To get the high current capability in the current the valves used in construction of the converter are connect

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To get the high current capability in the current the valves used in construction of the converter are connected in

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Option B: Parallel

Explanation & Concepts:
To achieve high current ratings in HVDC valve assemblies, thyristors (or other power semiconductor devices) are connected in parallel. This arrangement allows the total load current to be divided among multiple devices, ensuring that no single component exceeds its maximum current-carrying capacity.

Working Principle: In power converter design, the total current $I_{total}$ is distributed across $n$ parallel-connected paths. Since $I_{total} = I_1 + I_2 + ... + I_n$, connecting devices in parallel increases the effective current capacity of the valve. Careful matching of device characteristics and implementation of current-sharing circuits is necessary to ensure uniform distribution and prevent thermal runaway in individual thyristors.

Key Formulas: $I_{valve} = \sum_{i=1}^{n} I_i$ — total current capacity calculation for parallel devices; $P_{loss} = I_{valve}^2 \cdot R_{on}$ — conduction loss representation in high current valves

Key Points: Parallel connection increases current capacity.; Series connection increases voltage blocking capability.; HVDC converter valves use a series-parallel combination to achieve high voltage and current ratings.; Thyristor valves in HVDC systems often consist of hundreds of devices in series.

Advantages: Increased current handling capability; Redundancy in case of single device failure; Lower overall conduction losses

Disadvantages: Requires careful current balancing circuits; Complexity in gating and thermal management

Applications: HVDC converter stations; Static VAR Compensators (SVC); High-power industrial motor drives

Additional Info: In practice, HVDC valves use 'modular' construction where devices are arranged in series-parallel combinations to satisfy both voltage and current requirements of the transmission line.. Option A is used to increase voltage capability, while Option B is used for current.

Answer: B is correct — Parallel connection is employed to divide the total load current among multiple semiconductor devices, thereby increasing the effective current-carrying capacity of the converter valve.

Exam Tip: Remember: S-V (Series = Voltage) and P-I (Parallel = Internal current/Capacity) as a mnemonic for power device stacking in HVDC.

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Option A: Series

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Option C: Series-parallel combination

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Option D: Star or Delta manner

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