Usage:
Troubleshooting Guide
General
Before attempting to repair the SRCR Generator, be familiar with the operating principles of the generator and the applicable wiring diagrams.
 |
Do not lower or raise the excitier assembly with generator operating. When the engine-generator is operating, do not touch the aluminum heat sink because it is electrically charged. The rectifiers can be damaged if metal contact is made between the aluminum heat sink and the generator frame. Voltages up to 230 are present on the static exciter terminal board. |
 |
|
Generator Rated Above 600 Volts 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. |
|
Voltage and cycles are directly proportional to RPM. A four pole, 60 cycle, 230 volt, 1800 RPM generator operating at low idle (1200 RPM) produces 153 volts at 40 cycles. When troubleshooting for voltage that is too high, a generator can usually be operated at low idle RPM (never below low idle RPM). The lower voltage produced by slow generator RPM would still be high when compared to the generator RPM. If slow generator RPM does not lower the high voltage enough, stop the electric set immediately. Excitation components can be damaged in a few seconds by the heat resulting from high voltage.
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.
3. Verify the diagnosed trouble by checking with appropriate test instruments.
Keep these fundamentals in mind:
- 1. A generator is an energy converter. It can not deliver more power than the engine driving it.
- 2. Electric motors are energy converters. The motors automatically 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 must increase proportionately.
- 3. A generator is essentially a constant speed device. RPM that is 5 to 10 percent above or below rated RPM can cause large variations in terminal voltage.
- 4. Generator heating is the result of line current. The higher the line current, the greater the heat.
- 5. A voltmeter and ammeter or a kW meter will not necessary indicate the KVA load on a generator because of the power factor of the load.
- 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 230 volts, 157 amperes, 0.8 power factor will be fully loaded when delivering 230 volts and 125.6 amperes.
- 7. Current will flow only through clean, solid connections. Vibration can and does loosen switchboard fasteners.
- 8. Electrical instruments are not precisely accurate. Five percent difference in readings between two instruments is common. Multi-scale instruments can exhibit five 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. Do not hurry governor adjustments. Allow time for a governor to respond to adjustments.
- 11. A large percentage of reported electrical faults result from undetected mechanical deficiencies. Take time to examine the entire installation carefully and methodically. Separate mechanical from electrical deficiencies.
- 2. Electric motors are energy converters. The motors automatically 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 must increase proportionately.
NOTE: For information on the electrical and mechanical characteristics of SRCR generators, make reference to the section INDUSTRIAL DIVISION DATA SHEETS: No. 70.0 and TECHNICAL INFORMATION FILE (TIF).
Generators up to Serial No. 199
A. Stator.
B. Rotating field.
D. Power rectifier.
E. Main heat sink.
F. Field rectifier.
H. Auxiliary heat sink.
J. Controlled rectifier.
L. Build-up relay.
M. Sensing reactor.
N. Voltage level potentiometer.
P. Isolation transformer.
O. Voltage control choke.
R. Regulator gain resistor.
S. Regulator gain potentiometer.
T. Voltage droop transformer.
U. Voltage droop potentiometer.
V. Noise suppression unit.
W. Noise suppression capacitor.
X. Regulator assembly.
BR. Build up resistor.
FU. Fuse.
** SS. Surge suppressor. **
**If not equipped with fuses and a surge suppressor, these units can be installed if necessary.
GENERATOR STATIC EXCITER AND REGULATOR ASSEMBLY D311 and D320 SRCR Generators Illustrated.
Generators above Serial No. 200
A. Stator.
B. Rotating field.
D. Power rectifier.
E. Main heat sink.
F. Field rectifier.
H. Auxiliary heat sink.
J. Controlled rectifier.
L. Build-up relay.
M. Sensing reactor.
N. Voltage level potentiometer.
P. Isolation transformer.
O. Voltage control choke.
R. Regulator gain resistor.
S. Regulator gain potentiometer.
T. Voltage droop transformer.
U. Voltage droop potentiometer.
V. Noise suppression unit.
W. Noise suppression capacitor.
X. Regulator assembly.
BR. Build up resistor.
FU. Fuse.
