Analysis of Phase Magnetic Field Effect of Vacuum Circuit Breakers in Electrical Engineering Hou Chunguang, Cao Yundong, Lai Changxue, Sun Jing 2 (School of Electrical Engineering, Shenyang University of Technology, Shenyang 110023, Liaoning, China; 2 Shenyang Quality Inspection Institute, Shenyang 110021, Liaoning, China) Vacuum Circuit Breaker In the process of breaking, the three-phase current is simulated in the entire variable period, and the influence of the three-phase current on the magnetic field between phases at different phase angles is obtained. In order to reduce the mutual influence of the magnetic fields, the ferromagnetic material is used as a shield between the three-phase quenching chambers. The changes in the maximum magnetic induction values ​​under different lengths and thicknesses of ferromagnetic materials are analyzed. The development of miniaturization provides a theoretical basis.

2: The development of the A power system and the enhancement of its transmission capacity have brought higher and higher requirements to low-voltage power equipment. For example: high execution can nine breaking capacity and miniaturization. In order to improve the breaking capacity of low-voltage high-current power equipment and further miniaturization, many measures have been proposed, such as optimizing contact shapes, improving contact materials, and adopting longitudinal magnetic field technology.

Vacuum circuit breakers have been widely used in the low-medium voltage field due to their many advantages such as strong breaking capacity, long life, simple structure, easy maintenance, easy miniaturization, non-combustion, and explosion. In order to further miniaturize the vacuum circuit breaker, two methods can be applied: reducing the size; reducing the arcing distance or achieving zero arcing.

However, with the continuous increase of the breaking capacity of the vacuum circuit breaker and its decreasing volume, the phase-to-phase magnetic field in the process of breaking off plays an increasingly important role, and its influence cannot be neglected.

This article mainly simulates the change of the magnetic field of each phase within one cycle of the breaking of the vacuum circuit breaker, and calculates the influence of the magnetic field between phases when breaking. The variation of the maximum magnetic induction under the shielding of ferromagnetic materials of different lengths and thicknesses was analyzed.

1 Mathematical Model Establishment In order to calculate the magnetic field distribution of a three-phase vacuum circuit breaker, a three-dimensional mathematical model was established using the finite element method. The following differential equation is satisfied: a type of boundary condition ls=C (constant) permeability.

The variation of this problem is expressed as 1 2 Calculation Example 2.1 Calculation Model The calculation model of the vacuum circuit breaker is as shown. Since the cross section of the actual busbar is rectangular, the equivalent model and the cross-section mesh are shown.

2.2 Calculation results and analysis The vacuum circuit breaker of this structure, short-circuit current and phase-to-phase distance are 50kA and 110mm, respectively. In order to clearly reflect the influence of phase-to-phase magnetic fields, the vacuum circuit breaker performs magnetic field simulation over the entire change cycle of the current. The sum shows the distribution of magnetic fields between phases when the current phase angles are 75* and 165*, respectively. The maximum magnetic induction intensity at this time is 0. Based on the design principle of the vacuum circuit breaker, the maximum magnetic induction intensity between the contacts is 0.2T under normal operating conditions. However, when the current phase angle is 165*, only A and C are two. Connected current and B phase current, the maximum magnetic induction intensity of phase B is 0.1242T. The magnetic field distribution is as shown. Therefore, it can be seen that in the case of high currents, the influence of the phase-to-phase magnetic field must be considered.

A, C two-phase power, B phase is not energized, the magnetic field distribution map equivalent model mesh map phase angle is 75, the magnetic field distribution map under the action of the magnetic field, the arc between the contacts burning horizontal The electromotive force as shown, under the influence of this force, will affect the effect of the longitudinal magnetic field on the arc, causing the arc to be deformed or stretched laterally, from an approximately circular shape to an elliptical shape, making the arc current distribution more concentrated. The arc voltage is increased, which increases the arc energy and is not conducive to the breaking of the contacts.

A, C two-phase power, B phase is not energized, B phase of the electric power In order to reduce the phase of the magnetic field, many companies in the circuit breaker to join the metal partition, or in the vacuum interrupter plus metal housing , such as Siemens 3AH5 type. When the phase angle is 16 and the magnetic field distribution is shown. 165. At the time of the magnetic field profile t in order to further analyze the ferromagnetic materials A and C of different thicknesses and lengths, two-phase currents are passed, and when the B-phase currents are not, the thickness of the ferromagnetic material is 5mm, the length is 50100mm, and the length is A magnetic field of 100 mm and a thickness of 210 mm was simulated. With the addition of the ferromagnetic material length, the maximum magnetic induction intensity of the B phase is shown in Table 1. From the data in the table, it can be seen that the maximum magnetic induction intensity gradually decreases as the ferromagnetic material length increases. Table 2 shows the maximum magnetic induction value length when the length of the ferromagnetic material is 90mm and the thickness of the thickness gauge 1 is 5mm/the maximum magnetic induction intensity value when the length of the table 2 is 90mm. When the thickness/degree is 2~10mm, the magnetic induction of the B-phase is maximum. The change in intensity. As can be seen from the table, with the increase of the thickness of the ferromagnetic material, the maximum magnetic induction intensity of the B phase gradually decreases.

3 conclusions This article has analyzed the influence of the phase magnetic field of different phase angles in the current cycle of the large current vacuum circuit breaker in the whole change cycle of the current, and after adding ferromagnetic shielding between phases, the maximum magnetic induction under the effect of ferromagnetic shielding of different length and thickness Changes in intensity were analyzed. From the analysis results, we have reached the following conclusion: For medium-voltage vacuum circuit breakers with large currents, the maximum magnetic field strength between the phases has a great influence on the longitudinal magnetic field between the contacts, so the influence of the magnetic field between the phases cannot be ignored. .

After adding the ferromagnetic material between the arc extinguishing chambers of the vacuum circuit breaker, a reasonable selection of the length and thickness of the ferromagnetic material can greatly reduce the maximum magnetic induction intensity generated between the phases, thereby reducing the arc voltage and reducing the arc energy. It helps to improve the breaking capacity and miniaturization of vacuum circuit breakers. It provides a theoretical basis for promoting the development of vacuum circuit breakers in the direction of miniaturization and large breaking capacity.

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