Introduction

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When servicing or repairing electric power generation equipment, do the following: a. Make sure the unit is off-line (disconnected from utility and/or other generators power service), and either locked out or tagged "DO NOT OPERATE". b. Make sure the generator engine is stopped. c. Make sure all batteries are disconnected. d. Make sure all capacitors are discharged. When power generation equipment must be in operation to make tests and/or adjustments, high voltage and current are present. Make sure the testing equipment is designed for and correctly operated for the high voltage and current tests being made. Improper test equipment may fail and present a high voltage shock hazard to its user.

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Do not connect the generator to a utility electrical distribution system, unless it is isolated from the system. Electrical feedback into the distribution system can occur and could cause personal injury or death. Open and secure the main distribution system switch or, if the connection is permanent, install a double throw transfer switch to prevent electrical feedback. Some generators are specifically approved by a utility to run in parallel with the distribution system and isolation may not be required. Always check with your utility as to the applicable circumstances.

Test Equipment

6V7070 Heavy Duty Digital Multimeter

Caterpillar Digital Multimeters measure voltage, resistance or current up to 10 amps. The diode function checks rectifiers. See Special Instruction SEHS7734 for the operation of 6V7070.

4C4693 Regulator Tester

The 4C4693 Regulator Tester is a bench top instrument used to test VR3F regulators. This provides a way to check a regulator without using a generator set. When using this tester to test a VR3F regulator at 60 Hz, connect jumper across terminals 6 and 10. When using this tester to test a VR3F regulator at 50 Hz, remove jumper across terminals 6 and 10.

Schematics - 4/6 Lead Self-Excited Generators

VR3F With Power Transformer

VR3F With Power Transformer And Sensing

Schematics - 10/12 Lead Self-Excited Generators

Troubleshooting

Introduction

Check for loose or corroded terminals. Make sure wire connections are correct. Check power transformer PT2 fuses (if equipped) and regulator fuses. Check accuracy of voltmeter and frequency meter/tachometer.

To reduce troubleshooting time, simplify the system or circuit by eliminating non-essential components such as remote voltage control, manual control, etc. If, at this point, it is determined that the basic system is functioning, the circuits or components can be added back in, one at a time until the problem is located.

If elimination of non-essential components does not correct the problem, the troubleshooting procedure will check components in the basic system. If all other basic components (i.e. rotating field assembly, exciter stator, etc.) are operating correctly, then replace the VR3F regulator. As a last step after confirming correct operation under no load conditions, operate the generator under a load.

The VR3F regulator is serviced as a complete unit. Its fuse holder and fuses are the only replaceable part. VR3F regulators must be checked through the bench test before making a claim on warranty (see Bench Test).

Problem List

Problem 1 - No AC Voltage.

Problem 2 - Low AC Voltage.

Problem 3 - High AC Voltage.

Problem 4 - Unstable AC Voltage.

Problem 1 - No AC Voltage

Procedure A - Check AC Voltage At Regulator Between Terminals 20 And 22

* If above 360 volts on 4/6 lead generators or 180 volts on 10/12 lead generators:

Check meters.

* If 0 volts:

Flash the field. See SR4 Generator Service Manual, SENR3985.

* If 0 to 15 volts:

Go to Procedure B.

Procedure B - Check Power Transformer PT2 Fuses

* If fuse(s) have failed:

Look for possible short circuits that could cause fuse failure such as shorted exciter field L1, etc. Make sure the minimum operating speed for the four pole generator is above 1200 rpm or the six pole generator is above 800 rpm.

* If fuse(s) are okay:

Go to Procedure C.

Procedure C - Isolate Regulator

Disconnect leads from regulator terminals F1 and F2. Connect a 12 volt automotive type battery across exciter leads F1 (+) and F2 (-). Operate generator at half of the rated speed. Then slowly increase rpm.

* If voltage at regulator terminals 20 and 22 is 0 to 15 volts (AC), shutdown the generator and:

a. Check exciter stator L1 continuity.

b. Check rotating rectifiers CR1-6 (rotating rectifier block).

c. Check surge suppression diodes CR7-8 (varistors).

d. Check main rotor L3 continuity.

e. Check exciter rotor L2 continuity.

