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Antenna Parametrization for the Detection of Partial Discharges

Article in IEEE Transactions on Instrumentation and Measurement · May 2013

Impact Factor: 1.79 · DOI: 10.1109/TIM.2012.2223332

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6 authors, including:

Guillermo Robles

University Carlos III de Madrid

67 PUBLICATIONS 318 CITATIONS

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Ricardo Albarracín

Universidad Politécnica de Madrid


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Eva Rajo-Iglesias


154 PUBLICATIONS 1,336 CITATIONS

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Juan Manuel Martínez-Tarifa



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Available from: Guillermo Robles

Retrieved on: 02 June 2016

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1569264829 1

Antennas parametrization for the detection of partial

dischargesG. Robles∗, M. Sánchez-Fernández†, R. Albarracín∗, M.V. Rojas-Moreno∗, E. Rajo-Iglesias† and J.M.

Martínez-Tarifa∗

∗ Departamento de Ingeniería Eléctrica†Departamento de Teoría de la Señal y ComunicacionesUniversidad Carlos III de Madrid, Leganés - 28911 Madrid (Spain)

Email:[email protected]

Abstract —Partial Discharge (PD) detection is awidely extended technique for electrical insulation di-agnosis. Ultra High Frequency (UHF) detection tech-niques appear as a feasible alternative to traditionalmethods thanks to their inherent advantages such asthe capability to detect partial discharges on-line and to

locate the piece of equipment with insulation problemsin substations and cables. In this paper, four antennasare thoroughly studied by means of their theoreticaland experimental behavior when measuring electro-magnetic pulses radiated by partial discharges activity.The theoretic study of the band of frequencies in whichthe pulse emits and the measurement of the parametersS 11 is complemented with the frequency response andwavelet transform of a set of 500 time signals acquiredby the antennas and the results are analyzed in detail.

Index Terms—Antennas measurements, partial dis-charges, UHF antennas, UHF measurements, dielectricmeasurements, wavelets.

I. Introduction

Electrical insulation is a key issue in power systemsreliability. It is well known that oil-impregnated paperin power transformers, epoxy resins in generators andpolyethylene in power cables are subjected to severalmechanical, thermal and electrical stresses that degradetheir behaviour leading to unexpected failures of theseexpensive assets and to power outages [1]. A well-knownageing mechanism of electrical stress is partial discharges(PD) activity [2]. Partial discharges are low energy ion-izations that take place in microscopic sites of electricalinsulation due to its lack of homogeneity in permittivityand dielectric strength. This is typical in air voids within

solid and liquid insulations where, even rated voltagesapplied to the power apparatus, provoke ionizations of the air. Partial discharges do not cause an immediatefailure of electrical insulation, but degrade its propertiesdue to chemical and physical attack [3]. Moreover, partialdischarges can be a symptom of other ageing mechanismsmentioned above [4]. For all these reasons, partial dis-charges measurements have been standardized as tests forelectrical equipment maintenance [5]. In these classicaltests, a capacitive branch is connected to the equipmentterminals to detect high frequency pulses created from PD.The pulse amplitude is represented superimposed to the

phase of the applied voltage (Phase Resolved Partial Dis-charge patterns, PRPD patterns) in order to distinguishbetween different kinds of partial discharges [2]. However,PD measurements are usually made in industrial facilitieswhere high levels of electrical noise are always present.

This makes difficult the interpretation of the PD patternand the diagnosis of the insulation. PD recognition is doneby analysing PD pulse waveforms acquired with inductivedevices as High Frequency Current Transformers (HFCT),Rogowski Coils or inductive loops [6], [7], [8]. In any case,these measurements require the disconnection of electricalequipment before installing the measurement setup. Inaddition, all these techniques cannot locate PD sourcesgeometrically, which could be useful for power equipmentmaintenance. Electro-acoustic and Ultra High Frequency(UHF) emissions from partial discharges can be measuredto overcome these limitations, [9]. The first option usespiezoelectric sensors to detect pressure waves propagating

through oil, which rejects any electrical noise coupling tothe acquired signals [10]. However, these sensors cannotdetect PD occurring inside solid dielectrics; they havetypically low sensitivity and narrowband, which makesit difficult to detect PD that are close in time [9]. Asmentioned before, another new research trend for PDdetection is the use of antennas for UHF detection of partial discharges. This technique is based on non-contactmeasurements, so its application to on-line measurementsis appropriate [11], [12], [13]. These sensors can also beused for any kind of insulating material and give ex-cellent results in PD location in large facilities such assubstations [14]. Moreover, the increasing number of High

