# ELECTRICAL ENGINEERING SCIENCE

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ELECTRICAL ENGINEERING SCIENCE

CHAPTER 1 POWER SOURCES

Content Classification of power sources.
Electrochemical primary and secondary batteries and introduction to fuel cells.

Classification of Power sources
There are two types of power sources 1) Voltage source 2) Current source

Symbols of Power Sources

Voltage Source A device which can produce a continuous force to move the electrons (or,Â continuous voltage) through the wire connected into the two terminals of the device is called a Voltage Source. There are two types of the Voltage Source which are: Direct Voltage Source Alternating Voltage Source

Direct Voltage Source A device which produces a continuous direct voltage output is called a Direct Voltage Source. For example: Cells , Battery , DC Generator. A direct voltage is the kind of voltage whose polarity remains the same. Direct Voltage causes the current to move only in one direction continuously.

Alternating Voltage Source
A device which produces a alternating voltage output is called a Alternating Voltage Source. For example: AC Generator , DC to AC converter etc. A alternating voltage is the kind of voltage whose polarity is reversed periodically. Alternating Voltage causes the current to move in one direction for a period and then in another direction for another period.

Ideal Voltage Source An Ideal Voltage source is a kind of Voltage source whose internal resistance is zero. Such that the supplied voltage does not changes even if the external load resistance changes.

Current Source A current source is a device which provides the regular flow of electrons or current on a circuit. A current source is a type of voltage source which have enough EMF and surplus electrons so as to produce the flow of electrons.

Direct Current Source The current source made of Â a Direct Voltage Source is called Direct Current Source.

Alternating Current Source
The current source made of Â a Alternating Voltage Source is called Alternating Current Source.

Ideal Current Source A current source which provides a constant current without any relation with the voltage supplied to the load is called Ideal Current Source.

Electro Chemical Primary and Secondary Batteries

Electrochemical Cell An electrochemical cell is a device capable of either generating electrical energy from chemical reactions or facilitating chemical reactions through the introduction of electrical energy.

Difference between Cell & Battery
The cell is the basic single electrochemical unit which converts chemical energy to electrical energy. Battery refers to a stack (group) of Cells

CLASSIFICATION OF BATTERIES
There are four types of batteries. 1. Primary Batteries (or) Primary Cells 2. Secondary Batteries (or) Secondary Cells 3. Fuel Cells (or) Flow Batteries 4. Reserve cell

Primary Battery Primary cells are those cells in which the chemical reaction occurs only once and the cell becomes dead after sometime. These batteries are used as source of dc power. Eg : Dry cell (Leclanche Cell) and Mercury cell, lithium cell, Carbon-Zinc cell, Silver-oxide cells. Primary cells can be further classified as either wet or dry.

Secondary Battery These are the cells that can be recharged by passing an electric current through them and can be used again and again. Ex: 1) Lead storage battery 2) Nickel-Cadmium battery 3) Lithium-ion cell battery

Comparison between Primary & Secondary cell
Primary battery or cellÂ  Secondary battery or cell Lower initial cost. Higher initial cost. Higher life-cycle cost (Rs/kWh). Lower life-cycle cost (Rs/kWh) if charging in convenient and inexpensive. Disposable. Regular maintenance required. Periodic recharging required. Replacement readily available. Replacements while available, are not produced in the same sheer numbers as primary batteries.

Comparison between Primary & Secondary cell
Primary battery or cell Secondary battery or cell Typically lighter and smaller; thus traditionally more suited for portable applications. Traditionally less suited for portable applications, although recent advances in Lithium battery technology have lead to the development of smaller/lighter secondary batteries. Longer service per charge and good charge retention. Relative to primary battery systems, traditional secondary batteries exhibit inferior charge retention. Not ideally suited for heavy load/high discharge rate performance. Superior high discharge rate performance at heavy loads

Comparison between Primary & Secondary cell
Primary battery or cellÂ  Secondary battery or cell Not ideally suited for load-leveling, emergency backup, hybrid battery, and high cost military applications. Ideally suited for load-levelling , emergency backup, hybrid battery and high cost military applications Traditionally limited to specific applications. The overall inherent versatility of secondary battery systems allows its use and continuing research for a large spectrum of applications.

INTRODUCTION TO FUEL CELLS
A fuel cell is like a battery which generates electricity from an electrochemical reaction. Fuel cell uses external supply of chemical energy and can run indefinitely, as long as it is supplied with a source of hydrogen and a source of oxygen (usually air). It contains two electrodes i.e. anode and cathode separated by solid or liquid electrolyte. It needs two types of fuel : 1) hydrogen 2) oxygen(air)

Fuel Cell

Fuel Cell

Fuel Cell Overall reaction: 2 H2(gas)+ O2 (gas)â†’2 H2O + energy

PARTS OF FUEL CELL â€¢ Anode â€¢ Cathode â€¢ Electrolyte + catalyst â€¢ Hydrogen gas â€¢ Oxygen(air)

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.

Types of Fuel Cell Polymer Electrolyte Membrane Fuel Cells (PEMFC)
Direct Methanol Fuel Cells (DMFC) Alkaline Fuel Cells (AFC) Phosphoric Acid Fuel Cells (PAFC) Molten Carbonate Fuel Cells (MCFC) Solid Oxide Fuel Cells (SOFC) Regenerative Fuel Cells (RFC) Zinc Air Fuel Cells (ZAFCs) Microbial Fuel Cells (MFCs)