Testing And Adjusting

Usage:

Introduction

NOTE: For Rewind Data and Connection Diagrams, see Rewind Data for SR 4 Generators, Form No. SENR2924.

Troubleshooting

General

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Before working inside the generator, make sure that the starter motor can not be activated by any automatic or manual signal.

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When the engine-generator is operating, voltages up to 240 are present on the regulator terminal board. The heat sinks and other regulator components have an electric charge. Components will be damaged if a metal contact is made between the generator frame and the heat sinks or other regulator parts. Safety procedures must be followed.

A large percent of the electrical problems are caused by mechanical defects. Take time to carefully inspect the total installation. Keep the mechanical defects separate from the electrical defects.

For practical purposes, the generator is a constant speed unit. RPM that is 5 to 10 percent higher or lower than the rated rpm can cause terminal voltages that are 5 to 10 percent higher or lower than the rated output.

Generator heat is caused by line current. The higher the line current, the hotter the generator will become.

A voltmeter and ammeter or KW meter does not necessarily show the KVA load on a generator because of the power factor of the load.

Before working on the generator, be sure you understand the operating principles.

Find the operating trouble and use the wiring diagram and troubleshooting guide to find the probable cause.

When troubleshooting for voltage, a generator can normally be operated at a low rpm. Voltage and frequency will change directly with rpm. A four-pole, 60 Hertz, 240 volt, 1800 rpm generator at a low idle of 1200 rpm will have an output of 160 volts at 40 hertz.

NOTE: For information on mechanical and electrical characteristics of SR 4 generators, make reference to the section INDUSTRIAL DIVISION DATA SHEETS: No. 70.0.1 and the TECHNICAL INFORMATION FILE (TIF).

Test Instruments

A volt-ohm-milliammeter with 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

The 6V3030 Digital Multimeter can also be used. By itself or with other tools, it can do the following:

1. Test rectifiers with the special diode function.

2. Measures resistance of the revolving field and stator winding of the generator or exciter winding.

3. With the 6V4960 AC Current Probe, the multimeter can measure current in the range 10A to 1000A rms (at a circuit-to-ground voltage of 650 V rms maximum.) See Special Instruction, Form SEHS8011 for warnings and more information on how to use the current probe.

6V3030 DIGITAL MULTIMETER

A circuit continuity tester, similar to the 8S4627 (circuit continuity tester) can be used for checking low resistance continuity. This tool can also be used to check rectifiers and controlled rectifiers. It uses a 3-volt battery source. This is all that is needed to activate the gate of a controlled rectifier.

A Kelvin or Wheatstone bridge can be used to measure the resistance of the revolving field and stator winding of the generator or the exciter armature.

A 500 to 1000 volts megohmeter is needed to measure the insulation resistance of the generator stator, revolving field, exciter armature, and exciter field.

A DC ammeter with the correct current shunt is used to measure the current of the exiter field.

A clamp-on volt-ammeter with a 0 to 600 volts and 0 to 600 amperes scales is used to measure line voltage and line current. Some generators are rated higher than 600 amperes, but these units are normally connected with two or more conductors in parallel per phase. To measure line current for these generators, measure the current in each conductor per phase and add the currents together.

NOTE: See WARNING below, if generator is rated over 600 volts.

A direct-reading tachometer is used to measure rpm. When exact frequency control is needed, a direct comparison can be made with outside line power.

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On generators with higher than 600 volts rating do not use direct-reading test equipment to measure line voltage or line current, (even though the instrument has higher voltage capacity). Voltage and current transformers with a high voltage rating must be used. On power circuits higher than 600 volts, direct-reading meters CAN have failure of insulation.

Where the same adjustments are necessary on two or more units, (as in parallel operation) use the same instrument for measuring all voltages.

In many of the following resistance test procedures, the ohmmeter connecting polarity (positive or negative) is given for testing the respective component.

NOTE: The identification of lead polarity on ohmmeter instruments is not necessarily the same.

POLARITY CHECK OF OHMMETER TERMINAL
1. Selector switch. 2. Selector switch. 3. Mark to show polarity of ohmmeter cables.

Volt-ohm-milliameter cable polarity must be known. The red, positive "+", color on the cable of an ohmmeter can be either positive (+) or negative (-) and identification of each cable is needed.