NOTE: For more information, see SR4 Generator Service Manual, SENR3985.

* If balanced AC voltage between regulator terminals 20-22-24 increases with rpm:

Go to Procedure D.

Procedure D - Isolate Attachments

Reconnect leads to regulator terminals F1 and F2. Disconnect all attachments such as manual voltage control, remote voltage control, droop transformer, etc. Do not disconnect the power transformer PT2 (if equipped) or isolation transformer assembly T2 (if equipped).

NOTE: If remote mounted voltage adjustment is disconnected, connect jumper across terminals 4 and 7.

Check all connections to VR3F regulator, regulator fuses and power transformer PT2 (if equipped) or isolation transformer assembly T2 (if equipped).

* If generator output voltage is normal:

Check attachments.

* If voltage at regulator terminals 20 and 22 is 0 to 15 volts:

a. Go to Procedure E (if equipped with PT2).

b. Replace regulator.

c. Bench test the regulator. See Bench Test.

Procedure E - Check Connections And Continuity Of Power Transformer PT2 Wiring

Remove PT2 secondary fuses. Check continuity of secondary fuses.

Isolate PT2. Disconnect wire 20GEN, from PT2 terminal 20.

Check continuity of wires 20GEN and 24GEN from PT2 to main stator L4.

Check wire 30 continuity from the wire 30 secondary fuse to the transformer.

Check wire 31 continuity from the wire 31 secondary fuse to the transformer.

Check continuity of wire 30 from wire 30 fuse to regulator terminal 30.

Check continuity of wire 31 from wire 31 fuse to regulator terminal 24.

* If no continuity:

Repair or replace wires or fuses.

* If continuity is okay:

Go to Procedure F.

Procedure F - Power Transformer PT2 Typical Resistances

Reinstall the PT2 secondary fuses. Wire 20GEN remains disconnected. Disconnect VR3F wires 30 and 31 from PT2 terminals 30 and 31.

Measure the primary winding resistance between terminals 20 and 24.

Measure the secondary winding resistance between terminals 30 and 31.

The resistances must be as per the Power Transformer PT2 Typical Winding Resistance chart.

* If the resistance measurements are not correct:

Replace PT2.

* If the resistance measurements are correct:

Go to Procedure G.

Procedure G (For VR3F With Power And Sensing) - Check Wiring Connections And Wiring Continuity Of Isolation Transformer Assembly T2

Remove T2 secondary fuse. Check continuity of fuse.

Isolate the isolation transformer assembly T2. Disconnect and isolate wires 20GEN, 22GEN and 24GEN from terminals 1, 2 and 3 of isolation transformer assembly T2. Check continuity of wires 20GEN, 22GEN and 24GEN from isolation transformer assembly T2 to main stator L4.

Disconnect and isolate wires 20, 22, 24 and 30 from terminals 20, 22, 24 and 30 of T2. Check continuity of wires 20, 22, 24 and 30 from the isolation transformer assembly T2 to VR3F terminals.

* If no continuity:

Repair or replace wires or fuse.

* If continuity is okay:

Go to Procedure H.

Procedure H - Isolation Transformer Assembly T2 Typical Resistances

Reinstall T2 secondary fuse. Wires 20GEN, 22GEN and 24GEN remain disconnected from terminals 1, 2 and 3 of isolation transformer assembly T2. Wires 20, 22, 24 and 30 remain disconnected from terminals 20, 22, 24 and 30.

Check the winding resistance of isolation transformer assembly T2. The resistance must be as per the Isolation Transformer Assembly T2 Typical Winding Resistance chart.

* If the resistance measurements are not correct:

Replace isolation transformer assembly T2.

* If the resistance measurements are correct:

a. Replace VR3F regulator.

b. Bench test the regulator. See Bench Test.

