D7E Track-Type Tractor Hydraulic, HVAC, and Electrical Systems Caterpillar

Isolation and Grounding of the Power System

Hazardous electrical system voltages are created during the operation of the Electric Drive System. The hazardous voltages are electrically isolated from the machine frame.

The housing for each component of the Electric Drive System is connected to the machine frame by a ground strap. The bus bars, the power transistors, the generator windings, and the windings for the motor that are conducting electricity are isolated from frame ground. All of these components are located in an enclosure that is electrically grounded to the machine frame.

In addition to grounding the housing for each component to the machine frame, the housings are grounded to each other and to the machine frame by a bonding ground wire system.

The housings for the following main components are connected to the bonding ground wire system:

• The Generator

• The Power Inverter

• The Electric Drive Propulsion Module

• The Accessory Power Converter (APC)

• The Motor Control for the Water Pump "If Equipped"

• The Electric Motor for the water Pump "If Equipped"

• The Air Conditioning System

Each component has either a green bonding ground wire or a wire inside an accessory power system cable dedicated to bonding. Each component also has a ground strap that connects the bonding wire system to the machine frame. The ground bonding wire system and the grounded housing for the electrical components ensure that all of the housings for the electrical components are at the same electrical potential as frame ground at all times.

The connections for the bonding wires are illustrated in the "System Schematics" section in the back of this manual and in the Electrical System Schematic.

In addition to the ground bonding wire system, each of the individual electrical conductors that are used in the Electric Drive System for the Power Train and the Accessory Power System are surrounded by a grounded sleeve. The sleeves for each conductor are mechanically connected to a grounded housing for a component. The sleeve may be connected at both ends.

The grounded sleeves on the conductor serve several purposes. The sleeve serves as a shield to ensure that any electrical "noise" or magnetic fields that are created during the operation are discharged to frame ground. This discharge prevents electrical interference that could occur with the control circuits that are located close to electrical conductors for the power train. The grounded sleeves over the conductor also ensure that any "leakage" of electrical voltage through the insulation of a conductor will be directed to the machine frame.

The redundant grounding systems and the electrical isolation of power train operating voltages from the machine frame ground ensure that a fault to frame ground will not result in one component having a greater electrical potential than any other component in the system. All of the components are at the same potential as frame ground at all times.

When possible, avoid contact with energized power train system components and conductors when the engine is running.

Note: If a bonding ground wire, shielding wire, or a ground strap must be disconnected, the bonding ground wire, shielding wire or the ground strap must be reconnected before the engine is started.

Ground Fault Detection

A ground fault occurs in an electrical system when there is an unintended path to frame ground. The amount of current that will leak through the unintended path will depend on the electrical resistance of the material that is between the voltage source and the ground source. Generally, the amount of leakage to ground is small.

A small amount of leakage to ground from the electric drive system or accessory power system will not affect the performance of the machine. Also, a small amount of leakage to ground will not damage system components. If a larger amount of leakage to ground occurs, the performance of the components in the system can be affected and damage to the components can occur.

A ground fault detection system is present in the Accessory Power Converter (APC). The ground fault detection system monitors the electrical isolation between the system voltage and frame ground at all times during machine operation.

The APC ground fault detection system can detect small amounts of leakage to ground. In most instances, the detection system can detect specific types of leakage to ground. The type of leakage that is detected will help to identify the section of the electric drive system with the ground fault.

If leakage to ground in the system is approaching a level that could affect the performance of the machine, the APC will communicate the level of leakage to the Implement Electronic Control Module (ECM). The Implement ECM will activate a level 2 ground fault event in order to indicate the level of severity.

If leakage to ground is detected in the system that is at a level or above a level at which machine performance could be affected or damage to components could occur, the APC will communicate the level of leakage to the Implement ECM. The Implement ECM will activate a level 3 ground fault event in order to indicate the level of severity.

If a CAN A Data Link system diagnostic code (CID 2986 FMI 9) has been activated by the Implement ECM, the ECM will monitor a hard wired PWM output circuit that is connected between the APC and the ECM. The APC will activate a PWM duty cycle on the circuit that will indicate that a ground fault is present in the system.

