hvdc final

By Jijo Francis S7, EEE

HVDC TRANSMISSION AND SHORT CIRCUIT CURRENT CONTRIBUTION OF HVDC LIGHT

HVDC TRANSMISSION AND SHORT CIRCUIT CURRENT CONTRIBUTION OF HVDC LIGHT

The first dc link was set up in 1954 in between Swedish main land and the island of Gotland.

The use of an HVDC link in an ac system requires converter stations at each end of the line.

INTRODUCTION

LINE DIAGRAM OF HVDC SYSTEM OPERATION

G.S C1

GENERATING STATION

SENDING END

STEP-UP TXR

CONVERTER STATION 1

C2

CONVERTER STATION 2

RECEIVING END

STEP-DOWN TXR

Comparison b/w HVDC & EHV-AC system

CHARACTERISTICS EHV-AC SYSTEM HVDC SYSTEM

1.) Line Cost2.) Skin Effect3.) Line losses4.) Power Transfer5.) Voltage Control

HigherPresentHighLimitedDifficult

LowerAbsentLowNo LimitEasier


6.) Compensation Required.7.) Corona & Radio Interference.8.) Reliability.

Series & shunt Compensation.More.

Lesser.

No Compensation Less.

More.


9.) Short-circuit currents.10.) Control System

11.) Stability of AC networks.

Large

Simple,cheaper& limited.Very Low.

Small

Difficult , costlier & fast.

Much Higher.

LIMITATIONS OF HVDC TRANSMISSION

• Costly Terminal Equipment.• More Maintenance of line conductors.• Difficult Voltage Transformation.• HVDC Circuit Breakers are not available.• Side effect due to Earth current.• Block Reactive Power.• Presence of Harmonic Distortion.

HVDC LIGHT

HVDC LIGHT ???

HVDC Light® is an environment friendly technology for modern electrical power transmission systems.

HVDC Light® cables are buried underground/underwater.

HVDC LIGHT TECHNOLOGY

• HVDC Light is a high voltage, direct current transmission Technology .

• It consists of two converter stations and a pair of underground cables interconnecting each converter station.

• The converter stations are designed to be unmanned and virtually maintenance-free.

• This technology provides the HVDC Light converter with a switching speed 27 times faster than a traditional HVDC, thyristor controlled converter.

TECHNICAL FEATURES

• Advantageous for long distance cable transmission.

• Power reversal without interruption.• Can start up dead A.C network.• No increase of short circuit current.• Equal or longer service life than XLPE AC

cables.

HVDC LIGHT INSTALLATIONS

• The HVDC Light transmission system mainly consists of two cables and two converter stations.

• Each converter station is composed of a voltage source converter (VSC) built up with IGBTs, phase reactors, ac filters and transformer.

• By using pulse width modulation (PWM), theamplitude and phase angle (even the frequency)of the converter AC output voltage can be adjustedsimultaneously.

APPLICATIONS OF HVDC LIGHT

• In feed of Small scale power ;

e.g. small hydraulic generators, wind mills

& solar power harvesters.

• Feed small loads.

• Asynchronous grid connection.

SHORT CIRCUIT CURRENT CONTRIBUTION OF HVDC LIGHT

• One of the most concerned issues from customers is the contribution of HVDC

Light to short circuit currents. • The main reason for being interested in this

issue is that the contribution of the HVDC

Light to short circuit currents may have some significant impact on the ratings for the circuit breakers in the existing AC systems.

• Both the theoretical analyses and practical simulations have been performed and the results show that withHigher short-circuit current the voltage stability andperformance is likely to be improved.

• If the HVDC Light contributes a higher short-circuit current, the voltage dip due to distant fault is possibly reduced and thereby the connected electricity consumersmay suffer less from disturbances.

PROOF

• Consider the single line diagram of a transmission system :-

• The possible maximum relative short circuit current increment (ΔImax) is determined by the short circuit ratio(SCR).

• It is found that the ΔImax is inversely in proportional to the SCR as shown in the figure.

• The short circuit ratio (SCR) is defined as the short circuit capacity of the AC system observed at CCP bus divided with the power rating of the converter.

It can be seen from thefigure that the contribution of HVDC Light results in asignificant impact only onthe current of LINE1, fault current in LINE3 &LINE4 is slightly reduced& the load current inLINE5 is slightly increasedcompared with noHVDC Light connected.

• It is important to observe from Figure that the higher thefault current, the higher the bus voltage.

• The higher faultcurrent may have some negativeimpact to the circuit breakers.However, the resulted higher busvoltage during the fault mayhave a positive impact to thevoltage and power stability ofthe AC network & the connected electricity consumers maysuffer less from the disturbance.

CONCLUSIONS:

• HVDC transmission system - used for higher range than the EHV-AC system. More Reliable – Best Method.

• HVDC LIGHT – The new tool for transmission. High Short Circuit Current Contribution – Voltage Stability – Less Disturbance in T.S – Customers benefited.

REFERENCES1.) DC Transmission based on voltage source converters, Gunnar Asplund,Kjell Eriksson and Kjell Svesson,1997.

2.) The ABCs of HVDC transmission technologies,IEEE Power and

Energy Magazine,2006.

3.) A course in Electrical Power , J.B. Gupta.

4.) On the Short Circuit Current Contribution of HVDC Light, (IEEE) Y. Jiang-Häfner, M. Hyttinen, and B. Pääjärvi.

5.) Wikipedia & other web resources.

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