SIMOREG 6RA70 F005 Fault: Bypassing Peer-to-Peer for Single Motor

SIMOREG 6RA70 F005 Fault: Bypassing Peer-to-Peer for Single Motor Operation

When a tandem DC mill loses one of two coupled 750 kW motors and the operator must continue production on a single motor, the SIMOREG 6RA70 armature drive may trip on F005 (field circuit fault) the moment the second field drive is electrically disconnected. This article documents the field-proven parameter changes that allow the 6RA7075-6DV62-0 common armature drive to operate with a single field drive (6RA7013-6DV62-0), without the peer-to-peer communication that previously synchronized M1 and M2.

1. System Overview

The original installation uses two coupled 750 kW DC motors (M1 and M2) to generate 9000 kg of mill tension. The two armatures are connected in series and supplied from a single common armature converter:

Each field converter independently sets the field current of its respective motor. The two field drives exchange actual field-current and field-voltage values with each other (peer-to-peer) and with the armature drive so that the common armature converter can compensate for EMF differences between the two machines and maintain stable load sharing.

2. Why the F005 Fault Appears After One Motor Is Removed

F005 on a SIMOREG 6RA70 is the field circuit monitoring fault. The drive continuously evaluates whether the measured field current (P425 readout) and the field voltage plausibility match the requested setpoint. When the peer-to-peer link expected signals from a second field drive and that drive's hardware is suddenly disconnected, the armature drive loses a key BICO input that the original logic used to declare the field loop "healthy".

In the tandem configuration the armature drive uses a connector such as U221:02 to route a status or actual-value word from the M2 field drive into the armature's closed-loop control. If the M2 field drive is physically removed from the bus, the connector is no longer updated. Depending on how the fault word is configured inside U220–U259, the monitoring block interprets the stale/missing value as a field circuit malfunction and trips on F005.

Removing one motor from the system therefore changes three things at once:

1. Hardware topology: the M2 field winding is open, so the M2 field drive has nothing to excite.
2. Peer-to-peer data: the armature drive stops receiving fresh actual values from the M2 field drive.
3. Mechanical load: the single 750 kW motor must now deliver the full 9000 kg tension; armature current demand rises.

Of these, items (1) and (2) are what cause F005. Item (3) is what causes P100 to need adjustment.

3. Peer-to-Peer Communication Architecture in SIMOREG 6RA70

SIMOREG 6RA70 drives use the USS / PROFIBUS peer-to-peer model combined with the proprietary BICO (Binector / Connector) technology. Each drive is a BICO node with three layers:

U220 – U259 are the free, software-wired processing connectors (visible only with the S00 technology option / DriveMonitor). Each U parameter has an index that selects a signal source. The chassis accepts the assignment, performs scaling, and exposes the result as a normalized value that downstream control blocks can read.

Typical peer-to-peer wiring for the tandem mill uses indices like:

• U220:01 = Status word of M1 field drive
• U220:02 = Status word of M2 field drive
• U221:01 = Actual field current of M1 (normalized)
• U221:02 = Actual field current of M2 (normalized) — value 6003 in the working parameter set
• U222:xx = Field voltage of M1 / M2

The signal number 6003 in U221:02 corresponds to the connector that carries the M2 actual field current into the armature drive. Because M2's field drive is being bypassed, the source of that connector must be re-pointed to a valid local signal — typically a fixed value or a "field OK" binector from the M1 field drive — so the monitoring block in the armature converter never sees a stale word.

4. Bypass Procedure: Step-by-Step

Use DriveMonitor or the SIMOREG OP1S operator panel to make the following changes on the armature drive only (6RA7075-6DV62-0). The M1 field drive and the bypassed M2 field drive do not require parameter changes for the trip to clear, provided the M2 field drive is electrically isolated.

4.1 Prerequisites

• Confirm M2 armature and field windings are isolated and locked out.
• Confirm the M2 field drive is powered down and its field output is open-circuited at the drive terminals (U1, V1, C1, D1).
• Read and archive the existing parameter set on all three drives with DriveMonitor (Upload → File → Save as).
• Verify DriveMonitor version supports the S00 technology option (firmware ≥ 2.x on the 6RA70 platform).

4.2 Parameter Changes on the Armature Drive

1. Set the rated armature current to match the single-motor load:
   • P100 = 5.7 (rated armature current in the parameter-set units; this is the value the Siemens engineer set in the field to keep the single 750 kW motor within the 6RA7075 envelope).
2. Re-point the M2 field-actual connector to a healthy local source:
   • U221:02 = 6003 (keep the existing index that defines the M2 actual field current; the value 6003 is the connector that lets the monitoring block read a real, internally generated field-current signal so the F005 check passes).
3. Disable or re-route the M2 peer-to-peer status words in U220 / U222 so the armature drive no longer waits for M2 telegrams. Typical assignments in this application:
   • U220:02 = 0 (clear the M2 status-word input).
   • U222:02 = 0 (clear the M2 field-voltage input).
4. Save the parameter set to the drive's non-volatile memory: DriveMonitor → RAM → ROM (P052 = 1 to write, then confirm).
5. Run a controlled down ramp (P390 / ramp-down time) and then a normal ON command.

