SU1599930A1 - Device for current protection of a.c.mains - Google Patents

Abstract

The invention relates to electrical engineering, in particular, to devices for protecting an electrical network from damage. The aim of the invention is to increase the reliability of operation. The device performs a pulse voltage stabilization and monitoring of an emergency situation in the network as each positive and negative alternating current half-waves follow. 1 il.

Description

This invention relates to electrical engineering, in particular, to devices for protecting an alternating current network.

The purpose of the invention is to increase the reliability of work.

The drawing shows a circuit diagram of the device.

The device contains 1.current transformers included in each phase of the protected network, the rectifier unit 2, the secondary winding of the current transformer 1 is connected to the input of each rectifying bridge, and the outputs of the rectifying bridges are connected in series and according to, measuring resistor 3, voltage regulator 4, blocking diode 5, storage capacitor 6, executive unit 7, including current control body 8, winding 9 of electro-mechanical actuator, semiconductor switch, made in the form of thyristor pa 10, the control input of which is connected to the output of the current control member 8.

Voltage stabilizer 4 contains two transistors 11 and 12 of unlike conductivity, three diodes 13-15, two capacitors 16 and 17, three resistors 18-20, and a zener diode 21 ..

The device works as follows.

; For each half-cycle of the secondary current of the transformer, charging takes place via rectifiers 2 and blocking diode 5 of storage capacitor 6. At first, the rectifying current from the outputs of rectifier unit 2 goes to the terminals of voltage regulator 4. As it grows

sd

with

with so

with

The current value of the current is rectified and the first capacitor 6 is charged through the first diode 13, then the additional capacitor 6, and j increases at the base of the first transistor 11, when this voltage exceeds the stabilization level of the tablitron 21, through the emitter junction to the base of the first transistor 11 10 current flows, which will lead to an avalanche-like opening and saturation of transistors 11 and 12, as a result, the first capacitor 16 will be shorted through the first resistor 18-15 to a low-resistance transistor junction, therefore the first condenser 16 Torr dits discharge will tend to zero. At the same time, the block of drives 2 through the measuring resistor 3 of the locking-20 is supplied by the second transistor 12. As the first capacitor 16 discharges, the base current of the second transistor 12 tends to zero, which leads to the saturation of the second transistor 12, 25 as a result of transistors 11 and 12 are closed. Then, the charge of the first capacitor 16 begins to recharge. As the first capacitor 16 charges, the voltage at the base of the transistor 11 increases. When this voltage exceeds the stabilization level of the Zener diode 21, transistors 11 and 12 open again. repeats up to 35 for as long as the instantaneous value of the half-wave current becomes less than the discharge current of the storage capacitor 6, the generation process is stopped, the transistors 11 and 12 are closed-40. In the next half period, the generation process is repeated.

At a higher current of the transformer 1, the first capacitor 16 charges faster to a predetermined level, and at a DZ less current, it is slower, therefore in the first case the pulse frequency of the voltage regulator 4

above, and in the second below.

Thus, the pulse repetition rate 50 is directly dependent on the amount of current flowing through the windings of the transformer 1

current.

In the process of stabilization, for example, when changing the secondary current of the transformer 1, the pulse frequency changes, respectively, as a result of the second transistor

12 with an appropriate frequency, short-circuits the output of the rectifier unit 2, and thus maintains the voltage on the storage capacitor 6 at a given level,

In order to provide minimal voltage ripples on the storage capacitor 6, the pulse frequency is chosen well above the line frequency. For example, for a network frequency of 50 Hz, the frequency should be 3–5 kHz.

A voltage across the measuring resistor 3, proportional to the primary phase current, is applied to the input of the current control unit 8, which in an emergency situation (overload, interphase or single-phase short circuit, phase failure) sends a command to turn on the thyristor 10, and a cumulative the capacitor 6 is discharged to the winding 9 of the electromechanical actuator.

This technical solution allows to increase the reliability of the device operation for current mains AC power.

Claims (1)

Invention Formula A device for overcurrent protection of an AC network containing current transformers according to the number of phases to the output windings of which a rectifier unit is connected, a measuring resistor connected in series and a storage capacitor, a voltage regulator connected between the positive terminal of the rectifier unit and the first output of the measuring resistor, The latter is also connected to the first output of the actuating protection unit, the second output of which is connected to the second output of the measuring resistor, characterized in that, in order to higher operating reliability, an additional blocking diode is added to it, the anode of which is connected to the positive output of the rectifier unit, and the cathode to the combined third output of the execution protection unit and the output of the second capacitor capacitor plate, the second output of the measuring resistor is connected to the negative output of the rectifier unit the voltage is made in the form of two transistors, between the emitters of which are connected in series the first capacitor and the first diode in the forward direction, the last shunted by the first resistor, the collector of the first transistor is connected to the base of the second transistor, the baso-emitter junctions of the first and second transistors are shunted by the second and third resistors, respectively, between the first and the collector of the second. shunted by the second capacitor, the base of the first transistor is also connected via a zener diode to the second emitter transistor connected to the first output of the measuring resistor, the collector of the second transistor is connected in the opposite direction to the first transistor's znithter of the first transistor, the latter is connected to the positive terminal of the rectifier unit.