DE2923590C2 - Switching device for circuits with inductances - Google Patents

Description

The invention relates to a diode formed from a power thyristor and an anti-parallel connected diode Switching device for switching inductive circuits.

When switching off circuits with inductivities occur due to the reduction of the with the Inductances associated magnetic field overvoltages, which can damage the in the inductive Circuit contained components and / or other parts of the electrical power network. Task of Invention is to design the initially mentioned switching device so that when switching off a overvoltages occurring in the inductive network branch remain within permissible limits.

According to the invention, the device described in the introduction is designed so that the thyristor of the switching device (ptH) has a commutation circuit formed from a capacitor (CK), a choke (LK) and a thyristor (ptK) and the capacitor (CK) of this circuit is also off a capacitor (CU), a choke (LU) and a thyristor (ptU \) formed and an attenuator in the form of an ohmic resistor (RU) containing oscillating circuit is connected in parallel.

With a switching device according to the invention, as in the following with reference to the circuit in more detail is explained, a division of the shutdown process on a larger number of switching processes and thus one corresponding distribution of the magnetic energy of the inductance to be switched off is achieved, while at the same time the energy that is allocated to each switching process in the mentioned resistance of the circuit in heat is implemented. The overvoltages that occur during the shutdown process can be in permissible Limits are kept, as will be shown later.

An exemplary embodiment of the invention is described below with reference to the drawing, in this, shows

Fig. 1 is a circuit diagram of a erfindungsgemälJen ^r> device,

2 to 6 in the form of diagrams the voltage or current curve on or in the various circuit elements and

7 and 8 show a series and parallel connection, respectively

κι several Umschwing- and discharge circles.

In Fig. 1, an inductive circuit to be switched on and off is denoted by L. It is fed by a network, of which only one isolating switch Tr for currentless switching is shown. For one and

Γ) Switching off under load is used by a main thyristor ptH, to which a diode is connected in antiparallel. The current flowing in the circuit is marked with /. A commutation circuit is connected in parallel to the main thyristor ptH. It contains a commutation condenser

2 (i sator CK, a commutation inductance LK and a commutation thyristor ptK. The commutation current is denoted by iK. The capacitor CK is via a high-ohmic charging resistor via a separate and not shown

2 ~> circuit precharged to voltage UL . The resistance RCK is so high that the charging current is negligible during the swinging process described below.

In parallel to the capacitor CK there is an oscillation

JO circle. It contains a reversing capacitor CU with a charging resistor RCU, a reversing inductance LU and a reversing thyristor ptUi. The circuit mentioned is further via an anti-parallel connected diode and a reversing thyristor ptU 2

r> an ohmic resistor RU connected in parallel. The current in the oscillating circuit is denoted by iU.

The mode of operation of the switching device is as follows: Before switching off, the voltage UN is applied to the network branch L , the capacitor CK is on the

-κι voltage UCK = - UL charged. The capacitor CL / is charged to the voltage UCUmin.

When a switch-off pulse is applied, the thyristor ptK is triggered . The capacitor CK drives a current pulse through the choke LK, which the

<r> Load current i commutated from the main valve ptH into the commutation branch. The current / now flowing through CK and LK charges CK linearly to a positive voltage, as shown in FIG. 2 is shown for time a . If after this time the voltage UCK reaches a

in a certain value UCKmax, then the reversing thyristor ptU \ is ignited. The charge on CK oscillates during time b in FIG. 2 via LU to CU , so that at the end of the reversal process CK the voltage UCkmin and CU the voltage

« UCUmax has. From this point in time, CK is recharged by the current, while CU is discharged again to the initial voltage UCUmin by triggering the thyristor ptU2 in a damped full oscillation after waiting for a protection period TsptUi. The discharge takes place via CU, LU and R / U, whereby the energy transferred during the swing from CK to CU is converted into RUm heat.

As noted, FIG. 2 shows the charging and discharging of the capacitor CK. The charging time a increases

M decreasing current / to, as shown in FIGS. 3 and 4 'is bowed.

4 shows the course of the switching voltage Us, which oscillates between the values Usmin and Usmax . you

Mean value Us is higher than the mains voltage UN The current / initially decreases linearly

d /

iff

and finally disappears with an .osinus shaped Course.

F i g. 5 shows the course of the voltage UCU at the reversing capacitor during the time a + b in FIG. 2, ie during the charging and discharging of the capacitor CK, and FIG. 6 shows the course of the current in the reversing capacitor CU during the same time.

To the Schakungsprinzip "even with extreme Circuit conditions z. B. to be able to use low voltage and high Lasistrom, the Commutation capacitor any number of recharging and discharging circuits in parallel or in series will. Additional diodes ;; "" separate the Transfer circles during unloading from each other. F i g. 7 shows such a parallel connection and FIG. 8th a series connection of several discharge circuits.

In the electronic switch according to the invention, the energy resulting from the circuit inductance is used to build up the required sound voltage, the excess energy being converted into heat in the resistor RU. During the switch-off process, the mean switching voltage remains constant, a predetermined maximum value not being exceeded. In addition, the lower value of the switching voltage USmin is always above the voltage UN of the network.

The electronic switch designed according to the invention is wear-free and is suitable for both Switching off dike and alternating current. In the latter case, there is one in each strand of the AC system such a switch is provided. Such a switch is usually used for switching off alternating current be used when a very fast shutdown is to be achieved, d. H. within a Half period. One advantage of the switch according to the invention is that the circuit can be inductive as desired can and the switching time can be varied as required The components used also require apart from the main thyristor, no forced cooling, so that the device is inexpensive in the Manufacturing is.

For this purpose 3 UUiU Zeidiiuinuen

Claims (3)

Patent claims: 1. Switching device formed from a power thyristor with an anti-parallel diode for switching inductive circuits, characterized in that the thyristor of the switching device (ptH) has a commutation circuit formed from a capacitor (CK), a choke (LK) and a valve (ptK) and the capacitor (CK) of this circuit is connected in parallel with an oscillating circuit which is also formed from a capacitor (CU), a throttle (LU) and a valve (ptUl) and contains an attenuator in the form of an ohmic resistor (RU). 2. Switching device according to claim 1, characterized in that the attenuator (RU) is connected via reversing valves (ptU2) in parallel to the capacitor (CU) and throttle (LU) . 3. Switching device according to claim 1, characterized in that the commutation circuit (CK, LK) is assigned several oscillating circuits (CU, LU) in a parallel or series connection.