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The Necessity of On-site Verification of SF6 Density Relay

SF6 gas has excellent insulation performance, arc extinction performance, and stable chemical properties, and is widely used in power systems, especially in various high-voltage switchgear. Due to on-site operations, the rubber seals of SF6 gas density relays located on outdoor high-voltage switchgear are subject to varying degrees of damage due to the impact of climate changes throughout the year, and the density relays may have poor contact due to infrequent operation. From the perspective of actual operation, it is very necessary to regularly inspect the operating SF6 density relays and pressure gauges.

SF6 gas density relay field validation method

Key inspection items of SF6 gas density relay

  • Alarm (supplemental gas) initiation pressure value.

  • Alarm (supplemental gas) return pressure value.

  • Lockout initiation pressure value.

  • Lockout return pressure value.

  • When the SF6 gas density relay is equipped with a pressure gauge, the displayed value of the pressure gauge should be checked.

Detection method of density relay calibrator

Currently, the calibration of density relays is primarily performed using a density relay calibrator for testing.

The density relay calibrator is used to verify density relays. The testing principle involves an MCU (Microcontroller Unit) automatically converting the temperature and contact action values of the density relay into corresponding equivalent pressure values at 20°C, thus achieving the detection of the density relay. During the testing process, the valve switch is closed to isolate it from the main gas chamber. The calibration gas port is connected to the density relay calibrator through a hose, and the instrument automatically completes the relay calibration.

Issues in the Inspection and Verification of SF6 Gas Density Relays

  • Disassembling and assembling density relays may damage the original gas circuit sealing, making it difficult to ensure the original sealing performance.

  • Newly installed density relays have undergone long-distance transportation and vibrations, which may affect their accuracy and stability.

  • On-site installation and maintenance time are usually tight, and it takes a long time to remove them from the equipment and send them to the laboratory for examination.

Based on our practical experience, inspecting SF6 gas density relays and pressure gauges on-site generally yields good results.

Precautions for On-Site Verification of SF6 Gas Density Relays

  • Safety measures must be taken, and corresponding inspection and operation procedures should be established.

  • The inspection work should typically be conducted after the equipment is powered off. Before the inspection, the DC power supply connected to the density relay must be disconnected, and the corresponding connection lines for alarm and locking contacts must be disconnected to prevent them from connecting with secondary circuits and sampling signal lines, affecting the inspection loop, and ensure that other equipment's normal operation is not affected.

  • Pay attention to protecting the sealing surface of the tube joint, replace the sealing gasket after calibration, and use a leak detector for airtightness testing.

  • Pay attention to cleaning the tube joints before and after calibration to prevent impurities and unqualified gas from entering the main body. If necessary, rinse with a small amount of qualified SF6 gas.

  • Pay attention to the connection between the equipment body and the SF6 gas density relay. After calibration, it must be restored and confirmed by reinspection.

  • Perform SF6 gas recovery. During the operation of electrical equipment, SF6 gas can decompose into various toxic and corrosive gases and solid decomposition products, which not only affects the electrical performance of the equipment but also endangers the safety of operators and maintenance personnel.

SF6 circuit breakers are vital protection and control elements in power systems, and SF6 gas density relays are essential components to ensure the safe operation of SF6 electrical equipment. Their performance directly affects the safe operation of electrical equipment. Therefore, regular testing of their reliability and accuracy is crucial. The inspection cycle, items, and requirements for density relay inspection should comply with relevant regulations and standards. Years of practical experience have shown that inspection work should be based on the actual conditions of the equipment, comply with relevant safety regulations, establish practical methods and procedures, and pay attention to relevant matters to ensure equipment safety and the correctness of inspection work.

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Lanso Instruments INC.
233 W 1st St #210, North Vancouver, Canada
233 W 1st St #210, North Vancouver, Canada