How to correctly select the original thyristor for induction melting furnace system

The correct selection of power electronic devices such as thyristors and rectifiers is of great significance to ensure the reliability of the complete equipment and reduce equipment costs. The selection of components must consider factors such as its use environment, cooling method, circuit type, and load characteristics, and take into account the economics while ensuring that the parameters of the selected component have a margin.

Because the application fields of power electronic devices are very wide and the specific application forms are various, the following describes only the selection of thyristor components in rectifier circuits and single-phase inverter circuits.

1, Rectifier circuit device selection

Power frequency rectification is one of the most commonly used fields of thyristor components. Component selection mainly considers its rated voltage and rated current.

(1) Forward and reverse peak voltages of thyristor devices VDRM and VRRM:

Should be 2-3 times the component's actual maximum peak voltage UM, that is, VDRM / RRM = (2-3) UM. The corresponding UM values of various rectification lines are shown in Table 1.

(2) Rated on-state current IT (AV) of thyristor device:

ITThe IT (AV) value of the thyristor refers to the average value of the power frequency sine half wave, and its corresponding effective ITRMS = 1.57IT (AV). In order to prevent the component from being damaged by overheating during the work, the actual effective value flowing through the component should be multiplied by the safety factor 1.5-2 before it can be equal to 1.57IT (AV). Assuming the average load current of the rectifier circuit is Id and the effective value of the current flowing through each device is KId, the rated on-state current of the selected device should be:

IT (AV) = (1.5-2) KId / 1.57 = Kfd * Id