SINAMICS DCM Field Contactor Control: Parameter Reference and Fault Behavior

The SINAMICS DC Master (DCM) converter controls the armature and field circuits of a DC motor through two independent power sections. The field section requires its own contactor for safe disconnection during commissioning, emergency stop, and certain fault conditions. Selecting the wrong control signal for this contactor — or misconfiguring the field pulse enable during faults — results in unexpected armature or field collapse, failed dynamic braking, and motor coast-down. This reference documents the correct BICO source signal (r53195.0, r53210.2, r53081.0, or r53010.04) for the field contactor, the behavior of the relevant parameters (p50082, p50097, p50071, p50094) under fault conditions, and the recommended parameterization for 2-quadrant (2Q) and 4-quadrant (4Q) drive topologies.

1. Field Supply Architecture in SINAMICS DCM

The SINAMICS DCM (6RA80 series and 6RA70 legacy) consists of a fully-controlled thyristor bridge for the armature circuit and a separate, single-phase half-controlled or fully-controlled bridge for the field circuit. The field bridge draws its supply from the same three-phase AC line feeding the armature bridge, but operates at a lower current rating (typically 5 % to 10 % of the armature rated current). For details on the field supply unit ratings, refer to the SINAMICS DCM as Field Supply Unit application document.

Key ratings of the field section:

The field section includes an integrated field contactor (or external contactor commanded by a drive output). The contactor's coil is driven through terminal X177 (or a digital output on a Terminal Module TM15/TM31) and the source of the command signal is selected via BICO interconnection. The contactor must close before the field thyristors are fired and must not open while current is circulating in the field winding to avoid contact welding.

2. Why a Field Contactor Is Required

The field contactor performs three functions:

1. Isolation during maintenance: Provides a visible break in the field circuit, satisfying EN 60204-1 §5.5 for safe isolation.
2. Field reversal in 2Q drives: In a 2-quadrant (single converter bridge) topology, reverse rotation is achieved by reversing field polarity with a reversing contactor. The field contactor in this case is actually a field-reversing contactor pair.
3. Pre-charge and demagnetization: Closes only after the field capacitors have charged and the firing pulses are inhibited; opens only after the firing pulses are inhibited and the field current has decayed below 5 % of I_FN.

3. Candidate BICO Source Signals

Four signals are commonly considered as the source for the field contactor command. Each has a distinct semantic meaning in the DCM state machine:

3.1 r53010.04 — Drive Ready / Running

Bit 04 of status word r53010 indicates the drive is in operating state "ON" and no shutdown command is active. This signal is the cleanest choice when the field contactor should be released in lockstep with the enable command. During a fault (F30001, F30002, F06100, etc.) the bit resets and the field contactor opens. The field pulses are also blocked at this moment, so the contactor opens under no current — a safe condition.

3.2 r53195.0 — Field Sequence Output

This signal is the explicit "close field contactor" command from the field sequence control state machine. It remains true while field current is established, even if the armature is stopped. It releases on: line contactor open, OFF1/OFF2 with extended delay, or after the field current has decayed below threshold p50395.

3.3 r53210.2 — Field Direction Forward

Bit 2 of r53210 indicates the commanded field direction. It is not a contactor close command; it is a polarity selector used in 2Q drives with reversing contactors. Using it as a sole source for the field contactor is incorrect because the signal does not account for enable, fault, or current state.

3.4 r53081.0 — Field Active

This is the "field on" status bit used in older 6RA70 firmware. It indicates that the field firing pulses are enabled. It is independent of n < n_min when p50082 = [4] (field continuously on) is set. This makes r53081.0 a useful source when the field must be maintained during a no-speed condition, but it requires careful parameterization to avoid dropouts at low speed.

