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| Illustration 1 | g03671408 |
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The generator is mounted between the truck frame rails | |
The power for the "Electric Drive Train System" on the 794 AC is created by the generator. The generator is isolation mounted between the frame rails forward of the rear axle housing. The generator is coupled to the engine by a torsional coupling.
The generator rotates at the same speed as the engine. Therefore, no speed sensors are installed on the generator. The "Drivetrain ECM" monitors the engine speed and will use this data to determine the speed of the generator.
The eight pole synchronous generator is rated at 2410 kW at 1800 rpm full load. Maximum speed at no load (in NEUTRAL or when dumping) is 1960 rpm.
At 1800 rpm, the generator produces three phases of AC voltage at a level of 1930 VAC line to line.
The voltage and electrical current produced by the generator will determine the amount of power available for the two traction motors.
The generator consists of the following main components:
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| Illustration 2 | g03657666 |
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Generator stator windings (rotor removed) | |
The stator is a part of the generator housing. Interior slots that are cut into the housing contain the stator or armature phase windings. The windings are coated with a resin insulation and are isolated from the stator housing. The stator windings are connected in a configuration that will produce the three phases of AC voltage output. The voltage is created by the rotation of the DC charged main rotor windings.
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| Illustration 3 | g03657668 |
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Generator rotor assembly removed - the rotating rectifier is covered in this view (1) Main rotor windings (2) Exciter stator assembly (3) Exciter field winding | |
The generator rotor assembly is the rotating part of the generator, built around the generator shaft. Main rotor (1) contains the DC field windings that induce the AC current into the stator windings as the rotor is rotated.
The Exciter Stator Assembly (2) is located next to the "Generator Rotor Assembly". The "Exciter Stator Assembly" is bolted to the front-end plate of the generator and does not rotate with the rotor.
The assembly contains the "Exciter Field Winding" (3), wound around iron cores. The "DC Field Winding" leads are connected to the positive and negative "Generator Excitation Field Regulator" (EFR) current output circuits. The current, sent to the field windings from the EFR, determines the strength of the magnetic field.
The amount of EFR DC output current that is sent to the pole windings is determined by the "Drivetrain ECM" commands to the EFR. This DC current from the EFR creates the magnetic field in the exciter field windings. The greater the DC current from the EFR, the greater the magnetic field which will result in greater voltage output from the generator.
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| Illustration 4 | g03671551 |
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Typical view of the "Exciter Rotating Assembly" (4) Ring resistor (5) Rotating exciter armature three phase windings (6) Rotating rectifier assembly | |
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| Illustration 5 | g03671555 |
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Rotating "Rectifier Diode" connections and the connections to the exciter armature and the main rotor windings (7) Diode base leads. - The three base leads on the red diodes in the assembly are anode (+) connections to the conductive DC positive rotating plate. The three base leads on the black diodes in the assembly are connections to the conductive DC negative rotating plate. The main rotor leads are connected to these conductive plates. (8) Diode flying leads. One diode anode (+) flying lead and another diode cathode (-) flying lead are connected at each of three connection nodes to an exciter armature AC connection lug. | |
The "Exciter Rotating Assembly" is mounted on the "Generator Rotor Shaft" next to the "Generator Rotor Assembly". The assembly consists of a rotor or armature with three phase windings inserted into slots in the armature, a "Rotating Rectifier Assembly", and a ring resistor.
The armature windings are in line with the "Exciter Stator Windings". The three phase leads from the armature windings are connected to a "Rotating Rectifier Assembly". The assembly is mounted on the "Generator Shaft" in front of the armature windings.
The voltage generated by the rotation of the exciter rotor or armature through the magnetic field of the exciter stator is used by the main rotor to create the magnetic field by the rotating rectifier.
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| Illustration 6 | g03657662 |
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| Illustration 7 | g03657669 |
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| Illustration 8 | g06424841 |
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The polarities of the two different diodes used in the "Rotating Diode Assembly" with the red and the black leads. | |
The "Rotating Rectifier Assembly" is a full wave bridge rectifier. The assembly consists of six individual diodes and two rotating plates.
Each of the six diodes has a "flying lead" connection and a "base lead" connection. For three of the diodes, the flying lead is the anode (+) connection and the base lead is the cathode (-) connection. The other three diodes have the flying lead as the cathode (-) connection and the base lead as the anode (+) connection. The six diode base leads are connected to either the DC negative rotating plate or the DC positive rotating plate.
The Ring Resistor is connected between the DC positive plate and the DC negative plate. The resistor is in place to protect the diodes from voltage spikes in the main rotor.
The diodes can be tested for proper operation and are serviceable. A failure of one or more of the rectifier diodes could cause the generator output to be low or erratic. If a problem is suspected with the operation of the rotating rectifier, refer to the Testing and Adjusting, "Generator Exciter - Test" section in this manual to test the operation of the diodes.
