SU335728A1 - AC CONTACTOR WITH WIRELESS-FREE SWITCHING - Google Patents

Description

The invention relates to: low voltage electrical apparatus.

Known AC contactors with arc-free commutation, containing a non-contact controlled element connected in parallel with the main contacts, have a complex (structurally or functionally) control circuit that does not ensure reliable operation of the device in the case. In addition, in the known contactors of the drip through short circuit in the network at the moment of the electrodynamic rejection of the main contacts, a very large current flows through the controlled elements, causing their damage.

The proposed contactor does not have the indicated disadvantages thanks to the fact that it is equipped with a current source, the primary winding of which is introduced into the main circuit, and each secondary winding is connected through a rectifier to the control element of the shunt serial circuit: contacts - current transformer. In order to protect contactless elements during a short circuit, a series circuit is introduced into each control circuit of each element, consisting of a blocking voltage source and (a contactless key controlled by sensors for the magnitude and rate of rise of current in the circuit of the main contacts.

FIG. 1 is a schematic diagram of a writeable AC contactor with arc-free Commutation; in fig. 2 - variants of the contactor circuits using different contactless controlled elements; pas figs. 3 is a schematic diagram of a contact made for industrial use.

In parallel with the main contacts / contactor, two controllable contactless elements 2 and 3 are connected in the forward and reverse directions with respect to each other (in Fig. 1, for convenience of description, they are depicted as thyristors). The main element of the control circuit is the current transformer 4, the primary winding 5 of which is connected in series with the contacts 1, and two secondary windings 5 and 7 through the sensors 8 and 9 are connected to the control electrodes of the thyristors 2 and t3, respectively.

The protection circuit of the thyristors during a short circuit in the network consists of sources 10 and 11 of blocking voltage, contactless switches 12 and 13, controlled by sensors 14 of the current and the rate of rise of current 15. The current sensor can —– as in the main circuit pi, and in the secondary circuit of the transformer. Zener diodes 16 and 17 provide protection for the control transitions of the corresponding thyristors at high currents in the main circuit.

The process of turning the contactor on and off is as follows. When the contacts / are closed and the main current B appears, the current transformer 4 alternately supplies the triggering trigger for the thyristor electrodes 2 and 3. At the moment of the contact rebound, the current flowing through the contacts is diverted to the thyristor, polarity which corresponds to the direction of the current in the circuit. The voltage on the contacts does not exceed the value of the direct voltage drop across the thyristor, which means arc re-formation. In the switched on state of the contactor, the current through the thyristors can be almost neglected, since in this case a voltage of several tens of millivolts is applied to them (the voltage drop on the contacts). When the contactor is disconnected in the same way as in the case of vibration, when the contacts 1 are opened, the current flowing through them is diverted to the corresponding thyristor. When the current flows from the contact circuit to the thyristor, the control signal from the output of the current transformer rapidly drops to zero. The circuit is disconnected when the current passes through zero in a conducting thyristor. As follows from the description of the operation of the contactor, the current through the thyristors when the circuit is disconnected is no more than half a period.

The current transformer for this contactor is selected based on the following requirements:

a) providing a control signal sufficient to turn on the thyristor at the lowest current of the main circuit;

b) limiting the maximum current through the rectifier and the control circuit of the gyristor in the mode of limit overload in the network;

c) the current transformer should not saturate (With the maximum allowed current switched by the contactor.

The trigger threshold of the contactless switches 12 and 13 from the current sensor 14 is selected in the range between the maximum operating current and the current at which the voltage drop across the contacts creates a current in the thyristor close but less than the holding current. Obviously, the current at which the electrodynamic junk contacts occur, lies above this range.

Consequently, in the switching mode of the operating currents, the contactless keys remain open, and when the contacts open, the current flows into the thyristors. In the end-to-end short-circuit mode, as the current rises, the output ' signal of the sensor 14 increases. When one of the keys operates, the control signal shunts depending on the polarity of the current in the circuit, and, as mentioned above, its value is less current hold. Therefore, with a further increase in short circuit current and garbage

contacts current does not pass through the thyristors. At the contacts, an arc discharge occurs with a duration determined by the time the short-circuit current is turned off by the protective devices. installed in line with the contactor. After termination of the emergency mode, the contactor is suitable for further work (it is possible to replace or clean the contacts). Thus, the use of this circuit eliminates the damage of thyristors during a short circuit.

In order to reduce the thyristor lock-in time, after the key has been triggered in series with the contactless keys, additional sources 10 and / or O. providing the supply of the blocking voltage to the circuit are included: cathode – control electrode.

At higher speeds of increase of the short circuit current, the time gap corresponding to the change in current from the maximum operating current to the current at which the current in the thyristor reaches the holding current,

may be insufficient to restore the thyristor locking properties. To eliminate this residual, it is proposed to control the key simultaneously from the sensor 14 and from the sensor 15 with the output

signal proportional to the rate of increase of current. This ensures that the keys are actuated at the beginning of the process of increasing the short-circuit current, as a result of which the reliability of the thyristor lock-up is increased.

The protection circuit of thyristors in the event of a short circuit, adopted in the described contactor, can be used in all known contactors with arc-free switching. In the proposed contactor, instead of two thyristors one simistor 18 (: fi | G. 2a) or any other device similar to the above elements can be used. For contactors that are not used in single-pole ion-filling, for the purpose of cost reduction, it is possible to use an uncontrolled diode 19 instead of one of two parallel contacts of contactless controlled elements (Fig. 26). As contactless keys 12 and 13

(see Fig. 3) this circuit uses a low power thyristor and a transistor. The key threshold is determined by the voltage to stabilize the Zener diode connected to the base circuit of the transistor. Current sensor role

The secondary windings of the current transformer 4 are performed. At the same time, they are also sources of blocking voltage.

The scheme works as described above. Circuit: resistor 20 - capacitor 21 protects: controlled contactless elements from short-term overvoltages in the network, and also limits the magnitude and rate of voltage rise on them in the switching mode.

Subject invention

1. A recurrent-current contactor with arc-free commutation, containing a noncontrollable controllable element connected in parallel to the main contacts, characterized in that, in order to increase the reliability during contactless control of said element, it is equipped with a current transformer whose primary winding is introduced into contacts, and each secondary winding is connected via a rectifier to a control circuit of a controllable contactless element that shunts a series circuit; main contacts - current transformer.

2. Contactor Io p. 1, characterized in that, in order to protect the contactless controllable elements during a short circuit in the main contact circuit, a control circuit is introduced into the control circuit of each contactless control element, consisting of a blocking voltage source and contactless a key controlled by current sensors and current rise rates in the main contact circuit.

The priority of claim 2 is calculated from 08.XII.1969 on the filing date of application no. 1383372 / 24-7.

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