Research On UHF Method For PD Detection In Power Transformer

Power Transformer is main equipment in Electric Power system, and its price is very high, so Maintenance is quite necessary for Transformer. There are Scheduled Maintenance and Break down Maintenance for Transformer traditionally, traditional methods of Maintenance are compulsive and blindfold,these two not only spend manpower and material resources, but also bring more potential trouble while the components frequently taken down, and synchronously reduced overall life of Transformer. Since the severe fault of traditional methods of Maintenance, a new one plays a more and more important role which Maintenance is determined according to the fieldwork conditions of Transformer, and that's what we would call Condition Based Maintenance. Condition Based Maintenance is schemed according to the results of various instruments and visitatorial records of personnel, on the basis of the analysis of technicians and the current status of Transformer.Condition Based Maintenance is concerned with monitoring technology and diagnosis technology deeply, that is to say , we can get current status of Transformer by sorts of monitoring methods. Most of faults involve insulation for Transformer, and monitoring for Partial Discharge (PD)can reflect the insulation status of Transformer in advance, find the fault within Transformer on time, and prevent potential and paroxysmal events. Considering what have discussed above, in this dissertation, I designed a set of UHF (ultra high frequency) monitoring system on Partial Discharge of Transformer. This system can monitor the real-time signal of PD UHF, and then get the insulation status and the running conditions of Transformer.Comparing with traditional method of monitoring impulse current of PD directly, UHF method has quite a few advantages, such as better anti-jamming, much more information, and more sensitive. The UHF signal produced by impulse current of PD can be received by UHF sensor, there is UHF sensor-plane helix antenna designed in this article, Whose bandwidth is between 500MHz to 1500MHz. Two sides of this antenna are feed by 50ohm coaxial line, the Hertzian waves signal is converted to high frequent current signal by the same frequency and the current signal can be transferred into industry computer by coaxial line.The signal frequency received by the antenna is very high, normally it can exceed one GHz. Usually the sample card can not collect so high frequency signal, and it is not necessary to collect the total signal because what we need is the peak value of the signal, and then to know the severe degree of the PD of Transformer relatively .A signal disposal cell based on Frequency Mixing is designed in this dissertation, it can reduce the frequency of original UHF signal to facilitate a common sample card and it is not at the expense of Peak-Value and phasic character of original UHF signal.