Power Systems
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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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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

  • 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


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

Contactor

Main Power Line

Spot Weld


Configurations for Spot Welding Transformers

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


W. Stanley, Resistance Welding

McGraw-Hill, 1950


Parallel/Series Tap Switches

Es

Es

(a) Parallel

(b) Series

S2

S1

Vp

P2

P1

Es

Es

S2

S1

Vp

P2

P1


Transformer Tap Switch

Es

Vp


Induced Magnetic Filed

Saturation Induction

Remnant Induction

Coersive Force

Applied Magnetic

Field

Structure & Properties of Materials,

Wiley, 1967


X = reactance in Ohm

L = inductance in Henry

f = frequency in Hertz

Z = impedance in Ohm

R = resistance in Ohm

Rp

Xs

Rs

Xp


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

P

P

V

I

V

I

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

Pav = VavIav cos(f)


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

  • Machine Design

  • Single-Phase versus Three-Phase Current

  • Frequency

  • Reactance/Resistance of the Secondary Loop

  • Magnetic Material in the Throat


Increased Throat Length

X

R

Increased Angle

Decreased Power Factor

Resistance Welding Manual,

RWMA, 1972


Ferrous Material in Throat

X

R

Reduced Power Factor

Resistance Welding Manual,

RWMA, 1972


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


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


Timing Controls

At what point in time do we close the contactor

  • Non-synchronous Controls

  • Synchronous Controls

  • Microprocessor Control = Synchronous


Synchronous Timing Accuracy

Electronic Control Res. Weld,

McGraw-Hill, 1943


Transient Currents with Non-Synchronous Timing

Electronic Control Res. Weld,

McGraw-Hill, 1943


Electronic Control Res. Weld,

McGraw-Hill, 1943


  • Control of Secondary Current

  • Transformer Tap Setting (Turns Ratio)

  • Phase Shift Heat Control


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


Welding Handbook


“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


Actual

Condition

FiringAngle

Hangover Angle

Related to R/L ratio

Androvich “Resistance Welding Constant Current Heat Control”,

AWS Sheet Metal ConfV, 1992


IRN = Normalized Available

RMS Current

Androvich “Resistance Welding Constant Current Heat Control”,

AWS Sheet Metal ConfV, 1992


Tsai, Experimental Study of Weld Nugget Expan,

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


Link to:

Phase Shift Heat Control Demo


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


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


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

Center-Tapped Transformer

Bridge-Type Rectifier

Primary Current Secondary Current


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


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

Half Wave

Full Wave

Primary Current

Primary Current

100% Heat

10% Heat

Secondary Current

Secondary Current


*

*

*

*

120°

Half Wave

120°

Full Wave

120°


Spinella, D., “Al RSW: Capital and Operating Costs”,

AWS Xsheet Metal Conf, 1996


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


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


  • 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


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 Converter

1

Controller A

2

Controller B

3

Controller C


Frequency Changer System

(a) Frequency-Changer

(b) Rectified


  • Advantages

  • Power Factor > 98%

  • Balanced Loading

  • Balanced Electrode Wear

  • Disadvantages

  • Cost

  • Control Problems


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

Oscillator

Rectifier

AC

HF

DC

AC

60 Hz

400, 600, or

1200 Hz


Advantages

Disadvantages

  • Cost

  • Newer Process – Still Under Development

  • High Power Factor > 98%

  • Less Core Material

  • Lighter & Smaller – suitable for robots


Homework

Duty Cycle


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