J. Ardila, R. Albarracín, J.M. Martínez-Tarifa, G. Robles

Outline Introduction Partial discharge (PD) phenomenology Radio-frequency emission of partial discharges The Vivaldi antenna Spectral Power Ratios (PR) Measurements Conclusions

Outline Introduction Partial discharge (PD) phenomenology Radio-frequency emission of partial discharges The Vivaldi antenna Spectral Power Ratios (PR) Measurements Conclusions

Introduction – What are PDs? Partial discharges (PD) are the dielectric breakdown of a gas within solid/liquid insulation systems due to highly concentrated electric fields. They are rapid flows of charge carriers lasting some nanoseconds. They do not provoke a direct failure of the whole dielectric, but provide electrical ageing.

Introduction – What are PDs? PDs can also be a consequence of other degradation mechanisms which lead to defects inside the insulation. It is a quite common phenomenon in high-voltage (HV) electric machines and power cables. Measuring these types of discharges is of importance because their number and amplitude is related to ageing of insulation in electric equipment.

Introduction – Measuring PDs PDs can detected using capacitive couplers. This can help measuring the phase-resolved partial discharge (PRPD) patterns. The phase occurrence sometimes enable the identification of noise and the type of PD.

Partial discharges emit energy in the radiofrequency (RF) range. (+) Useful for on-line measurements. (-) Electromagnetic interferences mainly from FM and TV. Introduction – Measuring PDs

Partial discharges emit energy in the radiofrequency (RF) range. (+) Useful for on-line measurements. (-) Electromagnetic interferences mainly from FM and TV. Different types of antennas can be used to measure that type of emission. Introduction – Measuring PDs

Partial discharges emit energy in the radiofrequency (RF) range. (+) Useful for on-line measurements. (-) Electromagnetic interferences mainly from FM and TV. Different types of antennas can be used to measure that type of emission. The frequency spectrum depends on the PD site and multipath reflections. Introduction – Measuring PDs

Partial discharges emit energy in the radiofrequency (RF) range. (+) Useful for on-line measurements. (-) Electromagnetic interferences mainly from FM and TV. Different types of antennas can be used to measure that type of emission. The frequency spectrum depends on the PD site and multipath reflections. There is useful information in the spectrum that can help to separate PD from electromagnetic interference. Introduction – Measuring PDs

Outline Introduction Partial discharge (PD) phenomenology Radio-frequency emission of partial discharges The Vivaldi antenna Spectral Power Ratios (PR) Measurements Conclusions

Size 9 cm x 12 cm x 0.15 cm. Highly directive. FM noise in the range 88 – 108 MHz will be rejected. Description

Outline Introduction Partial discharge (PD) phenomenology Radio-frequency emission of partial discharges The Vivaldi antenna Spectral Power Ratios (PR) Measurements Conclusions

Spectral power ratios fTfT

f 2L f 1L fTfT

Spectral power ratios 0 ≤ f 1L <f 2L, f 1H <f 2H ≤ f T and f 1L <f 2H f 2H f 1H f 2L f 1L fTfT

Spectral power ratios 0 ≤ f 1L <f 2L, f 1H <f 2H ≤ f T and f 1L <f 2H The Power Ratios (PR) map

Spectral power ratios The technique is helpful for pulse separation. Good results when applied to HF/VHF inductive sensors.

Outline Introduction Partial discharge (PD) phenomenology Radio-frequency emission of partial discharges The Vivaldi antenna Spectral Power Ratios (PR) Measurements Conclusions

Measuring setup 2-channel NI-5152 digitiser with sampling frequency of 2 GS/s High-voltage variable source up to 18 kV to create PD in the test objects RF signals Syncronization

The algorithm acquires 2000 time windows of 0.5 μs (1ms) and then starts over up the completion of 20 ms. The amplitudes of the RF pulses in the 0.5 μs window and the high-voltage phases of occurrence in the 1 ms periods are plotted to obtain the PRPD pattern. The data acquisition is fragmented because the memory of the acquisition board is limited to 64 MB per channel. Signal acquisition

First step: Low voltage, 400 V, so there is no PD activity. Electromagnetic background noise is mainly due to: Frequency Modulation (FM) Radio Digital Audio Broadcasting TV Noise characterization

PRPD pattern and average frequency spectrum for electromagnetic noise

Test objects Surface discharges Internal discharges

Twisted pair High trigger to acquire only PD pulses Voltage set to 900 V. Distance to antenna: 80 cm Distance to antenna: 150 cm

Twisted pair High trigger to acquire only PD pulses Voltage set to 900 V. Distance to antenna: 80 cm Distance to antenna: 150 cm

Twisted pair Power ratios (PR) map for PD: f 1L = 40 MHz, f 2L = 160 MHz, f 1H = 440 MHz, f 2H = 560 MHz. f T = 1 GHz. 80 cm 150 cm

Twisted pair Noise and PD: same HV and reduced trigger level. 80 cm 150 cm

Twisted pair Noise and PD: same HV and reduced trigger level. 80 cm 150 cm The green cluster seems to be PD...

Twisted pair The green cluster is selected and plotted in a PRPD pattern: Surface PD is confirmed. Noise can be rejected. 80 cm150 cm

Contaminated ceramic bushing High trigger to acquire only PD pulses. Voltage set to 16 kV. 80 cm 150 cm

Contaminated ceramic bushing High trigger to acquire only PD pulses. Voltage set to 16 kV. 80 cm 150 cm

Contaminated ceramic bushing Power ratios (PR) map for PD: f 1L = 24 MHz, f 2L = 220 MHz, f 1H = 213 MHz, f 2H = 399 MHz. f T = 400 MHz. 80 cm 150 cm

Contaminated ceramic bushing Noise and PD: same HV and reduced trigger level. 80 cm150 cm

Contaminated ceramic bushing Noise and PD: same HV and reduced trigger level. 80 cm150 cm The green cluster seems to be PD...

Contaminated ceramic bushing The green cluster is selected and plotted in a PRPD pattern: Surface PD is confirmed. Noise can be rejected. 80 cm 150 cm

Internal discharges High trigger level to acquire only PD pulses. Voltage set to 11 kV. Antenna located at 80 cm.

Internal discharges High trigger level to acquire only PD pulses. Voltage set to 11 kV. Antenna located at 80 cm. Intervals used for PR maps: f 1L = 23 MHz, f 2L = 203 MHz, f 1H = 224 MHz, f 2H = 386 MHz, f T = 1 GHz.

Internal discharges Noise and PD: same HV and reduced trigger level.

Internal discharges Noise and PD: same HV and reduced trigger level.

Internal discharges Noise and PD: same HV and reduced trigger level.

Outline Introduction Partial discharge (PD) phenomenology Radio-frequency emission of partial discharges The Vivaldi antenna Spectral Power Ratios (PR) Measurements Conclusions

Inexpensive antennas can capture radiofrequency pulses due to partial discharge activity. There are bands of frequencies where the energy received is increased when measuring PD. Conclusions

Inexpensive antennas can capture radiofrequency pulses due to partial discharge activity. There are bands of frequencies where the energy received is increased when measuring PD. The use of the power ratios maps gives good separation results for radiofrequency signals, being able to characterize noise and PD in a PRPD. Conclusions

If noise is previously characterized, new clusters in the PR map could be an indication that PD may be occurring in the electrical asset. Later on, a deeper analysis in an scheduled disconnection of the electrical machine using conventional PRPD measurements could be made. Conclusions

J. Ardila, R. Albarracín, J.M. Martínez-Tarifa, G. Robles

Review of spectra Noise Twister pair PD Bushing PD Internal PD