RU2737349C1 - Insulation control system for electric circuits with blind-earthed neutral - Google Patents

Abstract

FIELD: electric power engineering.

SUBSTANCE: invention relates to electric power engineering and is intended for operational ponied control of insulation resistance of cable lines under operating voltage in three-phase networks with blind-earthed neutral. System comprises, on each branch of a controlled three-phase network connected to a corresponding user, current sensors, as well as a unit for indication of normal and emergency conditions of insulation of electric networks with a blind-earthed neutral, which determines an emergency state of insulation resistance when it decreases below the permissible level. Current sensors installed at each branch of controlled three-phase network consist of transducer-converter of differential leakage current, installed on four-wire cable, and sensor-converter of differential leakage current installed on PE-conductor. Each of the transducer transducers consists of a shielded housing in which there is a conversion and transmission module in the form of an analogue-to-digital converter and through hole for branching of controlled three-phase network of transducer differential leakage current converter, installed on four-wire cable, enveloped by Rogowski coil, which is connected to input of corresponding conversion module in form of analogue-to-digital converters, and transducer-transducer of differential leakage current, installed on PE-conductor, enveloped by Rogowski coil, which is connected to input of corresponding module of conversion and transmission of signals in form of analogue-to-digital converter. Modules of conversion and transmission of signals are connected in series and connected to unit for indication of normal and emergency conditions of insulation resistance, made in form of digital data processing unit.

EFFECT: high reliability, validity, efficiency and accuracy of control.

1 cl, 3 tbl, 7 dwg

Description

The invention relates to the electric power industry and is intended for operational per-feeder monitoring of the insulation resistance of cable lines under operating voltage in three-phase networks with a dead-grounded neutral. It can be used to create devices for feeder (selective) control and measurement of the insulation resistance of alternating current networks with a solidly grounded neutral.

In networks with a solidly grounded neutral, in case of short-circuits to the frame (ground) through a certain transition resistance, automatic shutdown based on the use of overcurrent protection will not work. This mode is extremely dangerous, since the flow of even small currents in fractions of an ampere in insulation defects localized in the volume leads to insulation pyrolysis and, ultimately, to fire.

With an increase in the total length of the cable network of the power supply system, the conditions for electrical and fire safety deteriorate, and the reliability of power supply to consumers also decreases.

In this regard, there is a task to improve the accuracy, efficiency and reliability of monitoring the insulation resistance of AC networks with a dead-grounded neutral.

There is a known device [RU 2092862, C1, G01R 27/08, 10.10.1997] containing a zero sequence current transformer, the primary windings of which are connected on one side to a current source, and on the other to a controlled network, as well as a device for measuring electrical power , the voltage winding of which is connected to the phase of the current source and as it contains a milliwattmeter, the tone winding of which is connected to the secondary winding of the zero sequence current transformer, and a switching device, the contact of which is connected parallel to one of the phase contacts of the input power switching device of the controlled network.

The disadvantage of this device is the relatively low accuracy and reliability of control.

The closest in technical essence to the proposed one is a device for monitoring insulation resistance and leakage current in electrical installations [RU 2229764, C1, H2H 3/16, 05/27/2004], containing a network generator with a measuring circuit, an actuator, an actuator connected in series with the load , and indication of normal and emergency states, moreover, the measuring circuit is made in the form of a zero sequence current sensor, the output of which is connected to the input of the first rectifier, the positive output of which is connected to one terminal of the capacitive filter in the form of a capacitor and the thyristor control electrode, the negative output of the first rectifier is with another output of the capacitive filter, with the cathode of the said thyristor and the negative output of the second rectifier, the positive output of which is connected to the anode of the thyristor, the input of the second rectifier is connected in parallel with the first indicator of the normal and emergency state indication unit connected to the second indicator atator, the other terminal of which is connected to the neutral wire, parallel to the first indicator, two closing contacts of the first and second relays included in the actuator are connected, the winding of the first relay through a diode is connected by one terminal to a parallel connected capacitor, the other through the first limiting resistor - to one of the phases after the contact of the magnetic starter, connected in series with the machine, forming the actuator, a reset button is connected to the connection point of the diode anode and the parallel-connected closing contacts of the first and second relays, the other output of which is connected to the network phase between the contacts of the machine and the magnetic starter, winding of the second relay is connected by one terminal to the junction point of the closing contacts of the first and second relays and the first and second indicators, the other to the neutral wire, between the neutral wire and the mentioned phase wire, a second limiting resistor and a test control activation button are connected in series , the winding of the magnetic starter is connected to the line voltage between the contacts of the machine and the starter through the second opening contact of the second relay.

