ACTUAL Exam Questions and CORRECT
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Describe the electron theory. - The basis of our understanding of electricity is the
electron theory. this theory states that all matter that is everything that occupies space and has
weight is composed of tiny invisible units called atoms. Atoms in turn are subdivided into still
smaller parWhat is the minimum depth allowable for direct buried cables operating in the range
of 601-22000 volts?ticles, protons, neutrons and electrons. The protons and neutrons make up
the central core, or nucleus, of the atom, while the electrons spin around this central core in
orbits. the Protons and electrons are charged with small amounts of electricity. the proton
always has a positive charge while the electron has a small negative charge.
Define an electric current. - The flow of free electrons when a voltage is applied.
Define a conductor. - Materials having many free electrons make good conductors of
electricity. Copper, Aluminum
Define an insulator. - Materials having few free electrons make poor conductors and can
be used to insulate electricity.
What are three samples of good insulators? - Glass, porcelain, rubber polyethylene and
fiberglass.
What is the unit of electric current? - Amp or Ampere
,What instrument is used to measure electric current? - Ammeter
What is the unit of electric pressure? - Volt , Voltage is the electric force or pressure that
is determined by the potential difference between any two points in a circuit.
Draw a schematic diagram to illustrate the proper methods of connecting instruments to a
single-phase motor to measure electric current and the electric pressure supplied to the motor.
Voltmeter in parallel, Ammeter in series. -
What is the unit of electric power? - Watt
Draw a schematic illustrating the method of connecting a wattmeter in a single-phase circuit to
measure the power consumed. -
What is the unit of electric energy? - Watt-hours or kWh Electricity must act for a period
of time in order to do useful work. The power expressed in watts tells how much electricity is
working, and the hours express the time during which it acts. The product of these two factors
gives the amount of work done. Power × Time = energy Watts × Hours = Watt Hours
What instrument is used to measure electric energy? - Watt-hour Meter (typical house
meter)
What is the formula for Ohm's law? - E=I×R I = R=
Define an alternating current. -
, What is the unit of an alternating-current frequency? - Number of Cycles per second
Hertz or (Hz)
Define the power factor of an alternating-current circuit. - Power Factor - when an
alternating voltage and the current which it causes to flow rise and fall in value together and
reverse direction at the same instant, the two are said to be ' in phase' and the power factor is
unity. Watts = Volts × Amps × Power Factor Power Factor =
Describe the theory of operation of an electric transformer. -
Describe a typical electric system, itemizing the major parts of the system - €Generation:
Nuclear, Fossil Fuel, Hydro Electric €Generated between 13,200 and 24,000 volts €Stepped up
to transmission voltages between 138,000 and 765,000volts€Transmission Substations step
down to Subtransmission voltages between 34,500 and 161,000 volts €Distribution Substations
step down to voltages between 4160/2400 and 34,500/19,920 volts -Underground and
Overhead Branch Circuits • Transformers step down voltages to 120/240, three phase voltages
of 120/208 or 277/480.
What is a transmission line? - A set of conductors energized at voltages over 69,000 volts
and transmitting large blocks of electrical energy over relatively long distances.
How do the voltage levels of transmission, sub-transmission, and distribution lines compare? -
High voltages used for AC transmission lines are 115,000; 138,000; 161,000 volts - Extra-
High-voltage (EHV) Lines are energized at 345,000 - 765,000 volts.
When are direct-current transmission lines used? - Overhead direct-current transmission
circuits are used where it is desired to transmit large amounts of power over long distances or
to interconnect 2 AC systems that are not synchronized. E.g. a 400,000 Volt line could operate
with one conductor positive and one conductor negative.