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 600V are present in these areas near or on the regulator: 1. the regulator terminal strip 2. the excitation transformer terminal strip (self-excited generator only) Do not short these terminals to ground with any part of the body or any conductive material. Loss of life or injury could result from electrical shock or injury from molten metal.

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An electrical shock can be received from the regulator capacitor (C1) when the engine-generator is not in operation. To avoid possible injury, discharge the stored charge using an 100 ohm resistor across C1 terminals.

The following general rules should be read and used as a guide when troubleshooting a generator:

1. 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.

2. The generator is basically 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.

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

4. 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.

5. Before working on the generator, the operating principles must be understood.

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

7. When troubleshooting for voltage, a generator can normally be operated at a low rpm. Voltage and frequency will change directly with rpm.

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

Test Instruments

Caterpillar Digital Multimeter - can be used for many of the voltage and resistance checks. Rectifiers can also be checked with the special diode function. For further information on using the digital multimeter, see Special Instruction, Form SEHS-7734-01.

Caterpillar AC current probe (clamp-on type) - used with the Caterpillar Digital Multimeter, it can measure current in the range 10A to 1000A rms (at a circuit-to-ground voltage of 650 rms maximum). See Special Instruction, Form SEHS8011 for warnings and information on how to use the current probe.

Volt-ohm-milliameter (needle movement type) - 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.

Temperature has an effect on electrical equipment. When measuring resistance of 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.

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.

Continuity tester - 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. It uses a 3 volt battery source.

Megohmeter - A 500 to 1000 volts megohmeter is needed to measure the insulation resistance of the generator stator and exciter field.

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

Clamp-on volt-ammeter - A clamp-on volt-ammeter with a 0 to 600 volts and 0 to 600 amperes scale 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 the following WARNING if generator is rated over 600 volts.

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

Tachometer - 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.

Kelvin or Wheatstone bridge - A Kelvin or Wheatstone bridge is needed to measure the resistance of the revolving field and stator winding of the generator or the exciter armature.

Troubleshooting Procedures For Generator/Regulator

There are six test sequence charts in the Troubleshooting Procedures:

No AC Voltage (PM Excited System)No AC Voltage (Self-Excited System)Low AC VoltageHigh AC VoltageUnstable AC Voltage (PM Excited System)Unstable AC Voltage (Self-Excited System)

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.

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

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After working on a generator, the main output leads (wires) on the generator must be checked. They must be held in place so they do not move against the frame. Movement against the frame can wear away the insulation on the leads. This can cause personal injury or death and/or damage to the generator as a result of an electrical short.

Troubleshooting Charts

NO AC VOLTAGE (PM EXCITED SYSTEM)

No AC Voltage (Self-Excited System)

AC Voltage Too Low (Either Excited System)

AC Voltage Too High (Either Excited System)

Lack Of AC Voltage Stability (PM Excited System)

Lack Of AC Voltage Stability (Self-Excited System)

Troubleshooting Chart Index

Possible Causes And Verification Procedure

Exciter Field Current And Voltage

For specific and up-to-date values of exciter current and voltage, make reference to the Technical Information File (TIF) (on microfiche). However, the following chart can be used as a general guideline for no load values of exciter field volts and amps. The stator and rotor winding temperature should be as follows:

1. for standby - 130°C (266°F) plus ambient temperature.

2. for continuous - 90°C (194°F) plus ambient temperature.

Exciter Field Current And Voltage Chart

Procedure For First Operation After Repair

VOLTAGE ADJUSTMENT CONTROLS
R1 Voltage droop control. R2 Voltage level control. R3 Gain control.

1. Remove the left side access panel of the generator.

2. Loosen the locknuts on the voltage droop, voltage level, and voltage gain controls.

3. Turn the voltage droop control R1 counterclockwise to zero droop and tighten the locknut.

4. Turn the gain control R3 counterclockwise to zero, then turn the gain control to about 1/4of full range of clockwise travel.

5. Perform required maintenance on engine before starting.

6. Start the engine and allow it to warm.

7. Increase engine speed to full governed speed (high idle).

8. Observe the voltmeter reading. If desired voltage is not indicated, set no load voltage with voltage level control R2.

9. Close the load circuit breaker and apply full load gradually. Adjust governor control until nameplate frequency is on the Hertz meter.

10. If voltmeter reading -

a. Increases with full load applied, turn gain control R3 slightly in counterclockwise direction.

b. Decreases with full load applied, turn gain control R3 slightly in clockwise direction.

11. Remove load, adjust voltage level control R2 if necessary to obtain desired voltage.

12. Apply the load, observe voltmeter reading. Repeat steps 9 thru 12 until no load voltage equals full load voltage.

13. Tighten the locknuts on all controls and install the access panel of the generator.

14. Circuit breaker (1) will open if excessive field current should occur. Push to reset the circuit breaker. If breaker opens again, go to the TROUBLESHOOTING section.

Flashing The Field - (Self-Excited Generator)

If the generator rotating field (L4) 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 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.

The Effect Of, And Testing For Moisture In SR-4 Generator Windings

Moisture can cause severe problems in electrical generators. It can lead to costly generator repairs. This section gives information on how to check for the effects of moisture on generators and how to help prevent moisture from damaging the generator.

Effects Of Moisture On Windings

If moisture is allowed to remain in contact with an electrical winding, some of the moisture will eventually be absorbed. This will lower the resistance of the winding insulation. The insulation used on the windings of Caterpillar generators is moisture resistant, but constant exposure to moisture will gradually lower the insulation's resistance.