The disadvantage of the closest technical solution is the relatively narrow functionality, since it lacks the ability to control the insulation in the PE conductor. In addition, the closest technical solution has a relatively low efficiency, since when determining the insulation resistance, it is necessary to make an additional connection to each of the phases of the load resistance and then determine the insulation resistance according to the results of measurements of the artificially created asymmetry in each of the phases. This leads to a decrease in the accuracy and reliability of control, as well as to an unjustified complication of the device. All this leads to a decrease in the arsenal of technical means that can be used to control the insulation resistance of electrical networks with a dead-grounded neutral.

The objective of the invention is the task of creating a modern system for monitoring the insulation resistance of electrical networks with a solidly grounded neutral, which is made on a modern digital element base and has simplicity, reliability, reliability, efficiency and control accuracy.

The required technical result is to increase the reliability, reliability, efficiency and accuracy of control.

The problem is solved, and the required technical result is achieved by the fact that, in a system containing installed on each branch of the monitored three-phase network connected to the corresponding consumer, current sensors, as well as an indication unit for normal and emergency states of the insulation resistance of electrical networks with a solidly grounded neutral, determining the emergency state of the insulation resistance when it drops below the permissible level, according to the invention, the current sensors installed on each branch of the monitored three-phase network consist of a differential leakage current transducer installed on a four-wire cable and a differential leakage current transducer installed on PE-conductor, and each of the transducers consists of a shielded housing, in which a module for converting and transmitting signals in the form of an analog-to-digital converter is installed and a through hole is made for branching I monitored three-phase network of a differential leakage current transducer installed on a four-wire cable, covered by a Rogowski coil, which is connected to the input of the corresponding signal conversion and transmission module in the form of an analog-to-digital converter, and a differential leakage current transducer installed on the PE conductor , covered by the Rogowski coil, which is connected to the input of the corresponding module for converting and transmitting signals in the form of an analog-to-digital converter, while the modules for converting and transmitting signals in the form of analog-to-digital converters are connected in series and connected to the unit for indicating normal and emergency conditions of insulation resistance electrical networks with a solidly grounded neutral, made in the form of a digital data processing unit.

The claimed technical solution is shown in the drawing:

in fig. 1 - functional diagram of the system for monitoring the insulation resistance of electrical networks with a solidly grounded neutral (an example of a four-wire cable without a grounding PE conductor);

in fig. 2 - functional diagram of the system for monitoring the insulation resistance of electrical networks with a solidly grounded neutral (an example of a five-wire cable with a grounding PE-conductor);

in fig. 3 - functional diagram of the system for monitoring the insulation resistance of electrical networks with a dead-grounded neutral (an example of a five-wire cable with a grounding PE-conductor);

in fig. 4 - photo of the unit for indicating normal and emergency conditions, made in the form of a digital data processing unit;

in fig. 5 - design of the body of the unit for indicating normal and emergency states, made in the form of a digital data processing unit;

in fig. 6 - design of the differential leakage current transducer (6a - with Rogowski coil, 6b - with enlarged Rogowski coil, 6c with Rogowski coil for PE conductor);

in fig. 7 is a photo of differential leakage current transducers (shown in FIG. 6).

The drawing indicates:

1 - three-phase network with a dead-grounded neutral;

2 - differential leakage current transducer mounted on a four-wire cable;

3 - current consumers;

4 - unit of indication of normal and emergency conditions, made in the form of a digital data processing unit;

5 - dispatcher's workplace;

6 - differential leakage current transducer mounted on the PE conductor.

The system for monitoring the insulation resistance of electrical networks with a dead-grounded neutral works as follows.

The developed system for monitoring the insulation resistance of electrical networks with a solid-grounded neutral is designed to monitor the state of insulation in cable distribution networks with a solid-grounded neutral up to 1000 V in order to predict, plan preventive measures and repair work to prevent insulation breakdowns and ground faults.

The system for monitoring the insulation resistance of electrical networks with a dead-grounded neutral contains current sensors installed on each branch of the monitored three-phase network 1, installed on each branch of the monitored three-phase network, which consist of a differential leakage current transducer 2 installed on a four-wire cable and a transducer 6 differential leakage current installed on the PE conductor.