SS. Surge suppressor. **
**If not equipped with a surge suppressor, it can be installed if necessary.
GENERATOR STATIC EXCITER AND REGULATOR ASSEMBLY
Test Instruments
Most electrical troubleshooting can be accomplished with a volt-ohm-milliammeter having scales of approximately the following values:
AC Volts ... 0-12, 0-100, 0-300
DC Volts ... 0-50, 0-100, 0-150
Ohms ... x1, x10, x100, x1000
DC Amps ... 0-3
If the generator rotating field or stator winding resistance is to be measured, a Kelvin or a Wheatstone Bridge is required.
If the generator stator and revolving field insulation resistance is to be measured, a 500 or 1000 volt megohmmeter is required.
If the generator revolving field amperes are to be measured, a DC ammeter with an appropriate ampere shunt is required.
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 each conductor per phase and add the individual conductor currents.
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 rated over 500 volts. When the lamps stay of uniform brilliance (maximum brightness or completely out, depending upon electrical connection), generator frequency is precisely equal to that of the utility line. (Tachometers can be point calibrated by this arrangement at the synchronous engine speed, 1200, or 1800 RPM at 60 cycles.)
Many of the test procedures that follow designate the ohmmeter lead polarity (positive or negative) to use on the component being tested.
NOTE: Lead polarity markings of ohmmeter instruments are not to any standard. The lead marked in red, positive, "+" on some volt-ohm-milliammeters is at a positive potential when the instrument is used as an ohmmeter; on others, the lead marked in red, positive or "+" is a negative.
See Fig. 1. Another volt-ohm milliammeter (multimeter) can be used with the test ohmmeter to determine the correct polarity of the leads.
With one instrument selector switch (1) set for DC volts and the test ohmmeter selector switch (2) set for ohms, alternately connect the leads of both instruments until both instruments indicate a reading (at the same time).
The red, positive or "+" lead from the instrument with selector switch (1) set on DC volts is now connected to the test ohmmeter positive lead. Mark the ohmmeter to indicate the polarity of the ohmmeter leads (3). The correct positive and negative leads on the test ohmmeter are now identified and are to be used as marked when performing the following tests.
FIG. 1. OHMMETER TERMINAL POLARITY CHECK
1. Selector switch. 2. Selector switch. 3. Mark to indicate polarity of ohmmeter leads.
NOTE: THE SRCR generator excitation circuit can be turned either OFF or ON without stopping the generator when a SPST toggle switch is installed in the excitation circuit. Install the switch in series in the lead from the main heat sink to the build up relay (No. 2 pin terminal).
Initial Operating Procedure After Repair
The engine should not be operated at rated RPM immediately after the cause for the faulty condition has been repaired. The following procedure may prevent additional failures if the actual cause of the faulty condition was not detected.
1. Remove build-up relay L and disconnect wire 8 from regulator assembly X.
2. Start the engine and operate it at low RPM. The residual magnetism in the field should produce approximately 2 to 10 volts (generator output). A shorted controlled rectifier J will allow the field to produce higher output voltage.
3. Stop the engine and install build-up relay L.
4. Start the engine and operate it at low idle RPM. The output voltage will vary (up and down) when the points in the build-up relay are properly operating. If the output voltage is 2 to 10 volts and steady either the build-up relay points are open or the controlled rectifier is open (or the blocking rectifier BD is open, if the generator is so equipped). If the build-up relay points remain closed, generator voltage will be higher and steady.
5. Stop the engine and reconnect the wire to terminal 8.
6. Start the engine and operate it at low RPM. The output voltage should be approximately 66% of generator rated voltage. If the output voltage is either too high or is not steady the reference circuit may be open or the regulator assembly may be defective.
7. With the engine operating at low idle RPM and the generator producing a steady voltage (approximately 66% of rated voltage), slowly increase the RPM to rated RPM. Adjust the voltage level control to generator rated voltage. The generator is now ready to use.
Troubleshooting Detailed Guide
I. No AC Voltage
|
Refer to the WARNINGS in the GENERAL section of the troubleshooting guide before proceeding with any of the following checks. |
|
NOTE: NO AC VOLTAGE could have been preceded by a transient condition of high AC voltage. If the excitation circuit is equipped with fuses, this high voltage could have "blown" a fuse. Installing a new fuse will not correct the condition of high transient AC voltage. A substitute fuse must not be used. See topic III. AC VOLTAGE TOO HIGH.
