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Induction Motor Interview Questions with Answers | Part-1

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Equipment Used in HVDC Transmission System | Block Diagram of HVDC System | Types of HVDC Sytem

Equipment Used in HVDC Transmission System | Block Diagram of HVDC System | Types of HVDC Sytem


HVDC Transmission System
Equipment Used in HVDC Transmission System | Block Diagram of HVDC System | Types of HVDC Sytem


The block diagram of HVDC transmission system is shown in below figure.

Block Diagram Of HVDC Transmission System

  • Supply

The 3 phase AC supply is first passed through AC filter to remove harmonics and then stepped up through step up transformer.This gives high AC voltage which is ready for transmission. 

  • Converter 1 ( Rectifier )

This high AC voltage is converted to high DC voltage by series connected converter.

The series connected converters are used to increase the voltage rating. Normally these are 12-pulse converters to reduce ripple voltage.

  • Smoothing Inductor

The DC voltage of the converter is then filtered by the smoothing inductors. Thus ripple free high DC voltage is obtained.


This high DC voltage is then transmitted over the DC transmission line.


Observe that the DC transmission line has +kV and -kV with respect to ground.


This is purposely done to balance the voltage of two transmission lines with respect to earth.

  • Converter 2 ( Inverter )

At the receiving station again the DC voltage is filtered and given to converter-2 which acts as an inverter.

The output of the converter-2 is stepped down and passed through AC filters.Thus the 3 phase  AC supply is finally obtained at the receiver side.

Note : that converter-1 as well as converter-2 are series connected 3 phase controlled rectifiers.

The transmitting side converter-1 acts as a rectifier and receiving side converter acts as an inverter.

The advantage of this system is that, the HVDC
link becomes bidirectional.

  • Harmonic filters

These filters are used to eliminate harmonic waves and produce reactive power at line commutated converter stations.

Odd numbered harmonics are produced at AC side and even numbered harmonics are produced at DC side.

Harmonic filters consists of series LC circuits.
Spurious signals are also eliminated by filters.

Such filters are located near alternating current terminal of static inverter transformer.

  • AC Switch Gear

It consists of circuit breaker for over-current protection of the converter transformers, isolating switches, grounding switches, measurement and protection.

Lightening arresters are also used to protect system from lightening.

Types of HVDC Systems

There are three types of HVDC System, which is described below:

  • 1. Monopolar Link

The monopolar link has only one conductor. The ground or sea is used as a return path.


The monopolar link is operated with negative polarity to keep corona effects.


Figure of monopolar link is shown in below diagram:

HVDC System
Monopolar Link | Types of HVDC System


  • 2. Bipolar Link

The bipolar link has two conductors: Positive and negative with respect to ground. The ground does not carry any current.

There are two converters on each side and they are connected in series.

Figure of Bipolar link is shown in below diagram:

HVDC System
Bipolar Link | Types of HVDC System


  • 3. Homopolar Link

Two conductors with the same polarity are
Current flow operated with common ground return. It has reduced insulation cost.

The Figure of Homopolar link is shown in below figure:

HVDC Transmission System

 Homopolar Link | Types of HVDC System


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