Tracking transformer downtime: the rise of online monitoring

With transformer fleets aging worldwide, proper condition-based maintenance is more necessary than ever. Reliable online dissolved gas analysis monitoring – when done right – is an essential tool to keep fleets operational, reduce risks and lower maintenance costs, writes Juhani Lehto

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Balancing automation with process and personnel management is crucial

Credit: Vaisala

Power transformers are integral to the successful operation of modern power grids. Any failures can result in considerable periods of downtime, which will not only have a significant impact on a company’s finances, but also its reputation.

Financially speaking, extensive transformer servicing can cost upwards of €100,000 ($110,000), while a replacement transformer can cost up to €4 million – and this is before associated production losses are factored in. The reputational cost of extended downtime or blackouts, however, can be incalculable. A clear understanding of the risks involved in transformer operations, and how best to mitigate them, is therefore crucial to ensuring long-term fiscal security.

Proper maintenance of power transformers is not a new concern; however, the combination of several risks peaking at the same time makes it very topical. In today’s world, utility companies, industrial plant operators and service providers are faced with growing pressure to maximize the performance and lifetimes of their transformers.

Most urgent of these risks, perhaps, is the challenge posed by the ever-increasing demand for electric power, coupled with aging infrastructure. Between 2000 and 2010, global energy demand grew by 26 per cent. With the United Nations predicting rapid growth in the world’s population (from 6.7 billion in 2011 to 9.7 billion by 2050), this will place even greater strain on global power generation and supply.

Meanwhile, many transformers are already operating beyond their intended lifespan in an effort to keep pace with demand. While designed with a lifespan of 40 years in mind, the average age of transformers in operation is now 42 years, increasing the likelihood of failure and, in turn, power outages and fires, with each additional year.

Online monitoring system

Credit: Vaisala

At the same time, however, the problem is compounded by the recent lack of investment in new transformers. In the US, for instance, transformer investment peaked in 1974 before reaching a low in 1996 from which it has still not adequately recovered. This pattern is repeated across the world, and is a major contributing factor to driving up the average age of transformers.

With these raised stakes, transformer monitoring becomes even more important.

Dissolved gas analysis

At the very outset of transformer monitoring, faults were fixed as they were discovered. These maintenance strategies were clearly unsustainable as global reliance on electricity increased, and they were gradually superseded by prevention plans incorporating annual oil testing of each transformer.

More recently, the industry has been able to make use of condition-based maintenance, which enables companies to prioritize the transformers that most urgently require attention. This in turn, allows resources to be allocated appropriately. For example, the industry must closely monitor generator step-up transformers, those in substations that have critical connections to other locations, and those with a track record of serious gassing problems.

In the past few years, online monitoring has been developed as a more efficient means of identifying faults and addressing them at an early stage, before they become major maintenance issues. Online monitoring enables companies to track moisture, temperature and gas levels, and eliminates the risk of improper oil sampling.

Dissolved gas analysis (DGA) is a particularly widespread method used in the assessment of large power transformers, and is conducted by examining the dissolved gases found in their transformer oil. When an internal transformer fault or material aging occurs, various gases are formed as by-products of the chemical reactions resulting from cellulose or oil molecules breaking down. Based on these, DGA methods can then be used as a diagnostics tool to identify the type of fault that has occurred or is in danger of developing.

Online DGA monitoring can also provide historical data, which companies can use to spot trends. Using trend data is vital to identifying potential problems and determining the right course of action.

Part of what makes online DGA monitoring so powerful is that it is possible to combine this monitoring of trends with the detection of early fault warnings. With this information, utilities can effectively maintain their fleets through condition-based maintenance strategies.

An ability to identify trends and a thorough knowledge of transformer conditions are essential in deploying effective annual condition-based maintenance plans. Accurate, real-time data provides the most up-to-date picture of which transformers need immediate attention and the potential consequences of inaction. This forms a sound basis for making the most cost-effective maintenance decisions. As a result, online DGA monitoring is increasingly becoming standard practice for transformer fleets.