A second volt-ohm-milliammeter (multimeter) can be used with the test ohmmeter to find the correct polarity of the connecting cables.

Turn one instrument selector switch (1) to DC volts, and turn the test ohmmeter selector switch (2) to ohms (RX1). Connect the cables of both instruments together until both instruments have a meter indication at the same time. (Change the cables if necessary).

The red, positive "+", lead from the instrument with selector switch (1) on DC volts is connected to the positive lead of the test ohmmeter. Put a mark on the ohmmeter to show the polarity of the ohmmeter cables (3). The correct positive and negative identification of the cables has been made.

On the digital multimeter, the above procedure is not necessary. Polarity is indicated on the readout.

For further information on using the digital multimeter, see Special Instruction, Form SEHS-7734.

Temperature has an effect on electrical equipment. When measuring resistance of a cold components, you will get a lower indication than you will at higher temperatures. Ohmmeters in general are not accurate. Given values of resistance will be different (up to 10 percent), if the total error of instrument method, temperature and the tolerance of the part add in one direction.

Troubleshooting Procedures For Generator/Regulator

There are four test sequence charts in Troubleshooting Procedures. Each is for a different problem. The problems are:

No AC VoltageLow AC VoltageHigh AC VoltageUnstable AC Voltage

NOTE: Before making any of the tests, first read all the information on this page and all the information in General and in Test Instruments.

Follow the test sequence chart exactly. This test sequence chart is in a logical order to find the problem with the minimum amount of time and work. By making each test in the exact step-by-step order shown on the test sequence chart, the serviceman can be sure that, at the end of the test sequence chart, the components are all good.

NOTE: If a bad part is found and a replacement part is installed, test the replacement part also. Then do the rest of the tests as shown in the test sequence chart. In this way all the bad parts will be found. This is important because one bad part can cause damage to several other parts. Then do the PROCEDURE FOR FIRST OPERATION AFTER REPAIR.

NOTE: If the AC voltage is less than 25 volts, use the No AC Voltage test sequence chart.

A separate section for troubleshooting problems with the generator mounted control panel, automatic start/stop system, follows the GENERATOR/REGULATOR test procedures.

Test Sequence Charts

NOTE: If the serviceman is familiar with the troubleshooting procedure and procedures for checking components, the following able of resistance values may save time in troubleshooting. It should be noted that these values are approximate and could change with new component changes.

No AC Voltage

AC Voltage Too High

Lack Of AC Voltage Stability

Troubleshooting Chart Index

No AC Voltage

1. Voltmeter Has a Defect.

2. Open (Tripped) Thermal Protector (TP).

3. Open Fuse (F1).

4. Engine Low Idle rpm Too Low.

5. Defect in Rotating Rectifiers (CR1 thru CR6); Surge Suppression Diodes (CR7, 8); Exciter Armature (L4); or Exciter Field (L3).

6. Exciter Field (L3) is Open.

7. Open or Short Circuit.

8. Grounded Circuit.

9. Loose Wire Connections.

10. Wrong Regulator or Generator Connections.

11. Shorted Rotating Rectifiers (CR1 thru CR6).

12. Short Circuit in Field Rectifier (CR10).

13. Loss of Residual Magnetism.

14. Controlled Rectifier (CR9) Has a Defect.

15. Rectifier Module (A2) Has a Defect.

16. Regulator Module (A1) Has a Defect.

17. Shorted Surge Suppression Diode (CR7 or CR8).

18. Shorted Surge Suppression Diode (CR11).

19. Open Suppression Reactor (L1).

20. Open SCR Reactor (L2).

21. Shorted Suppression Capacitor (C2).

22. Shorted RFI Suppression Capacitor (C1).

AC Voltage Too Low

1. Voltmeter has a Defect.

5. Defect in Rotating Rectifiers (CR1 thru CR6); Surge Suppression Diodes (CR7, 8); Exciter Armature (L4); or Exciter Field (L3).

