35 / 2024-03-29 14:51:34

Electromagnetic Radiation Test of Molded Case Circuit Breaker during Switching Operation

Electromagnetic Radiation,circuit breaker,primary and secondary fusion,transient electric and magnetic fields

Due to the rapid development of primary and secondary fusion technology in smart grid, the electromagnetic interference generated during the action of switchgear often affects the normal operation of secondary smart devices. This paper takes the molded case circuit breaker as an example. The transient electric and magnetic fields induced by the circuit breaker at the moment of action will interfere with the secondary intelligent devices around the circuit breaker. Therefore, it’s significant to explore the electromagnetic interference problem in the fast transient process of circuit breakers. This study aims to analyze the electromagnetic interference generated during the switching operation of molded case circuit breakers under different voltages, currents and phases.

The experiments have been conducted under voltage levels of 400V, 800V, and 1150V and current levels of 15kA, 20kA, 30kA, 40kA and 50kA, and breaking phase angle of 0°, 60°, 90° and 150°. The variation and characteristics of electromagnetic interference in transient processes are studied by measuring the electrical and magnetic fields generated after the circuit breaker tripping at same voltage threshold. The schematic diagram of the experimental system is shown in Fig.1, different levels of system voltage and current are applied to the circuit breaker through a short circuit generator and the transient electromagnetic field derivative waveform during the closing process is measured by using the D-Dot probe and the B-Dot probe. Therefore, the arc voltage and current are synchronously collected during the separation of the moving and static contacts. After electric power is applied on the circuit breaker and its static and movable contact are separated, arc plasma will appear between two contacts, transient electric field will be generated due to the voltage fluctuation and transient magnetic field is induced due to short circuit current. Taking the test condition of 400V, 20kA, 0° as an example, the electric and magnetic fields near the circuit breaker in the form of output voltage through an oscilloscope are shown in Fig.2. After obtaining the experimental results, the waveform of the electromagnetic field during the arcing process was subjected to Fourier transformation to obtain its distribution in the frequency domain, as shown in Fig.3. Then, the spectral data of the part with frequencies greater than 4.688MHz was extracted. Fig.4 shows the derivative waveform recovered to the time domain by inverse Fourier transform, Finally, the time domain waveform of the high frequency part of the electromagnetic field is obtained by digital integration.

According to experimental results, the maximum electric field generated during the arcing process is 63.61kV/m, and the maximum magnetic field is 181.8A/m. These results provide basis for the formulation of electromagnetic compatibility test of the primary and secondary fusion devices.