Simovert Masterdrive VC 22kW Braking Unit Installation Guide

1. Overview

This reference documents the field installation of an external braking chopper (braking unit) and a braking resistor on a Siemens SIMOVERT MASTERDRIVES Vector Control (VC) compact inverter, 22 kW frame size, MLFB 6SE7024-7ED61-C. The procedure applies to the Type E compact unit family (6SE702x series) used in 380–480 V three-phase supplies driving induction or servo motors with high inertial loads, vertical axes, or fast deceleration profiles.

The DC-link bus of a standard 400 V class inverter sits at approximately 1.35 × VLL when rectified, nominally 540 V DC on a 380 V mains supply and roughly 648 V DC on a 480 V mains supply. Without a means of dissipating regenerated energy, the bus can rise above 750 V DC and trigger either a DC-link over-voltage trip (fault F002 / F008 depending on firmware) or, in the worst case, destroy the electrolytic capacitors and IGBT modules. The braking chopper monitors the DC-link voltage; once a programmable threshold is crossed, an internal IGBT switches the external braking resistor across the bus, dissipating the regenerative energy as heat.

2. Prerequisites

1. Verified drive identification: MLFB 6SE7024-7ED61-C, serial T-S90347500056, 22 kW continuous, 51.7 A nominal input at 380–480 V 3AC, 50/60 Hz, Z_min = 1%.
2. Three-phase supply confirmed as 380–480 V AC, 50/60 Hz with the impedance ratio declared by the utility above the Zmin limit.
3. Drive firmware version known (read from r060 or operator panel) — chopper threshold voltage default values differ between firmware 1.x, 2.x, and 3.x releases.
4. Available panel space for the chopper module (DIN-rail or backplate mount) and an external resistor location with unrestricted airflow or forced ventilation.
5. Tools: torque-limiting screwdriver (1.2 Nm for control terminals), insulated torque wrench for power lugs, category IV digital multimeter, opto-isolated USB-to-RS232 converter for OP1S panel or DriveMonitor commissioning software.
6. Personal protective equipment rated for 1 kV DC and 250 °C surface contact.

3. Drive Identification and DC Bus Analysis

The MLFB 6SE7024-7ED61-C breaks down as follows:

Calculate the rectified DC-link nominal voltage for your specific mains:

• At 380 V AC line-to-line: VDC = 1.35 × 380 = 513 V DC nominal (no-load approximately 540 V DC).
• At 400 V AC: VDC = 540 V DC nominal.
• At 480 V AC: VDC = 648 V DC nominal.

The braking chopper turn-on threshold is typically factory-preset to 750 V DC for the 400 V class, providing roughly 750 / 648 = 1.16 times nominal headroom. Adjust this upward only if the supply is proven stable at 480 V AC and the motor insulation system tolerates the corresponding switching transients.

4. Braking Chopper (Braking Unit) Selection

The MASTERDRIVES compact unit accepts an external braking chopper module from the 6SE7031-xxx accessory family. For a 22 kW frame, the matched chopper module is typically designated 6SE7031-0ES87-2FE0 (or the regional equivalent under 6SE7090-0XX84 series), rated for 50 A continuous DC switching current and 100 A peak. The chopper plugs into the dedicated braking-unit connector on the lower power terminal block of the compact unit.

Confirm the chopper is ordered against the correct regional catalog (NA, EU, AP) by cross-referencing the Siemens COMOS or Industry Mall selection tool before purchase. The drive must be de-energized for module installation; never hot-plug a chopper.

5. Braking Resistor Sizing Calculations

Three quantities drive resistor selection: peak braking power, continuous dissipation, and ohmic value. Compute each step explicitly:

Step A — Required ohmic value. The minimum resistance is set by the chopper's peak current limit. For 80 A peak at 760 V DC threshold:

Rmin = Vthresh / Ipeak = 760 V / 80 A = 9.5 Ω

Select the next standard EIA value above Rmin — typically 10 Ω for a 22 kW Masterdrive VC. A lower resistance forces the chopper into current-limit fold-back and the resistor will not dissipate rated power.

Step B — Peak braking power. This is the regenerative power the drive can return when decelerating the mechanical load:

Ppeak = J × ω × (dω/dt)

Where J is total inertia reflected to the motor shaft, ω is angular velocity, and dω/dt is the deceleration rate. For a typical hoist or centrifuge, P_peak lands between 30 kW and 60 kW. For vertical-axis braking of a 22 kW motor:

Ppeak ≥ 1.5 × Pmotor = 1.5 × 22 kW = 33 kW

Step C — Continuous dissipation. Use the duty cycle of the braking action over a 120 s reference window:

Pcont = Ppeak × (tbrake / tcycle)

For a hoist with 10 s active braking every 60 s: Pcont = 33 kW × 10/60 = 5.5 kW. For a centrifuge with sporadic braking (10 s every 5 minutes): Pcont = 33 kW × 10/300 = 1.1 kW.

Step D — Resistor selection matrix.

If sourcing third-party resistors, the Allen-Bradley 1332-IN006 brake resistor installation guide provides the canonical mechanical and grounding rules (mount external to enclosure, exposed to free circulating air, ground via mounting screw when not in grounded cabinet). Equivalent installation rules for SEW-Eurodrive MOVITRAC-style resistors are documented in the SEW-Eurodrive braking resistor installation manual.

