Schemes for turning on heating elements of electrothermal installations

The heating elements of electrothermal installations are designed for a certain value of power and voltage. To ensure a nominal mode, the heating elements are connected to the supply network with the corresponding voltage.

During the operation of the heating electrothermal installation, the power of the electric heaters can be adjusted, for example, by changing the supply voltage Un or the resistance of the heater Rn. The easiest way is to adjust the power in stages by switching the heating elements of electrothermal installations to different connection schemes. In this case, either the number of elements connected to the network and their total resistance, or the voltage in each of them, changes.

Heaters up to 1 kW are usually single-phase, and above 1 kW - three-phase.

Single-phase heaters with adjustable power have two or more heating elements (sections).They regulate the power of such installations by switching sections, including parallel or series. So the maximum power will be for parallel connected sections:

where R.1n — resistance of one heater, Ohm; n — the number of sections in the electrothermal installation.

In the case of serially connected sections of an electrothermal plant, its power will be minimal:

The ratio of these powers at the same value of supply voltage is:

For three-phase electrothermal installations, the number of sections is a multiple of three, therefore, taking into account the fact that such a connection is a symmetrical system:

Schemes for turning on heating sections: a and b - single-phase and three-phase electric heating devices

For three-phase electrothermal installations, where the elements in the sections are connected according to the «star» scheme:

For three-phase electrothermal installations, where the elements in the sections are connected according to the "triangle" scheme:

Power Ratio:

Ptr / Pzv = 3/1

By changing the switching circuit of the heating elements, the power can be adjusted stepwise, which is applicable when exact temperature maintenance is not required, and such adjustment is called stepwise.

By changing the supply voltage Usup, you can also adjust the power and more accurately maintain the temperature. Such regulation is called smooth.