Resolving Siemens SIMOVERT F011 Fault on 6SE7021-8TB61 Drives

Problem Overview

An F011 fault on a Siemens SIMOVERT 6SE7021-8TB61 inverter or a paired 6SE7028-6EC85-1AA0 Active Front End (AFE) rectifier/regenerator is one of the most common latched conditions encountered on 6SE70 MASTERDRIVES equipment that is approaching or has exceeded ten years of service. The fault typically surfaces after a mains disturbance such as a brown-out, voltage sag, or momentary loss, but the root cause is rarely the mains event itself. The brown-out acts as the trigger that exposes a marginal current transformer (CT), an aged electrolytic DC link capacitor, or a degraded gate-driver path on the CUSA, VSB, or IGD control cards.

This reference covers the complete field-proven diagnostic and recovery sequence for the F011 condition observed on 480 V three-phase systems, including CT isolation using parameter P832, factory reset with the P-key acknowledge, control card swap as a definitive power-stage versus control-stage isolation test, AFE choke CT replacement on the rectifier/regenerator chassis, and companion F103 ground-fault handling with DC-link fuse diagnostics. The procedures below are aligned with the Siemens SIMOVERT MASTERDRIVES 6SE70 operating instructions and are written for engineers who need to decide whether to bench-repair or replace a drive before committing capital to a $9,000-class replacement.

For firmware, parameter, and wiring reference, the authoritative documents are the SIMOVERT MASTERDRIVES Compendium and the 6SE70 Operating Instructions, both available on the Siemens Industry Online Support portal under product tree Drive Technology / Converters / Low-voltage converters / SIMOVERT MASTERDRIVES.

Affected Hardware and Fault Topology

The failure pattern is typically observed on the following catalog numbers when they are deployed in an Active Front End topology with regenerative line-side converter:

The two units are mechanically and electrically coupled through a shared DC bus. F011 on the inverter therefore reflects a fault either inside the inverter module or in the AFE feeding the DC link. The diagnosis must address both ends of the bus.

F011 Fault: Root Cause Analysis

F011 on the 6SE7021-8TB61 is reported by the CUSA control card as an overcurrent / converter protection trip. The most common root causes seen on 10-year-old units, in descending order of field frequency, are:

1. Current transformer (CT) saturation or open secondary in the AFE choke or inverter output stage. This is the dominant cause observed in the field and is the trigger that most often survives a mains brown-out.
2. IGBT module gate-driver fault on the IGD card, producing a VCE-monitoring or short-circuit trip that latches immediately on the next precharge.
3. DC link precharge resistor or capacitor degradation causing an inrush overcurrent that the CT interprets as a fault.
4. CUSA control card EEPROM corruption from a brown-out. Parameter download is possible, but factory reset is blocked, which is a strong indicator of corrupted non-volatile memory rather than power-stage damage.
5. VSB (Voltage Sensing Board) mis-read producing a false DC-link undervoltage condition that propagates as F011 on some firmware revisions.

The brown-out or voltage sag acts as the stress event that pushes an already marginal component across its failure threshold. Replacing the drive without identifying the failing component risks the same fault reappearing on the new unit if the upstream mains quality or the AFE choke is the actual source.

Current Transformer (CT) Failure Mechanism

Each SIMOVERT inverter output stage and each AFE choke is equipped with three current transformers, one per phase. The CTs are toroidal, hall-effect or iron-core types, depending on the production date, and they deliver a proportional current signal to the CUSA / IGD card for closed-loop current control and short-circuit protection.

CT failure modes observed in field service include:

• Open secondary winding: produces a saturated, full-scale signal on the affected phase; CUSA interprets this as a short-circuit and latches F011 within one switching cycle.
• Short between secondary turns: reduces the CT ratio on the affected phase; asymmetry between L1, L2, and L3 readings triggers a phase-current imbalance trip.
• Core saturation under inrush: a brown-out followed by a re-energization creates a high dI/dt inrush that pushes the CT into saturation. Once saturated, the secondary signal collapses and the CUSA cannot reconstruct phase current, producing a permanent F011 that cannot be reset by software.
• Mechanical fracture of the CT body: caused by thermal cycling over years of operation; produces an intermittent F011 that becomes permanent after the next thermal shock.

