorted, but it may fail open. It may change its operating characteristic to such an extent that performance in the static excitation circuit is not satisfactory, thus a simple ohmmeter test will not detect a faulty rectifier that has changed is dynamic operating characteristics.

Testing Power Rectifiers

See Fig. 37, 38 and 39. Due to the non-linear characteristics of power rectifiers, an ohmmeter check will not give an accurate indication as to the quality of the rectifier. Such a test will indicate only if the rectifier is open or shorted. Since most rectifiers that fail will fail shorted, an ohmmeter check is the most logical starting point in troubleshooting the power rectifiers.

FIG. 37. TESTING POWER RECTIFIERS

A typical good rectifier will show approximately 10 to 15 ohms resistance in the forward direction and 75,000 ohms or more in the reverse direction, as measured with a commercial ohmmeter. Meters of this type utilize a dry cell battery (usually 1 1/2 volts) to cause a current flow to permit a direct reading resistance measurement. The rectifiers used in the SRSE Generators are rated 35 or 50 amperes and 300 or 600 peak inverse voltage. Obviously, 1 1/2 volt DC can not be used to check such a rectifier up to its rated current and voltage values.

If a power rectifier (1), under test does not test open or shorted with an ohmmeter and the operating characteristics of the generator indicate a faulty rectifier, it is necessary to test the questionable rectifiers dynamically to determine accurately whether the rectifier is defective or not.

FIG. 38. WIRING DIAGRAM
1. Power rectifier. A. Ammeter. V. Voltmeter.

Dynamic Testing of Power Rectifiers

A-DC Ammeter 0-75 amps scale

V-DC Voltmeter 0-4 volt scale

Test rectifier installed in heat sink.

Type S Rectifiers (35 Ampere Rating)

Adjust the DC supply voltage to obtain 35 amperes DC through meter (A). The DC voltage across meter (V) should be no more than 1.3 volts.

Type T Rectifiers (50 Ampere Rating)

Adjust the DC supply voltage to obtain 50 amperes DC through meter (A). The DC voltage across meter (V) should be no more than 1.2 volts.

FIG. 39. TEST SET UP
1. Power rectifier. 2. Ammeter. 3. Voltmeter. 4. Separate DC source. 5. Hand rheostat.

Installation of Power Rectifiers

See Fig. 40. Silicon stud-mounted diodes are manufactured with a variety of base and stud sizes. The use of the mounting stud accomplishes two functions; that is, electrical connection to the rectifier base and the transfer of thermal losses from the rectifier to the heat sink and cooling medium. The electrical connections are readily made with conventional screw type terminals. However, proper mounting to achieve low thermal resistance is not so readily accomplished. Consequently, take the following steps to obtain good terminal transfer of rectifier heat losses.

The nut of a replacement power rectifier must be tightened to the torque specified to obtain maximum pressure of the two mating surfaces and, yet, not cause mechanical distortion of the rectifier base. Overtightening could stress the silicon crystal and cause changes in electrical characteristics or actual cracks in the crystal.

NOTE: A 9M6331 Pound-Inch Torque Wrench (2) (accurate in the listed torque range) should be used when tightening power rectifiers (1).

1. Apply a thermally conductive lubricating film between the two mating surfaces to exclude the partially stagnant air which acts as a thermal insulating film.

2. Tighten the nut on the power rectifier stud to the torque value shown in the chart.

FIG. 40. INSTALLING POWER RECTIFIERS
1. Power rectifiers. 2. Torque wrench.

3. If a torque wrench is not available, tighten the rectifier stud nut finger tight against the lockwasher. Then tighten the nut an additional 60 degrees (one flat). Do not exceed this or the specified torque.

Contact between the rectifier base and the heat sink (even when both are machined smooth) is actually a large number of point contacts. Between the points of contact is a thin film of dead air, which is a thermal barrier. To eliminate this thermal barrier, a thin film of thermally conductive lubricant should be applied to both mating surfaces before tightening. 4L7464 Silicone Grease (similar to Dow Corning #11 Compound) is recommended. A similar material, General Cement No. 8101 Silicone Grease, is available in one ounce tubes. This and other similar products can be purchased locally.

Exciter Reactors

The following tests give a check of:

1. Exciter reactor polarity.

2. Exciter reactor windings.

To make the tests, AC (alternating current) and DC (direct current) voltmeters are needed. The 6V3030 Digital Multimeter Group can be used. Other voltmeters which have the necessary range, including panel types with a dial face and needle, can also be used.

6V3030 DIGITAL MULTIMETER

Polarity Test

1. Connect a 6 or 12 volt battery and a switch to the H1 and H3 terminals. Connect a DC voltmeter to the X1 and X2 terminals. The positive (+) battery terminal must be connected to H1. The negative (-) battery terminal must be connected to H3.

CONNECTIONS FOR EXCITER REACTOR POLARITY TEST

2. Adjust the voltmeter to a 10 or 20 volt scale. For some reactor windings, it will be necessary to use a lower voltage scale to get an indication.

3. Look at the voltmeter and move the circuit switch to the "ON" position. The desired indication is a positive (+) voltage on the digital multimeter, or a needle movement up the scale on a dial face voltmeter. The indication will be only temporary, and the meter will go back to zero.

4. After two seconds or more, move the switch to the "OFF" position. The desired indication is a negative (-) voltage on the digital multimeter, or a needle movement down the scale (below the zero) on a dial face voltmeter. This indication, like the one in Step 3, will be only temporary, and the meter will go back to zero.

NOTE: Do not move the switch to either the "ON" or "OFF" position at intervals of less than two seconds. Shorter intervals will not permit stability in the flow of current.

5. Do Steps 3 and 4 again with the voltmeter connected to Y1 and Y2, then with the voltmeter connected to Z1 and Z2. This will make sure all the connections have the correct identification marks.

If the polarity of the "H" winding is not known, it can be checked as follows:

a. The single terminal on one side of the reactor is H1 and the two terminals on the opposite side are H2 and H3.

b. Connect a 115 Volt AC source to H1 and to either terminal on the opposite side (H2 or H3).

c. Check the voltage between the H1 terminal and the terminal on the opposite side which is not connected to the 115 Volt source (the third terminal).

d. If the voltage measures less than 115 Volts (approximately 105 Volts), the voltmeter is connected to H1 and H2, and the 115 Volt source is connected to H1 and H3.

e. If the voltage measures more than 115 Volts (approximately 126 Volts), the voltmeter is connected to H1 and H3, and the 115 Volt source is connected to H1 and H2.

This permits correct identification of the "H" winding terminals.

Winding Test

1. Connect a 115 Volt AC source across H1 and H3. Connect AC voltmeter across reactor terminals X2 and X1. Make tight electrical connections for accuracy in voltage measurements.

CONNECTIONS FOR EXCITER REACTOR WINDING TEST

2. With the AC voltage source "ON", check and make a note of the voltages at X2, Y2, and Z2. Also, check the source voltage across H1 and H3.

3. If the voltage of the AC source is not exactly 115 Volts, find the correction factor and multiply the voltages in the chart by this factor.

Example: If the AC source voltage is 119 Volts, the correction factor will be 119 ÷ 115 = 1.038. Multiply the chart voltages by 1.038.

4. Check the X2, Y2, and Z2 voltages found in Step 2 with the respective X2, Y2, and Z2 voltages shown in the chart, or the corrected voltages if corrections were made in Step 3. Each of these voltages must be in the range shown for the specific winding and reactor.