10. Wrong Regulator or Generator Connections.

16. Regulator Module (A1) Has a Defect.

23. Open Rotating Rectifiers (CR1 thru CR6).

24. Engine rpm Too Low.

25. Load Too High or Not Balanced.

26. Voltage Level Control Setting Too Low (R2).

27. Voltage Droop Control Setting Too High (R1).

28. Regulator Gain Control Setting Too Low (R3).

45. Current in Exciter Field (L3) Is Not Stable.

46. Defect in Voltage Level Rheostat (R2).

47. Defect in Voltage Droop Potentiometer (R1).

48. Rotor Winding (L5) Defect.

AC Voltage Too High

1. Voltmeter Has a Defect.

10. Wrong Regulator or Generator Connections.

14. Controlled Rectifier (CR9) Has a Defect.^*

15. Rectifier Module (A2) Has a Defect.^*

16. Regulator Module (A1) Has a Defect.^*

29. Engine rpm Too High.

30. Voltage Level Adjustment Too High (R2).

31. Reverse Polarity on Voltage Droop Transformer (T1).

32. Regulator Gain Control Setting Too High (R3).

33. Open Regulator Gain Rheostat (R3).

34. Open Field Rectifier (CR10).^*

35. Load Not Balanced.

36. Regenerative Load Power Too High.

37. Open Regulator Power Resistor (R4).^*

38. Open Voltage Reference Circuit.

^*This item can cause a condition of temporary high AC voltage. The result is normally permanent damage to components. The secondary or visible condition is no AC voltage and an open fuse (F1).

Lack of AC Voltage Stability

1. Voltmeter Has a Defect.

4. Engine Low Idle rpm Too Low.

9. Loose Wire Connections.

14. Controlled Rectifier (CR9) Has a Defect.

16. Regulator Module (A1) Has a Defect.

32. Regulator Gain Control Setting Too High (R3).

33. Open Regulator Gain Rheostat (R3).

39. Lack of Load Stability.

40. Too Much Vibration of Suppression Reactor (L1).

41. Lack of Engine rpm Stability.

42. Damping Resistor Open (R5).

43. Temporary Short Circuit in RFI Suppression Capacitor (C1).

44. Temporary Short Circuit in Suppression Capacitor (C2).

Troubleshooting Chart

Automatic Start/Stop System (Generator Mounted Control Panel)

The charts that follow give some of the problems and probable causes for trouble with automatic start/stop systems.

Test Of Regulator Exciter Assemblies - (Regulator Removed From Generator)

FABRICATED TOOLING - FT1488

The special fabricated tooling (FT1488) provides a way to test the power generator regulator - exciter assemblies. It allows testing after repairs without connecting to the generator set.

Test Procedure

1. Preparation

A. Connect regulator-exciter to the FT tester as directed by connection chart.

B. Set voltage, droop and gain controls full CCW.

C. Set tester variac control CCW.

D. Turn power switch on.

2. Relay Test

A. Turn the variac slowly CW, at 90 ± 20 volts, there should be slight drop in the field voltage as the relay energizes.

3. Level control test

A. Set voltage level control to mid-range position.

B. Increase the variac position, raise generator voltage, until the field voltage starts to decrease and the load lamp starts to dim. This condition should occur between 200 and 260 volts on the generator voltmeter.

C. Turn the voltage level control CW, the field voltage should increase and the load lamp should brighten.

D. Turn the voltage level control CCW, the field voltage should decrease and the load lamp should dim.

4. Gain control test

A. Set variac, generator voltmeter, to 240 volts.

B. Adjust level control till load lamp is dim.

C. Turn gain control CW, load lamp brightness should increase, field voltage should increase.

5. Droop control test

A. Set gain control CCW.

B. Set variac, generator voltmeter, to 240.

C. Adjust level control till load lamp is dim.

D. Turn droop control CW, load lamp should go out, field voltage should decrease.

NOTE: If the load lamp gets brighter and field voltage increases, reverse the secondary leads of transformer T3. This should only occur the first time the tester is used.

Testing Power Rectifiers And Controlled Rectifiers

The power rectifiers and controlled rectifiers, used in the SR 4 Generator Sets, are of the stud mounted type. You must be extra careful during the installation, testing and replacement of these components.

Failure of these units can be caused by:

1. Too much current.

2. Too much voltage.

3. Too much heat.

4. Wrong torque during installation.

The type of failure normally found in a rectifier or controlled rectifier is a short circuit from anode to cathode. An open circuit failure will not be seen with any frequency. Controlled rectifiers can have a failure with either a short or an open from gate to cathode. The performance of the excitation and regulation circuits can be less than desired as a result of a change in the characteristics of these components. This type of failure can not be found with an ohmmeter or continuity tester.

