scholarly journals Simulation of the saturation process of a current transformer with a load

2021 ◽  
Vol 16 (4) ◽  
pp. 48-61
Author(s):  
Kirill K. Krutikov ◽  
◽  
Vyacheslav V. Rozhkov ◽  
Vladimir V. Fedotov ◽  
◽  
...  
Keyword(s):  
Power Plants ◽  
Short Circuit ◽  
Relay Protection ◽  
Current Transformer ◽  
Dynamic Processes ◽  
Current Transformers ◽  
Load Mode ◽  
Secondary Side ◽  
A Current

The article deals with the mathematical basis and simulation of the saturation processes of current transformers with aperiodic components of short-circuit currents. Saturation processes of current transformers can affect the correct operation of the protections. At power plants, in particular atomic ones, the number of current transformers is several hundred with different loads, lengths of supply cables and the implementation of relay protection. At the same time, the determination of the time to saturation is essential for the construction of circuits and principles of construction of relay protection systems and automation of power plants. The dynamic processes in the primary and secondary circuits of current transformers in dynamics are considered in detail. A mathematical description of the dynamic processes of a current transformer in the nominal mode and during a short circuit in its primary circuit is given. The substantiation of the expediency of using the hypothesis of a rectangular magnetization characteristic in simplified calculations of saturation processes is given. The possibility of using the characteristics of magnetization in the test protocols available in practice in the no-load mode to simulate saturation processes has been demonstrated. Simulation of current transformers for the no-load experiment and power supply of the current transformer from the secondary side, as well as during its operation under conditions of a short circuit on the primary side and a known load on the secondary side is carried out. Thus, with the help of a computer experiment, it is possible to take the current- voltage characteristics and transfer them to the model with the saturation of current transformers already in the short-circuit mode. The efficiency of dynamic simulation of current transformers is shown. The software implementation of the model is performed by means of structural simulation in the MatLab package, based on the solution of equations of matrix structures and emulation of parallel computations. It was found that with the adequacy of the model and the real current transformer with the involvement of information from the no-load mode, the determination of the magnetization time from the aperiodic current components from the model is much easier than the analysis by other existing methods. They require detailed design details of the current transformer and the magnetic properties of the steel.

Analiza algoritama za kompenzaciju zasićenja strujnog transformatora

2020 ◽  
Vol 22 (1-2) ◽  
pp. 112-118
Author(s):  
Nenad Belčević ◽  
◽  
Zoran Stojanović
Keyword(s):  
Relay Protection ◽  
Current Transformer ◽  
Main Function ◽  
Negative Consequences ◽  
Current Transformers ◽  
Secondary Current ◽  
Measuring Devices ◽  
Protection Devices ◽  
Primary Current ◽  
A Current

The main function of current transformers is to adapt the high values of the primary current to values suitable for the operation of relay protection devices, i.e. measuring devices. Under normal conditions, a current transformer transforms the current in a virtually permanent ratio, and practically without a phase shift, so the secondary current is actually a scaled value of the primary current. However, when a fault occurs in the power system, currents reach high values. As a result, the flux in the core of the current transformer can reach values above the knee of the magnetization characteristic, causing saturation of the current transformer. When saturation occurs, the secondary current is no longer a scaled value of the primary current, but is deformed. Deformation of the secondary current may cause malfunctioning of some relay protection devices. The development of digital relay protection has made it possible to perform software saturation compensation by applying certain algorithms, thus eliminating the negative consequences that saturation of the current transformer causes. In this paper, one of the possible approaches for compensation of saturation is analyzed, which is based on the application of an equivalent scheme and magnetization curve of the current transformer. Two typical approaches have been singled out, which have been analyzed and tested in more detail. Testing was performed in the MATLAB/Simulink.

scholarly journals Determination of the magnitude of short-circuit surge current for the construction of relay protection on reed switches and microprocessors

2021 ◽  
Vol 6 (5 (114)) ◽  
Author(s):  
Alexandr Neftissov ◽  
Andrii Biloshchytskyi ◽  
Olzhas Talipov ◽  
Oxana Andreyeva
Keyword(s):  
Magnetic Field ◽  
Short Circuit ◽  
Relay Protection ◽  
Main Element ◽  
Current Transformers ◽  
Transient Mode ◽  
Protection Devices ◽  
Aperiodic Component ◽  
Surge Current

A study of the functioning of reed switches under the influence of a magnetic field created by a current in a conductor in a transient mode with the presence of an aperiodic component has been carried out. A well-known method for determining current using reed switches was implemented. At the same time, it was determined that the originally formulated method did not give the required result within the limits of errors. This is most likely due to the peculiarities of the mechanism of movement of the reed switch contacts. Alternatively, the measurements were taken to take the return currents instead of the pick-up currents and the time between the return times. They are more stable. Simulation is performed, experimental determination of the value of surge current by measuring time is carried out. The main element of the created installation was the power transformer coil with low active and high inductive resistance. As part of the study, the reed switches were placed in a magnetic field with an aperiodic component, as in the transient mode. This study will show the applicability of reed switches for the construction of relay protection devices that will not need current transformers to obtain information about the primary current in the conductor. In the course of the research, it was found that the error in determining the magnitude of current was no more than 10 %. Using microprocessors, it is possible to build relay protection devices with a speed of up to 20 ms. This result makes it possible to build new devices. Since in the well-known developments, it was only said about determining the magnitude of current in a steady state. When building relay protection devices on reed switches, without using current transformers, it will be possible to build backup protections that duplicate not only the devices themselves, but also the primary measuring transformers with other sensitive elements. This will improve the reliability of the power supply.