CT failures are not equally distributed across phases. Field data shows that L3 fails first in roughly 60% of cases, with L1 second. L2 is statistically rare. This asymmetry is attributed to the CT placement geometry inside the AFE choke and the higher thermal load on the outer phases.

Diagnostic Procedure Using Parameter P832

Parameter P832 in the SIMOVERT 6SE70 function plan is the phase-current diagnostic parameter. It displays the instantaneous current feedback from the L1 and L3 CTs as raw or scaled values, and it is the primary tool for confirming a CT failure before opening the chassis.

Procedure to read P832:

1. Apply control voltage to the drive (24 V standby or main 480 V, per site procedure). Do NOT enable the inverter output.
2. On the PMU (Parameterization Unit) keypad, press P to enter parameter mode.
3. Enter 832 and press P again to display the parameter index.
4. Use the up/down arrows to step through the indices that return phase-current feedback values. The exact index layout is firmware-revision dependent; consult the parameter list for the unit's firmware baseline.
5. Compare the three phase readings under no-load (motor disconnected or rotor locked) conditions.

Reading P832 requires that the drive has booted past its initial self-test. If the drive will not boot past F011 to expose the parameter tree, the P832 read must be performed on a known-good sister unit with the same firmware, or the CUSA card must be moved to a healthy chassis to read the CTs in isolation. The card-swap procedure is described later in this reference.

Step-by-Step Fault Reset Procedure

The SIMOVERT 6SE70 family offers two reset pathways: a software acknowledge that clears the fault bit, and a factory reset that reinitializes the parameter set. For F011 conditions triggered by an F011 latched by hardware (CT, IGBT, or precharge), the software acknowledge alone is never sufficient. The hardware fault condition remains, and the next precharge will re-latch F011 within milliseconds.

Software acknowledge (does NOT clear a hardware F011):

1. Press P on the PMU to acknowledge.
2. Observe whether READY returns. If not, the fault remains latched at hardware level.

Factory reset with backup:

1. Connect a PC running SIMOVIS or DriveMonitor to the drive via RS232 or PROFIBUS.
2. Upload the parameter set to a backup file (.dn or .par format).
3. Confirm the backup is valid by opening it in the SIMOVIS parameter editor.
4. Issue the factory reset command (parameter P970 = 1, or the menu path Factory Settings / Reset). Some firmware revisions require a separate security parameter to be set first.
5. Power-cycle the drive (control voltage off, wait 30 s for DC link discharge, then re-apply).
6. Press P on the PMU at the prompt to acknowledge any remaining fault.
7. Download the backup parameter set to the drive.
8. Verify the fault word reads zero before attempting to enable.

After reset, if F011 reappears within 200 ms of the precharge, the diagnosis is hardware: CT, IGBT, or precharge resistor. Reset attempts beyond two power cycles are wasted time and stress the remaining healthy components.

Control Card Isolation by Card Swap

The definitive way to determine whether the fault is in the power stage or in the control electronics is to swap the CUSA, VSB, and IGD cards with a known-good sister unit of identical catalog number and firmware revision. Card swap is the field-engineering equivalent of a bench-test, and it costs nothing in parts if a healthy sister unit is available on site.

Procedure:

1. Identify a sister drive of the same 6SE7021-8TB61 MLFB and, ideally, the same firmware version (check parameter P060 or the firmware label on the CUSA card).
2. Lock out and tag out the 480 V supply to both drives. Wait five minutes for DC link discharge and verify with a CAT IV meter at the DC+ and DC- terminals.
3. Remove the CUSA card from the suspect drive (top slot on most 6SE70 chassis). Place it on an ESD-safe mat.
4. Install the CUSA card from the healthy drive into the suspect chassis.
5. Apply control voltage only. Do NOT apply main 480 V yet.
6. Read P832 through the borrowed CUSA card. The CTs of the suspect chassis are now visible.
7. If P832 shows the asymmetry on the suspect chassis, the CT is confirmed faulty regardless of which CUSA card is in place.
8. If P832 is now clean, the original CUSA card was the fault source. Reinstall the original CUSA in the healthy chassis to confirm it latches F011 there (reverses the diagnosis).

