Explanation on the five precautions of high-voltage switchgear

"Interlocking" is generally described as: preventing misopening and misclosing of circuit breakers; preventing opening and closing of isolating switches with load; preventing live hanging (closing) of ground wires (grounding switches); preventing grounding (switches) from closing; preventing Entering the electrified interval by mistake. The above five items to prevent electrical misoperation are referred to as "five preventions". "Five prevention" devices can generally be divided into three categories: mechanical, electrical and comprehensive. At present, there are many types of high-voltage switches on the market, and most of them have relatively complete interlocking methods. However, there are still many high-voltage switchgear interlocks, especially mechanical interlocks, that are imperfect and cannot fully meet the "five prevention" requirements. To this end, this article focuses on putting forward some opinions on mechanical interlocking and discussing with colleagues.

     Interlocking implementation method
   In fixed cabinets and handcart cabinets. As we all know, the isolating switch does not have a special arc extinguishing device and generally cannot be used to connect or cut off the load current. In the fixed cabinet, the interlocking relationship between the circuit breaker and the isolating switch is clear, that is, the isolation can only be operated when the circuit breaker is broken.
The mechanical interlocking relationship between switches, isolating switches and circuit breakers is easier to implement. For example, in CC-1A(F), in order to prevent the isolating switch from opening and closing under load, a sector-shaped impact block and a circular plate structure are often used to cooperate with the elastic positioning lock on the CS6-1 mechanism that operates the isolating switch.
When the circuit breaker is closed, the circular plate prevents the positioning lock from being pulled out, thereby preventing the circuit breaker from opening under load. However, the situation of the handcart cabinet is different. The handcart bursting out is actually equivalent to the isolating and opening closing operation in the fixed cabinet. Therefore, the interlocking requirements for the isolating switch also apply to the entry and exit requirements of the handcart.
beg. When the handcart moves between the test position and the working position, it must be ensured that the circuit breaker is in the open state and must not be closed, that is, it should have the so-called "closing lockout". In various types of handcart cabinets that are put into operation, the "closing" electrical lock generally uses a travel switch that reflects the position of the handcart.
The contacts are connected in series to the closing circuit of the circuit breaker.
   The operating sequence of the isolating switches on both sides of the circuit breaker. The GG-1A(F)-07 plan stipulates the operating sequence of the isolating switches on both sides of the circuit breaker as follows: During a power outage, the line side isolating switch must be opened first; during power transmission, the bus side isolating switch must be closed first. Its function is
In order to ensure that in the event of incorrect operation, the protection function of the circuit breaker can be used to minimize the scope of the accident and avoid artificial expansion of the accident. The reason for disconnecting the line-side isolating switch first during a power outage is: if a misoperation occurs during a power outage, such as the circuit breaker has not disconnected the power supply, the circuit breaker must be disconnected first.
When disconnecting the isolating switch, the switch is disconnected under load; or when disconnecting the isolating switch, the isolating switch of the line that should not be stopped is mistakenly connected, which will cause an arc short circuit. In the above situation, if the line-side isolating switch is separated first, since the arc short-circuit point is outside the circuit breaker, the protection device of the switch will trip to remove the fault, reducing the scope of the accident. On the contrary, when transmitting power, if the circuit breaker is mistakenly in the closing position and then the bus side isolating switch is closed, it means that the bus side is transmitting power with load. An arc short circuit will inevitably occur, causing the fault to expand. In this case, if you close the bus side isolating switch first and then close the line side isolating switch, it is equivalent to using the line side isolating switch to close with load. Once an arc short circuit occurs, since the short circuit point is outside the circuit breaker, the circuit breaker protection It can trip the circuit breaker, remove the fault and reduce the scope of the accident. Therefore, when transmitting power, the bus side isolating switch must be closed first.
   It is certainly a good thing to be able to open and close the isolating switch according to the above operating sequence, but in fact it is difficult to ensure that the isolating switches on both sides of the circuit breaker are operated in strict accordance with the above sequence. For ring network switches and bus coupler switches, it is difficult to distinguish between the busbar and the line side. For the opponent car cabinet, the contacts on both sides of the circuit breaker are in and out at the same time. If the current transformer is installed outside the isolating switch, the situation will also be different. Therefore, only by ensuring the interlocking reliability between the circuit breaker and the isolating switch can the above-mentioned problem of misoperation of the isolating switch be fundamentally solved.

