On-Line Partial Discharge Monitoring System for Power Transformers Based on the Simultaneous Detection of High Frequency, Ultra-High Frequency, and Acoustic Emission Signals

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.

Non-Contact High Voltage Measurement in the Online Partial Discharge Monitoring System

“…If the system registers acoustic and electromagnetic pulses simultaneously, it can be assumed with a high probability that their source is partial discharges. Figure 1 shows the result of an eight-day PD monitoring carried out on a 31.5 MVA power transformer [12]. The Pearson correlation coefficient between the hourly distribution of the UHF and AE pulses was r = 0.87 with significance p = 0.001, which means a very strong positive correlation and confirms the presence of partial discharges.…”

“…The default partial discharge detectors are acoustic emission sensors optimized to detect discharges occurring in oil-paper insulation [33]. The system has also been adapted to work with high-frequency current transformers (HFCT), UHF antennas, and active dielectric windows [12]. The detailed structure of the system and examples of its implementation for monitoring power transformers are discussed, among others, in [23].…”

“…With such an advanced degree of transformer overexploitation, relying only on periodic diagnostics is With such an advanced degree of transformer overexploitation, relying only on periodic diagnostics is insufficient and generates too high a risk. For this reason, in the last dozen or so years, the intensity of work on the development of online partial discharge monitoring systems has been increased [9][10][11][12][13]. These systems most often use the acoustic emission (AE) method or electromagnetic methods for recording signals in the high frequency (HF), very high frequency (VHF), and ultrahigh frequency (UHF) radio frequency bands [14][15][16][17][18][19].…”

Non-Contact Methods for High-Voltage Insulation Equipment Diagnosis during Operation

“…Thus, the possibility of contactless detection of sources of electric fields appears important to determine the degree of their influence on the surrounding space. Additionally, the registration of local overvoltage in transformer windings, in high-voltage insulators and cables, can indicate the presence of insulation defects, which ultimately cause damage and even destruction of the insulating elements [9][10][11][12][13][14][15][16][17][18][19]. Therefore, it is necessary to control the occurrence of local overvoltage during the high-voltage insulation operation.…”

Flexible Sensor Array Based on Transient Earth Voltage for Online Partial Discharge Monitoring of Cable Termination

“…PD measurement methods based on electrical, acoustic, chemical, and mechanical phenomena associated with the PD process have been used for many years as nondestructive offline or online techniques for insulation condition evaluation of high-voltage equipment [ 4 , 5 , 6 ]. These methods include the pulse current method (IEC 60270) [ 7 ], HF (3–30 MHz) [ 8 ], VHF (30–300 MHz) [ 9 ], UHF (300 MHz–3 GHz) method [ 10 , 11 , 12 ], the transient earth voltage (TEV) method [ 13 , 14 , 15 ], the acoustic emission method [ 16 , 17 , 18 ], and the oscillating wave test method [ 19 ].…”