Rotating rectifiers (CR1, CR2 and CR3) and field rectifier (CR10) are of the normal polarity type; that is the terminal end is the anode and the stud end is the cathode. Rotating rectifiers (CR4, CR5 and CR6) are of the reverse polarity type; that is the stud end is the anode and the terminal end is the cathode.

Controlled rectifier (CR9) is made with the stud end as the anode, the longest terminal end is the cathode and the shorter terminal end is the gate.

Ohmmeter or continuity tester (8S4627) checks can be made on these rectifiers but only to find short or open circuit conditions. To do these tests, the positive cable is connected to the anode and the negative cable to the cathode, then reverse the cables.

A shorted rectifier will have an indication of zero or very low resistance with an ohmmeter, or the light will be on with the circuit tester in both directions. An open rectifier will have an indication of infinity (maximum) on an ohmmeter or no light indication with the continuity tester in both directions. A "good" rectifier will have a much greater reverse resistance (cathode positive; anode negative) than forward resistance (cathode negative; anode positive). Typical reverse resistance is 30,000 ohms to 300,000 ohms. Typical forward resistance is less than 10 ohms.

The values you get can change with different meters.

A "good" controlled rectifier will have both forward and reverse resistance from anode to cathode of 30,000 ohms to 300,000 ohms but they must be approximately the same.

To make a test of the gate circuit of a controlled rectifier, connect the positive and negative cables of an ohmmeter to the gate and cathode terminals. Read the value of resistance. Reverse the cables and read the value again. A shorted gate will have an indication of zero resistance in both directions. An open gate will have an indication of an infinite (maximum) resistance in both directions. A "good" controlled rectifier will have a forward (gate to cathode) and reverse (cathode to gate) resistance that are about the same and approximately 10 to 200 ohms.

To make a test of the "turn-on" characteristic of the controlled rectifier use the continuity tester (8S4627). Put the positive cable of the tester on the stud end (anode) and the negative cable on the cathode terminal. Temporarily put a wire between the terminals of the gate and anode. The tester light will come on and be on until one of the cables is removed. If the light does not come on, the rectifier is bad. Install a new rectifier.

The stud used to install these rectifiers has two purposes; to give an electrical connection and a method of taking the heat away from the rectifier through the heat sink.

Be careful during the installation of a power rectifier or controlled rectifier on the aluminum heat sink. The threads on the rectifier and the contact surfaces on both the rectifier and the heat sink must be clean. Apply a small amount of 5P8937 or 5P9210 Thermal Joint Compound to the contact surfaces.

NOTE: A pound-inch (N·m) torque wrench (check accuracy in the respective torque range) must be used for installation of power rectifiers and controlled rectifiers.

The replacement of rotating rectifiers (CR1 through CR6) can be done more easily by removing the heat sink asemblies from the cooling fan. Positive heat sink (E1) has a mark "POS" and the edge has a red paint mark. Negative heat sink (E2) has a mark "NEG" and the edge has a black paint mark.

To remove the heat sink assemblies, each of the electrical connections must be opened. The assembly is fastened to the fan with two 5/16 in. tap-tite bolts. When these bolts are installed again, after removal, they must be tightened to a torque of 144 to 216 pound-inch (16.3 to 28.1 N·m). When you install the rotating rectifiers, put the terminal so that it is parallel to the long edge of the heat sink. This makes it easier when you are ready to connect the wires from the exciter armature (L4).

The replacement of controlled rectifier (CR9) and field rectifier (CR10) can be easily done by removing the rectifier module (A2) from the regulator chassis. To remove the module, each of the connections to spade terminals (6, 8, 10, 11 and 19) must be disconnected. The module can then be easily removed. The solder connections on controlled rectifier (CR9) and field rectifier (CR10) can be safely opened with a soldering gun and needle-nose pliers. When you install either of these units use a resin-core solder of the typically 60/40% (tin/lead) type. Use extra care to be sure that too much heat does not destroy the rectifers.

