Resolving SIMOREG 6RA70 F006 and F58 Faults During Commissioning

Problem Overview: Commissioning a 6RA7025 for an 800 A Mill Motor

The application is a screwdown-mill stand driven by a separately-excited DC machine rated 320 kW / 800 A armature / 440 V DC armature / 30 A field / 220 V DC field. The available converter is a SIMOREG DC Master 6RA7025-6DVD62-Z, with an in-house-assembled six-thyristor bridge (six modules, 1200 A / 1200 V) and a pulse-amplifier (gate firing) board retrofitted in place of the original power stack.

On first power-up the unit trips F006. Raising P086 > 0 suppresses F006 but immediately raises F58 (value 10), after which the drive will not enable. Because the 6RA7025-6DVD62-Z is a factory-built unit with a fixed power-section rating, the root-cause is not a parameter mismatch alone — the converter's armature current-sensing transducer (burden network) and field-current-sensing transducer are sized for a different load class than 800 A. F006 and F58 are the visible symptoms of that under-sizing combined with the standard procedure P086 calibration.

Drive Identification: What 6RA7025-6DVD62-Z Actually Covers

The SIMOREG DC Master 6RA70 family covers rated armature currents from ~15 A to ~2200 A. The 6RA7025 sub-family is the mid-range 600 A device, factory-fitted with current transformers and burden resistors matched to that rating. The trailing "Z" in -6DVD62-Z designates a customer-specific variant (often a changed firmware/parameter set or non-standard options card). It does not mean the unit can be re-rated to 800 A by software alone.

For software version 3.1 (the version explicitly named in field reports of this issue) the parameter set is documented in the 6RA70 Operating Instructions, Parameter List section. The Operating Instructions are available from Siemens Industry Online Support under entry ID 21650545.

Why a 6RA7025 Cannot Directly Run an 800 A Motor

The current loop in a 6RA70 measures armature current via current transformers on the AC side (or, in some 15 A to 30 A frames, a DC shunt on the DC side). The CT secondary current is dropped across a precision burden resistor, and that millivolt signal is scaled by the CUD1 board to produce P100 (armature-current setpoint normalization). Two hardware realities bound the situation:

1. CT turns ratio and burden value are selected at build time. For a frame that expects 600 A primary, the burden resistor network terminates the CT at the design milliampere value — typically 60 mV nominal — at full load.
2. Pulse-amplifier firing board isolation is sized for the frame's commutation voltage. Pushing 800 A through 600 A buswork increases I²t dissipation above the heatsink rating.

Consequently the proper engineering responses are — in order of preference — either:

• Replace the entire chassis with the next current frame (6RA7026 / 7027 / 7028 in the same series).
• Use the SIMOREG CM (Customer Module) variant — a control electronics-only version intended to drive an external power section. This is the path explicitly described in Chapter 6 of the SIMOREG DC Master catalogue DA21.

Burden Resistor Sizing for the Rebuilt Power Section

When the power section is reworked with user-supplied thyristors (the six 1200 A / 1200 V modules noted in this case) the burden network that converts primary current to a measurable signal must be rebuilt. The general engineering rule that drives Siemens' internal selection is:

A worked calculation for a generic 800 A, 5 A secondary CT:

R_burden_total = V_burden / I_CT_sec
               = 5 V / 5 A
               = 1.00 ohm
P_burden_total = (5 A)^2 * 1 ohm = 25 W
R_burden_per_phase = 1.00 / 3 = 0.333 ohm
P_burden_per_phase = (5/sqrt(3))^2 * 0.333 = 8.3 W

Derating: select resistors with ≥ 2x margin
   → 50 W total / 25 W per phase minimum
   → recommend 3x: 75 W total / 50 W per phase

The same formula applies to the field circuit: for a 30 A field winding driven from a 30 A field stack:

