SINAMICS S120 5kW SLM with 16kW Line Reactor: Mismatch Risks

1. Overview: The Supply Chain Mismatch Problem

A common supply-chain problem on installed SINAMICS S120 Booksize machines is the unavailability of the 5 kW or 10 kW line reactor. The 5 kW Smart Line Module (SLM), part number 6SL3130-6AE15-0AB1, is documented in the SINAMICS S120 Booksize Power Sections manual as requiring the matching 5 kW line reactor 6SL3000-0CE15-0AA0 and the 5 kW line filter 6SL3000-0HE15-0AA0. When the 5 kW reactor is on a 200 working-day lead time, engineers are tempted to substitute a 16 kW reactor 6SL3100-0EE21-6AA0 from local stock.

This substitution is not permitted by Siemens and is not safe in service. The 16 kW reactor has approximately one-third the inductance of the 5 kW reactor while being rated for more than three times the continuous current. Combining it with a 5 kW SLM defeats the protective function of the reactor, shifts the resonant point of the line filter, and produces precharge, DC-link, and harmonic-distortion faults the SLM is not designed to ride through.

The remainder of this reference documents the affected part numbers, the technical reasons the mismatch is unsafe, the available alternatives, the parameter set to verify on the S120, and the commissioning procedure for the eventual replacement.

2. Affected Components and Part Numbers

The complete list of components involved in the 5 kW front end of an S120 Booksize drive, and the matched 16 kW counterparts, is given below. Every item in the 5 kW chain must be replaced as a set if a 16 kW line reactor is to be used legally.

The SLM is a regulated IGBT infeed with sinusoidal line current and regenerative capability. Unlike an unregulated Basic Line Module (BLM), the SLM actively controls the DC link voltage to 1.35 × V_line (≈ 600 V DC at 400 V AC line) and uses the line reactor as both a current filter and an energy-storage element for the line-side IGBTs. Reactor sizing is therefore part of the control-loop design, not just a passive protection component.

3. Function of the Line Reactor in an S120 Smart Line Module

The line reactor is an iron-core three-phase inductor connected between the AC line and the line-side input of the SLM. In the SINAMICS S120 Booksize design it performs four distinct functions:

1. Limits di/dt and peak inrush current during the precharge of the DC-link capacitors when the line contactor closes.
2. Filters the switching-frequency current drawn by the IGBT bridge so that the line-side harmonic content (THDi) stays within the 5–8 % range typical of the SLM.
3. Decouples the line filter capacitor bank (in the 6SL3000-0HE15-0AA0 filter) from the AC source impedance, preventing the LC network from resonating at a harmonic of the line frequency.
4. Limits short-circuit current in the event of a thyristor or IGBT failure, protecting the upstream circuit breaker from nuisance tripping.

Each of these functions depends on the reactor's nominal inductance L_N, its saturation curve, and its continuous current rating. A reactor designed for a different power class fails one or more of these functions in a non-linear way: simply having "more iron" is not better.

4. Why Reactor Sizing Matters: Inductance vs. Current

The 5 kW and 16 kW line reactors used in the S120 Booksize are not just different sizes; they have different inductance values, different saturation characteristics, and different acoustic signatures. The table below summarises the published ratings and the typical inductance values taken from the Siemens Booksize manual.

The percentage voltage drop u_k is the same by design (≈ 2 % at rated current), but at the 5 kW SLM's 8.5 A operating current the absolute voltage drop across the 16 kW reactor is:

u_k(16kW @ 8.5 A) = 2 % × (8.5 / 27) ≈ 0.63 %

That is roughly one-third of the voltage drop the SLM is designed to see. The control loop in the SLM measures the line voltage at its input terminals and uses the difference between that and the line voltage to set the firing angle of the IGBTs. With only a third of the expected voltage drop, the SLM operates in an uncontrolled region of the line synchronisation and will repeatedly try to push additional reactive current into the DC link, tripping on F30002 (DC link overvoltage) or on F30011 (line phase failure) depending on the load transient.

Using the standard formula for peak inrush current into a capacitor through a series inductor:

I_peak = V_LL × √2 / (ω × L)

where ω = 2πf (50 Hz or 60 Hz line). The peak inrush during precharge at 400 V line, 50 Hz, is:

• 5 kW reactor (4.0 mH): I_peak ≈ 400 × 1.414 / (2π × 50 × 0.004) ≈ 450 A peak
• 16 kW reactor (1.4 mH): I_peak ≈ 400 × 1.414 / (2π × 50 × 0.0014) ≈ 1 286 A peak

Substituting the 16 kW reactor therefore allows nearly three times the inrush current into the SLM's precharge resistor and DC-link capacitor bank. The 5 kW SLM's precharge resistor is sized for the 450 A peak of its matched reactor; at 1 286 A peak the resistor will either open-circuit (blowing the precharge fuse) or solder the contacts of the precharge contactor, depending on which element fails first. The internal control will flag this as F30132 (precharging fault) or F30002 (DC link overvoltage).

