Selection of vacuum circuit breaker mechanical parameters

Selection of vacuum circuit breaker mechanical parameters
Core tips: Selection and maintenance of drop-type fuses Wang Jianzhong Power Supply Branch of Daling City, Shanxi Province (037500) One of the most commonly used short circuit protections for 10kV distribution line branch lines and distribution transformers is drop-type fuses. Economical, affordable, convenient operation, adaptability to outdoor environment and other characteristics

Selection and maintenance of drop-type fuses Wang Jianzhong Power Supply Branch of Daling City, Shanxi Province (037500) One of the most commonly used short-circuit protections for 10kV distribution line branch lines and distribution transformers is the drop-type fuse, which is economical and economical. It is widely used in the primary side of 10kV distribution lines and below 350kVA distribution transformers for back-up protection and system and equipment investment and cutting operations.

It is installed on the branch line of the 10kV distribution line and can reduce the power outage range because it has an obvious disconnection point, has the function of isolating switch, creates a safe working environment for maintenance lines and equipment, and increases the number of maintenance personnel. Sense of security. Even in the case of a load, it is allowed to stop and transmit power, so it is popularized in 10kV distribution lines and distribution transformers.

The working principle of a drop-type fuse The drop-type fuse fuse tube at both ends of the upper and lower moving contacts rely on the fuse system tight, push the upper moving contact into the duck bill protruding part, the phosphor bronze and other systems The upper static contact is pressed against the upper moving contact, so the tube is firmly stuck in the duck bill. When the short-circuit current melts through the melt, an arc is generated, and the tube-lined steel paper tube generates a large amount of gas under arc use, and extinguishes the arc when the current passes through zero. As the melt blows, under the action of the upper and lower moving contact springs of the melting tube, the melting tube falls rapidly, the circuit is disconnected, and faulty section lines or faulty equipment are removed.

Falling-type fuses have problems with rough product technology, poor manufacturing quality, insufficient contact spring elasticity, and poor contact and spark overheating.

The rotating shaft of the fusion tube is rough and inflexible, so that the angle of the fusion tube does not meet the requirements of the regulations. In particular, most of the size of the fusion tube does not meet the requirements of the regulations, or the duckbill is tossed to death, and the melted tube cannot melt after melting. Rapid drop, can not be cut off in a timely manner, contact bad contact, resulting in electric spark.

The rated breaking energy of the fuse is small, and its lower limit value is less than the three-phase short-circuit capacity of the protected system. At present, 10kV outdoor drop-type fuses are divided into three models, namely, the upper limit of 50A, 100A, 200A.200A is 200MVA, the lower limit is 20MVA. Some products fuse size and fuse fixed contact part size is not suitable, easy to loosen, In the event of an external force, vibration, or windy weather, it will fall and fall by itself. This will not only reduce the amount of electricity sold, but also make it difficult to guarantee the supply reliability index.

Falling-type fuse selection The 10kV drop-type fuse is suitable for use in the surrounding air without vibration of the conductive powder machine, and is likely to cause damage to components.

Closing speed Due to the relatively high static withstand voltage level of the vacuum switch tube at rated open distance, the closing speed of the vacuum circuit breaker is significantly lower than the brake speed. In order to minimize the electrical wear caused by the pre-breakdown during the closing process of the contacts and to avoid the welding of the contacts, a certain closing speed must be provided. However, an excessively high closing speed not only increases the closing power of the operating mechanism, but also increases the closing shock of the switch tube, which greatly reduces its service life. Under normal circumstances, the closing speed of the vacuum circuit breaker of 10kV class is 0.4~0.7m/s, and it can be taken as 0 when necessary. Contact closing bounce time The closing time of the vacuum circuit breaker is a measure of the performance of the vacuum circuit breaker. One of the important signs is related to the contact bounce pressure, closing speed, opening distance of the circuit breaker and the contact material of the vacuum switch tube, and also related to the structure of the switch tube, the structure of the circuit breaker, and the installation and commissioning. The smaller the contact bounce closing time, the better its performance, the longer the bounce time, the more severe the electrical wear of the contacts, the easy to generate closing overvoltage, when closing the short circuit current or capacitor, and carrying out the dynamic and thermal stability test This will cause the contact to weld. In addition, the longer the contact bounce jump time, seriously jeopardize the service life of the bellows of the switch tube. 10kV copper-chromium contact material of the vacuum circuit breaker closing bounce time does not exceed 2m, other contact material vacuum circuit breaker closing bounce time can be relatively large, but not more than 5ms. 8 three-phase synchronous vacuum circuit breakers The synopolarity of the three poles indicates the degree of closure or separation of the three poles at the same time. Since the synchronization of closing and closing is relative, the values ​​are not much different. Therefore, only the three-phase synchronization is evaluated.

Circuit breakers with poor three-phase synchronization will severely affect the breaking capacity of the circuit breakers, and prolong the arcing time easily. Because the circuit breaker's closing and closing speed is faster and the driving distance is shorter, it is not difficult to achieve the parameter requirements through accurate debugging. Generally, the closing time of the circuit breaker does not exceed 1 ms. 9 Coaxial movement of static and dynamic contacts The coaxiality of the contact has specific requirements for the real switch tube and can be ensured by the manufacturing process. The switch tube installed on the operating mechanism can ensure the coaxiality, and has a direct relationship with the type of the operating mechanism and the installation process. . For the hanging mechanism, the coaxiality mainly depends on the operating mechanism, and the influence on the coaxiality of the floor-standing mechanism is also very large. In the installation process, it must be avoided that the switch tube is subjected to shear force and shear force. Concentricity is generally less than 2mm. (:2004-05

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