HVDC transmission, also known as High Voltage Direct Current transmission, is a method of transmitting electrical power over long distances using direct current (DC) instead of alternating current (AC). HVDC transmission offers several advantages over traditional AC transmission, including lower losses, increased power transfer capability, and the ability to connect asynchronous grids.

One of the key components in HVDC transmission is the pulse converter, which is responsible for converting AC power into DC power at the sending end and vice versa at the receiving end. The pulse converter consists of rectifiers and inverters, which convert AC to DC and DC to AC, respectively.

Explanation of the correct answer:

The correct answer is option 'D' - pulse converters. Here's why:

1. Role of Pulse Converters:
a) The pulse converters play a crucial role in HVDC transmission as they convert the AC power generated by the power stations into DC power for transmission.
b) At the receiving end, they convert the transmitted DC power back into AC power for distribution to the grid.

2. Elimination of AC Filters:
a) AC filters are not needed in HVDC transmission because the AC power generated by the power stations is directly converted to DC power by the pulse converters.
b) Unlike in AC transmission, there is no need for AC filters to remove harmonic components or maintain the power quality.

3. Elimination of DC Filters:
a) Similarly, DC filters are not required in HVDC transmission as the pulse converters ensure a smooth DC waveform with minimal harmonic distortion.
b) The pulse converters perform the necessary filtering and smoothing of the DC power, eliminating the need for additional DC filters.

4. Importance of Transformers:
a) While AC filters and transformers are not required in HVDC transmission, it's important to note that transformers are still used at both the sending and receiving ends.
b) However, the transformers used in HVDC transmission are different from traditional AC transformers.
c) HVDC transformers are specifically designed for high-voltage DC transmission and are often referred to as converter transformers.

In summary, the correct answer is option 'D' - pulse converters. HVDC transmission relies on pulse converters to convert AC power into DC power for transmission and vice versa. AC filters, AC transformers, and DC filters are not needed in HVDC transmission due to the inherent properties of the pulse converters and the design of the transmission system.