Accurate fault location is essential for  submarine cables

Remote test for critical infrastructure

It is difficult to determine where the fault lies in non-destructive testing and remote conditioning monitoring techniques, but applications are now being devised to solve this.

Last summer, the Engineering and Physical Sciences Research Council (EPSRC) announced it would jointly fund a centre for non-destructive evaluation (NDE) and remote testing for the equipment that goes into critical infrastructure. The EPSRC’s £5.4m grant over six years is to be matched by industrial partners of the NDE Research Association.

Led by London’s Imperial College, the UK Research Centre in Non-Destructive Evaluation pulls together researchers from the universities of Bristol, Manchester, Nottingham, Strathclyde and Warwick and more than 40 companies across major industry sectors including aerospace, nuclear, and oil and gas. Their aim is to detect defects and extend the life and prevent failure of critical UK infrastructure such as pipelines, power stations and aircraft.

Remote monitoring improves the chances of responding to damaged equipment before its condition deteriorates to the point of failure. Terry Wilson, IT principal at Duke Energy in the US, describes how a large-scale rollout of monitoring systems has paid off: “We monitor over 10,000 critical pieces of equipment at power plants. We have 1200 [National Instruments] CompactRIOs controlled from our monitoring centre at Charlotte, North Carolina. In one instance, the system found a bearing defect on a blower motor. The discovery allowed plenty of time to plan a repair months ahead during scheduled downtime. All the analysis and detection were performed remotely.”

A number of technologies are being developed to watch for engineering defects. Vibration sensors are key components for monitoring bearing and similar problems in rotating machinery, such as turbines. Static equipment such as pipelines presents greater challenges.

Researchers at the University of Strathclyde, for example, have turned to ultrasound to uncover potentially critical problems with the welds that hold together pipes and nuclear-reactor casings.

“One particular type of weld, made of austenitic steel, is notoriously difficult to inspect. We were able to devise solutions involving the use of ‘chirps’ – coded signals with multiple frequencies which vary in time,” says Katherine Tant, a research associate in Strathclyde’s Department of Mathematics and Statistics.

By varying the duration and frequency of the waves, the results can be used to recreate an image of the component’s interior. She adds: “The type of flaw identified depends on the method used. An analogy would be the type of echoes produced by clapping loudly in a cave. A single clap may allow you to judge the depth of the cave while a round of applause will give rise to a range of echoes, perhaps allowing you to locate boulders.”

Some types of NDE require that the system get reasonably close to the problem. To test structural steel cables, Germany’s Fraunhofer Institute developed FluxCrawler, a robot that employs magnetic flux leakage measurements to find deep cracks and other problems. The institute is also developing robots for testing undersea cables.

Time-domain reflectrometry has been used for a number of years to find breaks and similar problems in buried electrical cables from local access points.

At the other end of the scale, the combined properties of the entire network can result in devastating outages, such as the 2003 blackout of the US north-eastern region. Here, distributed measurements are critical.

The emergence of the smart grid is helping to drive the evolution of systems that rely on the ability to synchronise hundreds and possibly thousands of real-time measurement units. Electricity suppliers want to upgrade the monitoring in their networks to respond to sudden shifts in supply and demand as more renewables are added to the grid. A key technology to support this trend is the synchrophasor.

Synchronised measurement

Megger product manager Andrew Sagl claims: “Synchrophasors are the new heartbeat of the grid. They improve the grid reliability by allowing real-time monitoring of the transmission system. This allows the utility to respond to disruptions in much shorter time frames, which have reduced outages by up to 60 per cent.”

Although a recent development in electricity grid monitoring, the core concept of phasor measurement dates back to the end of the 19th century with the work of Charles Proteus Steinmetz, who developed mathematical techniques for analysing AC networks. Almost a century later, in the late 1980s, Virginia Tech researchers Arun Phadke and James Thorp developed the idea of synchronising phasor measurements in a large-scale network to a common clock – derived from the atomic clocks carried by GPS satellites.

Unlike a heartbeat, the measurements are much faster, ranging from 30 pulses of data a second from each ‘phasor measurement unit’ (PMU) to more than 100. One issue with synchrophasor deployment until recently has been that of standardisation. Operators found that equipment from different vendors used subtly different approaches that made it hard to reconcile the measurements. China developed its own standards to support the rollout of its Wide-Area Monitoring Systems (WAMS) from the mid-2000s. But an international standard has since appeared in the shape of the IEEE C37.118.1 standard for PMU messages.

The development of the North American Synchrophasor Initiative (NASPI) has led to the connection of more than a hundred PMUs feeding data to a central controller in Tennessee that has generated the openPDC open-source project to make its technology available to a wider user base.

Companies such as National Instruments have added support for the standard to their products. NI has ported PMU software to its Grid Automation System, a CompactRIO hardware platform that runs a deterministic version of Linux Real-Time which is suitable for the Labview software and custom applications code.

Along with Labview installations, Megger’s equipment has been used in a number of trials including the STRONg2rid project, funded by Nordic Energy Research. In another project, Omicron worked with Alston Grid UK to test the PMUs for suitability in a wider grid implementation.

Sagl says: “The next step will be to start using synchrophasors at the distribution level. The challenge here will be cost. Smart grid technologies may very well change the business model of the utility. In the past the utility has been the energy provider. As distributed generation increases we will see more energy providers. The utility’s key role may become the transmitter of the energy.”

This trend shifts the business model towards one based on service quality, Sagl adds. “In the past the old business model was about low cost. It was all about taking money out of the grid. The smart grid changes this model and puts money back into the grid.”

The smart grid, along with other parts of the critical infrastructure, will in turn drive new trends in instrumentation.

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