SU550694A1 - Device for arc-free switching of direct current circuits - Google Patents

Description

voltage) - the control circuit is disconnected, the main thyristor can not be turned off, the load current flows for a long time, which leads to its failure and reducing the reliability of the device as a whole. In addition, the contactor allows it to operate with a short on time, since the charge time of the switching coaddensor is limited by the value. Insufficient amount of wear resistance of the contactor due to the use of auxiliary contacts and auxiliary relay contacts. In modern relays, electrical wear resistance does not exceed 0.5-2.0 million cycles, while the wear resistance of a contactor should be at least 10 million cycles, in accordance with current requirements. The voltage on the switching capacitor and in the control circuit of the main thyristor exists during the whole time of the contactor being turned on, and for normal operation of the apparatus it is enough to have the voltage on these elements only at the moment of switching, as a result of which the overall working life of the contactor decreases.

The aim of the invention is to improve the reliability of the device for arc-free switching of DC circuits, reducing its cost and size with ease of operation. This is achieved by using an additional current transformer for charging the switching capacitor in the proposed device, the primary winding of which is connected in series with the main thyristor, one of the secondary windings is connected in series with the main contacts, and the other through an additional diode connected in parallel with the auxiliary thyristor.

The drawing is a schematic diagram of the described device.

Parallel to the main contacts 1 are connected the main thyristor 2 and the forced switching unit, consisting of auxiliary thyristor 3 and capacitor 4. In series with the thyristor 2, the primary winding 5 of the current transformer is turned on. The secondary winding 6 of the transformer is connected in series with the main contacts, and the secondary winding 7 via diode 8 is connected in parallel to the thyristor 3. A block 9 is connected between the anode and the control electrode of the thyristor 2 to control the main thyristor. The control takes place by the magnetic field of the current flowing in the contacts 1. The block 9 is made on the basis of the key. A block 10 is connected between the control electrode of the thyristor 3 and the cathode of the thyristor 2, which operates at the charge of the capacitor 4. The block 10 is also made on the basis of a key.

The process of turning on and off the device is as follows.

With the closure of contacts 1 and the occurrence of current in the main circuit, the key of the block 9 is turned on, preparing the thyristor 2 to be turned on, and the transformer core is re-magnetized into a (conditionally accepted) negative saturation.

When the device is turned on, the current passes through the contacts completely. In this state, the capacitor is uncharged and there are no control currents in the thyristors.

When the device is disconnected and contacts 1 are opened, the voltage on them reaches the level of turning on the thyristor 2 and the last

included. The current from the circuit of contacts flows into the circuit of the thyristor 2 and the winding 5 of the transformer. The voltage drop on the open thyristor 2 is insignificant, which provides an almost non-arcing opening of the contacts 1. When

When the current in the circuit of contacts 1 disappears, the key of the block 9 opens, removing the control signal. The load current, flow through the winding 5 of the transformer, remagnetizes its core, and the circuit: Winding 7 - diode 8 - thyristor

2 — capacitor 4 begins to flow a current, charging the latter to a voltage with a polarity corresponding to the normal operation of a capacitive forced switching unit. After the end of the charge of the capacitor, the key of the block 10 is triggered, causing the thyristor 3 to turn on and the current to flow from thyristor 2 to the thyristor circuit 3.

A negative (with respect to the thyristor 2) voltage on the capacitor causes

the thyristor 2 is locked. The capacitor 4 is recharged by the load current to a voltage with the polarity indicated on the drawing in brackets. The load is disconnected at full recharge of capacitor 4, when the current is

In thyristor 3, it will become lower than the holding current.

After locking the thyristor 3, the capacitor 4 is discharged, giving energy to the network along the circuit: winding 7 - diode 8 - direct current source - valve 11. Depending on the value

disconnecting current, the residual voltage across the capacitor can vary from zero to the supply voltage. If the capacitor remains charged, then the next time the contacts are turned on, it is discharged through

winding 7 and contacts.

When the main contacts vibrate when the contactor is turned on, the thyristor 2 turns on and shunts them similarly

as it happens when the contactor is disconnected, but the forced switching device does not operate, because the capacitor 4 does not have time to charge during the contact bounce time before the switch on key of the unit 10.

Thus, the proposed device has an increased reliability of operation due to the fact that the magnitude of the charging voltage of the switching capacitor does not depend on

the presence of supply voltage, and is determined by the magnitude of the switching current; in the on and off states, its circuit is de-energized; thyristors and control circuits form an autonomous unit that does not require pitapi from an auxiliary source, nor

from the main network, which greatly simplifies the operation of the device.

Claims (4)

1. The UK patent 1048997, cl. H2J, 1966. 2. The patent of France 1413392, cl. H 02R, 1965. 3. The patent of France 1413393, cl. H 02R, 1965. 4.Contactors of a series N firms CEM, catalog “Contactents Speciax, 1966, p. 109, France (prototype).