Relationship between low-voltage circuit breaker clearance, creepage distance and low-voltage system - News - Global IC Trade Starts Here.

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I. Overview Due to the relatively backward development of China's electrical industry, the lack of varieties, specifications and performance of low-voltage circuit breakers, the lack of perfection of current design specifications, and the user's unclear understanding of the product, the actual use of low-voltage circuit breakers There are some unreasonable and even erroneous usages in engineering applications, resulting in difficulties in operation and maintenance, increased failures, and long-term security risks. This article only makes a preliminary discussion on the issues that are universal, and hopes to cause common concern of manufacturers and users!
Second, how to choose the low-voltage circuit breaker First, it depends on the ultimate short-circuit breaking capacity and short-circuit breaking capacity of the selected circuit breaker. The International Electrotechnical Commission IEC947-2 and China's equivalent IEC GB4048.2 "Low-voltage switchgear and control The standard of equipment low-voltage circuit breakers clearly defines the ultimate short-circuit breaking capacity and short-circuit breaking capacity of the circuit breaker.
The second is to look at the clearance and creepage distance of the selected circuit breaker, determine the electrical clearance of the electrical products, must be based on the insulation of the low-voltage system, and the insulation coordination is based on the instantaneous overvoltage is limited to the specified impulse withstand voltage The instantaneous overvoltage generated by the electrical appliances or equipment in the system must also be lower than the impulse voltage specified by the power system. therefore:
(1) The rated insulation voltage of the electrical appliance should be ≥ the rated voltage of the power supply system (2) The rated impulse withstand voltage of the electrical appliance should be ≥ the rated impulse withstand voltage of the power supply system (3) The transient overvoltage generated by the electrical appliance should be ≤ the power system Rated impulse withstand voltage III. Analysis of the cause of the circuit breaker accident The accident statistics of the circuit breaker for many years on the site show that the main types of operation accidents are as follows:
(1) Operational failure;
(2) insulation failure;
(3) Poor opening and closing performance;
(4) Poor electrical conductivity.
The causes of accidents can generally be broadly divided into two major categories: technical reasons and work reasons. The so-called technical reasons refer to the defects of the product itself or the mode of operation; the so-called work reasons refer to the fault of the workers who caused these defects. The following is a brief analysis of the reasons for these two aspects.
The first aspect: analysis of the technical reasons of the accident (1) failure of the operation failure is manifested as dragging or malfunctioning of the circuit breaker. Since the most basic and important function of the high voltage circuit breaker is to operate correctly and quickly remove the grid fault. If the circuit breaker is dragged or misplaced, it will pose a serious threat to the power grid. The main reasons are: 1 to expand the scope of the accident, which may cause only one loop fault to be expanded to the entire busbar, or even the entire plant, the whole plant blackout; 2 if extended The fault removal time will affect the stability of the system and increase the damage of the controlled equipment; 3 cause non-full phase operation. The result is often caused by abnormal operation of the grid protection and oscillation, which is easily expanded into a system accident or a large-scale blackout.
The main reasons for the malfunction are:
(1) Operating mechanism defects;
(2) Mechanical defects of the circuit breaker body;
(3) Operation (control) power supply defects.
(2) Insulation accidents Circuit breaker insulation accidents can be classified into internal insulation accidents and external insulation accidents. The damage caused by internal insulation accidents is usually greater than the external insulation.
1. Insulation accidents in internal insulation accidents mainly include casing and current transformer accidents. The main reason is that the influent water is damp; secondly, the oil quality is degraded and the oil quantity is insufficient.
2, the external insulation accident external insulation accident is mainly caused by flashover and lightning strikes caused by circuit breaker flashover, explosion accidents. The main reason for the pollution flash is that the leakage distance of the porcelain bottle is small and it is not suitable for use in the dirty area. Secondly, the circuit breaker seeps oil and oil leakage, which makes the porcelain skirt easily accumulate pollution and cause flashover.
(3) Breaking and closing performance accidents Breaking and closing tasks are the most severe tests for circuit breakers. The main reason for most of the breaking and closing accidents is that the circuit breaker has obvious mechanical defects, followed by lack of oil or oil quality. There is also a lack of ability to interrupt the circuit breaker. However, the former is more, because there are a considerable number of accidents that occur in small and small capacity, even in divided and combined load currents.
(IV) Poor Conductive Performance Accidental accident statistics analysis shows that poor electrical conductivity faults are mainly caused by mechanical defects. Among them are: 1 poor contact. Including contact surface is not clean, contact size and contact pressure is insufficient; 2 shedding, jamming. Such as copper and tungsten contacts falling off; 3 loose screws at the contact; 4 soft connection broken.
The second aspect: analysis of the working reasons of the accident (1) Poor manufacturing quality The poor manufacturing quality mainly includes three aspects: design performance, parts processing and assembly failure.
1. Poor design performance In recent years, a considerable part of the accidents that occur during the operation of the circuit breaker is that the original design performance of the product is poor. The most common examples are the failure of the domestic hydraulic mechanism and the spring mechanism to be exposed during operation. It is understood that most of these hydraulic mechanisms and spring mechanisms are gradually exposed after a large number of operations. For example, the problem of water in some outdoor products is the best example of design flaws. Because some outdoor products have not been tested for rain resistance during development, they have been exposed to water in harsh weather conditions.
2, poor quality parts, poor quality parts, is an important cause of circuit breaker operation accidents. According to the on-site statistics, factors that cause unqualified products and poor quality of parts account for a large proportion. In operation, accidents caused by the screw of the insulation tube, the breakdown of the arc extinguishing plate, the failure of the spring, the defect of the sealing ring, etc., all occur, but several aspects are concentrated: (1) The strength of the porcelain bottle is not enough. (2) The casting is unqualified. (3) The casing insulation deteriorates quickly. (4) The quality of the seal is poor. (5) The performance of secondary components is poor.
3, poor assembly quality, poor assembly quality, is one of the reasons for poor manufacturing quality. Mainly: (1) wrong installation, missing installation. (2) The thread is not tightened and the split pin is not open. (3) The interior is seriously unclean.
(2) Whether the use of improper products can operate normally, in addition to the performance of the product itself, it also depends on the user's use level. The main performance of improper use in operation has the following two aspects:
1. Installation and adjustment of improper installation and adjustment are one of the basic factors that affect the normal operation of the product. There are many operating accidents because the products are not put into operation according to the manufacturer's specifications. There are generally three cases: (1) improper adjustment of the auxiliary switch. (2) The screw is not tightened and the split pin is not open. (3) The seal is not placed properly.
2. Improper operation and maintenance and improper operation and maintenance are another important cause of operational accidents. There are three common aspects: (1) The oil circuit breaker is short of oil. (2) Poor insulation. (3) Poor mechanical maintenance.