Analysis Of National Grid Low Voltage Cabinet Standards

Analysis of National Grid Low Voltage Cabinet Standards

The standardized design of the State Grid stipulates almost all requirements and dimensions for the primary and structural design of cabinets, including bus specifications and positions, component installation positions, as well as requirements for secondary wiring and terminal layout of switchgear. The space that switchgear manufacturers can utilize is very small, so for manufacturers specializing in cabinet production, it is relatively simple to only install according to the circuit breakers of mainstream frame circuit breaker manufacturers The interface size design, installation board, and busbar layout bracket are sufficient. The complete set factory will provide the corresponding cabinet for the circuit breaker to be selected.

For manufacturers who only produce switchgear, they choose frame circuit breakers and molded case circuit breakers that meet the requirements of national grid standard cabinets for switchgear design, complete the verification work of national grid companies, and participate in national grid bidding. The switchgear manufacturers here attach great importance to the cost-effectiveness and flexibility of their products. For example, the breaking capacity of A's frame circuit breaker is 85kA, while B's frame circuit breaker is 65kA. Perhaps the prices of the two frame circuit breakers are the same, as if A's cost-effectiveness is higher, and the standardized technical specifications require 65kA. Which product should we choose for testing? High parameters, high standards, setting thresholds to win orders, wrong.

The bidding for State Grid standard cabinets will not compare your breaking current capacity, but rather meet the structural design, component parameters, State Grid review, and type testing requirements of standardized technical documents. Therefore, most switchgear manufacturers will choose B manufacturer's components for testing, which has greater universality and flexibility. It is convenient to replace circuit breakers based on the price in the future, and cannot be hung from a tree, making it difficult to replace circuit breakers.

That said, the component list can include frame circuit breakers from multiple manufacturers, but apart from testing this one, although circuit breakers from other manufacturers meet the requirements of the State Grid, can they definitely pass the test when placed in a cabinet? This requires a big question mark.

The bus specifications are fixed, and the insulation brackets are the same. The insulation and dynamic thermal stability issues are not significant. The cabinet structure is consistent, and there are no problems with the protection level or internal arc. However, for temperature rise, especially for compact cabinets, it is very difficult. The temperature rise is based on the heating situation of the frame circuit breaker itself, and many manufacturers cannot pass the temperature rise test for circuit breakers. The bus specifications and standards have been fixed, and the connection design can be similar. Based on IEC60890 calculation, the 700mm wide, 800mm deep, and 2200mm high switch cabinet has a ventilation hole of 200mm2. The internal heating power of the switch cabinet is 1000W to achieve thermal balance, and the copper bar 2-10 * 100 current is 2500A, with a heating power of 600W. Therefore, if the circuit breaker heats up more than 400W, it will break the temperature balance and cause excessive temperature rise. If there is no customized design for copper arrangement, it is difficult to pass the temperature rise.

The connecting parts of the dynamic and static contacts inside the circuit breaker, as well as the plug-in contacts of the withdrawable circuit breaker, are the places where the heat generation is the highest and not easy to dissipate. Different manufacturers have different technologies and processes, and even different models of the same manufacturer generate different heat. Therefore, even if the same busbar system and cabinet shell are the same, the temperature rise will also be different. Therefore, direct substitution without experimental verification is not advisable.

As a component manufacturer, it is necessary to truly define products according to the parameters required by the national grid standard cabinet standards. The requirements must be met, such as electrical life and mechanical life, which must meet the standards. Do not excessively high parameter performance, such as Ics and Icu, with a single and complete report, rather than a patchwork test report. On the basis of meeting the standards, it is necessary to have a clear understanding of the advantages and disadvantages of one's own circuit breaker, especially in terms of installation and use. It is necessary to provide the best recommendations based on the application of the switchgear, such as suggestions for heat dissipation based on one's own heating situation, where holes need to be opened on the side and bottom, how to overlap the connecting bars, how to fix them, etc., in order to provide a complete solution to the complete factory, complete the prototype together, and complete the grid connection test

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