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Engineering Stromrichter Induktion Elektrolyse Elektromobilität - Engineering Converters Induction Electrolysis ElectricMobility 

Converters for Channel Furnaces

Unlike induction crucible furnaces, channel furnaces have a closed core made of transformer sheets. This results in a significantly lower reactive current requirement for the inductor compared to a crucible furnace of similar power.

This lower reactive current requirement allows for control with a simple converter without a resonant circuit. In this simple converter design, the inductor is alternately connected to the so-called DC link voltage.
The current rise is limited by the inductance of the coil(s) and, due to the circuit design, is not sinusoidal but rather triangular.


The current rise is limited by the inductance of the coil(s) and, due to the circuit design, is not sinusoidal but rather triangular. The adjacent image shows a typical current waveform of this simple converter without a resonant circuit.
As soon as the DC link voltage is applied, the inductor current rises quite steeply, limited only by the inductor's inductance. At the end of the pulse duration, which controls the power, the current falls back towards zero, and the DC link voltage is then applied to the inductor in the opposite direction.

Although this type of converter has gained some popularity, we recommend a resonant circuit inverter with a sinusoidal furnace current. At one of our customers, identical channel furnaces on two production lines were operated in parallel for many years, but with different inverter designs. The inductor with the sinusoidal control consistently achieved a longer service life.

Consequently, the simple converter design was converted to a resonant circuit converter with a sinusoidal furnace current.

The adjacent image shows the Fourier analysis of the current waveform in the upper image.

The amplitudes of the contained frequencies are plotted, starting with the amplitude of the fundamental frequency (50 Hz).
It is clearly evident that there are significant proportions of multiples of the fundamental frequency with pronounced amplitudes.
These significant proportions of multiples (especially 150 Hz, 250 Hz, and 300 Hz) reduce the efficiency of the inductor and shorten its service life.

The adjacent image shows the inductor current after the converter was converted to a resonant circuit design.
Due to the design, the current waveform is exactly sinusoidal, and the inductor operates at its best efficiency with maximum service life.

However, the disadvantages described are offset by the more complex circuitry of a resonant circuit converter, which entails higher investment costs.
Considering the often very long operation time of more than two decades, the resonant circuit converter solution is more cost-effective.

The converter can be equipped with HSG technology.

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