Dirt can make the problem worse because it can hold the moisture in contact with the insulation. Salt (from sea air) can also make the problem much worse. This is because salt tends to absorb moisture from the air. When the salt and moisture combine, they make a good electrical conductor.

If moisture has caused the main stator winding (L5) to have a low resistance to ground, current can flow from the main stator winding to ground when the generator is operated. Because of the high voltage between this winding and ground, the current flow could become high enough to cause additional break down of the insulation and damage the winding. Generator down time and significant repair cost can be the result of insulation breakdown.

If moisture has caused the exciter field winding (L2) to have a low resistance to ground, a current can flow from the exciter winding to ground. The voltage between this winding and ground is much less than between the main stator winding (L5) and ground, so an insulation breakdown is not likely to occur. But an electrolysis process can cause copper to be eroded from the winding until the winding becomes an open circuit.

Rotor windings are not as sensitive to moisture as the main stator winding or the exciter field winding. This is because the rotor is electrically isolated from ground and much lower voltages are involved.

Generators should be stored in a clean, dry area with minimal ambient temperature variation. Ambient temperature variation can cause condensation to form moisture on the generator windings. One method to stop condensation is to use space heaters or similar devices to heat the inside of the stored generator. Before a generator that has been stored is put into service, perform a megohmmeter test on the main stator and exciter field windings.

Measuring Insulation Resistance

The insulation resistance of an electrical winding can be measured with a megohmmeter. This instrument applies a high voltage (500 to 1000 volts) between the insulated winding and ground and then measures the very small current that flows in that circuit. It converts that very small current flow into a resistance reading.

Before using a megohmmeter to check the insulation resistance of the main stator winding, disconnect any external grounds, loads, meters or controls. Also disconnect the voltage regulator, terminals 20, 22, 24 and 26. Connect all the sections of the stator windings together in the normal high or low voltage connections. Connect one lead of the megohmmeter to one of the stator windings and the other lead to the generator frame or ground. Follow the megohmmeter manufacturer's directions and measure the stator windings insulation resistance. The megohmmeter reading must not be less than 1 megohm. If the reading is less than 1 megohm, the winding must be dried.

Before using a megohmmeter to check the insulation resistance of the exciter field winding, disconnect the F1 and F2 exciter field leads from the regulator. Connect one megohmmeter lead to either the F1 or F2 field lead; make sure the other field lead is not touching anything. Connect the other megohmmeter lead to the generator frame or ground. Follow the megohmmeter manufacturer's directions and measure the resistance of the exciter field insulation. The megohmmeter reading must not be less than 1 megohm. If the reading is less than 1 megohm, the winding must be dried.

One megohm is an approximate value for determining if the winding insulation resistance is sufficient. That is, it can be possible to operate the generator with less than one megohm resistance without failure. However, a generator with low winding insulation resistance is far more likely to have a failure than a generator with acceptable insulation resistance.

Methods For Drying Generator Windings

One of the best methods for drying the generator winding and preventing a moisture build-up is the use of space heaters. The same type space heaters used in marine generator applications can be installed. Operate the space heaters for at least 4 hours, then repeat the megohmmeter test. Continue to operate the space heaters until the megohmmeter reading is greater than 1 megohm. See the next section, Space Heaters, in this manual for information on location and connection of space heaters.

Another method that can be used to dry the winding is to put the generator in an oven. Heat the generator to approximately 65° C (150° F) for four hours. Repeat the megohmmeter test.

Reconditioning

If the megohmmeter test reads less than 1 megohm after drying or if a reading of 1 megohm or higher cannot be maintained with space heaters, the insulation has deteriorated and should be reconditioned. Generator reconditioning should be done by an electrical shop. During reconditioning the generator is disassembled. The windings are thoroughly cleaned and oven dried. If megohmmeter tests of the winding insulation resistance can be brought up to an acceptable level, the winding may be resealed by dipping in a tank of insulating varnish.

Recommended Periodic Insulation Resistance Checks

Use a megohmmeter to check generator winding insulation resistance periodically. The frequency of the megohmmeter test is determined by the generator's environment and by previous megohmmeter test indications.

Megohmmeter test every 6 months if the generator is installed in an enclosed building with relatively low humidity and minimal temperature variations.

Megohmmeter test every 3 months if the generator is not protected from the elements by an enclosed building.

Megohmmeter test every week and use space heaters if the generator is exposed to a sea water environment or if the surrounding conditions are very humid (relative humidity above 75%) or if a recent megohmmeter test reading was less than 3 megohms. In applications where salt and high humidity are present, space heaters must be operated whenever the generator is not operating under load. This is the only way to maintain megohmmeter test readings above 1 megohm.

Space Heaters

Introduction

SPACE HEATER LOCATION
1. Space heaters.

The SR-4 generator can operate in high humidity conditions without problems. However, problems can occur when the generator is idle and the surrounding air is warmer than the generator. Moisture can form on the windings and result in poor performance and even result in damage to the windings.

Space heaters (1) come as standard equipment on marine generator sets. All generators have drilled holes to accommodate later installation of a space heater.

Connection To External Source

SPACE HEATER TERMINAL STRIP (Self-excited generator - cover removed from left side)

SPACE HEATER TERMINAL STRIP (PMG GENERATOR - cover removed from left side)

An external source of either 115 or 230 (200 V at 50 Hz) volts A.C. is required to operate the space heaters.

SPACE HEATER CONNECTION TO EXTERNAL SOURCE H1, H2, H3, H4. Terminal strip terminals.
1. Heater coil (two).

If 115 VAC source is available, connect both heaters in parallel across the source (L1-L2). If 230 VAC source is available, connect both heaters in series across the source (L1-L2).