The system for monitoring the insulation resistance of electrical networks with a solidly grounded neutral also contains a block 4 for indicating the normal and emergency states of the insulation resistance of electrical networks with a solidly grounded neutral, made in the form of a digital data processing unit, which determines the emergency state of the insulation resistance when it drops below the permissible level.

In addition, in the insulation resistance monitoring system of electrical networks with a solid-grounded neutral, current sensors installed on each branch of the monitored three-phase network consist of a differential leakage current transducer 2 installed on a four-wire cable and a differential leakage current transducer 6 installed on PE conductor, and each of the transducers consists of a shielded housing in which a signal conversion and transmission module is installed in the form of an analog-to-digital converter and a through hole is made for branching the monitored three-phase network of the differential leakage current transducer installed on a four-wire cable , covered by a Rogowski coil, which is connected to the input of the corresponding signal conversion and transmission module in the form of an analog-to-digital converter, and a differential leakage current transducer installed on the PE conductor , covered by the Rogowski coil, which is connected to the input of the corresponding module for converting and transmitting signals in the form of an analog-to-digital converter, while the modules for converting and transmitting signals in the form of analog-to-digital converters are connected in series and connected to the unit 4 for indicating normal and emergency states of resistance insulation of electrical networks with a solidly grounded neutral, made in the form of a digital data processing unit.

Block 4 of digital data processing consists of a case, which contains a power supply unit with rectifier units for the main and reserve supply voltages and automatic input of a reserve, an anti-interference unit, display devices, a microcomputer, an interface unit with connectors for connecting transducers and for connecting to computer (computer) of the operator's workplace 5. On each branch of the monitored network 1, made with a five-wire cable with a PE-conductor, a differential leakage current transducer 2 installed on a four-wire cable and a differential leakage current transducer 6 installed on a PE grounding conductor are installed.

In the developed system, the Rogowski coil is used as the primary sensitive elements of the differential leakage current transducers. The Rogowski coil design is an air-core current transformer. The coil is wound on an air core of such a size that a bus with the measured current can be passed through its hole. To reduce stray capacitance, the turns should be wound at equal distances from each other and to one side. To exclude the influence of the turn created by the coil itself, its end is returned to the beginning, laying along the circumference of the toroid. Due to the fact that the output voltage is usually low, as a rule, the coil is shielded from electrical noise. In this case, the screen should not form a short-circuited loop. The coil leads must also be shielded, with one of the leads connected to the shield and grounded.

Since the measured currents are very small, it becomes difficult to transmit them due to high attenuation and low noise immunity. To solve these problems, an analog-to-digital converter is installed in the immediate vicinity of the Rogowski coil (in one housing), which converts the received analog signal into digital form and transmits it to the processing unit. Thus, the zero sequence current measured by the Rogowski coil and converted into digital form is transmitted to digital data processing practically without being affected by interference and without damping.

At present, prototypes of the system of per-feeder monitoring of the insulation state have been manufactured and passed state tests, the transducers of which are shown in Fig. 6 and FIG. 7.

A distinctive feature of the used current transducers is the low power of the output signal in comparison with voltage current transformers, the designs of which were formed quite a long time ago, therefore, the standard values of their output parameters were determined by the level of development and state of automation equipment in the middle of the 20th century. The high output power of the used transformers was justified, since they were powered by the automation and protection relays, measuring and recording instruments. Modern information and measurement systems (IMS) have at their inputs either signal processors with built-in analog-to-digital converters (ADCs), or separate ADCs, which do not require such powerful signals to obtain an acceptable signal-to-noise ratio, which led to the emergence and widespread adoption of low power current sensor concepts.

Structurally, the digital data processing unit is a structure consisting of the following main elements: anti-jamming units;

units of rectifiers of the main and reserve supply voltage;

automatic transfer of reserve (ATS);

block of interfaces;

devices for indicating measurement results.

The developed system performs the following functions:

• ranking of numbers of cable connections depending on the value of the leakage current;

• comparison of leakage currents with preset thresholds for generating warning messages and alarms.

