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Rectification at the ends of E.H.V. d.c. transmission is done by using
Shunt generations
Power capacitances
SCR
Motor-generator set
SCR
In E.H.V. (Extra High Voltage) d.c. transmission, rectification at the sending end and inversion at the receiving end are achieved using high-power semiconductor valves. Modern HVDC converters employ Silicon Controlled Rectifiers (SCRs) or Thyristors due to their high power handling capacity, fast switching capabilities, and efficiency.
In E.H.V. (Extra High Voltage) d.c. transmission, rectification at the sending end and inversion at the receiving end are achieved using high-power semiconductor valves. Modern HVDC converters employ Silicon Controlled Rectifiers (SCRs) or Thyristors due to their high power handling capacity, fast switching capabilities, and efficiency.
VdтАЛ=VdoтАЛcos(╬▒)тИТIdтАЛRcтАЛ тАФ D.C. output voltage of a converter with firing angle ╬▒
RcтАЛ=╧А3XcтАЛтАЛ тАФ Commutating resistance per bridge
The conversion process utilizes a bridge configuration (typically a 6-pulse or 12-pulse Graetz bridge) comprising multiple series-connected SCRs. By precisely controlling the firing angle (╬▒) of these thyristors, the alternating current (a.c.) input is rectified into unidirectional direct current (d.c.) output. The high-voltage capability is achieved by stacking numerous SCRs in series to withstand the massive transmission potential.
HVDC systems require power electronic converters for interfacing with AC grids.
Thyristors (SCRs) are used for their ability to handle voltage levels up to hundreds of kV.
The converter acts as a rectifier at the sending end and as an inverter at the receiving end.
12-pulse bridges are standard in HVDC to reduce harmonic distortion.
High efficiency with low power losses.
Fast control of power flow through firing angle variation.
Ability to interconnect asynchronous AC networks.
Generates harmonics requiring expensive filtering.
Requires substantial reactive power support (VAR compensation).
Bulk power transmission over long distances.
Submarine cable power links.
Asynchronous interconnection of regional grids.
SCRs are preferred over earlier technologies like mercury-arc valves due to smaller size and no maintenance.
Option A (Shunt generators) is obsolete for HVDC. Option B (Power capacitances) relates to reactive power compensation, not rectification. Option D (Motor-generator sets) is inefficient and bulky for EHV applications.
C is correct тАФ SCRs (thyristors) are the fundamental building blocks used in modern HVDC bridge converters for power rectification.
Remember that in HVDC, the converter is a reversible device; it acts as a rectifier when firing angle ╬▒<90┬░ and as an inverter when ╬▒>90┬░.