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Power Systems

Power Systems. Power Systems. Learning Activities View Slides; Read Notes, Listen to lecture Do on-line workbook Do Homework. Lesson Objectives When you finish this lesson you will understand: Control of the high electrical power systems, transformer control Timing functions

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Power Systems

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  1. Power Systems

  2. Power Systems • Learning Activities • View Slides; • Read Notes, • Listen to lecture • Do on-line workbook • Do Homework • Lesson Objectives • When you finish this lesson you will understand: • Control of the high electrical power systems, transformer control • Timing functions • Calculation of the heat • Troubleshooting Keywords Power Systems, Single Phase AC, Single Phase Rectified, Three Phase, Three Phase Rectified, Frequency Changer, Inverter, Transformer, Tap Switches, Saturation, Hysteresis, Reactance, Inductance, Resistance, Impedance, Power Factor, Duty Cycle, Timing Controls, Synchronous, Phase Shift Heat Control, SCR, half wave rectified, Full Wave Rectified

  3. Cooling System Mechanical System Force generation system Pneumatic/Hydraulic system Motor or foot-operated system Electrode application system Rocker arm or pinch type Press or direct action type Portable system Electrical System Single-phase system Single-phase rectified system Three-phase rectified system Frequency changer system Frequency inverter system Machines and Equipment

  4. Block Diagram of Single-Phase Spot Welder Contactor Main Power Line Spot Weld

  5. Configurations for Spot Welding Transformers (a) Stacked, Shell Type (b) Stacked, Core Type (c) Wound Type

  6. W. Stanley, Resistance Welding McGraw-Hill, 1950

  7. Parallel/Series Tap Switches Es Es (a) Parallel (b) Series S2 S1 Vp P2 P1 Es Es S2 S1 Vp P2 P1

  8. Transformer Tap Switch Es Vp

  9. Induced Magnetic Filed Saturation Induction Remnant Induction Coersive Force Applied Magnetic Field Structure & Properties of Materials, Wiley, 1967

  10. X = reactance in Ohm L = inductance in Henry f = frequency in Hertz Z = impedance in Ohm R = resistance in Ohm Rp Xs Rs Xp

  11. Power Factor AC Current DC Current Ohm’s Law • Z= Impedance • X= Reactance • Frequency of AC • Geometry of Secondary • Magnetic Material I= Current V= Voltage R= Resistance Power = VI =KW (kilowatts) Power = KVA

  12. Power Factor P P V I V I (a) Purely Resistive Load (b) Resistive and Reactive Load Pav = VavIav cos(f)

  13. Power Factor = Cos If: I=10,000 amps V=10 volts Kva=100 Kw=70.7 If: R=X pf = 70.7%

  14. Variables Affecting Power Factor • Machine Design • Single-Phase versus Three-Phase Current • Frequency • Reactance/Resistance of the Secondary Loop • Magnetic Material in the Throat

  15. Increased Throat Length X R Increased Angle Decreased Power Factor Resistance Welding Manual, RWMA, 1972

  16. Ferrous Material in Throat X R Reduced Power Factor Resistance Welding Manual, RWMA, 1972

  17. Power Factor Correction Capacitors Contactors (Switched Simultaneously) AC Power Supply High Impedance DC Charging Circuit (a) Shunt Capacitors (b) Series Capacitors Normally-Closed Contactor Welding Contactor Discharging Resistor AC Power Supply Tuned Capacitor

  18. Duty Cycleis the power level at which a transformer can operate for some fraction of time without overheating Percent Rated Load 100% 50% Percent Duty Cycle

  19. Timing Controls At what point in time do we close the contactor • Non-synchronous Controls • Synchronous Controls • Microprocessor Control = Synchronous

  20. Synchronous Timing Accuracy Electronic Control Res. Weld, McGraw-Hill, 1943

  21. Transient Currents with Non-Synchronous Timing Electronic Control Res. Weld, McGraw-Hill, 1943

  22. Electronic Control Res. Weld, McGraw-Hill, 1943

  23. Control of Secondary Current • Transformer Tap Setting (Turns Ratio) • Phase Shift Heat Control

  24. Gate Cathode Anode • Rules for SCR Conduction • can conduct when anode is + with respect to cathode • once initiated, can only be stopped by removal of anode voltage • initiated by a pulse on ignitor

