DE1184413B - Two-stage switching of single-phase consumers, e.g. B. from induction coils fed with mains frequency - Google Patents

Description

Two-stage switching of: single-phase consumers, e.g. B. from with mains frequency powered induction coils The invention relates to a strong and weak stage existing two-stage switching of single-phase consumers, e.g. B. from with mains frequency powered induction coils, which are made up of capacitors and inductors Balancing arrangement are connected to a three-phase network.

Balancing systems for converting a single-phase load into a symmetrical one Three phase loads are well known. The single-phase consumers are often used here between two external conductors of the supply network and a capacitor bank as well one or more choke coils connected in a triangle to the third outer conductor. The single-phase consumer is, if it is inductive, with the help of capacitors compensated to cos phi = 1. For a symmetrical network load the Balancing reactances are designed so that their reactive powers VT times are smaller than the active power of the consumer.

For electrical heating systems, especially those that are fed with mains frequency Induction coils, it is often useful to start with a high power (high level) and then to keep the temperature constant or to warm up a weak output (weak level) to continue heating. About the performance and thus To reduce the voltage is - as shown in Fig: 1 - a regulating transformer 1 upstream, which is designed as an autotransformer and with the help of the three-pole Contactor 2 can be connected to the power supply network (RST). For loading of the induction furnace 3 at full power (high level) is the three-pole contactor 4 switched on, and to act on the induction furnace with lower power (Weak level) the three-pole contactor 4 is switched off and that with the taps 5 of the transformer 1 connected three-pole contactor 6 switched on. At 7 she is Capacitor control battery for compensation and with 8 the capacitor control battery designated for symmetrization. The one labeled 9 is also used for balancing Step choke coil.

The disadvantage of such arrangements is mainly that they through the use of the regulating transformer and the required tap changer and the associated three-pole contactors are too complex and expensive and in addition, a lot of space is required for these facilities. That of the invention The underlying task is to create a two-stage circuit that is much simpler in structure and also has an increased level of operational reliability having. According to the invention this is achieved in that in the three-phase Feed line switching means are provided ,, which `the sole disconnection of a Enable phase conduction so. that the Symmetrierungskapaztät at the weak level or the balancing inductance in series with the compensated consumer.

In a further development of the invention, when the weak level is switched on by reducing the balancing capacity or by increasing it. the. Symmetrizing inductance the active power in the consumer can be further weakened. It is also advantageous that the during. ' the weak level .parallel to the consumer and symmetry capacity existing branch balancing inductance can be switched off and / or enlarged is. Finally, it is advantageous that the currency of the eh wax, level-parallel to the branch consisting of consumer: and balancing inductance. lying Balancing capacity can be completely or partially switched off.

From the known arrangement according to FIG. 1 is an exemplary embodiment according to the invention in Figs. 2, 3 and 4 shown.

In Fig. 2 is the consumer V, z. B. an induction coil, with the associated parallel capacitor control battery Cx for compensation on the two busbars 10 and 11, which can be connected to the phase line R and T via a single-pole contactor 12 and 13, respectively. The middle busbar 14 is connected to the phase line S via the single-pole contactor 15. Between the busbars 12 and 14, the balancing capacitors C $ s and C, and optionally further capacitors are arranged such that they can be switched off. Between the busbars 10 and 14 , the stepped choke coils Ls 1 and L, z are arranged such that they can be switched off.

In the event that full power is required from the network (high level) the single pole contactors 12, 13 and 15 are switched on. On the other hand, the low power (weak level) is required, either the single-pole contactor 12 are turned off, so that a switching arrangement according to FIG. 3 is present, or only the single-pole contactor 13 can be switched off, so that a switching arrangement according to FIG. 4 is present.

As shown in FIG. 3 can be seen, is through the capacitor CK Compensated consumer V in series with the balancing capacitor control battery C, and parallel to this the balancing stepped choke coil, which can be switched off or its size can be changed L5.

In the case of the in FIG. The arrangement shown in Figure 4 is that through the capacitor CK compensated consumer V in series with the balancing step reactor L, and parallel to it the disconnectable balancing capacitor control battery C5.

The transition from the strong to the weak stage takes place by that the mains phase that is connected to the consumer V and the balancing capacitor (F i g. 3), is disconnected from the mains with the help of a single-pole contactor. Analogue to do this, the transition from the strong to the weak stage can be achieved by switching off the Phase, which is due to the consumer and the balancing inductance (F i g. 4). Such a switching process can be used instead of single-pole contactors can also be carried out with a single-pole and a two- or three-pole contactor, especially when this switching device is installed in an existing system and a subsequent installation of the device according to the invention is under consideration is pulled.

The balancing inductance can be switched off or reduced with advantage so that the capacitive current is compensated. the Weak level between two outer conductors of the network is usually so small that this Asymmetry is allowed.

If there is an operating state in which the power factor of the three mains currents and that of the consumer is 1.0, the active power of the consumer drops to 25% when switching to the weak level. Have. If the capacitance, which is otherwise used for balancing and is now connected in series to the consumer, is reduced, which is easily possible by switching off individual regulating capacitors, the active power of the consumer continues to decrease according to the following formula: where x = - C; Cs NV = active power of the consumer with balancing circuit (high level); N = active power of the consumer when connected in series (weak level); C, = balancing capacity (nominal); C = effective capacitance of C "; if this is adjustable.

Substituting values for x results in the following table: Ny IN 1 1 4 II 1-2. 7th --- 1- . 10 It is therefore possible to reduce the active power of the consumer for the weak level to a quarter or to an even smaller bet without additional funds.

The two-stage circuit according to the invention can be mixed in many ways Apply advantage. This is particularly the case with induction heating systems, Where the workpieces are usually very screaming and where the required Heizlezstg gradually decreases during the holding time to heat the work piece. By using the two-stage circuit according to the invention, temperature control is required During this time, the weak level is not periodically interrupted, but rather it can gradually decrease by simply switching off individual capacitor units Needs can be reduced and adjusted, resulting in a very precise temperature control results.

Claims (4)

Claims: 1. Consist of strong and weak stages & two-stage switching of single-phase consumers, e.g. B: from induction coils fed at mains frequency; the symmetry arrangement via a capacitor and choke coils are connected to a three-phase network, characterized in that class in the three-phase Feed line switching means are provided that the sole disconnection of a Enable phase line, so that the balancing capacity in the weak stage (G,.,) Or the balancing inductance (L,) in Ree with the compensated consumer (V) lie. 2. Two-stage circuit according to claim 1, characterized in that with activated weak level by reducing the balancing capacity (CS) or by increasing the balancing inductance (Ls) the active power in the consumer (V) can be further weakened. 3. Two-stage circuit according to claims 1 and 2, characterized in that the during the weak stage parallel to the consumer (V) and balancing capacity (Q existing branch lying syxnrnetrierungsinduktiv (L,) can be switched off and / or enlarged (FIG. 3). 4. Two-stage switching according to the Claims 1 and 2, characterized in that the parallel during the weak stage to the branch consisting of consumers (V) and balancing inductance (L,) lying balancing capacitance (Cs) can be completely or partially switched off (F i g. 4). Documents considered: German Auslegeschrift No. 1112 573; ASEA-Z, 6 (1961), pp. 21-22.