Lee Renforth

Neural network based classification of partial discharge in HV motors

This paper discusses the general application of using Neural Networks (NN) to classify six different types of Partial Discharge (PD). Stator winding failures contribute about 30–40% of the total motor failures according to IEEE and EPRI. Ninety percent (90%) of electrical failures on High-Voltage (HV) equipment are related to insulation deterioration. Large datasets were collected for motors with PD defects as well as PD-free machines. The datasets of PD were pre-processed and prepared for use with a NN using statistical means. It was possible to utilise the advantages offered by multiple NN models to classify the PD defects with a maximum recognition rate of 94.5% achieved, whereas previous research work did not exceed a classification accuracy of 79%.

A new technique for the remote partial discharge monitoring of the stator insulation of high-voltage motors located in “Ex” (hazardous) locations

The authors present a paper on the application of a new technique for the remote on-line partial discharge monitoring of the stator insulation condition of in-service, high-voltage rotating machines. The technique applies wideband, ferrite-based high frequency current transformer sensors and high resolution measurement technology. This remote partial discharge monitoring technique has significant advantages when monitoring motors which are located in Ex hazardous gas zones in oil and gas and petrochemical facilities. The paper includes a technical review of published papers covering some of the history of the development of modern, on-line partial discharge sensors and measurement systems for rotating machines. This is followed by a comparison of the various partial discharge sensor options available and an introduction to the remote wideband partial discharge monitoring measurement technique employed by the authors. A case study from a recent pilot project (August 2011) where the new remote partial discharge monitoring measurement techniques were successfully trialed to measure partial discharge activity of in-service 10 kV motors in an oil processing facility is also presented.

Continuous, remote on-line partial discharge (OLPD) monitoring of HV EX/ATEX motors in the oil and gas industry

This paper presents results from the continued application of a new technique for the remote online partial discharge (OLPD) testing and monitoring of in-service high-voltage (HV) explosive atmosphere (Ex)/atmosphere-explosive (ATEX) motors operating in hazardous gas zones. The technique employs high-current wideband high-frequency current transformer sensors located remotely from the motor under test, at the switchboard end of the HV feeder cable. Significant cost and operational benefits can be gained from this remote monitoring technique as the stator winding condition of these motors can be monitored without having to enter the hazardous gas (Ex/ATEX) zone. The work described in this paper is a continuation of that carried out by the same authors, as reported at the 2012 IEEE Petroleum and Chemical Industry Technical Conference, and includes the development of proposed condition guidelines for assessing the condition of the stator winding insulation systems of large populations of aged HV motors, based on an OLPD “league-table” database. Two case studies are presented wherein the HV stator insulation condition and reliability of in-service motors, operating in hazardous gas zones, and HV generators were assessed using both online and offline partial discharge (PD) testing and monitoring techniques. The case studies emphasize the importance of carrying out extended continuous OLPD monitoring of in-service rotating HV machines to detect underlying trends in PD activity over time. This paper concludes with how condition monitoring data can support reliability-centered maintenance and condition-based management regimes.

Experiences from over 15 years of on-line partial discharge (OLPD) testing of in-service MV and HV cables, switchgear, transformers and rotating machines

The authors present a paper on the application of online partial discharge (PD) testing and monitoring technology for the insulation condition assessment of in service medium voltage (MV — 3.3kV to 45kV)) and high voltage (HV — 66kV to 750kV) cables and plant. The paper begins with a short summary of the different economic ‘DRIVERS’ which apply to both public utility and industrial HV networks. The paper presents some of the test techniques employed and the on-line PD sensor technology used to test in-service power cables, switchgear, transformers, rotating machines, CTs/VTs and other HV plant. The paper concludes with some case studies of past projects carried out by the authors from on-line PD test projects testing a wide range of MV & HV assets in electricity networks around the world.

Partial discharge pulse propagation, localisation and measurements in medium voltage power cables

This paper considers the measurement and propagation of partial discharge pulses on distribution class power cable circuits, with the idea of attempting to determine discharge location sites on cables based on the parameters of individual pulses. Single-ended discharge location techniques based on partial discharge pulse parameters and shape will not be as accurate as time-domain reflectometry methods but can be done on-line without the need for double-ended techniques. Power cables used for the transmission of 50/60 Hertz electrical power, are by design not intended to carry transients or partial discharge pulses. The geometry and construction of such power cables present a transmission line that can heavily attenuate and distort the partial discharge pulses, making their detection and discrimination all the more difficult. Experimental and field work has been carried out to develop basic knowledge rules to describe how the time-domain parameters of individual pulses alter as a function of the distance propagated from the discharge sites for medium voltage power cables.

High-Voltage Rotating Machines: A New Technique for Remote Partial Discharge Monitoring of the Stator Insulation Condition

In this article, a new technique is presented for the remote online partial discharge (OLPD) monitoring of the stator insulation condition of in-service, high-voltage (HV) rotating machines with a focus on the Ex/ATEX HV motors used in the petrochemical industry. The technique applies wideband, ferrite-based high-frequency current transformer (HFCT) sensors and high-resolution measurement technology. This remote PD monitoring technique has significant advantages when monitoring motors located in Ex/ATEX hazardous gas zones in oil and gas and petrochemical facilities.

