SINAMICS G120C 87Hz Configuration: Parameters and Commissioning

Overview: What 87Hz Operation Is and When to Use It

The 87Hz characteristic is a constant-torque operating mode that allows a standard 50Hz induction motor to deliver 1.73 times its nameplate power without exceeding its rated current. It achieves this by reconnecting a 400V/50Hz motor in Delta (so its phase voltage is 230V), then driving it from a 400V inverter that has been programmed to ramp the output up to 87Hz. The 87Hz limit is not arbitrary; it is the frequency at which the inverter's output V/Hz ratio (400V / 87Hz = 4.6 V/Hz) equals the motor's Delta-connected V/Hz ratio (230V / 50Hz = 4.6 V/Hz), preserving constant flux.

This mode is heavily used in:

• Conveyor systems where a single oversized drive must power multiple small motors in parallel
• Centrifugal pumps and fans where increased speed delivers more flow at the same mechanical envelope
• Mixers, extruders, and machine tool spindles where the operator needs headroom above 50Hz for process tuning
• Replacement of older pole-changing Dahlander motors

Two factors make this mode attractive. First, the motor delivers the same continuous torque as it would in standard 50Hz Star operation, but at up to 1.73x the speed, so mechanical power scales by 1.73x. Second, a 230V Delta motor driven from a 400V DC bus system can be fed from a 400V drive without an output transformer. The trade-off is that the drive must be sized to deliver the higher current, and the motor must be wired in Delta at the terminal box, not Star.

The 87Hz Theory: V/Hz, Delta Connection, and the √3 Relationship

A three-phase induction motor's electromagnetic torque is proportional to V/Hz. Above base frequency, the supply voltage is capped at the DC bus limit, so V/Hz falls and torque falls proportionally with speed (the field-weakening region). The 87Hz trick preserves V/Hz above 50Hz by changing the motor's geometry:

The 1.73 (√3) factor appears twice:

1. Voltage ratio: 400V line-to-line ÷ 230V phase = √3
2. Frequency ratio: 87Hz ÷ 50Hz = 1.74 ≈ √3

Mechanical consequences:

• Speed: 1.73× the nameplate 50Hz speed (e.g., a 4-pole 1450 rpm motor at 50Hz runs at ~2500 rpm at 87Hz)
• Torque: equal to nameplate torque (because V/Hz is preserved and current is preserved)
• Power: torque × speed = 1.73× nameplate (e.g., a 4kW Delta motor delivers ~6.9kW at 87Hz)

The slip at 87Hz also rises, which is why motor cooling matters. A TEFC (totally enclosed fan-cooled) motor at 2500 rpm is being cooled by a fan that is moving 1.73× the air mass but the motor surface heat is now 1.73× the dissipation. A separately force-ventilated (IC416) motor is recommended for continuous 87Hz duty, or duty cycle must be reduced.

Prerequisites and Site Audit Checklist

Before changing any parameters, gather the following on site. Most 87Hz installations fail because one of these is overlooked.

1. Motor nameplate data for every motor on the drive, with photo of each plate. Capture kW, V, A, Hz, rpm, cos φ, insulation class, and IP rating.
2. Terminal box wiring photo and re-identification of the bridge links. A 400V/690V motor typically has links for Star; a 230V/400V motor has links for Delta. Confirm against the motor's data sheet, not just the rating plate.
3. Number of motors in parallel, cable run from drive to each motor junction box, and any output reactors, dU/dt filters, or sine-wave filters in the line.
4. Drive part number including the Control Unit suffix (e.g., 6SL3210-1KE18-8AF1) and firmware version (read with r0018 or via the BOP-2 / IOP status screen).
5. Total motor current: sum of rated currents in the Delta connection. This is the figure the drive's current limit must be set against, not the Star rating.
6. Mechanical load envelope: max speed, max torque, duty cycle, and any gearbox ratio. Operating above 50Hz may push the load past its design limit.
7. Cooling: standard TEFC at 1.73× speed generates 1.73× windage loss in the rotor and 1.73× iron loss; verify TENV or IC416 ventilation is sufficient.
8. Cable capacitance: long motor cables (>50m) cause high dV/dt charging currents that can trip the drive or destroy the motor insulation. For 87Hz installations with long cables, add a dU/dt filter (e.g., Siemens 6SL3202-0AE...) or sine-wave filter (6SL3202-0BE...).