Problem 2 - Low AC Voltage

Procedure A - Check Engine RPM (Frequency)

Procedure B - Adjust Voltage Level

The voltage level adjustment range must be within +10 to -25% of rated voltage.

* If the voltage level cannot be adjusted as described:

a. Check accuracy of voltmeter.

b. Go to Procedure C.

Procedure C - Check AC Voltage Between Regulator Terminals 20 And 22

* If greater than approximately 360 volts on 4/6 lead generators or 180 volts on 10/12 lead generators:

Check meters.

* If lower than 360 volts on 4/6 lead generators or 180 volts on 10/12 lead generators:

Go to Procedure D.

Procedure D - Isolate Regulator

Disconnect leads from regulator terminals F1 and F2. Connect a 12 volt automotive type battery across exciter leads F1 (+) and F2 (-). Operate generator at half of the rated speed. Then slowly increase RPM.

* If voltage at regulator terminals 20 and 22 is less than 100 volts, shutdown the generator and:

a. Check rotating rectifiers CR1-6 (rotating rectifier block).

b. Check surge suppression diodes CR7-8 (varistors).

c. Check exciter stator L1 resistance between F1 and F2 leads. Exciter stator resistance should be approximately 3 to 5 ohms.

NOTE: For more information, see SR4 Generator Service Manual, SENR3985.

* If balanced AC voltage between regulator terminals 20-22-24 increases with RPM:

Go to Procedure E.

Procedure E - Isolate Attachments

Connect exciter stator L1 leads to regulator terminals F1 and F2. Disconnect all attachments such as manual voltage control, remote voltage control, droop transformer, etc. Do not disconnect power transformer PT2 (if equipped) or isolation transformer assembly T2, (if equipped).

NOTE: If remote mounted voltage adjustment is disconnected, connect jumper across terminals 4 and 7.

Check all connections to: VR3F regulator, regulator fuses, power transformer PT2 (if equipped) or isolation transformer assembly T2, (if equipped).

* If generator output voltage is normal:

Check attachments.

* If voltage at regulator terminals 20 and 22 cannot be adjusted to rated voltage and rated frequency at no load:

a. Replace regulator.

b. Bench test the regulator. See Bench Test.

Problem 3 - High AC Voltage

Procedure A - Check Engine RPM (Frequency)

Procedure B - Adjust Voltage Level

The voltage level adjustment range must be within +10 to -25% of rated voltage.

* If the voltage level cannot be adjusted as described:

a. Check accuracy of voltmeter.

b. Go to Procedure C.

Procedure C - Check Connections To Regulator

* If connections are correct:

Go to Procedure D.

Procedure D - Isolate Attachments

Disconnect attachments such as manual voltage control, etc. Do not disconnect power transformer PT2 (if equipped) or isolation transformer assembly T2, (if equipped). Operate at rated rpm.

NOTE: If remote mounted voltage adjustment is disconnected, connect jumper across terminals 4 and 7.

* If generator output voltage is normal:

Check attachments.

* If voltage cannot be adjusted to rated voltage at rated frequency:

a. Replace regulator.

b. Bench test the regulator. See Bench Test.

Problem 4 - Unstable AC Voltage

Procedure A - Check Engine RPM

* If governor operation is unstable.

a. Correct engine problem. Reference engine service manual.

b. Go to Procedure B.

Procedure B - Check For Loose Connections

* If connections are okay:

Go to Procedure C.

Procedure C - Isolate Regulator

Disconnect leads F1 and F2 from their respective terminals on the regulator. Connect a 12 volt automotive type battery across exciter leads F1 and F2. Operate at half of rated speed and then slowly increase rpm.

* If voltage at regulator terminals 20-22 is unstable, shutdown the generator and:

a. Check connections to rotating rectifiers, main field poles and other connections on the rotating (revolving) field.

b. Check connections to excitor stator L1.

* If stable balanced AC voltage between regulator terminals 20-22-24 increases with rpm:

Go to Procedure D.

