1 / 24

Objectives

Objectives. Learn about 3 Phase vs. 1 phase F&N vs. 1 phase F&F Electricity Pricing Electric systems. Single-Phase vs. Three-Phase. For three phase: P=√3 E I. Ref: Tao and Janis (2001). Grounding. What is electrical ground? Why do we ground electrical devices/systems?

kolar
Download Presentation

Objectives

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Objectives • Learn about • 3 Phase vs. 1 phase F&N vs. 1 phase F&F • Electricity Pricing • Electric systems

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

  3. 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

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

  5. 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

  6. 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.

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

  8. 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, 12.60 $/peak kW/month • Assume no power factor charges

  9. Solution

  10. 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

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

  12. Wiring method –Raceways • Electric tubes • Rigid conduits • Wire ways • Bus ducts • Underflow • Different variation www.hhrobertson.com/

  13. 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

  14. Current-Carrying Capacity Ref: Tao and Janis (2001)

  15. Tubing size Ref: Tao and Janis (2001)

  16. Other Issues • In general, no more than 40% of raceway can be filled with wiring • Why? • To prevent extensive heat up • To prevent physical installation of wires

  17. Conductor Rules • Explain each of the following: • No more than 4 90 ° bends are allowed between pull boxes • In the same conduit: • No mixing of high- and low-voltage conductors • No mixing control and power conductors • No mixing phone and power conductors • Do place all three phases in the same conduit

  18. Receptacles (duplexes) Number Shape Voltage rating Current Rating Number of poles and wires Switches Type (NEC rating) Contact method Speed of operation Voltage rating Number of poles Method of operation Enclosure Duty Other (dimming) Receptacles and switches

  19. Protective Devices • What are we protecting from? • Overcurrent • Overvoltage • Circuit breakers • Switch that responds to thermal or short circuit loads • Can be bimetal, magnetic, or electronic • Reusable, remote control, compact, can be used as disconnect switch • Fuses • Melting metal • Self destructive, larger

  20. Why use fuses instead of circuit breakers? • Fuses can be used multiple times • Fuses are more aesthetically pleasing • Fuses are safer • Fuses cause less damage to equipment

  21. Ref: Tao and Janis (2001)

  22. Motor starters • ON-OFF switches are NOT for motors • Motor circuit-rated switches • Reduce the current during the start until the motor rich full speed • Protect the motor form overload • Emergency power systems Batteries Power generators

  23. Summary • Describe role of electrical system components • Calculate billing for an electrical system given the rate structure • Size conduit and conductors given current requirements and conductor type

  24. Reading Assignment Tao and Janis: Whole chapter 11

More Related