Generator Control and Operation
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| Illustration 9 | g03671562 |
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View of the location of the "Exciter Field Regulator" (EFR) on the right-hand side of the frame | |
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| Illustration 10 | g06424899 |
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"Generator Exciter Field Regulator" connections | |
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| Illustration 11 | g03657702 |
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The "Generator Excitation Field Regulator" (EFR) is on the right-hand side of the frame. | |
The "Drivetrain ECM" will use the EFR to control the operation of the generator. The EFR is mounted on the right-hand side of the frame.
The "Drivetrain ECM" will send PWM duty cycle current command signals to the EFR. The ECM command signals will determine the amount of electrical current that the EFR will send to the "Generator Exciter Winding". The PWM duty cycle range that the ECM will use for the current command circuit is 5 percent to 95 percent.
Based on these signals, the EFR will send a 0.0 amp to 20.0 amp DC electrical current to the "Exciter Stator Windings". A 5 percent signal would result in less than 1.0 amp of current being sent to the "Exciter Stator Windings" and a low generator output. A duty cycle of 95 percent will result in 20.0 amp of current being sent to the "Exciter Stator Windings" and a high generator output.
The level of electrical current that the EFR sends to the "Exciter Stator Windings" affects the stator magnetic fields. A stronger "Exciter Stator Magnetic Field" results in a greater generator output.
When a low electrical current or no electrical current is being sent to the "Exciter Stator Windings" by the EFR, the generator will produce a small output level of "residual voltage" of approximately 75 VAC or less.
The EFR DC current output that is sent to the "Exciter Stator Windings" and the rotation speed of the generator determine the level of generator output voltage and current that will be supplied to the "Inverter DC Power Bus".
To provide the power to supply the output electrical current, the EFR receives a 24.0 VDC system control power through a 40.0 amps circuit breaker. The EFR "boosts" the system voltage to 144.0 VDC. This voltage is the EFR output voltage on the exciter (+) and exciter (-) circuits that are connected to the "Exciter Stator Windings". Capacitors are used for this process.
After machine shutdown, the exciter current circuits can contain hazardous voltage levels for approximately 5 minutes as the capacitive voltage is discharged. If service is required on the EFR, wait for at least 5 minutes after engine shutdown before disconnecting the four contact exciter circuit connectors. In addition, wait for at least 5 minutes before entering the "Generator Auxiliary Connection Enclosure". Always use a multimeter to verify that there is 50.0 VDC or less at any exposed exciter circuit contacts before any other action is taken.
The "Drivetrain ECM" controls the operation of the generator based on operator control inputs, the speed status of the traction motors and communication from the two motor control ECMs.
During machine operation, the EFR monitors the internal control circuits and monitors the level of output current that is being sent to the exciter stator windings. The EFR will use two PWM feedback circuits that are connected to the "Drivetrain ECM" to indicate the EFR operational status.
The "Drivetrain ECM" uses the 5.0 VDC sensor power supply to provide the power supply for both of the PWM feedback circuits.
The EFR will use a PWM duty cycle signal on a dedicated current feedback circuit to provide an indication of the level of output current that is being sent to the "Exciter Stator Winding".
The acceptable PWM duty cycle range of the current feedback signal is 3 percent to 97 percent. The duty cycle will correspond to the 0.0 amp to 20.0 amp EFR current output.
If an abnormal condition is detected, the EFR will use a diagnostic feedback circuit to send a PWM duty cycle signal to the "Drivetrain ECM". The percentage of the PWM duty cycle is used to indicate different fault conditions that the EFR has detected to the "Drivetrain ECM".
The following table lists the PWM duty cycle signals that the EFR will use for diagnostic feedback and the indications to the "Drivetrain ECM":
| EFR Diagnostic Feedback PWM Signals | |
| PWM Duty Cycle Percentage | Indication to the Drivetrain ECM |
| Less than 5% | Feedback line short to ground. |
| 10% | EFR not enabled, power, and PWM are received - waiting for “EFR Enable” command. |
| 20% | EFR in Standby - Internal boost voltage is high with output command disabled. |
| 30% | Input voltage out of range |
| 40% | Output short circuit - Output shorted high or low |
| 50 % | Normal operation - No faults present. |
| 60% | Output open circuit. |
| 70% | Output current too high |
| 80% | PWM command from Drivetrain ECM out of the normal range (3% to 97%) |
| 90% | Undefined internal EFR fault. |
| 100% | Feedback circuit shorted to another voltage source. |
At key start switch ON, the EFR checks for abnormal conditions in the circuits and checks for normal system voltage input. If these conditions are normal, the EFR will set the diagnostic feedback circuit to an approximate 10 percent duty cycle. This duty cycle indicates that the EFR has not detected a problem and is waiting for the enable signal from the "Drivetrain ECM". The duty cycle will remain at approximately 10 percent until the ECM sends the enable signal.
