RU2473158C1 - Device of selective monitoring and protection against earth faults in circuit with isolated neutral - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device is equipped with additional transistor switches, contactors with opening and closing contacts, a light diode to indicate a number of a disconnected network line and a button for opening, connected in series with a contactor winding. Introduction of additional elements provides for automatic disconnection and identification of the emergency network line number. Simultaneously the device automatically switches to monitoring the next network line with the lowest resistance of insulation with indication of the number and value of resistance of this line insulation. Availability of a button, which opens a circuit of a faulty line contactor winding, makes it possible to perform short-term monitoring of faulty line insulation resistance, both at the start and in process of repair, which considerably simplifies and speeds up its performance.

EFFECT: higher safety and reliability of network operation.

1 dwg

Description

The invention relates to devices for monitoring insulation resistance and protective shutdown in electrical networks with insulated neutral.

A device for monitoring insulation resistance (Merlin Gerin-France catalog, Vigilohm System XM-100, XM-200, XD1, XD12 devices) containing a 2.5 Hz operating voltage generator, zero sequence current transformers installed on the network lines, and blocks for determining, monitoring and indicating the insulation resistance of individual sections of the network with isolated neutral. The disadvantage of this device is the absence of protective shutdown circuits of the controlled network section while reducing its insulation resistance below an acceptable level.

A device is known for protection against a single-phase earth fault in a network with isolated neutral (patent RU 2089031, IPC H02H 3/16, 08/27/1997) containing zero-sequence current transformers, rectifiers, memory and integrating elements, closing keys, and threshold switches elements, executive bodies, starting element, zero sequence voltage transformer, control unit, short-pulse shaper and OR elements. The disadvantage of the device lies in its complexity and, as a consequence, in low reliability, as well as in the absence of elements to indicate network status.

Closest to the proposed device is a selective control of insulation resistance (A.S. SU 1786449 A1, IPC G01R 27/18, 01/07/1993), containing a non-industrial frequency current source, current sensors, amplifiers, phase-sensitive organs, zero-sequence voltage filter, threshold unit, insulation resistance indicator, unit for highlighting the highest voltage and block for indicating the line number with reduced insulation resistance. The disadvantage of this device is the absence of circuits for protective disconnection of network branches when they are shorted to ground.

The proposed device, along with monitoring the insulation resistance of emergency and pre-emergency network lines, also provides a protective shutdown of emergency lines with an indication of their number, which increases the safety of operation of the network and the troubleshooting.

The drawing shows a functional diagram of a device for selective monitoring and protection against earth faults in a network with isolated neutral.

The device contains a source of 1 current non-industrial frequency, one

from the outputs of which is connected to the neutral of the controlled network, and the other is connected to the ground. Zero-sequence current transformers 5, 6, 7 are installed on lines 2, 3, 4, connected through selective amplifiers 8, 9, 10 with one input of phase-sensitive blocks 11, 12, 13, the other inputs of which are connected to the output of the zero-sequence voltage filter 14, and the outputs to the inputs of the block 15 allocation of the highest voltage. The inputs of the insulation resistance indicator 17 and the threshold unit 18 are connected to one output 16 of the block 15, and the inputs of the transistor switches 22, 23, 24 are connected to the other outputs 19, 20, 21, and the LEDs 26 are connected between the collectors and the power bus 25 through the limiting resistors 27, 28 indicate the line number of the network with reduced insulation resistance.

The device is equipped with second transistor switches 29, 30, 31, connected in series with the first switches 22, 23, 24. The outputs of block 18 are connected to the inputs of the switches 29, 30, 31, and are connected respectively between the key collectors 29, 30, 31 and the power bus 25 through the limiting resistors, LEDs 32, 33, 34 indicate the number of the disconnected line 2, 3, 4; reverse diodes 35, 36, 37 and connected in series with the buttons 38, 39, 40 to open the windings of the contactors 41, 42, 43. The main opening contacts 44, 45, 46 of the contactors 41, 42, 43 are connected to the input of the corresponding lines 2, 3, 4 networks, and auxiliary closing contacts 47, 48, 49 between the key collectors 29, 30, 31 and the common bus 50.

Block 15 is made in the form of operational rectifiers 51, 52, 53, the inputs of which are connected to the inputs of block 15, the outputs 54, 55, 56 are combined and connected to the output 16 of block 15, and the outputs 57, 58, 59 are connected to the outputs 19, 20, 21 blocks 15.

