Openable current transformers are also commonly called open-close current transformers. Generally, they refer to handheld transformer products that can be installed and used for a long time without opening the measured circuit, or can measure existing circuits at any time as needed.
In actual applications, there are many cases where equipment is added to existing circuits. Since it is never allowed to disconnect cables or busbars for power-off installation during the construction process, conventional closed-loop products cannot meet the installation requirements, and the use of open-type products becomes the only solution.
The principle of openable products is the same as that of conventional closed-loop products, but when the product is produced, the openable product cuts the closed high-magnetic permeability circuit according to the product structure to form two parts of the high-magnetic permeability circuit, and then winds the secondary winding on the two parts or one part of the high-magnetic permeability circuit. After the winding is completed, the two parts of the high-magnetic permeability circuit and the secondary winding above are combined into a closed magnetic circuit to form a complete transformer product. In actual use and installation, it can be repeatedly opened and combined again to achieve the purpose of power-off installation.
Due to the difference in structure, the magnetic circuit of the openable product is cut into at least two parts. Even if the combination is perfect, there is still a large magnetic resistance at the joint, resulting in a large leakage magnetic field. Therefore, for transformers with the same aperture, size and parameters, the openable product is much worse than the closed-loop product in performance, and there is a large difference in linearity accuracy. Especially when the open-type product is used for residual current detection, the leakage magnetic field at the joint causes the product balance characteristic index to be very poor, and a very large cost must be invested to ensure it, especially for large-sized products, which greatly increases the cost of use. Therefore, in actual production and application, the cost and price of the open-type residual current transformer with the same accuracy level and requirements are much higher than those of the closed-loop product.
With the continuous development of magnetic materials and the continuous improvement of the production process of magnetic materials, and the continuous improvement of the production process of transformers, the accuracy of the openable transformer has also been further improved. Some products can reach the standard requirements of 0.2 or even 0.1.
At present, the soft magnetic materials that can be used in the production of open-type products are generally: silicon steel materials, nanocrystalline alloy materials, Permalloy materials and ferrite materials. Silicon steel materials are mainly used for the production of openable products for large current measurement and protection, and can basically meet the requirements of level 0.5 or level 1; nanocrystalline alloy materials are mainly used for the production of openable products for current measurement and residual current detection, and have a much higher initial magnetic permeability than silicon steel materials, so the accuracy can be better guaranteed and can be made higher. It's just that the process requirements are high and the cost is high. Permalloy materials are mainly used in precision measurement and residual current detection. Basically, it is a material that can make the transformer the highest in precision with current technology applications. It can be costly and have high process requirements. It is only used in applications with high requirements and insensitive to cost.
In recent years, with the development of software, the nonlinear characteristics of the transformer output can be corrected by software, which reduces the requirements of the equipment for the transformer a lot. On equipment with less high requirements, ferrite materials have appeared in the application of power frequency current transformers. This type of product has the characteristics of poor load capacity, small output signal, and low accuracy, but its price is also low.
From the cost point of view, it is necessary to comprehensively calculate the installation cost and the reliability and cost of the product to select the openable current transformer product. In any case, as long as there are conditions to install closed-loop current transformer products, closed-loop products should be installed first to increase the stability, reliability and detection accuracy of the system, while having the lowest hardware cost. Only when it is impossible to install without power off, open products are selected. At the same time, it is necessary to consider that since most soft magnetic materials are made of iron elements, they will rust in a humid environment. As the rust progresses, the performance of the transformer will gradually deteriorate, and the system will become less reliable and stable. Unless Permalloy materials and waterproof products are selected, the problem of rust on the iron core is difficult to avoid.
The company's openable products have 4 series and dozens of specifications according to the appearance and application. It can meet the current measurement, monitoring and protection of most electrical lines and equipment; monitoring of current in AC motors, lighting equipment, heating, ventilation and air conditioning devices; and the use of power management and building self-control system engineering. In special cases, it can be designed and produced according to project needs.