5. Compatibility Analysis: 5 kW SLM with 16 kW Line Reactor

From the inductance, current, and fault analysis above, the 5 kW SLM paired with a 16 kW line reactor exhibits the following unacceptable behaviours, in order of when they appear during a typical cold-start sequence:

1. Precharge fails (F30132) within the first 200 ms after the line contactor closes. The precharge resistor overheats because the inrush peak is ≈ 2.85× the design value.
2. DC link overvoltage (F30002) once the SLM IGBTs start switching. The reduced voltage drop on the 16 kW reactor means the SLM cannot regulate the DC link to 600 V DC; the actual DC link rises to ≈ 660–700 V and trips on the overvoltage threshold.
3. Line filter monitoring (F30600) trips because the LC resonant frequency of the 5 kW line filter shifts when its series inductance is reduced. The filter is no longer tuned and the SLM's monitoring routine detects a filter current outside the expected envelope.
4. Line filter overheated (F30650) follows within minutes of continuous operation. The detuned filter draws additional reactive current, the filter capacitors heat up, and the thermostat in the filter opens.
5. I²t converter overload (F30005) accumulates slowly because the SLM's IGBTs are forced to switch additional reactive current to keep the DC link at 600 V. The IGBT junction thermal model trips after ≈ 30 minutes at full motor load.

Even if the SLM is configured to suppress individual faults (p2101 mask), the underlying problem remains: the SLM and the reactor are no longer a matched pair, and the energy balance on the DC link is not maintained. Long-term reliability is compromised even if short-term operation appears stable.

6. Specific Risk: Precharge, Inrush, and Harmonic Behaviour

The three technical risks for a 5 kW SLM running on a 16 kW reactor are:

6.1 Precharge and DC-link stress

The 5 kW SLM has a 110 µF DC-link capacitor bank. With the 16 kW reactor's lower inductance, the resonant frequency of the L-C circuit is:

f_r = 1 / (2π × √(L × C)) = 1 / (2π × √(0.0014 × 110e-6)) ≈ 405 Hz

That is well above the 50/60 Hz line frequency but inside the SLM's 8 kHz IGBT switching range. The DC-link voltage will ring on every line half-cycle, and the SLM's own line synchronisation will misfire occasionally. The fault buffer typically records this as F30002 (DC link overvoltage) on the rising edge of the ringing.

6.2 Harmonic content (THDi)

The SLM is rated for ≤ 5 % THDi on its 5 kW matched reactor. With a 16 kW reactor the line-side inductance is insufficient to filter the SLM's 8 kHz switching component, and the measured THDi rises to 10–14 % depending on line impedance. This pushes the installation out of compliance with IEEE 519 at the 5 kW point of common coupling and may trip the upstream reactive-power compensation capacitor bank.

6.3 Filter detuning

The 5 kW line filter 6SL3000-0HE15-0AA0 contains a capacitor bank tuned to resonate with the 5 kW reactor at a harmonic of the line frequency. With the 16 kW reactor, the resonant point moves up by a factor of √(4.0/1.4) ≈ 1.7×, putting it close to the 11th harmonic (550 Hz at 50 Hz line). The filter begins to amplify 11th-harmonic currents from the line rather than attenuate them, which is the failure mode of F30650 (line filter overheated).

7. Practical Alternatives When the 5 kW Reactor is Unavailable

When the 5 kW line reactor is on a 200 working-day lead time, the documented engineering choices are listed below in order of preference. The decision logic is shown in the inline SVG flowchart further down.

7.1 Option A — Wait and hold the spare 5 kW SLM offline

Keep the existing 5 kW SLM, 5 kW filter, and the 5 kW motor modules operational on a temporary feeder without the 5 kW line reactor. This is not permitted by Siemens and is unsafe for the reasons in Section 5. Use this option only as a last resort and only if the drive can be physically locked out for the duration of the wait.