Note: Anytime that the engine is OFF, the key start switch is in the ON position and no abnormal conditions are detected, the EFR feedback circuit PWM duty cycle should be 10 percent - waiting for enable.
At engine startup, the "Drivetrain ECM" will determine if the correct drivetrain system conditions are present that will allow EFR operation. When the conditions are correct, the ECM will check the feedback duty cycle. If the EFR feedback signal is 10 percent, the "Drivetrain ECM" will send an enable signal to the EFR by creating a PWM signal using an ON/OFF driver enable circuit. The duty cycle of this enable signal will be in the range of 5 percent to 95 percent.
The EFR will detect the enable duty cycle and set the diagnostic feedback circuit duty cycle to 50 percent, signaling to the "Drivetrain ECM" that the EFR is ready for operation.
Once enabled and during normal EFR operation, the PWM duty cycle of the diagnostic feedback circuit will remain at 50 percent. The duty cycle indicates to the "Drivetrain ECM" that no detected fault conditions are present. If the EFR detects that the enable signal from the ECM is no longer valid or if the EFR detects an abnormal condition in a circuit, the duty cycle of the diagnostic feedback circuit will be changed to one of the listed values in the table.
When the ECM detects the change in the duty cycle, the ECM will disable EFR operation. The ECM will disable the operation of the electric drive train. The ECM will activate a diagnostic code for the involved circuit that will indicate the detected condition.
The diagnostic codes that the "Drivetrain ECM" can activate for the EFR circuits are:
MID 081, CID 3008 - FMI's 02, 03, 04, 08 - Generator Excitation Field Regulator Diagnostic Feedback Line. - A problem has been detected in the diagnostic feedback circuit or the return circuit.
MID 081, CID 3009 - FMI's 03, 05, 06 - Generator Excitation Field Regulator Current Drive Circuit. - A problem has been detected in the exciter (+) circuit or the exciter (-) circuit that is used to send current to the "Exciter Stator Windings".
MID 081, CID 3425 - FMI's 03, 05, 06 - Generator Excitation Field Regulator Enable Line, - The PWM enable signal from the "Drivetrain ECM" has been interrupted.
MID 081, CID 3460 - FMI 08 - Generator Excitation Field Regulator Command Line. - The PWM current command signal from the "Drivetrain ECM", used to control the EFR current output, has been interrupted.
MID 081, CID 3500 - FMI's 03, 04, 08 - Generator Excitation Field Regulator Current Line. - The PWM current feedback signal that is used to inform the "Drivetrain ECM" of the status of the output current has been interrupted.
MID 081, CID 3501 - FMI's 04, 07 - Generator Excitation Field Regulator. - This code is activated for different conditions depending on the FMI code that is activated. Refer to the troubleshooting procedure in this manual for the code that is active.
Note: A loss of the "Drivetrain ECM" 5.0 VDC sensor power supply to the EFR will cause the current feedback circuit and the diagnostic feedback circuit to go to a high-voltage condition (FMI 03). The ECM will activate a CID 3500, FMI 03 diagnostic code for the current feedback circuit AND a CID 2008, FMI 03 diagnostic code for the diagnostic feedback circuit. If both of these codes are active, always verify that the "Drivetrain ECM" 5 VDC power supply is present at the harness connector for the EFR.
Note: When a high current condition is detected in the EFR current drive circuits, the "Drivetrain ECM" will activate an MID 081, CID 3009 - FMI 06 diagnostic code. A possible cause of this condition can be one or more faulty rotating diodes in the generator rotating diode assembly. Refer to the troubleshooting procedure for this diagnostic code in this manual for more information.
The troubleshooting procedures for these EFR diagnostic codes will provide more details for possible causes of the code that is active.
After the engine is started and the EFR is enabled, the DC current output that is sent from the EFR to the "Exciter Field Winding" will result in a magnetic field being set up on the stationary "Exciter Stator Windings".
When the rotating three-phase exciter armature (rotor) windings pass through the magnetic field, three phases of AC voltage are created in the armature windings which are connected to the "Rotating Rectifier Assembly".
The full wave bridge rectifier converts the three phases of AC voltage to a DC voltage. The three phases of AC voltage enable the rectifier to convert to a DC voltage that has little ripple.
This DC voltage is converted through the diodes to the positive (+) plate and the negative (-) plate in the rectifier assembly. These plates are connected to the Generator main rotor windings. The converted voltage creates the rotating main rotor magnetic field.
As the rotating main rotor magnetic field passes the three-phase connected "Generator Stator Windings", AC voltages and currents are induced that result in the generator three phases of output.