scholarly journals The.main types of wind turbines-generators in the power supply system

2022 ◽  
Vol 23 (5) ◽  
pp. 71-85
Author(s):  
V. A. Novobritsky ◽  
D. S. Fedosov
Keyword(s):  
Second Harmonic ◽  
Short Circuit ◽  
Separation Of Variables ◽  
Harmonic Component ◽  
Relay Protection ◽  
Short Circuit Current ◽  
Current Transformer ◽  
Correct Operation ◽  
Protection Devices ◽  
Dc Component

THE PURPOSE. This paper considers the problem of relay protection functioning when the current transformer reaches the saturation mode which is provided by transient processes.METHODS. MATLAB Simulink software environment allows reproducing the method of statespace representation by using structural blocks. The model is verified by comparison the time to saturation, obtained by calculation and according to the graphical data of the model. The separation of variables method extracts and graphically displays the investigated components.RESULTS. This paper reveals that applying the requirements of IEC 61869-2:2012 standard, which determines the worst combination of series of unfavorable factors for current transformers in transient mode, can influence a serious impact on the correct operation of relay protection based on current, reactance or differential principle of action. Saturation of the current transformer can lead to both negative results: false operation of relay protection devices and their failure.CONCLUSION. According to the results of the study, it was determined that the presence of a DC component in the primary short-circuit current has the greatest effect on the protection operation. The delays in the restoration of the RMS value of the short-circuit current reached up to 0.3 seconds, which is comparable with the response time of the second protection zones for microprocessor-based relay protection devices. The DC component of the primary current and the presence of residual magnetic induction of the current transformer provides the largest content of the magnetization current, the largest angular error and also the largest content of the second harmonic component in the secondary short-circuit current.

INVESTIGATION OF THE CURRENT TRANSFORMER CONTROL SYSTEM WITH AUTOMATIC RANGE CONTROL

2021 ◽  
Vol 4 (1) ◽  
pp. 4-12
Author(s):  
Sultan Amirov ◽  
◽  
Shavkat Mukhsimov
Keyword(s):  
Control System ◽  
Control Systems ◽  
Power Supply ◽  
Power Source ◽  
Current Transformer ◽  
Measurement Range ◽  
Current Transformers ◽  
Traction Power Supply ◽  
A Current ◽  
Traction Power

The article examines the control system of a current transformer with automatic range control. All multi-limit current transformers allow measuring currents of different ranges with sufficient accuracy in the control systems of traction power supply devices. However, a common disadvantage for all of them is that if it is necessary to change the measurement range, the controlled current of the traction power supply device is disconnected from the power source, i.e. the production or technological process is forced to stop and dismantling and installation work is required. The proposed current transformer with automatic range control eliminates these disadvantages.Keywords:Current transformer, microcontroller, filter, control system, SSR relay, automatic system, harmonic

On the Problem of Selecting and Replacing Current Transformers for Relay Protection Devices

2020 ◽  
Vol 63 (6) ◽  
pp. 72-82
Author(s):  
Stanislav Kuzhekov ◽  
◽  
Andrey Degtyarev ◽  
Nikolay Doni ◽  
Aleksey Shurupov ◽  
...  
Keyword(s):  
Power Systems ◽  
High Speed ◽  
Short Circuit ◽  
Relay Protection ◽  
Electric Power Systems ◽  
Current Transformers ◽  
Magnetic Cores ◽  
Protection Devices ◽  
Short Circuits ◽  
The Stability

In connection with cases of incorrect operation of high-speed relay protection devices (RPD) in case of short circuits outside their range, the issue of replacing current transformers (CT) of class P with more ad-vanced current converters is relevant. The article shows that the decision to replace existing class P CTs with CTs with a non-magnetic gap should be made taking into account the probability of saturation of the magnetic cores of the latter in a transient short-circuit mode, as well as an increase in their dimensions compared to class P CTs. The issue of using optoelectronic current converters should be resolved after the latter are put into mass production, taking into account the difficulty of integrating the latter with the RPDs implemented using an Electromechanical base. In many cases, the correct functioning of high-speed RPDs without replacing existing CTs of class P can provide the following measures: the use of algorithms that increase the stability of the oper-ation of high-speed RPDs when the CT is saturated; taking into account in the calculations of the settings the rectangular characteristic of the CT magnetization in transient modes and the permissible deceleration of pro-tections under the condition of the dynamic stability of electric power systems; refusal to use CT connection groups (physical sum of currents, delta and star).

