
Harmonic filters
Harmonic filters
The effective method to eliminate he harmonic current that siliconcontrolled rectifier equipment of largecapacity induction furnace caused is to filter the harmonic at the input port of siliconcontrolled rectifier equipment of induction furnace, Figure: 112
About the computation of harmonic current which caused by siliconcontrolled rectifier equipment of induction furnace, when we know the shortcircuit capacity of power grid, parameters of the inductionfurnace transformer and rated power of induction furnace, we can follow â€˜Mutual interference between semiconductor power converter and power grid and prevention method guide.
Power factor of induction furnace is 0.93 generally, when the siliconcontrolled rectifier equipment works under full voltage, the added filter also has the powercompensated function.
The precise value of the harmonic current which caused by siliconcontrolled rectifier equipment of largecapacity induction furnace now is measure by the theoretical calculation and surveys.
Relations between harmonic of siliconcontrolled rectifier equipment of M.F. intermediate frequency induction furnace and shortcircuit capacity of power grid:
In order to ensure performance of various electric equipment in the power system, the interference degree of power grid caused by siliconcontrolled rectifier equipment must be controlled. Table 1 lists permissible value of harmonic current that siliconcontrolled rectifier equipments are allowed to inject into the power grid.
Voltage
UKV

Corresponding shortcircuit
capacity of power grid
SkMVA

harmonic frequency and permissible
value of harmonic current IK
(rootmeansquare
value) A

2

3

4

5

6

7

8

9

10

11

0.38

10

53

30

27

61

13

43

9.5

8.1

7.6

21

6 or 10

100

14

10

7.2

12

4.8

8.2

3.6

3.2

4.3

7.9

35 or 63

260

5.4

3.6

2.7

4.8

2.1

2.1

1.6

1.2

1.1

2.9

>= 110

750

4.9

3.9

3

4

2

2.8

1.2

1.1

1

2.7

Voltage

Corresponding shortcircuit
capacity of power grid
SkMVA

harmonic frequency and permissible
value of harmonic current IK
(rootmeansquare
value) A

12

13

14

15

16

17

18

19



0.38

10

6.0

18

5.4

5.1

7.1

5.7

4.2

3



6 or 10

100

2.4

6.7

2.1

2.9

2.7

2.5

1.6

1.5



35 or 63

260

1.1

2.5

1.5

0.7

0.7

1.3

0.6

0.6



>=110

750

1

3

1.4

1.3

1.2

1.2

1.1

1



Before Harmonic suppression measures were taken, in order to ensure waveform distortion factor of power grid within the permitted range, the power of siliconcontrolled rectifier equipment must be limited, Figure 11 is the relations of siliconcontrolled rectifier, shortcircuit capacity of power grid and the rectifying phases which power department recommends.




