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With the increased demands regarding the reliability, availability, safety and affordability of key public infrastructures, it becomes increasingly challenging for asset owners and managers to achieve a proper balance amongst performance, risk and cost. As a response, operators of critical infrastructures need sound solutions to maximize the value of their assets, meanwhile realizing their business values and objectives. This requires well-defined decision-making processes with an adequate risk management concept embedded.

Condition based assessment of OLTCs has become more popular in recent years, and the importance of reliable and accurate diagnostic techniques is being realized. The work described in this paper aims to improve existing diagnostic techniques, develop new ones and combine some techniques (hybrid) in order to realize a highly reliable set of diagnostics for tap changers. Topics addressed in this paper include motor power measurement, dynamic resistance measurement and vibro-acoustic measurement, the latter designed and tested as part of this project. Preliminary results show that in particular a combination of aforementioned techniques may lead to improved condition assessment and may lead towards automated and online monitoring of tap changer operation.

Power transformers are crucial components in networks for the transmission and distribution of electrical power. For the network manager, the health of the transformer fleet is of high importance in order to ensure a reliable grid. It requires appropriate maintenance processes and replacement decisions to safeguard that reliability. For monitoring the health, or condition, of transformers, an abundance of measurement options is at the disposal of the asset manager. In this column, we will address how an asset manager can best use these options to his benefit. Firstly, this contribution discusses the interaction between asset management and measurements. Secondly, we will present what diagnostic options and measurement policies are at the disposal of the asset manager, and discuss a number of relevant choices to be made and aspects to be taken into account.

The primary function of power transformers is to transform voltage levels for transmission and distribution. Often, transformers are equipped with a device to adjust the voltage ratio by changing the turns ratio: the tap-changer. About 30% of all European substation transformer failures are attributed to tap-changer failure, as well as about 22% of the failures in which a fire or explosion has occurred. Although the contribution of tap-changer failures has decreased over the years, it justifies appropriate measures to timely identify tap-changer defects and mitigate failure risks. In this paper, we present an overview of tap-changer diagnostic options, and discuss recent developments, in particular concerning improved techniques for dynamic resistance measurement.

As blood tests provide information about a person’s state of health, oil analyses provide information about the condition of a transformer. Transformer oil testing has proven to be an excellent tool for early defect identification in preventive maintenance of oil-filled transformers. It has permitted extended service life by giving a measure of both oil and solid insulation condition, and by identifying the presence of incipient thermal and dielectric faults. When performed regularly, oil analysis will help the asset manager run a cost-effective maintenance program for transformers. This column addresses some recent developments in oil analysis, such as sustainable alternatives for mineral oil, an alternative marker for analysis of paper degradation, and online transformer oil monitoring.

Modern asset management systems make use of risk based decision methodologies. This means that not only the frequency or the consequence of an event is regarded, but also the product of both. In order to transform operational and maintenance data into decision information that supports the asset manager in taking well-substantiated decisions, use is made of health and risk indexing methods. A health index is used to represent the condition or health of an asset; a risk index is used to represent the associated risk of a failing or defective asset. Several methodologies are in use to perform health and risk indexing. In this contribution, we will discuss the features and requirements of such methods. In particular, we will discuss some of the key challenges faced when developing and implementing health and risk indexing in asset management decision making.

In 2014, the ISO 55000 standard on asset management was issued, providing an internationally recognized framework for asset management that utilities can adopt to enhance the asset performance while controlling the risks at acceptable costs. This standard is, deliberately, made applicable to different kinds of organizations and assets, hence it does not elaborate on the management of specific assets in specific organizations. As a result, it is the utility’s responsibility to translate this framework into technical asset management processes along the lifecycle of assets. This was recognized in the 2015 IEC White Paper on Strategic asset management of power networks, which has eventually resulted in the formation of a new IEC Technical Committee (TC 123) dealing with the management of network assets in power systems. In this contribution, I will focus on power transformers and discuss the difference between asset management and managing assets. Further, I will explore options of introducing something like power transformer asset management, which, on the one hand, needs to be in compliance with ISO 55000, but on the other, needs to provide more detailed guidance to asset managers and operators.

Power transformers are valuable assets in the power network, with the primary function to regulate the transmission and distribution voltage. The regulating device is the tap changer which sets the turn ratio. Tap changer failure is one of the leading causes of high-voltage power transformer failure. Most tap changer failures are caused by degrading contacts. Contact degradation may be the result of contact wear or of arcing-induced carbon deposition during on-load-tap (OLT) changes. Contact degradation increases contact resistance, causing increased heating and arcing, eventually leading to possible failure of the power transformer. Proper maintenance, therefore, requires a diagnostic system which can assess the condition of the contacts. The research presented is aiming at automated defect recognition and localisation from measured dynamic resistance measurement patterns, for two types of tap changers, the 'Diverter Switch' type and the 'Selector Switch' type OLT changer.

To secure the quality of the installed asset base, in this case power transformers, utilities and industries rely on quality assurance. This paper will focus on quality assurance in the early phases of the lifecycle, prior to operation. Elements contributing to this quality assurance are specification, design review, quality review of the manufacturer or production, and testing. The question will be addressed what quality assurance options are available and meaningful. Moreover, the paper presents specification as one of the possibilities of quality assurance and discusses the specification requirements and options in more detail. These days, transformer requirements increasingly involve sustainability aspects. Such aspects may include the environmental impact, energy efficiency and losses, and the lifetime and recycle options of the materials. This paper will discuss how such sustainability aspects may be incorporated in the transformer specification, and reflect on present practice using experience from decades of projects worldwide.

This paper discusses a decision-support model for asset managers to prioritise assets requiring additional maintenance or replacement, by estimating asset remaining-lifetime and failure impact. The asset health and risk model (AHRM) being the heart of this model is based on dedicated asset-condition assessment functions in combination with usage-based condition estimations and a statistical approach using Monte Carlo simulations. This results in a health index colour code with two dimensions. The colour itself gives an indication of expected remnant life or additional maintenance requirements and the colour intensity gives an indication of the assessment reliability, thereby providing a clear and easily readable dashboard for the asset manager. A risk-based approach is used for further decision support. For each asset a risk-impact categorization is provided and plotted in a risk matrix, enabling risk prioritization on both probability and impact. The paper describes the methods behind the model.

Based on the observation of time-resolved avalanche current waveforms in electronegative gases, three different types of avalanches can be distinguished. The first distinction is that between electron avalanches and ion-dominated avalanches. Electron avalanches are further subdivided into electron avalanches with and without delayed electrons. Delayed electrons are the result of consecutive attachment and detachment processes. Experimental identification of the different avalanche types requires an experimental set-up with a time-resolution in the order of 1 ns. The conventional avalanche model, which involves effective ionization and drift, gives an adequate description only for electron avalanches without delayed electrons. An extended model, which also incorporates electron detachment and ion conversion processes, in principle describes all three kinds of avalanches. When the extended model is applied to the evaluation of measured waveforms, the often-quoted abnormal pressure dependencies in the electron drift velocity and the effective ionization coefficient disappear for the gases studied in this paper.