Voltage DC applications in power grids require that PDare detected without synchronization signals [15], whichcan be solved with antennas. The main drawback of PDdetection through antennas is the presence of noise sourcesdue to FM, TV, GSM, WiFi emissions, so the antennaresponse to both PD and noise is an interesting researchtopic for PD detection [16], [17]. The comparison of severalantennas had been presented before [12], but a deeperanalytical background for these devices (monopole, zigzag,cone shaped...) was missing in order to model PD and noisedetection capability. A good theoretical model for patchantennas is found in [18] and [19], but the response to PD

https://www.researchgate.net/publication/44338476_Electrical_power_equipment_maintenance_and_testing_Paul_Gill?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==http://-/?-https://www.researchgate.net/publication/3340565_Degradation_of_Solid_Dielectrics_due_to_Internal_Partial_Discharge_Some_Thoughts_on_Progress_Made_and_Where_to_go_now?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/4377837_Electrical_Insulation_for_Rotating_Machines_Design_Evaluation_Aging_Testing_and_Repair?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/273172045_High-Voltage_Test_Techniques_-_Partial_Discharge_Measurements?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==http://-/?-https://www.researchgate.net/publication/224569382_Inductive_Sensor_for_Measuring_High_Frequency_Partial_Discharges_Within_Electrical_Insulation?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/3406036_Using_Rogowski_coils_for_transient_current_measurements?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/233741471_Implementation_of_a_Rogowski_coil_for_the_measurement_of_partial_discharges?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224359757_Detection_and_Location_of_Partial_Discharges_in_Power_Transformers_using_Acoustic_and_Electromagnetic_Signals?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/231023331_Acoustic_measuring_of_partial_discharge_in_power_transformers?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224359757_Detection_and_Location_of_Partial_Discharges_in_Power_Transformers_using_Acoustic_and_Electromagnetic_Signals?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224359753_Partial_Discharge_Measurement_in_the_Ultra_High_Frequency_UHF_Range?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224359765_Optimisation_of_a_Sensor_for_Onsite_Detection_of_Partial_Discharges_in_Power_Transformers_by_the_UHF_Method?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/262367481_Detection_of_Partial_Discharges_by_a_Monopole_Antenna_in_Insulation_Oil?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224363965_RF-Based_Partial_Discharge_Early_Warning_System_for_Air-Insulated_Substations?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224215974_Diagnostic_of_HVDC_systems_using_partial_discharges?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/4055880_A_Non-Intrusive_Partial_Discharge_Measurement_System_based_on_RF_Technology?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/232250454_Antenna_selection_and_frequency_response_study_for_UHF_detection_of_partial_discharges?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224359765_Optimisation_of_a_Sensor_for_Onsite_Detection_of_Partial_Discharges_in_Power_Transformers_by_the_UHF_Method?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224148558_Electromagnetic_Waves_from_Partial_Discharges_and_their_Detection_Using_Patch_Antenna?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/254059538_Electromagnetic_Waves_from_Partial_Discharges_in_Windings_and_their_Detection_by_Patch_Antenna?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/273172045_High-Voltage_Test_Techniques_-_Partial_Discharge_Measurements?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224569382_Inductive_Sensor_for_Measuring_High_Frequency_Partial_Discharges_Within_Electrical_Insulation?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/232250454_Antenna_selection_and_frequency_response_study_for_UHF_detection_of_partial_discharges?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/3406036_Using_Rogowski_coils_for_transient_current_measurements?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/4055880_A_Non-Intrusive_Partial_Discharge_Measurement_System_based_on_RF_Technology?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224359753_Partial_Discharge_Measurement_in_the_Ultra_High_Frequency_UHF_Range?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/44338476_Electrical_power_equipment_maintenance_and_testing_Paul_Gill?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224148558_Electromagnetic_Waves_from_Partial_Discharges_and_their_Detection_Using_Patch_Antenna?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/233741471_Implementation_of_a_Rogowski_coil_for_the_measurement_of_partial_discharges?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/231023331_Acoustic_measuring_of_partial_discharge_in_power_transformers?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/262367481_Detection_of_Partial_Discharges_by_a_Monopole_Antenna_in_Insulation_Oil?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224359765_Optimisation_of_a_Sensor_for_Onsite_Detection_of_Partial_Discharges_in_Power_Transformers_by_the_UHF_Method?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224359765_Optimisation_of_a_Sensor_for_Onsite_Detection_of_Partial_Discharges_in_Power_Transformers_by_the_UHF_Method?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/4377837_Electrical_Insulation_for_Rotating_Machines_Design_Evaluation_Aging_Testing_and_Repair?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224363965_RF-Based_Partial_Discharge_Early_Warning_System_for_Air-Insulated_Substations?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224215974_Diagnostic_of_HVDC_systems_using_partial_discharges?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/254059538_Electromagnetic_Waves_from_Partial_Discharges_in_Windings_and_their_Detection_by_Patch_Antenna?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224359757_Detection_and_Location_of_Partial_Discharges_in_Power_Transformers_using_Acoustic_and_Electromagnetic_Signals?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224359757_Detection_and_Location_of_Partial_Discharges_in_Power_Transformers_using_Acoustic_and_Electromagnetic_Signals?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/3340565_Degradation_of_Solid_Dielectrics_due_to_Internal_Partial_Discharge_Some_Thoughts_on_Progress_Made_and_Where_to_go_now?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-


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and noise sources is not presented.

This manuscript is an important step forward in themodelling of the antennas and the study of the PD powerwith respect to the results presented in [17], where theauthors compared the power spectra for different typesof antennas when measuring internal partial dischargeswithout any further analysis on the antenna design and

parametrization. First, through a typical Gaussian pulsemodel for PD, the spectrum of the signal derived inthe antenna is analytically obtained. Furthermore, a re-lationship between the half-amplitude PD pulse widthand the PD placing in frequency and its bandwidth isgiven. Second, S 11 parameters are measured to validatethe antenna design and the antenna matching, to ensurethat the manufacturing has been correct and to guaranteethat the antennas will measure in the band of frequenciesof interest. Additionally, the S 11 is measured for antennaswith and without ground plane. Third, a new test objectis designed to create a cylindrical hollow inside a stack of transformer paper layers and to control the PD activity

and the results derived from their study. And fourth, newenergy studies are done based on the wavelet transformand representing the energy in different bands of frequencyto compare the behavior of the antennas.