A. Faulty Voltmeter
1. Check voltage with a meter known to be accurate.
2. Check fuses and connections in switchgear voltmeter circuit.
B. Open or Short Circuit
1. Disconnect lead C2 from terminal 26 and C1 from terminal 13 (disconnect C1 from the noise suppression unit if the generator is so equipped). Check the continuity of the rotating field through these disconnected leads. Measure the resistance using a Kelvin or Wheatstone Bridge across the slip rings. Resistance should measure between .5 and 1.5 ohms on high voltage generators between .25 and .5 ohms on low voltage generators.
2. Disconnect the generator leads from the load. Disconnect the stator from terminals 22, 24 and 26. Check the continuity of the stator through terminal leads T1, T2 and T3. Use a Kelvin or Wheatstone Bridge to measure the resistance of the stator. Resistance should measure less than .1 ohm.
C. Grounded Circuits
FIG. 2 ROTATING FIELD INSULATION TEST
1. Positive lead. 2. Megohmmeter. 3. Rear fan.
1. See Fig. 2. Disconnect leads C2 from terminal 26 and C1 from terminal 13 (disconnect C1 from the noise suppression unit if the generator is so equipped). With positive lead (1) of megohmmeter (2) connected to either C1 or C2 and the negative lead connected to a blade of rear fan (3), measure the insulation of the rotating field. The insulation should measure no less than 1.5 megohms for generators of 600V and less, 3.25 megohms for 2400V generators.
NOTE: Insulation resistance measures should be taken with the windings at 104°F (40°C). The test potential should be applied for one minute. The resistance value doubles for each 18°F (10°C) reduction in winding temperature. Moisture and/or foreign materials in the windings will affect the measures. Generator drying procedures are covered in the Operation and Maintenance Instructions.
2. See Fig. 3. Disconnect the generator leads from the load and insulate the neutral (if the generator is a 10 lead wire generator, connect leads T1 to T7, T2 to T8, T3 to T9 and T4, T5, T6 to T0-these four connected leads are neutral). Disconnect the stator from terminals 22, 24 and 26. With positive lead (1) of megohmmeter (2) connected to either T1, T2 or T3 and the negative lead connected to generator cover, measure the insulation of the stator winding. The insulation should measure no less than 1.5 megohms for generators rated under 601 volts and no less than 3.25 megohms for generators rated up to 2400 volts.
FIGURE 3. STATOR WINDING INSULATION TEST
1. Positive lead. 2. Megohmmeter. 3. Generator cover.
D. Shorted Power Rectifiers (Phase Diodes)
FIG. 4. POWER RECTIFIER REVERSE RESISTANCE TEST
1. Negative lead. 2. Main heat sink.
See Fig. 4. Disconnect the flexible pigtails from terminals A1 and A2 on the heat sink terminal board. With negative lead (1) connected to a pigtail and the positive lead on main heat sink (2), the reverse resistance should measure above 30,000 ohms. Test both rectifiers.
E. Open Power Rectifiers (Phase Diodes)
Disconnect the flexible pigtails from terminals A1 and A2 on the heat sink terminal board. With the ohmmeter positive lead connected to a pigtail and the negative lead on the power rectifier stud, the forward resistance should measure about 10 ohms.
F. Shorted Power Rectifier (Field Diode)
Disconnect the flexible pigtail from terminal F- on the heat sink terminal board. With ohmmeter negative lead connected to the pigtail and the positive lead on the power rectifier stud, reverse resistance should measure above 30,000 ohms.
G. Open Controlled Rectifier (Gate to Cathode)
Disconnect the flexible pigtail from the auxiliary heat sink and the gate lead from terminal G on the heat sink terminal board. With the ohmmeter positive lead connected to the gate lead and the ohmmeter negative lead connected to the pigtail (cathode), the resistance should measure between 10 and 100 ohms.
NOTE: Controlled rectifiers and power rectifiers can not be tested completely with an ohmmeter. For further tests see the topic TESTING POWER RECTIFIERS AND CONTROLLED RECTIFIERS.
H. Open Gain Resistor
See Fig. 5. Disconnect gain resistor lead (2) from terminal F+ on the heat sink terminal board. Check the continuity with one ohmmeter lead connected to lead (2) and the other ohmmeter lead connected to auxiliary heat sink (1). The resistance should measure less than .1 ohm.
