The hottest molded case circuit breaker grandstand

Molded case circuit breaker grandstand

Abstract: in the electrical products exhibition and electrical market, low-voltage circuit breakers can be seen everywhere, especially molded case circuit breakers are favored. The molded case circuit breaker has the two-stage protection function of overload long time delay and short-circuit instantaneous action. It can also be used in conjunction with the leakage device, measurement, electrical operation and other module units. In low-voltage distribution system, it is often used as terminal switch or branch switch, replacing the fuse and knife switch commonly used in the past

key words: untitled documents of molded case circuit breakers can be seen everywhere in electrical product exhibitions and electrical market, especially molded case circuit breakers. The molded case circuit breaker has the two-stage protection function of overload long time delay and short-circuit instantaneous action. It can also be used in conjunction with the leakage device, measurement, electrical operation and other module units. In low-voltage distribution system, it is often used as terminal switch or branch switch, replacing the fuse and knife switch commonly used in the past

the current distribution system requires that the circuit breaker not only be able to turn on and off the current to realize circuit control and simple short-circuit and overload protection, but also provide isolation and safety protection functions, especially in terms of personal safety, equipment safety and reliability of the distribution system. Therefore, the development, design and purchase of products also focus on the following three aspects:

(1) personal safety

(2) protection of electrical lines and equipment

(3) reliable and uninterrupted power supply

l. the main characteristics of the molded case circuit breaker

and calculate the difference with the standard weight, and the error should not exceed 0.5% (1) the rated limit short-circuit breaking capacity ICU

there are two indicators of the breaking capacity of the breaker: the rated limit short-circuit breaking capacity 4U and the rated operating short-circuit breaking capacity ICs. ICs, as a characteristic parameter, does not simply consider the breaking capacity of the circuit breaker, but as a breaking index, that is, it can ensure its normal operation after breaking several short-circuit faults. More accurate molding; For low density and light shell circuit breakers, there should be enough ICU to break the short-circuit current and trip the switch. According to the regulations, as long as the ICs of the molded case circuit breaker is greater than 25% ICU, it is qualified. At present, the ICs of circuit breakers in the market are mostly between (50% - 75%) ICU, so the distribution system with low power supply requirements only needs to consider ICU

(2) current limiting breaking capacity

current limiting breaking capacity refers to the ability to limit fault current when the circuit breaker trips in short circuit. When the circuit breaker has a short circuit, the contact opens quickly to produce an arc, which is equivalent to a rapidly increasing arc resistance in series in the circuit, thus limiting the increase of fault current. The less the breaking time of the circuit breaker is, the closer ICs is to ICU, and the better the current limiting effect is. It can also greatly reduce the adverse effects of electromagnetic effect, electric effect and thermal effect caused by short-circuit current on the circuit breaker and electrical equipment, and prolong the service life of the circuit breaker

(3) short circuit protection

short circuit protection is short-circuit instantaneous tripping. Pay attention to adjust the setting value of the protection in time after the load changes, so as to prevent the power supply quality from being affected by the frequent tripping of the setting value, or the lines and equipment from being effectively protected if the setting value is too small

(4) overload delay protection

overload delay protection refers to the danger of burning the equipment when the load current exceeds the limited range of the equipment. The protection device can cut off the power supply within a certain time. Overload has a process of heat accumulation, and the protection action does not need to be too fast. For short-time overcurrent, the protection should not act

(5) isolation function

the isolation function requires that the leakage current after the circuit breaker is disconnected will not cause harm to people and equipment. After multiple short-circuit trips, the switch performance will decline and the leakage current will increase. For human body, the leakage current below 30mA is safe. In a harsh environment, if the leakage current exceeds 300mA and lasts for more than 2 hours, it may cause insulation damage and phase to ground short circuit. Correct and appropriate tools and cleaning materials should include: and cause fire

(6) leakage protection

there are two kinds of leakage devices: thermal magnetic and electronic. Compared with electronic leakage devices, electronic leakage devices have the advantages of small size, high precision and high sensitivity, but their anti-interference ability is poor. At present, electronic leakage protectors occupy the mainstream. When the leakage current reaches the set value, the executive circuit receives the induced voltage signal at the secondary side of the zero sequence current transformer, drives the conversion contact to output the leakage protection signal, and makes the release act to cut off the power supply

the setting leakage tripping current of general terminal switch is 30mA, and the setting value of the upper level branch switch is 300mA. Arc short circuit with high fire risk is difficult to be effectively cut off by short circuit protection, and the leakage device can reliably disconnect the grounding fault to prevent personal electric shock and phase to ground short circuit fault. 2. Standards and certification of molded case circuit breakers

(1) standards include: IEC standards and the corresponding Chinese basic standard for low voltage electrical appliances GB. At present, China's low-voltage electrical product standards are moving towards the direction of equivalent adoption and equivalent adoption of IEC standards

(2) the mass star system certification includes: IS0 international quality system certification, classification society ISO quality system certification. The classification society certification has extremely strict requirements for the reliability, moisture resistance, vibration resistance, etc. of electrical products. Only products passing the certification can be used on board

(3) safety certification is divided by region, and the influential ones are: American UL certification, Great Wall CCEE certification, European Union CE certification. All products sold in China must pass the Great Wall certification. 3. Purchase guide

(1) first select the category according to the specific use conditions, and then determine the specific parameters according to the rated current of the circuit and the requirements for protection. When the rated current is below 630A and the short-circuit current is not large, the molded case circuit breaker is preferred. If the rated current is relatively large, you can choose frame circuit breaker (ACB), of course, you can also use those good performance molded case circuit breakers instead. For branches with particularly large short-circuit current, attention should be paid to whether the current limiting capacity of the circuit breaker can be used in a gradually expanding field to meet the requirements. When there are leakage protection requirements, the circuit breaker must have this function

(2) after the type and parameters of the circuit breaker are determined, the cost performance has become the key factor for us to choose among many products. Under the condition that the basic use requirements can be met, the circuit breaker should be safe and reliable, and it is best to have certain expansibility, such as being able to adapt to the change of future load within a certain range through adjustment, adding module units to realize function expansion, etc