D. Djairam

The influence of square voltage waveforms on transformer insulation break down voltage

The use of Voltage Source Converters (VSCs) in HVDC transmission and, more generally, in flexible AC transmission systems (FACTS), raises concerns over the endurance of turn/turn insulation of grid/converter interface transformers. In this paper, tests performed on oil-impregnated paper specimens are discussed. The results indicate clearly that shorter rise times and higher repetition frequencies have a strong impact on both partial discharge inception voltage and breakdown voltage. These results suggest that deeper investigation might be important to understand the long term behavior of these insulation systems.

The development of an electrostatic wind energy converter (EWICON)

A method of directly converting wind energy into electrical energy is proposed, called an electrostatic wind energy converter (EWICON). The method is based on transporting electrically charged particles against the direction of an electric field by the wind and accumulating them at a collector. The electrospray-method is used to create the charged particles. Two implementations of the EWICON and their properties are discussed, one with a separate collector and one with the system itself as a collector. Based on practical considerations, a choice has been made for the latter implementation. This system has been tested and this resulted in a conversion of 7% of the wind energy into electrical energy, whereas conventional wind turbine systems have an efficiency of 45% at their rated speeds. Improvements are suggested that could lead to an efficiency of the EWICON in the range of 25 - 30%

Investigation of the effects of fast transients on a transformer's paper insulation

Identifying future trends in the power grid is vital in the extension of the life of its already aging components. Fast transients are the new factors that need to be taken into consideration as their high repetitive frequencies and fast rise times accelerate the aging of the paper insulation in devices such as transformers. As will be outlined below, an aging set-up has been proposed to study these effects on paper insulation in relation to the time to failure. The aging waveform generation is discussed together with the steps taken to assess the influence of the fast transients. Initial test results will be presented on paper samples used in a transmission transformer showing that the transient waveform has a factor of 2 in shortening the life time of the cellulose.

Optimization of maintenance for power system equipment using a predictive health model

In this paper, a model-predictive control based framework is proposed for modeling and optimization of the health state of power system equipment. In the framework, a predictive health model is proposed that predicts the health state of the equipment based on its usage and maintenance actions. Based on the health state, the failure rate of the equipment can be estimated. We propose to use this predictive health model to predict the effects of different maintenance actions. The effects of maintenance actions over a future time window are evaluated by a cost function. The maintenance actions are optimized using this cost function. The proposed framework is applied in the optimization of the loading of transformers based on the thermal degradation of the paper insulation.

Development and Implementation of a Maturity Model for Professionalising Maintenance Management

An overall corporate strategy was the further improvement and professionalization of the maintenance management organisation at the third largest Dutch electricity and gas distribution network operator in the Netherlands. This contribution discusses the development and implementation of a Maintenance Management Maturity Model (M4). Principally, the M4 is developed for measuring and monitoring the integral corporate vision of a set of multidimensional domains which are necessary for maintenance management professionalization. Maturity levels as measured in 2012 and 2014 are given for gas and electricity network assets. This contribution describes the development and practical application of a maintenance management maturity model, which is found to be a structured guide for implementing new maintenance related activities, evaluating existing activities and directing continuous improvement activities. By looking back into these maturity levels, the maintenance organisation can clearly make insightful which domains have improved or not.

Statistical approach to establish failure behaviour on incomplete asset lifetime data

Asset failures, that needs to be managed, has an uncertain characteristic and analysis of uncertainty is essential to Asset Management (AM). Forecasting the technical performance of assets forms an integral part of strategic and operational activities within AM. To establish the failure behaviour of assets requires a significant degree of reliable asset information, which, in many practical cases, is not sufficiently rich or available to provide a basis for straightforward decision-making. In this paper a practical and systematic statistical methodology is used for dealing with incomplete asset lifetime data. The method described in this paper is based on a statistical parametric method and is applied with the aim of obtaining an indicator of the future failure expectancy with a certain confidence interval. On the whole, the paper concludes that, even though input data was either missing or incomplete, it is in certain cases possible to develop sensible probability models. These models take into account uncertainty and ultimately can be applied to facilitate the asset manager in AM decision-making. In addition to applying statistical methods, this contribution highlights the vital role of engineering and expert knowledge in interpreting the statistical results.

Risk-Based Approach to Maintenance Management Applied on Power Transformers

The power network utility sector is facing immense changes in their operation and management activities due to the deregulation of the market structure. Therefore, asset management (AM) is seen as an essential method to ensure control, gain knowledge and improve decision-making while these changes occur. Risk management is seen as a mainstream regime to enable AM to fulfil the mentioned drivers, because risk provides an analytical dimension with the characteristics of being comparable, measurable and manageable. Maintenance management is an essential part within AM, as it forms the means to track and ensure measurable asset performance throughout the asset lifecycle. In this contribution, we introduce risk incorporated Reliability Centered Maintenance (RCM) method based on the overall corporate risk management principles. In the developed method, the traditional Risk Priority Number (RPN) approach used in RCM studies has been expanded in order to deal with the consequences of asset failure modes on multiple corporate business values.

A novel method of wind energy generation-the electrostatic wind energy converter

Since ancient times humanity has been harnessing the power of the wind in various forms, such as discovering the planet in sailboats, creating living space in the Dutch polders, or providing bread by flour-grinding windmills. Since 1887 wind has also been used to generate electricity as the shift to renewable energy production is being made [1]. In order to fulfill the long-term carbon emission goals set by, for example, the EU for 2050, the share of renewable energy (wind, solar, hydro, biofuels) needs to increase substantially [2]. Of these various means of renewable energy, wind energy is still the largest part. Therefore, wind farms, both decentralized and bulk, are being constructed. In 2010 wind energy constituted 2.5% of the global electricity production [3]. The article explores a novel method of wind energy generation using an electrostatic wind energy converter or EWICON.

Repetitive transient aging, the influence of rise time

Power electronic devices are becoming very popular as they are linked with renewable energy sources. Their primary use is to switch between DC and AC waveforms so that the energy generated at locations such as wind farms and solar plants can be used by the power grid. Although cheap and reliable, power electronic converters generate repetitive transients that affect HV components such as transformers and cables. The three main features of these transients, repetition frequency, rise time and magnitude are the cause of premature failure in the insulation system of HV devices. Rise time is responsible for the energy injected into the paper insulation as it determines the speed at which cellulose fibers are polarized. This causes movement at a molecular level which weakens the insulation. Increasing the speed at which the transient reaches its maximum level causes bigger damages to the insulation. Polarity also has an effect. Results are presented in this contribution when transients of different rise time are applied to oil impregnated cellulose.

Converting wind energy to electrical energy using charged droplets in an electric field

Conversion of wind energy to electrical energy can be achieved when charged droplets are transported against the direction of an electric field. This method is used in an electrostatic wind energy converter (EWICON). The charged droplets can either be created using electrohydrodynamic atomisation (EHDA) or by high pressure monodisperse spraying (HPMS) in combination with induction charging. In this paper, these two spraying methods have been implemented in the EWICON system using water as a spraying liquid. Both methods have yielded a positive efficiency.