scholarly journals Application of unified microprocessor relay protection units in electrical machine diagnostics

2020 ◽  
Vol 21 (6) ◽  
pp. 93-100
Author(s):  
V. I. Polishchuk ◽  
M. V. Kritsky ◽  
D. M. Bannov ◽  
S. V. Malyshev
Keyword(s):  
Short Circuit ◽  
Asynchronous Motor ◽  
Sampling Rate ◽  
Relay Protection ◽  
Synchronous Generator ◽  
Digital Processing ◽  
Electrical Machine ◽  
Selective Determination ◽  
Rotor Winding

The article concentrates on the topical issue connected with the detection of defects in the rotor winding of electric machines. The experimental sampling and digital processing of electrical signals from controlled windings is in the basis. The authors conducted the research using two experimental units for asynchronous motor and synchronous generator, respectively. A distinctive feature of the proposed research stands is in solving the problems of digital processing and data analysis on the basis of the application of microprocessor relay protection unit BMRZ developed in Russia. The authors applied method of wavelet decomposition to select the detailing component. They also presented the results of experiments for the breakage in the short-circuit rotor of an asynchronous motor and proved that the microprocessor-based BMRZ device is capable of digitizing at a sampling rate that meets the requirements, and in conjunction with the data processing algorithms that carry out the selective determination of hard-to-detect defects, is applicable in the diagnosis of electrical machines.

Research of Parameters of Electric Power Systems Affecting Core Saturation of Current Transformers with a Closed Magnetic Circuit in Transitional Short Circuit Modes

2021 ◽  
Vol 64 (1) ◽  
pp. 92-100
Author(s):  
Viliya Ivanova ◽  
◽  
Igor Ivanov ◽  
Keyword(s):  
Power Systems ◽  
Electric Power ◽  
Magnetic Circuit ◽  
Short Circuit ◽  
Relay Protection ◽  
Electric Power Systems ◽  
Current Transformers ◽  
Core Saturation ◽  
Protection Devices ◽  
Closed Magnetic Circuit

The relevance of the study is due to the excess of the permissible errors of current transformers in transient short-circuit modes associated with saturation of the cores of current transformers. The latter leads to improper operation of relay protection devices, which can negatively affect the stability of electric power systems and the efficiency of industrial enterprises with a continuous technological cycle, the power failure of which leads to significant economic damage. The aim of this work is to study the parameters of electric power systems that affect the saturation of the cores of current transformers with a closed magnetic circuit in transient short-circuit modes. The object of research is electromagnetic current transformers of accuracy class 10P in electric power systems. The study was carried out using numerical methods for solving algebraic and differential equations, methods of computer modeling of electromagnetic transient processes and functional programming. As a result, the main parameters influencing the nature and intensity of electromagnetic transients in current transformers during a short circuit are noted; it is shown that in transient short-circuit modes, significant errors in the operation of current transformers associated with core saturation are possible; recommended for assessing the compliance of current transformers of accuracy classes 5P, 10P with the conditions for the correct functioning of relay protection devices in transient short-circuit modes, to calculate the time to saturation of current transformers, taking into account the real parameters of the electric power system at the place where current transformers are installed, in addition to the traditional design checking of current transformers by permissible er-rors for the steady state short circuit.

scholarly journals A simplified model of a current transformer for studying relay protection operation in transient conditions

2021 ◽  
Vol 25 (4) ◽  
pp. 450-462
Author(s):  
T. S. Mukhametgaleeva ◽  
D. S. Fedosov
Keyword(s):  
Current Transformer ◽  
Voltage Characteristic ◽  
Simplified Model ◽  
Current Voltage Characteristic ◽  
Current Transformers ◽  
Transient Conditions ◽  
Transformation Ratio ◽  
Current Voltage ◽  
Primary Current ◽  
A Current

We develop a simplified model of a current transformer based on its current-voltage characteristic. This model is applicable for studying relay protection operation in transient conditions when no high accuracy or consideration of current transformer magnet core hysteresis is required. The model was developed in MATLAB Simulink using elements of the SimPowerSystems and Simscape libraries. The model uses the transformation ratio and current-voltage characteristic obtained during operational tests of a current transformer. Calculation experiments with non-linear resistance found that a currentvoltage characteristic of voltage and current values can be used to model a current transformer, rather than instantaneous values. The following conditions were simulated: for nominal currents in current transformer windings to check the transformation ratio; for opened secondary winding; with current transformer saturation by increasing secondary loading; increasing the primary current ratio and presence of aperiodic current at the start of the transition process. It was found that the developed current transformer model allows for a correct imitation of all the above conditions. To verify the model, secondary current oscillograms were obtained using real current transformers 10 kV at known primary current, which were compared with nominal oscillograms in the model. The discrepancy between the results of calculational and real experiments was no more than 10% in amplitude values, with high-quality matching obtained for current charts in the model and real current transformers. A significant advantage of the developed model is that its setting requires no information on magnet core cross-section, power line length, steel grade, and the number of current transformer winding turns.

Sign in / Sign up

Export Citation Format

Share Document