SEMIKRON SKKH570/16E Retrofit-Compatible Thyristor Module

SEMIKRON SKKH570/16E Retrofit-Compatible Thyristor Module: Legacy System Compatibility & Smooth Upgrade

The SEMIKRON SKKH570/16E is a high-current thyristor (SCR) power module rated at 570 A average on-state current and 1600 V repetitive peak off-state voltage, widely deployed in legacy industrial drive systems, rectifier cabinets, and DC motor control platforms. As original equipment manufacturers discontinue support for aging control architectures, the SKKH570/16E has become a critical retrofit component for engineers tasked with extending the operational life of existing automation lines without full system replacement. NINERMAS maintains verified stock of this module, fully tested and backed by a 12-month warranty, to support planned and emergency retrofit projects worldwide.

Upgrade Compatibility Table

Retrofit Planning for Existing Automation Systems

Replacing the SKKH570/16E in an operating plant requires a structured approach that accounts for the interdependencies between the power module and the surrounding control architecture. In most legacy DC drive cabinets, the thyristor module works in conjunction with a dedicated firing board — commonly a SEMIKRON SKHI 22A or SKHI 61 gate driver — which generates the precise gate pulses needed to control conduction angle and output voltage. Before removing the failed module, engineers should document the existing gate pulse waveform using an oscilloscope, as any deviation after replacement will directly affect motor speed regulation and torque response.

The DC bus capacitor bank and snubber network adjacent to the SKKH570/16E must also be inspected during the retrofit. Aged snubber capacitors and resistors can cause voltage spikes that damage a new module within hours of commissioning. Similarly, the DC link choke or line reactor upstream of the rectifier bridge should be checked for insulation integrity and inductance value, as degraded inductance increases di/dt stress on the thyristor junctions.

For systems using a PLC-based supervisory layer — such as a Siemens S5-115U, S7-300, or Allen-Bradley SLC 500 — the retrofit plan should include a review of the analog speed reference signal path from the controller’s analog output module to the drive’s reference input. If the original drive used a ±10 V reference and the replacement firing board accepts 0–10 V, a signal conditioning module or isolation amplifier will be required to prevent control loop errors. In multi-drive lines, the master-follower speed synchronization logic in the PLC program must be verified to ensure the retrofitted drive responds identically to the original.

Panel-level considerations include verifying that the existing AC input contactor, fusing, and bus bar ratings are adequate for the SKKH570/16E’s 570 A continuous current rating. The heatsink assembly must be cleaned and inspected for corrosion or warping; a flatness deviation greater than 0.05 mm at the module mounting surface will create hot spots that reduce module lifespan. Thermal compound should always be replaced during installation. If the original heatsink is water-cooled, inspect the coolant flow rate and inlet temperature to confirm they remain within the module’s thermal resistance specifications.

In applications where the SKKH570/16E drives a wound-field DC motor, the field excitation circuit — often controlled by a smaller thyristor module such as the SEMIKRON SKKT57/16E or a dedicated field controller — should be tested independently before reconnecting the armature circuit. This isolates any field winding faults that could otherwise be misdiagnosed as a power module failure. HMI screens displaying motor current, speed feedback, and fault codes should be reviewed to confirm that the engineering units and scaling factors remain valid after the retrofit, particularly if the drive’s current transducer or shunt resistor was also replaced.

For plants migrating from legacy analog drives to digital control platforms, the SKKH570/16E can serve as an interim power stage while the control electronics are upgraded. Pairing the module with a modern digital firing board that supports PROFIBUS DP or Modbus RTU communication allows the existing PLC to retain supervisory control while gaining improved diagnostics and remote parameter access. This phased approach — replacing the power semiconductor first, then upgrading the control layer — minimizes the scope of any single outage window and allows production to resume quickly between phases. Where I/O expansion is needed during the migration, modules such as the Siemens ET 200S distributed I/O or a Phoenix Contact Inline I/O terminal block can be integrated into the existing control cabinet without requiring a full rack replacement.