In summary, in this paper four different types of anten-nas, two monopoles with different lengths, a trapezoidalzigzag and a commercial logperiodic antenna, are studiedas candidates to measure partial discharges. In Section II,PDs electromagnetic emission is characterized in order tofind the target band of frequencies where the manufac-tured antennas should work; also it is shown the design andimportant parameters of the antennas and the S 11 param-eter is measured for all of them. Section III explains the

measuring setup to generate and detect partial discharges.Finally, Section IV shows the measurements and the studyin the frequency domain of the pulses acquired with theantennas to conclude that theoretical and experimentalresults match and specifically, monopole antennas are goodcandidates as sensors for PD detection.

II. Modeling of the Antennas

When designing an antenna for sensing purposes oneof the key issues to take into account is the type of signal

this antenna should detect, specifically the bandwidth thatthe signal occupies. A simplified model for the PD pulsescan be found in the literature [18], where the waveformis modeled with a Gaussian shape and the half-amplitudewidth is given by a parameter T h. The response of theantenna follows the time derivative of the PD current I (t)and therefore, under this model, the spectrum S PD(f ) of the signal that the antenna should detect can be easilyobtained. If the normalized (I 0 = 1) PD waveform is givenby:

I (t) = I 0e−

tt0

2(1)

−! −"#$% −"#& −"#!% " "#!% "#& "#$% !!"

−'

!"−(

!"−%

!"−!

!""

)! +,

- .

/ 0

1 ) 2 -

3 4 5 6

Fig. 1: Approximate bandwidth of the detected PD gen-erated signal.

where t0 = T h

2√

log 2, then the amplitude of the spectrum

sensed would have the form

|S PD(f )| = 2π√ πft0e

−

(2πft0)2

4 (2)

also plotted in Fig. 1.It should be noticed that through that formulation the

spectrum has been characterized in terms of the nor-malized frequency f n = f × T h. This allows, by solvingnumerically for the 3 dB bandwidth, to obtain the PDbandwidth in terms of the T h parameter. For that it isnecessary to obtain the two solutions f minn and f

maxn for

f n ≥ 0 from this equation:1

2 maxf n |S PD(f n)| = π√ π

√ log2f ne−

π2f 2n4log2

(3)

The solutions are f minn = 0.12 and f maxn = 0.72.

Consequently the signal would be approximately locatedin the band of 0.12/T h—0.72/T h Hz, as shown markedwith a thicker trace in Fig. 1. The relationship obtainedgiven those values for the 3 dB bandwidth and consideringthat the typical values of T h for internal discharges arebelow 1 ns, will locate the detected signal in the UHFband. Those are shown in Fig. 2, where the PD bandwidthis plotted versus T h parameter and as a reference, theUHF band frequency is also given. Thus all the antennasproposed should at least cover part of this band.

Once located the antenna working frequencies, thereare some other antenna characteristics that should bedefined to specifically match our sensing environment andthose are the radiation pattern, that also characterizes theantenna directivity, and the antenna efficiency by meansof the S 11 parameter.

The radiation pattern needed is determinant in thedesign of an antenna, and our focus for the applicationaddressed should be radiation patterns with medium tolow directivity, as for instance, omnidirectional ones. Thereason for that is that, although in our case study themeasurement environment is controlled and therefore we

https://www.researchgate.net/publication/232250454_Antenna_selection_and_frequency_response_study_for_UHF_detection_of_partial_discharges?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224148558_Electromagnetic_Waves_from_Partial_Discharges_and_their_Detection_Using_Patch_Antenna?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==http://-/?-http://-/?-http://-/?-https://www.researchgate.net/publication/232250454_Antenna_selection_and_frequency_response_study_for_UHF_detection_of_partial_discharges?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/224148558_Electromagnetic_Waves_from_Partial_Discharges_and_their_Detection_Using_Patch_Antenna?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==http://-/?-http://-/?-http://-/?-http://-/?-http://-/?-


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10−10

10−9

10−8

107

108

109

1010

Th [s]

F r e q u e n c y [ H z ]

detectable fmin

detectable fmax

300 MHz

3 GHz

UHF Band

Fig. 2: Range of T h values that fall within the UHF band.

have information about the position of the PD source, itis still interesting to cover as many directions for incomingpower as possible, showing this way the suitability of the

proposed designs where the source of PD is not clearlylocated. Also, simple designs are of interest, since oncewe had shown the validity of the proposed antennas inthe testing scenario, large deployment of elements aretypically needed for monitoring and location leveragingthe importance of inexpensive sensors.