Once the Implement ECM has been notified of the level of severity and the general location of a ground fault, the ECM can activate one or more of five ground fault events that will indicate the severity level and the general location of the occurrence.

The following list contains the level of severity and the action that must be taken when a ground fault event is activated at that level:

Level 2 Ground Fault Event - The APC detection system has detected a low level of leakage to ground. The detected ground fault will not damage machine components at the detected level. Machine operation can continue. The ground fault could be caused by moisture around a connector. Continue to monitor the ground fault condition. If the level 2 ground fault remains active or if the level 2 ground fault resets and then activates repeatedly, the machine must be safely shutdown at the earliest opportunity in order to find the cause of the problem. Operating the machine with an active level 2 ground fault could result in a more severe condition that could damage components. Refer to the troubleshooting procedure for the specific active level 2 event that is listed in the Troubleshooting section of this manual.

Level 3 Ground Fault Event - The APC detection system has detected a level of leakage to ground that could damage machine components if machine operation continues. An immediate safe machine shutdown is required. Exit the machine. Refer to the troubleshooting procedure for the specific active level 3 event that is listed in the Troubleshooting section of this manual.

A ground fault can occur in the AC section or the DC section of the electric drive system. In most instances, the ground fault detection system will determine the section of the system that is the cause for the ground fault. The event that is activated by the Implement ECM will indicate the section of the system that is involved. If the detection system is not able to determine the section of the system with the ground fault, the Implement ECM will activate a level 3 general ground fault event code (E715).

The APC ground fault detection system will use different methods to detect a ground fault in the AC section of the system or the DC section of the system.

In most instances, the ground fault detection system can narrow the location of the ground fault to a specific section of the AC volt system or a specific component.

In the DC section of the system, the ground fault detection system monitors the "Frame Balance" of the DC bus. A leakage of DC current to frame ground will cause an imbalance of voltage on the DC bus. An imbalance of voltage on the DC bus can also be determined in the AC system when certain power transistors are passing current (closed) between the AC system and the DC Power Bus.

The percentage of deviation from the frame balance can be viewed using Cat ET or on the message display. The amount of deviation in frame balance will be displayed as either a positive (+) or a negative (-) percentage of deviation in frame balance. The range that can be displayed is negative (-) 100 percent to positive (+) 100 percent with 00 ± 5.0 percent as the normal frame ground potential.

To view the percentage of frame balance with the message display, refer to the "Machine Status" screen, then the "Accessories" screen, then "Frame Balance". To view the percentage of frame balance using Cat ET, from the main menu, refer to the "Status" menu, then the "Accessory Power Converter" menu, then "Ground Fault Frame Balance".

The following list describes frame balance percentage values and the resulting event activity:

• A frame balance deviation of approximately 00 ± 5.0 percent is the normal frame balance. No amount of DC leakage is detected.

• A deviation in frame balance of less than ± 20 percent is acceptable. No event will be activated.

• A deviation in frame balance of greater than ± 20 percent but less than ± 50 percent, will activate a level 2 event.

• At a frame balance deviation of greater than ± 50 percent, will activate a level 3 event. An immediate safe machine shutdown is required.

Note: During machine operation, the observed frame balance may read at a lower value than what is observed with the Engine OFF using the Low Voltage Diagnostic Power Supply. This difference is normal. When the Engine is OFF, the detection system is more sensitive to a shift in the frame balance. (The use of the Low Voltage Diagnostic Power Supply is discussed further on in this section).

The conditions that can cause a ground fault in the Electric Drive System for the power train are listed in the order of probability:

• Moisture is present at a connector or the connectors that are used in the Electric Drive system for the Power Train.

• Dirt or contamination is inside of a connector seal.

• The insulation in one of the conductors of the drive train has failed.

• A winding is shorted to the housing of the Generator, a drive motor, the HVAC system, or the Motor for the Electric Water Pump "If Equipped".

• There is an internal failure in the Power Inverter, the APC, or the Motor Control for the Water Pump "If Equipped".

Moisture is a common cause for ground faults when connectors are not properly tightened and secured with lock wire. Moisture that accumulates around electrical connectors and the seals for components can cause electrical leakage to ground. Dirt or contamination at a connection point can also be a common cause of a low-level leakage. When a connector is disconnected, always ensure that the connection points are clean and dry before reconnecting. Ensure that all seals are in place and that all connections are tight.

