Radiation noise due to EMI noise generated by the driving circuits of LED lighting devices in a medical imaging room was reduced by decreasing the noise source in the driving circuits and changing the number of corrections in EMI filters. Noise attenuation and filter changes enabled driving circuits that reduced the electromagnetic waves. Such circuits were efficiently designed by using capacitors and inverters in a given space. Therefore, the malfunction of radiation devices can be minimized by using EMI-reduction filter circuits, and reliable operation of medical devices can be expected by blocking electromagnetic waves.
In this paper, we studied the magnetic composite sheets for electromagnetic wave noise absorber of quasi-microwave band by using soft magnetic FeSiCr and Fe50Ni flakes with the thickness of about 1 μm and polymer. The magnetic hysteresis curve including saturation magnetization and residual magnetization and the complex permeability characteristics of the composite sheets were investigated to clarify the mixing effect on electromagnetic wave absorption properties. The saturation magnetization was decreased about 10% while the residual magnetization was increased about 15% and the real parts of complex permeability at below 500 MHz were increased 0.6～4 while those values at above 500 MHz were decreased 0.4～2.5 according to the change of contents of FeSiCr and Fe50Nipowders. As a result, the reflection loss can be moved to the lower frequency from 2∼3 GHz to 1∼1.5GHz as the contents of Fe50Ni flaky powder into FeSiCr flaky powder was increased up to 50%.
This paper dealt with the radiated electromagnetic wave detection of partial discharge (PD) in oil for insulation diagnostics of oil-immersed transformers. Three types of electrode system were fabricated to simulate the insulation defects that could occur in oil-immersed transformers. Frequency components of radiated electromagnetic wave in oil was measured by broadband bi-conical antennas of 300 MHz∼2 GHz and a spectrum analyzer of 9 kHz∼3 GHz. Frequency component of electromagnetic waves from PD in oil were highly distributed at 500 MHz. From the result, a narrow-band monopole antenna with the center frequency of 500 MHz was fabricated. We could detect PD signal in insulation oil without an influence of external noise by a measurement system which consists of the prototype monopole antenna, a LNA (Low Noise Amplifier), an oscilloscope and a spectrum analyzer.
This paper dealt with the measurement and analysis of electromagnetic waves radiated from a partial discharge (PD) source in insulation oil to apply condition monitoring of oil-immersed transformers. Two types of narrow-band monopole antennas with the resonant frequency of a 500 MHz and a 1 GHz were designed and fabricated. Also, a needle plane electrode system was manufactured to simulate PDs and the curvature radius of the needle is 10 pm and the diameter of the plane is 60 mm. Electromagnetic wave was measured by the PD measurement system with the monopole antennas. Detection sensitivity of the fabricated antenna was compared for the same P1) magnitude; 620 mVpeak for the 500 MHz antenna and 960 mV1,t for the 1 GHz antenna to the PD magnitude of 74 pC. Consequently, the 1 GHz monopole antenna is more effective to detect PDs in oil immersed transformers.
Frequency domain measurement of propagation loss for ultra high frequency (UHF) partial discharge in the winding of power transformer using a spectrum analyzer and pulse generator is presented. We compared the performance of the method using a network analyzer with and without a winding. Using a network analyzer simplifies the measurement and offers better dynamic range and frequency range. It also provides precise propagation loss within the winding in frequency domain at UHF range. We applied this method to measure UHF propagation loss of transformer mock-up, modeled 154 kV 20 MVA power in KEPCO substation.
This paper describes the characteristics of electromagnetic wave propagation wave propagation in power transformer. A transformer which is similar which is similar to 154 kV single phase on-site transformer unit was provided for the purpose of the experiment. The 12dieletric windows on the transformer enclosure to install UHF(ultra high frequency) sensors and the full scale mock ups of winding and the core were also euipped in the transformer. Every sensors to be installed to the transformer was tested and verified whether they show same characteristics or not beforethe experiment. A discharge gap which was used as a PD (partial discharge) source moved to or not before the experiment. A discharge gap which was used as a PD (partial discharge) source moved to several necessary locations in the transformer to simulate dielectrie defects. Propagation times of electromagnetic wave signal from PD source to sensors decided by the routes of both reflection phenomenon and diffraction phenomenon were compared each other. The experimental results showed propagation route of the PD signal makes an effect on the frequency spectrum of front part of the signal and the magnitude of the signal and propagation time of the signal when the signal is captured on the sensor
A Study on the Operation Characteristics of Arc Fault Detection Device under Arc Generation Heejun Kwon, SungHwan Kim, Jihee Lee, Kiseok Kim, Haiyoung Jung International Journal of Fire Science and Engineering.2024; 38(2): 27. CrossRef
Highly Sensitive Partial Discharge Sensor with Remote Monitoring Capabilities Kyoo-Nam Choi The Journal of the Korea institute of electronic communication sciences.2015; 10(3): 349. CrossRef
Harmonics Analysis of Leakage Current due to Artificial Contamination of Distribution Arresters Jae-Jun Park The Transactions of The Korean Institute of Electrical Engineers.2012; 61(9): 1306. CrossRef
Analysis of Leakage Current Waveforms for Transmission Line Porcelain Insulators due to ESDD Contamination Jae-Jun Park The Transactions of The Korean Institute of Electrical Engineers.2012; 61(10): 1461. CrossRef
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