| Nine of the 12 system current sensors for the measurement of the traction motor phases and the Generator phases (71) Motor 2 phase current sensors - left to right: M2BCT, M2ACT, M2CCT (72) Generator phase current sensors - left to right: GENA CT, GENB CT, GENC CT(73) Motor 1 phase current sensors - left to right: M1CCT, M1ACT, M1BCT |
| Current sensor locations (74) Chopper current sensor (CMCT) in the grid connection enclosure on the lower left front of the Inverter Cabinet. (75) Contactor current sensor (BMCT) located in the rear right-hand side of the Inverter Cabinet.(76) DC bus current sensor (DCCT). |
Note: For detailed schematic diagrams of the Inverter Cabinet connections for each of the system current sensors, refer to the Testing and Adjusting, "System Schematic" section in the back of this manual.
Twelve current sensors, also called current transformers (CT), are used to monitor the current of various circuits in the electric drive system. Ten of the CT's are rated for 3000 amps. The other two CT's are rated for 1500 amps. A label on the side of each CT lists the amperage rating as either "3KA" or "1.5 KA".
An arrow is molded on the top of each CT. The direction of the arrow is matched to the direction of current flow in the monitored circuit when the CT is installed.
For troubleshooting, a CT can be switched with another CT that is rated for the same amperage. Do not switch a 1500 amp rated CT with a 3000 amp rated CT.
The 12 CT's, the rated amperage, the function of each CT and the controlling ECM are listed below.
CT's that provide input to the Motor 1 ECM:
- M1ACT (3000 A) - monitors the AC current of the Traction Motor 1 phase A Inverter output.
- M1BCT (3000 A) - monitors the AC current of the Traction Motor 1 phase B Inverter output.
- M1CCT (3000 A) - monitors the AC current of the Traction Motor 1 phase C Inverter output.
- Contactor current sensor (BMCT) (1500 A) - monitors the DC current through Contactor Grid. Current should only flow in this circuit when the retarding contactors are closed.
- Chopper current sensor (CMCT) (1500 A) - monitors the DC current through the Chopper Grid. Current should only flow in this circuit when the Chopper Module is active or when the Crowbar has been activated.
CT's that provide input to the Motor 2 ECM:
- M2ACT (3000 A) - monitors the AC current of the Traction Motor 2 phase A Inverter output.
- M2BCT (3000 A) - monitors the AC current of the Traction Motor 2 phase B Inverter output.
- M2CCT (3000 A) - monitors the AC current of the Traction Motor 2 phase C Inverter output.
- DC bus current sensor (DCCT) (3000 A) - monitors the DC current of the DC Power Bus that is rectified from the Generator output.
- GENA CT (3000 A) - monitors the AC current of the Generator phase A output.
- GENB CT (3000 A) - monitors the AC current of the Generator phase B output.
- GENC CT (3000 A) - monitors the AC current of the Generator phase C output.
Each of the CT's are supplied with +/-15.0 power supplies from the controlling ECM. Each CT will supply a positive (+) signal circuit and a negative (-) signal circuit to the ECM.
When current is flowing through a monitored circuit, a hall effect element in the sensor detects the created magnetic field. The CT converts the field to a voltage output that can range from - 10.0 VDC to + 10.0 VDC. The ECM will equate the amplitude of the voltage signals to a specific current for the circuit.
Each motor control ECM monitors the signal circuits of each CT for diagnostics. If an abnormal circuit condition is detected, the ECM will activate a diagnostic code.
2.-Retarding Grid Blower Inverter
| Retarding Grid Blower Inverter power supply connections, control circuit connections, and three phases of output to the Grid Blower Motor connections |
| Retarding Grid Blower Inverter located in the rear right-hand side of the Inverter Cabinet |
| Retarding Grid Blower Inverter pilot relay (77) Inverter Cabinet ground block located in the upper right hand (facing front of truck) low voltage compartment in front of the terminal blocks(78) Retarding Grid Blower Inverter pilot relay located next to the ground block |
The Retarding Grid Blower Inverter (RGBI) is used to create the three phase AC power supply for the grid blower motor. The grid blower motor is a three phase AC induction motor. The motor turns the fan that is used to cool the grid resistor elements.
The grid resistor elements are used as a resistive load primarily when the retarding mode is used.
When electrical current is directed through the resistor elements, the electrical energy is converted to heat energy. The process creates a large amount of heat in a short amount of time. The heat must be dissipated quickly in order to prevent the resistor elements from overheating.
In order to control the grid blower motor, the RGBI receives a DC power supply from circuits that are connected to tapped connections on one of the contactor grid resistor elements.
When the retarding contactors close, DC bus voltage is sent through the grid 2 resistor elements. This supplies the DC voltage to the RGBI. The RGBI inverts the DC voltage to three phases of modulated PWM voltage in the same manner as the drive train system Inverter supplies for the traction motors.
The RGBI uses internal power transistors to invert the DC voltage to three phases of modulated PWM voltage that the blower motor will see as AC voltage. The frequency of the PWM voltage will determine the rotational speed of the blower motor.
The frequency of the PWM voltage and the resulting speed of the fan is dependent on the DC voltage supply that is received by the RGBI from the tapped contactor grid circuits.
Internal electronics in the RGBI measure the DC supply voltage and an internal software map determines the frequency of the output voltage at a ratio of 5.55 VDC to 1 hz.
During retarding, the RGBI will use the maximum frequency for the inverted output voltage in order to operate the fan at the maximum speed.
