| Resistor assemblies in located in the rear of the cabinet. Left - Inverter Active Resistor Assembly. Right - Discharge Resistor Assembly |
Two resistor assemblies are located in the rear left-hand side of the Inverter Cabinet. Each resistor assembly consists of four separate resistors.
The assembly on the left-hand side is the Inverter Active LED Resistor assembly. The assembly on the right-hand side is the Discharge Resistor Assembly.
The two assemblies look identical, however, the two assemblies are not interchangeable. The resistance values of the resistors in each assembly are not the same.
Inverter Active LED Resistors
| Inverter Active Lamps illuminated indicating that the Inverter DC Power Bus voltage is greater than 150.0 VDC |
The Inverter Cabinet is equipped with two Inverter Active Lamps that are located above the Retarding Contactor compartment. The two LED lamps are illuminated any time that the voltage on the DC Power Bus is greater than 150.0 VDC. The lamps will operate regardless of the state of the key start switch.
The Inverter Active Lamps are used as a visual aid in order to indicate the status of the DC Power Bus. The Inverter Active Lamps are not designed or intended to be used as an absolute indication that the DC Power Bus has been discharged. Regardless of the state of the Inverter Active Lamps, the DC Power Bus voltage must be manually measured using a high voltage meter. The voltage must be verified to be below 50.0 VDC before any service procedure or maintenance procedure can be performed on any of the electric drive system high voltage components.
Refer to the Troubleshooting, "Electrical Shutdown and Voltage Discharge" section of this manual for the procedure to verify that the system high voltage has been properly discharged.
| Four Inverter Active LED Resistors located in the rear cabinet |
| Inverter Active LED Resistor connections |
In order to enable the Inverter Active Lamps to turn ON when the voltage of the DC Power Bus is greater than 150.0 VDC and turn OFF when the voltage of the DC Power Bus is less than 150.0 VDC, two resistors are connected in series with each lamp.
Each resistor is a 35 kohm resistor that is rated for 500 watts.
An LED protection resistor is connected in parallel with each lamp in order to protect the lamp from voltage spikes. These resistors are a part of the LED lamp assembly.
Discharge Resistors
| Four discharge resistors located in the rear cabinet |
The Discharge Resistor Assembly consists of four 15 kohm resistors that are rated for 500 watts.
This resistor assembly is used for several functions. The primary function of the resistors is to provide a connection point for the Ground Fault Detection Sensor. This voltage sensor is used to detect ground faults in the electric drive system.
One set of two series connected resistors are connected in parallel with another set of two series connected resistors. The DC positive (+) bus is connected to one end of the resistor configuration and the DC negative (-) bus is connected at the other end.
The voltage sensor is connected between each set of the series connected resistors. The voltage at the point of sensor connection will always be exactly half of the total voltage of the DC Power Bus voltage. This center point creates a balanced voltage reference point of connection for the voltage sensor.
If a fault to ground occurs somewhere in the system, the balance of the DC bus voltage will shift from the original center reference point to either the (+) side or the (-) side of the bus. The Ground Fault Detection Sensor detects this shift. The amount of shift from the original reference point indicates the amount of ground fault "leakage" that is occurring. The frequency and the direction of the shift will indicate whether the ground fault is in the AC section of the system or in the DC section of the system.
For more information on the operation of the Ground Fault Detection Sensor, refer to the "Voltage Sensors" section that follows.
Another function of the Discharge Resistor Assembly is to provide a path to ground that will discharge the voltage of the DC Power Bus if other discharge components such as the Retarding Contactors or the Chopper Module should fail to active.
A discharge of the DC voltage only through the resistor assembly will occur in approximately 15 minutes.
Voltage Sensors
Three voltage sensors are used in the electric drive system. The DC Bus Voltage 1 Sensor (DCPT 1) and the DC Bus Voltage 2 Sensor (DCPT 2) voltage sensors are connected between the DC positive (+) bus and the DC negative (-) bus. As discussed in the previous section for discharge resistors, the Ground Fault Detection Sensor is connected to a voltage divider circuit. The sensor is used to detect ground faults in the system.
DC Bus Voltage 1 Sensor (DCPT 1), DC Bus Voltage 2 Sensor (DCPT 2)
| Upper photo - DC Bus Voltage 1 Sensor (DCPT 1) (L) and Ground Fault detection Sensor (R) location in the crowbar tray, lower photo - DC Bus Voltage 2 Sensor (DCPT 2) in the rear cabinet |
| The DC Bus Voltage 1 Sensor (DCPT 1) connections in the Inverter Cabinet |
| The DC Bus Voltage 2 Sensor (DCPT 2) connections in the Inverter Cabinet |
The DC Bus Voltage 1 Sensor (DCPT 1) and the DC Bus Voltage 2 Sensor (DCPT 2) are used to monitor the voltage level of the DC Power Bus.
Each of the voltage sensors are monitored by the Motor 1 ECM and the Motor 2 ECM. The voltage status is provided to the Drivetrain ECM over the CAN B Data Link circuits.
The voltage sensors receive +15 VDC and -15 VDC power supplies from a motor control ECM. A sensor ground is connected to the cabinet ground block that is located below the terminal blocks in the cabinet.
