1. Objectives Revie Capacitors and Inductors Learn about Transformers
3 Phase vs. 1 phase F&N vs. 1 phase F&F
Electricity Pricing

2. Capacitors
Consists of two conductive plates separated by a dielectric layer.

3. Dynamic System t (or ) is time

4. Example
Find i as a function of C , R and VB

5. Solving Differential Equation
The transient response is the time required for the capacitor to fully charge, and is equivalent to about 5 time constants or 5T. 5T

6. We need a resistor

7. Solving the Differential Equation
time required for the inductor to get full current is equivalent to about 5 time constants or 5T.

8. Summary

9. High voltage systems

10. Ref: Tao and Janis (2001)

11. Transformers Change - Voltage [E] and - Current [I]
Across a transformer
I1E1 = I2E2
Es/Ep = Ns/Np

12. Single-Phase vs. Three-Phase
For three phase:
P=√3 E I
Ref: Tao and Janis (2001)

13. Grounding What is electrical ground?
Why do we ground electrical devices/systems?
Protect equipment
Lightening strike
Protection of people
Sometimes need ungrounded power
If the hot side touches ground, it can put out of service our circuit
Isolate ungrounded systems

14. Neutral and 3-phase system
If system is well
balanced
the current
through the
neutral wire is 0

15. Why Three-Phase? Larger loads
Smaller wire sizes (because higher voltages)
P = EI = I2R= E2/R (E = IR)
More efficient use of neutral wire
3 needed for efficient operation of equipment

16. Power Factor
Difference between power supplied and power that does useful work “working power”
P=E I cos θ
θ is the phase difference between current and voltage
For circuits that contain reactance (Inductor and Capacitors)
For three phase
P=√3 E I cos θ
Commercial buildings pay for power factor.

17. Electricity Billing Electrical Use (energy) Peak Demand (power)
Power factor
Which is largest portion of residential bill?
What about for commercial buildings?

18. Example: September cost of Electricity for ECJ
Assume ECJ is 120,000 ft2 and that it needs, on average, 8 W/ft2 for 8 hours a day, 6 W/ W/ft2 for 4 hours a day, and 4 W/ft2 for 12 hours a day
Use Austin Energy Large Primary summer service rate
1.5¢/kWh, $/peak kW/month
Assume no power factor charges

19. Solution large primary service $/kW $/kWh Daily $ 12.60 $ 0.015 hours$ $
hours kW
kWh 8
960
7680
demand
$12,096.00 4
720
2880
energy
$ 7,344.00 12
480
5760
TOTAL
16320
Total
$19,440.00

20. Other Pricing Strategies
Time of use pricing
Becoming more common for residential and commercial
Electricity cost related to actual cost
Requires meter
Interruptible pricing
Utility can shut off electricity for periods of time

21. Conductors Material Form Composition Voltage class Insulation Covering
Temperature rating
AWG American Wire Gage

22. Wiring method –Raceways
Electric tubes
Rigid conduits
Wire ways
Bus ducts
Underflow
Different variation

23. Design issues with conductors
Material (copper/aluminum)
Size of conductor (pg. 365)
Conduit requirements
Location
Residential or Commercial
With or without raceways
Compression fittings or set screws
Threaded connections
NEC and local codes