The antenna efficiency is the second parameter to betaken into account when designing antennas. Efficiencydepends on the antenna losses given by the ohmic lossesof materials (metals and dielectric) and also on the mis-matching losses, that is the S 11 parameter. In simpleresonant antennas and in the low frequency range weare targeting, the ohmic losses are negligible and the

antenna efficiency can be defined as e = 1 − |S 11|2. ThusS 11 parameter, would be the reference measurement todetermine the resonant frequency of the antenna, the rangeof frequencies where the antenna is well matched (antennabandwidth) 1 and also the key parameter to determine theantenna efficiency for each of the working frequencies of the antenna.

Monopole antennas hold the design needs mentioned sofar: simplicity, omnidirectional patterns and, in additionto that, it is relatively simple to tune the antenna to workin a particular range of frequencies [13]. The monopoleantenna in its basic design consists on a wire with a lengthof approximately λ/4, being λ the wavelength of the mainfrequency tuned [20]. Compared to a dipole, this antennadoes not need a balun and this makes it much more conve-nient and therefore more used in practice. In theory, thisantenna should have an “infinite” ground plane to havea good behavior and also to achieve the omnidirectionalradiation pattern with a maximum directivity of around 5dB.

Thus, the radiation pattern of an ideal λ/4 monopole

1The reference value to consider that the antenna is well matchedis typically below -10 dB.

ˆ z

ˆ x ˆ y

Fig. 3: Theoretical normalized radiation pattern for a λ/4monopole.

antenna has a shape as:

r(θ, φ) =

cos2(π2cos(θ))

sin2(θ) (4)

where φ (0 ≤ φ ≤ 2π) is the azimuth angle defined inthe (x̂ŷ) plane, θ (0 ≤ θ ≤ π/2) is the elevation angleand we assume that the monopole antenna has its axisalong the ẑ direction as it is shown in Fig. 3. It shouldbe noted that the radiation pattern does not depend onφ, leading to the omniazimuthal (radiation all around thewire with rotational symmetry) radiation pattern and alsothat, given the infinite ground plane, it radiates only inhalf space.

When the monopole has a truncated ground plane of not many wavelengths the directivity is reduced. We must

remember here that the directivity gives the limit valuefor the antenna gain, which is the product of directivityand efficiency. Nevertheless, it should also be said, thatit is always possible to do a monopole antenna withoutground plane. In this case, all surrounding objects actas ground plane and we can see how the antenna stillworks. However, the efficiency is reduced and sometimesthe operating frequency is shifted with respect to thetheoretical one. Also, different manufacturing of monopoleantennas could lead to slights variations with respect tothe ideal radiation pattern, but in general terms all of themkeep the zero radiation in the direction of the axis ẑ anda similar level of radiation in all the azimuthal directions.

We suggest then to use three different monopoles thathave been manufactured with this aim with and withoutground plane. Two of them will have different lengths tocover the target range of frequencies and for the last one azigzag geometry is proposed which is known that can helpas well in matching and therefore could be more efficient.The first monopole design is 5 cm in length. With that,the theoretical resonant frequency is at 1.5 GHz and itsdirectivity is around 2 dB for the deployment withoutground plane and 5 dB for the infinite ground plane.The second monopole is 10 cm in length and this againleads to a 750 MHz resonating frequency and the same

http://-/?-https://www.researchgate.net/publication/262367481_Detection_of_Partial_Discharges_by_a_Monopole_Antenna_in_Insulation_Oil?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/258433128_Antenna_Theory_Analysis_and_Design?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==http://-/?-https://www.researchgate.net/publication/262367481_Detection_of_Partial_Discharges_by_a_Monopole_Antenna_in_Insulation_Oil?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==https://www.researchgate.net/publication/258433128_Antenna_Theory_Analysis_and_Design?el=1_x_8&enrichId=rgreq-7e8050bf-cced-4bdc-8aa1-170395fb15e4&enrichSource=Y292ZXJQYWdlOzIzNjY1ODk5NjtBUzoyMzExMTgxMjk1OTQzNjhAMTQzMjExNDI2NDU5OA==http://-/?-http://-/?-http://-/?-http://-/?-


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Fig. 7: Test object especially designed to have internaldischarges inside a cylindric void 1 mm in diameter and1.75 mm in height.

a vacuum machine and then sealed. This layout creates acylindric hole measuring 1 mm in diameter and 1.75 mmin height, where the dielectric permittivity is lower thanthe paper’s. Then, the sealed stack is placed between twoelectrodes and immersed in transformer oil to minimizethe appearance of surface discharges along the plastic bag.One of the electrodes is connected to high voltage and theother to ground. When high voltage is applied to the stack,the electric field will be larger inside the cylinder than inthe rest of the homogeneous dielectric and most of internalpartial discharges will occur in that region.

According to Standard IEC 60270, a coupling capacitoris connected in parallel to the test object to provide apath to ground for the high frequency current pulsescreated by partial discharges, see Fig. 8. These conductedpulses are measured with a HFCT with a bandwidth upto 40 MHz connected to an oscilloscope to confirm thatthe detected UHF pulses are a consequence of partialdischarges activity.

The high voltage source is a Schleich BV 702210 trans-former with a GLP1-e HV control module that can reachup to 18 kV. It has been found that partial dischargesactivity starts around 10 kV and it is stable. Hence, thehigh voltage source is slowly set slightly above the incep-

tion voltage and the measuring campaign starts. Pulseswere acquired at 11 kV.

