Abstract
The article presents a novel on-line partial discharge (PD) monitoring system for power transformers, whose functioning is based on the simultaneous use of three unconventional methods of PD detection: high-frequency (HF), ultra-high frequency (UHF), and acoustic emission (AE). It is the first monitoring system equipped in an active dielectric window (ADW), which is a combined ultrasonic and electromagnetic PD sensor. The article discusses in detail the process of designing and building individual modules of hardware and software layers of the system, wherein the most attention was paid to the PD sensors, i.e., meandered planar inverted-F antenna (MPIFA), high-frequency current transformer (HFCT), and active dielectric window with ultrasonic transducer, which were optimized for detection of PDs occurring in oil-paper insulation. The prototype of the hybrid monitoring system was first checked on a 330 MVA large power transformer during the induced voltage test with partial discharge measurement (IVPD). Next, it was installed on a 31.5 MVA substation power transformer and integrated according to the standard IEC 61850 with SCADA (Supervisory Control and Data Acquisition) system registering voltage, active power, and oil temperature of the monitored unit. The obtained results showed high sensitivity of the manufactured PD sensors as well as the advantages of the simultaneous use of three techniques of PD detection and the possibility of discharge parameter correlation with other power transformer parameters.
Highlights
Power transformers are very important devices of public and industry use, requiring high capital investment
The registration of the radio signals in the VHF/ultra-high frequency (UHF) band generated by the partial discharges is carried out with the use of antennas mounted in special dielectric windows [36,37] or antennas put in the tank interior through oil valves [38,39]
The results of the analysis showed that the compared groups differ compared groups differ from one another statistically, which means that the oil temperature level from one another statistically, which means that the oil temperature level differentiates the number differentiates the number of partial discharge (PD) pulses
Summary
Power transformers are very important devices of public and industry use, requiring high capital investment. In combination with the SCADA (supervisory control and data acquisition) system, which is installed on the majority of substations, they allow to find the correlation between PD intensity and power transformer parameters, e.g., voltage or oil temperature [14,15] It increases the credibility of insulation system condition assessment and enables the introduction of current limitations of power transformer exploitation, assuming that its condition is not critical, and it does not require an immediate shutdown. When the system registers pulses simultaneously by all methods and the fluctuations of their intensity are similar, with high probability one may assume that they are generated by partial discharges As it was mentioned before, the credibility of the diagnosis may be increased by finding a correlation between PD parameters and power transformer parameters registered by the SCADA system.
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