Epoxy resin casting type current transformer

Overview of voltage and current transformers A typical transformer uses the principle of electromagnetic induction to convert high voltage into low voltage, or convert large current into small current, to provide suitable voltage or current signals for measuring devices, protection devices, and control devices. The voltage transformer commonly used in power systems has a primary side voltage related to the system voltage, which is usually hundreds of volts to hundreds of kilovolts, and the standard secondary voltage is usually 100V and 100V/; while the current transformer commonly used in power systems has a primary side current of several amperes to tens of thousands of amperes, and the standard secondary current is usually 5A, 1A, 0.5A, etc.   1. Principle of voltage transformer The principle of voltage transformer is similar to that of transformer, as shown in Figure 1.1. The primary winding (high voltage winding) and the secondary winding (low voltage winding) are wound on the same iron core, and the magnetic flux in the iron core is Ф. According to the law of electromagnetic induction, the relationship between the voltage U of the winding and the voltage frequency f, the number of turns of the winding W, and the magnetic flux Φ is: 2. The principle of the current transformer It is also similar to the transformer in principle, as shown in Figure 1.2. The main difference from the voltage transformer is that under normal working conditions, the voltage drop on the primary and secondary windings is very small (note that it does not refer to the voltage to the ground), which is equivalent to a transformer in a short-circuit state, so the magnetic flux Φ in the iron core is also very small. At this time, the magnetic potential F (F=IW) of the primary and secondary windings is equal in magnitude and opposite in direction. That is, the current ratio between the primary and secondary of the current transformer is inversely proportional to the number of turns of the primary and secondary windings.   3. Terminals and polarity of transformer windings The voltage transformer winding is divided into the head end and the tail end. For a fully insulated voltage transformer, the voltage to the ground that the head end and the tail end of the primary winding can withstand is the same, while for a semi-insulated voltage transformer, the voltage that the tail end can withstand is generally only about a few kV. A and X are commonly used to represent the beginning and end of the primary winding of the voltage transformer, and a, x or P1, P2 are used to represent the beginning or end of the secondary winding of the voltage transformer; L1 and L2 are commonly used to represent the beginning and end of the primary winding of the current transformer, and K1, K2 or S1, S2 are used to represent the beginning or end of the secondary winding. Different manufacturers may have different numbers, usually with subscript 1 for the beginning and subscript 2 for the end.   When the induced potential of the terminals is in the same direction, they are called the same-name terminals; conversely, if the same-name terminals are connected to the same-name terminals, the magnetic flux they generate in the iron core is also in the same direction. The terminals with the same number as the beginning or the same end and the same induced potential direction are called subtractive polarity windings, and the voltage of the terminals is the result of subtracting the induced potential of the two windings. The correct number in the transformer is defined as subtractive polarity.   4. The main structural differences between voltage transformers and current transformers (1) Both voltage transformers and current transformers can have multiple secondary windings, but voltage transformers can have multiple secondary windings sharing one core, while current transformers must have independent cores for each secondary winding. There are as many cores as there are secondary windings.   (2) The primary winding of a voltage transformer has many turns and thin wires, while the secondary winding has fewer turns and slightly thicker wires. The primary winding of a high-voltage current transformer used in a substation has only 1 to 2 turns and thick wires, while the secondary winding has more turns. The thickness of the wire is related to the rated value of the secondary current.   (3) When the voltage transformer is operating normally, it is strictly forbidden to open the low-voltage terminal of the primary winding and short-circuit the secondary winding. When the current transformer is operating normally, it is strictly forbidden to open the secondary winding.   Hemei Electronics is committed to the research, development, production and sales of amorphous, nanocrystalline and Permalloy core products. Its main products include: Permalloy, silicon steel strip, silicon steel core, nanocrystalline core, Permalloy core, high-power transformer core, nanocrystalline magnetic ring inductor, electromagnetic ring coil, split-type current transformer, common mode inductor coil, precision current transformer and other products with good stability and high electrical parameters.

According to the installation location, the split current transformer can be divided into indoor and outdoor. The indoor type is less than 20kV; the outdoor type is greater than 35kV and above.   According to the installation method, it can be divided into wall type, support type and load type. The wall-mounted type is installed in the hole of the wall or metal structure to save the wall bushing; the support type is installed on the plane or column; the load type is 35kV and above transformer bushing or multi-oil circuit breaker oil tank. It is called sleeve type.   Split current transformers can be divided into dry type, casting type, oil-immersed type, etc. according to insulation performance. Dry impregnated insulation glue is suitable for the opening and closing of low-voltage household current transformers; the casting type uses epoxy resin as the insulating material, which is mainly used for current transformers of 35kV and below; the oil-immersed type is mostly outdoor.   According to the coupling mode of high and low voltage components, the new split current transformer can be divided into electromagnetic wave coupling, capacitive coupling and photoelectric coupling. Among them, the optical current transformer has better performance. The new type of open-close current transformer is characterized by no direct electromagnetic connection between high and low voltage, which greatly simplifies the insulation structure; no need to consume a lot of energy during the measurement process; no saturation, wide measurement range, fast transient response, high accuracy; light weight and low cost.   In the same circuit, a large number of open-close current transformers are usually required. High-voltage current transformers are usually composed of multiple independent magnetic cores and secondary windings, without magnetic connection, and the primary winding is shared, forming multiple secondary windings with the same current ratio and current mutual inductance. Equipment For open-close current transformers of 110kV and above, the primary winding is usually divided into several groups, and the series and parallel connections of the windings are changed by switching to obtain a mutual inductance ratio of 2:3.