Detecting Transient Faults on Overhead Networks
Medium & High Voltage Electricity Networks
UK Power Networks, United Kingdom
UK Power Networks is the United Kingdom’s biggest distribution network operator (DNO) and delivers electricity to more than 8 million homes in London, the East and South East of
England. It is transforming itself from a Distribution Network Operator, which simply delivers electricity, to a Distribution System Operator (DSO), which enables a smart, flexible
system that responds to customers’ needs.
The company says its vision for the future proposes significant changes to enable medium voltage electricity networks to enable consumers to use new and emerging technologies.
BUSINESS CHALLENGE
As part of its effort to continuously improve, UK Power Networks is constantly assessing ways to reduce the number of power outages and their duration. UK Power Networks has more than 46,000 km, or 28,500 miles, of overhead line networks that can occasionally be damaged by high winds, bird strikes or tree contact.
These can result in short power interruptions known as transient fault outages. Transient events typically include short variations of fault current without causing a sustained power outage. Transient events that are cleared automatically by very short interruptions from breakers or reclosers are referred to as momentary fault events.
It can take 6 to 10 hours, on average, to identify the exact location of a transient fault on overhead lines, especially when the outage occurs at night, is in a hard to reach location, or takes place during a storm. Once a fault it located it can then take an additional 1-2 hours to fix it. Reducing the expense and time associated with finding and repairing faults is an important component of reducing customer minutes lost.
Today, the company uses traditional fault passage indicators (FPIs), known as fault current indicators (FCIs) in the United States, to help them identify when faults occur on its overhead electrical system. However, there are several challenges with using FPIs.
While FPI alarms integrate with UK Power Networks’ GE PowerOn™ advanced distribution management system, they lack capabilities to help locate transient faults. They are not effective at detecting momentary line disturbances or developing faults and do not capture fault waveforms.
Due to less sophisticated triggering and classification methods, they may also generate false indications of actual outages or the true location of faults. As a result, operational staff then must be sent out to search for the fault location. This is done through a systematic process of opening the manually operated OHL switches installed along the route, energizing segments and ‘walking the line’ until the fault location is found.
This is a time consuming process.
SOLUTION OVERVIEW
UK Power Networks has recently undertaken a ground breaking project to improve customer service and was looking for new technology to help reduce power interruptions and customer minutes lost on its overhead networks. Funded by the Network Innovation Allowance (NIA), an incentive of the United Kingdom’s Office of Gas and Electricity Markets (Ofgem), part of the project’s objective is to develop algorithms that can predict fault location on overhead circuits and that distinguish false alarms from true outages.
To accomplish its goal, UK Power Networks selected the Aclara Grid Monitoring platform comprised of smart grid sensors and Predictive Grid® analytics software. The power sensors are easily deployed on overhead lines via hot stick, even in remote locations. The data they provide, including voltages, will allow the company to develop a real-time impedance model at the time of a fault, allowing precise location of the faults without having to ‘walk the line’.
“Our goal is to reduce the duration of supply interruptions by directing linesmen to the most likely fault locations. The trial will demonstrate Aclara’s “distance to fault” algorithm to
improve restoration times. ‘We are regularly reviewing Aclara power sensor input as part of UK Power Networks’ overall quality of supply improvement program and hope to make more strides in preventing network failure conditions.” PETER LANG – UK Power Networks’ Project Manager
UK Power Networks has installed over 400 power sensors on 11kV overhead lines on 45 feeders as part of an implementation of the Aclara Grid Monitoring platform in two of its three geographical regions – its East and South East areas.
The Aclara Grid Monitoring platform will continuously monitor load and power quality in places where troublesome overhead circuits have caused many supply interruptions. They are battery-free smart grid sensors capable of monitoring real-time voltage on distribution networks to within 0.5% accuracy.
Power sensors are installed on overhead lines with hot sticks and require no calibration or additional, pole mounted equipment.
These specific line sensors were installed for three reasons:
1 – To allow UK Power Networks to gain better network visibility on its overhead circuits and reduce the time it takes to identify permanent faults that are located on specific spurs or between sectionalised points on the main line.
2 – To reliably detect and resolve developing or transient faults caused by events including branches touching power lines, animal incursions, bird strikes, and defective equipment.
3 – To reduce the length of supply interruptions by directing linesmen to the most likely fault locations.
The Aclara power sensor is a highly integrated and rugged solution that is a fraction of the cost of traditional kits of equipment with equivalent functionality. It introduces additional OpEx savings due to its simple installation and highly reduced maintenance costs compared with similar alternatives.
