Electrical Engineering

1. Electrical Engineering The Inside Story

2. Overview of AC Power Unit Carla L. Hoyer E3 Texas A&M University Summer 2003

3. Ocean: Unit Topic Green: Teacher-Led PP Pink: Student Activity and Assessment

4. Electrical Engineers Improve our lives by: • Generating Electrical Power • Electrical Power Transmission • Electrical Power Distribution • Designing Electrical and Electronic Devices • Computers • Research

5. Texas A&M Power Engineering Research • Dr. Karen Butler-Purry, P.E. • Mirrasoul J. Mousavi • Bill Spooner • Thomas Tamez • Andre Williams • Daniel Limbrick • Gaurav Garg • Robert Davidson • Sanjeev Srivastava • Torrey Thompson

6. Research Problem: Can power failures be predicted/prevented? • Failure of Electrical Cables • Failure of Electrical Transformers

7. Predicting Transformer Failure…Before its too Late During the operation of the transformer, insulation inside deteriorates. When the gradual aging gets more severe, arcing discharge or incipient fault may occur. This may cause a short circuit between the adjacent turns of primary or secondary winding leading to a catastrophic failure. This catastrophic failure may damage other equipment, buildings and even people near the transformer. Therefore, it is desirable to develop a method that detects any unusual current activities in the primary or secondary winding of the transformer before they become destructive and damage the transformer.

8. Inside a Transformer Coiled Wires DielectricInsulation

9. What’s an Incipient Fault? The situation of degraded insulation in the transformer before short circuit and failure occurs is referred to as an Incipient Fault.

10. What Causes Insulation Breakdown? Thermal stresses Internal heating due to overloads Ambient temperature Electrical stresses Excessive Voltage gradient Mechanical stresses Assembly configuration Short circuit and centrifugal forces Vibration Moisture

11. Top 5 Reasons to Research Predictors of Transformer Failure Why Detect Incipient Faults? • To improve the reliability of power systems • To provide early warning of electrical failure • To reduce unplanned outages • To enhance the public safety • TO SAVE $$$$ MILLIONS

12. Test Setup for Insulation Experiments Rheostat BNC Adapter Constant Resistors DC Supply Power Supply Meter Electrode system

13. What Do We need to Know About to Understand Transformer Failure Research? • Power =VI=I2R • What is Alternating Current? Comparison to DC • How do you make Alternating Current? Electromagnetism and Induction • Why do we use Alternating Current? Transformers

14. So, What is AC Power, Anyway? AC and DC Power – what’s the difference?

15. AC and DC Power – What’s the difference? • DC is the kind of Electrical Current found in Batteries. • DC stands for Direct Current • AC is the kind of Electrical Current found in the outlets of homes and businesses • AC stands for Alternating Current

16. AC and DC Power – What’s the Difference? Batteries are a source of DC Power • To be spontaneous, ∆G must be Negative • ∆G = -nFε • So, ε has to be + for ∆G to be negative, and electrons to move ε°= +1.0 - ε°= -0.5 +

17. Can electrons go back and forth between + and – poles in batteries? • From – to + poles, ε = +1.0V – (-0.5V) = +1.5V, so electrons will move spontaneously from anode to cathode • ∆G = -nFε = -nF(+1.5V), so ∆G <0. ε°=+1.0 - + ε = +1.5V ε°= -0.5

18. Can electrons go back and forth between + and – poles in batteries? NO! • From + to - poles, ε = -0.5V – (+1.0V) = -1.5V, so electrons will not move spontaneously from cathode to anode • ∆G = -nFε = -nF(-1.5V), so ∆G >0. NO GO! ε°=+1.0 - X ε = +1.5V + ε°= -0.5

19. AC and DC Power – what’s the difference? • So, in DIRECT CURRENT, the electrons move DIRECTLY from the anode to the cathode • The current flows from the cathode (+) to the anode (-) – opposite the electron flow • DIRECT CURRENT PRODUCES A ONE-WAY CURRENT FLOW. THERE CAN BE NO BACK-AND-FORTH!

20. DC Current is a One-Way Street Is Alternating Current also a one-way street? Let’s do some Science… Alternating Current Lab

22. DC Power Supply Results

23. DC Power Supply Results DC Voltage, Current and Light Intensityare INDEPENDENT of time

24. AC Power Supply Results

25. AC and DC Power – what’s the difference? • In DC Power, current can only move in one direction • In AC Power, the current alternates direction Next Class: How do they get AC current to ‘cha-cha’?

