988K XE Wheel Loader Caterpillar

Generator (Phase Resistance) - Test

Usage:

Test Overview

The purpose of this test is to determine if the generator phase has a higher resistance than it should. A phase that has breaks in some of the conductor wire may have enough difference in resistance compared to the other phases, that it could cause a phase imbalance, high current, de-saturation, or other event.

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The Power Train Electric Drive System will contain hazardous voltage levels during machine operation and for a period of time after machine shutdown.
Do not remove any covers that will expose energized electrical components while the engine is operating. Do not remove any covers that will expose the energized electrical components while the components remain energized following an engine shutdown.
Do not perform any type of electrical maintenance on the orange hazardous voltage conductors or the power train components while the engine is operating.
Do not perform any type of electrical maintenance on the orange hazardous voltage conductors or the power train components while the components remain energized following an engine shutdown.
Always perform the safe shutdown and de-energizing procedure before performing electrical service on the Power Train Electric Drive System.

Failure to follow these instructions could result in personal injury or death.

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In order to avoid the build up of hazardous live voltages on the exposed surfaces, all grounding wires must be properly connected at all times during engine operation.
Any disconnected grounding wires (including the grounding bond wires, the conductor shield wires, the power inverter grounding straps and the component housing grounding straps) must be properly reconnected before the engine is started.

Failure to follow these instructions could result in personal injury or death.

Required Tools

The 430-8927 Meter is used to test the conductors and the windings in the generator.

Test Preparation

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Table 1
Stator Lead Color Identification
Phase	Identifying Color
A1	Blue
A2	Red
B1	Yellow
B2	Green
C1	White
C2	Black

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Table 2
Test Preparation	Values	Results
1. Safe Shutdown Procedure This procedure must be performed before service is performed in an area that is in the vicinity of power train hazardous voltage components and conductors to ensure that the DC power bus voltage has discharged properly. Reference: Refer to the Troubleshooting, "Electrical Maintenance Guidelines" section of this manual. Perform the "Safe Shutdown Procedure for Electric Drive Wheel Loaders" before proceeding with this procedure.	The Safe Shutdown Procedure for Electric Drive Wheel Loaders has been performed. DC voltage has been discharged to less than 50.0 VDC.	OK: The Safe Shutdown Procedure for Electric Drive Wheel Loaders has been performed. The monitoring system display and the hazardous voltage indicator indicate that DC voltage is less than 50 VDC. The hazardous voltage has been properly discharged. The power train system for the machine can now be serviced. NOT OK: The DC voltage is greater than 50.0 VDC on the Monitoring System Display or Hazardous Voltage Present Indicator. REPAIR: Wait for at least 10 minutes. Repeat the “Safe Shutdown Procedure for Electric Drive Wheel Loaders”. If the voltage is greater than 50.0 VDC, voltage is still present in the system. Measure the voltage between ground and the conductors with a multimeter. Verify that there is less than 50.0 VDC present between all exposed bus contacts before any other action is taken. NOTE: Do not make personal contact with the exposed conductors until you have manually measured for voltage between ground and the conductors. Proceed to the next test step.
2. Remove Generator Phase Cables from Inverter. A. Remove front doghouse plate from the inverter. Note: Measure the voltage between each of the phase cables and frame ground after the enclosure cover is removed. Do not make personal contact with the exposed contacts until you have verified that there is little or no voltage present (50 VDC or less). C. Check the compartment for moisture or coolant. Oil will be present in the case. Check for proper cable installation to the phase cables. If the terminal ends are not squarely seated on the lugs, loosening will occur over time. D. Remove the cable assemblies from the lugs and place them out of the way. Make sure that the cable assemblies do not contact the inverter lugs.	The power inverter case does not have water or coolant. The phase cables are squarely seated and tight on the lugs.	OK: The power inverter case does not have water or coolant. The phase cables are squarely seated and tight on the lugs. Proceed to “Test Procedure” NOT OK: The power inverter case contains water or coolant. Or, there is a problem with one of the lugs. REPAIR: Determine the source of the water/coolant. Or, correct the cable lug installation. Verify that the problem has been corrected. If the problem has been corrected, proceed to “Test Procedure”.

Test Procedure

This test procedure will indicate whether the phase resistance is too high for one of the three phases.

There are three different

Phase A
Phase B
Phase C

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Table 3
Troubleshooting Test Steps	Values	Results
1. Phase Resistance Test. A. Move both generator and drive motor cables assemblies out of the way. Make sure that the cables do not contact the Inverter lugs. B. Connect the ohmmeter to the end of each phase cable being tested. This will allow the meter to pass current through that phase. C. Test the phase and record the measurements. D. Repeat steps 1A - 1C for each phase A, B, and C.	Resistance of each phase measurement is within 5% of each other.	OK: The resistance of each phase is within 5% of each other. Phase cables are functioning properly. Resume normal machine operation. NOT OK: One of the phase resistance measurements is greater than 5% of either of the other two phases. Proceed to Test Step 2.
2. Check the phase resistance at the generator lugs. A. Remove the phase cable assemblies from the generator lugs. B. Using the ohmmeter, check the resistance between each phase and ground on the lugs on the generator. Record each measurement. C. Repeat steps 2A - 2B for each phase.	Resistance of each phase measurement is within 5% of each other.	OK: The resistance of each phase is within 5% of each other. The generator is functioning properly. Repair: The phase cables are causing the issue. Replace the phase cable assemblies and perform this test again to verify the problem has been corrected. NOT OK: One of the phase resistance measurements is greater than 5% of either of the other two phases, indicating that the stator is damaged. Repair: The phase cables are NOT causing the issue. Replace or repair the stator and perform this test again to verify the problem has been corrected.