This card swap isolates the diagnostic to one of three domains: power stage, CUSA control card, or AFE choke / CT. It is the single highest-value procedure available before committing to a chassis replacement.

AFE Choke CT Replacement Procedure

When the diagnosis confirms a CT failure inside the AFE choke of the 6SE7028-6EC85-1AA0 rectifier/regenerator, the CT can be replaced in the field without replacing the entire unit. The AFE choke is a passive three-phase reactor with three toroidal CTs slipped over the line-side conductors before the IGBT bridge.

Replacement procedure:

1. Lock out and tag out. Verify zero energy on the 480 V input and zero DC bus voltage.
2. Open the rectifier/regenerator chassis and locate the three CTs on the line-side busbars. Mark L1, L2, L3 clearly before disconnecting any wiring.
3. Photograph the secondary wiring harness and connector orientation. The CT secondary polarity must be preserved; reversing polarity produces a negative current reading that the CUSA interprets as a feedback fault.
4. Remove the failed CT. Inspect the busbar insulation for arc tracking or discoloration from the CT failure; replace any heat-damaged insulation.
5. Install the replacement CT with the correct orientation (line-side dot or arrow aligned to the source per Siemens documentation).
6. Reconnect the secondary harness and torque the terminal blocks to the value stamped on the connector.
7. Perform an insulation resistance test (megger) on the line-side busbars at 1000 V DC to ground. Reading must be >100 MΩ.
8. Reassemble, apply control voltage, and read P832 to confirm symmetry.
9. Apply main 480 V and run a no-load precharge test. Confirm F011 does not latch.

F103 Ground Fault on the 6SE7028-6EC85-1AA0 Rectifier/Regenerator

When the inverter-side F011 is cleared but the rectifier/regenerator logs F103, the system has detected a ground fault on the AFE side. F103 is a hard ground-fault trip and will not reset until the path to ground is cleared. The F103 path includes the input line-side wiring, the rectifier IGBT modules, the DC link, the precharge resistors, and the output to the inverter DC bus.

Diagnostic isolation procedure for F103:

1. Lock out and tag out the 480 V supply to the rectifier/regenerator only. Leave the inverter side isolated but with its own DC link discharged.
2. Disconnect the DC link cables between the rectifier/regenerator and the inverter. This separates the two units for ground-fault isolation.
3. Megger the rectifier/regenerator alone at 1000 V DC between each phase (L1, L2, L3) and ground. Reading must be >100 MΩ.
4. Megger the DC+ bus to ground, then DC- to ground, separately. Reading must be >100 MΩ on each.
5. If any reading is below 5 MΩ, the fault is in the rectifier/regenerator and the unit must be opened to the module level.
6. Re-megger the inverter side (DC link to ground) to confirm the fault is not propagated from the inverter.

Fuse diagnostics:

If the DC link fuse on the 6SE7028-6EC85-1AA0 has blown and blows again immediately upon energizing, the fault is downstream of the fuse and is almost always a shorted IGBT module or a precharge resistor that has failed to a low-resistance state. In this condition:

• Do NOT continue to replace the fuse and re-energize. Each re-energization stresses the IGBT modules and may escalate a single-module failure into a three-module failure.
• Open the rectifier/regenerator chassis and inspect the IGBT modules visually for cracked cases, bulging, or carbon tracking.
• Perform a diode-test on each IGBT module with a digital multimeter. A shorted module will read low resistance in both polarities on the collector-emitter terminals.
• If a module is shorted, replace the full IGBT stack. Siemens ships IGBT modules as matched triples; never replace a single module in a three-phase stack.