B. Antennas deployment

As explained above, different antennas with differentfrequency ranges were used to measure the radiation of partial discharges. A logperiodic antenna UHALP 91088Awith a range from 250 MHz to 2.4 GHz, two monopolesantennas, 5 and 10 cm long, and a trapezoidal zigzagantenna. As shown in Section II, monopolar antennas withan appropriate ground plane improve the reception due to

Fig. 8: Setup displaying the layout of the four antennas,the test object and the coupling capacitor in parallel withthe test object.

the better matching of the resonant frequency and the aug-mented directivity. Under this assumption, two monopoles10 cm long were manufactured, one with ground plane andthe other without ground plane to measure the differenceswhen detecting partial discharges. The trapezoidal zigzagantenna also had ground plane but not the monopole 5 cmlong because it is so short that the connector behaves asground plane.

The antennas are deployed around the test object andtheir outputs connected to an oscilloscope with RG-223coaxial cables. The position of the antennas in the mea-surement environment is an important issue that should betaken into account, since the distance between the antennaand the source of the PD should force the antennas to workin the far field region. The reason for that is to assurethat we are working in a distance where the radiationpattern does not change with distance. Since the threemanufactured antennas have dimensions smaller than λ/2,it is convenient that they are placed at a distance of approximately 1-2 λ (40-80 cm for the monopole 10 cmlong). In the case of the logperiodic, this distance must

be longer as the antenna size is larger. At the same time,it should be noted that the radiated field decays inverselyproportional with the distance and when comparing re-ceived signal levels, therefore all antennas should be placedat the same distance from the PD source. Thus, specialattention has been put to maintain the same distance, 45cm, between the test object and all the monopole antennasshowing another advantage of the use of monopolar typeof antennas as we can be quite close to the source of thedischarges if required. The logperiodic has been placed at alonger distance, 90 cm, to ensure that it measures far-fieldradiation and with the dipoles parallel to ground.

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UHF acquisitions were made in a Tektronix DPO72548-bit, 40 GS/s, 4 channel oscilloscope, where the responseof each antenna to partial discharge pulses was registered.During the experiments in laboratory, most factors werecontrolled to assure uniformity in the measurements andseries of 500 pulses were recorded at 10 GS/s and processedto guarantee that the results were statistically reliable.

IV. Measurements

Measurements were taken to demonstrate experimen-tally the theoretical results for the characterized antennasobtained in Section II. A total of 500 signals were acquiredfor every antenna, first without and then with partialdischarges. The Fast Fourier Transform (FFT) with arectangular window was calculated for all signals to obtainthe spectra and then averaged to reduce its variance. Thisprocess is repeated whenever a frequency plot is displayedin the paper.

A. Background noise

The first step is the characterization of the backgroundnoise present in the laboratory. This is done by measuringrandomly 500 time signals acquired with all of the an-tennas and calculating their averaged spectra. The resultsare shown in Fig. 9 where FM radio, Digital Audio Broad-casting, TV Broadcasting, GSM-GPRS and WiFi signalsare clearly captured. In some cases, the antennas behavioris already seen in this figure. The 10 cm monopole andthe trapezoidal zigzag antenna have good response in theTV Broadcasting band whereas the 5 cm long monopolehas a poor reception at these frequencies. The logarithmicantenna has a flat response in the range of frequenciesshown in the plots according to its data-sheet so it willbe used as the reference for the rest of the antennas.The background noise for the 10 cm long monopole andthe trapezoidal zigzag without ground plane were alsoacquired and was essentially the same as the detected withthe monopole with ground plane so they have not beenplotted.

B. Monopoles 10 cm long with and without ground plane

Measurements were taken with this two antennas tocheck if there are significant differences in the acquisitions.In the case the monopoles 10 cm long, the main frequencyis in 750 MHz so receptivity should be good at this

frequency and its multiples. Fig. 10 represents two partialdischarge pulses measured with these monopoles in a timewindow of 200 ns at 11 kV. Though they seem to bevery similar, a closer study of the front wave shows thatthere is a larger high frequency content in the signalacquired with the monopole with ground plane. This isbetter seen in the averaged spectra of 500 pulses takenwith both antennas and shown in Fig. 11. As expected, themagnitudes in the band around 750-800 MHz have beenincreased demonstrating that a ground plane improves thereception. Even more, the band from 1100 MHz to 1600MHz has increased noticeably with the ground plane and

Monopole 5 cm.

Monopole 10 cm with ground plane.

Trapezoidal zigzag with ground plane.

Logperiodic.

Fig. 9: Noise backgrounds spectra in volts for all theantennas.

it is there, precisely, where the first multiple 1500 MHzlies.

C. Antennas behavior

The next set of measurements is done for all the an-tennas. Actual pulses inside the dielectric have rise times

shorter than 1 ns so, according to Fig. 2 the emission willapproximately be in a wideband from 100 MHz to 2 GHz.An example of a partial discharge pulse measured with theantennas is shown in Fig. 12. The pulse starts at the sametime for all of antennas but the logperiodic because it wasplaced farther. Though the signals are different, they havethe same structure: before the trigger there is backgroundnoise, then there are fast variations of the signal for thefirst nanoseconds due to the direct wave propagation of the pulse and multipath propagation, and then there isradiation at lower frequencies due to the impulsive natureof the partial discharge. Again, 500 time signals were

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Monopole 10 cm without ground plane.