I. Defective Voltage Build-Up Relay
See Fig. 6. Inspect resistor BR between pin connections 4 and 5. Install a new resistor if necessary. Disconnect the build-up relay leads from terminals G and K on the heat sink terminal board. Check the continuity through the build-up relay (the contact points are normally closed) by connecting ohmmeter lead (1) to disconnected build-up relay lead K and the other ohmmeter lead to main heat sink (2).
FIG. 5. CHECKING THE GAIN RESISTOR
1. Auxiliary heat sink. 2. Lead.
FIG. 6. BUILD-UP RELAY CONTINUITY CHECK
1. Ohmmeter lead. 2. Main heat sink.
J. Loss of Residual Magnetism
FIG. 7. RESIDUAL MAGNETISM CHECK
1. Heat sink.
See Fig. 7. Run engine at high idle speed and measure the AC voltage across terminals 22 and 24. If the reading is less than 3 to 5 volts residual magnetism may be lost. See the topic FLASHING THE FIELD.
|
When the engine is running, heat sink (1) is electrically charged. |
|
K. Open Noise Suppression Unit
Disconnect the lead wires from terminals 22 and 23, 24 and 25, 26 and 27. Check for continuity (under .1 ohm resistance) through disconnected leads 22 and 23, 24 and 25, 26 and 27. On generators with a noise suppression unit (See Fig. 8A), mark the wires and disconnect them from the unit. Check for continuity (under .1 ohm resistance) through terminals C1 and 28, 26 and 27, 24 and 25, 22 and 23.
L. Shorted Noise Suppression Capacitor
See Fig. 8. Disconnect the leads from the screw terminals on the capacitors. Check the capacitors individually for shorts from the screw terminals to the case ground. On generators with a noise suppression unit (see Fig. 8A), mark the wires and disconnect them from the unit. Check the unit for shorts. There should be no continuity from terminal C1 to ground, 26 to ground, 24 to ground, 22 to ground.
FIG. 8. SHORTED CAPACITOR CHECK
FIG. 8A. NOISE SUPPRESSION UNIT
M. Defective Brushes or Poor Seating
1. See Fig. 9. Use a scale (2) to check spring (1). If spring tension is less than specified in the brush chart, install new springs.
FIG. 9. TYPICAL GENERATOR BRUSH SPRING TENSION CHECK
1. Brush spring. 2. Brush spring scale.
2. See Fig. 10. Brushes (3) must slide freely in holders (4).
3. When a brush is worn to the minimum length specified in the brush chart, install a new brush. Reseat a brush with sandpaper.
4. Check brush wire connections.
5. Check the color and smoothness of the slip rings. Polish and clean the slip rings when necessary.
FIG. 10. BRUSH CHECK
3. Brushes (four). 4. Brush holders (two).
N. Loose Connections
1. Check all terminal connections for tightness.
2. Inspect for broken or damaged wires.
O. Incorrect Generator or Exciter Connections
1. Check generator lead connections. See generator nameplate for correct lead connections.
2. Check the wire connections of the exciter-regulator system and the noise suppression assembly. See appropriate SRCR GENERATOR WIRING DIAGRAM.
| NOTICE |
|---|
Before starting the engine see the topic INITIAL OPERATING PROCEDURE AFTER REPAIR. |
II. AC Voltage Too Low
|
Refer to the WARNINGS in the GENERAL section of the troubleshooting guide before proceeding with any of the following checks. |
|
NOTE: The fault condition of LOW AC VOLTAGE could have been preceded by a transient high AC Voltage. If the excitation circuit is equipped with fuses, high voltage could have "blown" the fuses between terminals 23 and 11, 28 and 12. See topic III, AC VOLTAGE TOO HIGH.
A. Faulty Voltmeter
Refer to topic I, NO AC VOLTAGE, paragraph A.
B. Engine Speed Too Low
FIG. 11. CHECKING ENGINE SPEED
1. Generator cover. 2. Plug opening.
1. See Fig. 11. Remove the plug from generator cover (1). Through plug opening (2), check the engine speed with an accurate tachometer. A reliable frequency meter can be used.