Voltage Regulator Module (A1)

One of the components used in the voltage regulator assembly on the SR 4 Generator is the regulator module (A1). It is completely sealed unit. Failure of the regulator is usually caused by failure of other components in the circuits of the voltage regulator assembly.

A regulator module (A1) with a defect can cause any of the following conditions:

No AC voltageAC voltage too lowAC voltage too highLack of AC voltage stability

NOTE: Do not install a new regulator module (A1) until you have thoroughly tested all of the other components and circuits in the voltage regulator assembly.

Tests can be made on the regulator module when the engine is running or is stopped. To test the regulator when the engine is running, install a single-pole, single-throw (SPST) switch in series with wire (24). This switch must have the ability to automatically turn off when it is released. Screw terminals must be on the switch.

NOTE: Remove wire (24) from terminal (24). Connect switch to wire (24). Install another wire between the other side of the switch and terminal (24).

Start the engine and run it at 1200 to 1250 rpm. Close the switch for a moment and read the value of the line voltage. If the generated voltage is approximately the same percent of rated voltage as the low idle rpm is of rated rpm, the regulator is working correctly.

SPTS SWITCH INSTALLED IN SERIES IN WIRE (24).

Example: If an electric set is rated for 240 volts at 1800 rpm (60 hertz), it will generate 160 volts at 1200 rpm (40 hertz).

Run the engine at high idle rpm and close the switch for a moment. Read the line voltage while the switch is closed. If the line voltage is approximately the same as rated voltage, the regulator module is working correctly. If the failure condition does not change, the regulator module can have a defect.

Procedure For First Operation After Repair

Do not run the electric set at rated rpm immediately after repair. The following procedure can prevent new failures if the CAUSE of the first failure condition was not correctly found.

1. Disconnect wires (10 and 19) from regulator assembly (A1). Cover the terminal of wires (10 and 19) with insulation tape.

2. Start the engine and run it at 1200 to 1250 rpm. The residual magnetism in the exciter field (L3) and the rotating field (L5) will give approximately 3 to 4 volts as measured at terminals (20) and (22). If the controlled rectifier has a short circuit, the generator will give a higher output voltage. Install a new controlled rectifier (CR9).

3. Stop the engine and connect wires (10 and 19) to spade terminals (10 and 9) of regulator assembly (A1).

4. Start the engine and run it at 1200 to 1250 rpm. The output voltage will be approximately 67 to 70 percent of the generator rated voltage. If the output voltage is too high (much higher than 70 percent of rated voltage), the failure is probably in the regulator module (A1).

5. With the engine running at a low idle rpm and the generator giving a constant voltage (approximately 60 to 70 percent of rated voltage), move the governor control to let the engine come up gradually to rated rpm. Make an adjustment to the voltage level control (R2) until the generator is at rated voltage. The generator is now ready to use.

Flashing The Field

If the generator rotating field (L5) or the exciter field (L3) have a loss of residual magnetism, the magnetism can be put back by "flashing" the exciter field winding with a direct current 6 volt source. This source can be a 6 volt battery or a stationary battery charger.

Dynamic Flashing (Engine Running)

With the engine stopped, connect a voltmeter (one with a high degree of accuracy) to terminals (20 and 22). Connect the positive "+" cable of the six volt source to terminal (F1). Start the engine and run at low idle rpm. Put the negative cable of the six volt source on terminal (F2) while reading the voltmeter. As soon as the voltmeter has an indication, remove the negative cable from terminal (F2).

NOTE: If the negative cable of the DC source is held on terminal (F2) too long, the generator voltage can become too high and cause fuse (F1) to open. An ON-OFF switch in the DC source makes the work safer and easier. If a battery is the 6 volt source, a blocking diode in series with the battery decreases the chance of blowing (opening) the fuse (F1).

Flashing With Engine Stopped (Static Flashing)

With the engine stopped, disconnect exciter field (L3) wires; (F1) from terminal (F1) and (F2) from terminal (F2). Connect the positive "+" cable of the six volt source to wire (F1). Put the negative "-" cable from the source and wire (F2) together for a moment, (two or three times). DO NOT HOLD THEM TOGETHER FOR MORE THAN ONE OR TWO SECONDS.

NOTE: According to theory, this method has the effect of putting residual magnetism back in the exciter field.

A more practical method is to flash the field with the engine running. This is dynamic flashing.