The bench-test idea of applying 24 VDC to the unit to find the faulted circuit is a low-energy verification that will identify open secondary windings and certain logic faults, but it will not identify a shorted IGBT module because the 24 V supply cannot forward-bias the IGBT. The 1000 V megger is the correct tool for that isolation.

DC Bus Discharge and Electrical Safety

The 6SE70 DC link stores lethal energy for several minutes after the 480 V supply is removed. The internal bleeder resistors discharge the link to below 50 V in approximately five minutes, but this is a function of the resistor health and the ambient temperature. Always assume the bus is live until you have measured it.

Brown-Out and Voltage Sag: Trigger vs. Root Cause

A brown-out or voltage sag does not directly cause F011 on a healthy drive. The sag must interact with a marginal component to produce the latched fault. The most common interactions observed are:

• CT saturation during inrush after the sag clears: the high dI/dt of the recovery inrush pushes a partially-degraded CT into saturation.
• DC link capacitor inrush: aged electrolytic capacitors present a lower impedance at the moment of re-energization, producing a brief overcurrent that a healthy CT will accept but a marginal CT will mis-read.
• Precharge resistor overload: aged precharge resistors have higher cold resistance but lower hot resistance; the brown-out thermal cycle pushes them past their drift limit and they fail short on the next precharge.
• Control card EEPROM corruption: brown-outs below the CUSA's brown-out detector threshold corrupt the parameter set in non-volatile memory, producing a "parameter set invalid" condition that blocks the factory reset.

For a ten-year-old drive, it is reasonable to assume that at least one of these components has degraded to the point of marginal reliability. The decision to bench-repair versus replace should weigh the cost of the replacement parts (CT, precharge resistors, electrolytic capacitors, CUSA card) against the cost of a new drive. The $9,000 price point cited for a 6SE7021-8TB61 replacement is at the upper end of the bench-repair break-even.

Repair vs. Replace Decision Matrix

Verification and Commissioning Procedure

After the repair is complete and before returning the drive to production service, perform the following verification sequence. Each step has a pass criterion that must be recorded on the commissioning sheet.

1. Insulation resistance: Megger all input phases to ground and DC bus to ground at 1000 V DC. Pass criterion: >100 MΩ.
2. Precharge test: Apply control voltage only. Observe the precharge relay closing and the DC bus voltage rising to the expected value within 5 seconds. Pass criterion: DC bus reaches nominal minus 5% within 5 seconds, no F011 latched.
3. No-load run: Apply main 480 V and enable the inverter with no motor connected. Run for 60 seconds at zero speed reference. Pass criterion: no fault, output voltage waveform balanced, P832 symmetric.
4. Loaded run: Connect the motor and run at 25%, 50%, and 100% of rated speed for 5 minutes each. Monitor motor current balance. Pass criterion: phase currents balanced within 5%, no F011.
5. Regenerative test: Drive the motor to over-speed and observe the AFE feeding power back to the line. Pass criterion: no F103, line current and voltage waveforms clean.
6. Parameter backup: Upload the final parameter set and store it in the site documentation system.

Field-Proven Caveats

• The "tow truck" anecdote in the field record shows that an F011 traceable to a single CT can clear after a repositioning of the CT on the busbar (rotating which phase pair the CT monitors). This is a temporary workaround that buys hours to days of operation, not a permanent repair.
• If the factory reset is permitted but the parameter download fails, the CUSA card has a firmware checksum mismatch. Reprogamming requires the Siemens SIMOVIS service tool with the correct firmware file; the file must match the hardware revision (CUSA version 1.x vs 2.x vs 3.x are not cross-compatible).
• Card swap between units of different firmware revisions will produce parameter defaults that do not match the application. Always note the firmware version (visible on the CUSA label and parameter P060) before swapping.
• Two F011 faults observed on sister drives at the same site usually indicate a common-mode trigger (mains quality, environmental temperature, or shared precharge supply) rather than two independent component failures.

FAQ