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Section IV Electricity Review

Section IV Electricity Review. Electrical Definitions. Voltage is the electric potential energy per unit of charge. The units are Volts, V Current is the time rate of charge motion measured in units of Amperes or Amps for short, A

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Section IV Electricity Review

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  1. Section IVElectricity Review

  2. Electrical Definitions • Voltage is the electric potential energy per unit of charge. The units are Volts, V • Current is the time rate of charge motion measured in units of Amperes or Amps for short, A • Electrical Power is measured as the product of voltage and current to give Watts, W (i.e. Watts = Volts x Amps)

  3. Electrical Definitions • dc is an acronym for Direct Current implying currents and voltages that have constant values. • A battery is considered a dc voltage source • ac is an acronym for Alternating Current meaning the current and voltage vary their values over time. • The electric utilities produce and deliver ac voltage and current

  4. Three-Phase Power • The electric grid is designed to produce 3 separate ac voltages that are separated in their time oscillations by a fixed amount. These ac voltages have tightly controlled values of peak voltage, time variation (periodicity), and relative time separation or phasing between them.

  5. Electric Power • Calculating electric power from ac voltages and currents must be done with some care. The values used for power calculations are called rms (root-mean-square for those who really want to know). It suffices for us to know that the rms value we need is the peak value divided by the square root of 2. • You might be interested to know that the wall plug in your home delivers 120 V , the rms value.

  6. Electrical Definitions • An electronic system that converts ac voltages and currents to dc waveforms is called a Rectifier. • An electronic system that converts dc voltages and currents to ac waveforms is called an Inverter. • An electronic system that converts dc voltages and currents to another dc value is called a dc-to-dc Converter. Often all these types of systems are generically called Power Converters.

  7. Electric Power • There are two parts to power associated with ac systems: • Real or Average Power, P, is the power that does work. • Reactive Power, Q, is associated with the part of the electric system that inadvertently stores energy. Q does no work and is generally undesirable, but always present.

  8. Safety Comments • It is a misconception that high voltages are lethal. In reality the charge motion (current) through the body is what causes injury or death. However, for current to flow through the body, the resistance of the skin must be broken down. The voltage associated with the electrical system can accomplish this breakdown at only about 50 to 100 V. Also, high voltage systems are typically for high powered applications and hence can provide large currents; more than lethal amounts. Bottom Line: Don’t fool around with the electrical systems! ALL ELECTRICAL WORK SHOULD BE DONE BY QUALIFIED ELECTRICIANS OR ENGINEERS

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