Ratio Of Current Transformers Research Articles

The test bench for simulation impact of core saturation on the current transformer on coordination of inverse relay protection

When the measurement-type Current Transformer (CT) is used for protection schemes, this condition causes problems related to the operation of the protection relay. This performance can provide the right output to be captured by the relay when using the CT type of protection system, and measurement CT will be appropriately used as a measurement instrument. When the primary current is greater, the denser the flux flowing in the iron core, and when a certain primary current value is reached, the iron core is unable to accommodate the flux that must be flowed. As a result, the value Es is unable to rise again, so the error ratio begins to rise, and the secondary current output is distorted. This research aims to design a tool that can display the distortion that occurs in the secondary current, and this research will evaluate its impact on the characteristics of the inverse-type overcurrent relay. The research method is R&D (Research & Development) by configuring a prototype analog test table so that saturation occurs on the CT connected to the protection relay. The results of the research Simulation of protection coordination failure due to core saturation can be shown, and the design of core saturation test equipment can be demonstrated. The root cause of core failure can be traced from the disconnection time deviation that occurs at the protection relay. The design of core saturation test equipment can be implemented to display protection failures due to core saturation and show the correlation between the voltage excitation curve and relay disconnection time. Testing CT ratio 30/5 with a burden of 1.5 VA, the operating limit is 183.3% of the primary rated rating, meaning that for CT with a primary rated current of 30 amperes, testing up to 60 amperes shows the results have not occurred core saturation.

Modeling and simulation analysis of current transformer based on magnetizing current as the solution variable

PurposeThis paper aims to develop a model that reflects the current transformer (CT) core materials nonlinearity. The model enables simulation and analysis of the CT excitation current that includes the inductive magnetizing current and the resistive excitation current.Design/methodology/approachA nonlinear CT model is established with the magnetizing current as the solution variable. This model presents the form of a nonlinear differential equation and can be solved discretely using the Runge–Kutta method.FindingsBy simulating variations in the excitation current for different primary currents, loads and core materials, the results demonstrate that enhancing the permeability of the B–H curve leads to a more significant improvement in the CT ratio error at low primary currents.Originality/valueThe proposed model has three obvious advantages over the previous models with the secondary current as the solution variable: (1) The differential equation is simpler and easier to solve. Previous models contain the time differential terms of the secondary current and excitation flux or the integral term of the flux, making the iterative solution complicated. The proposed model only contains the time differential of the magnetizing current. (2) The accuracy of the excitation current obtained by the proposed model is higher. Previous models calculate the excitation current by subtracting the secondary current from the converted primary current. Because these two currents are much greater than the excitation current, the error of calculating the small excitation current by subtracting two large numbers is greatly enlarged. (3) The proposed model can calculate the distorted waveform of the excitation current and error for any form of time-domain primary current, while previous models can only obtain the effective value.

Coordination of protective relays in distribution systems considering uncertainty caused by renewables and demands based on orthogonal experiments

The operations of distribution systems are more challenging than in past decades because of the penetration of distributed generation (DG). Several serious problems may be caused by DG, such as bi-directional power flow in a distribution line, different levels of fault currents and uncertainty in power generation. This paper investigates the coordination of inverse-time overcurrent relays (OCRs) in distribution systems with uncertain distributed power generation and loads. A novel method is presented in this work, considering different scenarios along with two levels of uncertainty caused by DGs (photovoltaics and wind) and bus loads, to determine fault currents using Taguchi orthogonal experiments. Nonlinear optimization is then employed to find the optimal settings of inverse-time OCRs in distribution systems and to identify infeasible current transformer ratios. Simulation results obtained from a 9-bus system and a modified IEEE 33-bus system show that the proposed method outperforms the traditional point-estimation method (PEM). For the 33-bus system, the mean values of similarity indices based on the probability density function are obtained by the proposed method, and they are 0.979 and 0.975, which are closer to unity, for time multiplier setting (TMS) and pick-up setting (PS), respectively, than those (0.953 and 0.951 for TMS and PS, respectively) obtained by the PEM. The mean values of error indices based on the cumulative distribution function are obtained by the proposed method, and they are only 0.0007 and 0.0085 for TMS and PS, respectively, while those obtained by the PEM are 0.0011 and 0.0110 for TMS and PS, respectively.

