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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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Presentation Transcript
slide2

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

machines and equipment
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
block diagram of single phase spot welder
Block Diagram of Single-Phase Spot Welder

Contactor

Main Power Line

Spot Weld

configurations for spot welding transformers
Configurations for Spot Welding Transformers

(a) Stacked, Shell Type (b) Stacked, Core Type (c) Wound Type

parallel series tap switches
Parallel/Series Tap Switches

Es

Es

(a) Parallel

(b) Series

S2

S1

Vp

P2

P1

Es

Es

S2

S1

Vp

P2

P1

slide10

Induced Magnetic Filed

Saturation Induction

Remnant Induction

Coersive Force

Applied Magnetic

Field

Structure & Properties of Materials,

Wiley, 1967

slide11

X = reactance in Ohm

L = inductance in Henry

f = frequency in Hertz

Z = impedance in Ohm

R = resistance in Ohm

Rp

Xs

Rs

Xp

slide12

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

power factor
Power Factor

P

P

V

I

V

I

(a) Purely Resistive Load (b) Resistive and Reactive Load

Pav = VavIav cos(f)

slide14

Power Factor = Cos

If: I=10,000 amps

V=10 volts

Kva=100

Kw=70.7

If: R=X

pf = 70.7%

variables affecting power factor
Variables Affecting Power Factor
  • Machine Design
  • Single-Phase versus Three-Phase Current
  • Frequency
  • Reactance/Resistance of the Secondary Loop
  • Magnetic Material in the Throat
slide16

Increased Throat Length

X

R

Increased Angle

Decreased Power Factor

Resistance Welding Manual,

RWMA, 1972

slide17

Ferrous Material in Throat

X

R

Reduced Power Factor

Resistance Welding Manual,

RWMA, 1972

power factor correction capacitors
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

slide19
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

slide20

Timing Controls

At what point in time do we close the contactor

  • Non-synchronous Controls
  • Synchronous Controls
  • Microprocessor Control = Synchronous
slide21

Synchronous Timing Accuracy

Electronic Control Res. Weld,

McGraw-Hill, 1943

slide22

Transient Currents with Non-Synchronous Timing

Electronic Control Res. Weld,

McGraw-Hill, 1943

slide24

Control of Secondary Current

  • Transformer Tap Setting (Turns Ratio)
  • Phase Shift Heat Control
slide25

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
idealized phase shift heat control
“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

slide28

Actual

Condition

FiringAngle

Hangover Angle

Related to R/L ratio

Androvich “Resistance Welding Constant Current Heat Control”,

AWS Sheet Metal ConfV, 1992

slide29

IRN = Normalized Available

RMS Current

Androvich “Resistance Welding Constant Current Heat Control”,

AWS Sheet Metal ConfV, 1992

slide30

Tsai, Experimental Study of Weld Nugget Expan,

Paper B1, Sheet Metal Welding Conf V, AWS, 1992

slide32

Link to:

Phase Shift Heat Control Demo

slide33

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

slide34

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

machines and equipment1
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
single phase rectified system
Single-Phase Rectified System

Center-Tapped Transformer

Bridge-Type Rectifier

Primary Current Secondary Current

slide37

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

machines and equipment2
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
three phase rectified system
Three-Phase Rectified System

Half Wave

Full Wave

Primary Current

Primary Current

100% Heat

10% Heat

Secondary Current

Secondary Current

slide40

*

*

*

*

120°

Half Wave

120°

Full Wave

120°

slide42

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

slide43

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
slide44

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
machines and equipment3
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
slide46

Frequency Converter

1

Controller A

2

Controller B

3

Controller C

frequency changer system
Frequency Changer System

(a) Frequency-Changer

(b) Rectified

slide48

Advantages

  • Power Factor > 98%
  • Balanced Loading
  • Balanced Electrode Wear
  • Disadvantages
  • Cost
  • Control Problems
machines and equipment4
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
frequency inverter system
Frequency Inverter System

Oscillator

Rectifier

AC

HF

DC

AC

60 Hz

400, 600, or

1200 Hz

slide51

Advantages

Disadvantages

  • Cost
  • Newer Process – Still Under Development
  • High Power Factor > 98%
  • Less Core Material
  • Lighter & Smaller – suitable for robots
slide52

Homework

Duty Cycle

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