Fig. 10: Partial discharge pulses measured with twomonopoles 10 cm long with and without ground plane.


Monopole 10 cm without ground plane.

Fig. 11: Partial discharge spectra for two monopoles 10 cmlong with and without ground plane.

acquired and their spectra calculated and averaged toobtain the frequency response of the antennas. The results

are shown in Fig. 13. The differences with the plots inFig. 9 are evident since there is energy in all the measuredband up to 2.5 GHz that even hides strong broadcastingemissions of radio and TV. As expected, the monopole 5cm long has an outstanding behavior in the band from1100 MHz to 1700 MHz and shows that partial dischargesemit, at least, in that band. The monopole 10 cm longwith ground plane has also good reception in this bandbut also at lower frequencies centered in 700 MHz wherethe 5 cm monopole is not so good. The trapezoidal zigzagwith ground plane has more sensitivity around 500 MHzthough can also measure energy in the higher frequency

Monopole 5 cm.



Logperiodic.

Fig. 12: Partial discharge pulse measured with every an-tenna.

band as the first two antennas. Finally, the logperiodicantenna captures energy in all the band as expected.

The cumulative power in bands of 250 MHz has beencalculated and plotted in Fig. 14 to have a better under-standing of the power distribution in frequency. In thiscase, the magnitude at every frequency of the spectra is

divided into √ 2 to obtain the root mean square and thensquared to calculate the power. The powers are summed inbands of 250 MHz and the result is the cumulative powerin that band.

The cumulative power of the background noise of Fig.9 is displayed in Fig. 14 as triangles joined by a dashedline. The averaged cumulative power of the signals withpartial discharges is presented as squares joined by a solidline. Finally, every cumulative magnitude is shown as adot per spectrum to have a measure of the dispersion of the acquisitions.

The logperiodic antenna can be considered as the refer-

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Monopole 5 cm.



Logperiodic.

Fig. 13: Averaged spectra of 500 pulses acquired with theantennas.

ence because it has almost a flat response up to 2.5 GHz.Then, it can be clearly seen in its frequency response thatpartial discharge pulses have energy in all bands up to1750 MHz. From this frequency the differences betweennoise and partial discharges power is negligible in all theantennas. The plot for the logperiodic also shows that the

increments in power compared to the background noiseare quite constant in the rest of the bands. Consideringthis premise, the specific antenna behavior in frequencycan be easily deduced from the rest of the plots. In thosebands were the increment in power is larger, the antennahas better response than when the increment is lower.Then, the 5 cm monopole has an outstanding response inthe band from 1250 MHz to 1500 MHz, a good responsefrom 1000 MHz to 1250 MHz and from 1500 MHz to 1750MHz and a very poor response in the band from 500 to1000 MHz. The 10 cm monopole with ground plane has anoverall good response from 1000 MHz to 1750 MHz and the

Monopole 5 cm.



Logperiodic.

Fig. 14: Cumulative power in 250 MHz bands for 500pulses acquired with the antennas with partial discharge() and without partial discharge ().

rest of the band it is very similar to the zigzag antenna.Compared to the rest of the monopoles, the trapezoidalzigzag with ground plane behavior is not so good in theUHF band and it seems to be only remarkable in the lowestfrequency bands from 0 to 500 MHz, though this is clarified

in Table I.This table gives the same information as Fig. 14 but

specifying the numerical values. The light grey shadedcells correspond to the last columns where the differencesbetween noise and partial discharges are negligible. Thedark gray shaded cells are frequencies where the differencesare remarkable (10 dB or more), whereas the mediumgray shade represents changes of at least 7 dB. In thecase of the trapezoidal zigzag antenna, the effect of thepartial discharges is not so noticeable and two cells havebeen shaded with medium gray: one of them is at lowfrequencies and the other is from 1250 to 1500 MHz.

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0-250 250-500 500-750 750-1000 1000-1250 1250-1500 1500-1750 1750-2000 2000-2250 2250-25005 cm 845 346 72.4 114 491 2210 306 99.1 72.6 49.5

Noise 153 59.3 67.2 98 55.6 54.5 56.9 104 70.8 60.910 cm 2180 186 170 195 234 399 191 78 95.7 31.6Noise 422 28.3 77.8 106 18.7 19.9 22.5 44.4 84.2 27.2

Zigzag 3640 244 250 106 92.2 175 103 45.8 48.4 74Noise 1140 37 84.9 64.5 17.6 18.5 21 33.9 43.1 28.9

Logperiodic 16500 3930 674 653 295 260 341 329 197 116Noise 1260 370 409 545 53.5 52.6 55 153 81.6 63.8

TABLE I: Average cumulative power in V

2

× 10−9

for the four types of antennas measuring partial discharges andbackground noise. The columns are the frequency bands in MHz.

This study shows that the zigzag antenna is not a goodcandidate to measure partial discharges and, therefore,monopoles with long lengths should be discarded. How-ever, the choice between the other two monopoles remainsunclear because they seem to have similar behavior infrequency. An additional study based on the wavelet trans-form has been made to find out the best option. Thewavelet transform decomposes the time signals into N levels of details, Dn, and an approximation A1 using a

filter bank. Then, the details are calculated by filteringthe original signal in frequency intervals from f s/2n+1 tof s/2n where f s is the sampling frequency and n is thenumber of the detail. The discrete wavelet transform wasdone using a Daubechies wavelet with order 5 and 7 levelsof decomposition to cover the most important frequencyintervals. These are shown for every detail in Table II. Theapproximation level is the signal that remains in the lowerfrequency interval [0 − 39.0625] MHz.

