Semikron SKKT106/16E Retrofit-Compatible Thyristor Module

Semikron SKKT106/16E Retrofit-Compatible Thyristor Module: Legacy System Upgrade & Smooth Migration

The Semikron SKKT106/16E is a dual thyristor (SCR) diode module rated at 106 A average on-state current and 1600 V repetitive peak reverse voltage (VRRM). Widely deployed in industrial AC/DC converters, motor drive front-ends, soft-starters, and regenerative braking circuits, this module remains a critical spare for legacy automation lines that were designed around Semikron’s SKKT and SKKD platform. As original production timelines extend and OEM supply chains tighten, sourcing a verified, pre-tested SKKT106/16E is the fastest path to restoring uptime without redesigning the power stage.

Each unit supplied by NINERMAS undergoes pre-shipment electrical verification covering forward voltage drop (VT), gate trigger current (IGT), holding current (IH), and leakage current (IDRM/IRRM) against Semikron datasheet limits. A 12-month warranty is included from the date of shipment, covering manufacturing defects and parametric failures under rated operating conditions.

Upgrade Compatibility Table

Retrofit Planning for Existing Automation Systems

Legacy drive cabinets built around the Semikron SKKT106/16E typically pair this thyristor module with a complementary freewheeling diode module such as the SKKE81/16 or SKKD81/16 on the same heat sink assembly. Before ordering, confirm whether the diode module also shows signs of thermal fatigue — bond wire lift and solder voiding often progress in parallel on modules that share the same thermal cycling history. Replacing both simultaneously eliminates a second unplanned outage within the same maintenance window.

The gate firing signals for the SKKT106/16E are typically generated by a dedicated firing board or a DSP-based control card. In Siemens SIMOREG DC Master drives, the C98043-A7002 firing board interfaces directly with the thyristor gates; in ABB DCS800 platforms, the SDCS-CON-4 control board manages the firing angle. Neither board requires reconfiguration when replacing a like-for-like SKKT106/16E — the gate impedance and trigger threshold remain within the original design envelope.

Power supply integrity is a prerequisite for a successful retrofit. The 24 VDC auxiliary rail feeding the gate driver and control logic should be verified with a calibrated multimeter before and after module replacement. In older cabinets, the SITOP PSU100S 24 V/10 A or equivalent DIN-rail power supply may show output ripple exceeding 200 mV peak-to-peak after years of capacitor aging — a condition that can cause erratic gate firing even with a new thyristor module installed. Replacing the auxiliary PSU as a precautionary measure during the same shutdown is a low-cost insurance step.

Terminal wiring at the AC input and DC output bus bars must be inspected for oxidation and re-torqued to specification. Copper bus bars connected to the SKKT106/16E anode and cathode terminals should be cleaned with isopropyl alcohol and re-torqued to 4–5 N·m (M6 bolts) using a calibrated torque wrench. Loose connections are a leading cause of premature module failure in retrofit applications and will void the warranty if identified as the root cause of a return.

For systems that include an HMI panel — such as a Siemens TP700 Comfort or Weintek MT8071iE — no screen updates are required for a thyristor module swap. The HMI communicates with the PLC or drive controller, not with the power module directly. However, if the retrofit is part of a broader control system migration that also involves replacing a legacy Siemens S5-115U or S5-135U PLC with a modern S7-300 or S7-1500, the HMI project will require re-compilation and download after the controller IP address and data block structure are updated.

I/O expansion during the same retrofit window is common. Engineers often take the opportunity to add a Siemens SM321 digital input module or SM331 analog input module to the existing S7-300 rack to capture additional process signals — motor temperature, DC bus voltage feedback, or cooling fan status — that were not monitored in the original design. These additions improve predictive maintenance capability without requiring a new control cabinet.

For sites migrating from PROFIBUS DP to PROFINET, a Siemens IM153-2 ET 200M interface module or a PN/DP coupler can bridge the legacy field devices to the new network segment while the thyristor stage remains unchanged. This phased approach — power hardware first, communication protocol second — minimises the scope of any single shutdown and reduces commissioning risk.

Programming cable access is required if the drive or PLC parameters need to be re-verified after module replacement. A Siemens PC Adapter USB A2 or PROFIBUS MPI cable should be on-site before the maintenance window begins. Parameter backup (RAM to ROM save, or Step 7 / TIA Portal upload) must be completed before power is removed from the control section to protect the existing program logic.

Downtime Control During System Migration

Minimising unplanned downtime during a thyristor module replacement requires a structured pre-shutdown checklist. Before isolating the drive cabinet, capture a full parameter upload from the controller using Step 7, TIA Portal, or the drive’s own keypad backup function. This protects motor ramp times, current limits, speed references, and PID tuning values that may not be documented in the original commissioning report.

The physical replacement of the SKKT106/16E takes approximately 30–60 minutes for a trained technician: isolate and lock out the AC supply, discharge the DC bus capacitors (verify <50 VDC with a calibrated meter), remove the bus bar connections, unbolt the old module, apply fresh thermal interface material (0.1–0.2 mm bond line), install the new module, re-torque all connections, and restore power in sequence. Gate firing can be verified in open-loop mode at reduced voltage before returning the drive to automatic control.

To protect original program logic, never clear the PLC memory during a power module replacement unless a full program reload from a verified backup is confirmed. The control section of most DC drives and PLC racks remains powered through a separate UPS or battery-backed 24 VDC supply during the AC isolation phase — confirm this before proceeding. If the site does not have a UPS on the control rail, arrange a portable 24 VDC source to maintain PLC memory and HMI communication continuity throughout the swap.

Post-installation commissioning should include a no-load firing angle sweep from α = 90° to α = 15° while monitoring DC output voltage with an oscilloscope or power analyser. Asymmetric firing — visible as unequal positive and negative half-cycle amplitudes — indicates a gate connection issue or a mismatched thyristor pair and must be resolved before reconnecting the motor load. A successful commissioning run at 25%, 50%, and 100% rated load confirms that the retrofit is complete and the system is ready for production handover.

Retrofit Support FAQ

Q1: Is the SKKT106/16E a direct replacement for the SKKT106/14E or SKKT106/12E?
Yes. The SKKT106/16E is pin-compatible and footprint-identical to the /14E (1400 V) and /12E (1200 V) variants. Upgrading to the /16E provides a higher voltage margin, which is beneficial in networks with elevated transient levels. No mechanical or wiring changes are required.

Q2: What pre-shipment tests are performed on each unit?
Every SKKT106/16E is tested for forward voltage drop (VT at rated current), gate trigger current (IGT), holding current (IH), and off-state leakage (IDRM/IRRM) before dispatch. A test report is available on request. Units that fail any parameter are quarantined and not shipped.

Q3: How do I confirm wiring compatibility before installation?
Compare the existing bus bar bolt pattern (M6, SEMIPACK 2 outline) and gate connector pinout against the Semikron SKKT106/16E datasheet. If the original module is a Semikron SKKT series, the replacement is direct. For third-party equivalents with different outlines, a bus bar adapter plate may be required — contact our technical team with the original module part number for confirmation.

Q4: What does the 12-month warranty cover, and how is a claim processed?
The warranty covers manufacturing defects and parametric failures under rated operating conditions for 12 months from the shipment date. To initiate a claim, contact sale@ninermas.com with the order number, failure description, and photos of the installation. Modules showing evidence of overvoltage, reverse connection, or mechanical damage are not covered. Replacement units are dispatched after fault confirmation, typically within 3–5 business days.