As the load is connected to PLMT(Power Load Management Terminal) through CT(Current Transformer),the impedance of CT secondary circuit will change if there is electricity-theft. The ST(Signal Transformer) is designed in the current measuring circuit of PLMT to realize signal isolation and monitor the impedance change of CT secondary circuit in real-time. Combined with the impedance matching circuit of ST, the effect of electricity-theft at CT primary or secondary side on ST input impedance is analyzed. Being sensitive to impedance change,specific high-frequency signals are injected into ST,which are sampled and processed by microprocessor AT91SAM7S256. The mean square amplitude of sampled high-frequency signals diffens according to different electricity-theft means. The experiment shows that,the theftproof device can find and identify the electricity-theft quickly and accurately.%负载电流经电流互感器(TA)接入电力负荷管理终端内部的交流采样装置,若存在电流法窃电行为,TA二次回路的阻抗会发生变化.在终端内部电流计量回路设计了信号变送器ST(Signal Transformer),以实现强弱信号的隔离,并实时监测TA二次回路的阻抗变化;结合ST的阻抗匹配电路,详细地分析了TA一次/二次侧不同的窃电手段对ST输入阻抗的影响;利用高频信号对阻抗变化敏感的特性,向ST注入特定频率的高频振荡信号,并由微处理器AT91SAM7S256对流经ST的高频信号进行数据采集和处理;窃电手段不同,微处理器采集的高频信号均方幅值也不同.试验表明,该防窃电装置可快速、准确地识别发生在TA一次/二次侧的窃电行为及具体的窃电方式.
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