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 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.

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.

scholarly journals An Artificial Neural Network Developed in MATLAB-Simulink for Reconstruction a Distorted Secondary Current Waveform. Part 1

2021 ◽  
Vol 64 (6) ◽  
pp. 479-491
Author(s):  
Yu. V. Rumiantsev ◽  
F. A. Romaniuk
Keyword(s):  
Neural Networks ◽  
Signal Processing ◽  
Digital Signal Processing ◽  
Relay Protection ◽  
Digital Signal ◽  
Current Transformer ◽  
Current Waveform ◽  
Secondary Current ◽  
True Value ◽  
Protection Devices

Recently, there has been an increased interest in the use of artificial neural networks in various branches of the electric power industry including relay protection. Аrtificial neural networks are one of the fastest growing areas in artificial intelligence technology. Recently, there has been an increased interest in the use of аrtificial neural networks in the electric power engineering, including relay protection. Existing microprocessor-based relay protection devices use a traditional digital signal processing of the monitored signals which is reduced to a multiplying the values of successive samples of the monitored current and voltage signals by predetermined coefficients in order to calculate their RMS values. In this case, the calculated RMS values often do not reflect the real processes occurring in the protected electrical equipment due to, for example, current transformer saturation because of the DC component presence in the fault current. When the current transformer is saturated, its secondary current waveform has a characteristic non-periodic distorted form, which is significantly differs from its primary (true) waveform, which causes underestimation of the calculated RMS value of the secondary current compared to its true value. In its turn, this causes to a trip time delay or even to a relay protection devices operation failure. The use of аrtificial neural networks in conjunction with a traditional digital signal processing provides a different approach to the functioning of both the measuring and logical parts of the microprocessor-based relay protection devices, which significantly increases the speed and reliability of such relay protection devices in comparison with their traditional implementation. A possible application of the аrtificial neural networks for the relay protection purposes is the fault occurrence detection and its type identification, current transformer secondary current waveform distortion restoration due to its saturation up to its true value, detection the distorted and undistorted sections of the current transformer secondary current waveform during its saturation, primary power equipment abnormal operating modes detection, for example, power transformer magnetizing current inrush. The article describes in detail the stages of the practical implementation of the аrtificial neural networks in the MATLAB-Simulink environment by the example of its use to restore the distorted current transformer secondary current waveform due to saturation.

scholarly journals Range Automatic Adjusted Current Transformer Primary Winning

2021 ◽  
Vol 12 (3) ◽  
pp. 3142-3147
Author(s):  
Amirov Sultan Fayzullayevich Et.al
Keyword(s):  
Correction Factor ◽  
Driving Forces ◽  
Operating Mode ◽  
Current Transformer ◽  
Measuring Range ◽  
Secondary Current ◽  
Measuring Devices ◽  
The Difference ◽  
Protection And Control ◽  
And Control

The article discusses the issue of introducing a correction factor for protection and control devices, as the value of the secondary current in a certain range of the auto-adjustable current transformer does not correspond to the value of the secondary current in another range determined by the difference of magnetic driving forces generated by the components of the primary current. Alternatively, an algorithm has been developed to account for the measurement error in this condition in an automatic system that controls the operating mode of the current transformer. It was also found that the output data should be transmitted taking into account the correction factor in order to ensure the proper operation of the protection and measuring devices when the current transformer is switched to another measuring range in the measuring range.

Simulation Model for Assessing Operational Performance of Current Transformers

2007 ◽  
Vol 18-19 ◽  
pp. 71-77
Author(s):  
I. Sule
Keyword(s):  
Simulation Model ◽  
Current Transformer ◽  
Operational Performance ◽  
Current Transformers ◽  
Correct Operation ◽  
Operational Conditions ◽  
Secondary Current ◽  
Protection Scheme ◽  
The Core ◽  
Instrument Transformers

In determining the correct operation of relays of a protection scheme, proper representation of instrument transformers and their behavior in conditions where there can be saturation, is very critical. The main objective of this paper is to develop simulation model for assessing the operational performance of Current Transformer (CT). In order to test the validity of the developed model, three cases of CT operational conditions were considered, with data collected from Gombe, 330/132/33kV PHCN substation. The simulation results revealed various configuration performance responses that could affect relay protective schemes to different degrees. The CT responses revealed that the secondary current and voltage were distorted when the core flux linkages exceeded the set 9.2 pu saturation limit. It is concluded that the model developed for the CT of interest yield satisfactory results.

Compensation of nonlinearities in a current transformer for the reconstruction of the primary current

2001 ◽  
Vol 9 (4) ◽  
pp. 565-573 ◽  
Author(s):  
S. Bittanti ◽  
F.A. Cuzzola ◽  
F. Lorito ◽  
G. Poncia
Keyword(s):  
Current Transformer ◽  
Primary Current ◽  
A Current

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 A Novel Methodology to Sense CT Saturation Using Numerical Protection Relays

2020 ◽  
Vol 5 (6) ◽  
Author(s):  
S.S. Raut ◽  
S.S. Hadpe
Keyword(s):  
Power System ◽  
Electronic Device ◽  
Secondary Current ◽  
Protection Relay ◽  
Important Input ◽  
Intelligent Electronic Device ◽  
Protection Devices ◽  
System Designs ◽  
Maximum Reliability ◽  
Primary Current

The necessity for dependability and safety in power system is rising at an alarming rate as the power system designs are getting more & more complex. In order to ensure maximum reliability, the numerical protection relays must receive accurate measurements. One of the most important input measurements desired by the relay is current. Nevertheless, the current measurements expected from current transformers (CTs) can be inaccurate due to occurrence of a phenomenon called as CT saturation. CT saturation causes distortion in the secondary current, which is not linearly proportional to the primary current, leading to mal-operation of protection devices. Therefore it becomes extremely vital that the numerical protection relay, also known as intelligent electronic device (IED) senses the CT saturation condition and blocks its operation so as to avoid mal-operation of the IED which may lead to supply interruption, further resulting in production losses and undesirable switching of the sensitive equipments affecting system reliability and customer satisfaction. This paper includes a review of the background about CTs & proposes a novel methodology to exclusively sense the CT saturation using the numerical protection relays reliably and cost effectively.

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