Procedure D - Isolate Attachments

Reconnect leads to regulator terminals F1 and F2. Disconnect all attachments such as manual voltage control, remote voltage control, droop transformer, etc. Do not disconnect power transformer PT2 (if equipped) or isolation transformer assembly T2, (if equipped).

NOTE: If remote mounted voltage adjustment is disconnected, connect jumper across terminals 4 and 7.

Check all connections: VR3F regulator, regulator fuses, power transformer PT2 (if equipped) or isolation transformer assembly T2, (if equipped).

* If generator output voltage is normal:

Check attachments.

* If voltage at regulator terminals 20-22 is unstable at rated frequency with no load:

a. Replace regulator.

b. Bench test the regulator. See Bench Test.

Bench Test

NOTE: Before making a warranty claim, use this Bench Test procedure to check VR3F regulators.

NOTE: The 4C4693 Regulator Tester with NEHS0535 Operating Manual is available for bench testing regulators. The following procedure is an alternate method of bench testing regulators.

Bench Test Circuit
(1) Voltage level rheostat. (2) Jumper - remote voltage control. (3) Jumper - single phase sensing. (4) 100W Light bulb. (5) AC power source. (6) On/Off switch. (7) Jumper - slope selection. (8) Jumper - operating frequency selection.

1. Construct and connect the bench test circuit.

2. Install jumper (3). This sets the regulator for the required single phase sensing. Install jumper (2). Jumper (2) is always present unless a remote voltage control is attached. Install jumper (8) if testing at 60 Hz and remove jumper (8) if testing at 50 Hz.

3. Turn switch (6) to the OFF position. AC power source (5) must be:

60 Hz units ... 220 to 240 VAC

50 Hz units ... 180 to 200 VAC

4. Remove protective screw from voltage level rheostat (1).

5. Turn voltage level rheostat (1) counterclockwise until the rheostat ratchets.

NOTE: Voltage level rheostat (1) is a multiple turn rheostat. The adjusting screw on the rheostat does not have a fixed stop. When the rheostat reaches the end of adjustment, a ratchet action begins. This can be felt with the adjusting tool. The adjusting screw can be turned past the rheostat stop (ratchet action) without further changing the rheostat setting.

6. Turn switch (6) to the ON position.

NOTE: If an isolation or step-down transformer is used between AC power source (5) and the regulator, it must have sufficient capacity. Measure the AC voltage between terminals 20 and 24 of the regulator. If this voltage changes more than 0.5 VAC when light (4) turns ON, a bigger transformer is required.

7. Turn voltage level rheostat (1) clockwise until light (4) first turns ON (approximately ten turns). The light should increase and decrease in intensity as rheostat (1) is turned clockwise and counterclockwise respectively. After 10 to 15 seconds at maximum intensity, light (4) should go OFF.

* If light (4) operates as described:

Regulator is okay.

NOTE: To retest the regulator, if light (4) operated as described, turn switch (6) to the OFF position for 15 seconds. If this is not done light (4) will not turn back ON.

* If light (4) reacts different than described:

Replace VR3F regulator.

Attachments

Remote Voltage Control

Partial View Of Regulator
(1) Potentiometer. (2) Jumper. (3) Regulator.

Generator output voltage level can be controlled from a remote location. This is done by connecting potentiometer (1) between terminals 6 and 7 on voltage regulator (3).

Remove jumper (2) between terminals 4 and 7 for remote voltage level control.

For acceptable voltage control, the remote mounted potentiometer must be 10k ohms ± 5% with three turns minimum and a dielectric strength of 1000 VAC minimum.

The terminals of the remote mounted potentiometer are fragile. The wiring connected to remote mounted potentiometer (1) should not have a diameter larger than 18 gauge. Larger diameter wire is not recommended. The wire should be 600 volt class with a 90°C (194°F) insulation.

NOTE: Either jumper (2) or remote potentiometer (1) is required for regulator operation. If one or the other is not connected the regulator will go to maximum voltage.

