SU792425A1 - Device for overload and short-circuiting protection of dc network - Google Patents

Description

The invention relates to electrical engineering and can be used to protect direct current circuits.

A device for protection of a direct current circuit is contained, which contains reed switches covered by a common current winding, included in the output transistor of the control unit's emitter, and one of the reed switches is connected to a base-emitting shunt circuit. transition of the mentioned transistor.

The device does not automatically turn on the load after the fault has been rectified.

The closest in technical essence to the invention is a device for protecting a current source from abnormal conditions, containing a reed switch connected through an amplifier to an actuator and controlled by the current of the protected circuit t.

The drawback of the device is the lack of control over the state of the load circuit and the limiting of the overload current of the protected circuit.

The aim of the invention is to expand the functionality of the device.

The goal is achieved by the fact that a device for protection of a direct current circuit against overloads and short circuits, containing a reed switch, covered by a current winding and connected through an amplifier to an operating winding of an executive body, the current winding being connected to the protected circuit in series with the closing contact of the executive body, the threshold element and resistors, equipped with a remote switch, a diode and a thyristor connected in series with the tripping winding of the actuator, in parallel with The current winding and the closing contact of the actuator are switched on, the circuit is connected from the series-connected disconnecting contact of the actuator, the closing contact of the remote switch, the limiting resistor and the diode, the input of the threshold element connected to the limiting resistor and its output to the thyristor control electrode, parallel to the reed switch, the disconnecting contact of the remote switch is turned on and in series with

they make closing contact of the executive body.

The drawing shows a diagram of the device.

It contains a current winding 1, inside of which the reed switch 2 is located, the executive body 3 (for example, a remote switch) with a working 4 and disconnecting 5 windings and its contacts 6-10, a threshold element 11 made on a single junction transistor 12, resistors 13-16 and capacitor 17, auxiliary remote switch 18 with working 19 and disconnecting 20 windings and with contacts 21, 22, thyristors 23 and 24, diode 25, resistor 26, limiting resistor 27 and load 28.

The device works as follows.

In the initial state, remote switches 3 and 18 are off, their contacts 6, 8, 10, 22 are open, and contacts 7, 9, 21 are closed. In this case, the thyristors 2, 24 are turned off, the load is 28 o6ecTOvteHa, the protection device itself is also de-energized and does not consume energy. In this state, the device is before the command to turn on.

The command to turn on in the form of a short pulse (0.025-1s) arrives at the working winding 19 of the auxiliary Switch 18 and switches it to the working state. In this case, the switch 18 by contact 21 will shunt the reed switch 2, and by the contact 22 on the circuit: plus power supply pin 9 - pin 22 - resistor 27 - diode 25 - load 28 - minus power supply supplies test current to the load.

Further, if the load resistance 28 is nominal, then the voltage drop across it and the diode 12 will charge a capacitor 17 through a resistor 16 to a voltage at which the single junction transistor 12 is turned on and a pulse is sent to the control electrode of the thyristor 24. The thyristor 24 will operate and turn on the working winding 4 of the remote switch 3. The remote switch 3 switches to the operating state. In this case: the opening contact 7 will open the anode circuit of the thyristor 24 and it will turn off; make contact 6 closes the anode circuit of the thyristor 23; the closing contact 8 is closed and will prepare to turn on the control electrode circuit of the thyristor 23; contact 9 opens and shuts off the single junction transistor 12 and the load supply circuit with the test current (resistor 27, diode 25); power contact 10 closes and supplies 2.8 with a rated current.

Thus, the load will be locked with a rated current, and the protection device itself will practically consume no energy.

In this state, the device will stay until the command to shut down or until an overload (short circuit) occurs. In the first case, the shutdown winding 20 of the auxiliary remote switch 18 will arrive in the form of a short pulse (0.025-1s) to turn off the command and switch it to its initial state. The contact 27 closes and the power supply source through the contacts 8, 21 and the resistor 26 is supplied to the control electrode of the thyristor 23. At the same time, the contact 22 opens. The thyristor 23 will operate and turn on the tripping winding 5 of the actuator 3, which will switch to the initial state. Thereby, the device will completely return to its original state and will remain there until the next command comes on.

Do the second case, due to the failure of the load, its resistance will decrease, and the current will increase to the value to which the current organ is tuned. An increase in current will increase the magnetic field current winding 1 and trigger the reed switch 2. Plus, the power supply through contacts 8, 2 and resistor 26 will go to the control electrode of thyristor 23, the thyristor will work and switch actuator 3 to its initial state. But since the commands to disconnect the device from the outside (to the winding 20 of the switch 18) were not received, the load would not be completely de-energized; across the circuit plus the power source - pins 9, 22 - resistor 27 - diode 25 - load 28 - minus the power source the test current will flow.

But, since the load resistance has decreased, the voltage drop across the load 28 and the diode 25 will not be sufficient to turn on the single junction transistor 12. The protection device will remain in this state until the fault is eliminated. When the load resistance is restored to the nominal value, the transistor 12 turns on, it turns on the thyristor 24, and the latter switches the actuator 3 to the operating state. The load is again supplied with rated current.

In the event that a load failure (decrease in resistance or short circuit) occurred when the device was in the off state and the load was de-energized upon the arrival of a command to turn on, switch 18 turned on and, as in previous cases along the circuit: plus power supply pins 9 and 22 - resistor 27 - diode

25 - load 28 - minus power supply; the load is supplied with test currents. But, since the resistance of the faulty load is less than nominal, the voltage drop across the load will not be sufficient to turn on transistor 12, therefore the thyristor 24 does not turn on and the actuator 3 does not turn on. The device will remain in this state until the fault is eliminated or until it arrives shutdown commands. Thus, the load even for a short time will not short the power source. Moreover, the control of the health of the load is carried out with each inclusion of the load. This achieves both the reliable operation of the power source itself and the consumers.

Claims (2)

1. USSR author's certificate number 216825, cl. H 02 H 3/08 1967. 2. USSR author's certificate number 377936, cl. H 02 H 7/12, 1973.