ELECTRICAL BASICS (Chapter 8)

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ELECTRICAL BASICS (Chapter 8)

• Electrical terms
• Electricity magnetism
• Electricity
• Circuits
• Magnetism
• Electrical units
• Electric potential or eletromotive force
• Electric current
• Resistance
• resistance of a conductor is affected by
  (additional information)
• type of material
• length directly proportional to the length of a
  conductor
• cross-section area or thickness
• temperature directly proportional to the
  temperature of a conductor
• Electrical power
• Energy (additional information)
• The term energy is used to express work
• Energy PowerTime
• Unit of energy is kilowatt-hour (kWh)

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ELECTRICAL BASICS

• Calculations and examples
• Ohm's Law (additional information)
• Current (I or A), electric potential (V or E),
  and resistance (R) are related to each other, and
  a variance in one will affect the others. This
  relationship is known as Ohm's Law.
• Current (I or A) is directly proportional to
  voltage (V or E)
• Current (I or A) is inversely proportional to
  resistance (R)
• Power formulas

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GENERATION AND DISTRIBUTION (Chapter 9)

• Power, work, and energy
• Demand and consumption
• Electric current DC or AC
• Generating efficiency
• Cogeneration

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GENERATION AND DISTRIBUTION (Chapter 9)

• Direct current (DC) (additional information)
• In DC, electrons always move in the same
  direction
• Polarity of the generator remains always the
  same.
• Alternating current (AC) (additional information)
• polarity of the generator or alternator reverses
  periodically
• current varies periodically in value and
  directions, first flowing in one direction in the
  circuit and then flowing in the opposite
  direction
• Generation of AC (additional information)
• generated using a combination of physical motion
  and magnetism
• simplest form of AC generator is constructed
  using a single loop of wire placed between the
  poles of a permanent magnet and then rotating it
  by some suitable mechanical means.
• magnetic lines of force are interrupted with the
  rotation of loop
• an electromagnetic force is induced in the loop
• EMF thus produced exists between the two ends of
  the loop
• slip rings and brushes attached to each end of
  the loop apply the generated EMF to an external
  circuit.

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GENERATION AND DISTRIBUTION

• How the current alternates (additional
  information)
• When the loop is parallel to the magnetic lines
  of force, no magnetic flux is interrupted and no
  EMF is induced to the loop. As it begins to
  rotate, it cuts the magnetic flux at an
  increasing rate reaching a maximum when it has
  rotated a quarter turn (i.e. 90).
• As the rotation continues, the EMF is still in
  the same direction but is decreasing in value. A
  half revolution (i.e. 180 ), the loop is again
  parallel to the magnetic lines and no magnetic
  flux is interrupted EMF at this point equals 0.
  As the rotation continues further, the sides of
  the loop reverse position and the induced EMF
  reverses polarity therefore, direction of the
  flow of current also reverses. The EMF increases
  to a maximum again at 3/4 turn (i.e. 270 ) and
  declines to 0 when the rotation is completed.
• Cycle of AC (additional information)
• Each complete rotation by the loop of wire (or
  armature coil) within the poles of magnet is
  called a cycle.
• Frequency of AC (additional information)
• The number of cycles per second is known as the
  frequency of the voltage or current
• The unit used to measure this frequency is Hertz
• In the United States, the frequency for
  alternating current is 60 Hertz.
• Use of AC results in the reduction of
  transmission loss.

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GENERATION AND DISTRIBUTION (Chapter 9)

• Example of transmission loss reduction
• Watt Current2 x Resistance
• If current (A or I) 20 and resistance (R) 4,
  then transmission loss (W) 202x4 1600
• The loss can be reduced by decreasing R. If R
  were decreased by half to 2, then W 202x2 800
• The loss can also be reduced by decreasing
  current. If it were decreased by half to 10,
  then W 102x4 400
• It is obvious that if current is decreased by
  half, transmission loss would be reduced by a
  factor of 4.
• In case AC, the stepping up and stepping down of
  current and voltage can be achieved by using a
  transformer.

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GENERATION AND DISTRIBUTION (Chapter 9)

• Single-phase and three-phase power
• Single-phase (additional information)
• a single armature coil creates a complete cycle
  of voltage and current
• requires one 'hot' wire and a neutral wire
• Three phase (additional information)
• use of three separate coil conductors equally
  spaced (_at_ 120 ) around generator armature
• in order to obtain the value of line voltage,
  phase voltage (either neutral-to-phase or
  phase-to-phase) has to be multiplied by ?3 or
  1.73 (e.g. if single-phase voltage is 208, then
  the corresponding three-phase voltage would be
  208 ?3 360)
• a three-phase system with an Y-connection
  requires 3 'hot' wires and a neutral wire.

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GENERATION AND DISTRIBUTION (Chapter 9)

• Transformers
• Power distribution
• Transformers (additional information)
• Used for stepping up or stepping down voltages
  and current
• Consists of iron core surrounded by two circuit
  loops (windings)
• Capacity rated in kVA
• Power factor (PF)
• Grounding

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ELECTRICAL RATING OF EQUIPMENT (Additional
information)

• Voltage rating
• Maximum voltage that can be safely applied
  continuously to an equipment. The rating is
  primarily determined by
• Type and quantity of conductor insulation used
• Physical spacing between electrically energized
  parts of the equipment
• Current rating
• Determined by the maximum operating temperature
  at which the components of an equipment can
  operate continuously and properly
• maximum operating temperature is determined by
  the type of insulation of the conductor
• the maximum safe operating temperature of
  conductors having cotton braid as insulation
  would be 65 C
• Current which will be producing this temperature
  would be the maximum permissible current for the
  conductor
• the maximum safe operating temperature of
  conductors having silicone or glass compound
  would be 150 C
• Consequently, the maximum permissible temperature
  for the same conductor would increase