30-07-2012, 11:40 AM
Fundamental Electrical Theory
Electrical Theory[1].ppt (Size: 509.5 KB / Downloads: 50)
Objectives
Basic electrical theory including ohm's law and its derivations
Generator theory
Generator construction and control mechanisms including prime movers and power ratings
Fundamentals of electric motor theory including construction, power rating, usage, and control mechanisms.
Compare the uses for AC and DC electric power and their transmission methods.
Definitions
Current (I): flow of electric charges per unit time or “flow rate”, measured in “amperes” or “amps” (A)
Electromotive Force (emf) (E): a potential difference or “electric pressure” which drives the flow of charges, measured in “volts” (V)
Resistance ®: an electrical circuit’s opposition to current flow, measured in “ohms” ()
Conductor: a material which offers little resistance to current flow, e.g. silver, copper, iron, etc…
Insulator: a material which offers high resistance to current flow, e.g. wood, paper, plastic, etc...
Direct Current (DC)
Current flow is unidirectional and of constant magnitude
Ohm’s Law: current in a circuit is directly proportional to the applied voltage and inversely proportional to the circuit resistance
Basic Circuit Properties
Electrons flow (-) to (+)
Kirchoff’s Law of Voltages
Sum of all voltages in a complete ckt is zero
Choose arbitrary current flow
If current encounters (+) terminal 1st, then (+) voltage
Voltage drops preceded by (-) sign if in the same direction as electron flow
Current into and out of a point is constant
Generator Parts
Prime mover: mechanical work which turns the rotor, may be a steam turbine, gas turbine, diesel engine...
Armature windings: the conductor in which the output voltage is induced
Field windings: the conductors used to produce the electromagnetic field (needs a DC power supply)
Stator: stationary housing of the generator
Rotor: rotates inside the stator, moved by a prime mover (steam turbine, gas turbine, diesel…)
Sliding contacts (slip-rings and brushes): used to conduct the field or armature current to and from the rotor
Commutator - maintains output current in one direction (DC generators)