Original Siemens Inverter/Converter EBG Resistor /Balancing Resistor 2X5K5/PF 96517 2X5K5PF

2X5K5/PF | Matched Pair Snubber Resistors — 2 × 5.5kΩ / Power Film / Thyristor and SCR Module Circuit Protection

Snubber Resistors — Essential Protection for Thyristor Circuits

The 2X5K5/PF provides two matched 5.5kΩ power film resistors for use in RC snubber circuits across thyristor (SCR) modules. Snubber circuits are a fundamental protection requirement in thyristor power conversion — they are not optional additions but an integral part of correct thyristor circuit design.

Two conditions that snubber circuits must address in thyristor applications:

dv/dt protection: If the rate of rise of voltage (dv/dt) across a blocking thyristor exceeds the device's specified limit, the thyristor can trigger without a gate signal — causing uncontrolled conduction and circuit malfunction. The snubber capacitor limits dv/dt by absorbing the voltage rise rate through the RC time constant.

Overvoltage suppression: Circuit inductance (transformer leakage inductance, bus bar inductance, cable inductance) stores energy that converts to voltage spikes when thyristor current suddenly commutates off. The snubber circuit absorbs this energy, preventing voltage spikes from exceeding the thyristor's 1600V blocking voltage rating.

Key Product Information

RC Snubber — How the Resistor and Capacitor Work Together

The snubber resistor (2X5K5/PF) works with a matched snubber capacitor to form the protective RC circuit across each thyristor:

Capacitor role: The snubber capacitor directly limits dv/dt by absorbing charge — when voltage rises rapidly across the thyristor, the capacitor absorbs current proportional to C × dv/dt, limiting the voltage rate of rise.

Resistor role (2X5K5/PF): The 5.5kΩ series resistor in each snubber serves two functions:

1. Capacitor discharge limiting: When the thyristor fires and the snubber capacitor discharges through the newly conducting thyristor, the resistor limits the discharge current rate (di/dt). Without the resistor, the capacitor discharge current would impose an unacceptable di/dt on the thyristor at turn-on — potentially exceeding the device's critical rate of rise of on-state current and causing local hot-spot damage in the silicon.
2. Oscillation damping: The snubber RC circuit forms a series-resonant circuit with the circuit inductance. Without the resistor, this circuit would oscillate at its resonant frequency — producing ringing voltages above the supply peak. The resistor critically damps the circuit, converting oscillation energy to heat rather than voltage peaks.

Application Scenarios

SKKT430-16E or SKKT460-16E snubber circuit: Each thyristor in an SKKT-series module requires its own snubber circuit. For a three-phase six-pulse bridge with three SKKT460-16E modules (six thyristors total), six RC snubber circuits are needed — the 2X5K5/PF provides matched resistor pairs for two snubber circuits per package.

Phase-controlled AC controller: Single-phase or three-phase AC voltage controllers using antiparallel thyristor pairs require snubber circuits on each pair. The 2X5K5/PF matched pair provides the resistors for one AC controller thyristor pair.

FAQ

Q1: Why is a matched pair (2X5K5/PF) more useful than buying individual resistors?

In thyristor circuits, snubber components typically come in pairs — one for each thyristor in a dual module or for the two antiparallel devices in an AC controller. Factory-matched pairs ensure the two resistors have identical resistance values, guaranteeing symmetrical snubber performance across both thyristors. This is more reliable than measuring individual resistors and hoping their tolerances match closely enough.

Q2: What snubber capacitor is used with the 2X5K5/PF resistors?

The correct snubber capacitor value depends on the thyristor circuit's specific parameters — supply voltage, circuit inductance, thyristor's dv/dt rating, and desired damping factor. The capacitor must be a film type rated for the full supply voltage plus the expected overvoltage spike — typically a polypropylene or metallised film capacitor rated for the circuit voltage. The RC time constant (R × C) should be optimised to limit dv/dt below the thyristor's specification while maintaining adequate oscillation damping through the RC impedance.

Q3: How much power must the 2X5K5/PF snubber resistors dissipate in service?

Snubber resistor power dissipation depends on the snubber capacitor value, supply voltage, and switching frequency. The energy stored in the snubber capacitor at full supply voltage (½ × C × V²) is dissipated in the snubber resistor at each thyristor turn-on event. At 50Hz in a three-phase bridge, each thyristor fires 50 times per second. The average resistor power is: P = ½ × C × V² × f. For typical snubber capacitances in SEMIPACK 5-class circuits (approximately 0.1–0.47µF at 1600V), the resistor power is in the range of 0.5–5W per resistor — confirm from the specific circuit parameters.

Q4: What temperature rating is required for the 2X5K5/PF snubber resistors in industrial applications?

Snubber resistors in industrial thyristor circuits should be rated for continuous operation at the maximum expected cabinet ambient temperature plus the resistor's own self-heating. Industrial control cabinet ambient temperatures typically reach 40–55°C. Add the resistor's temperature rise from dissipated power. Power film resistors in industrial grades are commonly rated to 125°C or higher — select the specific 2X5K5/PF variant with a temperature rating appropriate for the installation's thermal environment.