Contactor Basics

Automation and Drives

s

Low VoltageControls & Distribution

Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

Power Contactors

Introduction


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

• It is an electro-mechanical switching device• It is a remotely operated device• It should be capable of making,carrying and

breaking currents under normal conditions and during operating overload conditions

• It is placed nearest to the load center

e.g. for Switching motors, lights, capacitors,heaters,furnaces etc

• High service reliability in terms of high mechanical and electrical life is demanded

• It is an electro-mechanical switching device• It is a remotely operated device• It should be capable of making,carrying and

breaking currents under normal conditions and during operating overload conditions

• It is placed nearest to the load center

e.g. for Switching motors, lights, capacitors,heaters,furnaces etc

• High service reliability in terms of high mechanical and electrical life is demanded

What is a Contactor ??

Basics


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

Construction

A contactor consists of 3 subsystems

• Electromagnet system• Contact and Arc quenching system• Housing

A contactor consists of 3 subsystems

• Electromagnet system• Contact and Arc quenching system• Housing

Construction


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

Internal construction 3TF 50 AC Contactor

Box terminals Arc chute with arc quenching plates

Current path withZ-shaped contact pieces

Magnet coil

Magnet system

Auxiliary contact block

Mechanical interlock prevents closingof contacts when arc chute is removed

Construction

Construction


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

Operating Principle

X = total stroke

Y = Opening

X-Y = wipe

1 2

A1

A2

Coil

Y

Moving magnet

Return spring

Fixed contact

Moving contactContact spring

Fixed magnet

X

Operation


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

DC-Operation

50 100 150

20

40

60

80

105

1000

1500

500

i[mA]i[mA]

t [ms] t [ms]

imax =1630 mA

imax = 45 mA

b) DC-Economy circuita) DC-Magnet system

Construction

Closing and holding currents


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

90

70

60

50

40

30

20

10

4 5,5 7,5 11 15 18,5 22 30 37 45 55 75 90 110 132 160 200 250 335 4500 1 2 3 4 6 8 10 12 14 Size00

P AC-3 400V/50Hz

HoldingpowerP [W]

DC-Magnet system

AC-Magnet system

DC-Economy circuit

Magnet Systems

Operation

Comparison of holding power


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

Critical Parameters

• Stroke

• Wipe

• Contact pressure

• Pick-up VA

• Hold-on VA

• Coil current

• Stroke

• Wipe

• Contact pressure

• Pick-up VA

• Hold-on VA

• Coil current

Parameters


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

Mechanical LifeSwitching ON/OFF at no load

3TH30 – 30 million

3TF30/31/32/33 – 15 million

3TF44 upto 3TF57 – 10 million

Electrical lifeContact life at the specified breaking current

The life depends on the type of Duty

Electrical life curves are available for each rating

Mechanical LifeSwitching ON/OFF at no load

3TH30 – 30 million

3TF30/31/32/33 – 15 million

3TF44 upto 3TF57 – 10 million

Electrical lifeContact life at the specified breaking current

The life depends on the type of Duty

Electrical life curves are available for each rating

Parameters

Parameters


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

In the E shaped Magnets

- Air gap reduces to Zero

- The contactor fails to drop out

- Shading rings breaks

Damage to mechanical parts

Damage to Springs

In the E shaped Magnets

- Air gap reduces to Zero

- The contactor fails to drop out

- Shading rings breaks

Damage to mechanical parts

Damage to Springs

The contact Silver material wears away The contact Silver material wears away

Electrical Life is over when

Parameters

ParametersParameters

Mechanical Life is over when


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

Make/breakoperationsat 690V

Make/breakoperationsat 400V

107

6

4

2

106

6

4

2

105

6

4

2

104

6

4

2

103

1 Ia (A) 2 4 6 10 20 40 60 100 200 4009 12 16 22 32 384 5,5 7,5 11 15 18,5

Ie (A)PN (kW)

Contactor Type

3TF303TF31

3TF323TF33

3TF44

3TF45

6

4

2

106

6

4

2

105

6

4

2

104

6

4

2

103

Parameters

Parameters

Contactors - High Electrical Endurance


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

Contacts with 30% remaining life

Parameters

Parameters

Electrical Endurance


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

Formula L = 5 x (U2)x u R x P x Coswhere...U = Rated coil voltageu = Voltage drop ( 5%) P = Coil VA / W at pick-upCos Power factor of coil at pick-upR = Ohmic resistance of cable

