During the design of intermediate frequency power supply, the following principles can be followed to select the appropriate inverter thyristor according to the actual application:

1. Select according to the working frequency band of intermediate frequency power supply:

a) KK type thyristor with frequency of 100hz---500hz and selected off time of 20 µ s-45 µ s.

b) KK type thyristor with frequency of 500hz---1000hz and selected off time of 18 µ s-25 µ s.

c) KK type thyristor with frequency of 1000hz---2500hz and selected off time of 12 µ S-18 µ s.

d) Kkg type controllable with the frequency of 2500hz---4000hz and the selected off time of 10 µ s-14 µ s.

e) Ka type thyristor with a frequency of 4000hz---8000hz and a selected off time of 6 µ s---9 µ s.

2. Select according to the output power of intermediate frequency power supply:

According to the theoretical calculation of parallel bridge inverter circuit, the current flowing through each thyristor is 0.455 times of the total current. Considering enough margin, thyristors with the same size as the rated current are usually selected.

a) Thyristor with power of 50kw-100kw and selected current of 300a/1400v. (380V incoming phase voltage)

b) Thyristor with power of 100kw-250kw and selected current of 500a/1400v. (380V incoming phase voltage)

c) Thyristor with power of 350kw-400kw and selected current of 800a/1600v. (380V incoming phase voltage)

d) Thyristor with power of 500kw-750kw and selected current of 1500a/1600v. (380V incoming phase voltage)

e) Thyristor with power of 800kw-1000kw and selected current of 1500a/2500v. (660V incoming phase voltage)

f) 2000a/2500v thyristor with power of 1200kw-1600kw. (660V incoming phase voltage)

g) Thyristor with power of 1800kw-2500kw and selected current of 2500a/3000v. (1250v incoming phase voltage)