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Abstract- In the present paper the various technologies available so far for wireless transmission of electricity and the need for a Wireless System of Energy Transmission is being discussed to find its possibility in actual practices, their advantages, disadvantages and economical consideration. This paper is mainly concentrated on: i) the most popular concept known as Tesla Theory and ii) Resonant charging of electrical and electronic appliances. Many concepts, research papers, patents are available on wireless transmission of electricity but the commercial technologies are yet to be materialized. The paper also discusses the possible ways to get useful and practical results out of all research carried out so far elsewhere.
I. INTRODUCTION
A switch to cleaner transmission of power, as computer stores large amount of data in its memory, those using it are named a paper less society. Now is the time to
make people a wireless society, and this is possible by means of wireless energy transfer methods. As time and technology advance, wireless transmission of power seems to be promising one.
A. Drawbacks in wired systems
Electrical power accounts for much of the energy consumed. Much of this power is wasted during transmission from power plant generators to the consumers. The resistance of the wire in the electrical grid distribution system causes a loss of 26% to 30% of the energy generated. There fore, the loss implies that our present system of electrical transmission is 70% to 74% efficient. We feel pretty whimsical while watching poles, towers and substations, on the roadside, which carry man-made conductors for transferring power through long distances. In our country which is hugely populated and consume high megawatts of power there arise frequent faults [4,5,6,7,8].
B. A fault arises mainly due to
Technical problems in a substation
Lightning discharges on the conductor
Tree falling on the lines
Short circuiting the phases by birds
C. Broadly classified as
Shunt fault (short circuit)
Series fault (open conductor)
A shunt type of fault involves a power conductor connected to ground, or short circuit between the conductors. These types of faults are characterized by increase in voltage, frequency, and fall in current in the faulted phases.
D. Shunt faults are classified as
Line to ground fault
Line to line fault
Double line to ground fault
Three phase fault
E. Series faults are classified as
single open conductor fault
two open conductors fault
These are the disadvantages while power is transmitted through conductors. In order to avoid these transferring power.
II. METHODS
“Wireless transmission of power is the process that takes place in any system where electromagnetic energy is transmitted from a power source to an electrical load without inter connection of wires. The wireless energy transfer methods are important in our present life.”
A. Near Field:
1. Electro magnetic induction
2. Resonant Induction
B. Far Field:
1. Tesla Theory
2. Electro magnetic radiation
3. Microwave Transmission
A.1. Electro magnetic induction
The transfer of energy takes place by electro magnetic coupling through a process known as induction.
A.1.1.Examples:
The electrical transformer is probably the simplest example for wireless energy transfer.
In the induction cooker electrical energy is wirelessly transferred into
the cookware where it is converted into heat for cooking.
A.1.2. Drawbacks:
The receiver must be relative close proximity to the transmitter in order to be coupled with it.
It is short lived.
A.2. Resonant induction
"Resonant inductive coupling" has key implications in solving the main problem associated with non-resonant inductive coupling and electromagnetic radiation; specifically, the dependence of efficiency on transmission distance. Electromagnetic induction works on the principle of a primary coil generating a predominantly magnetic field and a secondary coil being within that field so a current is induced in the secondary. This results in a relatively short range due to the amount of power required to produce an electromagnetic field. Over greater distances the non-resonant induction method is inefficient and wastes much of the transmitted energy. This is where the resonance comes in and helps efficiency dramatically by "tunneling" the magnetic field to a receiver coil that resonates at the same frequency. Unlike the multiple-layer secondary of a non-resonant transformer, such receiving coils are single layer solenoids with closely spaced capacitor plates on each end, which in combination allow the coil to be tuned to the transmitter frequency thereby eliminating the wide energy wasting "wave problem" and allowing the energy used to focus in on a specific frequency increasing the range.
B.1. Tesla theory
Nicola Tesla – a great physician, concluded that the earth is an electrical conductor, and that an electric current can made to propagate undiminished for distances of thousand miles. It was also found that earth’s natural electrical charge can be made to oscillate by impressing upon it very low frequency current waves of certain length – definitely related to its diameter ; and resistances of the and relative shortness compared to its diameter.
In the distant future this method could allow for elimination of many existing high tension power transmission lines and facilitate the inter connection of electric generation plants in a global scale. In this process, the air will serve as a conductor for the current produced and also be the transmission medium. This system may be of even less resistance than through ordinary copper wire.
