What are the methods for selecting the circuit breaker at the low voltage side of the distribution box transformer?

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As a circuit distribution box, the distribution box plays the role of measuring and judging the shutdown and power transmission. In case of circuit failure, it is also conducive to maintenance and convenient shutdown and power transmission. But nothing is perfect, and the distribution box needs to be improved.


Selection of circuit breaker at low voltage side of distribution transformer


      Low voltage circuit breakers can be divided into selective and non selective types according to their functions. Selective circuit breakers are used for circuit breakers at low voltage side of transformers; Low voltage circuit breakers can be divided into 1p, 2p, 3P and 4P according to the number of poles. Under normal working conditions, the rated frequency and rated voltage of low-voltage circuit breaker are respectively compatible with the frequency and nominal voltage of the circuit; At the same time, it shall meet the breaking capacity under short circuit conditions.


  Example analysis


      For the three-phase transformer with a capacity of 315KVA, taking the Schneider circuit breaker as an example, the setting and selection process of the main circuit breaker at the low voltage side of the transformer is as follows:


   ( 1) Calculate the rated current on the low voltage side of the transformer:


   ( 2) Determine the setting current of long-time-delay overcurrent release of low-voltage circuit breaker. According to the contents of 1.1 and in combination with Schneider circuit breaker selection manual, the setting current of long-time-delay overcurrent release is 1250A.


   ( 3) Determine the setting current of short delay overcurrent release of low-voltage circuit breaker. According to 1.2, the setting current of short delay overcurrent release is 4 × 1250=5000A。


   ( 4) According to the above calculation and in combination with Schneider circuit breaker manual, the model of circuit breaker is Mt 12 N1 / 3P mic5.0.


    1. Space distance of components. The size of the box can be appropriately increased to increase the electrical safety distance between various components.


    2. Anti rust ability. Chemical coating with heat insulation performance can be sprayed in the box to reduce radiation and reduce the temperature in the box. At the same time, a layer of antirust and anti-corrosion coating shall be sprayed inside and outside the box to prevent it from premature failure.


    3. Improvement of heat dissipation system. Because the distribution box will generate a lot of heat during operation, if the heat dissipation capacity of the equipment is not strong, it will affect the normal operation of the equipment. Therefore, the heat dissipation system of the distribution box needs to be improved.


In the use of the fan distribution box, what we need to complete first is the circuit route design diagram of the fan distribution box, because better circuit routes exist, so that the fan distribution box can operate better, and it will not fail to operate normally due to route failure. What's special about the fan distribution box


It can start and stop manually, or through remote control. The equipment has status indication. In the line design, there is short-circuit protection and overload protection. There is a button indicator operation interface, power indication and operation indication. Its relay output control has stable performance.


  The safety of industrial production is inseparable from the protection of electric box. Unlike other industrial instruments and equipment, it has a huge body. Although it is slightly bulky, it always protects the safety of factory production.


        In our daily production activities, we often use nothing more than electrical equipment. We cannot install it at will. An operation error or other external factors may lead to electrical equipment failure or accident. These potential hazards can be effectively isolated through the electric box. Different models of electric boxes play different degrees of isolation effect. For example, our general chemical production workshop must have places where electricity is needed. For this flammable and explosive environment, we must put the electrical components into the cabinet. Therefore, the protection grade of the electrical box required at this time is very high.


        We must learn to use the electric box reasonably. Only by using the corresponding electric box in different environments can we play a big guarantee function.


  During the installation and construction of the distribution box, some of its safe operation matters have become the primary premise of the work. Therefore, some relevant safety and fire-fighting measures are specified during the construction of distribution box.


    1. Installation electricians and welders must work with certificates.


    2. The personnel participating in the construction shall carefully study the safety operation procedures and establish the post responsibility system.


    3. The insulation resistance test shall be conducted by two people to prevent electric shock injury.


    4. Before the formal power project is powered on, the protective grounding wire must be reliably connected and clearly marked.


    5. The sheath and pad of insulating tools shall be intact without damage, and the tools with serious aging shall be replaced in time.


  1. During electric welding, someone must "watch the fire" to prevent the fire slag from igniting the surrounding articles. The welding site shall be equipped with fire extinguishers and fire fighting water. After the electric welding operation is completed, carefully check whether there is any fire hazard on the site, and only after confirming the safety   You can leave the site.
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