A device for selective monitoring and protection against earth faults in a network with isolated neutral operates as follows.

The imposed current from source 1, spreading along lines 2, 3, 4 and, closing through the corresponding resistance and insulation capacitance to the ground, acts on the zero sequence current transformers 5, 6, 7. Amplified by selective amplifiers 8, 9,10, the output voltages of transformers 5, 6, 7 go to the first inputs of blocks 11, 12, 13, to the second inputs of which a reference voltage is applied from the output of the filter 14. Blocks 11, 12, 13 convert the input variable voltages to constant positive voltages, the value of which is proportional to the leakage currents through the insulation resistance of the corresponding lines 2, 3, 4 of the controlled network. In block 15, at the combined outputs 54, 55, 56, the highest input voltage is allocated, for example, from block 11, which corresponds to the maximum active leakage current in line 2. This voltage is supplied to indicator 17, which displays the value of insulation resistance (the reciprocal of the leakage current), and block 18, controlling its permissible value. At the same time, negative voltage appears at the output 57 of the rectifier 51, and positive voltages appear at the outputs 58, 59 of the rectifiers 52, 53, under the influence of which the transistor 22 opens and the transistors 23, 24 are closed. At the same time, the LED 26 lights up, signaling that line 2 has a low insulation resistance. When the insulation resistance in line 2 decreases below the permissible level, block 18 is triggered by the output voltage of which transistor 29 opens. As a result, both transistors connected in series Lines 22 and 29 are open and a low potential appears on the collector of transistor 29, causing the contactor 41 to trip. Using the opening contacts 44 of the contactor 41, the faulty line 2 is disconnected, and using the making contact 47, the contactor 41 is self-locking. The diode 35 protects the transistor 29 from the counter-electromotive force in the coil of the contactor 41. At the same time, the LED 32 lights up, signaling the disconnection of line 2. After disconnecting the line 2, the voltage at the output of block 11 drops to zero, the voltage at the output 19 of block 15 becomes positive, the transistor 22 closes, and LED 26 goes off. Block 15 selects a voltage corresponding to one of the disconnected lines 3, 4 with a minimum insulation resistance. The indicator 17 displays the value of the insulation resistance of this line, and the LED 27 or 28 its number. Block 18 controls the magnitude of the leakage current and, if it exceeds the permissible value, is triggered by acting through the transistor 30 or 31 on the contactor 42 or 43 and causing the next faulty line 3 or 4 to turn off. In this case, the LED 27 or 28 goes out and the LED 33 or 34.

The number of device-controlled lines of a branched electric network is practically unlimited. The device provides maintenance personnel with information about the numbers of disconnected lines, about the line number with the lowest value of insulation resistance (pre-emergency line) and about its specific value.

The buttons 38, 39, 40 contained in the device allow you to briefly open the winding circuits of the contactors 41, 42, 43 of one or another faulty (disconnected) line 2, 3, 4. At the same time, the faulty line is forcibly connected to the network, and the resistance value is displayed on indicator 17 isolation in the emergency line, knowledge of which is necessary before and during the troubleshooting process. After completing the repair, pressing the corresponding button 38, 39, 40 again removes the self-locking contactor 41, 42, 43 and the repaired line 2, 3, 4 is constantly connected to the network.

Thus, the proposed device provides increased security for the operation of the network due to the automatic shutdown of the damaged section of the network, high information content and versatility of use.

Claims (1)

A device for selective monitoring and protection against earth faults in an isolated neutral network, containing a non-industrial frequency current source, one of the outputs of which is connected to the neutral of the controlled network, the other is connected to ground, zero sequence current transformers installed on the network lines and connected through selective amplifiers with some inputs of phase-sensitive blocks, the other inputs of which are connected to the output of the zero-sequence voltage filter, and the outputs are connected to the inputs of the selection block voltage, with one output of which the inputs of the insulation resistance indicator and the threshold block are connected, with the other outputs are the inputs of transistor switches, between the collectors of which and the power bus there are LEDs for indicating the line number with low insulation resistance, characterized in that it is equipped with second transistor switches connected in series with the first and to the inputs of which the output of the threshold block is connected, and between the collector of each key and the power bus, respectively, the LED pa off line network, and a reverse diode connected in series with a button for opening the contactor coil, the major break contacts which are included in the respective input line network, and the auxiliary normally open contact - between the collector and the common bus key.