Transcript Engineering 43 Chp 9

Engineering 43
Chp 9 [8-9]
House Power
Bruce Mayer, PE
Licensed Electrical & Mechanical Engineer
[email protected]
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
Outline – AC Steady State Power
 Instantaneous Power Concept
• For The Special Case Of Steady State
Sinusoidal Signals
 Average Power Concept
• Power Absorbed Or Supplied During in
Integer Number of Complete Cycles
 Maximum Average Power Transfer
• When The Circuit Is In Sinusoidal Steady
State
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
Outline – AC SS Power cont.
 Effective or RMS Values
• Heating Value for Sinusoidal Signals
 Power Factor
• A Measure Of The Angle Between Current
And Voltage Phasors
 Power Factor Correction
• Improve Power Transfer To A Load By
“Aligning” Phasors
 Single Phase Three-Wire Circuits
• Typical HouseHold Power Distribution
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
Single Phase, 3Wire Circuits
 Power Supplied to Most
Houses And Other
Residences Takes This
form
Neutral Wire
 For residential Electrical
Power Service
Engineering-43: Engineering Circuit Analysis
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Van  Vnb  V  115Vrms0
then
Vab  2V  230Vrms0
 115V → Lights and
convenience (3-prong)
Outlets
• Powered from
“Line” to Neutral
 230V → Large
Appliances, e.g; Electric
Ovens, Air Cond, Dryers
• Run “Line-to-Line”
Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
Residential Electrical Service
110/115/120 Vac Circuits
Run Line→Neutral
PG&E Electrical Service
Utility Connection
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220/230/240 Vac Circuits
Run Line→Line
Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
Actual Residential Wiring
Two,
100
Amp
CBs
 Circuit Breaker
Power Distribution
Panel
 WattHour Meter
 Main Service
Disconnect CB
• 200 Arms Service
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
– BathRooms
• 230Vrms
30A/2Pole CBs
– Clothes Dryer
– Oven
• 115Vrms
20Arms CBs
– Appliances
• 115Vrms
15Arms CBs
– Convenience
OutLets
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
Distribution Panel
• 115Vrms
15Arms GFICB
Single-, 3W Electrical Power
 In A “Balanced”
Condition, The Loads
across the two Sources
are EQUAL
 In the N-n Branch for
Equal Loads by KCL
 V V
  0
I nN  I aA  I bB   

 ZL ZL 
 Thus the Current in the
Neutral Wire is ZERO
• This is the Ideal Condition
• And the Neutral Wire is
(theoretically) NOT
NEEDED
 Next, Account for
• Line Impedances
• Line-to-Line Loads
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
1-, 3W Pwr cont
 A more Realistic
230Vac, 1 Ckt Model
+
 Analyze Ckt by
Superposition
Engineering-43: Engineering Circuit Analysis
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 If Any Line or Load Z’s are
Unequal, Then Ineutral  0
Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
Example – Unbalanced Load
 Given a 1, 3Wire Household Power Load
I aA
31A
1A
 By KCL at A, B, N
I aA I L I R
I bB  I S I R
I S  PS V  24 120  0.2 Arms
I nN I S I L
I R  PR V  7200 240  30 Arms
Engineering-43: Engineering Circuit Analysis
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 Assuming Resistive Loads
I L  PL V  120 120  1 Arms
Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
Example – Unbalanced Load cont
 Then The ENERGY use
Energy   p(t )dt  Paverage  Time
 For Each Load, Daily
Elights  0.12kW  8Hr  0.12kW  7 Hr  1.8kWh
Erange  7.2kW  (2  1  1) Hr  28.8kWh
Estereo  0.024kW  (5  3) Hr  0.192kWh
 The Total
Daily Energy Usage
Edaily   E k  30.792kWh
Engineering-43: Engineering Circuit Analysis
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 Then The Total Cost at
15¢/kWh
Cost  30.79kWh  $0.15 / kWh
 Cost  $4.62 / day
  $139 / month
Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
Electrical Safety
 Globally, Electrical Power
Systems Run at
Frequencies of either
• 60 Hz
– USA, Most Asia
•
50 Hz
– Most of Europe
 The Danger From
Electricity is not the
Voltage, but the
CURRENT Thru the
Human body
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
Grounded Neutral
 Typical 1, 110/115/120 Vrms Household Power Wiring
 Note The Neutral Wire is Tied To the Ground Wire
• The Neutral and GND wire are Run in Tandem to all Loads
 But, The GROUND conductor Does NOT Carry any
Working Current; so Why is it there?
• As a Safety PreCaution; Illustrate Function by Way of Example
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
Example – Grounded Case
When switched-on the tool-case is energized
CB
Drill
Case
without the ground connector the
user can be exposed to the full
supply voltage!
Conducting due to wet floor
If the case is grounded then “Joe” is at the Case, i.e. GND, Potential, and Cannot
Receive A Shock. Essentially the supply is shorted Around Joe, and the Circuit
Breaker Trips to open the circuit.
•The Tripped CB Alerts Joe that Something is Wrong Somewhere.
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
Numerical Example
 Another Shorted Drill; Ground Prong Removed
Wet
skin
150
400
150
Limbs
trunk
Ground prong REMOVED
R(dry skin)
R(wet skin)
R(limb)
R(trunk)
15kOhm
150Ohm
100Ohm
200Ohm
Suggested resistances
for human body
Engineering-43: Engineering Circuit Analysis
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1
120
I body 
 171mA
701
Can cause ventricular fibrillation
Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
Numerical Example
 A 7.2 kV Power-Line Falls on Car. The Driver can Get
Out or Stay in. Which is better?
7200V
Car body is good conductor
Tires are
insulators
Wet Road
Option 1.
Driver opens door and steps down.
Conduction Path = ARM + TRUNK +
LEG
R(dry skin) 15kOhm
R(wet skin) 150Ohm
7200
Ibody 
R(limb)
100Ohm
Rdry skin  2 Rlimb  Rtrunk
R(trunk)
200Ohm
I  460mA Very dangerous!
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Option 2:
Driver stays inside the
car
• No Path to GND 
Suggested resistances
for human body
Ibody  0

Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt
WhiteBoard Work
 Let’s Work Text
Problems
•
•
•
•
9.79
9.80
9.78
9.32
7200 Vrms
Rarm
100
Rtrunk
200
I
Engineering-43: Engineering Circuit Analysis
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Rarm
100
7200V
Bruce Mayer, PE
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt