Relationship between low-voltage circuit breaker clearance, creepage distance and low-voltage system - News - Global IC Trade Starts Here.
I. Overview Due to the relatively underdeveloped state of China's electrical industry, there is a lack of variety, specification, and performance in low-voltage circuit breakers. Additionally, design standards are not fully mature, and users often have limited understanding of these products. As a result, improper or even incorrect usage of low-voltage circuit breakers in engineering applications has led to operational difficulties, increased failures, and long-term safety risks. This article aims to provide an initial discussion on common issues and hopes to raise awareness among both manufacturers and users. II. How to Choose a Low-Voltage Circuit Breaker The selection of a low-voltage circuit breaker primarily depends on its ultimate short-circuit breaking capacity and short-circuit breaking capacity. According to IEC 947-2 and GB 4048.2, the standard for low-voltage switchgear and control equipment clearly defines these parameters. Another important factor is the clearance and creepage distance of the circuit breaker. The electrical clearance must be based on the insulation level of the low-voltage system, and the insulation coordination should ensure that transient overvoltages are within the specified impulse withstand voltage limits. Therefore: 1. The rated insulation voltage of the device should be ≥ the power supply system's rated voltage. 2. The rated impulse withstand voltage of the device should be ≥ the system's rated impulse withstand voltage. 3. The transient overvoltage generated by the device should be ≤ the system's rated impulse withstand voltage. III. Analysis of Causes of Circuit Breaker Accidents According to accident statistics from the field, the main types of circuit breaker failures include: (1) Operational failure (2) Insulation failure (3) Poor opening/closing performance (4) Poor electrical conductivity Causes can generally be divided into two categories: technical reasons and human factors. Technical reasons involve product defects or operational mode, while human factors relate to mistakes made during installation, operation, or maintenance. IV. Technical Reasons Behind Failures Operational failure refers to situations where the circuit breaker fails to operate correctly, such as delayed tripping or misoperation. This can lead to serious consequences, including extended fault areas, reduced system stability, and non-full phase operation. Common causes of malfunction include: - Defects in the operating mechanism - Mechanical faults in the circuit breaker itself - Issues with the power supply Insulation failures can occur internally or externally. Internal failures, such as those involving the casing or current transformer, are usually more severe due to moisture ingress or oil degradation. External failures often result from flashovers caused by pollution or lightning strikes. Poor breaking and closing performance is one of the most demanding tests for a circuit breaker. Most accidents are due to mechanical defects or insufficient oil levels. Some may also be caused by an inability to interrupt the current, though mechanical issues are more common. Poor electrical conductivity is typically caused by mechanical problems, such as poor contact, loose screws, or broken connections. V. Human Factors in Failures Improper manufacturing quality is a significant cause of failures. This includes poor design, substandard components, and poor assembly practices. For example, some hydraulic mechanisms fail after repeated operations due to design flaws, and outdoor products may suffer from water ingress if not properly tested. User-related issues also play a role. Improper installation, such as incorrect adjustment of auxiliary Switches or missing split pins, can lead to operational failures. Poor maintenance, like insufficient oil levels or inadequate cleaning, further increases the risk of accidents. In conclusion, ensuring the safe and efficient operation of low-voltage circuit breakers requires a combination of proper design, high-quality manufacturing, correct installation, and regular maintenance. Both manufacturers and users must take responsibility to prevent failures and maintain system reliability.
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