Quiz 1

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KeGrant
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214088
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Quiz 1
Updated:
2013-09-20 14:39:41
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Term 1
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  1. Why is it important to establish an equipotential zone:
    To eliminate step and touch voltage potential hazards
  2. What are current Transformers used for? Range? Effect of opening circuit?
    • For metering and protection
    • 0-5 Amps
    • Opening secondary side will cause dangerous situation to allow secondary to see dangerously high voltage(don’t open)
  3. What are potential transformers used for? Range?
    • For metering and Protection
    • 0-120 volts
    • OK to open secondary
  4. Define voltage
    Voltage is the electric pressure that pushes electrons through a conductor.
  5. Define Ohm
    Resistance to current flow in a purely resistive circuit.
  6. Define a Coulomb.
    • A quantity measurement of electrons.
    • 1 Coulomb = 6.25 * 10^18 electrons
  7. How can the polarity of an electromagnet be determined if the direction of current flow is known?
    The left hand rule… thumb = north magnetic pole and fingers = direction of current flow.
  8. Define Flux Density.
    A measurement of magnetic strength
  9. Define Saturation.
    When a magnet eventually reaches a point where its strength increases only slightly with an increase in current.
  10. Define Residual Magnetism.
    The amount of magnetism left in a material once the magnetizing force has stopped.
  11. State Kirchoff’s voltage law.
    The algebraic sum of voltage drops and sources in a closed circuit must = 0.
  12. State Kirchoff’s current law.
    The algebraic sum of currents entering and leaving a point must = 0.
  13. Name 3 factors that determine the amount of induced voltage in a coil.
    • -Number of turns of wire
    • -Strength of the magnetic field (flux density)
    • -Speed of the cutting action
  14. Describe current/voltage relationship in a purely inductive circuit
    Current lags voltage by 90 degrees
  15. Describe current/voltage relationship in a purely capacitive circuit
    Current leads voltage by 90 degrees
  16. To what is inductive reactance proportional?
    The inductance of the coil, and frequency of the line.
  17. What is frequency?
    The number of complete cycles per second.
  18. What is the formula for calculating instantaneous voltage?
    E(instant) = E(max) x sin angle theta
  19. List 3 factors that determine capacitance of a capacitor.
    • -Surface area of the plates
    • -Distance between the plates
    • -Type of di electric used
  20. Name two factors that determine the capacitive reactance of a capacitor.
    Frequency and capacitance.
  21. What is a transformer? What is the operating efficiency
    • A machine which operates magnetically and changes the voltage, current and impedance without changing frequency.
    • Operating Efficiency is 90%-99%
  22. What is the formula for Inductive Reactance(Xl)
    Xl=2*π*f*L
  23. What is the formula for Capacitive Reactance(Xc)
    Xc=1/2*π*f*C
  24. What is the formula for power in a 3 phase circuit
    P=1.732*Eline*Iline*PF
  25. What are 3 ways to calculate Power Factor(PF)
    • -PF=P/VA             
    • -PF=cos(angle theta)
    • -PF=Iresistive/Itotal
  26. What is a circuit breaker used for
    To interrupt both load and fault current
  27. What is capacitive reactance
    The current limiting property of a capacitor in an AC circuit
  28. What is inductive reactance
    The current limiting property of an inductor in an AC circuit
  29. Anytime a circuit breaker, disconnect switch or cutout is operated, one of the following six consequences occurs
    • -pick up load
    • -drop load
    • -energize
    • -de-energize
    • -make parallel
    • -break parallel
  30. What is a ground fault
    A current path to ground that was not the intended path
  31. What range of electric current causes death? How?
    • 50-200 milliamperes (mA)
    • Through defibrillation of the heart
  32. Define Watt
    The measure of power in an electric circuit
  33. What are 3 ways to calculate Power(single phase circuit)
    • P=E*I
    • P=I²*R
    • P=E²/R
  34. Define Current
    The rate of flow of electrons
  35. Define Ohm's Law
    • The electric relationship between voltage, current, resistance
    • E = I * R
  36. What is a dielectric?
    A material with an electric insulating quality
  37. Define Power Factor
    Comparison of true(real) power to apparent power in an AC circuit
  38. What is the formula for calculating impedance in a Reactor
    Rx = kV / (1.732 * I rating) * Z%

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