Monitoring Transformer Condition with MLP Machine Learning Model

Failures of large power transformers in transmission system are always followed by significant costs, which is especially problematic given that they present an unplanned expenditure. In addition from disrupting financial plans, these events can lead to lower system reliability. This paper describes the development and potential application of transformer winding temperature model based on multilayer perceptron class of artificial neural networks. Model is built in Python programming language with data collected over the span of one year for a single transformer. Three input features (oil temperature, winding current and outside temperature) are used in the input layer, aiming to predict the winding temperature in the transformer. By comparing the predicted winding temperature with the actual measured winding temperature, insights into the transformers internal condition can be derived. To demonstrate the models proposed application, two types of transformer condition degradation are simulated and a set of certain indicators based on statistical measures are explored

Minimisation of Generation Variability of a Group of Wind Plants

Minimisation of variability of energy delivered from a group of wind plants into the power system using portfolio theory approach was studied. One of the assumptions of that theory is Gaussian distribution of the sample, which is not satisfied in case of wind generation. Therefore, optimisation of a “portfolio” of plants with different goal functions was studied. It was supposed that a decision on distribution of a fixed amount of generation capacity to be installed among a set of geographical locations with known wind statistics is to be made with minimised variability of generation as a goal. In that way the statistical cancellation of variability would be used in the best possible manner. This article is a brief report on results of such an investigation. An example of nine locations in Croatia was used. These locations’ wind statistics are known from historic generation data

Statistical Properties of Electricity Generation from a Large System of Wind Plants and Demand for Fast Regulation

Experimental data of total wind generation, recorded at 5 minute intervals and published by the Bonneville Power Administration for the years 2007 to 2013, were analyzed on a year by year basis. All data were normalized to total installed power of wind plants. Statistical distribution functions were obtained for the following wind generation-related quantities: total generation as percentage of total installed capacity; change in total generation power in 5, 10, 15, 20, 25, 30, 45, and 60 minutes as percentage of total installed capacity; duration of intervals with total generated power, expressed as percentage of total installed capacity, lower than certain pre-specified level. The statistical distributions obtained from the data were used to devise simple, yet accurate, theoretical models. The models presented here can be utilized in analyses related to power system economics/policy, because they describe availability of wind energy resource in simple statistical terms relevant to interactions of wind generation with electricity system, and electricity markets. After a brief display of the models, the article concentrates on static properties of the observed system’s electricity generation related to its capacity credit, as well as on dynamic properties related to the demand for fast regulation (i.e., secondary and fast tertiary reserve). Both properties are important for technical planning of future electricity systems, as well as rational design of policy measures

Determining the Transmission Capacity of Existing Transmission Lines Under High Wind Generation Conditions

Determining the transmission capacity of existing transmission lines is determine by the conductor current. Transmission line can withstand current below thermal standpoint limit to avoid irreparable damage to conductor. The maximum value of current can be determined with static approach (STR – Static Thermal Rating) and dynamic approach (DTR - Dynamic Thermal Rating). STR is defined by simple calculations and does not change often throughout the year where the DTR is calculated for in time conditions taking into account atmospheric conditions, conductor geometry and conductor current. Most common approach to calculate conductor temperature is done by applying IEEE standard (IEEE 738, 2012) or CIGRE (TB601, 2014). Most congestion in the transmission network occurs during the higher production from wind farms when the wind have significant speed. It is to be expected that similar meteorological conditions (wind speed and direction) will occur on transmission lines in the immediate geographical area of wind power plants. In this paper, analysis of relations between atmospheric parameters (wind speed and direction, ambient temperature and solar radiation) and ampacity is described as functional dependence. Taking historical weather data from meteorological stations, atmospheric conditions on transmission line corridors and taking account the frequency of occurrence of individual meteorological variations ampacity of conductor will be determined. For such determined conditions that are influenced by a certain parameters variation of ampacity have a different rating scales. The obtained results will provide an insight into the current ampacity and the possibilities of the transmission line capacity during the high engagement of wind power plants

Transmission Grid Connection of Energy Storage Facilities - Overview and Challenges

Energy storage is an emerging technology that can provide flexibility for the electrical power system operation, especially in the conditions of large scale penetration of highly intermittent renewable energy sources. The paper gives an overview of energy storage technologies, giving the main technical characteristics and comparison of different energy storage features, like specific energy and power, price, number of cycles, expected lifetime, etc. Basic requirements for the connection of production and load facilities to the transmission network are described, as well as challenges regarding energy storage transmission grid integration. Finally, worldwide examples of energy storage grid connection projects are given

