Background

High Voltage Partial Discharge (HVPD) Ltd are experts in the field of On-line Partial Discharge (PD) testing and monitoring, supplying a complete range of On-line PD surveying and diagnostic test technology, PD monitoring technologies and PD test services to both utility and industrial clients across the worldwide electricity supply industry.

Partial Discharge (PD) activity is produced by incipient faults in both medium voltage and high voltage insulation and is now widely regarded as the best early indicator of insulation degradation, providing an 'early warning' against insulation faults which allows the mv/hv plant owner to take corrective action before catastrophic failure/explosion occurs. For all mv and hv cable and plant, internal partial discharge activity will be damaging, and will result in slow damage to the insulating medium, which in turn will lead to failure.

The foundations of the extensive knowledge-base held by HVPD Ltd in the field of on-line and off-line partial Discharge (PD) testing and monitoring has been built on the research and development work carried out by the HVPD Directors (Dr Lee Renforth and Dr Ross Mackinlay) over the past 30 years. This R&D activity includes pioneering work, which started in 1998, in the field of On-line Partial Discharge (PD) testing and monitoring of in-service, medium voltage and high voltage cable systems (tested with the plant 'live') and has been continued over the past 11 years.

The early work was carried out in conjunction with London Electricity (now EDF Energy UK) in their 11kV underground cable network in London, UK and included the world's first, on-line PD measurements of in-service, medium voltage (11kV) cables using high-frequency current transformers (HFCT's) in 1998. In these tests, split-core HFCT sensors were attached to earth connections of in-service, 11kV cables and wideband digital storage oscilloscopes (DSO) and fast analogue to digital data acquisition card were used to make high-resolution measurements of the PD activity detected.

These pioneering tests showed that reliable measurements of the PD activity in the cables and connected plant could be achieved using the new split-core HFCT sensor technique, without the need for an outage. This breakthrough was reported in a number of publications between 1999 and 2003 and has now led to this type of inductive, split-core HFCT sensor now becoming the sensor of choice for on-line PD measurements of both mv and hv cable installations.

The other sensor used throughout this 11-year period of research and development is the Transient Earth Voltage (TEV) capacitive coupler probe which is used in conjunction with the HFCT sensors. The TEV probe is seen as complementary to the HFCT as it detects high frequency PD pulses in the 'local' switchgear or plant whilst the HFCT is designed to detect lower frequency 'cable' PD's which have travelled some distance down a cable. By using a combination of the inductive HFCT and the capacitive TEV probes it is possible to test the entire cable and plant system.

"Our Knowledge is Your Power"

It has been the long-term philosophy of the HVPD Directors (Dr Lee Renforth and Dr Ross Mackinlay), over the course of the past 11 years, to pass on as much of our contained knowledge of on-line PD testing and condition-based asset management of mv and hv networks to our customers as we possibly could. In fact, this knowledge-transfer process was absolutely essential during the early years of the application of the technology (1998-2003), initially simply in order to convince, what was a sceptical industry that these insulation condition tests could be carried out at all!

After it was proven and then generally accepted that on-line PD measurements were both possible and reliable, there has been a further period of deliberation, over the past 5 years or so, as to whether significant cost-benefits can be achieved in terms of reducing network operating costs through the application of the new PD test and monitoring technologies. Whilst this debate goes on, a number of studies by HVPD on a wide range of mv networks from large, public utility networks to small, industrial process networks show that significant savings can be made in operating costs of running the networks through a careful, structured application of on-line PD test and monitoring technologies.

Now that on-line PD test and monitoring technology has now become widely accepted in the industry, over a decade after the initial pioneering work was carried out, HVPD continue to apply our long-term philosophy of continual knowledge-transfer to our customers. This is now achieved via our dedicated, customer-focussed PD test training courses (both at our HQ in Manchester, UK and at our customer's sites around the world) and our customer engineering support services which include data analysis services and asset management advice.

The knowledge transfer process from HVPD to our customers is initiated through an On-line PD Test Pilot Projects which are carried out by our highly-trained, in-house, specialist on-line PD test engineers. Typical pilot projects have a 1-week duration where on-line PD test surveys and diagnostic testing/monitoring are carried on a large number of cables and plant items in our customer's mv and hv networks. The results of the PD test survey and the recommendations to the client resulting are presented in a detailed project report which is reviewed with the client's engineers and managers. Pilot projects can also be coincided with training of the client's staff in the use of the on-line PD test technology whilst enabling HVPD to 'tailor' any testing methods to any specific site conditions, such as in high noise environments.

The Main Technical Challenges to Carrying Out On-line PD Tests

The main technical challenges in the field of on-line PD testing which have had to be overcome are electromagnetic noise mitigation ("reducing the noise") and PD pulse recognition ("seeing through the noise and picking out the PD's"). HVPD have developed three unique software algorithm solutions to solve both of these issues including a 'wavelet denoising', a knowledge-based PD pulse shape 'event recognition' and a 'precedence' detection module. All three of these algorithms are used in the PDGold©v5.0 software for the synchronous, 4-channel HVPD-Longshot™ unit whilst the HVPD-Multi™ multiplexed monitors utilise two of them in this unit's SmoothSurvey© software.