The discrete wavelet decomposition was applied to all500 signals from the monopole antennas when measuringPD, then, the energy of the signals in the details andthe approximation was calculated and, finally, the average

energy per detail and approximation. This is shown in Fig.15 for the three monopoles. The horizontal axis of theplot contains the approximation and the details orderedin the bands of frequency of Table II and the verticalaxis represents the average energy percentage. The zigzagantenna, white bars, captures more than 40 % of theenergy in the band of the detail 6 which is where FMradio is. The energy in detail 5, mostly correspondingto DAB radio, and the approximation, HF band, is alsosignificative. Therefore, the zigzag antenna is working inbands where the environmental noise is important andhides the PD pulse. In the case of the monopole 10 cmin length, more than 50 % of the energy is in the VHF

band whereas the monopole 5 cm in length captures morethan 60 % of the energy in UHF. This energy share isexpected from the results obtained for the parameter S 11and allows us to conclude that the shorter tested monopoleis the most adequate to measure PD.

V. Conclusions

The theoretical analysis done of the electromagneticradiation of partial discharges pulses shows that sensors inthe UHF range can detect them. Under this assumption,four antennas with different frequency behavior have been

A1 D7 D6 D5 D4 D3 D2 D10

5

10

15

20

25

30

35

40

45

Aproximation and detail levels

P e r c e n t a g e

o f e n e r g y

monopole 5 cm

monopole 10 cm

zigzag

Fig. 15: Percentage of the averaged energy in the detailsand approximation of the discrete wavelet transform whenmeasuring partial discharges.

Detail Interval (MHz) NoiseD1 2500 - 5000 —D2 1250 - 2500 GSM, UMTS, WiFiD3 625 - 1250 TV, GSM

D4 312.5 - 625 TVD5 156.25 - 312.5 DABD6 78.125 - 156.25 FMD7 39.0625 - 78.125 Inductive

A1 0 - 39.0625 Inductive

TABLE II: Seven detail levels and approximation of thewavelet decomposition and their frequency intervals if f s = 10 GHz. The third column relates the bands withthe corresponding environmental noise.

chosen to measure partial discharges. A deep experimentalstudy concludes that the two monopoles 5 cm and 10

cm long have good responses at frequencies above 1000MHz which corresponds to their λ/4 condition. The zigzagantenna is not so sensitive as the monopoles but it is moreappropriate for measuring at lower frequencies (below 500MHz) because its behavior is that of a monopole with16.5 cm in length. The logperiodic antenna is a goodreference to compare the results though its response isnot so good as the monopoles for frequencies above 750MHz. An additional study based on the wavelet transformcorroborates these results and shows that the monopole5 cm in length receives more the 60 % of the energy of the radiated signal in the UHF band designating it as the

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best option to measure partial discharges. Therefore, thisphenomenon can be measured with simple and inexpensivemonopoles in an efficient manner.

Acknowledgments

This research was supported by the Spanish Scienceand Technology Ministry under contracts DPI 2009-14628-C03-02 and TEC 2011-29006-C03-03. Tests were donein the High Voltage Research and Test Laboratory of Universidad Carlos III de Madrid.

References

[1] P. Gill, Electrical Power Equipment Maintenance and Testing .New York: Marcel Dekker, 1998.

[2] F. H. Kreuger, Partial Discharge Detection in High-Voltage Equipment . London: Butterworths, 1989.

[3] P. Morshuis, “Degradation of solid dielectrics due to internalpartial discharge: some thoughts on progress made and whereto go now,” Dielectrics and Electrical Insulation, IEEE Trans-actions on , vol. 12, pp. 905 – 913, oct. 2005.

[4] G. Stone, E. Boutler, I. Culbert, and H. Dhirani, Electrical Insulation for Rotating Machines: Design, Evaluation, Ageing,Testing and Repair . Series on Power Engineering, Piscataway-NJ: IEEE Press, 2004.

[5] IEC 60270, High Voltage Test Techniques. Partial Discharge Measurements, 3.0 ed., 2000.

[6] G. Robles, J.M.Mart́ınez, M. Rojas, and J.Sanz, “Inductivesensor for measuring high frequency partial discharges withinelectrical insulation,” IEEE Transactions on Instrumentation and Measurement , vol. 58, Nov 2009.

[7] D. Ward and J. Exon, “Using rogowski coils for transient currentmeasurements,” Engineering Science and Education Journal ,vol. 2, no. 3, pp. 105–103, 1993.

[8] M. Argüeso, G. Robles, and J. Sanz, “Implementation of aRogowski coil for the measurement of partial discharges,” Re-view of Scientific Instruments, vol. 76, no. 6, p. 065107, 2005.

[9] S. M. Markalous, S. Tenbohlen, and K. Feser, “Detection and lo-

cation of partial discharges in power transformers using acousticand electromagnetic signals,” IEEE Transactions on Dielectricsand Electrical Insulation , vol. 15, Dec 2008.

