Danfoss Turbocor TT Series, Service Manual, Page: 261 / 294

Motor/System
Status Description Trigger
Method
Troubleshooting
Rotor Starting
Torque Fault INS
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At low speed (startup) rotor angular position is not at correct value for a given speed, caused by low
shaft magnet strength, liquid flooded compressor or damaged touchdown bearings/physical contact
of rotating components.
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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
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.
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Verify the bearing calibration and levitation. Refer to Section 5.3 Bearing Calibration on page 263.
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Verify the Inverter. Refer to Section 4.22.2 Inverter Verification on page 176.
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Verify the Stator. Refer to Section 4.23.4 Motor Verification on page 195.
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Review Fault and Event Log details to determine conditions related to the fault.
Low Inverter
Current Fault AFT
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Suggests the compressor has no load, verify load is available. Minimum magnetizing power not
absorbed for given speed at the Inverter.
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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
Section 4.22.2 Inverter Verification on page 176.
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Verify the Stator. Refer to Section 4.23.4 Motor Verification on page 195.
DC Bus
Under/Over
Voltage Fault DFT
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At 0 RPM: If the measured DC Bus voltage is lower than Soft Start charge voltage, a DC bus voltage
fault is recorded. All 3-phase voltage information displayed in the SMT is calculated from DC bus
voltage, as measured by the Inverter.
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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
and Event Log details to determine conditions related to the fault.
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Measure the DC bus voltage using the DC Bus Test Harness. Refer to Section 1.10.1 General
Verification and Installation of the DC Bus Test Harness on page 26.
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Verify the Soft Start. Refer to Section 4.14.2 Soft Start Verification on page 115.
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Verify the SCRs. Refer to Section 4.18.2 SCR Verification on page 142.
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Verify the connections to the Inverter. Refer to Section 4.22.2 Inverter Verification on page 176.
24VDC
Under/Over
Voltage Fault RFT
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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 Backplane Verification on
page 214.
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Compare the measured voltages to the displayed readings in the Compressor Monitor Tool and Fault
and Event
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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 DC-DC
Converter Verification on page 204.
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Determine that one of the modules is not draining energy. Refer to Section 5.5.2 Determining the
Cause of an Energy Drain on page 271.
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If the fault occurs when the compressor is given the demand to run, the Inverter may be causing the
24VDC fault.
Low Motor Back
EMF Fault DFT
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The calculated magnetic strength of the shaft has fallen below the minimum limit. This can be a
temporary effect due to high load and elevated temperatures (will recover when cavity temperature
cools) or due to a permanent demagnetization of the shaft.
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If this fault occurs three times within a 30-minute period, a Lock-Out Fault will occur.
M-SV-001-EN Rev. H-1/23/2023 Page 261 of 294