Application of Superconductivity in Electric Power System

7/29/2019 Application of Superconductivity in Electric Power System

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Application of Superconductivity in Electric Power System

APPLICATION OF SUPERCONDUCTIVITY IN

ELECTRIC POWER SYSTEM

1.0. INTRODUCTION

With the discovery of High Temperature Superconducting

materials the possibilities of applications of the Superconducting technology in

power system have become very bright.

Superconductivity is characterized by an important feature of

zero resistivity, which means that superconductor is perfectly electrical conductor.

The other critical parameters are: critical Temperature, Critical Magnetic field and

critical current Density It has been recognized that for power system applications,

though the most important parameter is the critical current density other two are

also having their due importances.

Nevertheless the impacts of the superconductivity in the area of

power system need deep consideration. There are three major areas in the electric

power system where the emerging.

Superconducting technology will have wide applications :-

i) SUPERCONDUCTING GENERATOR.

ii) SUPERCONDUCTING TRANSMISSION LINE CABLES, and

iii) SUPERCONDUCTING ENERGY STORAGE SYSTEMS.

Over and above to these applications there are possibilities in exploring

superconductivity technology advantageously in system dampers, Fault Current

Limiters, phase shifters static VAR compensators, power converters, and in

sensors.

Govt. Poly. Washim. 1


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2.0. SUPERCONDUCTING GENERATOR

The difference between the basic design of a conventional and

Superconducting generator will be better appreciated in the light of the

fundamentals of generation.

In the generator, mechanical energy is converted into electrical

energy by rotating a conductor relative to magnetic field produced usually by an

electromagnet. The resulting flow of current in conductor generates its own

magnetic field . The final useful electrical output depends upon the interaction of

these two magnetic fields.

The electrical and magnetic loadings (current density and flux

density) determine the output from a generator. Neither of these can be increased

indefinitely due to certain limits.

The electrical loading (amp-conductors per meter ) is limited by

the rate at which the heat produced can be removed, so the temperature rise is

within the value that the insulation can withstand.

The magnetic loading is limited by magnetic saturation' ,which

in ordinary steel takes place at 1.4 Tesla. Therefore flux density cannot be

increased beyond this level, with using special steels.

These limits can be significantly relaxed by the using

superconductors. Field winding will provide at least four to five times higher

magnetic field with negligible DC voltage. This is possible because superconductors

have zero DC electrical resistance and extremely high (100,000 times more than



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copper conduction of the same size) current carrying capacity. Thus machines with

very high rated capacity are possible with superconductors.

Another very attractive feature of the Superconducting field

windings is that due to very high magneto motive force set up, it is not necessary to

use magnetic iron in the machine. Due to reduced rotor dimensions, the 'air gap' in

the machine can be expanded and greater machine stability could result.

2.1 ADVANTAGES

Any breakthroughs in generators can help in such rapid

expansion. Superconductors could be one such possibility.

The advantages of Superconducting generators are :

* Fifty percent reduction in size and weight for a given unit size.

* Approximately seventy percent lower transportation costs.

* Easier transportation.

* Cheaper foundations and buildings.

* One percent higher electrical efficiency.

* Higher stability due to lower machine reactance.

3.0 SUPERCONDUCTING MAGNETIC ENERGY

STORAGE SYSTEM (SMES)Apart from the apparent advantages of Superconducting

machines and Superconducting transmission lines, the application of

Superconducting coils for storage of electrical energy is receiving considerable

attentions. Such Superconducting magnetic Energy storage (SMES) coils would be



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charged during off peak hours by using power from the base load generating

systems and then would be discharged during hours of peak demands. The high

efficiency ( 95% ) of the SMES system makes possible large scale load leveling

which may in turn reduce many peaks generating units in redundancy.