B.2. Electro magnetic radiation
It is in the form of either radio waves or light, and can also be used to transfer power wirelessly. In case of radio waves, efficient power can be achieved by using shorter wavelength of electromagnetic radiation typically in the microwave range. A rectenna is used to convert microwave energy back into electricity.
In case of light, the power can be transmitted by converting electricity into a laser beam that is then fired at solar cell receiver. This is generally known as power beaming.
B.2.1.Drawbacks:
Conversion of light such as laser is usually very inefficient.
Atmospheric absorption causes loses.
Causes cancer for living organisms due to radiation.
B.3. Microwave transmission
Power transmission via radio waves can be made more directional, allowing longer distance power beaming, with shorter wavelengths of electromagnetic radiation, typically in the microwave range. A rectenna may be used to convert the microwave energy back into electricity. Rectenna conversion efficiencies exceeding 95% have been realized. Power beaming using microwaves has been proposed for the transmission of energy from orbiting solar power satellites to Earth and the beaming of power to spacecraft leaving orbit has been considered.
As the electro-magnetic induction and electro-magnetic radiation has disadvantages we are going for implementation of electrical conduction and resonant frequency methods. Of this, the resonant induction method is the most implement able due to the reasons given later.
In the distant future this method could allow for elimination of many existing high tension power transmission lines and facilitate the inter connection of electric generation plants in a global scale.
The microwave source consists of microwave oven magnetron with electronics to control the output power. The output microwave power ranges from 50w to 200w at 2.45GHz. a coaxial cable connects the output of the microwave source to a coax-to-wave adaptor. This adapter is connected to a tuning waveguide ferrite circulator is connected to a tuning waveguide section to match the wave guide impedance to the antenna input impedance.
The slotted wave guide antenna consists of 8 waveguide sections with 8 slots on each section. These 64 slots radiate the power uniformly through free space to the rectifying antenna (rectenna). The slotted waveguide antenna is ideal for power transmission because of its high aperture efficiency (>95%) and high power handling capability.
A rectifying antenna called rectenna receives the transmitted power and converts the microwave power to direct current (DC) power. This demonstration rectenna consists of 6 rows of dipole antennas, where 8 dipoles belong to each row. Each row is connected to a rectifying circuit which consists of low pass filters and a rectifier. The rectifier is a GaAs schottky barrier diode, that is impedance matched to the dipoles by allow pass filter. The 6 rectifying diodes are connected to the light bulbs for indicating that the power is received. The light bulbs also dissipate the received power.
This rectenna has a 25% collection and conversion efficiency, But rectennas have been tested with greater than 90%.
resonance frequency method:
Resonance phenomena:
A body vibrating at some frequency makes another body to vibrate at the same frequency. This is Resonance.
Example – while a playing a trumpet one can cause nearby trumpet to vibrate if both trumpets have same resonant frequency.
The induction of power can be different if electro-magnetic fields around the coils resonate at same frequency.
Using resonant frequency wireless power can be implemented for a house
WIRELESS POWER APPLICATIONS
The wireless system would reduce pollution and expenses resulting from the need to generate power, and to overcome and compensate for losses in the present grid.
This method would eliminate the need for an inefficient, expensive, and capital intensive grid of cables, towers and substations. There are some areas in the world where there is still in need for electrical power.
Examples in the global scale are….
Africa is in need of power to run pumps to tap into the vast resources of water under the Sahara desert.
Rural areas in countries like India and China
For the above mentioned areas, if power is not delivered they will for all time be left in darkness and never compete with other nations. Wireless transmission of power would provide worldwide distribution of off-peak demand capacity. Some nations like US have the capacity to generate more power than needed. The extra power available from the power plants is transmitted to other nations using wireless system of energy transmission.
VI. CONCLUSION
Imagine a future in which wireless power transfer is feasible: cell phones, household robots, mp3 players, laptop computers and other portable electronics capable of charging themselves without ever being plugged in, freeing us from that final, ubiquitous power wire. Some of these devices might not even need their bulky batteries to operate. The increasing demand for electrical energy in industrial nations is well documented. Therefore, there is an expectation of even faster rise in the demand for electric power in the near future. If this wireless transmission of power becomes a reality, then one day oil producers will become electricity suppliers to the world without adding green house gases – and a global energy grid could be in space.