Characterization of insulation papers using FTIR-ATR spectroscopy

The need to increase the productivity and capacity of power transformers has conditioned the production of insulating papers of a higher thermal class. For this purpose, various techniques of solid insulation modification were applied, which enable the increase in thermal and chemical stability of the insulating paper during the operation of the transformer. The applied additives, primarily dicyandiamide (DICY) and polyacrylamide (PAM), are one form of cellulose modification in the final stages of paper production. A significant difference between the papers is the nitrogen content in the paper, which is characterized by the addition of amine compounds (additives). The paper presents the application of infrared spectroscopy with totally attenuated reflection (FTIR-ATR) in the characterization of paper samples. The aim is to observe the difference between regularly kraft and thermally upgraded paper reflected in the presence or absence of characteristic functional groups for additives. The strip identification at 2194-2154 cm-1 confirmed the presence of dicyandiamide additives (DICY) in the spectrum of the sample of thermally upgraded paper, which is different compared with the spectrum of regular kraft paper.

Consideration of insulation coordination in power converters: Basic terminology and review of standards in the field

Insulation coordination in the field of power electronics has become a very important issue. It certainly deserves the attention of both designers and users of various topologies of power converter modules and devices. Over decades of experience in this area, a lot of experiential and practical data has been collected and documented in several key standards. The paper presents the basic terminology and basic types of insulation used in modern power converters, as well as an overview of relevant standards. Except being important for designers, the insulation coordination of the power converters has become also a very important issue for users.

Coordination between loss of excitation protection and minimum excitation limit function of voltage regulation system

Established practice is such that the relay protection system and excitation system are adjusted independently of each other, which very often leads to non-coordinated action. When network disturbance occur, it is necessary to provide that basic protection functions eliminate the fault if it is necessary, and that all generators respond so as to preserve system stability and use the most of their capabilities. The basic task of under excitation protection is to prevent damage to the generator in a not allowed mode of operation. Also it is important to prevent the absorption of large amounts of reactive power from system that can lead to voltage collapse or line failure in the transmission system. This paper deals with under excitation protection and minimal excitation limiter, which is a part of excitation system, as well as with coordination between them. In the paper the current and the proposed settings are presented regarding case studies of generators in power plants in "EPS".

High-voltage motors on-site testing

High-voltage motors are one of the most important components in thermal power plants and industrial facilities. However, they are often neglected in terms of preventive maintenance. Maintenance in power plants in Serbia still takes place according to the outdated model of maintenance based on fixed time intervals operations - time based maintenance. This is why emphasis has to be put on electrical testing of high-voltage motors in order to have a better insight into their condition, to prevent unwanted failures and to improve their service. This paper provides an overview of the currently available prophylactic tests of high-voltage motors. Also, the most common testing methods are described, which provide information on the current motor condition, so it is possible to make further repairs or corrective actions timely. Case examples and experiences from practice in power plants in Serbia are further presented and discussed in the paper.

Application of the Heidler function in electromagnetic transients programs

The paper analyzes the possibility of using the Heidler function in programs for electromagnetic transients. The parameters of the Heidler function are calculated for various standard waveforms, where greater accuracy is shown for certain waves than with the use of parameters defined by the standard. The calculated parameters for the selected waveforms are presented in the table and the possibility of using the table to estimate the certain waveform parameters not given in the table is shown. Possible ways of applying the Heidler function in programs for electromagnetic transients are presented.

Infrared sensors in special purpose technical assets

Special-purpose technical assets for measurement and monitoring are being rapidly developed with the goal of improving sustainable security and electronic protection of people and objects. A general division and application of intelligent infrared sensors in the security community is given in the paper. In a narrower sense, in the paper, a metrological overview of smart measuring sensors, devices, and systems is given. In a narrower sense, the paper analyses in detail the systems based on the use of thermal imaging cameras. A series of examples from world practice are given with the aim of illustrating the importance of measuring and monitoring IC systems use.

Consumers' influence in sustainable decarbonisation of future power system

Environmental protection and sustainable development cause a qualitative shift towards cleaner technologies in the field of electrical power. Countries with fossil fuel-based electricity generation have a questionable energy future regarding the independence and security of their end-users' supply. Therefore, it is necessary to explore all possible options for future development, taking into account the synergistic potential of other energy sources in electricity deficit compensation. That need will arise after the shutdown of fossil fuel power plants. It is necessary to mutually synchronize the development and application of different energy sources. For example, the large share of renewable energy sources with highly variable generation, without the presence of significant energy storage capacities or other sources that could compensate for these rapid power fluctuations, causes problems in energy balancing and disrupts power system flexibility and stability. Among the supporting pillars of a secure and decarbonised power system, special attention will be paid to the possible role and contribution of consumers; increasing their energy efficiency, using the heat capacity of buildings, demand response and direct demand side management.

Solving the problem of exploitation of transformers with corrosive sulfur by oil desulfurization using a strong inorganic base and organic solvent

Most power transformer failures are associated with the presence of corrosive sulfur compounds in mineral insulating oil, of which dibenzyl disulfide (DBDS) is the best known and most widespread corrosive sulfur compound. The oil of failed transformers usually contained DBDS, a compound with a pronounced affinity for the formation of copper (I) sulfide (Cu2S). Copper (I) sulfide is a compound that does not dissolve in oil, conducts electricity, and can be deposited on the paper insulation or copper conductor of the transformer. Created conductive paths between the windings can initiate turn-to-turn breakdown and failure of the transformer. Several technological procedures have been developed as a solution to oil corrosivity. The application of desulfurization technology developed by the Electrical Engineering Institute "Nikola Tesla" enables the efficient removal of DBDS and aging products from mineral insulation oils.

Coordination between relay protection functions and excitation system with generator capability curve

It is common practice for relay protection and excitation systems to be adjusted independently. That practice leads to the uncoordinated operation of some protective functions. This article presents the tuning of some important protection functions. The first step is loss of excitation protection adjusting and its coordination with the minimum excitation limiting function. Analyzing the coordination settings of this protection with the minimum excitation limiter in practice, it is often noticed that these functions are inadequately adjusted, so the capacitive part of the generator capability curve is not optimally used. That is in contradiction with the high need for capacitive reactive power in the transmission system. The second step refers to the coordination of the maximum stator current limiter in the excitation system with stator overload protection, overcurrent protection, and permitted generator stator overload. It is noted here that this coordination is often not adequately adjusted, leading to the following irregularities: -malfunction of the automatic voltage regulator in certain operating situations, which can lead to voltage collapse in the transmission system; -in some operating situations, there is no forcing of excitation current when it is most needed to preserve system stability.

Analysis of operation of transformer differential protection under current transformer saturation: Software simulations and relay testing

In the paper the analyses of the current transformer saturation influence to operation of differential protection are presented. Analyses are performed using a simulation tool and a relay model, as well as using the physical relay by injecting test currents from test equipment on relay inputs. The comparison of relay behavior in these two analyses has been performed and discussed. Network modeling has been performed in DIgSILENT PowerFactory and physical relay testing using DOBLE test equipment.