AUXILIARY TRANSFORMERS FOR CONTACTOR CONTROL
  

CONTACTORS

Auxiliary transformer rating
The auxilary transformer must be chosen considering the heaviest load possible during running or starting. 
The following contribute to the evalutation:. 
A = in-rush consumption of the contactors being energised;
B = steady state consumption;
C = consumption of other utilities (pilot light, solenoid valves, etc)
The exact calculation would require a separate evalutation of the active and reactive powers and the power factor. 
With an approximate calculation, the sum of these powers can be made with this formula below:
[VA] Transformer = A+B+C.
The following tables give therelative transformer power to control our contactors.
The transformers are characterised by a maximum 5% voltage drop.           

 Contactor

 Electromagnet data

Transformer

voltage drop

 in-rush

holding

Power

Maximum

 Type

 [VA]

cosfi

[VA]

cosfi

[VA]

[%]

 BG...06-BG...12

 30

0.86

4

0.27

30

5

 BF09-BF38

 65

0.75

8.5

0.3

63

5

 BF50-BF110

 210

0.5

18

0.3

100

5

 B115-B400

 300

1

10

1

160

5

 B500-B630 1000

 400

1

18

1

330

5

 B1250-B1600

 800

0.9

45

0.9

450

5

 Transformer protection fuses
   

 [VA]

Primary

Secondary

Fuse size aM

220/230V

380/400V

24V

48V

110V

220/230V
   

 30

0.25

0.16

2

2

1

1

 50

0.5

0.25

2

2

1

1

 63

1

0.5

4

2

2

1

 100

1

0.5

4

2

2

1

 160

2

1

8

4

2

2

 220

4

2

10

6

4

2

 230

4

2

16

8

4

2

 450

4

2

16

7

4

2

 630

6

4

25

16

6

4