power system engineering lecture 26

8/3/2019 Power System Engineering Lecture 26

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High Voltage DC (HVDC) Transmission

Chapter 7


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Introduction

First HVDC Commercial System (1954): 100 kV, 20 MW,

Mainland of Sweden to island of Gotland, Monopolar, Cable system.

Mercury arc technology

1972 onwards all the HVDC system use thyristor valves

The Biggest HVDC System: 300 kV, 6300 MW,ITAIPU Brazil.

Highest rating of device: 5 kV, 3 kA (now 10 kV, 4kA)

In India:

Sileru-Barsoor 200 kV 400 MW 196 km 1989

Rihand-Delhi 500 kV 1500 MW 814 km 1990

Talcher-Kolar 500 kV 2000 MW 1397 km 2003


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Advantages of HVDC

Less space compare to same voltage and power rating

Ground can be used as return conductor

Less corona loss and radio interference

No charging current and less power loss

Cheaper for long distance transmission No skin and Ferranti effect

Asynchronous operation is possible

No Switching transient

No transmission of short-circuit power in case of fault Power control possible

No compensation problem

No stability problem


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Advantages of HVDC

No technical limit to transfer the power except thermallimit

Fast fault clearing time

Cost of insulation is less


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Disadvantages

High cost of terminal equipment: Requires convertors stations at each end

which are expensive

However, for long distance (above 600)

and bulk power transmission, HVDC is

cheap

Introduction of harmonics

Blocking of reactive power flow

Point to point transmission is not possible Convertors can not be overloaded much

Reactive power absorbed by convertors

Distance

cost


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Types of HVDC links

1. Monopolar 2. Bipolar 3. Homopolar

Monopolar link

Only one energized conductor normally of negative polarity

Ground or sea water used as return path


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Types of HVDC links

Bipolar link

Two conductors with polarities (+ve and -ve) represented as Neutral points (junction between convertors) are grounded

If there is fault on one conductor other conductor can be used

with half of the rating


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Structure of HVDC System

Homopolar link

Two or more conductor with same polarity (generally -ve) Operates ground as return

If there is fault on one conductor other conductor can be used

with half of the rating


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Components in HVDC Transmission

Convertors

Convertor

transformer

Smoothing reactor

AC (Harmonic) filter Overhead lines

Reactive power

source

Earth electrode

DC Filters

Circuit Breakers


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Basics of Convertor

http://en.wikipedia.org/wiki/Silicon-controlled_rectifier
http://en.wikipedia.org/wiki/File:SCR.JPG


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Convertor Operation

5&6 6&1 1&2 2&3 3&4 4&5 5&6 6&1


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Current and Voltage in Convertors

-1.500

-1.000

-0.500

0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

0 90 180 270 360 450 540 630

5&6 6&1 1&2 2&3 3&4 4&5 5&6 6&1

1 1

4 4


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HVDC Links Connecting Different Regions

http://www.cdeep.iitb.ac.in/nptel/Electrical%20Engineering/Power%20System%20Operation%20and%20Control/Course_home_L36.html

power system engineering lecture 26

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