Danfoss Turbocor TT Series Service Manual page 261

Motor/System Trigger
Status Description Method
Rotor Starting INS
Torque Fault
Low Inverter AFT
Current Fault
DC Bus DFT
Under/Over
Voltage Fault
24VDC RFT
Under/Over
Voltage Fault
Low Motor Back DFT
EMF Fault
Troubleshooting
At low speed (startup) rotor angular position is not at correct value for a given speed, caused by low
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shaft magnet strength, liquid flooded compressor or damaged touchdown bearings/physical contact
of rotating components.
If this fault occurs three times within a 30-minute period, a Lock-Out Fault will occur.
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If fault or event logs show occurrence of Starting Torque fault after one Inverter Error, the Inverter
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should be verified and may require replacement. Refer to Inverter Error on page 260 or Motor
Single Phase Overcurrent Fault on page 260. Shaft or bearings may be mechanically damaged and
unable to turn.
Verify the bearing calibration and levitation. Refer to Section 5.3 B earing Calibration on page 263.
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Verify the Inverter. Refer to Section 4.22.2 I nverter Verification on page 176.
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Verify the Stator. Refer to Section 4.23.4 M otor Verification on page 195.
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Review Fault and Event Log details to determine conditions related to the fault.
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Suggests the compressor has no load, verify load is available. Minimum magnetizing power not
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absorbed for given speed at the Inverter.
Compressor is not pumping gas. Usually seen in open-air operation.
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Review the Fault Log for the level of Motor Current in the fault record.
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Zero motor current at zero RPM indicates a problem with the Inverter. Verify the Inverter. Refer to
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Section 4.22.2 I nverter Verification on page 176.
Verify the Stator. Refer to Section 4.23.4 M otor Verification on page 195.
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At 0 RPM: If the measured DC Bus voltage is lower than Soft Start charge voltage, a DC bus voltage
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fault is recorded. All 3-phase voltage information displayed in the SMT is calculated from DC bus
voltage, as measured by the Inverter.
Typically, this fault is recorded when power to the compressor is removed.
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Measure and compare the incoming main AC voltage to the compressor rated voltage.
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Compare the measured voltages to the displayed readings in the Compressor Monitor Tool and Fault
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and Event Log details to determine conditions related to the fault.
Measure the DC bus voltage using the DC Bus Test Harness. Refer to Section 1.10.1 G eneral
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Verification and Installation of the DC Bus Test Harness on page 26.
Verify the Soft Start. Refer to Section 4.14.2 S oft Start Verification on page 115.
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Verify the SCRs. Refer to Section 4.18.2 S CR Verification on page 142.
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Verify the connections to the Inverter. Refer to Section 4.22.2 I nverter Verification on page 176.
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Suggests the measured 24VDC supply voltage is out of range.
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Measure the 24VDC test points at the Backplane. Refer to Section 4.25.2.2 B ackplane Verification on
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page 214.
Compare the measured voltages to the displayed readings in the Compressor Monitor Tool and Fault
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and Event
Review Fault Log details to determine conditions related to the fault.
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If the measured voltage is incorrect, verify the DC-DC Converter. Refer to Section 4.24.2 D C-DC
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Converter Verification on page 204.
Determine that one of the modules is not draining energy. Refer to Section 5.5.2 D etermining the
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Cause of an Energy Drain on page 271.
If the fault occurs when the compressor is given the demand to run, the Inverter may be causing the
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24VDC fault.
The calculated magnetic strength of the shaft has fallen below the minimum limit. This can be a
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temporary effect due to high load and elevated temperatures (will recover when cavity temperature
cools) or due to a permanent demagnetization of the shaft.
If this fault occurs three times within a 30-minute period, a Lock-Out Fault will occur.
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M-SV-001-EN Rev. H-1/23/2023 Page 261 of 294