Drive Sizing Rule: The "Two Sizes Up" Constraint

For a 87Hz installation, the inverter must deliver 1.73 times the motor's rated current continuously. If the drive is rated at exactly the sum of motor nameplate currents, the I²t thermal model will trip on F07901 within minutes because the drive cannot source enough current to feed all parallel motors at their Delta rating while the motor voltage is held to 400V at 87Hz.

The field-proven rule is:

Drive continuous current rating ≥ 1.3 × sum of motor Delta rated currents (for single motor, this is the motor's own Delta current).

For parallel motors where the mechanical load is balanced, Siemens and most drive integrators recommend oversizing the drive by at least one frame size, and often two frame sizes. For example, three 4kW Delta motors (each ~17A at 230V) draw ~51A together. A drive rated at 62A (typically 30kW / 400V) is borderline; a 75A drive is the practical minimum, and 90A (37kW) is preferred for headroom.

If the drive is already installed at the sum-of-motors rating, the practical resolution is to add a bypass circuit so a smaller subset of motors runs at 87Hz, or to add active current sharing between drives.

Motor Wiring: Confirming Delta Connection at the Terminal Box

The motor terminal box must be rewired from Star to Delta. This is the single most common source of overload trips on 87Hz retrofits because the motor is left in Star while the drive is set for 87Hz, drawing 1.73× the expected current.

For a typical IEC low-voltage motor terminal box with six studs labelled U1, V1, W1, U2, V2, W2:

Re-check the nameplate. If the motor shows 230/400V, the nameplate's 400V rating is for Star operation; the motor must be Delta. If the motor shows 400/690V, it is already wound for Star at 400V and is not suitable for 87Hz without rewinding.

Parameter Map for the SINAMICS G120C

The following parameters must be entered for correct 87Hz operation on a G120C with CU230P-2, CU240E-2, or CU240S-2 (FW V4.6 or higher). All parameters reside in Drive Data Set 0 (DDS0) unless multi-motor Data Set switching is used. The procedure below is consistent with Siemens support entry 88963613.

After entering these values, run a motor identification (P1900 = 2) and accept the calculated motor data, then verify the new P0320 magnetizing current is reasonable (typically 0.4-0.6 × P0305).

STARTER and TIA Portal Commissioning Procedure

Siemens support entry 88963613 specifies commissioning via STARTER. For TIA Portal (used on G120C firmware V4.7+ and on all projects configured in TIA V13 SP1 or later), the same parameter set applies but the navigation is different.

Procedure with STARTER (classic)

1. Open STARTER, go online with the G120C, and create a new project offline if needed.
2. In the configuration tree, double-click Control Unit → Commissioning → Configuration wizard.
3. Select the appropriate power unit, set the line supply (3-ph 400V), and choose the motor standard (IEC).
4. Enter motor data, leaving P0304 at 230V for the Delta connection, P0305 at the motor's Delta current, and P0310 at 50Hz.
5. Set the application class to Standard Drive Control (SDC) (linear U/f) — do not select Dynamic Drive Control or vector modes.
6. In the Setpoint channel page, set P1082 = 87Hz and P2000 = 87Hz.
7. Skip the function module selection (no safety, no Braking Module unless required).
8. Click Finish and execute RAM to ROM (copy RAM to ROM) before going online.
9. Connect online, perform Motor identification with P1900 = 2 (still) and run the drive with a no-load ramp to 87Hz. Confirm the actual frequency reaches 87Hz and the current is within P0305.
10. Save the project to the drive's MMC card (if fitted) and to the PG/PC.