Engineers working on multi-axis drive lines should also account for the SEMIKRON SKiiP series intelligent power modules used in adjacent drive channels. If the SKKH570/16E is part of a larger rectifier assembly that feeds a common DC bus shared with inverter modules, the bus voltage stability during the retrofit window must be maintained using a temporary bus support supply or by isolating the affected channel while keeping adjacent channels operational. Programming cables such as the Siemens PC Adapter USB or the Rockwell 1784-U2DHP should be on hand to allow real-time monitoring of PLC diagnostics during the commissioning phase.

Downtime Control During System Migration

Minimizing unplanned downtime is the primary concern for any maintenance team undertaking a thyristor module replacement on a running production line. The recommended strategy is to pre-stage the replacement SKKH570/16E alongside all ancillary materials — thermal compound, M6 hardware, gate connector, and snubber components — before the scheduled maintenance window begins. A pre-shipment test report from NINERMAS confirms that the module has been electrically verified, reducing the risk of receiving a defective unit and extending the outage.

During the outage, the sequence should follow a defined lockout/tagout procedure: isolate the AC supply, discharge the DC bus capacitors to below 50 V (verified with a calibrated meter), and only then remove the failed module. The gate wiring harness connector pinout should be photographed before disconnection to prevent miswiring during reassembly. After installing the new SKKH570/16E and torquing the power terminals to the manufacturer’s specified value, a no-load gate firing test — applying gate pulses with the AC supply connected but the motor disconnected — confirms correct thyristor triggering before full load is applied.

If the control system uses a Siemens S7-400 or similar PLC with a CPU memory card, the existing program should be backed up to an external programming device before any work begins. This protects against accidental program loss if a power interruption occurs during the maintenance window. For drives integrated into a DCS environment via a 4–20 mA speed reference, the DCS operator should place the drive in manual mode and hold the speed setpoint at zero before the electrical isolation step, preserving the process state and allowing a smooth return to automatic control after commissioning.

Post-commissioning, the drive should be run at 25%, 50%, and 100% load in sequence, with current and temperature readings logged at each step. This stepped load test confirms that the thermal interface is performing correctly and that the firing angle is tracking the speed reference accurately. The entire replacement process — from isolation to full-load verification — can typically be completed within a four-hour planned maintenance window when all materials and documentation are prepared in advance.

Retrofit Support FAQ

Q1: Is the SKKH570/16E a direct replacement for the SKKH570/14E?
The SKKH570/16E (1600 V) and SKKH570/14E (1400 V) share the same current rating and package dimensions, making them physically interchangeable. However, the voltage class must match the application’s line voltage and required safety margin. Substituting a 1400 V module in a 1600 V-rated circuit is not recommended. NINERMAS can advise on the correct voltage class for your specific installation.

Q2: How do I verify gate driver compatibility before installation?
The SKKH570/16E requires a gate trigger current of approximately 150–250 mA with a minimum pulse width of 100 µs. Measure the output of your existing firing board (such as a SEMIKRON SKHI series driver) with an oscilloscope before installation. If the gate pulse amplitude or width is outside specification, the firing board parameters must be adjusted or the board replaced before the new module is installed.

Q3: What does the pre-shipment test cover, and what documentation is provided?
Every SKKH570/16E shipped by NINERMAS undergoes electrical verification including forward voltage drop, gate trigger current, and blocking voltage tests. A test report is available upon request. All units are covered by a 12-month warranty from the date of shipment. In the event of a warranty claim, NINERMAS provides technical support to assist with fault diagnosis and module exchange.

Q4: Can NINERMAS supply the SKKH570/16E for emergency orders, and what is the typical lead time?
NINERMAS maintains inventory of the SKKH570/16E to support both planned retrofit projects and emergency breakdown situations. In-stock units can typically be dispatched within 24–48 hours of order confirmation. For large-quantity orders or long-term supply agreements, contact our sales team to discuss scheduling and pricing. Emergency shipments via express courier are available to most destinations worldwide.