HVPD Ltd 4-Phase On-line PD Test & Monitoring Solution

HVPD present an integrated, 4-phase, condition-based asset management solution which combines the complete HVPD range of PD 'spot test' and PD monitoring technology. The solution provides the framework for a systematic and cost effective, condition-based asset management system which can identify, locate and monitor PD activity within the customer's network.

Studies by HVPD Ltd and others from around the world have shown that, through the careful application of a combination of On-line and Off-line PD 'spot-testing' and On-line PD monitoring systems, 'risk-of-failure' indices can be produced to support condition-based asset management decisions. By replacing or repairing cables and plant which have high levels of PD activity (and therefore a higher risk of failure) the MV and HV plant owner can target their maintenance budgets to the cables and plant in most need whilst simultaneously reducing the risk of faults on their network.

On-line Partial Discharge (PD) testing of cables and plant whilst they are 'live' has now become widely accepted as the most effective means for the assessment of the insulation health of medium voltage and high voltage plant and cables. Studies have shown that PD testing can be used as a tool for predictive maintenance and avoiding failure. With the advent of on-line PD testing of in-service plant the entire installed cable system (cable, joints and terminations) can be assessed under normal working conditions on-site without any need to de-energise or to take the cable out of service. Over the past 20 years XLPE insulation has become the insulation of choice for almost all new HV transmission class cable installations, and in such systems it is the cable joints and terminations that are most susceptible to PD activity and failure.

Economics for Large, Utility Medium Voltage Networks

HVPD studies on large utility MV networks show that the largest savings are to be made in deferring and/or targeting capital replacement programs of the cable population. This is simply due to the capital cost of replacement being so large compared to the other costs, that saving even a small amount of this cost tends to dominate the other costs. For example, in many utilities, the cost of an interruption is perceived as merely the cost of the repair, particularly when automatic re-configuration of the network is available.

Economics for Small, Industrial Medium Voltage Networks

HVPD studies on industrial customer networks show that in these cases, depending on the process which depends on the power supply, the cost of an interruption can dominate the capital cost of cable replacement. Oil platforms, industrial processes, nuclear reactors, data centres and other high profile or sensitive power supplies can have a very large cost of interruption (running into many millions of £'s per day!). Such customers have less difficulty in justifying the cost of diagnostic measurements, or complete system monitoring. As a 'rule-of-thumb', if the cost of an outage is greater than say £200k/day, such asset owners tend to be very much focused on the condition of their MV and HV plant!

Permanent vs. Portable Monitoring Solutions

The costs of installing permanent PD monitoring technology to monitor 100% of large utility networks are presently prohibitive (although this may change in the future). For example, for a typical UK utility with 1,000 primary MV substations, and a typical cost per monitor of £25,000, the projected capital costs for 100% coverage are £25 Million!

The alternative of using portable PD monitors, moved between different substations for a week at a time requires significantly less capital investment. For example, assuming 80% monitoring utilisation (of 40 weeks per annum per unit), 25x portable monitor units would be required to monitor the 1000 primary substations at a capital price of £750k, or £750 per substation. These portable monitors would require test technician resources, to install and de-commission the portable monitors on a weekly basis. With 25 units, 3x test technicians would be required at an estimated cost of £300k per annum. With analysis, databasing and reporting labour costs estimated at a further £150k a total cost operating cost of £450k per annum is estimated, or £450 per substation.

It is clear from the simple analysis above that an alternative to the large-scale installation of permanent PD monitors for large-scale MV networks is possible. The new portable and permanent PD test and monitoring technologies described below, when incorporated into a structured, condition-based asset management plan such as the 4-phase plan described herein can offer this alternative.

HVPD's Recommended 4-Phase PD Test and Monitoring Approach

Over the past decade HVPD have worked in close collaboration with a number of electricity transmission and distribution utilities around the world (including close collaboration with EDF Energy. Scottish Power Systems and Scottish & Southern in the UK) on the development of a range of on-line PD surveying, Diagnostic 'spot-testing' and PD monitoring technologies. These developments have included the handheld PDSurveyor™ PD Surveying Tool and the HVPD-Longshot™ Diagnostic PD Spot Tester, both of which have been used as portable units in the field for a number of years.

HVPD (and others) have proposed for many years that for the cost-effective, long-term condition-based management of medium voltage cables and plant, a 4-Phase PD Test and Asset Management Solution should be applied. This being as an alternative to the wholesale installation of permanent PD monitoring solutions which is presently not economically viable due to the very high cost.

