Basic of Electrical Energy

Please use this following link.....
http://www.facstaff.bucknell.edu/mastascu/elessonshtml/EEIndex.html

FUEL CELLS- The Next Generation Of Electrical Power

FUEL CELLS- An Introduction

Whereas the 19^th Century was the century of the steam engine and the 20^th Century was the century of the internal combustion engine, it is likely that the 21^st Century will be the century of the fuel cell. Full cells are now on the verge of being introduced commercially,revolutionizing the way we presently produce power. Fuel cells can use hydrogen as a fuel, offering the prospect of supplying the world with clean, sustainable electrical power. Hydrocarbons such as natural gas and alcohols like methanol are sometimes used. Fuel cells are different from batteries in that they require a constant source of fuel and oxygen to run, but they can produce electricity continually for as long as these inputs are supplied.

Welsh Physicist William Grove developed the first crude fuel cells in 1839. The first commercial use of fuel cells was in NASA space programs to generate power for probes, satellites and space capsules.

WHAT IS FUEL CELL?

Fuel cells are electrochemical devices that convert the chemical energy of a reaction directly into electrical energy.  The basic physical structure or building block of a fuel cell consists of an electrolyte layer in contact with a porous anode and cathode on either side. They convert hydrogen, or hydrogen-containing fuels, directly into electrical energy plus heat through the electrochemical reaction of hydrogen and oxygen into water. The reaction of this process is as follows: 

Anode Reaction: CO₃^-2 + H₂ → H₂O + CO₂ + 2e^-

Cathode Reaction: CO₂ + ½O₂ + 2e^- → CO₃^-2

Overall Cell Reaction: H₂ + ½O₂ → H₂O

Because hydrogen and oxygen gases are electrochemically converted into water, fuel cells have many advantages over heat engines. These include: high efficiency, virtually silent operation and, if hydrogen is the fuel, there are no pollutant emissions.  If the hydrogen is produced from renewable energy sources, then the electrical power produced can be truly sustainable.

The basic diagram of a Hydrogen fuel cell is shown in fig.1.1

Fig.1 Basic Diagram of a Hydrogen fuel cell

FUEL CELL APPLICATIONS

As a result of the inherent size flexibility of fuel cells, the technology may be used in applications with a broad range of power needs.  This is a unique feature of fuel cells and their potential application ranges from systems of a few watts to megawatts.

Fuel cell applications may be classified as being either mobile or stationary applications.  The mobile applications primarily include transportation systems and portable electronic equipment while stationary applications primarily include combined heat and power systems for both residential and commercial needs.

1. Transportation

Cars

All the world leading car manufacturers have designed at least one prototype vehicle using fuel cells.  Some of the car manufacturers (Toyota, Ford) have chosen to feed the fuel cell with methanol, while others have preferred to use pure hydrogen (Opel has used liquid hydrogen, General Motors has stored hydrogen in hydride form).  In the short term there is a general trend for the car manufacturers to use reformed methanol as the fuel type for the fuel cell.  However, over in the long term hydrogen remains the fuel of choice for the majority of the car manufacturers.

NECAR Program

The NECAR program, initiated in 1994, was designed in 4 phases leading to 4 prototypes of electric vehicles.  The aim of this program was to show the feasibility of such a vehicle and then to improve the technology during each of the design phases.

      Buses

In 1993, Ballard Power Systems demonstrated a 10 m light-duty transit bus with a 120 kW fuel cell system, followed by a 200 kW, 12 meter heavy-duty transit bus in 1995.  These buses use no traction batteries and operate on compressed hydrogen as    the on-board fuel. 

In 1997, Ballard provided 205 kW PEMFC units for a small fleet of hydrogen fuelled, full-size transit buses for demonstrations in Chicago, Illinois, and Vancouver, British Columbia. The marketing phase is envisaged for 2002.

2. Portable Electronic Equipment 

In addition to large-scale power production, miniature fuel cells could replace batteries that power consumer electronic products such as cellular telephones, portable computers, and video cameras.  Small fuel cells could be used to power telecommunications satellites, replacing or augmenting solar panels.  Micro-machined fuel cells could provide power to computer chips.

3.  Combined Heat and Power Systems

The primary stationary application of fuel cell technology is for the combined generation of electricity and heat, for buildings, industrial facilities or stand-by generators. Because the efficiency of fuel cell power systems is nearly unaffected by size, the initial stationary plant development has focused on the smaller, several hundred kW to low MW capacity plants.  “The plants are fuelled primarily with natural gas, and operation of complete, self-contained, stationary plants has been demonstrated using PEMFC, AFC, PAFC, MCFC, SOFC technology”.

Faraday's Law of Electromagnetic Induction

Electromagnetic Induction:

The phenomenon by which an emf is induced in a conductor when it is cut by magnetic flux is known as electro-magnetic induction.

Faraday’s First Law

It states that, When-ever a conductor cuts a magnetic field or vice-versa, an e.m.f. (electro-magnetic force) is induced in it and it sets up in such a direction so as to oppose the cause of it.

Faraday’s second law

It states that the magnitude of induced e.m.f. is equal to the rate of change of flux linkage.

Mathematically

e = -N dØ / dt

where   e= Induced emf
            N= Number of turns of coil
           dØ / dt = Rate of change of flux

the minus sign represents that the induced emf or current sets up in a direction so as to oppose the cause of it ( according to Lenz’s Law).

Lenz’s Law

Lenz’s law states that:

   "The direction of induced current is always such as to oppose the cause which produces it".
   That is why a –ive sign is used in Faraday’s law.