6. Mechanical Installation Requirements

Braking resistors reject all incoming energy as heat and require either unrestricted natural convection or forced-air cooling. Apply the following physical rules, summarized from the AutomationDirect GS3 braking component installation chapter and Yaskawa DB option document 2Y25-0300:

• Mount the resistor outside any sealed enclosure or, if internal, on a separate sub-panel with 100 mm clearance on all four sides.
• Resistor surface temperature can exceed 300 °C; never mount above or adjacent to cable runs, plastic junction boxes, or combustible material.
• Provide a wire-mesh guard to prevent incidental contact; the guard must not restrict airflow.
• Use Hi-Flex silicone-jacketed cable (rated 150 °C minimum) from the chopper terminals to the resistor. Cross-section sized for the continuous current: for 40 A continuous, use 10 mm² (8 AWG) copper minimum; for 80 A peak bursts, 16 mm² (6 AWG) is preferred.
• Ground the resistor chassis with a dedicated lead back to the drive PE bus or cabinet ground bar.
• When installed in a control cabinet, route the chopper-to-resistor cable at right angles to signal cables to minimize radiated EMI back into the control section.

7. Electrical Wiring and DC Link Connection

The wiring topology is short and direct: the chopper module sits in parallel with the drive's DC-link capacitors and switches the resistor across the bus when the threshold is exceeded.

The wiring steps:

1. Isolate the drive at the upstream disconnect, lock-out and tag-out, and wait five minutes for the DC-link to self-discharge below 50 V DC. Verify with a meter on the DC+ and DC- terminals.
2. Mount the chopper module to the backplate within 1.5 m of the drive, observing bend radius for the DC link cables.
3. Connect the chopper's two DC-link input terminals to the drive's DC+ and DC- power terminals using the supplied or approved pre-fabricated link. Torque to the value silkscreened on the terminal block (typically 2.5 Nm).
4. Run a two-conductor Hi-Flex cable from the chopper's output terminals to the braking resistor. Observe polarity-free wiring — the resistor sees DC and is non-polarized, but keep conductors paired to control radiated EMI.
5. Bond the resistor chassis to the cabinet PE bar with a dedicated green/yellow conductor, sized per local electrical code (typically equal to line conductor or one step down).

8. Parameter Configuration

For basic operation no parameter change is required. The braking chopper firmware monitors the DC bus independently and switches the IGBT when its internal threshold voltage is exceeded. This applies to all 6SE7024 compact MASTERDRIVES VC units regardless of firmware vintage.

However, several parameters are useful to verify and may need adjustment for advanced applications:

Parameter access requires either the OP1S operator panel or DriveMonitor commissioning software via the RS232 service port (X2) on the front of the compact unit. DriveMonitor is bundled with the DriveMonitor Starter Kit and supports offline parameter set diffing — always archive the original parameter set before making changes.

9. Commissioning and Verification

1. Pre-power visual: confirm torque marks on all power lugs, PE bonding present, resistor mounted with correct clearances, control wiring dressed away from power conductors.
2. Apply control power only (if separate) and read r070 — should display the rectified DC-link voltage matching your supply (540 V DC nominal for 400 V mains).
3. Issue a no-load run command at low frequency (5 Hz), check motor rotation and r070 — the bus should remain at nominal ± 5 V.
4. Issue a fast stop from 50 Hz with no mechanical load. r070 should briefly rise but not exceed P462; if it does, the chopper is firing. Listen for the characteristic 1 kHz switching whine from the chopper inductor — absence indicates the threshold is set above your actual bus peak or the chopper is disabled.
5. Increase load inertia on the motor shaft (or program a synthetic high-inertia ramp) and repeat the fast stop. Verify r070 clamps at the threshold value. Verify resistor surface temperature rises but stays within the resistor's rated envelope.
6. Capture a 10-second trace of r070 and the chopper duty cycle (r071 if available) to a Trend via DriveMonitor and archive it with the project documentation.
7. Restore any modified parameters, cycle power, and confirm a clean restart with no faults (especially no F002, F008, or F029 depending on firmware).

10. Troubleshooting Matrix

11. Documentation and Archiving

After successful commissioning, archive the following into the project record set:

• Original factory parameter set (DPE export from DriveMonitor).
• Modified parameter set with diff comments.
• Commissioning trace showing DC-link voltage clamping during worst-case braking.
• Resistor MLFB, ohmic value, peak and continuous ratings as installed.
• Chopper MLFB and firmware version (read from r060 or module label).
• Torque values applied to every power connection.
• Insulation resistance test record (megger) on the resistor branch with drive isolated.

For migration planning, note that the 6SE7024 MASTERDRIVES VC compact platform is in legacy support. Modern replacement platforms such as SINAMICS G120, G120C, or S120 accept braking choppers and resistors selected via the SINAMICS Selector in the Siemens Industry Online Support portal. Sizing rules transfer directly: 22 kW at 400 V maps to a 10 Ω / 6 kW continuous resistor with a 50 A peak chopper. See the Siemens Industry Online Support Knowledge Base for migration cross-references.