Procedure with TIA Portal (HSP for G120C)

1. Open TIA Portal, install the G120C Hardware Support Package if not already present (HSP for SINAMICS G120C V4.7 SP3 or later).
2. Insert the G120C into the device configuration with the correct order number (e.g., 6SL3210-1KE21-7AF1 for a 7.5kW 400V unit with PROFINET).
3. Open Device view → Parameters, switch to the Parameter view (not the wizard).
4. Navigate to Motor data and enter P0304 = 230, P0305 = motor Delta current, P0307 = nameplate kW, P0310 = 50.
5. In the Setpoint / ramp-function generator area, set P1082 = 87, P1120 = 20, P1121 = 20.
6. Under V/f control, set P1300 = 0 and explicitly zero out P1310, P1311, P1312, P1320, P1321.
7. Compile and download to the drive's non-volatile memory.
8. Execute a motor identification run and a 5-minute loaded test, monitoring r0027 (actual current), r0024 (output frequency), and r0034 (motor thermal load).

Multi-Motor Configuration: Parallel Motors on One Drive

The original enquiry on the Siemens support thread concerns multiple motors on a single G120C. The drive has no concept of "parallel motors" in the parameter set; it sees one equivalent motor with an equivalent current. The commissioning engineer must aggregate motor data:

1. Equivalent current P0305 = sum of all motor Delta-rated currents. For three 5.5kW Delta motors each rated 21A, P0305 = 63A.
2. Equivalent power P0307 = sum of all motor nameplate kW. 16.5 kW for the above example. This is what the drive's I²t model uses to scale thermal capacity.
3. Total cable length = sum of all branch cables to the furthest motor for purposes of the output filter selection. Above 50m total, add a dU/dt filter. Above 100m, add a sine-wave filter.
4. Current limit P0640 must be raised to the sum of the motors' stall currents (typically 6× rated for an induction motor inrush) to allow cold starts. For a single 21A motor, P0640 = 150% means 31.5A limit; for three motors summed, P0640 = 200% means 126A, which is within the headroom of a 30kW drive (62A) — confirming the need to oversize the drive by 2 frames as described above.
5. Single motor data set only. Do not use DDS switching for parallel motors, because the thermal model is a single accumulator. If individual motor protection is required, install a thermal overload relay (e.g., Sirius 3RB22) at each motor.

Verification, Commissioning Tests, and Oscilloscope Checks

After commissioning, perform the following verification steps in order. If any step fails, return to the parameter table and re-check.

1. No-load ramp test: with the motor uncoupled, ramp from 0 to 87Hz over 30s. Confirm the drive output voltage tracks 4.6 V/Hz throughout (e.g., at 30Hz, expect ~138V line-to-line). The IOP or BOP-2 should display output frequency r0024, output voltage r0025, and output current r0027.
2. Loaded run at 50Hz: with load applied, measure r0034 (motor thermal model utilization). At rated current, this should be 80-100% after 30 minutes. If it climbs above 100% and trips, P0305 is set too low or the motor wiring is still in Star.
3. Loaded run at 87Hz: hold for 15 minutes at full load. Watch r0034 and r0035 (drive thermal utilization). Both should stabilize below 100%. If r0035 climbs, the drive is undersized and a larger frame is required.
4. Insulation check: with the drive disconnected, megger the motor windings phase-to-phase and phase-to-ground at 500V. A 230V Delta motor should show >100 MΩ.
5. Vibration survey: 87Hz operation puts a 4-pole motor at ~2500 rpm, which is often above the first lateral critical of standard motor frames. If vibration exceeds 4.5 mm/s RMS per ISO 10816, re-balance the rotor or constrain the operating window to 70-75Hz.
6. Acoustic check: 87Hz operation is typically 6-8 dBA louder than 50Hz due to higher switching harmonics and 1.73× magnetostriction. Confirm the noise is within the site's environmental permit.

Fault and Warning Code Reference

The most relevant G120C fault codes for 87Hz installations:

For each fault, capture the diagnostic buffer (read r0947 indexed 0-7) and the timestamp r0949 before acknowledging, because the buffer is overwritten on the next fault.

Troubleshooting Matrix