Source: Relay Protection High Voltage Technology Exchange
Basic definition: Five prevention usually refers to the abbreviation of five types of error prevention functions that electrical equipment should have to ensure personal safety. It is one of the important measures for power safety.
1. What are the "five preventions" of electrical appliances? The electrical "five preventions" are:
1, preventing the isolating switch from opening and closing under load. (The isolating switch cannot be operated when the circuit breaker , load switch , and contactor are closed.)
2. Prevent misdiagnosis and misclosure of circuit breakers, load switches, and contactors. (Only the operating instructions corresponding to the operating equipment can operate the operated equipment)
3. Prevent the grounding switch from closing the circuit breaker and load switch when it is in the closed position. (Only when the grounding switch is in the open state, the isolating switch can be closed or the handcart can enter the working position, the circuit breaker can be operated, and the load-sharing switch can be closed)
4. Prevent the grounding switch from being closed by mistake when it is powered. (Only when the circuit breaker is in the open state can the isolation switch or handcart be operated, the handcart can be retreated from the working position to the test position, and the grounding switch can be closed)
5. Prevent entering the live compartment by mistake. (Only when the compartment is not electrified, the door can be opened to enter the compartment)
The "five prevention" functions of the electrical equipment misoperation prevention device include "preventing mis-opening and misclosing of circuit breakers". At this stage, prompt measures can be taken due to technical reasons. The remaining four prevention functions must take mandatory measures to prevent electrical misoperation.
2. The concept of "five preventions":
1, load-proof opening and closing isolation switch
2, prevention of mis-opening and mis-closing circuit breaker
3. Anti-load closing grounding switch
4. Anti-grounding switch to send load when closed
5. Anti-accidental entry into the live interval
3. How to realize the "five preventions"?
1. Prevent entering the live compartment by mistake: After the working trolley is moved to the "isolation/experiment" position, the grounded metal partition will automatically fall down to cover the live static contact part, preventing personnel who enter the cabinet for maintenance from contacting the live part. After the ground switch blade is closed, the mechanical interlock of the rear cabinet door allows the cabinet door to be opened.
2. Prevent the opening and closing of primary and secondary contacts under load: When the contactor is in the closed state, the connecting rod on the mechanical interlocking baffle propulsion mechanism linked to the contactor prevents the screw of the propulsion mechanism from rotating. With this design, the primary and secondary contacts cannot be opened and closed when loaded.
3. Prevent hanging of live wires ground wire : When the trolley enters the working position, the baffle of the propelling machine resists the curtain device of the grounding switch closing mechanism, so that the curtain cannot be opened and the grounding switch cannot be closed.
4. Prevent closing with ground wire: When the grounding switch blade is closed, the curtain plate device baffle will prevent the car from entering the cabinet, thereby avoiding the possibility of closing the contactor in the grounded state.
5. To prevent circuit breakers from being opened and closed by mistake: operating personnel always keep the procedures in mind and operate according to the operation tickets.
4. Conventional error prevention device
The design principle of the error prevention device is: All high-voltage electrical equipment that may cause misuse should be equipped with an error prevention device and a corresponding error prevention electrical locking circuit. There are four main conventional anti-accidental locking methods: mechanical locking, program lock, electrical interlocking and electromagnetic lock .
1. Mechanical locking
uses mutually restricted and linked mechanical mechanisms between the operating parts of the switch cabinet or outdoor gate knife to achieve the locking requirements for sequential actions. Mechanical locking does not require the use of auxiliary operations such as keys during operation, and can automatically unlock step by step according to the correct operation sequence. When misoperation occurs, automatic locking can be realized to prevent misoperation.Mechanical locking can realize forward and reverse locking requirements, and has the advantages of intuitive locking, not easy to be damaged, small maintenance workload, and easy operation.
However, mechanical locking can only be used between mechanical action-related parts inside the switch cabinet and outdoor blades, and the connection with the action of electrical components cannot be achieved with mechanical locking. The locking requirements between two cabinets, between the switch cabinet and the power distribution equipment outside the cabinet, and between the outdoor blade and the switch (other blades) are also beyond the reach. Therefore, in switch cabinets and outdoor switches, mechanical locking can only be used as the main method, and other locking methods must be supplemented to meet all five prevention requirements.
2. Program lock (or mechanical program lock)
uses a key to pass or replace with the operating program to meet the requirements of successive unlocking operations. Its biggest advantage is that key transfer is not limited by distance, so it has a wide range of applications. During the operation of the program lock, there are auxiliary actions of key transfer and key quantity change, which meet the requirements of the operation sequence that limits the unlocking conditions in the operation ticket, and are completely consistent with the walking route specified in the operation ticket, so it is easily accepted by the operators.
3, electrical locking
realizes the unlocking operation through the electromagnetic mechanism action of the electromagnetic coil. It is an indispensable locking component in the locking process to prevent accidentally entering the electrified interval. The advantage of electrical locking is that it is easy to operate and has no auxiliary actions. However, there are also the following outstanding problems during installation and use:
① Generally speaking, when the electromagnetic lock is used alone, it only has an unlocking function and no reverse locking function. It needs to be used in conjunction with an electrical interlocking circuit to have forward and reverse locking functions;
② As a locking component, the electromagnetic lock has a complicated structure. The electromagnetic coil is susceptible to moisture and mildew outdoors, and the insulation performance is reduced, which increases the failure rate of the DC system;
③ requires laying cables, which increases additional construction work;
④ needs to be connected to the auxiliary contacts of the operating mechanism. According to operating experience, auxiliary contacts are prone to poor contact, which affects the reliability of the action;
⑤ There is generally a lack of locking measures on the control switch of the circuit breaker.
4, microcomputer anti-accidental locking device
Since the early 1990s, microcomputer technology has entered the field of anti-accidental locking. Microcomputer mis-locking prevention device is a device that uses computer technology to prevent electrical misoperation of high-voltage switchgear. After more than 10 years of development, microcomputer anti-accidental locking devices have gradually matured and have been widely promoted in power systems. The microcomputer error prevention system uses software to convert a large number of secondary locking circuits on site into a five-proof locking rule library in the computer, realizing the digitization of error prevention and realizing error prevention functions that could not or were difficult to achieve in the past. It should be said to be a leap forward in the technology of preventing error locking of electrical equipment.
These locking methods have played an active role in preventing errors. Practice has proved that the advantages and disadvantages of various traditional locking methods have been fully demonstrated. After nearly ten years of development, microcomputer-based anti-accidental locking devices have been accepted by the majority of power system users. In substations with voltage levels above 110kV, microcomputer-based five-proof devices have become the mainstream product for anti-accidental locking. The number of microcomputer-based five-proof manufacturers is also increasing, and the types of products are increasing.
5. What do vicious misoperation accidents of 6kV and above refer to?
6kV and above power supply equipment, with load mis-pull (closed) isolation switch, live hanging (closed) grounding wire (grounding knife switch), with grounding wire (grounding knife switch) closing circuit breaker (isolating switch).
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