psc 4011 electricity: what’s the connection?. psc 4011: ac-dc, transmission & distribution...

PSC 4011

Electricity:

What’s the connection?

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


Direct Current (DC):

_Used to operate portable battery-operated devices (mp3 players, toys, remote controls, etc.)


Alternating Current (AC):

_ I (and V) regularly change direction

_ I (and V) are not constant

_Vrms = 0.707 Vpeak

_ Irms = 0.707 Ipeak

_ Change of direction is given by frequency value

*rms: root mean square value (average value)


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)


Practice

An electric range operates on 240 Vrms.

_Between which two voltage values does it oscillate?

_Calculate Irms and Ipeak when it draws 5000W of power.

Vrms = 0.707 Vpeak

Vpeak = Vrms / 0.707 = 240V / 0.707Vpeak = 339 V (-339V & 339V)

P = Vrms * Irms Irms = P / Vrms = 5000 W / 240 VIrms = 21 A

Irms = 0.707 Ipeak

Ipeak = Irms / 0.707 = 21A / 0.707Ipeak = 30 A (-30A & 30A)


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


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

Pprimary (Pp) = Psecondary (Ps)

Vp Ip = Vs Is

If Vs < Vp then Is > Ip

for Pp= Ps

Joule Effect more pronounced for secondary winding (P = RI2)


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

Pprimary (Pp) = Psecondary (Ps)

Vp Ip = Vs Is

If Vs > Vp then Is < Ip

for Pp= Ps

Joule Effect more pronounced for primary winding (P = RI2)


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)


Connection between transformer wires and bus bars (distribution panel):


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)


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


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


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)


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)


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


Outlets

Make possible to plug appliances

into the distribution circuit

Most popular: double outlet (accommodates two plugs)


Practice


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

psc 4011 electricity: what’s the connection?. psc 4011: ac-dc, transmission & distribution...

Documents

v s v p

p v rms

v s i p

p secondary p s v p

v s i s

primary winding p primary

secondary winding p

peak v peak