【作者】 龚细秀；

【导师】 李福祺；

【作者基本信息】 清华大学 ， 电气工程， 2005， 硕士

【摘要】 变压器局部放电在线监测通常采用高频检测法和特高频检测法。高频检测法符合标准,能获得试品的视在放电量指标;但抗干扰能力差,难于获得高的监测灵敏度。特高频检测法的抗干扰能力强,但测量结果只能用毫伏数表示,限制了它在电力部门的应用。显然,将两种方法联合起来使用,取长补短,是一个提高局部放电在线监测灵敏度的可行办法。空气中的电晕放电干扰是难于提高局部放电在线监测灵敏度的重要因素。为了确定局部放电特高频测量装置的测量频带,以抑制电晕干扰,需要了解油中和空气中放电信号的频谱特征。为了试验室研究的需要,研制了阿基米德螺旋天线传感器,并和 TDS-684C数字示波器一起组成了特高频检测装置。研究了油中和空气中模型的放电信号的频谱特征。结果表明:油中局部放电的频谱较宽,电磁波的能量主要集中在250MHz~1GHz 之间,而空气中电晕放电辐射的频谱能量主要集中在 200MHz 以下。研究认为,可以将 300MHz 作为他们的“频分点”。对特高频信号在金属箱体和自由空间内的传播特性进行了研究,结果表明:信号在金属箱体内的衰减比在自由空间慢,信号传播由于受到折、反射的影响,不同位置测到的信号幅值波动较大。因此可以认为,特高频检测法只能检测到局部放电信号的相对变化量。研制了实用的特高频检测单元。包括:拉杆式传感器、放大器、滤波器和检波器。检波得到的是特高频信号的高频分量,降低了数据采集卡的采样率。将特高频检测单元和变压器局部放电高频监测系统组合在一起,构建了联合监测系统。在实验室中对模型的放电进行了试验研究,结果表明:特高频法和高频法测量到的局部放电信号有很好的时域对应关系。测量数据可以用简单的信号处理软件,将高频信号中的干扰剔除,提高高频信号的信噪声比。同时利用高频检测回路进行放电量标定,可以获得符合标准的视在放电量指标。更多还原

【Abstract】 High frequency (HF) and ultra high frequency (UHF) measurements are adoptedin on-line partial discharge (PD) monitoring for power transformer. The HF method isin accord with the standard, and we can get the apparent discharge quantities with it.But it also has some disadvantage such as poor interference influences ability, so thatit is hard to achieve high sensitivity. While the UHF method has better interferenceinfluences ability, but it can only measure the relativity variety of the discharge, andthis is limited its use. Obviously, if we unite them to use their strong points to offsettheir weakness, we will get an efficient method to improve the sensitivity of on-linePD monitoring.The sensitivity of on-line PD monitoring for transformer has been improvedhardly because of the corona discharge in air. In order to confirm the measurefrequency band of the UHF measure devises for restricting corona interference, weneed to know the frquency characteristic of the discharge signals in air and in oil.We designed an Archimedean spiral antenna to receive the UHF signals, andbuild the UHF detection system with the TDS-684C digital oscilloscope to meet theneed of the laboratory study. In the laboratory, we studied the frequency characteristicof the discharge signals in air and oil. The results show that the frequency ranges ofPD in oil from 250MHz to 1GHz, and frequency ranges of PD in air is under200MHz. And then we can take the 300MHz as their “point of frequency boundary”.The spread characteristic of the UHF signals in metal tank and free space wasstudied. It shows that the attenuation of UHF signal in metal tank is slow than that inair. Due to the reflection and refraction, the amplitudes of UHF signal measured atdifferent positions are quite different. So the UHF method can only get the relativechange of the partial discharge signals.We also designed the practical UHF detect unit (PUDU) including the pull-rod,the UHF sensor, the UHF amplifier, the UHF filter and the UHF demodulation cell.The demodulation circuit can acquire the HF components of the UHF signals, whichwill reduce the sampling rate of the A/D card.Uniting the PUDU with the HF partial discharge monitoring system fortransformer, we can get a practical combine monitoring system. The experimentswere carried out with the new monitoring system to study the model discharge inlaboratory. The results show that the PD signals detected with the HF method arecorrespond with that detected with the UHF method in time domain. And we canremove the interference of the HF signals after simple signal processing to improvethe ratio of the signal to noise. At the same time, we can obtain the apparent dischargequantities by the HF detecting.更多还原