scholarly journals Analysis of Operating Modes of Oil-Immersed Power Transformers with a Voltage of 10 (6) / 0.4 kV

2021 ◽  
Vol 24 (4) ◽  
pp. 80-91
Author(s):  
A.E. Fokeev ◽  
I.N. Tumakov
Keyword(s):  
Ambient Temperature ◽  
Thermal Aging ◽  
Power Transformer ◽  
Spectral Composition ◽  
Operating Conditions ◽  
Power Transformers ◽  
Load Factor ◽  
Calculation Algorithm ◽  
Load Current ◽  
Aging Rate

The rate of thermal aging of the power transformers windings insulation depends on the effects of the electric field, mechanical stresses, temperature and processes that cause changes in these factors. A calculation algorithm is considered that allows determining the temperature of the most heated point of the windings of an oil power transformer at known values of the load current and ambient temperature. Calculation of the most heated winding point temperature and the rate of thermal aging of insulation for an oil power transformer at different ambient temperatures during the year, different values and different spectral composition of the electric load current showed that in some cases it is possible to violate the permissible operating conditions of power transformers. According to the calculation results, the dependences of the thermal aging rate of insulation on the ambient temperature are constructed, with different load parameters and different load coefficients of power transformers. For the considered modes, in the warm season, the value of the thermal aging rate of insulation significantly exceeds the nominal value. Based on mathematical models of oil power transformers with natural and forced oil circulation, expressions are obtained for determining the coefficient of reduction of the oil power transformers permissible load when the ambient temperature exceeds the normal value of 20 °C. On the basis of these expressions, for practical use, the dependences of the coefficient of reduction of the permissible load on the ambient temperature are constructed. The influence of ambient temperature must be taken into account when choosing the power of oil power transformers, for which it is assumed to operate in full redundancy mode or high load factor values (³ 0.8) in normal mode. To ensure the normative service life of the insulation of the windings, it is necessary to determine the design power of oil power transformers using the coefficient of reduction of the permissible load under the influence of higher harmonics of the current and the coefficient of reduction of the permissible load under the influence of ambient temperature.

Thermal Behavior of Power Transformers Filled With Waste Vegetable Oil-Based Biodiesel Under Dynamic Load

2021 ◽  
Vol 143 (9) ◽  
Author(s):  
Ehsan Ebrahimnia-Bajestan ◽  
Hani Tiznobaik ◽  
Paul Gheorghe ◽  
Mohammad Arjmand
Keyword(s):  
Heat Flux ◽  
Ambient Temperature ◽  
Vegetable Oil ◽  
Dynamic Load ◽  
Renewable Resource ◽  
High Heat ◽  
Transformer Oil ◽  
Power Transformers ◽  
High Heat Flux ◽  
Aging Rate

Abstract Petroleum-based oils are widely used as electrically insulating materials in high voltage power transformers for dissipating high generated heat flux and maintaining the temperature below critical values. The operating temperature of a transformer dominantly governs its aging rate. In the present research, a renewable coolant as a versatile substitution for the petroleum-based oils was investigated to be employed in the cooling of transformers. The studied coolant is a vegetable-based oil extracted from the waste cooking oils. A numerical model was developed to follow the instantaneous changes in the load profile and ambient temperature and predict the instantaneous hotspot temperature values in the transformer under dynamic load. Then, this thermal model was used to explore the capability of the studied vegetable oil in the cooling of transformers compared with conventional transformer oil. The realistic ambient temperature and loading profile, as well as thermal properties of oils and characteristics of a transformer, were applied as the model’s inputs. The aging rate of the transformer in the presence of vegetable oil was also compared with the conventional transformer oil. The results indicate a better cooling performance for the vegetable-based oil, where a hotspot temperature reduction of 3 °C was observed in comparison to the petroleum-based oil. Also, the model predicts a significantly longer life for the insulating system of the transformer when the proposed vegetable-based oil is employed. The results of this research suggest a sustainable way of reusing the waste of a renewable resource as an alternative insulating liquid for the cooling of high heat flux electric/electronic devices.

scholarly journals THE DEGREE OF POLYMERIZATION OF POWER TRANSFORMERS’ PAPER INSULATION

2019 ◽  
Vol 20 (9-10) ◽  
pp. 34-38 ◽  
Author(s):  
V. K. Kozlov ◽  
A. Kh. Sabitov
Keyword(s):  
Aging Time ◽  
Thermal Aging ◽  
Manufacturing Process ◽  
Degree Of Polymerization ◽  
Power Transformers ◽  
Aging Rate ◽  
Slowing Down ◽  
Starting Time ◽  
Exponential Decrease ◽  
Paper Insulation

The paper presents the results of research and analysis of literature data on the paper insulation's thermal aging. An exponential decrease in the degree of polymerization of paper insulation from the aging time is established, at the starting time of transformers’ operation the aging rate of paper insulation is maximal and after that its slowing down. It was found out that the degree of polymerization at the starting time of the transformer's operation can be in the range of 900 units, this is due to its drying during the manufacturing process.