The low voltage control circuits for the RGBI include a system control voltage power circuit that is fed through a pilot relay, a ground connection, three grounded harness code connections and two CAN B Data Link circuits.
If a grid-related fault condition causes the Drivetrain ECM to disable the operation of the retarding grid, control power must be cycled OFF and back ON in order to reset the RGBI. The RGBI pilot relay is used for this purpose. When the fault condition is cleared, the Motor 1 ECM will cycle the sinking driver relay circuit OFF and then ON in order to reset RGBI operation.
The harness code connections indicate the truck model that the RGBI is installed on. The harness code allows the RGBI to activate the correct software.
RGBI communication to each motor control ECM is conducted on the CAN B Data Link circuits. The RGBI can only send information. The RGBI cannot receive information from the other control modules on the data link.
The RGBI sends information to the controls indicating the status of the harness code, the output frequency, the current for each motor phase output, the internal temperature, and the voltage of the DC power supply from the grid 2 taps.
The RGBI also will use the data link to send status information for any detected fault conditions. When a fault condition is detected, the Motor 1 ECM will activate the appropriate Event. The Events that can be activated for RGBI fault conditions are:
- E1076 - Electric Retarding Grid Fan Motor Phase Current Incorrect
- E1077 - High Electric Retarding Grid Fan Motor Voltage Incorrect
3.-System Capacitors
DC Power Bus Capacitor
| DC Power Bus Capacitor |
The DC Power Bus Capacitor consists of two capacitors in one enclosure. The two capacitors are connected in parallel between the DC positive (+) bus and the DC negative (-) bus. The capacitors provide 1667 microfarads of capacitance.
All of the capacitors in the system that are connected between the positive and the negative DC bus are connected in parallel.
The capacitance of the DC Power Bus Capacitor is combined with the capacitance of the phase module internal capacitors and other system capacitors. The DC Power Bus Capacitor provides about one eighth of the total system capacitance. The system capacitance acts as a reserve that will help to maintain the power that is available on the DC Power bus during times of high demand.
In addition, the system capacitance helps to smooth the "ripple" on the DC Power Bus that is created by the rectification of the Generator three phase outputs.
When the Engine and the Generator are shut down, the large system capacitance will still be charged with high voltage that is close to the operating level of the DC Power Bus. This capacitive voltage must be discharged in order to avoid accidental or unintended discharge.
The following multiple processes are designed into the system to discharge this stored voltage at the time of machine shutdown:
- The retarding contactors close which shorts the DC positive bus and the DC negative bus through the contactor grid 2 resistors.
- The Chopper Module is activated which shorts the DC positive bus and the DC negative bus through the chopper grid 1 resistors.
- The voltage of the DC Power Bus will naturally discharge through the Discharge Resistor Assembly after about 15 minutes.
- The voltage of the DC Power Bus will naturally discharge through the Inverter Active LED Resistor circuits.
There is a slight possibility that multiple failures of the discharge systems could allow capacitive DC voltage to remain in the system after machine shutdown.
For verification that the voltage is discharged to less than 50.0 VDC, a manual measurement using a high voltage meter must be done before performing maintenance procedures on the machine high voltage electrical system. Refer to the Troubleshooting, "Electrical Shutdown and Voltage Discharge" section of this manual in order to verify that the capacitive voltage has been properly discharged.
Bulk Capacitors
| Bulk capacitors located in the Inverter Cabinet front left hand low voltage compartment |
| Bulk capacitor connections |
System 24 volt power is supplied to each of the bulk capacitors by the respective interface modules. The main function of the bulk capacitors is to provide emergency power to the interface modules if the motor control ECM was to lose system power.
During a power loss, the bulk capacitors will supply approximately 3 seconds of system power to the interface modules. The backup power will allow each interface module to shut down transistor operation under full control power.
A shutdown of transistor operation during a low control voltage condition can cause transistor misfires which could result in direct shorts across the DC bus.
Retarding Grid Blower Inverter Capacitor, Ground Detection Capacitor
| Upper photo - Ground Detection Capacitor located in the crowbar tray compartment. Lower photo - Retarding Grid Blower Inverter Capacitor located in the rear right-hand side of the Inverter Cabinet |
| Retarding Grid Blower Inverter Capacitor connections |
| Ground Detection Capacitor connections |
The Ground Detection Capacitor and the Retarding Grid Blower Inverter Capacitor are used as protection devices in the respective circuits. Both of the capacitors are identical.
Each module consists of three 1 microfarad capacitors in a single enclosure.
Two of the three capacitors in the Ground Detection Capacitor are connected in parallel to the Discharge Resistor Assembly. The third capacitor is connected between the voltage divider circuit and a ground connection.
The connection configuration provides a low resistance path to ground for high frequency voltage spikes on the DC bus that are caused by the high frequency switching of the power transistors. The resistor assembly enables more stable transistor switching.
The Retarding Grid Blower Inverter Capacitor is connected between the tapped DC positive (+) and the DC negative (-) circuits that are connected to the Grid 2 resistor elements.
When the retarding contactors close, the DC current from the power bus is directed through the contactor grid 2 resistors. The current energizes the tapped DC supply circuits for the Retarding Grid Blower Inverter (RGBI).
When the contactors open and close, there is a slight difference between the time that each contactor actually makes or breaks contact. This time differential can cause voltage spikes that are absorbed by the Retarding Grid Blower Inverter Capacitor which protects the RGBI circuits from possible damage.
See You Soon!!!
MARYGAR
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