SU210228A1 - DEVICE FOR UNKEBELERY AC LOAD LOAD COMMUTATION - Google Patents

Description

Devices are known for sparkless switching of an AC load, containing a day from a parallel connected power contact of a switching electromagnetic element and a switching element, such as a thyristor, in each phase and a control element.

The proposed device provides switching during the breakdown of the thyristor and more reliably due to the fact that a safety element is connected in series with the thyristor with a setpoint not exceeding the rated operating current, and an auxiliary contact of the switching electromagnetic element is connected to the thyristor control circuit, which closes before the power contacts opening after opening.

FIG. 1 shows a contact group of an electromagnetic switching element with a series closure of the auxiliary and power contacts; .on FIG. 2 is a schematic diagram of a device for a single-phase system with series closure of auxiliary and power contacts and with a switching element containing a thyristor connected in a bridge circuit; in fig. 3 is a schematic diagram of a device for a single-phase system with a switching element containing two thyristors connected in a cross-circuit with a shorted diagonal; in fig. 4 is a schematic diagram of a device for a single-phase system with a switching element comprising two thyristors connected in a counter-parallel manner; in fig. 5 is a schematic diagram of a device for a multi-phase system with series closure of auxiliary and power contacts; in fig. 6 - contact

a group of electromagnetic switching element with a successive opening of power and auxiliary contacts.

The device contains an auxiliary contact / electromagnetic switching

element, main contact 2, ballast resistance 3, switching element 4 with a thyristor connected by a bridge circuit, coil 5 of an electromagnetic switching element, AC source 6, electric power receiver 7, control contact 8, fuse 9, phase-regulating capacitor 10, source 11 control voltages for thyristors containing a transformer with two windings and two

straighteners.

The operation of the device is considered on the example of a multiphase variant (Fig. 5).

passes When the aforementioned state of the device changes, the auxiliary contact 1 first closes, which turns on the thyristor control circuit. Due to the fact that the opening of the thyristor occurs within a maximum of 5 microseconds, and the time of movement of the core of the normally operating device is at least hundreds of ms, then by the time of closing the main contacts 2, the thyristors of the switching elements 4 will be open. The current to the load from the moment of opening the thyristors to the final closing of the main contacts passes through them. This eliminates the arcing caused by the vibration of the contacts at the time of closing. After the main contacts are closed, the switching elements are shunted by them and, despite the closed state of the control circuit, the current does not pass through them.

When the circuit is opened, the main contacts 2 are opened before the auxiliary contact /. Therefore, in the initial mohment of opening the contacts 2, the current flowing into the load is perceived by open thyristors, which eliminates the appearance of an arc. After the auxiliary contact 1 is opened, the thyristor control circuit is cut off, and they close at the first current zero crossing.

To control the thyristor (thyristor |) in the circuits in FIG. 2 and 3 use a direct current source that supplies the electromagnet of the switching device; in the diagrams in FIG. 4 and 5 - control transformer //, the number of secondary windings (with rectifiers) which is equal to the number of phases for the bridge and cross thyristor circuits and the number of controlled valves when the latter are connected in parallel.

The pins of the transformer // and the transitions of the switching elements 4 (Fig. 5), marked with strokes, are not used in the first two cases.

A forced sequence of changes in the state of the main and auxiliary contacts, carried out constructively (Fig. 1), guarantees a clear, arc-free commutation. A similar sequence of operation of contacts 1 and 2 can be achieved by adjusting the contact springs.

To eliminate accidental failures associated with the breakdown of auxiliary or controlled diodes of the switching element 4, the latter are connected to the main contacts 2 through fuses 9.

When the diodes are in good condition, the energy of the short pulses that occur when the main contacts are switched is insufficient to melt the fuse insert. The melting insert burns only from the action of a continuous current, which appears when a short circuit of the electrodes in any of the diodes, which automatically leads to their disconnection. If the main contacts, despite the protection provided, are designed for. when the thyristor circuit is damaged, they will provide reliable impulse operation until the first routine inspection, i.e., until the damage is eliminated.

0 The power of the thyristors depends on the power of the circuit, the repetition of the commutation, the frequency of the alternating current and can be calculated from the allowable overload of the thyristors. Nominal melting current

5 of the insert depends on the same factors and must be chosen from the condition of its allotment combustion from the operating current of the circuit.

The resistance value of the resistor 3 in the circuits of FIG. 2, 3 is determined by the required control current and depends on the type of thyristor and the magnitude of the supply voltage. The capacitance of the capacitor 10 in the circuits of FIG. 4 and 5 depends on the same lrychins, as well as on the necessary phase of the control voltage. Application

5, the capacitor as a ballast controller, despite the presence of the inductance of the control transformer, allows you to have the necessary speed and phasing of the control circuit. Current in

The transient and the transition through resonance are limited by the resistance of the primary winding of the control transformer 11. This resistance may be relatively high due to the low power consumed by the transformer to control the thyristors.

The schemes and operation of devices with different options with opening contacts are similar to those discussed above.

Subject invention

Claims (2)

1. A device for non-sparking switching of an alternating current load, comprising a circuit of a parallel-connected power contact of a switching electromagnetic element and a switching element, such as a thyristor, in each phase and a control element, characterized in that, in order to ensure switching during the breakdown of the thyristor, sequentially with the indicated thyristor in each phase, a safety element is connected with a setpoint of not more than the rated operating current. 2. The device according to claim 1, wherein 5, in order to increase reliability, into a circuit control of said thyristors, an auxiliary contact of said switching electromagnetic element is included, which is closed before the power contacts are closed and opened after the same contacts are opened.