R_field_burden = V_fburden / I_fsec
                = e.g. 5 V / 5 A = 1.00 ohm   (typical CT-driven field card)
                or: for a 60 mV shunt, R = 60 mV / I_field_rated = 60e-3 / 30 = 2.0 milliohm

Parameter P086 and Field-Current Calibration

P086 sets the field-current setpoint for the field bridge. In the 6RA70 parameter list it is grouped with the field-optimization set (P082–P089) and is normally populated automatically by the field auto-tuning routine. When the power section is reworked and the field CT / shunt is changed, P086 — and the underlying scaling constants — no longer match. The standard commission gives two paths:

1. P051 = 25 (field optimization w/ rotation): the drive runs a self-test, ramps field current, and writes P086.
2. Manual entry: read the actual field current on P078.05 (field current actual), manually write P086 = P078.05 with the drive in o7.0 (no enable) mode.

Fault F006 — Root Cause Analysis

F006 in the SIMOREG 6RA70 fault dictionary is the Armature power section fault — the converter detected either:

• An unexpected armature-current flow with no enable, or
• A line-side or DC-side voltage that disagrees with the firing angle state, or
• A pre-charge failure (DC link below pre-charge threshold 15 ms after mains OK).

In this application F006 is the expected reaction to a 60 A / 800 A mismatch — the firmware sees current measured through a 600 A transducer but the user has now raised command beyond that range. The "fix" of setting P086 > 0 is not a fix at all; it changes the trip logic for the field card and exposes the next, more specific fault F58.

Fault F58 (value 10) — Field Monitoring Alarm

F58 belongs to the field-circuit alarm group. With value = 10 the firmware is reporting: field current actual is 10% outside the tolerance window (P089) around the commanded P086. Concretely this means:

|I_field_actual - I_field_command| / I_field_command > 0.10

Sub-causes specific to a reworked power section:

1. Field burden resistor missing or wrong value. The field CT outputs a fixed secondary current at rated primary. Without the right burden the CUD1 reads proportionally low (or high) and the closed-loop regulator drives the firing angle into a rail. P078.05 reads 0 A or saturates.
2. Field thyristor pulse-amplifier card powered but stack not gated. If the new gate driver board expects a different firing pulse pattern (single-pulse vs dual-pulse, or 50 Hz vs 60 Hz mains) the field bridge passes partial current. P078.05 will swing wildly.
3. Field rated parameters inconsistent with motor. P082 = 30, P083 = 220, but the retrofitted stack was wired for 30 A and the user's command P086 also = 30, so a properly sized burden should reach ~30 A. Any sustained deviation comes back as F58(10).

The recovery recipe is:

1. Stop (P086 = 0). Acknowledge F58.
2. Confirm field CT polarity with a clamp meter and a 1 A DC injection.
3. Measure burden voltage at the field board test pins at P086 = 10% — it should read 10% of full-scale.
4. Re-run P087 = 1 with the drive in P051 = 25 mode.
5. Read back P086 and re-issue enable.

Software Update — Section 13.1 Procedure

Per the Siemens KB entry 21650545, the 6RA70 firmware is updated via SIMOCOM U or DriveMonitor on a Windows XP (or later) commissioning PC, using a serial / USB-to-RS232 null-modem cable or PROFIBUS CP. The Operating Instructions' Section 13.1 outlines the procedure:

1. Save the existing parameter set via DriveMonitor (File → Upload from PG or RAM → Upload).
2. Power down, insert / connect the programming adapter (order code 6RA70xx firmware download adapter), power up.
3. Launch the firmware update tool, select the matching firmware (e.g. SW 3.1 for this drive), confirm the device is in Boot Loader state.
4. Execute the download — typically 6 to 12 minutes depending on the image. Wait for the green ACK before cycling.
5. Re-load the saved parameter set, then run the relevant optimization blocks (P051 = 25 for field, P051 = 27 for armature).
6. Verify on P60 (firmware version read-out) that the new build is active.