4. Configuration Parameters

The behavior of the field contactor and the field firing pulses is controlled by four primary parameters in the DCM expert list:

4.1 p50082 — Field Operating Mode

Setting p50082 = [1] energizes the field only while the drive is in operating state ON. The field de-energizes on OFF1, OFF2, OFF3, or fault. Setting p50082 = [3] keeps the field energized as long as the line contactor is closed and the electronics power supply is present, regardless of the operating state — this is the configuration used when the motor is heated by field current in standby. Setting p50082 = [4] adds a configurable run-on (p50094) after the drive goes to OFF, used for cooling fans and field-heated holding.

4.2 p50097 — Field Pulses in Case of Fault

By default, a fault trip blocks both armature and field firing pulses. When p50097 = [1] is set, the field pulses remain enabled during a fault, but the armature pulses are still blocked. This configuration is used when dynamic braking is required: the motor acts as a generator, the armature current decays through the field, and the kinetic energy is dissipated as heat in the armature resistance. Field pulses surviving a fault do not imply the field contactor remains closed — the contactor command is independent and is driven by p50071.

4.3 p50071 — BO 50771 Source

The parameter p50071 is the BICO source for Binector Output BO 50771, which in turn is wired to the digital output driving the field contactor coil (typically DO 0 on the Control Unit, or DO on a TM15). The default source in most DCM firmware revisions is r53010.04, which is the conservative choice: contactor follows the enable state.

4.4 p50094 — Auxiliary Systems Delay

Used only when p50082 = [4]. Specifies the run-on time (in seconds) the field remains on after the drive goes to OFF1. Default is 60 s. After this delay, the field contactor opens and (if p50097 = [0]) the field pulses are blocked.

5. Decision Matrix: Selecting the Correct Source

Use the following matrix to select the BICO source for p50071:

6. Recommended Parameterization for "Field On During Fault"

The most common requirement in hoist, elevator, and large mill drives is to maintain field excitation during a fault so that dynamic braking functions correctly. The recommended parameter set is:

p50082 = 1    ; Field on during run (release on OFF)
p50097 = 1    ; Field pulses remain enabled during fault
p50071 = r53010.04  ; BO 50771 source = "Drive running / no fault"
p50094 = 60   ; Auxiliary delay = 60 s (only relevant if p50082 = 4)
p50395 = 0.05 ; Field contactor open threshold (5% of I_FN)

With this configuration:

• During normal operation: the field contactor is closed, the field is energized, and the motor is controllable.
• On OFF1: the field contactor opens after the current decays below p50395. The field pulses are blocked.
• On OFF2 / OFF3: the field contactor opens immediately. The field pulses are blocked (r53195.0 resets).
• On fault (F30xxx, F06xxx): if p50097 = 1, the field pulses remain enabled. The field contactor (driven by r53010.04) opens. Dynamic braking still functions because the field is still present and the motor acts as a generator into the armature circuit.
• On line supply loss: the field contactor opens and the field pulses are blocked. Dynamic braking is not possible because the armature has no DC link support; the motor will coast.

7. The "Field On with p50082 = 4" Pattern

If the requirement is to keep the field contactor closed for a defined period after a fault (e.g., to allow a cooling fan to dissipate armature heat), use p50082 = [4] with a long p50094. In this mode:

p50082 = 4    ; Field on with delay-off
p50094 = 120  ; 120 s delay after OFF
p50097 = 1    ; Field pulses during fault
p50071 = r53081.0  ; "Field on" status (independent of operating state)

With p50082 = [4], the field contactor (via r53081.0) remains closed for p50094 seconds after the drive leaves operating state ON. This is the correct pattern when auxiliary systems (fans, pumps) must run on after the drive is stopped. Note: r53081.0 will drop if n < n_min in some firmware revisions, even with p50082 = [4]. Verify the actual state by reading r53081.0 in the trace during a controlled ramp-down to zero speed.