When the "Drivetrain ECM" determines that more or less generator output power is required, the ECM will command the EFR to adjust the output current to the exciter stator windings. When the EFR supplies more current to the exciter windings, the exciter stator magnetic fields will strengthen. The result is a higher level of current output from the generator. Less current to the exciter windings results in less output current being generated.
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| Illustration 12 | g03693680 |
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Generator internal components | |
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| Illustration 13 | g02077213 |
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Generator output connection diagram | |
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| Illustration 14 | g03671742 |
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The top Generator high-voltage enclosure that houses the three-phase output cable connections (A) Three-phase output cable connections (B) Generator auxiliary connection enclosure terminal strips | |
The three-phase output of the generator is directed to the AC bus bars in the "Inverter Cabinet" through three high-voltage cables. The AC bus bars in the cabinet are connected to two identical traction rectifier assemblies. One traction rectifier is connected in reverse as compared to the other rectifier. The rectifiers convert the three-phase AC voltage to the positive (+) and negative (-) sides of the "DC Power Bus".
During machine operation, the generator is cooled by the system cooling airflow. The cooling air is directed into the generator by duct work that is connected to the non-drive end cover plate.
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| Illustration 15 | g03693683 |
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Generator auxiliary connection enclosure terminal block connections - on the left-hand side of the generator | |
Generator Bearing Temperature Sensors
During machine operation, the "Drivetrain ECM" monitors the operating temperature of two of the "Generator Stator Windings". The ECM also monitors the operating temperature of the two generator shaft bearings.
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| Illustration 16 | g02080554 |
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Location "Generator Bearing Temperature Sensor" on the drive end | |
Each of the two generator shaft bearings has a probe type temperature sensor inserted in the generator housing. The temperature sensors monitor the operating temperature of the bearings.
The drive-end (engine end) bearing sensor is the "Generator Bearing 1 Temperature Sensor" and the non-drive end bearing sensor is the "Generator Bearing 2 Temperature Sensor".
The temperature sensors are base rated 100 ohm (at
The ECM will use an internal capacitance circuit to determine the resistance of the circuit.
The bearing temperature sensors are serviceable. When a bearing temperature sensor has failed, the sensor can be removed from the generator and replaced.
The expected resistance of a 100 ohm base rated RTD temperature sensor can be calculated for a known winding temperature by using the following calculations:
- The coefficient is .392 ohms per each Celsius degree of temperature
- The formula is: .392 ohms x temperature + 100 ohms = sensor resistance (ohms)
- For a temperature of 60°C, the calculation would be .392 ohms x 60 = 23.52 ohms + 100 ohms = 123.52 ohms.
- For a temperature of -10°C, the calculation would be .392 ohms x -10 = -3.92 ohms + 100 ohms = 96.08 ohms.
The resistance calculation for the temperature sensor resistance will only be useful if the approximate bearing temperature is known. If the resistance of RTD circuits between the signal wire and the return wire is known, the temperature of the bearing can be figured using the following calculation:
- The formula is: sensor circuit resistance (ohms) - 100/.392 = degrees Celsius
- For a circuit resistance 131.5 ohms, the calculation to find temperature would be 131.5 ohms -100 = 31.5 ohms divided by .392 = 80.5° C (177° F).
The "Drivetrain ECM" will activate a "Level 2 Event" if a bearing reaches a temperature of
If the "Drivetrain ECM" detects that there is a problem in a bearing sensor circuit, the ECM will activate a diagnostic code for the involved circuit (CID 3015 for "Bearing 1", CID 3016 for "Bearing 2").
Generator Stator Winding Temperature Sensors
Each of the three "Generator Stator Windings" has two temperature sensors imbedded in the winding.
The sensors are the same type of sensor that is used for the generator bearings. The temperature sensors are base rated 100 ohm (at
Refer to the calculations listed for the bearing sensors to calculate the resistance of the winding sensors.
The "Drivetrain ECM" will use two temperature sensors at any one time to determine the operating temperature of the stator windings. The two temperature sensors are referred to as the "Generator Winding 1 Temperature Sensor" and the "Generator Winding 2 Temperature Sensor". These names are used to differentiate the two separate sensor circuits. The names do not refer to specific temperature sensors.
The stator winding temperature sensors are not serviceable. If a temperature sensor has failed, one of the remaining four spare temperature sensors should be connected as a backup. The backup sensor can be connected at the terminal block in the auxiliary connection enclosure on the left-hand side of the generator.
If the "Drivetrain ECM" detects that the temperature of a winding is above the acceptable limits, the ECM will activate a "Level 2 Event" if a winding reaches a temperature of
If the "Drivetrain ECM" detects that there is a problem in a winding sensor circuit, the ECM will activate a diagnostic code for the involved circuit (CID 2780 for the winding 1 circuit, CID 2781 for the winding 2 circuit).