2. Full loads approaching unity power factor (1.0) can result in low engine speed. Reduce load so line amperage is 80% of nameplate amperes and speed will increase to rated speed.
C. Voltage Adjustment Too Low
See Operation and Maintenance Instructions for voltage adjustment procedure.
D. Voltage Droop Too High
If the voltage at no load is correct but the voltage at full load is low, See Operation and Maintenance Instructions for voltage adjustment procedure.
E. Regulator Gain Too Low
If the voltage at no load is correct but the voltage at full load is low, see Operation and Maintenance Instructions for voltage adjustment procedure.
F. Incorrect Generator or Exciter Connections
Refer to topic I, NO AC VOLTAGE, paragraph O.
G. Overload or Unbalanced Load
1. See Fig. 12. A tong-type ammeter can be used to check ampere load on each phase. If reading is higher than nameplate rating, reduce the load on the high phases.
FIG. 12. CHECKING AMPERE LOAD ON EACH PHASE
2. If the power factor of the generator load is below .8 power factor, reduce the load to the nameplate ampere rating.
3. A small load on generator phase 2 and heavy loads on phases 1 and 3 can result in low voltages on phases 1 and 3. Divide the complete generator load evenly on the three phases.
H. Open Power Rectifier (Phase Diode)
Refer to topic I, NO AC VOLTAGE, paragraph E.
I. Open Gain Potentiometer
See Fig. 13. If the voltage at no load is correct but is low at full load, check the continuity of the potentiometer. Disconnect potentiometer leads from terminals 4 and 13. Check the continuity (0 to 25 ohms) between leads (1) and (2).
FIG. 13. GAIN POTENTIOMETER TEST
1. Lead (from terminal 13). 2. Lead (from terminal 4).
J. Open Noise Suppression Unit
Refer to topic I, NO AC VOLTAGE, paragraph K.
K. Defective Voltage Regulator
See topic VOLTAGE REGULATOR ASSEMBLY
L. Isolation Transformer Incorrectly Connected
The isolation transformer primary is identified by numbered taps 1 and 2. The isolation secondary taps are 3, 4, 5, 6 & 7. Tap 3 is the secondary input. The large number printed on the sensing reactor corresponds to the other secondary tap connection.
| NOTICE |
|---|
Before starting the engine see the topic INITIAL OPERATING PROCEDURE AFTER REPAIR. |
III. AC Voltage Too High
|
Refer to the WARNINGS in the GENERAL section of the troubleshooting guide before proceeding with any of the following checks. |
|
NOTE: Conditions listed in paragraphs H, I, J, K, L, M, N, O, P, and Q, will cause a condition of transient high AC voltage that will generally result in permanent damage to one or more components. The secondary or observed fault condition will be no AC voltage.
A. Faulty Voltmeter
Refer to topic I, NO AC VOLTAGE, paragraph A.
B. Engine Speed Too High
Check the engine speed by using an accurate tachometer or frequency meter. See topic II, AC VOLTAGE TOO LOW, paragraph B.
C. Voltage Adjustment Too High
See Operation and Maintenance Instructions for voltage adjustment procedure.
D. Voltage Droop Control Polarity Reversed
If the voltage at no load is correct but at full load is too high, the voltage droop control polarity may be reversed. To change the polarity, transpose the leads from the voltage droop transformer connected to terminals 18 and 19. If transposing these leads corrects the high voltage fault, re-number the leads to correspond with the SRCR GENERATOR WIRING DIAGRAM.
E. Regulator Gain Too High
See Operation and Maintenance Instructions for voltage adjustment procedure.
F. Incorrect Generator or Exciter Connections
Refer to topic I, NO AC VOLTAGE, paragraph O.
G. Unbalanced Load
See Fig. 12. A tong-type ammeter can be used to check the ampere load on each phase. A heavy load on generator phase 2 and small loads on phases 1 and 3 can result in high voltage in phases 1 and 3. Divide the complete generator load evenly among the three phases.
H. Open Power Rectifier (Field Diode)
Disconnect the flexible pigtail from terminal F- on the heat sink terminal board. With the ohmmeter positive lead connected to the pigtail and the ohmmeter negative lead on the rectifier stud, the forward resistance should be approximately 10 ohms.
I. Shorted Controlled Rectifier
1. Disconnect the controlled rectifier pigtail from the auxiliary heat sink and the two leads to terminals G and K on the heat sink terminal board.