The voltage sensors provide a current output that is proportional to the voltage of the bus. At 3000 VDC, the current output of the sensor is 50 milliampere.
The current output circuit is connected at one of the terminal blocks. In order for the ECM to interpret the sensor current output, a 150 ohm burden resistor is connected between the sensor signal circuit and a ground connection at the terminal block.
Each ECM will receive an input from the signal side of the resistor and an input from the ground side of the resistor. These two inputs allow the ECM to measure the voltage drop across the resistor. The voltage drop will be used to calculate the bus voltage.
Each +/- 1.0 VDC drop across the resistor will be interpreted as a voltage of 412.0 VDC by the ECM.
If the voltage status information that the Drivetrain ECM is receiving from each motor control ECM is slightly different, the Drivetrain ECM will consider the higher voltage to be relevant.
If the voltage status information that the Drivetrain ECM is receiving from each motor control ECM is different by greater than 200.0 VDC, the Drivetrain ECM will activate a level 2 E1126 (DC Power Bus Voltage Mismatch) Event.
Motor 1 ECM will monitor the signal circuit of the DC Bus Voltage 1 Sensor (DCPT 1) for diagnostics. If an abnormal condition is detected, the ECM will activate a CID 2934 (DC Power Bus Voltage 1) diagnostic code.
Motor 2 ECM will monitor the signal circuit of the DC Bus Voltage 2 Sensor (DCPT 2) for diagnostics. If an abnormal condition is detected, the ECM will activate a CID 2935 (DC Power Bus Voltage 2) diagnostic code.
Ground Fault Detection Sensor
| The Ground Fault Detection Sensor connections in the Inverter Cabinet |
The Ground Fault Detection Sensor operates in the same manner as the two DC bus voltage sensors, however, the Ground Fault Detection Sensor is used to detect ground faults in the electric drive system.
The Ground Fault Detection Sensor voltage sensors receive +15 VDC and -15 VDC power supplies from the Motor 2 ECM. A sensor ground is connected to the cabinet ground block that is located below the terminal blocks in the cabinet.
The positive high voltage connection for the sensor is connected between each of the series connected resistors in the Discharge Resistor Assembly. The negative high voltage connection for the sensor is connected to a system ground. The voltage at the point of positive sensor connection will always be exactly half of the total voltage of the DC Power Bus voltage in reference to ground. This center point creates a balanced voltage reference point of connection for the voltage sensor.
If a fault to ground occurs somewhere in the system, the balance of the DC bus voltage will shift from the original center reference point to either the (+) side or the (-) side of the bus. The Ground Fault Detection Sensor detects this shift. The amount of shift from the original reference point indicates the amount of ground fault "leakage" that is occurring. The frequency and the direction of the shift are used to indicate whether the ground fault is in the AC section of the system or in the DC section of the system.
The Ground Fault Detection Sensor will provide a current output that is proportional to the voltage shift from the balanced voltage point of the bus.
The current output circuit is connected at one of the terminal blocks. In order for the ECM to interpret the sensor current output, a 453 ohm (5 watt, one percent tolerance) burden resistor is connected between the sensor signal circuit and a ground connection at the terminal block. This resistor provides a smaller and more accurate voltage measurement.
Each ECM will receive an input from the signal side of the resistor and an input from the ground side of the resistor. Two inputs allow the ECM to measure the voltage drop across the resistor which will indicate the amount of voltage shift from the balance point.
Each +/- 1.0 VDC drop across the resistor will be interpreted as a voltage of 145.0 VDC by each motor control ECM.
A small amount of electrical leakage to ground will not cause a problem in the system. Larger amounts can cause damage of the system components and may require immediate action.
The amount of voltage shift from the balanced point can be observed using the Cat ET service tool. The amount of shift will be displayed as a percentage.
For a ground fault that is detected in the DC section of the system, the percentage of shift and the related actions are:
- 0 percent to 30 percent - acceptable amount of leakage to ground, no indication will be activated.
- 30 percent to 60 percent - A level 2 E988 (DC Ground Fault) Event will be activated. Ground fault leakage at this level will not damage components in the system. The condition may require attention if the level 2 event remains active for a long time period (hours).
- 60 percent to 100 percent - A level 3 E988 (DC Ground Fault) Event will be activated. Ground fault leakage at this level could damage components in the system. An immediate safe shutdown of machine operation is required.
For a ground fault that is detected in the AC section of the system, the percentage of shift and the related actions are:
- 0 percent to 20 percent - acceptable amount of leakage to ground, no indication will be activated.
- 20 percent to 40 percent - A level 2 E1184 (AC Ground Fault) Event will be activated. Ground fault leakage at this level will not damage components in the system. The condition may require attention if the level 2 event remains active for a long time period (hours).
- 40 percent to 100 percent - A level 3 E1184 (AC Ground Fault) Event will be activated. Ground fault leakage at this level could damage components in the system. Immediate safe shutdown of machine operation is required.
Note: A 100 percent AC or DC ground fault will indicate a direct short circuit to frame ground.
For more information on the action that should be taken when a ground fault event is activated, refer to the Troubleshooting, "E988 or E1184" section of this manual.
See You Soon!!!
MARYGAR
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