• determination of numbers of cables with the worst insulation;

• creating a graph of signal changes in time;

• correction of alarm threshold values;

• archiving and visualization of information;

• comparative analysis of leakage currents, individual assignment of alarm thresholds, consideration of initial imbalances, the possibility of prompt reconfiguration;

• new differential current transducers provide high sensitivity, and various design options provide convenient and simple installation;

• the microcomputer implements an original algorithm for processing signals from 8, 16, 32 and more sensors, based on taking into account the peculiarities of a particular distribution network, which ensures high reliability in detecting developing insulation defects;

• monitoring the health of primary transducers;

• performing the necessary mathematical processing of parameter values;

• control of the reliability of parameters and serviceability of technical means of the lower level during the operation of the system, maintaining protocols and archives for errors, failures and other deviations from normal operating modes, as well as statistical information on the operation of equipment;

• formation and management of databases of accounting parameters, maintaining archives for solving problems: operational monitoring of the insulation state, calculating the predicted values of insulation resistance, generating screen forms for displaying reporting documents for billing periods, accumulating statistical information for analyzing and predicting the state of insulation, planning preventive measures, and repairs to improve the reliability of power supply;

• presentation and management of input and output of the necessary accounting information in the form of text, histograms, graphs, tables, etc. on the monitor screen;

• formation of printed documents of any form;

• the ability to connect additional tasks and processing accounting information.

The types of SCSI options developed by the applicant are presented in Table 1.

The main technical characteristics of the products are shown in Table 2.

Comparative characteristics of SCSI with other commercially available products "Astro * ISO-470" (LLC "Astro-UZO"), ISOMETER IRDH575 (Bender Russland) and HIS 500 (Hakel) are shown in Table 5.

The SCSI system works on the principle of zero sequence alternating current measurement, by converting the magnetic field created by three-phase currents in the monitored circuit into analog signals, which are converted into digital data. The implementation of such a system will allow to overcome a serious problem - the lack of existing technical means and methods for continuous monitoring of the state of insulation.

The system is open to the user and includes the necessary tools for maintenance, modernization and development. The tooling software has a convenient user interface and provides the generation of application software and the input of the necessary data in the form of a dialogue with the operator. The system allows you to process data using standard programs.

The use of a feeder-based insulation condition monitoring system as part of a software and hardware complex makes it possible to continuously monitor the insulation condition of all monitored connections, which is necessary to predict possible short circuits in the network with a sufficient time margin for operational measures.

The results of the tests carried out showed that the transducers have significant sensitivity compared to the current transformers used.

Implementation of the system of per-feeder monitoring of the insulation state will allow solving new, previously inaccessible tasks:

- monitoring the dynamics of changes in the state of insulation.

- to reduce the time spent by the electrical networks of the power supply system in emergency or pre-emergency state.

- to exclude emergency shutdown of consumers due to short circuits in the electrical networks of the SES caused by the aging of electrical insulation.

- the ability to control multiple objects (sections of the distribution network, responsible receivers of electricity).

- to ensure the efficiency of the search for the place of damage in the branched electrical networks of the SES.

Thus, the proposed system achieves the required technical result, which consists in increasing the reliability, reliability, efficiency and accuracy of control.

Claims (1)

The system for monitoring the insulation resistance of electrical networks with a solid-grounded neutral, containing current sensors installed on each branch of the monitored three-phase network connected to the corresponding consumer, as well as an indication unit for normal and emergency states of the insulation resistance of electrical networks with a solid-grounded neutral, which determines the emergency state of the resistance isolation when it drops below the permissible level, characterized in that the current sensors installed on each branch of the monitored three-phase network consist of a differential leakage current transducer installed on a four-wire cable and a differential leakage current transducer installed on a PE conductor , and each of the transducers consists of a shielded housing, in which a module for converting and transmitting signals in the form of an analog-to-digital converter is installed and a through hole is made for branching counter the monitored three-phase network by a differential leakage current transducer mounted on a four-wire cable covered by a Rogowski coil, which is connected to the input of the corresponding signal conversion and transmission module in the form of an analog-to-digital converter, and a differential leakage current transducer installed on the PE conductor, covered by a Rogowski coil, which is connected to the input of the corresponding module for converting and transmitting signals in the form of an analog-to-digital converter, while the signal conversion and transmission modules in the form of analog-to-digital converters are connected in series and connected to the unit for indicating normal and emergency states of insulation resistance of electrical networks with a deadly grounded neutral made in the form of a digital data processing unit.

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