3.1 OPERATING PRINCIPLE

A wire carrying electric current generates a magnetic field. The

higher the current, the stronger is the generated field. The current carrying wire,

wrapped as a coil is called the solenoid is proportional to the current and the

number of turns Superconducting solenoids made by wrapping a Superconducting

wire in the coil from are functionally superior to conventional solenoids because of:-

i) ZERO DC ELECTRICAL RESISTANCE

Due to zero resistance of superconductors very high currents of

the order of kilo amperes can be passed through an superconductor solenoid using

moderate voltage. The intensity of magnetic field generated can then be as high as

30 to 40 Tesla.

ii) NO RESISTIVE LOSSES

Unlike conventional solenoids, where resistive or PR losses

increase with current, Superconducting solenoids have no resistive losses thus if

two ends of a solenoids are short circuited, the current is in the 'persistent mode'

persistent super current generates a constant magnetic field which will last forever.

The virtue of 'supporting' constant magnetic field is used for storing electrical in

gigantic Superconducting solenoids.



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3.2 ADVANTAGES

If the high temperature superconductors of required properties

become available, the possible SMES can be operated at 750 higher temperature

than the one considered so far :

* IMPROVED GENERATION ECONOMICS,

* DAMPING OSCILLATIONS FOR SYSTEM REEIABILITY,

* IMPROVEMENT OF STABILITY LIMIT; &

* SPINNING RESERVE.

4.0 SUPERCONDUCTING TRANSMISSION LINE

CABLES

Transmission of electricity through a superconductor is

technically possible; however a Superconducting cable has to be cooled to

cryogenic temperature and therefor has to be underground. In comparison with the

existing underground cable a Superconducting cable has following advantages :

* ZERO RESISTANCE and, therefore, reduced losses.

* LOW VOLTAGE ( 86 KV / Phase ) and high current transmission.

* SMALL PHYSICAE SIZE of the cable due to high current carrying capacity

Reduced size implies very high power density. It would reduced excavation

costs by reducing the trench size.

*REDUCED CLEARANCE FOR TERMINAL FACILITIES. Generally, high tension

equipment is very bulky. If the amount of HT instrumentation is reduced it could

result in space saving.



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*NEAR TOTAL ELIMINATION OF RESISTIVE LOSS resulting in substantial saving

over the life time of cable.



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*QUICK RECOVERY AFTER FAULT Transmission line faults due to insulator flash

over are common on a transmission line. A given line can, however, sustain most of

these faults without causing any reliability problems in case of major fault however

conventional transmission lines may trip Recovery time under certain conditions is

also long. Superconducting cables on the other hand are expected within a few

milliseconds even from major fault where a conventional line takes hundreds of

milliseconds.

*HIGHER RELIABILITY Shorting of transformers and fires due to shorting of HT

equipment in Superconducting transmission would result in greater reliability.

*OVERLOAD CAPABILITY In the seemingly unlikely event of failure of 66 percent

of the available transmission lines, a Superconducting capacity to sustain the entire

fault current and overload current for as long as four hours.

4.1 ADVANTAGES

The advantages of Superconducting are :

*Zero resistance and therefore low-loss condition.

*Small conductor cross-section resulting in savings in materials.

*Two to three times higher overload capability over extended periods of time.

* Transmission of large blocks of power ( 5 GW and more ) with only a few

circuits.

* No Electro-magnetic interference with communications signals and radar

equipments.

* Reduced biological hazards.



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5.0 CONCLUSION

Most of the studies undertaken conclude that although the

application of Superconducting material in power system did indeed lead to

improved efficiencies, the capital cost and the cooling energy requirement

were too large and that it was not economically feasible to implement.



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BIBLIOGRAPHY

1. SUPERCONDUCTORS IN POWER SYSTEMS.

Jyoti Parikh & Madhuri Pai Allied Publishers.

2. HIGH TEMPERATURE SUPERCONDUCTORS

S.V. Subramanyam & E.S. RajaGopal Wiley Eastern Limited

3. Principles of ELECTRICAL MACHINE DESIGN

S.K. Sen.

4. POWER SYSTEMS : Proceeding of VI National Conference

M.V. Hariharan & Jyoti Parikh

5. POWER SYSTEMS : Proceeding of VII National Conference

S.K. Basu


Application of Superconductivity in Electric Power System

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