Series Boost - 10/12 Lead Self-Excited Generators

Series boost lets self-excited SR4 generators stay on the line, for approximately 10 seconds, when there is a short in the generating or load circuits. This gives circuit breakers a chance to trip in sequence. When circuit breakers trip in sequence, there is less chance for a loss of power to all of the electrical system.

Series boost consists of the series boost module and current transformer T2.

Reference: For the most current information on connecting to the primary side of the transformer, see Special Instruction, SELS0071.

Voltage sensing and power are applied to the series boost module from the voltage sensing terminals 22 and 24 of the regulator.

When the sensed voltage is within normal limits, an electrical signal is sent to the gate of a triac located in the series boost module. This triac short circuits the current transformer T2. This prevents any series boost during normal operation.

If there is a short circuit that causes the voltage at the regulator sensing terminals to drop to a low value, the control signal to the gate of the triac will be turned off. Current from current transformer T2 will be rectified and applied directly to exciter stator L1. This field current will be enough to give at least three times full load current into a short circuit. After approximately ten seconds a timer within the series boost module will again cause a control signal to be applied to the gate of the triac. The triac will short circuit the current transformer T2. Current flow to exciter stator L1 will be zero until the short circuit is corrected.

Manual Voltage Control

4/6 Lead Self-Excited Generators With Power Transformer

4/6 Lead Self-Excited Generators With Power Transformer And Sensing Transformer

10/12 Lead Self-Excited Generators

Manual Voltage Control Panel
(1) Switch (OFF, AUTO and MAN positions). (2) Voltage control rheostat. (3) Fuse.

The manual voltage control can be used to control generator voltage when there is a failure in the generator regulator assembly. It will manually control the current flow to exciter stator L1.

The manual voltage control panel has switch (1) and voltage control rheostat (2) for the manual operating mode.

Switch (1) is used to make the selection between AUTO, MAN and OFF. In the "AUTO" position, the VR3F regulator controls the generator voltage. In the "OFF" position, the voltage will go to zero. In the "MAN" position, generator voltage is controlled by voltage control rheostat (2).

NOTE: The Manual Voltage Control Panel must not be installed in a location that is subject to engine vibrations or directly to outside weather.

NOTE: When the manual voltage control is operating in the "Manual" mode, it is not necessary for the VR3F regulator to be connected to the generator. However, the manual control must remain connected to generator sensing lines No. 20 and No. 24.

Voltage Droop Transformer And Adjustment Rheostat For Parallel Operation

4/6 Lead Self-Excited Generators

Generator And Regulator Schematic
(1) Voltage droop transformer. (2) Voltage droop rheostat. (3) Lead. (4) Main stator.

10/12 Lead Self-Excited Generators

Generator And Regulator Schematic
(1) Voltage droop transformer. (2) Voltage droop rheostat. (3) Lead. (4) Main stator.

Operation of generators in parallel requires voltage droop as reactive load is increased. Droop transformer (1) and adjustment rheostat (2) are required to provide the voltage droop function. The transformer senses load current in lead (3) of main stator (4). Droop rheostat (2) provides adjustment of droop voltage. Rheostat (2) is located directly next to the regulator on the regulator mounting bracket.

Transformer (1) and rheostat (2) are standard on some generators and an attachment on others.

NOTE: Droop transformer (1) is a special ratio transformer.

NOTE: For 4/6lead generators, droop transformer (1) must be installed on generator phase lead T2 with transformer polarity connections as shown. For 10/12 lead generators, droop transformer (1) must be installed on generator phase lead T8 with transformer polarity connections as shown.

For operation of parallel generators in a zero droop mode (cross correct compensated), see Engine Data Sheet EDS75.5.

Single Phase Sensing - 10/12 Lead Self-Excited Generators

Connection Diagram For Single Phase Sensing
(1) VR3F regulator. (2) Jumper. (3) Main stator. (4) Exciter stator.

VR3F regulator (1) can be reconnected for single phase voltage sensing. This is used for special operations such as operating single phase loads with an open delta stator connection.

One sensing lead is disconnected (lead 22 in the illustration). Then jumper (2) must be provided between terminals 20 and 28 on the voltage regulator.