Retrofit Path A — SIMOREG CM Customer Module

The CM (Customer Module) variant is described in Chapter 6 of the SIMOREG DC Master catalogue DA21. It is the engineering-grade answer when the user's own power section (thyristors + pulse amplifier card) must be controlled. Practical sequencing:

1. Replace the 6RA7025 chassis with a CM-rated control electronics card (no internal power stack).
2. Wire the user's six-thyristor bridge and pulse amplifier to the CM firing-pulse outputs.
3. Install the burden network per the calculation above, on a DIN-rail heatsink if necessary.
4. Configure P100 / P082 / P086 from the motor nameplate exactly.
5. Run P051 = 25 and P051 = 27 in sequence before the first enable.

Advantage over rewriting an EPROM: the CM firmware fully supports the user's external stack, all faults and alarms behave normally, and over-current detection (P078) sees real secondary feedback from the rebuilt burden.

Retrofit Path B — EPROM Re-flash (Field-Caveat)

Field reports do describe EPROM re-flashes to alter P100 / P082 limits. This is mechanically possible — the 6RA70 EPROM holds the limit constants that define what the firmware considers "rated." However:

• The internal CT and burden card remain sized for 600 A. The firmware will trust a higher P100 and ask for 800 A; the analog front-end will clip and report corrupt current. F006 will return.
• Safety functions (ground fault, I²t motor protection, speed-dependent field weakening) assume the original rating and may produce unsafe scaling.
• Warranty and type-approval status of the rebuilt unit are void.

This path is therefore not recommended for an 800 A mill service. CM retrofit is the correct engineering answer.

Step-by-Step Commissioning Procedure for the Rebuilt 6RA7025 / CM Stack

The combined procedure — assuming the CM retrofit is in place and the burden network is correctly sized — is:

1. Mechanical inspection: confirm tightening torque on each thyristor module (typically 40 N·m for 1200 A capsule), gate-cathode lead polarity, and heatsink isolation to earth > 10 MΩ.
2. Insulation test: 1 kV DC between AC bus bars and earth for 60 s. No breakdown, leakage < 5 mA.
3. Control wiring: CUD1 terminal strip, field burden, field CT polarity, armature CT polarity (every label on a 6RA70 CT is "K / L" or "1 / 2" — respect them).
4. Pre-energisation with motor disconnected: apply control voltage, confirm P60 firmware, P051 mode, P082 / P083 from motor nameplate.
5. Field calibration: P086 = P082 (30 A). Enable P087 = 1. Wait for the controller to write back. Verify P078.05 = 30 A ± 1 A.
6. Armature calibration: motor still disconnected. P100 = 800. P101 = 440. Force P082 = 0 to keep field off; read P078.01 with a 5% armature command — should be 40 A ± 2 A.
7. Armature optimisation: P051 = 27. The drive runs a self-tune; expect noise from the gate firing pulses for ~60 s.
8. Motor connection — unloaded: close the output contactor with the field breaker still open. Bump enable at 5% armature voltage. Verify rotation direction; swap A+/A- if wrong.
9. Loaded run: ramp to full voltage; verify field is in regulation (P078.05 stable). Confirm F006 and F58 remain clear.
10. Load test at rated: drive the mill down to a calibrated reference (set screwdown), verify torque and current stay in band for 30 min.

Verification and Acceptance Test

Troubleshooting Matrix

Field-Proven Tips

• Always bench-test the rebuilt power section with a low-voltage (24 V) DC source through the burden network before connecting to mains. F006 trips can be exercised safely and the transducer scaling verified before energising at 440 V.
• Use shielded twisted-pair from the burden network to the CUD1 terminals. The 800 A / 5 A CT will deliver a strong low-frequency signal; PWM noise from gate firing couples into the loop if unshielded.
• Disable field weakening (P170 < > 1) until the basic loop is stable. The armature/field decoupling is a common source of late-arriving F58 alarms on first commissioning.
• Capture a parameter-set dump (DriveMonitor → Download → *."par") before every optimization step. This makes rollback trivial.