Transformers and Current Types
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Questions and Answers

What is the primary function of a step-up transformer?

  • To regulate frequency in electrical systems
  • To increase voltage while decreasing current (correct)
  • To decrease voltage while increasing current
  • To convert direct current to alternating current

Which unit is defined as the potential difference that moves one coulomb of charge between two points?

  • Coulomb
  • Ampere
  • Ohm
  • Volt (correct)

What does an ampere represent in an electrical circuit?

  • The resistance to the flow of current
  • The amount of charge flowing per second (correct)
  • The energy consumed per unit time
  • The force that pushes electrons through a conductor

Which unit is used to measure resistance in an electrical circuit?

<p>Ohm (D)</p> Signup and view all the answers

If a circuit has a potential difference of 12 volts and yields a current of 3 amperes, what is the resistance according to Ohm's Law?

<p>4 Ohms (A)</p> Signup and view all the answers

What is the relationship between voltage, current, and resistance in a direct current (d-c) circuit according to Ohm's Law?

<p>Current is directly proportional to voltage and inversely proportional to resistance. (B)</p> Signup and view all the answers

Which of the following units is used to express electrical energy?

<p>Watt-hours (B)</p> Signup and view all the answers

Which equation is not associated with Ohm's Law?

<p>E (J) = mcΔT (A)</p> Signup and view all the answers

What is the primary goal of effective electric load control?

<p>Reduce peak loads and lower demand charges. (C)</p> Signup and view all the answers

Which of the following loads is considered a 'sheddable' load?

<p>Non-critical batch process equipment (B)</p> Signup and view all the answers

Study Notes

Outdoor Transformers

  • H-frame transformer bank can have a capacity of up to 1,000 KVa
  • Cluster mounted on a single pole has a capacity of 225 Kva
  • Pad mounted transformers are a common type

Indoor Transformers

  • Dry type transformers are a common type
  • Askarel Insulated transformers use a synthetic non-flammable liquid for insulation
  • Oil Insulated transformers are installed in a fire rated transformer vault unless the capacity does not exceed 112.5 Kva

Transformer Rating

  • Step-up transformer increases voltage
  • Step-down transformer decreases voltage

Rotary Converters

  • Used for changing alternating current to direct current and vice versa.

Types of Current

  • Direct current flows at a constant rate in the same direction
  • Alternating current periodically varies in time rate and direction
    • A cycle is a complete set of changes in alternating current
    • The frequency of the current is the number of cycles per second, measured in Hertz
    • The frequency of lighting is typically 60 Hertz while motors may use 25 Hertz

Units of Electricity

  • Coulomb is the unit of electrical quantity, representing 6.25 x 10^18 electrons
  • Ampere is the rate of flow of one coulomb per second, or 6.25 x 10^18 electrons/second
    • Ampacity is the current carrying capacity of a wire or cable measured in Amperes
  • Volt is the unit of electric potential difference between two points
  • Ohm is the unit of resistance, allowing one ampere of current to flow when one volt is applied
    • Resistance is abbreviated as R in direct current circuits
    • Impedance, abbreviated as Z, is used in alternating current circuits
  • Watt is the unit of electric power, which is the rate at which electrical work is done
    • One kilowatt is equal to 1,000 watts
  • Watt-hour and kilowatt-hour are units of electrical energy, which is the capacity for doing work

Ohm's Law

  • Current (I) is directly proportional to voltage (V) and inversely proportional to resistance (R)
  • I (amp) = V (Volts) / R (Ohms)
  • Key equations:
    • W (Watts) = I^2R or VI
    • Whr = I^2R t
    • KWhr = I^2Rt/1000

Electric Load Control

  • Effective utilization of energy by reducing peak loads and lowering demand charge
  • Load shedding control, peak demand control, peak load regulation, and power use control are all examples of load control systems

Load Scheduling and Duty-Cycle Control

  • Electric loads are analyzed and scheduled to reduce demand by shifting large loads to off-peak hours and controlling the operation of loads

Demand Metering Alarm

  • A duty cycle controller is used to continuously meter demand and issue an alarm when a predetermined level is exceeded

Automatic Instantaneous Demand Control

  • Also known as "rate control"
  • An automated version of the demand metering alarm system, which automatically disconnects or reconnects loads as needed
  • Controllable loads are separated into sheddable and unsheddable loads
    • Sheddable loads include non-essential lighting, ventilation fans, space heating, and comfort cooling
    • Unsheddable loads include essential lighting, elevators, and refrigeration

Idealcurve Control

  • Compares the actual rate of energy usage to the ideal rate and controls kilowatt demand by controlling the total energy used within a metering interval

Electrical Systems

General

Definition of Electricity

  • Electricity is a form of energy generated by friction, induction, or chemical change.
  • It is the motion of free electrons through a conductor
  • Electric current travels at the speed of light, meaning conduction is considered instantaneous.
  • William Gilbert is known as the "Father of Electricity" for his studies on electricity
  • Electricity is a property of basic particles of matter, including electrons, protons, and neutrons

Sources of Electricity

Battery

  • A combination of two or more electric cells stores and supplies direct current through electro-chemical means
  • Primary batteries deliver electricity immediately upon being assembled
  • Secondary/Storage batteries require an external source of electricity to charge them before they can deliver a current

Generator

  • Converts mechanical energy into electrical energy
  • Alternating Current Generators (Alternators) produce most of the electrical energy used today
  • Direct Current Generators provide electricity for elevators, escalators, and certain signal systems

Other Dynamo Electric Machines

Motor

  • Converts electrical energy into mechanical energy

Transformers

  • Convert one voltage to another:
    • Step-up transformer converts lower voltage to higher voltage
    • Step-down transformer converts higher voltage to lower voltage
  • Oil-insulated Transformers and Dry-Type Transformers are the two major types of transformers

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Description

This quiz covers various types of transformers, their ratings, and the principles of direct and alternating current. Learn about outdoor and indoor transformers, as well as the function of rotary converters. Test your knowledge on voltage transformation and current characteristics.

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