Precise measurements and events captured by Aclara power sensors, combined with the sophisticated analytics in its sensor management system (SMS) software, including an algorithm that identifies the exact location of faults, provide highly accurate, real-time reporting of fault events. Thus, the Grid Monitoring fault location solution greatly improves restoration times.
Additionally, to build intelligence about what might cause a power failure in the future, Aclara’s SMS software classifies faults and disturbances that do not cause immediate outages. For example, incidents like momentary faults or line disturbances are categorized and can be filtered to show trends across a circuit or during certain times of the year.
This Predictive Grid® analytics capability of the Aclara SMS software lets UK Power Networks identify fault locations quicker, allowing engineers to study fault waveforms to better diagnose the true cause of fault events. It can predict and alert engineers and operators to early signs of developing fault conditions based on frequent patterns of transient conditions.
In addition, Aclara smart grid sensors are easily deployed towards the end of feeders and spurs, in locations where currents may be as low as 3A. This is important because battery-powered FPIs and sensors typically require at least 10A – and some up to 30A – to successfully keep the batteries charged. Therefore, the further you get away from the substation, the harder it is to identify faults because previously there were no solutions for low-current areas.
With the continuous reporting of power conditions, the deployment of Aclara’s smart grid sensors has also proven invaluable to help UK Power Networks gain better insight to the true load profile along its circuits. Better visibility of load and voltage conditions aids planners and network operators for both managing switching operations as well as long term network planning.
BUSINESS JUSTIFICATION
Use of Aclara smart grid sensors allows UK Power Networks to have much better visibility of fault Case Study: Grid Monitoring and disturbance conditions along circuits, leading
to changes in methods in working and business practices at the utility.
The company’s engineers now can go directly to the fault location, eliminating the need to ‘walk the line’ to find it. The deployment of Aclara smart grid sensors also demonstrates that transients or pre-faults can be accurately identified on the network. Analysing waveforms allows operational staff to be proactive in trying to identify the cause, allowing preventative maintenance before faults become permanent and cause network failures.
In addition, Aclara technology will help UK Power Networks meet its goals for reducing the number of power interruptions customers have and the length of the power interruption.
This project provides another key tool to support delivery of a more reliable electricity network. The solution enables UK Power Networks to implement improvements in the cost of network operations, replacing expensive manpower intensive processes.
At Aclara, we help utilities manage change, seek new approaches and harness data and new technologies to supply more efficient and reliable services to their customers. We offer a comprehensive suite of solutions comprised of meters and edge devices, advanced metering infrastructure (AMI), software, installation services and provision of labor with a single point of accountability. As an end-to-end, smart infrastructure solutions (SIS) partner we couple innovative technology with data-driven solutions to predict, plan and respond to system conditions across electric, gas or water distribution networks.
Aclara Sensors | WPD | Transitioning to a Low Carbon Future with Smart Grid Sensors
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The following blog has been republished with kind permission of Angelo Roviello, Area Sales Manager at Ensto, about the importance of Medium Voltage Training for Installers.
Malpractices during the installation of cable accessories are the main cause of interruptions and faults. The solution is sharing our know-how with the installers.
The use of high-quality cable accessories is a prerequisite for reliability in medium voltage cable networks. However, since most interruptions are due to the installation process, proper and systematic training of installers is needed in order to reduce the number of medium voltage power cable and system faults.
The electrification of continuously growing urban areas is based on cable networks, and in rural areas overhead lines are gradually moving underground. Constant shortage of power professionals and cable jointers brings in installers with various backgrounds.
At the same time, cable accessories have been developed into complete packages with product-specific installation instructions. A trained professional knows the importance of on-site preparations such as protecting against dirt and water. He also follows the installation instructions carefully to make the joint or ending last as long as the cable itself.
It is estimated that more than two thirds of unexpected interruptions in cable connections are due to faulty installation. In Central Europe, for example, the cabling activity is on high level, and the situation might be even worse.
Leading utilities look for a solution in two ways – by selecting tested, high-quality products, and by applying systematic product training of installers. They know that by improving the quality of installation work, the costs can be reduced significantly in the long run.
Ensto has been providing installation training for more than ten years in various markets. The concept is called Ensto Pro and includes events that consist of both theory-based lessons and hands-on installation exercises.
It is estimated that more than two thirds of unexpected interruptions in cable connections are due to faulty installation.
The products, in turn, are tested in accredited laboratories in accordance of international standards, and in addition to that, continuously in-house to ensure quality. The installation instructions are based on visual images to clearly point out critical steps and measures.
The final goal of all this is a correct installation, reliable operation of the network and lower total cost of ownership for the customer.