  25. Welding Handbook

  26. “Idealized” Phase Shift Heat Control (a) Current Controlled by Tape Settings (b) Current Controlled by Phase Shift Setting In Actual Case, Current can not instantaneously change

  27. Actual Condition FiringAngle Hangover Angle Related to R/L ratio Androvich “Resistance Welding Constant Current Heat Control”, AWS Sheet Metal ConfV, 1992

  28. IRN = Normalized Available RMS Current Androvich “Resistance Welding Constant Current Heat Control”, AWS Sheet Metal ConfV, 1992

  29. Tsai, Experimental Study of Weld Nugget Expan, Paper B1, Sheet Metal Welding Conf V, AWS, 1992

  30. Link to: Phase Shift Heat Control Demo

  31. Portable Trans Guns Transformer Integral with Gun Thus smaller in Size Nedorezov, J “Using Portable Transguns for Resistance Spot Welding”, Practical Welding Today, Nov-Dec 1997

  32. Nedorezov, J “Using Portable Transguns for Resistance Spot Welding”, Practical Welding Today, Nov-Dec 1997

  33. Cooling System Mechanical System Force generation system Pneumatic/Hydraulic system Motor or foot-operated system Electrode application system Rocker arm or pinch type Press or direct action type Portable system Electrical System Single-phase system Single-phase rectified system Three-phase rectified system Frequency changer system Frequency inverter system Machines and Equipment

  34. Single-Phase Rectified System Center-Tapped Transformer Bridge-Type Rectifier Primary Current Secondary Current

  35. Single-Phase Rectified System • Advantages • Higher Power Factor • More Uniform Heat Flow Pattern • Less pf Loss by Material in Throat • Disadvantages • Expensive • Need Heavy Duty Diodes • One Electrode Wears Rapidly • Load on one side of Three Phase Line • Balanced 3 phase hook-up needed A B C

  36. Cooling System Mechanical System Force generation system Pneumatic/Hydraulic system Motor or foot-operated system Electrode application system Rocker arm or pinch type Press or direct action type Portable system Electrical System Single-phase system Single-phase rectified system Three-phase rectified system Frequency changer system Frequency inverter system Machines and Equipment

  37. Three-Phase Rectified System Half Wave Full Wave Primary Current Primary Current 100% Heat 10% Heat Secondary Current Secondary Current

  38. * * * * 120° Half Wave 120° Full Wave 120°

  39. Spinella, D., “Al RSW: Capital and Operating Costs”, AWS Xsheet Metal Conf, 1996

  40. Comparison of Two PF on Three Machines High Ripple Roth, “Alternating Current Vs DC in Resistance Welding” AWS Sheet Metal Conf IV, 1990 Medium Ripple Low Ripple

  41. Comparison of Two PF on Three Machines • Both Single Phase and 3 Phase DC is best in low power factor (high inductive) circuits providing as much smoothing as possible • Phase shifting will increase ripple (more in single phase). Operate on the highest phase shift and lowest tap setting possible

  42. Disadvantages • Expensive • Need Heavy Duty Diodes • One Electrode Wears • Advantages • High Power Factor • Uniform Heat Flow • No need to balance hook-up • No pf loss by material in throat

  43. Cooling System Mechanical System Force generation system Pneumatic/Hydraulic system Motor or foot-operated system Electrode application system Rocker arm or pinch type Press or direct action type Portable system Electrical System Single-phase system Single-phase rectified system Three-phase rectified system Frequency changer system Frequency inverter system Machines and Equipment

  44. Frequency Converter 1 Controller A 2 Controller B 3 Controller C

  45. Frequency Changer System (a) Frequency-Changer (b) Rectified

  46. Advantages • Power Factor > 98% • Balanced Loading • Balanced Electrode Wear • Disadvantages • Cost • Control Problems

  47. Cooling System Mechanical System Force generation system Pneumatic/Hydraulic system Motor or foot-operated system Electrode application system Rocker arm or pinch type Press or direct action type Portable system Electrical System Single-phase system Single-phase rectified system Three-phase rectified system Frequency changer system Frequency inverter system Machines and Equipment

  48. Frequency Inverter System Oscillator Rectifier AC HF DC AC 60 Hz 400, 600, or 1200 Hz

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