4.3 Bypass Wiring of the M2 Field Drive

The attached bypass drawing removes the M2 field drive from the peer-to-peer bus and ties the M1 field drive output directly to the single 750 kW motor. The M2 field drive's armature terminals must be left open and its control electronics de-energized. The M1 field drive continues to receive its setpoint from the armature drive through the existing peer-to-peer PZD channel that has not been disabled.

5. F005 Root-Cause Matrix

Use this matrix when F005 appears on a SIMOREG 6RA70 after a topology change:

6. Drive Capacity Verification

Before running the mill on a single motor, confirm three thermal envelopes:

1. Armature converter envelope. The 6RA7075-6DV62-0 is a 210 A continuous armature converter. If the original two-motor load drew up to 210 A total (shared), the single-motor load may now demand 180–210 A from a single machine. Stay within 100 % continuous, 150 % for 60 s, 200 % for 10 s per the 6RA70 datasheet.
2. Single-motor armature envelope. The 750 kW motor nameplate armature current at full field must be checked against the new duty point. If the original share was 1500 V × 530 A ≈ 795 kW (per motor), the single motor at 9000 kg tension may briefly exceed its rated armature current during transients — re-tune P155 (torque limit) and P156 (current limit).
3. Field converter envelope. The 6RA7013-6DV62-0 feeding only M1 is now sized for the full field current of one motor. If the original was shared (two 6RA7013 units, one per motor), this is automatic. If a single 6RA7013 was previously shared, its current rating must be ≥ the single-motor field current.

6.1 Sizing Formulas

Three-phase apparent power drawn by the armature drive input:

kVA = sqrt(3) * V_LL * I_line / 1000

DC armature power at the motor terminals:

P_DC = V_A * I_A   (W)

Mechanical power developed at the shaft:

P_mech = V_A * I_A - I_A^2 * R_A - field losses - friction & windage

Verify that the chosen P100 / P102 values keep the calculated P_mech within 90 % of the single-motor rating to leave margin for the mill's transient tension peaks.

7. Commissioning and Verification

After the parameter changes, perform the following verification sequence before putting the mill back into production:

1. Pre-energization checks. Megger the M1 field winding to ground (≥ 100 MΩ at 500 V), confirm cabling, verify field-fuse continuity.
2. No-load test. Energize the M1 field drive only, command 10 % field current, verify P425 tracks and the field OK binector closes.
3. Armature pre-charge. Energize the armature drive in the bypassed configuration, leave speed setpoint at zero, verify no F005 over 5 minutes (this exposes stale peer-to-peer connectors before the motor spins).
4. Slow ramp test. Run the motor to 10 % speed with no mill load. Monitor armature current, field current, and the connector values U220–U259 in DriveMonitor trace.
5. Loaded ramp test. Engage the mill at low tension, ramp to 50 %, then 100 %. Watch for F005, F031 (overspeed), F035 (overcurrent). Verify the drive-healthy contactor closes.
6. Thermal soak. Run at rated tension for 30 min, log armature I²t and field I²t to confirm the single 750 kW motor is within its thermal curve.
7. Peer-to-peer trace. In DriveMonitor, record the actual telegrams on the bus; confirm the armature drive no longer requests PZD from the M2 field drive and that the M2 field drive is logged as "not connected" rather than "fault".

8. Re-Commissioning for Two-Motor Operation

When the rewound M2 returns to service, restore the original peer-to-peer wiring:

1. Reconnect the M2 field drive's USS / PROFIBUS cable.
2. Restore U220:02, U221:02, and U222:02 to their original signal numbers (download the archived parameter set).
3. Restore P100 to the original two-motor value.
4. Run the no-load test on M2 field drive, then perform a sync test at low speed to confirm the two field drives report consistent actual values to the armature drive.
5. Engage the mill at low tension and ramp; verify that the drive-healthy signal returns and that F005 does not reappear.

9. Common Pitfalls

• Assuming peer-to-peer is just telemetry. In the SIMOREG 6RA70 architecture, peer-to-peer connectors are part of the closed-loop logic. Disconnecting a node without re-pointing its connector index leaves the drive in an undefined state.
• Editing only P100. P100 alone will not clear F005; the monitoring block still needs a valid field-actual input on U221:02.
• Forgetting the S00 technology option. U220–U259 are not editable from the standard parameter list; DriveMonitor or the OP1S with the S00 enabled is required.
• Leaving the M2 field drive powered. A powered field drive with an open output stage can latch its own internal fault that propagates over the bus and confuses the armature drive's monitoring.
• Not saving to ROM. Parameter changes made only to RAM are lost on the next power cycle; P052 must be used to write the set to non-volatile memory.

10. Field-Reference Parameter Set (After Bypass)

Keep the original two-motor parameter set archived separately. The Siemens SIMOREG DC MASTER 6RA70 Operating Instructions (Order No. 6RX1700-0AD76 via the Siemens Industry Online Support portal) and the SIMOREG DC Master 6RA70 Function Description manual are the definitive references for BICO connector numbers (K0001, K0201, K0267, etc.) and the S00 option bit-mask. For firmware-specific behavior on the 6RA7075-6DV62-0 platform, consult the SIMOREG 6RA70 firmware release notes and the DriveMonitor parameter list for software version ≥ 06.04.

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