     Conflict between electrical safety regulations and interlocking requirements
   Over the years, statistics on electrical accidents have shown that personal injuries and deaths due to electric shock and electrical equipment accidents are often directly related to the technical and professional level of electrical workers. Strictly operating in accordance with electrical safety work procedures can effectively reduce and avoid misoperation accidents. but
In actual work, conflicts between procedures and interlocking often occur. For example, switch cabinets equipped with a grounding switch on the outlet side such as KYN28A-12 and JYN6-12 have an interlocking function. The cable compartment door (or cover) of the switch cabinet cannot be opened before the grounding switch is closed to prevent accidental entry. Charge interval. The regulations stipulate that the grounding switch can only be closed after confirming that the line is without power. This means that the cabinet door must be opened and the grounding switch can be operated only after the electrical test confirms that the line is without electricity. The regulations and interlocking requirements conflict with each other. In order to solve this kind of problem, the following methods can be adopted: First, install a live display on the line side, observe that there is no power and then close the grounding switch, or install an electromagnetic lock on the grounding switch operating lever to ensure that the grounding switch cannot be closed when the line is powered. . The second is to open a gap in the cabinet door to allow careful electrical testing. The third is to equip the cable room door (or cover) with an emergency unlocking device, which can be unlocked by professionals with special tools.

     Active interlocking and passive interlocking
   For each interlocking requirement in the "five preventions", whether it is a fixed cabinet or a handcart cabinet, despite the diversity of cabinet types and primary solutions, various solutions can be designed to achieve the interlocking function. To sum up, there are two main forms of mechanical interlocking, namely active and passive.
Mode. The so-called "active interlocking" means that in this interlocking state, if there are no normal unlocking conditions, it will not be unlocked, thus ensuring that misoperation cannot be performed at all. For example, when the circuit breaker is in the closed position, mechanically ensure that the isolating switch or isolating plug is locked and cannot be operated.
Even if the operation is incorrect, there will be no adverse effects. "Passive interlocking" means that in this interlocking state, unlocking conditions may occur due to abnormal reasons, causing the lock to be unlocked. If the isolating switch or push-pull handcart is operated in the locked state, although the isolating switch has not yet acted
Or the isolating plug does not move, but the circuit breaker is opened due to the existence of interlock, so that the interlock of the isolating switch or isolating plug is released. Obviously, this passive interlocking form will cause the circuit breaker to open accidentally.
   In the design of high-voltage switchgear, we do not want to use "passive" interlocking, and we should try to use "active" interlocking. For example, for a switch cabinet that uses a lever to enter and exit the handcart, when the circuit breaker is closed, the hole for the handcart to enter and exit the crank handle is mechanically blocked, and the crank handle cannot be inserted at all, and of course the handcart cannot move. Another example is that the insertion hole for operating the grounding switch is designed to be opened only under permitted conditions. Otherwise, the insertion hole will be blocked and incorrect operations will not be possible. Among the various types of switch cabinets currently in use, many mechanical interlocks adopt "passive" interlocking. As the design level of switch cabinets increases, this method should be avoided as much as possible.

     The integrity of the “five defenses” interlocking
   For the "five preventions" requirements in the national standards, in addition to the allowed reminder method of preventing mis-opening and mis-closing of circuit breakers, the other interlocking relationships must be fully realized in the switch cabinet structure. From the perspective of the operation of the switch cabinet, each interlocking requirement is reflected in a certain operating procedure, so both the closing and opening procedures must meet the interlocking requirements. Prevent the isolation of on-load opening and closing
Close; prevent live hanging (closing) of the ground wire (switch) and ground wire (switch) from closing. However, the above two requirements are sometimes not required to be implemented in the same cabinet but between cabinets. In this case, mechanical interlocking often cannot meet the requirements.

