Detailed Explanation Of The Principle And Usage Of High-voltage Disconnector In Substation

This article mainly talks about the basic principles and uses of vertical fuse switch disconnector, nhrt40 vertical fuse switch disconnector is used to isolate power supply, connect and disconnect circuits with small current, normal inspection of isolating switches, abnormal and accident handling methods and precautions of isolating switches.
1. Basic principles of isolating switches
Isolating switches do not have special arc extinguishing devices and cannot be used to cut off load current and short-circuit current, but they have electrodynamic stability and thermal stability, and will not automatically separate or burn contacts due to the passage of short-circuit current. Isolating switches should be used in conjunction with circuit breakers. They can only be operated after the circuit breaker is disconnected. It is driven by the operating mechanism to open and close the main switch. After opening, there is an obvious disconnection point.
2. Uses of high-voltage isolating switches
(1) Isolating power supply
Isolating switches can make the equipment that needs to be powered off have a clear disconnection point with the live parts. As the voltage increases, the insulation distance of the break increases as required, thereby ensuring the safety of the staff.
(2) Opening and closing parallel branches without impedance
1. Switch the equipment between one set of buses on the double busbar to the other set of buses.
2. When the circuit breaker is in the closed position, open and close the bypass knife switch in parallel with it.
(3) Connect and disconnect circuits with small currents
1. When the line is not grounded, open and close the no-load line with a capacitance current less than 5A
2. Open and close the no-load transformer with an excitation circuit not exceeding 2A
3. Open and close the voltage transformer and lightning arrester and the arc extinguishing coil and neutral grounding wire when there is no grounding fault in the system, and the principle and usage of high-voltage disconnectors in substations.
4. Open and close the load current below 10kV and within 15A and the circulating current below 10kV and within 70A
III. Technical requirements for disconnectors in operation
⑴ Disconnectors are allowed to operate for a long time at rated current and rated voltage. The temperature of the connector with the conductor should not exceed 70℃ during operation. Disconnectors do not have special arc extinguishing devices. Therefore, it is strictly forbidden to open and close with load.
⑵ Meet thermal stability requirements.
⑶ When the disconnector is in the disconnected position, there should be enough safety distance between the energized and power-off equipment.
4. Normal inspection of disconnector
⑴Whether the porcelain insulation is intact without cracks and discharge imagination.
⑵Whether the operating connecting rod and parts have open welding, deformation, rust, looseness, falling off, etc., and whether the nuts fastened by the connecting shaft pins are intact.
⑶Whether the locking device is intact, whether the pins are locked, whether the auxiliary contacts are in the correct position and in good contact, and whether the grounding of the mechanism housing is good.
⑷When the disconnector with a grounding knife is grounded, whether the three-phase grounding knife switch is in good contact.
⑸After the disconnector is closed, whether the two contacts are completely in the knife mouth, whether the contact between the contacts is good, and whether the temperature exceeds 70℃ under the rated current.
⑹After the disconnector passes the short-circuit current, check whether the insulator of the disconnector is damaged and has discharge marks, and whether the moving and static contacts and joints are melted. Principle and usage of high-voltage disconnectors in substations.
V. Abnormality and accident handling of disconnectors
1. The contact part of the disconnector on the busbar side is heated
When inspecting the equipment, the contact part of the disconnector can be judged by the hot air flow, heat or discoloration of the contact part, and whether the temperature of the contact part exceeds 70℃. The cause of the heat is usually the loosening of the compressed spring studs and surface oxidation. It should be handled separately according to different wiring methods.
① In the case of double busbar wiring: If the disconnector on the busbar side is heated, the circuit should be reversed to another set of busbars for operation, and then the heated disconnector should be pulled out.
When repairing the heated disconnector, the busbar should be shut down, and the circuit breaker of its circuit should also be shut down. The bypass circuit breaker can be used to operate it. If there is no bypass circuit breaker, the circuit should be shut down.
② In the case of single busbar wiring: If the disconnector on the busbar side is heated, the dispatcher should be reported to request load reduction. If there is a bypass circuit breaker, it should be used to operate it. If there is no bypass circuit breaker, it is best to shut down the line. If the load cannot be shut down and the load cannot be reduced due to load reasons, monitoring must be strengthened. When the heat reaches a relatively serious degree, the circuit breaker should be pulled open for accident handling.
When repairing the hot isolating switch, the busbar should be shut down, that is, all circuits on the busbar should be shut down, or the busbar should not be shut down, and the live operation method should be adopted.
2. The line isolating switch is hot
Its treatment method is the same as that of the single busbar isolating switch. The difference is that the isolating switch has a circuit breaker in series, which can prevent the development of accidents. Therefore, the isolating switch can continue to operate, but it needs to be monitored until it can be shut down for maintenance.
When repairing the isolating switch, its line should be shut down.
3. The porcelain bottle of the isolating switch is cracked or damaged
If the porcelain bottle of the isolating switch is cracked or damaged to a lesser extent, it can continue to operate, but when there is discharge or the degree of damage is serious, it should be shut down. Note: When operating the disconnector, do not pull it open with power on to prevent the porcelain bottle from breaking during operation and causing bus or line failure. For example, if the porcelain bottle of the bus side disconnector of its circuit is seriously damaged, the bus where it is located should be powered off, the circuit breaker of the circuit and the disconnector on the line side should be disconnected, and finally the disconnector should be pulled open.
4. The disconnector refuses to pull or close
When the disconnector refuses to pull or close, blind and forced operation should be prohibited, and the cause should be analyzed. Different treatment methods should be adopted for different fault causes.
① If the anti-error device (electromagnetic lock, mechanical lock, electrical circuit lock, program lock) fails, the operator should check whether the operation procedure is correct. If the procedure is correct, the operation should be stopped immediately and reported to the substation manager. It should be determined that the anti-error device has failed before the lock can be released for operation, or it can be handled as a defect and handled normally by the maintenance personnel before operation can be carried out.
② If the knife of the electric operating mechanism cannot be opened or closed, a multimeter should be used to measure whether the motor power supply has power. If the power supply is normal and the contactor is normal, it may be a motor failure. The motor power supply needs to be pulled open and changed to manual operation.
③ If the disconnector cannot be operated due to a mechanical failure of the transmission mechanism in the province, the dispatcher should be notified and the faulty disconnector should be transferred to maintenance for maintenance personnel to handle.
④ If the disconnector cannot be operated normally due to freezing or equipment corrosion, it should not be operated with a large impact force, but with a smaller driving force to shake back and forth to overcome the abnormal resistance.
⑤ When it is found that the contact part between the blade and the blade mouth of the disconnector is in conflict during operation, it should not be operated forcibly, otherwise it may cause damage to the supporting porcelain bottle and cause an accident. The disconnector should be powered off immediately.