[10] J. Ramírez-Niño and A. Pascacio, “Acoustic measuring of par-tial discharge in power transformers,” Measurement Science and Technology , vol. 20, no. 11, p. 115108, 2009.

[11] S. Tenbohlen, D. Denissov, S. Hoek, and S. Markalous, “Par-tial discharge measurement in the ultra high frequency (UHF)range,” Dielectrics and Electrical Insulation, IEEE Transac-tions on , vol. 15, no. 6, pp. 1544–1552, 2008.

[12] J. López-Roldán, T. Tang, and M. Gaskin, “Optimisation of a sensor for onsite detection of partial discharges in powertransformers by the UHF method,” Dielectrics and Electrical Insulation, IEEE Transactions on , vol. 15, pp. 1634 –1639,december 2008.

[13] C.-H. Jin, J.-Y. Lee, D.-W. Park, and G.-S. Kil, “Detection of partial discharges by a monopole antenna in insulation oil,”

in Proceedings of the 11th WSEAS international conference on Instrumentation, Measurement, Circuits and Systems, and Proceedings of the 12th WSEAS international conference on Robotics, Control and Manufacturing Technology, and Proceed-ings of the 12th WSEAS international conference on Multime-dia Systems & Signal Processing , IMMURO’12, (StevensPoint, Wisconsin, USA), pp. 27–30, World Scientific and Engi-neering Academy and Society (WSEAS), 2012.

[14] I. Portugués, P. Moore, I. Glover, C. Johnstone, R. McKosky,M. Goff, and L. van der Zel, “RF-Based partial discharge earlywarning system for air-insulated substations,” Power Delivery,IEEE Transactions on , vol. 24, pp. 20 –29, jan. 2009.

[15] A. Cavallini, G. Montanari, M. Tozzi, and X. Chen, “Diagnosticof HVDC systems using partial discharges,” Dielectrics and Electrical Insulation, IEEE Transactions on , vol. 18, pp. 275–284, february 2011.

[16] P. Moore, I. Portugues, and I. Glover, “A nonintrusive partialdischarge measurement system based on RF technology,” inPower Engineering Society General Meeting, 2003, IEEE , vol. 2,p. 4 vol. 2666, july 2003.

[17] G. Robles, J. Martínez-Tarifa, M. Rojas-Moreno, R. Albarracín,and J. Ardila-Rey, “Antenna selection and frequency responsestudy for UHF detection of partial discharges,” in IEEE Inter-national Instrumentation and Measurement Technology Confer-ence (I2MTC), may 2012.

[18] Y. Shibuya, S. Matsumoto, M. Tanaka, H. Muto, and

Y. Kaneda, “Electromagnetic waves from partial discharges andtheir detection using patch antenna,” Dielectrics and Electrical Insulation, IEEE Transactions on , vol. 17, pp. 862 –871, june2010.

[19] Y. Shibuya, S. Matsumoto, T. Konno, and K. Umezu, “Electro-magnetic waves from partial discharges in windings and theirdetection by patch antenna,” Dielectrics and Electrical Insula-tion, IEEE Transactions on , vol. 18, pp. 2013 –2023, december2011.

[20] C. Balanis, Antenna Theory: Analysis and Design . New York:Wiley-Interscience, 2005.

[21] Schwarzbeck Mess-Elektronik, http://www.schwarzbeck.de,UHALP 9108 A Data Sheet .

Guillermo Robles (SM’12) was born inMadrid, Spain, in 1969. He received the M.Sc.and Ph.D. degrees in electronic engineeringfrom the Universidad Pontificia de Comillasde Madrid, Madrid, in 1993 and 2002, respec-tively. He joined the Department of ElectricalEngineering, Universidad Carlos III de Madrid(UC3M), Leganes, Madrid in 2002, and heis an Associate Professor in this Departmentsince 2009. He is also with the High-VoltageResearch and Tests Laboratory (LINEALT),

Universidad Carlos III de Madrid. His research interests include thedesign of sensors, instrumentation and measurement techniques forhigh frequency currents, especially due to partial discharges in noisyenvironments, as well as the study and characterization of magneto-optic sensors based on the Faraday effect for the measurement of currents and the characterization of the behavior of magnetic mate-rials at high frequencies. He has co-authored more than 50 papers ininternational journals and conferences.

Matilde Sánchez-Fernández got herTelecommunications Engineer degree and herPhD from Polytechnic University of Madrid in1996 and 2001 respectively. She joined Univer-sity Carlos III of Madrid, Spain in 2000 whereshe holds an Associate Professor position since

2009. Previously, she worked for Telefónicaas a Telecommunication Engineer. She hasperformed several research stays at the In-formation and Telecommunication TechnologyCenter in Kansas University (1998), Bell-Labs,

New Jersey (2003-2006), Centre Tecnològic de Telecomunicacions deCatalunya, Barcelona (2007) and Princeton University, New Jersey(2011). Her current research interests are MIMO techniques, wirelesscommunications and simulation and modeling of communicationsystems and in these fields she has (co)authored more than 40 con-tributions to international journals and conferences. As an AssociateProfessor she is teaching several undergraduate and graduate courses(MSc. and PhD) related to Communication Theory and DigitalCommunications.

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