scholarly journals DETERMINATION OF “WEAK” BY POWER TRANSFORMERS RELIABILITY OF POWER SYSTEMS ACCORDING TO THE RESULTS OF FAILURE RISK ASSESSMENT UNDER EXTERNAL SHORT CIRCUITS

2021 ◽  
Author(s):  
Eugeniy I. Bardik ◽  
Mykola P. Bolotniy ◽  
Yaroslav S. Koval
Keyword(s):  
Mathematical Model ◽  
Risk Assessment ◽  
Power System ◽  
Electric Power ◽  
Power Transformer ◽  
Short Circuit ◽  
Electric Power System ◽  
Power Transformers ◽  
Electrical Network ◽  
Failure Risk

Background. The increase of technological violation intensity and its consequences severity is caused mainly by objectively existing aging and service life depletion of electrical equipment. The power industry liberalization exacerbates the reliable operation problem of the power system and requires identification of power system operation accompanied by the maximum emergency risk with possible cascade accidents development. Therefore, the model development task for assessment of the equipment failure risk based on the diagnostic results of technical condition in particular under short circuit in the external network is relevant today. Objective. The aim of the work is to develop a fuzzy mathematical model for probability assessment of power transformer failure in the presence of a windings defect, short circuit in external network and emergency risk assessment under power transformers out of service. Methods. The fuzzy set theory and fuzzy logic were used for developing a mathematical model of risk assessment of power trans- former failure. The problems of determining the “weak” in terms of power transformers reliability of power systems based on the results of failure risk assessment due to external short circuits were solved by methods of fuzzy logic and probabilistic-statistical simulation of electric power system modes. Results. The necessity of complex simulation of electric power system modes is substantiated for probability assessment of power transformer failure under electrical network disturbances. The simulation of technical condition of power transformer windings was carried out. The short circuit influence on operability level of power transformers of electric power system was investigated. The quantitative indicators of operational risk of electric power system were determined under power transformers out of service. Conclusions. The linguistic mathematical model for estimating the failure probability of power transformer windings in the presence of defect and short circuit in electrical network has been developed to determine the quantitative indicators of emergency risk in power system.

scholarly journals A Novel Methodology for Adaptive Coordination of Multiple Controllers in Electrical Grids

Mathematics ◽  
2021 ◽  
Vol 9 (13) ◽  
pp. 1474
Author(s):  
Ruben Tapia-Olvera ◽  
Francisco Beltran-Carbajal ◽  
Antonio Valderrabano-Gonzalez ◽  
Omar Aguilar-Mejia
Keyword(s):  
Power Systems ◽  
Power System ◽  
Electric Power ◽  
Large Scale ◽  
Short Circuit ◽  
Dynamic Performance ◽  
Low Frequency ◽  
Electric Power System ◽  
Design Stage ◽  
Positive Interaction

This proposal is aimed to overcome the problem that arises when diverse regulation devices and controlling strategies are involved in electric power systems regulation design. When new devices are included in electric power system after the topology and regulation goals were defined, a new design stage is generally needed to obtain the desired outputs. Moreover, if the initial design is based on a linearized model around an equilibrium point, the new conditions might degrade the whole performance of the system. Our proposal demonstrates that the power system performance can be guaranteed with one design stage when an adequate adaptive scheme is updating some critic controllers’ gains. For large-scale power systems, this feature is illustrated with the use of time domain simulations, showing the dynamic behavior of the significant variables. The transient response is enhanced in terms of maximum overshoot and settling time. This is demonstrated using the deviation between the behavior of some important variables with StatCom, but without or with PSS. A B-Spline neural networks algorithm is used to define the best controllers’ gains to efficiently attenuate low frequency oscillations when a short circuit event is presented. This strategy avoids the parameters and power system model dependency; only a dataset of typical variable measurements is required to achieve the expected behavior. The inclusion of PSS and StatCom with positive interaction, enhances the dynamic performance of the system while illustrating the ability of the strategy in adding different controllers in only one design stage.

scholarly journals Analysis of the Effect of Loading on the Transformers Usage Time

2021 ◽  
Vol 1 (2) ◽  
pp. 79
Author(s):  
Adi Syahputra Ritonga ◽  
Muchlis Abdul Muthalib ◽  
Muhammad Daud ◽  
Hamdi Akmal Lubis ◽  
Biswas Babu Pokhrel ◽  
...  
Keyword(s):  
Power System ◽  
Electric Power ◽  
Electric Power System ◽  
Power Transformers ◽  
Age Difference ◽  
Remaining Life ◽  
Calculation Results

The reliability and stability of the system in the operation of the electric power system is very important, in order to provide comfort in service to consumers. The transformer is a very important component in the electric power system, because it is used as a voltage adjuster for the load being served. This study discusses the effect of loading and temperature on the life shrinkage of 36/60 MVA power transformers in block 3 and block 4 carried out at PT. PJB UBJ O&M PLTMG Arun Lhokseumawe, Aceh. From the calculation results after 4 years the transformer operates, if the transformer is given a 100% load, the transformer will experience an age difference of 2.52 p.u/day so that it has a remaining life for of 10 years. As for the transformer that is given a load of 90%, the transformer will experience an age difference of 1.44 p.u/day so that it has a remaining life to perform operations for another 18 years. Then for a transformer that is given a load of 80%, the transformer will experience an age difference of 0.67 p.u/day so that it will have a remaining life to carry out the operation again for another 38 years. From the above calculation, the origin of the temperature obtained for the ONAN type of cooler in block 3 is 0.71 p.u/day and in block 4 it is 0.70 p.u/day. While the ONAF type of cooler in block 3 is 0.004 p.u/day and in block 4 it is 0.005 p.u/day. This is in accordance with the regulation SPLN50/1982 regarding transformer life shrinkage.