2. See Fig. 14. With ohmmeter positive (1) connected to the lead disconnected from terminal G and ohmmeter negative (2) to the lead from terminal K, the resistance should read between 10 and 100 ohms. The resistance is the same when the ohmmeter negative is moved to the pigtail.
FIG. 14. CONTROLLED RECTIFIER RESISTANCE CHECK
1. Ohmmeter positive (on gate lead). 2. Ohmmeter negative.
3. Check the forward and then the reverse resistance by connecting the ohmmeter leads to the pigtail and the rectifier stud. Take the reading and then transpose the ohmmeter leads and take this reading. Both forward and reverse resistance is above 30,000 ohms.
NOTE: Controlled rectifiers and power rectifiers can not be tested completely with an ohmmeter. See the topic, TESTING CONTROLLED RECTIFIERS AND POWER RECTIFIERS for further tests.
J. Open Noise Suppression Choke (Field Diode Circuit)
Disconnect the lead from the choke coil to terminal 27 and check the continuity (less than .1 ohm) between the lead and terminal 26.
K. Open Voltage Reference Circuit
1. See Fig. 15. Disconnect red lead (2) to terminal 20 (or 20A) and white lead (1) to terminal 17.
2. There should be continuity from the red lead (2) to the following:
- terminal 16 (voltage level potentiometer)terminal 9terminal 10 (voltage regulator assembly)terminal 15 (sensing reactor)terminal 24alternator lead line No. T8.
FIG. 15. CHECKING VOLTAGE REFERENCE CIRCUIT
1. White lead. 2. Red lead. 3. Terminals 17 and 18.
3. Check the voltage droop potentiometer (for continuity) at terminals 17 and 18 (3). Check for continuity from terminal 17 through the primary of the isolation transformer, through the sensing reactor to terminal 15.
The resistance of the individual components in the voltage reference circuit are: 0 to 25 ohms-voltage level potentiometer, 0 to 3 ohms-voltage droop potentiometer (115-230 volt generator) and 0 to 8 ohms (230-460 volt generators) 12 to 16 ohms-isolation transformer primary, 35 to 40 ohms-sensing reactor.
L. Open Isolation Transformer
1. See Fig. 16. Disconnect isolation transformer lead (1) from terminal 18 and lead (3) from terminal 10 (2).
2. Check the continuity of the transformer primary through lead (1), disconnected from terminal 18, and lead (3), disconnected from terminal 10. Disconnect the leads to terminals 1 and 2 on the regulator assembly and check the continuity (17 to 22 ohms) of the transformer secondary through these disconnected leads.
FIG. 16. ISOLATION TRANSFORMER CHECK
1. Lead. 2. Terminal 10. 3. Lead.
M. Open Filter Choke
Disconnect the filter choke leads from the regulator assembly terminals 3 and 5. Check for continuity (550-600 ohms) through the disconnected leads.
N. Open Gain Potentiometer
Disconnect the leads from the gain potentiometer to terminal K on the heat sink terminal board and to regulator assembly terminal 6. Check for continuity (0 to 25 ohms) between the lead from terminal 6 and terminal 4.
O. Defective Build-up Relay
1. Disconnect the lead from the build-up relay to terminal 20.
2. There should be continuity between the disconnected lead from terminal 20 and the following:
- relay pin socket No. 7 (0 ohms)relay pin socket No. 2 (10,000 ohms)relay pin socket No. 1 (10,000 ohms)main heat sink (10,000 ohms)
3. Remove the build-up relay from the panel and apply 110 volts direct current to pins 2 and 7 to open the contact points.
4. Either low idle speed may be too low to allow the contact points to open, or the contact points may not be free to open.
P. Regenerative Load Power Too High
When the main electric set load is an induction motor powering a lifting device, such as a crane or an elevator, the motor will act as a generator when the lift is lowering. If the rest of the electric set load is too small, or there has been no provision for a dynamic brake to absorb the regenerative power, it is possible for this regenerative power to drive the electric set. If the regenerative power is high enough, the electric set will overspeed causing the AC voltage to be too high.
