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May‘2003A&D CD-BD
Power Contactors
Introduction
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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May‘2003A&D CD-BD
Contacts with 30% remaining life
Parameters
Parameters
Electrical Endurance
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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
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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
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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
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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
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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
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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
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May‘2003A&D CD-BD
0
100
1000
3000
USp [V]
50 t [ms]
USp
Surge Suppression
Surges
Voltage surge without suppression
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May‘2003A&D CD-BD
0
20
200
USp [V]
0 t [ms]
USp
Surge Suppression
Surges
Voltage surge without suppression
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May‘2003A&D CD-BD
0
5
200
USp [V]
t [ms]
USp
0
Surge Suppression
Surges
Surge suppression through RC element
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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