Introduction to the Work Cycle of SF6 Density Relay Calibration

SF6 Relay includes the functions of pressure indication display and contact signal action. It is an important component for monitoring the gas insulation strength inside the SF6 electrical equipment at all times. This article combines the latest requirements of State Grid Corporation to discuss the verification work content and verification cycle, and finally classifies the verification work and proposes a new verification approach forSF6 Density Relay.

Introduction to SF6 Relay Verification Work

It should be noted that the calibration of SF6 relay imposes specific requirements on the calibration instrument and the main equipment. Firstly, the equipment with the SF6 relay to be calibrated must be in a power-off state (except for non-removable ones). Secondly, the equipment should meet the conditions for calibrating SF6 density relays, such as having stop valves and check valves in the pipelines and the ability to isolate the calibrated meter from the main equipment's gas circuit. As for the calibration instrument used, it is required to be an SF6 density relay calibrator that has passed inspection and has a measurement accuracy of no less than 0.4 class.

Performing this work on operational equipment carries risks such as SF6 gas leakage (which may occur during on-site calibration and the removal and installation of meters, leading to damage to the original seals), incorrect restoration of relay secondary wiring (which may result in restoration errors when removing and installing signal lines), and omission risks during site restoration (where forgetting to restore stop valves to their normal working state is possible). Based on this analysis, it is of great significance to reasonably arrange the calibration period for density relays in electrical equipment that meets the calibration conditions, and measures should be taken in a timely manner to rectify electrical equipment that does not meet the calibration conditions.

The Calibration Period for SF6 Relay

In the "Five Unifications and One Measure" management regulations of State Grid Corporation of China, various requirements for the calibration of SF6  relays are proposed based on different aspects as the latitude and different categories of equipment as the longitude. Whether the design and manufacturing meet the requirements for density relay calibration, whether strict inspections are carried out during handover and rectification of problems, whether changes in chamber pressure are noted during substation operation and maintenance inspections, and whether measures for maintenance and defect elimination are comprehensive, all determine whether the calibration of density relays needs to be conducted, whether the necessary conditions are met, and whether the process goes smoothly.

The "Management Regulations for Substation Testing of State Grid Corporation of China" provides detailed specifications on the testing items, periodicity, and standards for different equipment. The testing items, categories, periodicity, and standard forms for gas density meters (relays) are specified in the categories of SF6 circuit breakers, combination appliances, current transformers, electromagnetic voltage transformers, and bushings. Table 1 shows the calibration standards for density relays in combination appliances and SF6 circuit breakers.

Table 1 Calibration requirements for SF6 relay