Proven Results in Sweden
Ensto in Sweden has experience of systematic product training of medium voltage cable accessories since 2012.
“At that time large utilities had failures in their networks, and it was soon realized that they were not due to the product itself. These utilities welcomed our installation training, received excellent results and remain loyal customers today,” says Björn Gustafsson, Sales Director of Ensto in Sweden.
“Several years ago, one of the largest network owners in the country required its contractors to have all their installers trained on our products every four years. Now many other customers are doing the same,” he says.
Medium voltage accessory training is usually held on or near customer premises. The day starts with cable theory, sharing experiences and going through the steps of installation. After lunch is a time for hands-on installation in small groups. Gustafsson and the team organize trainings almost every week covering nearly all Swedish customers.
This also means that the Ensto team and installers know each other well, and it is easy to pick up a phone and call.
“Some installers have already been trained for two or three rounds. They still find the day very rewarding and an excellent opportunity to discuss and learn something new for their daily work.”
“Also, the customer feedback is encouraging. One of our long-standing customers trained all the installers to cold shrink joints. After that, there was not a single cable joint failure, no more penalties and no replacement costs. The installers were also delighted with their improved skills.”
Thorne & Derrick International are specialist distributors of LV, MV & HV Cable Installation, Jointing, Duct Sealing, Substation & Electrical Equipment – servicing UK and global businesses involved in cable installations, cable jointing, substation, overhead line and electrical construction at LV, 11kV, 33kV and EHV.
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Cable termination H3 | Uneven contamination before and shown after cleaning
Special Thanks To William Higinbotham President at EA Technology for allowing T&D to republish
Below is a great example of using partial discharge instruments to prevent failures without doing unneeded maintenance.
Cable terminations are often used outside on riser poles or substation structures to convert cables to overhead lines or busses. These terminations convert the very tightly controlled cable electric field into an uncontrolled air insulated application.
When applied properly, the field strengths are less than the insulation strength and therefore no partial discharge exists.
Under certain circumstances, even a well applied termination can have partial discharge as a result of contamination. Humid salt air leaves conductive deposits that often result in partial discharge. Because of this, terminations in coastal areas are highly prone to PD. Other types of contamination can result from pollution, or even dusty air. When an insulator gets unevenly coated in hydrophilic contamination, you can get what is called dry band discharge.
The uncontaminated sections of insulator tend to be hydrophobic, so the insulator has dry and wet areas that are insulating and conductive. This disturbs the field distribution and leads to discharge across the dry bands.
Given time this will erode the insulator and lead to flashover.
A high voltage asset owner in central Canada has numerous terminations on substation structures. Clearly salt contamination is not the issue. However other contamination is building up unevenly on their cable terminations.
This operator is very proactive and does periodic PD surveys of both indoor and outdoor assets as part of their regular preventative maintenance. They use the EA Technology UltraTEV Plus2 with the UltraDish attachment for scanning terminations from the ground.
Cable termination H3 with uneven contamination
Two of the terminations (H1 and H3) scanned returned very high levels of ultrasonic energy. The phase resolved plots show typical PD results. The source is frequency locked to the power system and the impulses are occurring twice a cycle, half a cycle apart. The levels are approaching 40dBuV which is very high. The ANSI/NETA MTS 2019 standard calls for immediate action on levels greater than 6 dBuV.
During the next scheduled outage, the insulators were cleaned and then rescanned. The ultrasonic energy was gone, proving that the discharge was a result of the contamination.
Cable termination H3 after cleaning
The immediate benefit is that these terminations are now less likely to fail. Long term the asset owner has learned how the PD survey process can be used to control cleaning cycles. Some terminations may need less frequent cleaning some may need more.
Ultrasonic PD results prior to cleaning
Ultrasonic PD results after cleaning
William G. Higinbotham has been President of EA Technology LLC since 2013. His responsibilities involve general management of the company, including EA Technology activities in North and South America. William is also responsible for sales, service, support, and training on partial discharge instruments and condition-based asset management. He is the author or co-author of several industry papers.
Thorne & Derrick International are specialist distributors of LV, MV & HV Cable Installation, Jointing, Duct Sealing, Substation & Electrical Equipment – servicing UK and global businesses involved in cable installations, cable jointing, substation, overhead line and electrical construction at LV, 11kV, 33kV and EHV.
THORNE & DERRICK Product Categories: Duct Seals | Cable Cleats | Cable Glands | Electrical Safety | Arc Flash Protection | Cable Jointing Tools | Cable Pulling | Earthing | Feeder Pillars | Cable Joints LV | Joints & Terminations MV HV
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