HVPD Research & Development

The PD-testing knowledge-base held by the HVPD directors, senior test and development engineers and the HVPD associate design consultants spans over one hundred years of combined experience in the application of on-line and off-line PD detection technology. This knowledge-base goes back to the early 1980's when the first on-line PD measurements of mv switchgear and the original VLF Off-line Power Supply were developed in the UK.

Over the past 11 years the focus of HVPD's R&D work has been on the application of On-line PD testing of in-service mv and hv cables and plant with the plant 'live'. This development has been carried out in conjunction with HVPD's PD Test and Development Engineers, our utility partners (including the UK DNO's EDF Energy, Scottish Power and Scottish & Southern) and a number of specialist external consultants (in the field of PD detection electronics and software).

Through a process of continual product and software developments combined with a wide range of both On-line and Off-line PD test projects with our utility and industrial customers (where significant applications knowledge has been gained) HVPD have been able to fashion our holistic range of PD test, location and monitoring technologies.

The HVPD knowledge-base has been supplemented by our University Research projects through the sponsorship of a number of PhD and MSc. students over the past 12 years in conjunction with a number of UK and International Universities, including most notably, The University of Manchester and Salford University in our home city of Manchester, UK.

Over the past 11 years, we have supplied On-line PD test technology and PD test services to a worldwide customer base in Europe, North America, the Middle East, South East Asia and Australasia. The applications knowledge obtained from this experience of testing different cables and plant, in different environments has also been.

Finally, and most importantly, the HVPD test and monitoring technology has been developed in close collaboration with the end users, to ensure that the PD test and monitoring technology meets the requirements of the market, with the correct functionality and easy usability. HVPD have collaborated in the development of our products with a number of end users ranging from large, electricity distribution and transmission companies to industrial clients with small, contained networks.

The accumulated knowledge of PD testing and monitoring from the above sources has been incorporated into the company's range of PD test and monitoring technology and our specialist On-line and Off-line PD testing services. The knowledge of On-line PD testing of mv and hv cables, switchgear, transformers and rotating plant is passed onto our customers by our highly trained PD Test Engineers via pilot projects, dedicated training courses and after-sales customer support packages.

The combined knowledge-base of the company grows year on year, as the company grows in size to enable continual development of our new PD test and monitoring products, on-line PD test techniques, new software algorithms and PD asset management databases. These developments are achieved by our team of 8 test and development engineers and 2 associate design consultants.

HVPD have already incorporated much of our contained knowledge-base into our unique range of PD test and monitoring technologies which utilise a number of intelligent, PD-analysis software algorithms, including wavelet analysis, precedence detection and RF noise reduction. This knowledge is passed on to our customers via our dedicated customer PD test training courses.

The HVPD Directors have consistently published the results of our developments at a number of international conferences around the world, with over 20 papers on PD test and monitoring of mv and hv networks published over the past 11 years. This includes a number of papers on mv network PD test and monitoring presented at CIRED Conferences between 2001 and 2009 and at a recent paper on the on-line PD testing of hv cables sealing ends at the CIGRE 2008 Conference. A selection of these range of publications are available on this website for download.

PD Test and Monitoring Technology Developments

HVPD hold substantial experience in the On-line PD 'Spot' Testing and Cable PD Mapping (location) of 11kV & 33kV Cables and Switchgear, with much of this experience in the UK having been developed from collaborative work with EDF Energy (formerly London Electricity) over the past 11 years. This work initially focused on the PD testing and monitoring of older in-service, underground paper cables (PILC) and solid-insulated switchgear with a view to the reliable life-extension of these ageing assets beyond their 'design life'.

It was found during these developments that by monitoring the condition of the insulation using PD detection, it is possible to provide reliable life extension of these assets with the potential for making huge savings to utilities as an alternative to wholesale cable & switchgear replacement programs of plant which has reached the end of its 'design life'.

Over the course of the past 6 years HVPD developed the portable, 4-Channel HVPD-Longshot™ PD Tester which was brought to the market in 2003, with the v3.0 PDGold© Software. This test technology has since been upgraded through 2x Software upgrades (in 2005 and 2007) to the present v5.0 PDGold© software. Through PD testing and training contracts with our customers over the course of this period, HVPD have developed a wide range of 'PD Test Knowledge Rules' for the On-line PD testing and monitoring of MV and HV Plant.

In recent years the HVPD have also applied the portable HVPD-Longshot™ 'spot' test technology to the on-line PD testing of newer polymeric cables (up to 500kV) and cable sealing ends through product supply and PD testing projects around the world. This technique utilises the we have been able to obtain first-hand marketing information which has shown an increasing interest in the application of On-line PD test and monitoring technologies, as electricity utilities and other HV plant owners become aware of the potential cost benefits which can arise from their application.

The PD diagnostic software and PD 'knowledge rules' which we have evolved from the projects described above have now been combined into the new range of permanent and portable PD Monitor systems which have been launched by HVPD in May 2009. These include the HVPD-Multi™ Monitor for primary substations and the HVPD-Mini™ Monitor for secondary substations.

For further information on these developments please contact HVPD.