Development of Circuit Breaker Partial Discharge Test System

Abstract: The traditional partial discharge detection method is difficult to be applied to live detection on site due to its low detection signal frequency, susceptibility to external interference, and power failure. Based on the site conditions, a set of partial discharge testing and data management system was developed to provide an accurate and effective detection method for the operating conditions of live equipment. The partial discharge detection experiment shows the practicability of the system, which greatly improves the automation level of circuit breaker testing and management.

  1 Introduction

Circuit breakers play an important role in cutting off the fault current in the power system. The large number of applications of circuit breakers with sulfur hexafluoride (SF6) gas as the insulating medium in the power system has greatly improved the reliability of the power system. However, due to the harsh operating environment and the change of operating time, SF6 circuit breakers will inevitably have the problem of insulation degradation characterized by partial discharge. On-line partial discharge monitoring of circuit breakers is an important technical guarantee. The ultra-high frequency (UHF) method that has emerged in recent years has been widely used in partial discharge monitoring due to its strong anti-interference ability and high sensitivity. The United Kingdom, Germany and many European countries have adopted ultra-high frequency (UHF) detection methods for partial discharge. In the newly revised IEC60270 and IEC60517 standards in 2000, this method has been used as the main method for partial discharge detection of circuit breakers and GIS equipment. one. Based on the partial discharge monitoring system of electrical equipment based on the ultra-high frequency method, this paper conducts on-site live monitoring of SF6 circuit breakers, and uses DELPHI and SQLserver2000 to develop data analysis and management software to realize the effective management of partial discharge data.

2. Partial discharge characteristics of electrical equipment

The spectral characteristics of electromagnetic waves produced by partial discharge are related to the geometry of the discharge source and the dielectric strength of the discharge gap. The pulse current waveform generated by SF6 gas or insulating oil has nanosecond pulse steepness, and the pulse duration is between 1ns and 100ns, so it can generate a large number of ultra-high frequency electromagnetic wave signals with frequencies above 300MHz.

The UHF detection technology is to receive ultra-high frequency (UHF) electromagnetic pulse signals generated by partial discharges in a wide frequency band of 300MHz~1500MHz. Because the UHF signal attenuates quickly when it propagates, the UHF electromagnetic interference signal outside the device under test (such as corona discharge in the air) not only has a narrower frequency band than the partial discharge signal inside the device, but its intensity will also decrease rapidly as the frequency increases. The UHF component that reaches the vicinity or inside of the device under test is relatively small, so that most of the air discharge pulse interference can be avoided.

3. UHF partial discharge test system composition

The computer is connected with the GPIB interface of the oscilloscope, and the collected data can be received according to the communication protocol for further comprehensive analysis and management. The functional block diagram of the software system is shown in Figure 2.



The entire system function can be divided into two parts:

(1) Data comprehensive analysis function: including collected data preprocessing, discharge location determination, discharge feature extraction and discharge result analysis, etc.

(2) Data management function: including analysis result storage, modification, query and deletion, etc., and data (including images) can be output in the form of reports and Excel, and the path of the output file is set by the user.

The system is built under the Chinese Windows operating platform, with friendly human-computer interaction interface, the main program uses D e l p h i visual programming, and the back-end relational database selects S Q LServer2000.

4. Breaker partial discharge test and analysis management

4.1 Field test

was tested on the spot, as shown in Figure 2:



4.2 Characteristics of Partial Discharge

It was found during the test that the measured signal patterns are basically the same, and have the following characteristics:



After operating the oscilloscope, it is initially determined that there is a discharge signal. After the test is completed, the GPIB communication card communicates and actively transmits it to the computer. The computer software further processes and manages the data.

4.3 Discharge type analysis

Ultra-high frequency test found that there is an obvious discharge signal. Through software processing, it is found that the amplitude is 2.27mV, which is converted into a discharge signal of about 2308pC. The discharge is obviously distributed in the first and third quadrants. The data in the third quadrant is obviously larger. The analysis considers it to be a discharge. As shown in Figure 5 and Figure 6.





UHF tests found that there are obvious discharge signals at 144 places, with an amplitude of 0.7mV, which is converted into a discharge signal of about 700pC. The discharge is obviously distributed in the 1, 3 quadrants, and the data in the 3 quadrants is obviously larger. After software analysis, it is considered to be a discharge, as shown in Figure 6.

Through on-site analysis, the tester believes that there is an obvious discharge signal on the GIS side near the 101Ⅱ bus, which is analyzed as a discharge, and it is recommended to deal with it as soon as possible.

4.4 Analysis results and suggestions

When the test voltage reaches 53kV, the partial discharge phenomenon reappears. When the test voltage reaches 64kV, the partial discharge signal amplitude is greater than 200pC. When the voltage reaches 48kV, the partial discharge phenomenon reappears. When the test voltage reaches 64kV, the partial discharge signal The amplitude is greater than 300pC, so it is recommended to perform power outage maintenance on this part.

4.5 Realization of data management

Using SQL SERVER to manage analysis results, manage various information databases of high-voltage circuit breakers in the database, and add data analysis and statistics functions in addition to basic operations, and output functions in the form of reports and Excel tables.

(1) The construction of the database

Database design is a system design. The database is composed of data tables. The main data tables are as follows:

1) Basic information data sheet of circuit breaker

Record the basic information of high-voltage circuit breakers. The structure and main fields of the table are: circuit breaker number, type, manufacturer, model, voltage level, delivery time and commissioning time. The field types are unified during software development. For example, the circuit breaker number format is specified as "FH-0001", and various time formats are set to the standard format of "year-month-day", such as "2010-02-03", This not only reduces the workload of the operator but also unifies the format, facilitating data comparison.

2) Circuit breaker information data sheet

Every time a running circuit breaker is monitored, a large amount of information must be entered into the data table, and the "circuit breaker number" is set as the main key. The data fields include the original data analysis results, main spectrum content, discharge type, and processing. Suggest. In addition, the test date, tester, and weather conditions are added to the data table fields. The primary key establishes its connection with the "Breaker Basic Information Data Sheet" to realize the joint management of the data sheet.

(2) Database operation

The operation of the database mainly includes operations such as connection with the database, information entry, modification, and query. Delphi uses the ADO method to operate the database, which mainly involves three categories of data sets, data sources and data-aware controls.

You can directly call the corresponding "methods" of the ADOQuery or ADOTable components, and you can also write the SQL query commands of the ADOQuery components. The system sets 5 query options in the historical data query interface: substation name, circuit breaker type, tester, test time period . Execute the SQL query statements of these query conditions in the program, and then display the results of the comprehensive query to the DBgrid data component to obtain the query results of the data.

(3) Database security

The data export function can be used for the security mechanism of the management system. The system is equipped with a user management authority module. The user authority used by the system is divided into: administrator, operator and public user. The public user authority has only the authority to view and print out; the operator carries out the maintenance of the circuit breaker data and the input operation of the test data; the administrator has the authority to perform all operations. The user table structure is: user name, password, and authority level. All modules are organically combined by the back-end database to realize data management.

  5 Conclusion

UHF partial discharge measurement technology makes up for the shortcomings of the current GIS equipment preventive test methods, making the partial discharge detection of circuit breakers more convenient and quick. Combining the actual situation of the substation and the existing test equipment, a set of circuit breaker partial discharge data analysis and management system was developed, and by using ultra-high frequency to detect the live partial discharge of SF6 circuit breakers, it proved that the entire test system meets the needs of the test site , Which greatly improves the efficiency of the circuit breaker partial discharge test and data management. (Author: Qian Shaofeng, Wang Wen)