More needs to be done, through early detection and improved inspection regimes, to mitigate the risks posed to critical infrastructure by unexpected transformer failures. Louise Frampton reports
Transformers are critical elements of power networks. When they fail unexpectedly, the impact on critical infrastructure – such as hospitals and industry – can be catastrophic. Poorly maintained, ageing global infrastructure is exacerbating the risk of failures, while downtime can result in many millions in lost revenue for businesses.
Experts warn more needs to be done to mitigate these risks, through early detection and improved inspection regimes. However, invasive onsite surveys can prove costly and dangerous. Finding an approach that tackles transformer failure, as quickly and safely as possible, is the holy grail for mission critical industries.
Jamie Stapleton, digital leader for ABB’s transformers business warns that the state of transformers across the globe is a major cause for concern – in the US, for example, the average age of installed large power transformers is 40 years, with 70% being 25 years or older.
In the UK, electrical infrastructure is in a similar state – with many transformers being more than 30 years old. Over time, stresses on the power grid, such as over voltages and short circuits, can cause wear and tear to transformers’ internal components. In addition, due to the transition to renewable energy, many transformers are experiencing load conditions today that they were not originally designed for. This is a serious cause for concern.
In some instances, transformer failures can be catastrophic – at their worst, they can cause loss of life and significant damage to the environment. In 2015, a nuclear power reactor 40 miles north of New York City was shut down following a transformer fire. In January 2018, an underground fire caused by a transformer failure led to the evacuation of Newark Liberty International Airport in the US. More recently, in December 2018, the New York Times reported that “an explosion turned New York’s night sky an electric blue” and La Guardia Airport was forced to ground all flights after the lights went out.
Even failures resulting in less catastrophic outcomes can have a major impact on business continuity and damage reputation
It is not surprising, therefore, that fears over the threat of transformer failure are high across industry – a recent survey, commissioned by Midel, found that 80% of respondents expressed concerns, six in 10 said they had experienced transformer failure in the past five years, while five in 10 said transformer failure would significantly impact or halt their business operations.
A lack of resilience and inability to quickly return to normal operating conditions is a particular worry – just 29% of organisations were confident of reinstating power supply immediately, 19% estimated it would take more than three days, 23% said a week, and 18% feared it would take a month or more. For some, the impact is likely to be even greater, however; 11% expected it would take more than six months to reinstate power.
Barry Menzies, global managing director at Midel, commented: “Transformers are critical components of our electricity infrastructure but the impact and extent of transformer failure is not widely documented. The Midel Transformer Risk Report shines a light on transformer failure and the findings are clear: it has a significant and prolonged impact on businesses. An interruption to business operations can be very expensive, demonstrates poor corporate social responsibility and impacts business continuity.
“The good news is that many of the causes of transformer failure are largely within the operators’ control. It is relatively straightforward to replace old equipment and components and upgrade maintenance regimes; however, the survey suggests a level of concern that indicates industry needs to think more strategically about asset management and dedicate more resources to mitigating the risk of failure.”
The quality of equipment and components was considered a top option for reducing transformer risk by 87% of respondents, followed by maintenance schedules (76%) indicating the importance of considering transformer failure from the outset. In addition to safety, the maintenance of transformers (or lack of it) was cited as the top cause for concern by respondents (61%), while nearly 70% said driving down operating and maintenance costs was a key motivator for improving transformer performance, indicating a potential conflict when it comes to cost versus maintenance scheduling.
“Safety will always be a top priority but operations and maintenance also weigh heavily on transformer owners and operators. Companies are feeling the strain of ongoing operation and maintenance costs, which worries them as they recognise the importance of a good operation and maintenance regime,” continued Menzies, adding: “Transformer failure risk is taken very seriously, and it stands to reason that transformer owners and operators would do everything in their power to reduce it. Using ester fluids is just one of the ways to address some of the causes of failure; not only do they better protect against fire and avoid harming the environment, they can also lessen the operations and maintenance burden, which was consistently cited as a top concern.”
