In the dynamic equalizing network for series-connected thyristors, a series (R–C) branch with a diode in parallel with R is placed across each device. The resistor R (with its parallel diode) primarily limits which current?

Introduction / Context:
When thyristors are connected in series, dynamic (transient) voltage sharing is improved by placing an R–C snubber across each device. A diode is often placed in parallel with the resistor so the capacitor has an asymmetrical charge/discharge path. Understanding the role of each element avoids device overstress.

Given Data / Assumptions:

• Each thyristor has a dedicated series R–C across it.
• A diode is connected in parallel with R (but not across C).
• Goal: equalize transient voltages and control dV/dt.

Concept / Approach:

During fast transients, the capacitor provides a low-impedance path to absorb voltage differences. The diode bypasses the resistor in one polarity so the capacitor can charge quickly through the diode (low resistance), while in the opposite polarity the capacitor must discharge through R, which limits the discharge current and slows the transient, aiding equalization.

Step-by-Step Solution:

Verification / Alternative check:

Snubber arrangements in data sheets show the diode orientation to give a low-impedance charge path and a controlled discharge path, preventing unequal voltage distribution during recovery transients.

Why Other Options Are Wrong:

• limits charging current: The diode bypasses R during charging.
• limits both: Only the discharge path is through R by design.
• none / surge-only: Misstates the designed function of R with the diode.

Common Pitfalls:

• Assuming R always limits both ways; the diode makes the network asymmetric.
• Confusing static equalizing resistors (large-value across each device) with dynamic R–C snubbers.

Final Answer:

limits discharging current