A ground fault that is caused by moisture will usually activate a Level 2 event. The code for this event is EID 0988. If this event is activated, the machine can continue to operate. When the machine warms up the moisture that is creating the event will usually evaporate. When the moisture evaporates, the event will be cleared. A connection may be loose somewhere in the system. Tighten connection at the most convenient time. This is even more likely when the ground faults activate after washing the machine.

If a level 2 event remains active for several hours, the machine should be shut down at the earliest opportunity. The cause for the problem should be diagnosed and repaired. Prolonged operation of the machine with an active level 2 ground fault could result in a more severe condition that may damage the machine.

Moisture and contamination in a connector can also cause a level 3 ground fault event. Failure of a seal or a loose connection could allow dirt or water to enter a connection point . A component that is failing could also be suspected as the cause for a level 3 ground fault event.

Another cause of a level 3 ground fault event can be a failure of the material that is isolating the conductor or component from frame ground. When a weakening or a break in the insulation of a motor occurs, an electrical leakage to ground may result in a ground fault. This condition can result in damage to the components in the system. A level 3 ground fault event requires an immediate safe machine shutdown. In some cases when the fault is very severe, the power train will be disabled and will remaine disabled until the parking brake is cycled. If a level 3 ground fault occurs, the ground fault must be diagnosed and repaired before the machine can resume normal operation.

The following event codes are ground fault event codes that can be activated by the Implement ECM:

EID 0715 - Level 3 - Ground Fault - An immediate safe machine shutdown is required. This event is a general ground fault warning. The EID 0715 Event is activated when the detection system cannot determine which part of the system the ground fault is located in. The EID 0715 Event will also be activated when a ground fault is detected and J1939 CAN A communication with the APC is not working.

EID 0988 - Level 2 or Level 3 - DC Ground Fault - The detection system has detected a ground fault in the DC section of the power train system. The amount of leakage that is detected will determine if this event is activated as a level 2 ground fault event or a level 3 ground fault event. A level 3 ground fault event will require an immediate safe shutdown of the machine.

EID 0989 - Level 3 - Drive Motor System AC Ground Fault - An immediate safe shutdown is required. The detection system has detected a ground fault in the Motor side of the AC system. The system consists of the Control 2 (motor control) side of the Power Inverter through the three-phase conductors to the windings of the two electric drive motors.

EID 0999 - Level 3 - Generator System AC Ground Fault - An immediate safe shutdown is required. The detection system has detected a ground fault in the Generator side of the AC system. The system consists of the Control 1 (Generator control) side of the Power Inverter through the three-phase conductors to the windings of the Generator.

EID 1066 - Level 3 - Water Pump System AC Ground Fault - An immediate safe shutdown is required. The detection system has detected a ground fault in the three-phase windings of the Electric Water Pump.

EID 1078 - Level 3 - HVAC System AC Ground Fault - An immediate safe machine shutdown of the AC system is required. The detection system has detected a ground fault in the three-phase windings of the electric motor for the HVAC compressor. In some cases, shutting down the AC system will allow the fault to clear. If the ground fault event is not active when the AC system is OFF, the machine operation can continue.

Low Voltage Diagnostic Power Supply

The APC is equipped with a low voltage diagnostic power supply that can be used to aid in diagnosing the cause of a DC system ground fault and AC system ground fault. When the machine has been safely shutdown, the low voltage diagnostic power supply can be activated. the power supply will energize the DC section and the AC section of the system. The low voltage diagnostic power supply will use the batteries for a power source.

After a hydraulic or electrical service procedure has been performed, the low voltage diagnostic power supply can be used to check the frame balance. Using the power supply in this manner can verify that a ground fault was not created during the service procedures. However, the detection system is more sensitive when the diagnostic power supply is ON. A frame balance percentage that is over the limits could be observed that may be lower during machine operation. When used in this manner, activate the diagnostic power supply before the procedure and again when the procedure is finished. Compare the before and after frame balance percentage values to determine if the procedure caused an elevation of the percentage.