The 4-phase, HVPD test and monitoring approach illustrated below in Figure 1 has been has now been presented at a number of International Conferences on MV and HV Plant Monitoring over the past 10 years, to widespread acclaim. The management approach provides for a systematic and cost effective methodology which can identify, locate and monitor PD activity within the customer's network.

The main benefit of this 4-phase solution is to provide the framework for a more cost-effective approach to PD testing and monitoring as an alternative to the large-scale installation of permanent PD monitoring systems. The approach is based on the on-line PD test and monitoring experience of the company's Directors and Senior Engineers which has been attained over the past 11 years and is based on the fact that only between 5 and 20% of MV assets in a network will have significant levels of PD activity. The key to any approach here is to ensure that any test and monitoring resources (and ultimately maintenance activities) are directed to this small percentage of the network.

It is through the pre-screening of all assets for PD quickly and cheaply in Phase 1 which makes it possible for the MV plant owners to identify those assets as having some cause for concern. These assets are then taken onto the next stage of the asset management solution, Phase 2 comprehensive, diagnostic PD testing and, if the diagnostic tests show up some real PD, then onwards again onto PD location (Phase 3) and then continuous PD monitoring (Phase 4). If the PD activity in the cables or plant which are being monitored increase beyond acceptable, cumulative PD activity measurement guidelines then remedial action and repair is recommended.

The HVPD 4-Phase PD Test & Monitoring Technology Solution

In May 2009, HVPD launched our newly developed range of portable and permanent remote-access PD monitoring technology, including the 16-Channel HVPD-Multi™ Portable Monitor, the 4-Channel HVPD-Mini™ Portable Monitor and the multiplexed, permanent versions of both technologies. These technologies have been developed in conjunction with both utility and industrial electricity network operators and are available in both portable and permanent versions.

The portable PD monitors are for mobile use in the field and operate as stand-alone units with built-in 3G Modem Mobile Communications. The permanent monitoring systems have been designed with a base unit and multiplexed, add-on units with up to 64 monitoring channels available on the HVPD-Multi™ Permanent Monitor. The permanent monitors can also be integrated into the customer's LAN, Ethernet or other plant communications systems (Modbus etc) via their standard communications interfaces.

With the addition of this new range of PD monitoring technologies to the HVPD's established PD surveying and PD 'spot-test' technology (including the PDSurveyor™ and HVPD-Longshot™ Diagnostic PD Spot Tester) HVPD can now offer technology to provide a complete, 'holistic' solution for the PD screening, diagnostic testing, location and PD monitoring of medium voltage networks, as per the requirements of the 4-Phase Approach.

This HVPD technology range is summarised below in the table in Figure 2.

PD Test or Monitor Device	No of channels (typically one PD sensor is installed per item of plant tested)	Typical Test or Installation Duration	Typical Test or Monitoring File Size	Onboard Data Storage Restriction
PDSurveyor™	3 (HFCT, TEV & Acoustic)	10-30 seconds per plant item	N/A	N/A
HVPD Longshot™ (with On-line Cable Mapping Expansion Kit)	4 (synchronous acquisition to within 2ns on all channels)	5-10 minutes and up 1 day in 'monitor mode'	8MB for 5 min test, 50MB per day in monitor mode	30 GB hard drive
HVPD-Mini™	4 (2x HFCT & 2x TEV, with precedence measure)	1 day (Portable unit) to Permanent installations	5kB per day 2MB for 1 year of data	1 year with data capture every 30 mins
HVPD-Multi™	16 (multiplexed)	1 day (Portable unit) to Permanent installations	100kB to 16MB per day	one year of data

With the newly launched HVPD-Multi™ and HVPD-Mini™ monitor technology, HVPD can now offer a complete range technology to provide a 'holistic' technology solution for the new application of on-line condition assessment of in-service MV networks.

This technology range includes a combination of PD screening, diagnostic testing, PD location and PD monitoring technologies for medium voltage networks which have been developed specifically for the cost-effective, HVPD 4-Phase Asset Management Solution which provides a process by which critical plant can be identified, located, monitored and managed.

Further Information

• Download Better Asset Management Guide
• Download HVPD 4-Phase PD Test & Monitoring Solution Document
• For further information, please contact us.