Current Status and Progress of Preventive Tests for Power Equipment



Preventive tests are an important part of the operation and maintenance of power equipment, and are one of the effective means to ensure the safe operation of power equipment. Over the years, high-voltage power equipment in power departments and large industrial and mining enterprises has basically been tested according to the requirements of the "Regulations for Preventive Tests of Power Equipment" (hereinafter referred to as the "Regulations") issued by the former Ministry of Electric Power, which has played a significant role in promptly detecting and diagnosing equipment defects.



　　In 1996, the former Ministry of Electric Power revised the "Regulations". The revised electric power industry standard DL/T 596—1996 "Regulations for Preventive Tests of Power Equipment" was officially issued and implemented in 1997.



　　Revision History of the "Regulations"



　　Since the 1950s, the "Regulations" have undergone a total of 5 revisions over the past 40 years, and the technology is relatively mature. The first two versions were relatively "Sovietized" in content and format, while the 1985 and 1996 versions gradually became "Sinicized".



　　The "Regulations" cover a wide range of content, and in fact, some content goes beyond the scope of preventive tests, belonging to the category of operation and maintenance in nature. Therefore, some people have suggested changing the name to "Regulations for Maintenance Tests of Power Equipment". The term "maintenance" here includes preventive maintenance, predictive maintenance, and defect-eliminating maintenance, which is more consistent with the actual content of the "Regulations". However, considering that the common understanding of "maintenance" is relatively narrow, and "preventive tests" has been used for a long time, the old name was finally retained.



　　Summary of the "Regulations" Content



　　The "Regulations" specify the test items, test cycles, and technical requirements for various commonly used power equipment in chapters. These test items integrate modern basic diagnostic technologies. By specialty, they belong to the technical fields of electrical, chemical, and mechanical, with most being electrical test items.



　　By the nature of the tests, the test items can be divided into 4 categories.



　　1. Periodic tests: These are preventive tests. They are conducted at regular intervals to promptly detect potential defects or hidden dangers in equipment. Examples include dissolved gas analysis in oil, winding DC resistance, insulation resistance, dielectric loss factor, DC leakage, DC withstand voltage, AC withstand voltage, and insulating oil tests.



　　2. Overhaul tests: These are inspection test items performed during or after major overhauls. In addition to periodic test items, they also include: through-bolt insulation resistance, partial discharge, oil tank sealing test, circuit breaker opening and closing time and speed, motor air gap, etc. Some of these are purely mechanical inspection items.



　　3. Fault diagnosis tests: These are tests conducted when periodic or overhaul tests reveal questionable or abnormal results, requiring further investigation to identify the fault or determine its location. These are also called diagnostic tests. They are only performed "when necessary". Examples include: no-load current, short-circuit impedance, winding frequency response, vibration, moisture content in insulating oil and oil dielectric loss, pressure relief device, and power frequency reference voltage test for zinc oxide arresters.



　　4. Predictive tests: These are tests conducted to assess the insulation life of equipment, to determine whether the insulation of the tested equipment can continue to be used for a period of time, or whether replacement needs to be scheduled in the near future. Examples include: insulation aging assessment of generator or condenser stator windings, polymerization degree of transformer insulating paper (board), and furfural content in oil.



　　From the above, it can be seen that many test items listed in the "Regulations" indeed go beyond the scope of regular periodic preventive tests.



　　Origin of Test Items, Cycles, and Technical Requirements



　　The test items and test cycles for various types of equipment (such as transformers, capacitors, SF6 switchgear, support insulators, etc.) are determined based on the reliability and safety of equipment operation, and whether to add, remove, or modify them is decided accordingly.



　　The sources and bases of technical requirements can generally be summarized into two categories:



　　1. The AC withstand voltage test voltage standard is formulated based on the insulation coordination design of the power system;



　　2. Many technical requirements are determined through the accumulation of test experience, statistical analysis, and years of practice, gradually modified and improved (such as technical requirements for dielectric loss, leakage current, absorption ratio, etc.).



　　Analysis and Judgment of Test Results



　　The "Regulations" emphasize that comprehensive analysis and judgment should be conducted on test results. That is to say,