The low voltage diagnostic power supply can only be used when the machine has been shut down and the Safe Shutdown Procedure For Electric Drive Tractors has been performed. The procedure is located in the Troubleshooting, "Electrical Maintenance Guidelines" section of this manual.

Activating and Using the Low Voltage Diagnostic Power Supply

In order to use the APC low voltage diagnostic power supply, the following machine conditions must be met:

• The Engine must be OFF and the Parking Brake must be engaged.

• The voltage of the DC Power Bus and the Accessory Power Bus must be below 50.0 VDC. The voltage must be verified using the message display or by using the Cat ET status screen. The voltage must be measured between any exposed conductors and frame ground. Use a volt meter to check for voltage before any service is performed.

• The engine starter motor must be disabled. Disable the starter motor by disconnecting the harness connector for the start solenoid that is located on the top of the starter motor. The Engine starter motor must be disabled in order to avoid an accidental Engine start when using the APC low voltage diagnostic power supply.

Once these machine conditions have been met and the conditions are verified, the low voltage diagnostic power supply can be activated.

• To use the key start switch to activate the diagnostic power supply, turn the key start switch to the ON position for at least 30 seconds. Then, do four OFF to ON key cycles. The diagnostic power supply should activate.

• To use Cat ET to turn ON the low voltage diagnostic power supply, select Diagnostics - Diagnostic Tests - Ground Fault Test - Manual. Follow the displayed instructions to turn ON the low voltage diagnostic power supply.

• When the low voltage diagnostic power supply is activated, the Hazardous Voltage System Energized Indicator (HV Present Indicator) will flash continuously at two second intervals.

• When the low voltage diagnostic power supply is active, a low DC voltage of approximately 25.0 VDC to 45.0 VDC will energize the DC system and the AC system. The voltage level is not what the user will look for when using the power supply. The voltage level will change as system components are disconnected. The user will be determining if the low voltage is present in different parts of the system or the user will determine whether the active ground fault clears as system components are disconnected. The low voltage power supply will also be used to monitor the percentage of DC frame balance.

• The key start switch must not enter the START position at any time during the procedure or when the APC low voltage diagnostic power supply is ON. If the key switch is moved to the START position at any time, the power supply will be turned OFF.

• In order to turn OFF the APC low voltage diagnostic power supply, turn the key start switch to the OFF position.

• During machine operation, the observed frame balance may read at a lower value than what is observed using the low voltage diagnostic power supply. This difference is normal. When the Engine is OFF and the diagnostic power supply is ON, the detection system is more sensitive to a shift in the frame balance. Consequently, if a ground fault event is not active when the machine is operating, do not assume that a significant ground fault is present if only indicated when the diagnostic power supply is ON. When in doubt, start the Engine and determine if a ground fault event is active. If a ground fault event is not active, the machine can be operated normally.

The low voltage diagnostic power supply allows for checking the operation of the DC system components and the APC system components in the following manner:

• The AC system can be disconnected from the system by disconnecting the DC Power Bus connector at the APC. When the low voltage diagnostic power supply is ON, determine if the fault to ground leakage is in the AC section or in the DC section.

• When a ground fault is indicated in the DC section of the system and the low voltage diagnostic power supply is turned ON, the user can check the DC voltage status of the APC input voltage, the DC Power Bus voltage, the Accessory Power Bus voltage, and the voltages at each of the components that are supplied DC power by the APC. The voltages can be checked using Cat ET in the Accessories status page. When the low voltage diagnostic power supply is ON, all of these voltages should be at approximately the same level. If the voltage at a specific component is much lower that the other components or is not present, a poor connection, an open circuit, or possibly a short circuit is present in the system.

• When a DC ground fault is active and a DC system conductor or component is disconnected, the low voltage diagnostic power supply will allow the user to check the DC Frame Balance. The Frame balance will determine if the ground fault is still active or is no longer active. The indication is that the disconnected section of the system or the disconnected component is most likely causing the problem. The disconnections can be done methodically in order to determine which part of the DC system the problem is in.

