[email protected] engr-43_lec-09-3_1-ph_3w_power.ppt 1 bruce mayer, pe engineering-43:...
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[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt1
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Bruce Mayer, PELicensed Electrical & Mechanical Engineer
Engineering 43
Chp 9 [8-9]Chp 9 [8-9]House House PowerPower
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt2
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Outline – AC Steady State PowerOutline – 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
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt3
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Outline – AC SS Power cont.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
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt4
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Single Phase, 3Wire CircuitsSingle Phase, 3Wire Circuits Power Supplied to Most
Houses And Other Residences Takes This form
For residential Electrical Power Service
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”
02302
0115
Vrms
then
Vrms
ab
nban
VV
VVV
Neutral Wire
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt5
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Residential Electrical ServiceResidential Electrical Service
PG&E Electrical Service
Utility Connection
110/115/120 Vac Circuits Run Line→Neutral
220/230/240 Vac Circuits Run Line→Line
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt6
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Actual Residential WiringActual Residential Wiring
WattHour Meter Main Service
Disconnect CB• 200 Arms Service
Circuit Breaker Power Distribution Panel
Two,100 AmpCBs
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt7
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Distrib
utio
n P
anel
Distrib
utio
n P
anel
• 115Vrms15Arms GFICB– BathRooms
• 230Vrms 30A/2Pole CBs– Clothes Dryer– Oven
• 115Vrms20Arms CBs– Appliances
• 115Vrms15Arms CBs– Convenience
OutLets
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt8
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Single-Single-, 3W Electrical Power, 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
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
0
LLbBaAnN Z
V
Z
VIII
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt9
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
1-1-, 3W Pwr cont, 3W Pwr cont A more Realistic
230Vac, 1 Ckt Model
Analyze Ckt by Superposition
+
If Any Line or Load Z’s are Unequal, Then Ineutral 0
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt10
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example – Unbalanced LoadExample – Unbalanced Load Given a 1, 3Wire Household Power Load
aAI A31
A1
By KCL at A, B, N
LSnN
RSbB
RLaA
III
III
III
Assuming Resistive Loads
rmsRR
rmsSS
rmsLL
AVPI
AVPI
AVPI
302407200
2.012024
1120120
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt11
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example – Unbalanced Load contExample – Unbalanced Load cont Then The ENERGY use
TimePdttpEnergy average)(
For Each Load, DailykWhHrkWHrkWElights 8.1712.0812.0
kWhHrkWErange 8.28)112(2.7
kWhHrkWEstereo 192.0)35(024.0
The Total Daily Energy Usage
kWhEEkdaily 792.30
month
dayCost
kWhkWhCost
/$
/.$
/.$.
139
624
1507930
Then The Total Cost at 15¢/kWh
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt12
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Electrical SafetyElectrical 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
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt13
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Grounded NeutralGrounded 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
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt14
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example – Grounded CaseExample – Grounded CaseWhen switched-on the tool-case is energized
without the ground connector theuser can be exposed to the fullsupply 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.
CB
DrillCase
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt15
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Numerical Example Numerical Example Another Shorted Drill; Ground Prong Removed
Ground prong REMOVED
R(dry skin) 15kOhmR(wet skin) 150OhmR(limb) 100OhmR(trunk) 200Ohm
Suggested resistancesfor human body
150150
Wet skin
400
Limbstrunk
1
mAIbody 171701
120
Can cause ventricular fibrillation
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt16
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Numerical ExampleNumerical Example A 7.2 kV Power-Line Falls on Car. The Driver can Get Out or Stay in. Which is
better?
Wet Road
Option 1.Driver opens door and steps down.Conduction Path = ARM + TRUNK +LEG
Option 2: Driver stays inside the car• No Path to GND
7200V
Car body is good conductor
Tires are insulators
R(dry skin) 15kOhmR(wet skin) 150OhmR(limb) 100OhmR(trunk) 200Ohm
Suggested resistancesfor human body
trunklimbskindry body RRRI
2
7200 0bodyI
dangerous! Very mAI 460
[email protected] • ENGR-43_Lec-09-3_1-Ph_3W_Power.ppt17
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
WhiteBoard WorkWhiteBoard Work Let’s Work Text
Problems• 9.79
• 9.80
• 9.78
• 9.32
R arm R armR t ru n k
1 0 0 1 0 02 0 0
I7 2 0 0 V
7 2 0 0 V rm s