| Summary: | 碩士 === 國立臺灣科技大學 === 電機工程系 === 101 === When a fault occurs in a power system, it will produce a huge nonlinear fault current, cause a surge, and damage the system security. When detected by traditional current transformers, this fault current, which has an exponential component, will cause iron core saturation and distortion in waveform detection. This condition will cause inaccurate measurements and protection. Furthermore, in some special environment such as long-range overhead lines, under-ground cables and remote environment, it will be difficult to use cables to transmit data. The cost of the installation will be very high.
Because of those problems, a novel electronic current transformer (ECT) is proposed in this study, which is based on coreless Hall current transformers. The main circuits of ECT include a signal sensing circuit, an analog-to-digital conversion circuit and a ZigBee transmission circuit to replace traditional current transformer, and save space. According to IEC standard 60044-8 about electronic current transformer specifications, the accuracy level of measurement must satisfy Class 0.5, and the protection error can satisfy 5P14. Considering the cost, this novel ECT uses a simple microcontroller and a built-in analog-to-digital converter to achieve required resolution. This design proposes a switching method to improve measurement range, and a delay sampling method to solve the problem that the ZigBee cannot transmit the current waveform in time.
In the experiment, this study has completed some tests, such as signal sensing process circuit test, load current accuracy test, and fault and large current warning mechanism test. Ranges of current measurements and rated at 600A for normal load current and the fault current can reach 8.4 kA.
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