JUMO thyristor controllers: Readily available. Exceptional service

When is the use of a thyristor controller beneficial?

A thyristor controller is always required when the power to a load needs to be regulated, rather than simply turned on and off. While switches are commonly used in simple heating applications, thyristor controllers are designed to regulate the power supplied to temperature-controlled heating elements.

How is the load current calculated?

For example, if a heating element with a nominal power of 60 kW and a nominal voltage of 400 V AC is used, the power controller must switch a load current of approximately 87 A AC (60,000 W / (3 × 400 V / √3)). In this case, a thyristor controller with a maximum current of 100 A AC is used. If three-phase loads are to be controlled in phase-angle operation, three phases must be switched. The same formula applies to the calculation of the power controller current.

How are thyristor controllers scaled?

Thyristor controllers are available for various maximum currents such as 20 A, 32 A, 50 A, or 100 A. If, for example, a one-phase heating element has a nominal power of 9 kW and a nominal voltage of 230 V AC, the power controller must switch a load current of approximately 39 A AC (9000 W/230 V). In this case, a power controller with a maximum current of 50 A AC is used.

Heating elements with higher nominal power are generally designed for three-phase use, which is why power controllers for three-phase operation are used here. If burst-firing operation is sufficient for these elements, only 2 of the 3 phases need to be switched.

When is pulse group or phase-angle operation used?

Two operating modes are generally available for power control in thyristor controllers: pulse-group mode and phase-angle operation. Which one is used depends on the application and the characteristics of the load.

Burst-firing operation is suitable for most applications involving metallic heating elements. It causes minimal grid disturbances and is generally the preferred operating mode when no special requirements apply.

Phase-angle operation is used when specific influence on the current progress is required. This is particularly the case with heating elements that have a low cold resistance, where high inrush currents can occur. In addition, this operating mode enables very fast and fine power control within each half-cycle.

Phase-angle operation generates higher levels of electromagnetic interference and reactive power, so it is typically used only when the application requires it.