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PSC 4011 Electricity: What’s the connection?

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PSC 4011: AC-DC, Transmission & Distribution Direct Current (DC): _I never changes direction _Voltage is constant* _Intensity is constant* * V & I are constant if R is kept constant

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PSC 4011: AC-DC, Transmission & Distribution Direct Current (DC): _Used to operate portable battery-operated devices (mp3 players, toys, remote controls, etc.)

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PSC 4011: AC-DC, Transmission & Distribution Alternating Current (AC): _ I (and V) regularly change direction _ I (and V) are not constant _V rms = 0.707 V peak _ I rms = 0.707 I peak _ Change of direction is given by frequency value *rms: root mean square value (average value)

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PSC 4011: AC-DC, Transmission & Distribution Alternating Current (AC): _Can be converted to DC using a rectifer _Use a transformer to increase or decrease voltage *DC can be converted into AC using an inverter (less common)

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PSC 4011: AC-DC, Transmission & Distribution Practice An electric range operates on 240 V rms. _Between which two voltage values does it oscillate? _Calculate I rms and I peak when it draws 5000W of power. V rms = 0.707 V peak V peak = V rms / 0.707 = 240V / 0.707 V peak = 339 V (-339V & 339V) P = V rms * I rms I rms = P / V rms = 5000 W / 240 V I rms = 21 A I rms = 0.707 I peak I peak = I rms / 0.707 = 21A / 0.707 I peak = 30 A (-30A & 30A)

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PSC 4011: AC-DC, Transmission & Distribution Power systems generate AC (at 60 Hz) AC is transmitted through high tension wires AC is rectified (or not) into DC for residential use AC’s voltage is changed by transformers for residential use

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PSC 4011: AC-DC, Transmission & Distribution Step down transformers Voltage secondary winding is lower than at primary winding Number of turns of secondary winding is less than the number of turns of primary winding Current intensity of secondary winding is higher than at primary winding P primary (P p ) = P secondary (P s ) V p I p = V s I s If V s I p for P p = P s Joule Effect more pronounced for secondary winding (P = RI 2 )

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PSC 4011: AC-DC, Transmission & Distribution Step up transformers Voltage secondary winding is higher than at primary winding Number of turns of secondary winding is more than the number of turns of primary winding Current intensity of secondary winding is lower than at primary winding P primary (P p ) = P secondary (P s ) V p I p = V s I s If V s > V p then I s < I p for P p = P s Joule Effect more pronounced for primary winding (P = RI 2 )

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PSC 4011: AC-DC, Transmission & Distribution From transformer to residential use: All wires from transformer go to the distribution panel (house’s electrical box) Distribution panel contains the main and the bus bars Each bus bar is connected to one of the wires from the transformer From distribution panel to house: branch circuits (circuit loops of two- way current)

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PSC 4011: AC-DC, Transmission & Distribution Connection between transformer wires and bus bars (distribution panel):

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PSC 4011: AC-DC, Transmission & Distribution Branch circuits (120 V) Between a live bus bar (120 V: black or red wire) and the neutral bus bar (0 V: white wire) Require one circuit breaker (after live bus bar) Branch circuits (240 V) Between two live bus bars (120 V: black and red wires) and the neutral bus bar (0 V: white wire) Require two circuit breakers (after both live bus bars)

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PSC 4011: AC-DC, Transmission & Distribution Conductors Quebec uses American Wire Gage (AWG) notation AWG notation’s high number, small diameter conductor AWG notation’s low number, big diameter conductor AWG notation’s high number, high resistance conductor AWG notation’s low number, low resistance conductor

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PSC 4011: AC-DC, Transmission & Distribution Practice Consider three conductor wires measuring 12, 14 and 16 AWG. _Which one is the largest? _Which one has the highest resistance? _Which one can carry the most current without overheating? 12 16 12

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PSC 4011: AC-DC, Transmission & Distribution General purpose branch circuits (for 120 V- outlets or rarely used appliances) Branch circuits that power several parallel outlets. Thus, the same power is provided to several independent outlets and light fixtures (e.g. for two bedrooms)

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PSC 4011: AC-DC, Transmission & Distribution Single purpose branch circuits (for 240 V- outlets or appliances that demand much more energy) Branch circuits that power one outlet. Thus, the highest possible power is provided to the outlet and appliance connected to it (e.g. electric range or clothes dryer)

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PSC 4011: AC-DC, Transmission & Distribution Single purpose branch circuits _Very useful in kitchen or workshops _Must avoid multiple plug connections (e.g. “octopus” configuration) in order to: Not exceed I supplied by wires or limited by fuse or circuit breakers Not risk overheating of wires or maybe even a fire

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PSC 4011: AC-DC, Transmission & Distribution Outlets Make possible to plug appliances into the distribution circuit Most popular: double outlet (accommodates two plugs)

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PSC 4011: AC-DC, Transmission & Distribution

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Practice

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PSC 4011: AC-DC, Transmission & Distribution

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Three-prong plugs Mostly for metal housing appliances Third prong is a safety precaution Third prong maintains housing at 0V (brings current to ground) Keeps you from electroshock

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