Causes of failure
A working group, previously formed by CIGRE (the international council on large electric systems), collected data on 964 major failures that occurred between 1996 and 2010, contributed by 58 utilities from 21 countries. Analysis showed that design and manufacturing accounted for 20% of all causes leading to transformer failures.
Other frequent faults leading to failures included insulation ageing and deterioration (15%), and improper maintenance and repair (10%). Almost 50% of failures, resulting in downtime, originated in transformer windings, with tap changers accounting for a further 23%.
Failures originating in the bushings most often led to severe consequences, such as fires and explosions, while dielectric mode failures were the highest contributor to failure modes, irrespective of transformer application.
Commenting on the data, industrial measurement expert Vaisala pointed out that regular monitoring through site visits and scheduled oil sampling can identify about half of all potential faults before they develop into a critical problem. However, online monitoring, which continuously gathers transformer data, will spot 90% of faults early. Asset owners can make use of online monitoring methodologies as part of their asset management strategies to identify and tackle issues as they arise – before they have a chance to cause significant damage.
In fact, state-of-the-art smart sensor devices are now being integrated during the manufacture of high-voltage transmission transformers to create a new breed of transformer. In April 2018, ABB launched its Ability Power Transformer, which connects through a set of diagnostic tools to deliver real-time performance data and insight into operations.
The build-up of heat, dissolved hydrogen, gas and moisture in the insulating mineral oil in transformers can all lead to premature failure or significant damage. These types of contamination reduce the dielectric strength of the oil as well as the cellulose paper insulation wrapped around the windings in some models.
Therefore, in the new digitally enabled transformer, sensors can measure not only the temperature of the oil but also key components inside the transformer, while monitoring oil quality and the accumulation of gas.
Despite the use of non-invasive condition monitoring techniques to determine possible faults, there are still routine and emergency situations that require costly internal inspections with major risk to both transformer structure and human inspectors. Robots are set to transform these internal inspection tasks, however, improving safety, avoiding extended downtimes and reducing maintenance costs.
Having delivered the first robotic inspection on a 50-year-old transformer for a North American utility, ABB has launched a new submersible robot to the UK market, to help operators control risk and limit the duration of outages for critical assets.
The conventional approach to inspecting transformers requires taking a unit out of service before draining it down; a technician will then enter the transformer to visually check the condition of components such as the windings, tap changer, insulation, gaskets and seals. This is a complex process that requires a risk assessment and a confined space entry, as well as time for cooling, draining down and oil handling. It can require an outage with a total duration of three or more days.
Not only does this approach involve a great deal of complexity and time, it carries with it a potential risk to human life and the risk of damage to the asset.
ABB’s TXplore is designed to enhance safety by eliminating the confined space risk to the technician, as well as risk of the technician causing damage while inside the transformer. Because the oil stays in place throughout the inspection, the robot also eliminates environmental and safety risks from oil spillage and enables a full inspection to completion in less than one day. The submersible robot is designed to balance ease of navigation with robustness, allowing the inspection of all areas of interest such as bushings, leads, tap changer, core top, core support and insulation etc. With the preservation of mineral oil quality of primary importance, the robot construction is optimised to leave no detectable footprint – either chemical or physical – as it operates within the transformer. The outer shell is also made of a high-performance plastic, which minimises the risk of electric coupling and structural damage to the transformer.
As the robot enters the unit instead of a human, no medical or environmental safety team is required during inspection. Only two employees, a robot pilot and a top-side equipment operator, are needed on site, therefore, which results in a dramatic reduction in personnel, time and costs, compared with human inspection. This would normally require a large team and require downtime of three or more days.
Ultimately, transformers are one of the most important components of the power grid and the industries they serve. Identifying weaknesses early and correcting them is key. The development of new technologies such as robotics and intelligent sensors will enable fast diagnosis of critical issues, without putting lives at risk – detecting issues before they can develop into costly failures.