• When an AC ground fault is active and a set of AC three phase cables are disconnected, the low voltage diagnostic power supply will allow the user to check the DC Frame Balance. Determine if the ground fault is still active or is no longer active. The disconnection would indicate that the disconnected section of the AC system is most likely causing the problem. The disconnections can be done methodically in order to determine which part of the AC system the problem is in.

• The grounded outer sleeve on the three phase cable that is connected between the Water Pump Motor Control "If Equipped" and the Electric Water Pump Motor "If Equipped" is grounded through the connector on the pump motor. When the cable is disconnected, the ground connection is lost. A ground fault in the cable will not be indicated since the cable sleeve is no longer grounded. Always use a jumper wire with clips connected between the disconnected connector and frame ground when the connector is disconnected from the pump motor connector.

Note: The low voltage diagnostic power supply should be OFF when a component or connector is disconnected. When a disconnection is needed, turn OFF the power supply. Wait 1 minute and then disconnect the component. Turn ON the low voltage diagnostic power supply.

Troubleshooting Active Ground Faults

Note: The APC contains two filter capacitors that are used in the ground fault detection system. One filter capacitor is internally connected between the positive ("+") DC Power Bus (contact A) and the housing for the APC (frame ground). The other filter capacitor is internally connected between the negative ("-") DC Power Bus (contact B) and the housing for the APC (frame ground). Some specific conditions that can cause a level 3 ground fault to be activated can also damage the filter capacitors in the APC. A ground fault in the motor windings or a Generator windings could damage the filter capacitors. When the APC is operated with a damaged filter capacitor, the APC will detect a constant ground fault condition when no ground fault condition exists. After a ground fault that is caused by the winding of a motor or the winding of a generator is repaired, the filter capacitors must be tested to detect any damage. If a ground fault has occurred in the windings for the drive motor or in the windings for the Generator, call the Dealer Solution Network (DSN). The DSN will provide further instructions on the procedure to follow to verify the status of the filter capacitors in the APC.

Insulation Testing

Illustration 1	g01515993
Handheld Insulation Tester

When a ground fault is present in the AC section of the power train electrical system, the integrity of the isolation material can be tested. An insulation tester will be used to check the degree of insulation resistance between the conductors or the motor windings and frame ground.

The Insulation Tester can also be used to check the integrity of the isolation material that is used in the DC section of the system. Using an Insulation Tester on some components in the DC section of the system could damage system control modules if not used correctly. Only use an insulation tester on control modules in the DC section of the system when instructed to in a procedure.

When an insulation tester, the positive side probe of the insulation tester is connected to a copper conductor or to a winding connection. The negative side probe of the insulation tester is connected to frame ground, a grounded component housing or, a ground wire. The insulation tester will be used to induce a voltage that is higher than normal into the conductor or winding that is being tested. The insulation tester will measure the voltage potential that is present on the frame of the machine or on a ground wire. The insulation tester will calculate the amount of resistance that is present in the isolation material that is between the two probes.

The resistance value that is measured will indicate whether the condition of the insulation that is being tested is in good condition or is not in good condition. When a conductor or a component such as a motor or a generator is tested, a reading of two megohms (two million ohms) or less of resistance between the component conductor or winding and frame ground is considered to be a poor level resistance. Action should be taken to correct the problem when two megohms or less of resistance is measured.

Note: Two megohm of resistance is the low threshold that is considered to be an acceptable level of insulation resistance for a motor winding, a generator winding or for the insulation of a conductor. The insulation resistance of motor windings or generator windings will be much higher when the component is considered to be in good condition. New conductors have insulation resistance that is many times greater than two megohms. When the insulation of a component measures slightly above two megohms, the insulation has deteriorated to a level that is adequate, but is not considered to be in good condition. In some cases, future problems may be avoided if a component that measures close to two megohm of insulation resistance is replaced.

A Handheld Insulation Tester 300-8648 Insulation Tester Gp is the recommended tool to use for checking the integrity of the isolation in the Power Train Electric Drive System.

Read the operating instructions for the 300-8648 Insulation Tester Gp. Become familiar with the operation of the tester before attempting to use the insulation tester. Instruction for using the handheld insulation tester will be presented in the troubleshooting procedures for the events where the tester can be used. However, the user should have a general knowledge of the operation of the tester before using the tester.