New techniques for on-line partial discharge testing of solid-insulated outdoor MV and HV plant

The authors present a paper detailing new techniques for on-line partial discharge (PD) testing of in-service, solid- insulated, medium and high voltage plant located in outdoor environments. Detection of electromagnetic radiation is a well known and documented method for location of PD signals. However interference signals from RF sources, corona and surface discharges can be a major problem when testing outdoors, obstructing the observation of internal PD and confusing measurements. Experience in these situations has led to the development of various new tools and test techniques for PD identification and discrimination of interfering signals and background noise. Shielding sensors have been employed with a multi-channel measurement system to assist in detecting signals that are external to the equipment under test with time-of-flight (TOF) analysis. Methods for automating the test procedure and data analysis have also been a key part in this research and will be fundamental to future developments.

ON-LINE PARTIAL DISCHARGE (OLPD) INSULATION CONDITION MONITORING OF COMPLETE HIGH VOLTAGE (HV) NETWORKS IN THE OIL & GAS INDUSTRY

The authors describe a new approach to on-line partial discharge (OLPD) insulation condition monitoring (CM) of complete high voltage (HV) networks (voltage range: 3.3 kV to 132 kV) in the oil & gas industry. The technique described is suitable for the condition monitoring of HV generators, switchgear, cables, motors and transformers. Comprehensive HV network OLPD condition monitoring coverage is achieved through the use of wideband, OLPD sensors and continuous monitors located at the central switchboards of the facility. The complete HV network condition monitoring system described in this paper is an extension of a CM system originally developed by the authors for remote OLPD monitoring of the stator winding condition of Ex/ATEX HV motors operating in hazardous gas zones. This technique utilises wideband, high frequency current transformer (HFCT) OLPD sensors located at the central HV switchboards to detect partial discharge (PD) signals that originate in remotely-connected HV plant and have propagated down the cable feeder circuit to the switchgear. This remote monitoring technique was presented by the lead author at the IEEE-PCIC 2012 [1] and IEEE-PCIC 2013 [2] for the application of OLPD condition monitoring of EX/ATEX HV motors, whilst avoiding the need to install sensors in the hazardous gas zone. In this paper, the authors describe how this remote OLPD monitoring technique can be extended to include the insulation condition monitoring of other HV assets including; generators, switchgear, cables and transformers, using the same wideband HFCT sensors attached to the HV cable terminations located at the central switchboards. The authors provide a number of case studies describing some past projects on the OLPD testing and monitoring of in-service HV generators, switchgear, cables, motors and transformers within the oil & gas industry. The applications knowledge obtained from these past projects on different plant types has been used by the authors in the development of this innovative, complete HV network condition monitoring solution.

On-line partial discharge detection and control on MV cable networks with ground fault neutraliser

The technique of controlling neutral voltage and current is applied in medium- and high-voltage electricity networks as a means of eliminating earth fault currents. The complete compensation of earth fault currents is achieved using modern power electronics developed by Swedish Neutral. The GFN Ground Fault Neutralizer uses beside traditional Petersen Coil technology a novel Residual Current Compensator (RCC) to archive a very fast and complete elimination of the earth fault current. Injection of voltage into the transformer neutral using this system, also allows control of the phase-ground voltages under normal operation. This in turn allows partial discharge (PD) activity in the cables and connected plant to be incepted and extinguished through voltage increase and reduction on a phase-by-phase basis, providing a very powerful diagnostic system. The paper presents results from on-line partial discharge (OLPD) testing combined with neutral voltage displacement on MV networks. Case studies are presented from testing with fabricated defects and on two MV networks as part of GFN system commissioning. (4 pages)

Remote monitoring of Partial Discharge activity within high-voltage rotating machines in hazardous locations

On-line Partial Discharge (PD) testing of rotating machines has traditionally been carried out using pre-installed High Voltage Coupling Capacitor (HVCC) sensors connected at the terminal box of the machine. These provide high impedance to low frequency signals (<; 10 MHz) and low impedance to the high frequency PD pulses (>; 10 MHz). The use of these sensors allows PD measurements to assess the integrity of the stator winding insulation of the machine to be made without the need to interrupt the running of the machine. Although the HVCC sensor is useful for machine-end capture of PD signals, there is often a need to perform PD testing of a rotating machine some distance away from the machine, such as at the switchgear cable end. Carrying out PD testing of rotating machines at the remote, switchgear end of the feeder cable is advantageous for motors located within Ex, hazardous gas zones, such as within the petrochemical industry and off-shore oil and gas environments. The authors report on preliminary results from PD testing carried out on in-service 10 kV motors which show how different areas of PD activity occurring within the stator windings of the motors can be reliably measured by placing wideband High Frequency Current Transformer (HFCT) sensors at the switchgear end of the supply cable.