hvdc transmission & its applications

Name: Pooja DubeyCourse: EEERoll No:120104026

HVDC Transmission

Transmitting power at high voltage and in DC form instead of AC is a new technology  proven to be economic and simple in operation which is HVDC transmission.

Since our primary source is

A.C,The three

basic steps are:-

1. Convert AC into DC (rectifier)

2. Transmit DC3. Convert DC into AC

(inverter)

Wind Power

AC Transmision Line

Converter Station

Inverter Station

AC Transmission Line

DistributionLine

HVDC Transmission Line

1)Converters2)Smoothing reactors3)Harmonic filters4)Reactive power source5)Electrodes6)Dc lines7)Ac circuit breakers

Homopolar link

Monopolar link

Bipolar link

HVDC Transmission can be broadly classified into:-

It uses one conductor.

The return path is provided by ground or water.

Use of this system is due to cost considerations.

A metallic return may be used where earth resistivity is too high

Each terminal has two converters of equal rated voltage, connected in series on DC side.

The junctions between converters is grounded.

If one pole is isolated due to fault, the other pole can operate with ground and carry half the rated load ( or more using overload capabilities of its converter line.)

It has two conductors each having same polarity, usually negative.

Since the corona effect in DC transmission lines is less for negative polarity, homopolar link is usually operated with negative polarity.

The return path for such a system is through ground.

Advantages of HVDC

Technical Advantages

EconomicAdvantages

Lesser Corona Loss and Radio interference.

The voltage regulation problem is much less serious for DC, since only the IR drop is involved. For the same reason steady state stability is no longer a major problem.

No skin and proximity and ferranti effect

Asynchronous operation possible between regions having different electrical parameters.

DC lines and cables are cheaper than AC lines or cables.

The towers of the DC lines are narrower, simpler and cheaper compared to the towers of the AC lines.

Line losses in a DC line are lower than the losses in an AC lines.

The disadvantages of HVDC are in conversion, switching, control, availability and maintenance.

There is nothing like DC transformer which can change the voltage level in a simple way. Voltage transformation has to be provided on the AC sides of the system.

The required converter stations are expensive and have limited overload capacity.

A 500V, 1500W, 810Km bipolar HVDC transmission line is set up between Rihand & Delhi.

In Vindhyachal back to back link is laid for exchange of power between Northern & Western regions.

The Talcher–Kolar is a 1450 km,200MW,

500V HVDC transmission connection between the eastern and southern regions in India. In 2007 the scheme was upgraded to 2500 MW.

Undersea cables, where high capacitance causes additional AC losses. (e.g. 250 km Baltic Cable between Sweden and Germany) .

HVDC offers powerful alternative to increase stability of a power system, with it power flow can be controlled rapidly and accurately.

Use of HVDC to interconnect two points in a power grid, in many cases is the best economic alternative and further more it has excellent environmental benefits.

Very large investment for example in China and India shows that HVDC very important in future especially in big, new industrial countries.