Q. Defective Voltage Regulator
See topic, VOLTAGE REGULATOR ASSEMBLY.
| NOTICE |
|---|
Before starting the engine see the topic INITIAL OPERATING PROCEDURE AFTER REPAIR. |
IV. AC Voltage Unstable
|
Refer to the WARNINGS in the GENERAL section of the troubleshooting guide before proceeding with any of the following checks. |
|
NOTE: The fault condition of AC VOLTAGE UNSTABLE could have been preceded by a transient high AC Voltage. If the excitation circuit is equipped with fuses, high voltage could have "blown" the fuses between terminals 23 and 11, 28 and 12. See topic III. AC VOLTAGE TO HIGH.
A. Faulty Voltmeter
Refer to topic I, NO AC VOLTAGE, paragraph A.
B. Engine Speed Unstable
1. When voltage and speed are unstable at no load, disconnect lead C2 from terminal 26 and C1 from terminal 13 (disconnect C1 from the noise suppression unit if generator is so equipped). If the engine runs unsteadily with C1 and C2 disconnected, the fault may be in the governor. If engine now runs steady, the exciter-regulator system is the fault.
2. When voltage and speed are unstable under load, a separate DC source of power (with a hand-controlled rheostat) of adequate rating is necessary. Disconnect and insulate the leads from terminals 17, 22, 24 and 26. Disconnect X2 from terminal 26 and C1 from 13 (if the generator is equipped with a noise suppression unit, terminals C1, 22 and 24 are on the unit.) With the rheostat in the negative lead of the DC soruce, connect the negative to C2 and the positive to C1. Run the engine and adjust the field excitation to obtain rated voltage. If the engine speed is unstable, the governor can be the fault. If the engine and speed are now steady, the exciter-regulator system is the fault.
C. Load Fluctuations
Unstable voltage and engine speed caused by continuous changes in load are not an engine or exciter-regulator system malfunction. The sequence of variation of different segments of the load should be checked from the view point of reducing the number of simultaneous load changes.
D. Loose Connections
Refer to topic I, NO AC VOLTAGE, paragraph N.
E. Defective Build-up Relay
Make certain the relay pins are tight in the pin sockets.
F. Engine Low Idle Speed Too Low
When the voltage at low idle oscillates, the engine speed may be near the build-up relay voltage pick-up speed setting. Increase engine low idle speed.
G. Defective Brushes or Poor Brush Seating
Refer to topic I, NO AC VOLTAGE, paragraph M.
H. Regulator Gain Adjustment Too High
See Operation and Maintenance Instructions for voltage adjustment procedure.
I. Noise Suppression Capacitors Intermittently Shorted
If the noise suppression capacitors should intermittently short to ground, the voltage will be unstable. Temporarily disconnect the capacitors form the circuit, one at a time, and observe the voltmeter.
J. Excessive Vibration of Exciter Components
If the coils are loose on the cores of either the sensing reactor, the isolation transformer or the filter choke, replace the components that are loose.
K. Defective Voltage Regulator Assembly
See topic VOLTAGE REGULATOR ASSEMBLY.
| NOTICE |
|---|
Before starting the engine see the topic INITIAL OPERATING PROCEDURE AFTER REPAIR. |
Testing Surge Suppressor
Mark and disconnect the surge suppressor leads from terminals F+ and F- on the heat sink terminal board. Touch the surge suppressor leads together to discharge the capacitor in the suppressor. Set the ohmmeter to read on the highest scale. Connect one ohmmeter lead to a surge compressor lead. Watch the ohmmeter when connecting the other ohmmeter lead to the suppressor lead. The ohmmeter needle should move toward zero and then return toward infinity.
Testing Power Rectifiers And Controlled Rectifiers
See Fig. 17. The power rectifiers and controlled rectifiers used in the SRCR generator are of the silicon diode type. Particular care must be exercised in the original installation, testing and replacement of the power rectifiers.
FIG. 17. RECTIFIERS
1. Controlled rectifier. 2. Power rectifiers.
Power rectifiers are subject to failure due to:
- 1. Excess current.
- 2. Excess voltage.
- 3. Excess heat.
- 4. Excessive tightening.
- 2. Excess voltage.
If a diode rectifier or a controlled rectifier should fail, it will normally fail shorted, but it may fail open.
