What measures can be taken to prevent oxidation of high-voltage circuit breaker contacts?

2025-02-27

High-pressure circuit breakers operate very frequently and are often affected by mechanical and electrical factors, which can lead to refusal to trip. For circuit breakers already in operation, if a fault recurs on the load side of the circuit breaker, refusal to trip will inevitably cause cascading tripping, expanding the scope of accidents and power outages, so it should be eliminated as soon as possible. Measures to reduce contact resistance and prevent contact oxidation include: (1) Using materials with low resistivity and compressive strength to manufacture contacts. (2) Increasing the pressure between the contact surfaces using springs or spring pads. (3) Plating easily oxidizable copper, brass, and bronze contacts with a protective layer of tin, lead-tin alloy, or silver to prevent increased contact resistance due to oxidation. (4) Coating aluminum contacts with a neutral Vaseline oil layer to prevent oxidation. (5) Using welded copper-aluminum transition joints. (6) The structure of the breakable contacts allows for a certain degree of relative sliding between the moving and stationary contacts, which can wipe away the oxide layer during opening and closing (self-cleaning effect), reducing contact resistance. The DHL-100P intelligent loop resistance tester is developed by Dingsheng Electric Power based on the Ministry of Electric Power standard SD301-88 "Regulations for the handover and preventive testing of 500KV AC power equipment" and the new version of "Preventive testing regulations for power equipment", which stipulates that the DC current for measuring the contact resistance of circuit breakers and isolators should not be less than 100A to ensure accurate test results. The loop resistance tester adopts the latest switching power supply technology, which can continuously output large current for a long time, overcoming the shortcomings of instantaneous current of pulse power supply, and can effectively break through the oxide film of switch contacts to obtain good test results.

