SU1734160A1 - Device for protection of network with insulated neutral against single-phase short-circuit to ground - Google Patents

Abstract

Use: network with isolated neutral. Essence: the introduction of the elements of the prohibition, NOT and the implementation of integrating elements controlled, control inputs of which are connected to the switch, increases the reliability of the protection device. 1 il.

Description

This invention relates to electrical engineering, in particular, to devices for relay protection against single-phase earth faults in insulated neutral networks.

The aim of the invention is to increase the reliability of operation.

The functional diagram of the device for protection against single-phase earth fault is shown in the drawing and is given for two connections, the total number of which can be any.

The device contains transformers 1 and 2 of zero-sequence current installed at protected connections 3 and 4, current-to-voltage converters 5 and 6 to rectified voltage (PTVN), integrating elements 7 and 8 (IE), comparators 9 and 10, drivers 11 and 12 control pulses (IGFs), thyristors 13 and 14, executive units 15 and 16 (EUT) with capacitors and diodes, a closing key 17, sensors of 18 and 19 control of the disconnected state of the circuit breakers (DKOSB), the source 20 of the thyristor power supply and executive bodies, transformer 21 voltage with secondary winding according to the open triangle scheme, which is a source of zero sequence voltage (NNP), starting body 22 (SW), switch 23, control unit 24 (control unit), element NOT 25, element OR 26, element MEMORY 27 and 28, elements matches 29 and 30.

The HVDC 5 and 6 consist of an intermediate transformer and a rectifier on an operational amplifier.

IE 7 and 8 are made on an operational amplifier with an RC circuit and a locking key. The time constants of the charge chain of capacitors are assumed to be the same for all connections.

Comparators 9 and 10 are made on the operational amplifier and have the same thresholds (setpoints) for operation.

As DKOSV 18 and 19, the auxiliary contacts of these switches or the Relay position can be used.

The power supply source 20 of thyristors and executive bodies is designed as a full-wave rectifier.

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The switch 23 is made up of two groups of 31 and 32 diodes connected in a star of opposite polarity with common united points, and a disconnecting key 33.

The CU 24 includes signal delay elements 34 (EZPS) and a ban 35.

The device works as follows.

In the absence of a single-phase ground fault in the network, the thyristors 13 and 14 are turned off, IO 15 and 16, ON 22, the elements MEMORY

27 and 28, EZPS 34 are in the initial state. Key 17 is open, key 33 is closed, a signal (logical O) is sent to the control inputs of IE 7 and 8. The voltages at the outputs of comparators 9 and 10 are missing. There is also no voltage at the control input of the CU 24.

When a single-phase ground fault occurs in the network, for example, at connection 3, software 22 is activated, while the key 17 is closed, the signal at the control inputs of the MEMORY 27 elements and

28 and at the same time, EZPS 34 starts up. Signals proportional to zero sequence currents appear at the outputs of the HTW 5 and 6. After a short delay, the output of element 34 is a signal arriving at the control input of the key 33.

When the switch 33 is opened, the voltages varying exponentially appear at the outputs of the integrating elements 7 and 8. When these voltages reach a higher threshold of the comparators 9 and 10, the signals at the outputs of the latter appear at the inputs of the IGS 11 and 12. The first signal at the output of the comparator 9 appears because it is installed in the protection channel of the damaged connection having the largest ground fault current.

When a signal is detected at the IGF 11 input, the thyristor 13 is turned on, the EUT 15 and the MEMORY 27 element are triggered. When the thyristor 13 is turned on, the control inputs of the IE 7 and 8 receive a signal (logical O). Their output voltages become close to zero. In this way, the possibility of operating the comparator 10 and turning on the thyristor 14 is excluded.

During the passage of the voltage supplying the thyristors and the executive bodies, through zero (or a value close to it), the thyristor 13 is turned off, voltages appear at the outputs of the integrating elements 7 and 8, which are amplified by

exponential law. When these voltages reach the threshold level of the operation of the comparators 9 and 10, the comparator 9 is first triggered again and the thyristor 13 is turned on.

In this mode, the device circuit works until the connection switch 3 is turned off. When the switch is activated (turned off)

0 the output of the sensors 18, 19 appears the signal of the logical unit, and at the output of the elements MEMORY 27 and 28 the signal of the logical unit disappears, as the signal at the output of the triggering organ disappears.

5 At the same time, however, it should be borne in mind that after switching off the switch of the damaged connection, the signal at the output of the triggering organ disappears not immediately, but some time after the alarm in the single-phase ground fault characterized by low-frequency damped current oscillations and zero sequence voltage.

5 Due to the fact that the signal at the output of the starting organ disappears not instantaneously, but with a certain delay, the signal at the output of element 25 appears with the same delay and the signal at the output of the triggering organ disappears.

0 22, the signal disappears at the output of element 34. Thanks to this operation algorithm, a false positive of the device does not occur in the postemergency mode of a single-phase earth fault after switching off

5 damaged attachment.

When short-term (self-liquidating) ground faults and various kinds of interferences appear in the network, the device comes into action, but due to relatively

0 of a large time switch-off time (tens of milliseconds) and due to the fact that the input signals by the thyristors are memorized for a limited time (the fraction of the half-period of the industrial frequency signal), and then automatically erased (when the half-wave of the supply voltage passes through zero), false (unnecessary) a) disconnecting switches from exposure to short pulses

0 (interference) does not occur.

Thus, the proposed device, which reacts to an amount proportional to the total earth fault current, provides protection such properties as selectivity, noise immunity and speed, as well as sensitivity. At the same time, its operation does not depend on changes in the parameters of individual connections and the network as a whole, the type of single-phase ground fault, phase and frequency

the relationship between currents and zero-sequence voltage does not require detuning from its own capacitive currents. And this, in turn, contributes to the stability of the operation and reliability of the protection.

The reliability of operation is also enhanced by the simpler circuit construction of this device, which distinguishes it from the prototype.

Claims (1)

Formula of the Invention A device for protection against single-phase ground fault in an insulated neutral network containing, according to the number of connections, series-connected zero-sequence current transformer, current to rectified voltage converter, integrating element, comparator and driver of control pulses, the output of which is connected to the control the thyristor electrode connected in series with the executive body, fed through the closing key of the common for all connections of the source Itani, constructed as a full-wave rectifier and is connected to the secondary winding of the transformer voltage wye-connected, the overall body of the trigger, with its input connected to the secondary winding of said voltage transformer connected according to the scheme open triangle, and the output - to controlling the said locking key, a common switch connected by first terminals to the anodes of the thyristors and made in the form of two groups of diodes connected in a star opposite to polarity and a disconnecting key connected between the common point of the groups of diodes and the ground, elements of coincidence in the number of connections, the inputs of which are connected to the outputs of the sensors for monitoring the disconnected state of the switches of the connections and the elements of MEMORY, a common element OR whose inputs are connected to the outputs of the said elements coincidence, and a delay element connected by its input to the output of the triggering organ, characterized in that, in order to increase the reliability of operation, it is provided with a BANGE element, the main the input of which is connected to the output of the delay element, and the control input is connected to the output of the OR element, the output of the BANGE element is connected to the control input of the switch disconnecting key, and the element NOT, connected to the output of the starting organ, and the output to the control inputs of the MEMORY elements, while the main inputs of the MEMORY elements are connected to the outputs of the executive bodies, and the integrating elements are controllable, the control inputs of which are connected to the second terminals of the switch.