Control of heating elements

Fundamental to understanding the operation and benefits of an electronic transformer are the ways in which heating elements can be controlled using a thyristor power controller and the specific advantages and disadvantages of each.

Control of heating elements

Fundamental to understanding the operation and benefits of an electronic transformer are the ways in which heating elements can be controlled by a thyristor power controller and the specific advantages and disadvantages of each.

Pulse control (burst firing control)

Pulse-controlled thyristors are fired at zero crossover and only full sine waves are switched. This ensures that neither harmonics nor reactive power are generated. The disadvantage of this otherwise trouble-free mode of operation is the voltage fluctuations that can occur if the mains supply is too weak. This effect, known as voltage flicker, causes unpleasant variations in the light intensity of all lighting installations that are connected to the same mains supply.

This method of control is preferred for components that are stable and do not change their resistance to a large extent. In the case of the HVAC industry, these are metal heating elements.

If using this control method, a suitable device would be the JUMO TYA thyristor power controller.

Disadvantages

• flickering

Phase control

In phase-angle mode, the thyristors are fired during each half-wave. This rapidly changing cycle enables continuous temperature control in dynamic systems. In addition, this mode of operation enables current limitation, which is particularly needed for low-resistance heating elements such as ceramic.

One disadvantage of this mode of operation is the interference caused by harmonics, which are created by the steep rise in the edge of the truncated half-waves of the mains voltage. Another disadvantage is the generation of reactive power even with a resistive load. This is caused solely by phase angle control and is therefore referred to as phase-controlled reactive power.

These disadvantages can be overcome with the IPC 300 electronic transformer.

Disadvantages

• harmonic distortion

• reactive power

Effects of phase control defects - harmonic distortion and reactive power

Harmonic distortion

Harmonic distortion, which is an inherent consequence of phase control, causes:

• Current fluctuations in the range of 50% to 200% of rated current

• Overloading of the neutral conductor with currents up to 3 times the rated current

• Malfunction and equipment failure

• Reduced system availability

• Impact on metering systems -> Production of defective parts

• Higher energy purchase costs

• Oversizing of the installation -> Increased investment costs

Reactive power

Reactive power can be compared to beer. If active power is beer in liquid form, reactive power is just foam, which represents no real value and only delays the real work being done and "pollutes" the power. Furthermore, when there is too much of it, it generates additional charges to the energy supplier.

The solution – the electronic transformer

Electronic transformer IPC 300

The solution for furnaces with molybdenum disilicide (MoSi2) or silicon carbide (SiC) heating elements that are phase-controlled is the JUMO IPC 300 electronic transformer. It was developed to control heating loads that previously required an additional transformer for power regulation.

Thanks to the integrated amplitude control, the mains current and output voltage of the Jumo IPC 300 are proportional to the required power of the heating element, so that additional compensation devices do not need to be purchased. Through this device, reactive power is compensated and current peaks are reduced - thus lowering energy costs. In addition, the IPC 300 power converter reduces interference such as flicker or harmonics.

Benefits of the IPC 300 electronic transformers in a nutshell

• lower electricity bills

• Reduced maintenance costs

• reactive power compensation - external compensation devices are not necessary

• cost savings

• prevention of current peaks

• ground detection on heating elements

• Possibility to perform a test with an existing furnace - JUMO will supply a test control cabinet with the IPC 300

Electronic transformer IPC 300 - applications

The electronic transformer IPC 300 will be particularly suitable for applications with molybdenum diatomite (MoSi2) or silicon carbide (SiC) heating elements. These are found in furnaces such as:

Cylindrical furnace (hardening or annealing furnace)

• Temperatures up to 1850°C

• MoSi2 heating elements

Cylindrical furnace (hardening or annealing furnace)

• Temperatures up to 1850°C

• MoSi2 heating elements

Dental furnaces

MoSi2 heating elements offer advantages for sintering zirconia dental implants

• Temperatures up to 1830°C

• MoSi2 enables fast heating and cooling of the furnace