Choosing effective monitoring

So what to look for when considering the right kind of online monitoring solution to a transformer? Above all, reliability is the most desirable feature. The data it provides must be dependable, if it is to be used as a basis for any decisions. If, however, utilities must still validate the online data through regular laboratory sampling, this increases the complexity and duration of the testing process and, consequently, costs.

The online monitor should not raise false alarms, as these create more work in the form of unnecessary maintenance trips or manual sampling, which in turn disrupts maintenance schedules and generates additional costs.

Low maintenance requirements are important in keeping lifetime equipment costs low

Credit: Vaisala

Since transformer lifetimes are typically several decades, any instruments used in conjunction with these must be similarly long-lasting. This sets high demands for the design and manufacture of DGA monitoring systems in particular, as these must be able to withstand a wide range of environmental conditions, including tropical and sub-zero climates.

In addition, installation of these devices should be simple and fast, so that a company’s own field technician can easily handle the process. The device should also require very little regular maintenance, if any. Any parts that need replacing or regular maintenance should be avoided.

All this is important in keeping the maintenance costs low over the full lifetime of the equipment.

The future transformer market

As with many industries today, technological advancements are similarly driving the power and transmission industry forward. Enhanced online monitoring devices are one of the exciting developments that will help move us into a new era of transformer maintenance in the coming years. As more companies adopt these technologies, the industry will be better placed to assess the return on investment they provide in preventing failures and faults from developing.

Another factor worth considering is how personnel trends are likely to impact the industry in future. The number of experienced personnel is diminishing, and, as a result, companies will need to find new ways of assessing the state of their assets. Online monitoring acts as a solution by providing valuable data without the need to invest in more personnel to carry out oil sample testing and similar manual operational tasks.

A significant benefit of online monitoring is the fact that it supports substation automation. In the future, online DGA monitors are likely to be deployed as standard equipment on all large transformers. This will open the door to unmanned substations with automated monitoring and, furthermore, to computer-assisted decision making on the system level.

The emergence of automated substations with online monitoring and computer-aided decision will be a significant step in reducing the level of maintenance costs involved. Unmanned substations require fewer personnel visits to the station locations, which are often remote.

More importantly, however, when all the automated substations in a fleet are connected to the same network, this enables asset managers to make maintenance decisions centrally for the whole fleet. This allows utilities to better prioritize those transformers that require the most urgent maintenance.

While the level of automation will inevitably increase, it will be equally important to balance its implementation with the effective management of processes and deployment of personnel. The devices themselves will alert asset managers to faults, but only technicians on the ground can take the action needed to address these issues before they threaten the successful operation of transformer fleets.

Whatever the future might bring, the industry will need to keep pace with technological developments in the field. Indeed, the key to avoiding costly transformer downtime may lie in finding the optimal balance between the use of manpower and technology.

Juhani Lehto is the Product Manager for OEM and Power Transmission business at Vaisala. www.vaisala.com

Optimus DGA Monitor

Vaisala has recently launched its new Optimus DGA Monitor for transformers.

As a result of its careful design and the patented technology, the monitor does not give false alarms. This is possible, firstly, because the monitor carries an IR sensor, based on Vaisala core measurement technology and components manufactured in the company’s in-house cleanroom. Secondly, the monitor uses vacuum gas extraction, which gives a fully representative sample and means there is no data fluctuation due to oil temperature, pressure, or type. The monitor stays reliable over time, as hermetically sealed and protected optics prevent sensor contamination, and long-term drift is eliminated with a unique autocalibration functionality.

The Vaisala Optimus DGA Monitor is designed to be installed in less than two hours; users need only connect the oil, power and communications. The user interface is browser-based, and no additional software is needed. In the case of a disturbance such as a power outage, self-diagnostics enable automatic recovery.

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