Design and Implementation of Partial Discharge Measurement Sensors for On-line Condition Assessment of Power Distribution System Components

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto. fi Author Muhammad Shafiq Name of the doctoral dissertation Design and Implementation of Partial Discharge Measurement Sensors for On-line Condition Assessment of Power Distribution System Components Publisher School of Electrical Engineering Unit Department of Electrical Engineering and Automation Series Aalto University publication series DOCTORAL DISSERTATIONS 152/2014 Field of research Power System and High Voltage Engineering Manuscript submitted 2 April 2014 Date of the defence 29 October 2014 Permission to publish granted (date) 4 July 2014 Language English Monograph Article dissertation (summary + original articles) Abstract Unplanned interruptions of power supply due to failure of critical components of the distribution network have considerable impact on the modern society. Efficient condition assessment can avoid the loss of critical components by early detection of incoming threats. One of the biggest shortcomings of today's progressing maintenance technology is the lack of low cost instrumentation solutions which are simple in implementation and easily applicable to the network. In this work partial discharge (PD) measurements have been considered for insulation condition assessment of distribution system components such as overhead covered conductors (CCs) and cables. A high frequency Rogowski coil induction sensor is designed for this purpose. An accurate electrical model of the sensor is necessary for efficient signal processing of the sensed signal and for reliable interpretation of the measured signal. A new method to determine the electrical parameters of Rogowski coil sensor is presented. In-depth analysis of the design stages of Rogowski coil is presented using experimental and simulated environment. Various geometrical designs of Rogowski coil are investigated to analyze the effects of geometrical parameters on high frequency performance of the coil. The guidelines presented regarding geometrical structure are useful when trading off the benefits for better mechanical and electrical design of such sensors. Location of the detected PD faults is an important task of the diagnostics system in power lines. The conventional techniques of locating PD faults have been known for a single section of a power line. However, these techniques are not suitable for power lines having multi-sections or for branched line networks. In this work, finding the location of PD fault on a power line is recognized as a two stage function; (i) identification of the faulty section, and (ii) location of fault point on the identified section. The direction of arrival (DOA) technique is introduced to identify faulty section whereas fault point location can be determined by conventional techniques. The technique is equally applicable for CC lines or cable networks. The DOA technique is integrated over a cable feeder and an on-line automated condition monitoring and diagnostic scheme is proposed. Low cost, non-intrusive installation and favorable operating features of Rogowski coil sensor make it suitable for development of an enhanced and automated diagnostic system which can easily be integrated into the distribution network.Unplanned interruptions of power supply due to failure of critical components of the distribution network have considerable impact on the modern society. Efficient condition assessment can avoid the loss of critical components by early detection of incoming threats. One of the biggest shortcomings of today's progressing maintenance technology is the lack of low cost instrumentation solutions which are simple in implementation and easily applicable to the network. In this work partial discharge (PD) measurements have been considered for insulation condition assessment of distribution system components such as overhead covered conductors (CCs) and cables. A high frequency Rogowski coil induction sensor is designed for this purpose. An accurate electrical model of the sensor is necessary for efficient signal processing of the sensed signal and for reliable interpretation of the measured signal. A new method to determine the electrical parameters of Rogowski coil sensor is presented. In-depth analysis of the design stages of Rogowski coil is presented using experimental and simulated environment. Various geometrical designs of Rogowski coil are investigated to analyze the effects of geometrical parameters on high frequency performance of the coil. The guidelines presented regarding geometrical structure are useful when trading off the benefits for better mechanical and electrical design of such sensors. Location of the detected PD faults is an important task of the diagnostics system in power lines. The conventional techniques of locating PD faults have been known for a single section of a power line. However, these techniques are not suitable for power lines having multi-sections or for branched line networks. In this work, finding the location of PD fault on a power line is recognized as a two stage function; (i) identification of the faulty section, and (ii) location of fault point on the identified section. The direction of arrival (DOA) technique is introduced to identify faulty section whereas fault point location can be determined by conventional techniques. The technique is equally applicable for CC lines or cable networks. The DOA technique is integrated over a cable feeder and an on-line automated condition monitoring and diagnostic scheme is proposed. Low cost, non-intrusive installation and favorable operating features of Rogowski coil sensor make it suitable for development of an enhanced and automated diagnostic system which can easily be integrated into the distribution network.