Formula L = 5 x (U2)x u R x P x Coswhere...U = Rated coil voltageu = Voltage drop ( 5%) P = Coil VA / W at pick-upCos Power factor of coil at pick-upR = Ohmic resistance of cable

Cross section of cable (sq mm) Resistance in km 1.0 21.70 1.5 14.47 2.5 8.71 4.0 5.45

Cross section of cable (sq mm) Resistance in km 1.0 21.70 1.5 14.47 2.5 8.71 4.0 5.45

Selection

Selection

Permissible Length of Control Cable


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

Rating = 0.33 x Sum of Pick up VA of all contactors to be switched on Simultaneously

e.g. : 3X 3TF33 and 2 x 3TF55 contactors are to be switched on Simultaneously

Total Pick up VA of contactors = 3064VA

Control transformer rating = 0.33 x 3064 – 1KVA

Rating = 0.33 x Sum of Pick up VA of all contactors to be switched on Simultaneously

e.g. : 3X 3TF33 and 2 x 3TF55 contactors are to be switched on Simultaneously

Total Pick up VA of contactors = 3064VA

Control transformer rating = 0.33 x 3064 – 1KVA

Selection

Selection

Choice of control transformer


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

Maintenance

•Overheating of contacts

•Chattering

•Humming

•Coil burning

•Welding of contacts

•Contact life

•Mechanical Life

•Overheating of contacts

•Chattering

•Humming

•Coil burning

•Welding of contacts

•Contact life

•Mechanical Life

Maintenance

Possible Problems in a contactor


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

Maintenance

• Arc Chamber interlock

• Mechanical interlocking of contactors

• Coil,main contacts replacement

• Auxiliary contact block replacement /

addition

• AC coil to DC coil conversion.

• Cleaning of magnets

• Examination of main contacts for erosion

• Arc Chamber interlock

• Mechanical interlocking of contactors

• Coil,main contacts replacement

• Auxiliary contact block replacement /

addition

• AC coil to DC coil conversion.

• Cleaning of magnets

• Examination of main contacts for erosion

Maintenance

Causes of Problems


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

Maintenance

• Do not operate contactor without Arc Chamber

• Do not use repaired contacts or coils or Arc chambers

• Do not file or rub the surface of contacts with abrasives

• Clean contacts with CRC 2-26

• Replace contact in pairs

• Proper connection of the cable/bus bar at the contactor terminal

• Please Ensure correct tightening torque

• Use only Genuine spare parts

• Do not operate contactor without Arc Chamber

• Do not use repaired contacts or coils or Arc chambers

• Do not file or rub the surface of contacts with abrasives

• Clean contacts with CRC 2-26

• Replace contact in pairs

• Proper connection of the cable/bus bar at the contactor terminal

• Please Ensure correct tightening torque

• Use only Genuine spare parts

Maintenance

Please ensure


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

Maintenance

Connection with Lugs / Busbars

Busbars Should be

• Wire brushed

• Wiped with clean cloth chambers

• Apply Dowells compound

• Tighten with requisite tightening torque

• Use bimetal washers when using 2 different metals

The mV drop across a joint should be less than 4mW

Connection with Lugs / Busbars

Busbars Should be

• Wire brushed

• Wiped with clean cloth chambers

• Apply Dowells compound

• Tighten with requisite tightening torque

• Use bimetal washers when using 2 different metals

The mV drop across a joint should be less than 4mW

Maintenance


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

0

100

1000

3000

USp [V]

50 t [ms]

USp

Surge Suppression

Surges

Voltage surge without suppression


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

0

20

200

USp [V]

0 t [ms]

USp

Surge Suppression

Surges

Voltage surge without suppression


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

0

5

200

USp [V]

t [ms]

USp

0

Surge Suppression

Surges

Surge suppression through RC element


s


Introduction

Basics

Constructions

Operation

Parameters

Maintenance

Surges

Selection

May‘2003A&D CD-BD

0

200

20

USp [V]

0 t [ms]

USp

= 0,6 V = USP

of diode

^

Surge Suppression

Surges

Surge suppression through diode

Contactor Basics

Documents

Transcript of Contactor Basics