An Innovative Solution for Type Testing of Power Transformers

2019 ◽  
Vol 20 (1) ◽  
Author(s):  
Manohar Singh ◽  
Vishnuvarddhan Telukanta ◽  
K S Meera
Keyword(s):  
Power Transformer ◽  
Short Circuit ◽  
Operating Conditions ◽  
Power Transformers ◽  
Test Facility ◽  
Online Testing ◽  
Testing Laboratory ◽  
Power Testing ◽  
Grid Operation ◽  
The Impact

Abstract Type tests are essential to assess the short circuit withstand capabilities of transformer windings. The mechanical durability of power equipment are checked against the mechanical forces developed during making/breaking short circuit operations. These type tests are generally carried out in indoor transformer test laboratories. Testing of Power Transformer for size more than 200 MVA in 765/400 kV voltage class in an indoor laboratory is not economically feasible. Now a days, power transformer manufacturers are fabricating single phase auto- power transformers of size up to 630 megawatt volt ampere (MVA) rating. Type testing of these transformers in indoor laboratories is not feasible. In view of this, strong short circuit fault feeding capabilities of the national grids can be utilized for type testing of these power transformers in an online manner. However, this may affect the grid operation/control during weak grid operating conditions. Recently, National High Power Testing Laboratory is established for testing of power transformer upto of 630 MVA. This is a unique online transformer test facility for testing of 765/400/220/132 kV class power transformers. An offline simulation has been carried out in this article, to assess the impact of online type testing on the Indian National grid. In this article, an online testing scheme has been presented which enables the national grid operator to analysis the prevailing grid condition & subsequently to decide the safe rating of the power transformer for online testing. The simulated results are cross checked with field results and it is found that simulated results are close to actual field results. The concurrence of simulated and field results helped in successfully commissioning of the testing laboratory.

Otkrivanje i analiza signala parcijalnih pražnjenja u energetskom transformatoru UHF metodom

2020 ◽  
Vol 22 (1-2) ◽  
pp. 96-101
Author(s):  
Đorđe Dukanac ◽  
Keyword(s):  
Detailed Analysis ◽  
Background Noise ◽  
Power Transformer ◽  
Partial Discharge ◽  
Spectral Composition ◽  
Partial Discharges ◽  
Power Transformers ◽  
Discharge Source ◽  
Useful Components

This paper presents the practical detection of partial discharge signals using a UHF sensor mounted on a power transformer and then the detailed analysis of a signal is done. The first part of the paper describes possible partial discharge sources in power transformers, UHF method and UHF sensor. In the second part of the paper, received signal at UHF sensor is considered. In order to accurately determine the magnitude of the partial discharge signal, especially if the location of the partial discharge source is far from the location of the UHF sensor, it is necessary to separate the signal from the background noise. This is only possible at intervals between individual bursts of the observed partial discharges. The spectral composition of the received signal is considered and a method for separating the present noise from the useful components of the partial discharge signal is established. The presumable main cause of partial discharges is evaluated.

Novel field-circuit assisted FEA of 110 kV power transformer for noise control and vibration reduction

2020 ◽  
Vol 64 (1-4) ◽  
pp. 289-298
Author(s):  
Li Li ◽  
Dianhai Zhang ◽  
Zhi Wang ◽  
Yanli Zhang ◽  
Xiaopeng Fan ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Goodness Of Fit ◽  
Power Transformer ◽  
Coupling Model ◽  
Power Transformers ◽  
Accurate Calculation ◽  
Load Current ◽  
Large Power ◽  
Novel Approach ◽  
Structural Force

The vibration and noise are serious problems for large oil-immersed power transformers, which directly affect the performance and stability of transformers. The no-load current, as the excitation source, is very important for accurate calculation of vibration and noise. This paper provides a novel approach based on the new field-circuit coupling model to calculate no-load current of large power transformers. For one 110 kV large oil-immersed power transformer, the multi-physics coupling problem including magnetic field, structural force field and acoustic field under alternating magnetic field is analyzed. Following the multi-physics coupling calculation, distributions of vibration and noise are obtained. To validate feasibility and applicability of the proposed method, the actual vibration and noise of transformer are measured experimentally. Finally, the simulation results are compared with experimental ones, which show better goodness of fit.