scholarly journals Influence of Oil-Filled Transformers Overload Capacity on the Throughput Capacity of the Electrical Network

2018 ◽  
Vol 61 (4) ◽  
pp. 310-320
Author(s):  
V. A. Anishchenko ◽  
I. V. Gorokhovik
Keyword(s):  
Service Life ◽  
Power System ◽  
Electric Power ◽  
Power Supply ◽  
Electric Power System ◽  
Throughput Capacity ◽  
Electrical Network ◽  
Economic Losses ◽  
Insulation Material ◽  
Overload Capacity

During the operation of the electric power system, there is often a need to overload its individual elements (generators, power transformers, overhead and cable power lines, switching electric devices) for a period lasting from several dozens of minutes to a day. The overloads can be caused by intentional disconnection of parallel elements of the system because of scheduled preventive repairs, post-accident disconnections, as well as an unexpected increase in electricity consumption due to the impact of various factors. The overload capacity of the system elements makes it possible to increase operational reliability of power supply to consumers without additional expenditures while maintaining, in most cases, the almost normal service life of electrical equipment. Oil-filled transformers have the greatest potential overload capacity power, which makes it possible to consider them as a significant source of increasing the capacity of the transmission and distribution networks of the electric power system. Excessive over-current of power oil-filled transformers significantly reduces reliability and reduces their normal service life. This is due to the accelerated process of wear of the insulation material of the transfer windings as a result of overheating of the transformer oil, that causes structural changes and, as a consequence, to mechanical damage to the insulation of the windings; the latter can cause an electrical puncture. On the other hand, underestimation of the permissible overload of transformers might result in economic losses due to under-produced products when the functioning of the part of the transformers connected in parallel are ceased for scheduled preventive maintenance or as a result of forced emergency shutdowns. Therefore, there is a need to assess the potential of reasonable increase in the throughput capacity of the electrical network and, accordingly, the reliability of the power supply system, taking into account the requirements for the permissible loads of transformers when the electrical network and various operating modes are being designed.

scholarly journals Investigating Phase Over-Current (OC) Protection in Medium-Voltage networks

2019 ◽  
Vol 4 (6) ◽  
pp. 41-49 ◽  
Author(s):  
Aniagboso John Onah
Keyword(s):  
Power System ◽  
Electric Power ◽  
Electric Power System ◽  
Normal Operation ◽  
Electrical Network ◽  
Power Circuit ◽  
Medium Voltage ◽  
Protection Scheme ◽  
Overcurrent Protection ◽  
Overcurrent Relays

Overcurrent protection is protection against excessive currents or current beyond the acceptable current rating of equipment. It generally operates instantly. Short circuit is a type of overcurrent. Magnetic circuit breakers, fuses and overcurrent relays are commonly used to provide overcurrent protection. There is always a need to protect expensive power equipment. Protective relaying is a very important part of any electric power system that comes into play during trouble, fault or abnormal condition. The purpose is to isolate unhealthy part of electrical power system while the rest continue their normal operation. The entire electric power system from source to load centers is exposed and subject to natural hazards. The effects of these hazards are capable of interrupting normal operations of the system. Since these hazards cannot be prevented, precautions are taken to minimize or eliminate their effect on the system. The relay is a basic component of any protection scheme. The information (or signals) received from the power system actuates the relay, when necessary, to perform one or more switching actions. The signals are proportional to the magnitudes and phase angles of power system voltages and currents. When the relay receives these signals, it decides to close (or open) one or more sets of normally open (or closed) contacts, and consequently, the trip coil of a circuit breaker will be energized to open the power circuit. This paper investigates over-current relay protection scheme applied to medium-voltage electrical network. Methods of current and time grading have been applied in the coordination of the overcurrent relays in a radial network. Different time/current characteristics of relays such as the normal inverse (NI), very inverse (VI), and extreme inverse (EI) have been examined in order to obtain optimum discrimination.

All-mode Validation of Calculations in the Analysis of Electric Power

2020 ◽  
Vol 11 (11) ◽  
pp. 28-37
Author(s):  
Aleksey A. SUVOROV ◽  
◽  
Alexander S. GUSEV ◽  
Mikhail V. ANDREEV ◽  
Alisher B. ASKAROV ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Differential Equations ◽  
Power System ◽  
Electric Power ◽  
Field Data ◽  
Transient Stability ◽  
Experimental Studies ◽  
Electric Power System ◽  
Adequate Model ◽  
Simulation Results

The transient stability is the main condition for reliability and survivability operation of electric power system. The transient stability analysis is an extremely complex problem. It uses the results of numerical integration of differential equations that form a mathematical model of the power system. However, the mathematical model of a large-scale power system contains a rigid nonlinear system of extremely high-order differential equations. Such system cannot be solved analytically. The simplifications and limitations are used for improving the conditionality of the power system mathematical model in time-domain simulation. It decreases the reliability and accuracy of the simulation results. In this regard, it becomes necessary to validate them. The most reliable way of validation is to compare simulation results with field data. However, it is not always possible to receive the necessary amount of field data due to many power system states and a large amount of disturbances leading to instability. The paper proposes an alternative approach for validation: using an adequate model standard instead of field data. The prototype of Hybrid Real Time Power System Simulator having the necessary properties and capabilities has been used as the reference model. The appropriate sequence of actions has been developed for validation. The adequacy of proposed approach is illustrated by the fragments of the experimental studies

Review of Short Circuit Current Prediction Technology in Electric Power System

2021 ◽  
pp. 311-327
Author(s):  
Xiren Miao ◽  
Shengbin Zhuang ◽  
Jiamin Li ◽  
Lingling Tang
Keyword(s):  
Power System ◽  
Electric Power ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Electric Power System
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