7.2 Option B — Replace the entire 5 kW front end with the 16 kW set

Order the following matched 16 kW set and replace all three components (SLM, reactor, filter) at the same time:

• SLM: 6SL3130-6AE22-0AB1 (16 kW)
• Line reactor: 6SL3100-0EE21-6AA0 (16 kW)
• Line filter: 6SL3000-0HE21-6AA0 (16 kW)

All motor modules downstream of the SLM continue to operate; the 16 kW SLM can supply any combination of 5 kW motor modules up to its 16 kW rating. The 16 kW SLM is a drop-in mechanical replacement for the 5 kW SLM in the booksize rack; firmware parameter changes are limited to p0220 (line filter type) and p0221 (line filter capacitance).

7.3 Option C — Use a 16 kW reactor temporarily, accept the risk

Install the 16 kW reactor in place of the 5 kW reactor and operate at reduced motor load (≤ 50 % of the 5 kW SLM's rating). This configuration is not documented, is not supported, and will not pass CE/UL inspection. It may keep the line running while the 5 kW parts are on order, but the SLM must be re-commissioned and the fault buffer monitored continuously.

7.4 Decision flowchart (SVG)

Engineers who take Option C should record the decision in the machine's EHS file, raise a deviation note with their machinery safety officer, and prepare a re-commissioning procedure for the moment the correct 5 kW parts arrive.

8. Configuration Parameters in SINAMICS S120

When the matched components are installed (Option A or B), the following parameters on the SLM's drive object must be checked and re-loaded. These are all on the infeed DO (typically DO number 2 in the S120 topology).

9. Commissioning and Verification Procedure

Use the following procedure to verify correct operation once the matched 5 kW or 16 kW parts are installed. The procedure is run with STARTER (≤ V5.4) or Startdrive (TIA Portal V15 and above).

1. Back up the existing project. Online → Drive unit → Upload to PG. Save the file with a date stamp.
2. Power down and lock out the S120 rack. Replace the SLM, reactor, and line filter as a matched set.
3. Verify mechanical fit of the new SLM in the booksize rack. The 16 kW SLM is the same width (50 mm) and depth as the 5 kW SLM and uses the same DC-link busbar adapter family.
4. Restore the parameter set from the backup. Adjust p0221, p0223, and p0224 to the values matching the new line filter (see Section 8).
5. Run infeed identification: set p3410 = 1 and pulse enable the SLM. The SLM runs the line-filter identification routine for ≈ 30 s. The result is written back to p0221–p0224.
6. Check the fault buffer for any of the following codes after identification:
   • F30002 — DC link overvoltage: clear, re-run identification with a stable line.
   • F30011 — Line phase failure: check the wiring and the line filter phase orientation.
   • F30132 — Precharging fault: confirm the precharge resistor has not opened.
   • F30600 — Line filter monitoring: re-check p0220 and p0221.
   • F30650 — Line filter overheated: confirm the line filter type and ventilation.
7. Capture a 10 s trace of r0070 (DC link voltage), r0024 (output frequency), and r0027 (actual current) at full motor load. Confirm that the DC link is stable at 600 V ± 2 % with no ringing on the rising edge.
8. Measure the line current THDi with a power-quality analyser (Fluke 435, Hioki PW3198, or similar) at the line-side of the reactor. The 5 kW matched configuration should read ≤ 5 %; the 16 kW configuration should read ≤ 4 % at 16 kW load.
9. Run the machine through a full duty cycle and confirm no F-code trips.
10. Save the final parameter set with p0971 = 1 and copy the file to the engineering archive.

10. Long-Term Reliability and Thermal Considerations

Beyond the immediate commissioning faults, an SLM operating on a mismatched line reactor accumulates lifetime damage on three components:

• Precharge resistor and contactor: rated for one inrush event at the design L. Each precharge on the wrong reactor removes ≈ 2–3× the design energy budget. After 10–20 precharge cycles the resistor drifts or the contactor welds.
• DC-link capacitor bank: the high-frequency ringing in the L-C circuit adds ripple current that is not counted in the capacitor's rated dV/dt or I_ripple. Lifetime is typically reduced by 50 % per 10 °C of additional hotspot temperature.
• IGBT modules: the additional reactive current flowing through the SLM IGBTs adds switching loss. At 50 % continuous load on the 16 kW reactor, the IGBT junction temperature rises by 8–12 °C, halving the module's thermal-cycling lifetime.

For these reasons, Siemens does not list any "mismatch permissible" configuration in the Booksize Power Sections manual. If a temporary mismatch is unavoidable, the conservative limits are: motor load ≤ 50 % of the SLM's nameplate rating, precharge cycles ≤ 5 per day, and a duty-cycle review at 1000 hours.

11. Frequently Asked Questions