A Solid-State On-Load Tap Changer for the Power Transformers of 10—0.4 kV Distribution Networks

Vestnik MEI ◽  
2020 ◽  
Vol 6 (6) ◽  
pp. 82-90
Author(s):  
Dmitriy I. Panfilov ◽  
◽  
Mikhail G. Astashev ◽  
Aleksandr V. Gorchakov ◽  
◽  
...  
Keyword(s):  
Solid State ◽  
Physical Model ◽  
High Speed ◽  
Power Transformer ◽  
Voltage Control ◽  
Power Transformers ◽  
Control Algorithms ◽  
Load Voltage ◽  
Tap Changer ◽  
Load Tap Changer

The specific features relating to voltage control of power transformers at distribution network transformer substations are considered. An approach to implementing high-speed on-load voltage control of serially produced 10/0.4 kV power transformers by using a solid-state on-load tap changer (SOLTC) is presented. An example of the SOLTC circuit solution on the basis of thyristor switches is given. On-load voltage control algorithms for power transformers equipped with SOLTC that ensure high reliability and high-speed operation are proposed. The SOLTC performance and the operability of the suggested voltage control algorithms were studied by simulation in the Matlab/Simulink environment and by experiments on the SOLTC physical model. The structure and peculiarities of the used simulation Matlab model are described. The SOLTC physical model design and its parameters are presented. The results obtained from the simulating the SOLTC operation on the Matlab model and from the experiments on the SOLTS physical model jointly with a power transformer under different loads and with using different control algorithms are given. An analysis of the experimental study results has shown the soundness of the adopted technical solutions. It has been demonstrated that the use of an SOLTC ensures high-speed voltage control, high efficiency and reliability of its operation, and arcless switching of the power transformer regulating taps without load voltage and current interruption. By using the SOLTC operation algorithms it is possible to perform individual phase voltage regulation in a three-phase 0.4 kV distribution network. The possibility of integrating SOLTC control and diagnostic facilities into the structure of modern digital substations based on the digital interface according to the IEC 61850 standard is noted.

The Heating System of Agricultural Facilities Using Excess Heat Power Transformers

2020 ◽  
Vol 67 (1) ◽  
pp. 42-47
Author(s):  
Anatoliy I. Sopov ◽  
Aleksandr V. Vinogradov
Keyword(s):  
System Design ◽  
Heat Supply ◽  
Cooling System ◽  
Power Transformer ◽  
Electric Heating ◽  
Heating System ◽  
Power Transformers ◽  
Large Power ◽  
Excess Heat ◽  
Power Centers

In power transformers, energy losses in the form of heat are about 2 percent of their rated power, and in transformers of large power centers reach hundreds of kilowatts. Heat is dissipated into the environment and heats the street air. Therefore, there is a need to consume this thermal energy as a source of heat supply to nearby facilities. (Research purpose) To develop methods and means of using excess heat of power transformers with improvement of their cooling system design. (Materials and methods) The authors applied following methods: analysis, synthesis, comparison, monographic, mathematical and others. They analyzed various methods for consuming excess heat from power transformers. They identified suitable heat supply sources among power transformers and potential heat consumers. The authors studied the reasons for the formation of excess heat in power transformers and found ways to conserve this heat to increase the efficiency of its selection. (Results and discussion) The authors developed an improved power transformer cooling system design to combine the functions of voltage transformation and electric heating. They conducted experiments to verify the effectiveness of decisions made. A feasibility study was carried out on the implementation of the developed system using the example of the TMG-1000/10/0.4 power transformer. (Conclusions) The authors got a new way to use the excess heat of power transformers to heat the AIC facilities. It was determined that the improved design of the power transformer and its cooling system using the developed solutions made it possible to maximize the amount of heat taken off without quality loss of voltage transformation.

scholarly journals Predicting the influence of the non-sinusoidal network mode on power transformers

2019 ◽  
Vol 114 ◽  
pp. 04005
Author(s):  
Ngo Van Cuong ◽  
Lidiia I. Kovernikova
Keyword(s):  
Service Life ◽  
Electric Power ◽  
Power Quality ◽  
Electrical Equipment ◽  
Operating Conditions ◽  
Transformer Oil ◽  
Power Transformers ◽  
Electrical Network ◽  
Electrical Networks ◽  
Current Harmonics

The parameters of electrical network modes often do not meet the requirements of Russian GOST 32144-2013 and the guidelines of Vietnam. In the actual operating conditions while there is the non-sinusoidal mode in electrical networks voltage and current harmonics are present. Harmonics result in overheating and damage of power transformers since they cause additional active power losses. Additional losses lead to the additional heat release, accelerating the process of insulating paper, transformer oil and magnetic structure deterioration consequently shortening the service life of a power transformer. In this regard there arises a need to develop certain scientific methods that would help demonstrate that low power quality, for instance could lead to a decrease in the electrical equipment service life. Currently we see a development of automated systems for continuous monitoring of power quality indices and mode parameters of electrical networks. These systems could be supplemented by characteristics calculating programs that give out a warning upon detection of the adverse influence of voltage and current harmonics on various electrical equipment of both electric power providers and electric power consumers. A software program presented in the article may be used to predict the influence of voltage and current harmonics on power transformers.

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