SU1638757A1 - Device providing overload and fault current protection - Google Patents

Description

The invention relates to the field of electrical engineering, in particular to the relay protection of electrical networks. The purpose of the invention to reduce the weight, size and simplification of the device. This goal is achieved by the fact that the power supply of the circuit is carried out from the same current sensors, from which a signal is obtained proportional to the current of the protected network, and by the fact that the unit for forming the time-current characteristic is made in the form of two transistors, four resistors, a Zener diode, a voltage divider, a time-sensitive capacitor and threshold element. 1 il.

The invention relates to electrical engineering, and can be used to protect electrical circuits and loads from damage by overload currents and short circuits in power supply systems.

The purpose of the invention is to reduce the weight, size and simplification of the device, obtaining the required time-current characteristics.

The drawing shows a circuit diagram of this device.

The device contains current sensors 1–3, rectifier bridges 4–6, resistors 7–9, Zener diode 10, diodes 11–15, unit 16 for forming time-current characteristics 16 and execution unit 17. Block 16 for forming time-current characteristics is designed as transistors 18 and 19 , resistors 20-23, a voltage divider on resistors 24, 25, zener diode 26, timing capacitor 27 and threshold element 28. The executive unit 17 is made in the form of a thyristor 29, a relay 30 and a capacitor 31. The drawing shows the switch 32.

Device for protection against overcurrent and short circuit currents works as follows.

When the contacts of the switch 32 are closed, a current flows through the power circuit. When current flows in the power circuit in the secondary windings of the current sensors 1-3, a current flows proportional to the current of the power network. The secondary current of current sensor 1 flows through a rectifier bridge 4, a resistor 7, diodes 14.15 and a zener diode 10.

At any current of the power circuit, the voltage of the secondary winding of the current sensor must rise to the breakdown voltage of the Zener diode 10, so that the secondary current flows through) 2. The voltage at the output of current sensor 1 (1) 1) is equal to the voltage drop across the Zener diode 10 (Cst.y) plus the voltage drop across the resistor 7, i.e.

C1 = DST. U + C «7.

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The resistance of the resistor 7 is chosen so that Ι2Κ7 "Set at the current of the power circuit I <1 _N , where 1n is the rated current. The voltage of the secondary winding at a current of the power circuit less than or equal to nominal is approximately equal to Shtloe.

This voltage through the diode 13 is supplied to the unit 16 for forming the time-current characteristic and at the same time charging the capacitor 19. Thus, the voltage 10 at the output of the current sensor consists of a constant voltage drop across the Zener diode 10 and a variable part of the voltage drop across the resistor 7 proportional to the current circuit. 15

The voltage drop across the resistor 7 is fed to the first input of the block 16 forming time-current characteristics. The presence of resistors 7–9 in the secondary circuits of current sensors 1–3 allows for separate adjustment of the device response taking into account the technological spread of 4 current sensors, the input voltage of the unit 16 for forming the time-current characteristic supplied from resistors 7–9 at one phase, two-phase and three-phase overload in the power circuit, differs at the same overload current in each phase by no more than 1.4 times, as the rectified one-, two- and three-phase voltage. This 30 provides the threshold current (1 _t p) and the response time of the device from overload currents in accordance with the requirements of the technical specifications for one-, two-, and three-phase overload in the power network. Without 35 diodes 11,12 and 13, load separation and power supply from all current sensors are impossible. Diodes 14, 15 provide compensation for the voltage drop across diodes 11–13.

The voltage drop across the resistors 7-40 9 applied to the first input is compared with the voltage at the midpoint of the voltage divider. When the network current is Ιτρ> 1n, the voltage at the first input becomes greater than the voltage from the voltage divider. Transistor 19 closes and transistor 18 opens. Through the transistor 18 current flows, which is determined by the voltage drop across the resistors 7-9 and the chain of 50 resistors 21, 22 and Zener diode serially connected. This time charging the capacitor 27 is charged.

When the voltage on the capacitor 27 reaches the threshold of the threshold 55 element 28, the latter opens and the capacitor 27 is discharged to the control electrode of the thyristor 29. The charging time of the capacitor 27 to the opening voltage

threshold element 28 and determines the response time of the device. The charge of the temporary capacitor 27 does not occur exponentially, but linearly. The thyristor 29 is opened and the relay 30 is receiving power, when it is triggered, the switch 32 turns off the damaged network.

By selecting resistors and zener diodes in block 16 for forming the time-current characteristic, as well as adding other resistors and zener diodes, one can obtain any desired time-current characteristic.

In the proposed device for protection, the circuit is powered from the same current sensors, from which a signal is obtained that is proportional to the current of the protected network, this reduces the weight and dimensions of the device.

Claims (1)

Claim A device for protection against current overloads and short-circuit currents, containing three current sensors, the primary windings of which are intended to be connected to the corresponding phase of the electrical installation, the input windings of the rectifying diode bridges are connected to the secondary windings of the current sensors, the first output terminals of which are combined through the corresponding resistor, Zener diode, the anode of which is connected to the first common output of the circuit, the cathode of the Zener diode is connected to the first input of the block forming the time-current characteristic, the first and W The supply inputs of which are connected between the first and second common terminals of the circuit, respectively, the time-current characteristic generation unit includes a series-connected time capacitor and a threshold element, the output of the last unit is connected to the output of the latter, the output terminals of which are connected between the common terminals of the circuit, five diodes, that, in order to obtain the required time-current characteristics, to reduce the weight, size and simplify the device, the anodes of the three diodes are connected to the corresponding m first output pins · rectifier diode bridges, the second output pins of which are combined and connected to the anode of the Zener diode, the cathodes of these diodes are connected to the second common output of the circuit, the fourth and fifth diodes are connected in series, while the anode of the fourth and the cathode of the fifth diode are connected between the common connection point of the resistors and the Zener cathode, respectively, in addition to the block forming the time-current characteristic five 1638757 6 Two transistors, four resistors, a zener diode and a resistive voltage divider are introduced, the first input of the specified block being the base of the first transistor, the collector of which is connected to the first common terminal of the circuit through the first resistor of the circuit, the collector of the second transistor is connected to the second terminal of the first resistor 10 resistive voltage divider connected between the common leads of the circuit, the emitters of the transistors are combined and connected in series to the second common lead of the circuit, an additional Zener diode is connected parallel to the third resistor, the cathode of which is connected to the base of the first transistor through the fourth resistor whose collector is connected to a time-dependent capacitor.