     Reliability of mechanical interlocking
   Regardless of the frequency of normal use, the mechanical interlocking device of the high-voltage switchgear should be flexible and reliable during its service life, and should be effectively moisture-proof, mildew-proof, rust-proof, and non-sticky. Its structure should be simple and clear, and it should be easy to operate and maintain. During the use of high-voltage switchgear, "irregular operations" may also be encountered due to operator negligence or abnormal operating force. In this case, highly reliable interlocking should be able to fully prevent or prevent possible "irregular operations" by the operator. Even if an incorrect operation is performed under certain circumstances, the incorrect operation should be correctable and normal operation can be easily restored without causing major equipment or personal accidents.

   For each interlocking requirement in the "five preventions", whether it is a fixed cabinet or a handcart cabinet, despite the diversity of cabinet types and primary solutions, various solutions can be designed to achieve the interlocking function. To sum up, there are two main forms of mechanical interlocking, namely active and passive.
Mode. The so-called "active interlocking" means that in this interlocking state, if there are no normal unlocking conditions, it will not be unlocked, thus ensuring that misoperation cannot be performed at all. For example, when the circuit breaker is in the closed position, mechanically ensure that the isolating switch or isolating plug is locked and cannot be operated.
Even if the operation is incorrect, there will be no adverse effects. "Passive interlocking" means that in this interlocking state, unlocking conditions may occur due to abnormal reasons, causing the lock to be unlocked. If the isolating switch or push-pull handcart is operated in the locked state, although the isolating switch has not yet acted
Or the isolating plug does not move, but the circuit breaker is opened due to the existence of interlock, so that the interlock of the isolating switch or isolating plug is released. Obviously, this passive interlocking form will cause the circuit breaker to open accidentally.
   In the design of high-voltage switchgear, we do not want to use "passive" interlocking, and we should try to use "active" interlocking. For example, for a switch cabinet that uses a lever to enter and exit the handcart, when the circuit breaker is closed, the hole for the handcart to enter and exit the crank handle is mechanically blocked, and the crank handle cannot be inserted at all, and of course the handcart cannot move. Another example is that the insertion hole for operating the grounding switch is designed to be opened only under permitted conditions. Otherwise, the insertion hole will be blocked and incorrect operations will not be possible. Among the various types of switch cabinets currently in use, many mechanical interlocks adopt "passive" interlocking. As the design level of switch cabinets increases, this method should be avoided as much as possible.

     The integrity of the “five defenses” interlocking
   For the "five preventions" requirements in the national standards, in addition to the allowed reminder method of preventing mis-opening and mis-closing of circuit breakers, the other interlocking relationships must be fully realized in the switch cabinet structure. From the perspective of the operation of the switch cabinet, each interlocking requirement is reflected in a certain operating procedure, so both the closing and opening procedures must meet the interlocking requirements. Prevent the isolation of on-load opening and closing
Close; prevent live hanging (closing) of the ground wire (switch) and ground wire (switch) from closing. However, the above two requirements are sometimes not required to be implemented in the same cabinet but between cabinets. In this case, mechanical interlocking often cannot meet the requirements.

     Reliability of mechanical interlocking
   Regardless of the frequency of normal use, the mechanical interlocking device of the high-voltage switchgear should be flexible and reliable during its service life, and should be effectively moisture-proof, mildew-proof, rust-proof, and non-sticky. Its structure should be simple and clear, and it should be easy to operate and maintain. During the use of high-voltage switchgear, "irregular operations" may also be encountered due to operator negligence or abnormal operating force. In this case, highly reliable interlocking should be able to fully prevent or prevent possible "irregular operations" by the operator. Even if in some cases the wrong
Misoperation should also be correctable and normal operation can be easily restored, so as not to cause major equipment or personal accidents.