Statistical Properties of Electricity Generation from a Large System of Wind Plants and Demand for Fast Regulation

Experimental data of total wind generation, recorded at 5 minute intervals and published by the Bonneville Power Administration for the years 2007 to 2013, were analyzed on a year by year basis. All data were normalized to total installed power of wind plants. Statistical distribution functions were obtained for the following wind generation-related quantities: total generation as percentage of total installed capacity; change in total generation power in 5, 10, 15, 20, 25, 30, 45, and 60 minutes as percentage of total installed capacity; duration of intervals with total generated power, expressed as percentage of total installed capacity, lower than certain pre-specified level. The statistical distributions obtained from the data were used to devise simple, yet accurate, theoretical models. The models presented here can be utilized in analyses related to power system economics/policy, because they describe availability of wind energy resource in simple statistical terms relevant to interactions of wind generation with electricity system, and electricity markets. After a brief display of the models, the article concentrates on static properties of the observed system’s electricity generation related to its capacity credit, as well as on dynamic properties related to the demand for fast regulation (i.e., secondary and fast tertiary reserve). Both properties are important for technical planning of future electricity systems, as well as rational design of policy measures

Lightning caused overvoltages on power transformers recorded by on-line transient overvoltage monitoring system

Transient overvoltages generated by lightning strikes or switching operations represent a significant risk to bushings and windings of power transformers. They cause stress on the insulation system and can, over time, cause dielectric failure and damage to power transformers. Many transformer failures are reported as dielectric failures and they are not necessarily linked to any particular event when they occur but may be the result of prior damage from transient overvoltage events. Lightning and switching overvoltage waveforms appearing at transformer terminals in real operating conditions may significantly differ from standard impulse voltage waveforms used during laboratory testing. The number and amplitudes of overvoltages which stress the insulation depend on various parameters such as the lightning strike density in the considered area, since it determines how often the transformer is stressed by lightning overvoltages. Since the overvoltage amplitudes at transformer terminals are usually unknown, an on-line overvoltage transient recorder can be used with the ability to sample, analyse and store transients in real-time. In this paper, an on-line transient overvoltage monitoring system (TOMS) for power transformers is presented that is capable to continuously record in real-time various kinds of transient overvoltages such as lightning or switching overvoltages. Special attention is paid to lightning caused transient overvoltages recorded at the terminals of 150 MVA power transformer. Recorded waveforms originating from lightning strikes to overhead lines are correlated with data from the lightning location system (LLS) and supervisory control and data acquisition (SCADA) system. Collected data about overvoltage stresses can be used as the basis for the assessment of the transformer insulation condition, estimation of health index and for analysis of various kinds of events such as faults or equipment failures

Harmonic Performance Analysis of Static Var Compensator Connected to the Power Transmission Network

The static var compensator (SVC) is a device which is designed to compensate reactive power, increase voltage stability and to reduce voltage fluctuations. Thyristor controlled reactors (TCRs) are composed of reactors in series with bidirectional pair of thyristors. Current through reactors can be continuously controlled by changing the firing angle of thyristor valves, thus the inductive power can be easily controlled. Typical applications of TCRs in AC systems are voltage stabilization and temporary overvoltage reduction, stability improvement, damping of power oscillations and load balancing. In this paper, harmonic performance analysis of SVC equipped with TCRs is presented. SVCs utilizing TCRs generate harmonic currents and therefore it is necessary to determine the effect of harmonics generated by the SVC on the power system and its elements. This includes interaction of the SVC with the system, the SVC performance under balanced and unbalanced operating conditions and finally, evaluation of countermeasures such as installation of harmonic filters. In order to carry out these analysis, it is necessary to determine harmonic characteristics of the network at the point of SVC connection, existing levels of harmonics, and to know appropriate standards regarding acceptable harmonic levels in the power system. Since harmonic distortions in the system are caused by the interaction between SVC and the system, all system contingencies which may affect system’s frequency response should be evaluated. Detailed power system model should be considered to make sure that parallel resonance points of system do not directly coincide with characteristic harmonics from the SVC. Harmonics generated by SVCs are largely dependent on the operating point within the SVC characteristic. A conservative approach is to use the maximum values of harmonics generated within the spectrum irrespective of the operating point. The results of harmonic performance analysis are important for appropriate design of SVC. Harmonic performance analysis related to SVC application which are presented in this paper include the determination of: frequency response of the transmission network impedance required for the specification and design of filters; the effects of SVC generated harmonics on the power system; the overall filter requirements and countermeasures to reduce harmonics to acceptable level