Reasons and handling methods for high-voltage circuit breaker refusal to trip

2025-02-27

High-pressure circuit breakers operate very frequently and are often affected by mechanical and electrical factors, resulting in frequent refusal to trip. For circuit breakers already in operation, if a fault recurs on the load side of the circuit breaker, a refusal to trip will inevitably cause cascading tripping, expanding the scope of accidents and power outages. Therefore, it should be eliminated as soon as possible. 1. Reasons for Circuit Breaker Refusal to Trip There are usually two reasons for a circuit breaker to refuse to trip: mechanical failure of the operating mechanism and electrical failure of the operating circuit. When a circuit breaker refuses to trip, the duty personnel should first determine whether the tripping circuit is intact based on the light indication. If the red light is not on, it indicates that the tripping circuit is not connected. At this time, check whether the operating fuse is blown or has poor contact, whether the contacts of the universal switching switch and the auxiliary contacts of the circuit breaker have poor contact, whether the coil of the anti-tripping relay is broken, whether the operating circuit is broken, whether the bulb and lamp are intact, etc. If the operating power supply is good, and the tripping core is weak, it indicates that the tripping coil operating voltage is too high, or the operating voltage is too low, the tripping core is stuck or detached, or the tripping coil itself is faulty. If the tripping core top rod transportation is good, and the circuit breaker still refuses to trip, it may be due to mechanism jamming or detachment of the transmission connecting rod pin. 2. Handling Methods for Circuit Breaker Refusal to Trip After identifying the cause of the refusal to trip, the duty personnel should remain calm and adopt different handling schemes according to the different nature of the fault. For example, during normal isolation operation, if the red signal light is not on, after confirming that the lamp is intact, the operating fuse should be quickly replaced and then the isolation operation should be performed. This should be done by two people, one remotely operating the switching switch and the other observing the isolation core movement on site, while paying attention to maintaining a safe distance. If the core movement is weak, it is core jamming; if the isolation core movement is normal, but the circuit breaker cannot be tripped, it indicates mechanical reverse jamming. At this time, the circuit breaker should be interrupted using the on-site mechanical isolation device. For air circuit breakers and SF6 circuit breakers, the air pressure must be normal before the mechanism can be interrupted. When it is necessary to perform isolation under emergency conditions, such as when the relay protection device operates or manual remote tripping fails, and may cause damage to the main equipment, the duty personnel should immediately manually open the upper-level circuit breaker, then go to the faulty circuit breaker and use the mechanical isolation device to interrupt the circuit breaker; if the mechanical isolation device cannot open the circuit breaker, the isolating switches on both sides of the faulty circuit breaker should be quickly disconnected, then the upper-level power supply should be restored, and the cause should be investigated before further processing; if time permits under accident conditions, the duty personnel should quickly run to the faulty circuit breaker and use the mechanical isolation device to open the circuit breaker; if the mechanical isolation device cannot be opened, the operating mode should be immediately switched, or the busbar circuit breaker or the upper-level circuit breaker should be used to open the circuit breaker, then the isolating switch should be used to isolate the faulty circuit breaker and restore the operating mode. Therefore, it is recommended to regularly use the DGK-S high-voltage switch dynamic characteristic tester to test the high-voltage circuit breaker to eliminate faults in a timely manner. The DGK-S high-voltage switch dynamic characteristic tester is a special high-voltage switch dynamic characteristic tester developed and produced by the Dingsheng Electric Research and Development Center to adapt to the dynamic characteristics of various indoor and outdoor low-oil, high-oil switches, vacuum switches, and sulfur hexafluoride switches. The internal processing of the DGK-S high-voltage switch dynamic characteristic tester uses a single-chip microcomputer as the core for sampling, processing, and output. Its main functional features are the use of Chinese prompts and graphic display in a human-computer dialogue mode, which is simple and fast, suitable for all models and voltage levels of SF6 switches, GIS combined electrical appliances, vacuum switches, and oil switches produced domestically and internationally. It meets the test conditions of live testing of bypass busbars in 500KV substations, accurately measuring time, speed, low voltage, and other functional parameters. The DGK-S high-voltage switch dynamic characteristic tester has many advantages such as intelligence, strong anti-interference ability, and high precision, and is widely favored by customers. However, it should be noted that because the circuit breaker itself is limited by the breaking capacity, it is forbidden to open it when any of the following faults occur, to avoid explosion accidents. (1) Oil circuit breaker without oil, severely lacking oil, or oil seriously carbonized. (2) When the insulating rod of a low-oil circuit breaker is broken. (3) When the gas circuit breaker pressure is too low and cannot be maintained. (4) When the hydraulic system of a circuit breaker using a hydraulic mechanism drops to zero. Once the above phenomena occur, the duty personnel should immediately remove the operating fuse of the circuit breaker, so that the circuit breaker cannot be opened remotely, and even if the circuit breaker is faulty, the protection device will not trip it. At the same time, the duty personnel should hang a "Do Not Operate" warning sign on the operating handle and the operating mechanism of the circuit breaker, and then handle it according to the following principles. (1) If a load circuit breaker fault occurs in the plant (factory) power supply, the load should be transferred according to the instructions of the director or dispatcher, then the busbar connected to the faulty circuit breaker should be de-energized, the circuit breaker should be opened, and then the operation of the upper-level circuit breaker should be restored. (2) If it is indeed a fault of the working power supply circuit breaker of a plant (factory) power supply, the backup power supply circuit breaker should be put into operation, the upper-level circuit breaker of the working power supply should be cut off, and then the faulty circuit breaker should be opened. (3) If a circuit breaker fault occurs and it is necessary to perform busbar switching, when using a busbar circuit breaker or bypass circuit breaker as a substitute, the relay protection specialist should be notified to adjust the setting, and then the relevant units should be notified to shut down for maintenance. When patrolling, if the duty personnel find the following abnormal phenomena, they should take decisive measures, first take measures to prevent the circuit breaker from automatically or remotely closing again, and then perform remote operation to quickly open the circuit breaker and de-energize it: (1) The circuit breaker bushing is cracked. (2) The circuit breaker catches fire. (3) A personal accident occurs that requires the circuit breaker to be opened immediately.

Key Technologies of Intelligent High-Voltage Switchgear

2025-02-27

High-voltage switchgear refers to indoor and outdoor AC switching equipment operating in power systems with voltages of 3kV and above and frequencies of 50Hz and below. It is mainly used for the control and protection of power systems (including power plants, substations, transmission and distribution lines, and industrial and mining enterprises), allowing for the switching of power equipment or lines in or out of operation according to grid operational needs, and quickly isolating faulty sections from the grid in case of equipment or line failures. This ensures the normal operation of the fault-free sections of the grid and the safety of equipment and maintenance personnel. Therefore, high-voltage switchgear is crucial transmission and distribution equipment, and its safe and reliable operation is of great significance to the safe and efficient operation of the power system.

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