Testing Power Rectifiers
See Fig. 18. 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. 18. TESTING POWER RECTIFIER
A typical good rectifier will show approximately 10 ohms resistance in the forward direction and 30,000 ohms or more in the reverse direction, as measured with a commercial ohmmeter.
NOTE: Commercial ohmmeters utilize a dry cell battery (usually 1 1/2 volts) to cause a current flow to permit a direct reading resistance measurement. Due to low reverse voltage and low forward current, the ohmmeter can not give an indication as to the quality of either a power rectifier or a controlled rectifier. The error in measuring reverse resistance of a rectifier may be as much as 100 to 1.
Testing Controlled Rectifiers
An ohmmeter check will not give an accurate indication as to the quality of the controlled rectifier. Such a test will indicate only if the controlled rectifier is either shorted or open. Place the positive lead of an ohmmeter on the stud and the negative ohmmeter lead on the pigtail. Take this reading and reverse the ohmmeter leads and compare the two readings. A shorted controlled rectifier will indicate zero or equally low resistance for both readings; an open will show infinite readings. If the controlled rectifier is neither shorted nor open, it will show approximately equal readings above 30,000 ohms. To test the gate circuit for either shorts or opens, alternate the positive and negative leads of the ohmmeter to the pigtail and gate lead. If the gate circuit is shorted, both readings will be zero; both readings will be infinite resistance if the gate circuit is open. If the gate circuit is neither shorted nor open, both readings will be nearly equal and be approximately 10 to 100 ohms.
Power Rectifier and Controlled Rectifier Installation
Be careful when mounting either a power rectifier or a controlled rectifier on the aluminum heat sink. The rectifier screw threads and mounting surfaces (rectifier and heat sink) must be clean. Apply a thin film of thermally conductive silicone grease to the mounting surfaces but not on the screw threads. 4J7464 Grease is suitable conducting lubricant.
See Fig. 20. Use an accurate pound-inch torque wrench to tighten the rectifiers. Correct torque values are listed in the RECTIFIER TIGHTENING CHART. Do not overtighten.
FIG. 20. INSTALLING RECTIFIERS
1. Rectifier stud nuts. 2. Torque wrench (pound-inch type).
Flashing The Field
The operation of the SRCR 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 3 to 5 volts when the engine is running at rated speed. 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 can be restored by exciting the revolving field windings with a DC voltage source. A storage battery of 24 volts would be a suitable DC source.
Static Flashing
With the engine stopped, disconnect rotating field leads C1 and C2 from terminals 13 and 26. Apply a DC voltage (from a separate source) across the rotating field by attaching a lead from the DC source negative to field lead C2 and momentarily touching field lead C1 (touch two or three times) with a lead from the DC source positive.
See Fig. 21. To assure success in flashing the rotating field, use a variable resistance in series with the DC source. Attach a lead from DC source negative (3) to field lead C2. Attach the variable resistance positive lead (1) to field lead C1 and the variable resistance negative lead to the DC source positive.
FIG. 21. FLASHING THE FIELD
1. Positive lead. 2. Control. 3. DC source negative.
Turn variable resistance control (2) to increase the current from zero to 25-30 amperes and then decrease the current to zero.
Dynamic Flashing
Flashing the field with the engine running is not recommended because of exposed terminals in the exciter and regulator assembly.
If it is necessary to flash the rotating field with the engine running, observe an AC voltmeter of sufficient voltage connected to alternator leads T1 and T2, while the field is flashing.
Attach a positive lead from a DC source to terminal 13 and the negative DC source lead to terminal 26. When the voltmeter begins to show voltage, carefully disconnect the DC source from terminals 13 and 26.
NOTE: If the rotating field was inadvertently flashed with reverse polarity, the field rectifier will fail due to high current.
Voltage Regulator Assembly
If a failure occurs in the voltage regulator assembly, the cause for the failure will usually be the result of a malfunction in the excitation or sensing circuit.
Isolate the voltage regulator assembly by disconnecting all of the leads from the regulator (1 through 10 or 10A). Use an ohmmeter to measure the resistance between the terminals listed in the VOLTAGE REGULATOR ASSEMBLY TEST CHART.
NOTE: Make certain the positive and negative ohmmeter leads are known before testing the voltage regulator assembly circuits. See topic, TEST INSTRUMENTS, to verify the ohmmeter leads.