26. So, How Do You Make Current Alternate? The Electron Cha-Cha And Magnetic Magic

27. Electromagnetism Magnetic Field Electric Field Induction

28. Electricity & Magnetism • Two Fields, 90 Degrees apart • MOVING electrons (Current) in a wire produce a Magnetic Field around wire • Unit of Magnetic Field Strength is the Tessla • A stronger Magnetic field is produced if the wire is Coiled • Strongest Magnetic field produced if wire coiled around conductor

29. Seeing is Believing…Create a Magnetic Field around a Wire Photo of Lab Setup

30. Magnetic Field v. # of Turns

31. The AC Generator • http://www.micro.magnet.fsu.edu/electromag/java/generator/ac.html

32. Why is Household Current AC instead of DC? Electromagnetic Induction and The Transformer

33. What You Pay for is POWER • Recall: Power (watts) = VI Ohm’s Law: V = IR (In AC, V=IZ) Substituting: P= IRI Simplifying: P= I2R P = f (I,R)

34. Imagine Your Neighborhood… • Needs 120 V • Needs 1000 ampere of Current to Avoid Brownout • Power = VI = 120,000 watt • The Power Plant Generator is 20 miles Away • The electricity is sent on a line with a resistance of 0.1 Ohm/mile

35. How Much Voltage has to Leave the DC Power Plant? Due to the Resistance in the Transmission Line, The voltage (∆V=IR) will drop during the trip: Voltage Sent = Volts Lost + Volts Needed = IR + Volts Needed = (1000amp)(.1ohm/mi)(20mi)+120V = 2000V + 120 V= 2120V

36. How Much DC Power is Lost on the Trip to Your Neighborhood? Power Lost = Power Sent - Power Received Power Received = VI = (120V)(1000amp) = 120,000 watts Power Sent = VI=(2120V)(1000amp) = 2,120,000 watts Power Lost = 2,120,000 watt -120,000 watt = 2,000,000 watt ( 94% lost!)

37. We lose our DC Power over Distance!! ∆V = IR What Can We Do? • Put an electric power plant on every street? • We don’t have 90°F superconductors – all wires will have resistance- no way out. • The problem is Current – the higher the current, the greater the voltage drop and power loss • Ideas?...

38. Transformer Lab Set-up

39. What if, somehow… • We sent the 120,000 watts of power at 60000V and 2 amps, then somehow transformed it into 120V and 1000 amp at your subdivision? ∆V = IR = (2amp)(0.1ohm/mi)(20mi) = only 4V lost Power loss = (4V)(2amp)= 8 watts NEGLIGIBLE POWER LOSS WITH LOW AMPS

40. Induction and the Transformer 2amp 60,000V AC 1000amp 120V AC The Relative Number of Turns Dictates the Output Current and Voltage

41. Induction Doesn’t Happen with DC • To get induction, there has to be a CHANGING magnetic field • With DC, current and voltage are constant, so the magnetic field strength doesn’t change • With AC, the magnetic field is always changing AC Allows Efficient Transmission

42. Where does DC fit into the Real World? • Portability • Smooth Output • Safety?? – The Great AC v. DC Debate: Westinghouse, Edison and the Electric Chair • The Houston METRO Rail System is 7.5 miles long and runs on 750VDC overhead wires.

43. Light Rail Field Trip Find Out: • Why engineers chose DC over AC? • How they avoid huge power losses over the 7.5 mile run? • How does the electrical power get the train car moving? • Do the cars’ lights and air conditioning run on DC from the cable?

44. Incipient Fault Research Scenario • Students Receive Scenario Sheet • Review Sample Trace (Next Slide) • After 3 minutes, “Any Questions?” • Verbal Strategic Instructions Find specific pattern unique to failing research transformer first THE NOTES ARE IMPORTANT Then, Find that pattern in live data • Handout Data Packets • Record Return Times • Think-aloud Debriefing

45. Current Spike Irregular Waveform Helpful Notes

46. Debriefing/Think-Aloud Unique Pattern- Irregular Waveform followed by spike

47. Debriefing/Think Aloud