8. 2-Quadrant vs 4-Quadrant Considerations

The choice of field contactor source depends heavily on the drive topology:

9. BO 50771 Wiring Procedure

The Binector Output BO 50771 is the internal logic signal that drives the field contactor output. The wiring is:

1. Open STARTER or the SINAMICS DCM commissioning tool (DriveMonitor or SIMOTION SCOUT). Connect to the drive via PROFIBUS or Ethernet.
2. Navigate to Expert List → Field → p50071.
3. Read the current BICO source. The default in firmware V1.4 and later is r53010.04.
4. To change the source, click the "BICO" button next to the parameter field and select the desired signal (e.g., r53195.0).
5. If using a free interconnection block (e.g., AND of r53195.0 and NOT r53210.2 for 2Q reversal), configure the free block first and point p50071 to its output.
6. Download to the drive (Copy RAM to ROM).
7. Cycle the electronics power supply to activate the new wiring.
8. Verify with the trace function: trigger a controlled ON, monitor r53010.04, r53195.0, r53081.0, and the digital output state. All three should transition within 50 ms of each other.

10. Verification Procedure

After parameterization, verify correct operation with the following steps:

1. Visual check: Manually command the contactor via STARTER (Control Panel → Field on). Listen for the contactor closure, measure the coil voltage, and confirm with a multimeter that the contactor main contacts are closed.
2. Current ramp test: Apply a small setpoint (5 % of rated field current). The field current should ramp to the setpoint within the field time constant (typically 0.5 s to 5 s). Use the trace to record p50050 (field current actual) and the BO 50771 status.
3. Fault trip test: Force a non-critical fault (e.g., trip the line contactor auxiliary contact). With p50097 = 1, verify the field current remains at the setpoint for at least 1 second after the fault. With p50097 = 0, verify the field current decays to zero within 100 ms.
4. OFF1 test: Command OFF1. The field contactor should open only after the field current has decayed below p50395. Use a clip-on ammeter on one of the field leads to measure the current at the moment of contactor opening — it should be less than 5 % of I_FN.
5. OFF2 test: Command OFF2. The field contactor should open within 50 ms. The field pulses are blocked. Verify that the field current decays through the field winding and the freewheel diode, not through the contactor.
6. Dynamic braking simulation: With the motor spinning at 50 % of base speed (use a prime mover or residual rotation), command a fault. With p50097 = 1, the armature current should build up as the motor acts as a generator, and the speed should decay exponentially. Without p50097 = 1, the speed will coast down (no braking torque).

11. Common Faults and Their Root Causes

12. Free Blocks and Custom Logic

For complex requirements (e.g., field on during fault only if certain conditions are met), use the free interconnection blocks in the DCM. Typical free blocks include:

• AND, OR, XOR: Combine r53010.04, r53195.0, r53210.2 with operator inputs.
• RS flip-flop: Latch the field contactor command during a transient fault.
• Timer (pickup / dropout): Add delay between the BICO source and BO 50771.
• Comparator: Compare field current to a threshold and override the contactor command if current is not flowing.

An example "field on during fault for 30 s, then release" logic:

; Free block 1: AND
  Input 1: r53010.04      ; Drive enable
  Input 2: r53195.0       ; Field sequence OK
  Output:  AND_1 → r53700.0

; Free block 2: Timer (dropout delay = 30 s)
  Input:   AND_1
  Output:  TIMER_1 → r53701.0

; Wire p50071 = r53701.0
; During fault, AND_1 resets to 0, but TIMER_1 holds for 30 s
; After 30 s, the field contactor opens

13. Commissioning Checklist

• ☐ Confirm drive topology: 2Q (single bridge) or 4Q (anti-parallel).
• ☐ Confirm field contactor rating: U_e, I_e, AC-3 duty, coil voltage.
• ☐ Read current p50071 source from the drive before making changes.
• ☐ Select new p50071 source per the decision matrix in Section 5.
• ☐ Set p50082 according to the desired field-on behavior.
• ☐ Set p50097 = 1 if dynamic braking is required during faults.
• ☐ Set p50094 if p50082 = 4.
• ☐ Set p50395 (field contactor open threshold) to 5 % of I_FN.
• ☐ Download parameters, cycle electronics power, repeat the verification tests.
• ☐ Document the final parameter set in the drive parameter sheet.

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