Overcurrent and ground fault relay protection settings at tranformator-1 150kV/20kV Braga substation

The occurrence of a malfunction at the substation results in power outages and losses in the electrical energy distribution system to consumers. Many tests are carried out to see the performance of the protection system, including the parameters of the over current relay (OCR) and ground fault relay (GFR) in the electrical energy distribution system. This research aims to analyze OCR and GFR values, analyze OCR setting, drop-off, and pick-up values, and analyze OCR time characteristics using DigSilent Power Factory 15.1 software based on existing equipment specification data at the Braga substation. The results show an OCR accuracy level of around 94% on the 20 kV and 150 kV sides. Meanwhile, 92.39% on the 20 kV GFR side and 94.87% on the 150 kV side. The setting value for the pick-up current is 0.92 A on the 20 kV side of the GFR and the drop-off current is 0.85 A on the 150 kV side with a pick-up current of 0.39 A and a drop-up current of 0.37 A. Setting a value on the 20kV side is greater than on the 150 kV side due to the difference in current transformer ratio values. The simulation results show that the OCR and GFR characteristic curves on both sides meet the criteria for a protection system with good performance.

Determining alpha plane characteristics of line current differential protection in two-terminal high voltage transmission with different current transformer ratio

Determining alpha plane characteristics of line current differential protection in two-terminal high voltage transmission with different current transformer ratio

ACCURACY OPTIMIZATION OF KWH HIGH VOLTAGE CONSUMER TRANSACTIONS WITH SELECTION OF CURRENT TRANSFORMER (CT) RATIO IN ACCORDANCE WITH CONTRACTED POWER

The greater growth of electricity consumption, especially for high voltage consumers, it is important for PLN to know the effect of the current transformer (CT) error ratio in the accuracy of the kwh of electricity transactions, by researching the error ratio of CT 400/1 and 800/1 R, S, and T phase. When the contracted power of 120 MVA can be used CT class 0.2s ratio 400/1 and 800/1 ratio, when using CT class 0.2s ratio 400/1 then the kwh meter can be set according to the CT ratio that is the ratio 400/1 because CT ratio 400/1 has a negative error ratio at loads below 73.59%, and positive error ratio at loads over 73.59% up to 100% load, and` when using CT class 0.2s ratio 800/1 then the kwh meter can set a CT ratio of 800 / 0.98 because CT ratio 800/1 has a positive error ratio of 0.02% from 1% load to 100% load, so that it does not harm the customer as a positive CT ratio error tolerance . This needs to be done in order to create justice between PLN and high voltage consumers in the calculation of kwh transactions.The greater growth of electricity consumption, especially for high voltage consumers, it is important for PLN to know the effect of the current transformer (CT) error ratio in the accuracy of the kwh of electricity transactions, by researching the error ratio of CT 400/1 and 800/1 R, S, and T phase. When the contracted power of 120 MVA can be used CT class 0.2s ratio 400/1 and 800/1 ratio, when using CT class 0.2s ratio 400/1 then the kwh meter can be set according to the CT ratio that is the ratio 400/1 because CT ratio 400/1 has a negative error ratio at loads below 73.59%, and positive error ratio at loads over 73.59% up to 100% load, and` when using CT class 0.2s ratio 800/1 then the kwh meter can set a CT ratio of 800 / 0.98 because CT ratio 800/1 has a positive error ratio of 0.02% from 1% load to 100% load, so that it does not harm the customer as a positive CT ratio error tolerance . This needs to be done in order to create justice between PLN and high voltage consumers in the calculation of kwh transactions.

A Novel Approach for the Error Correction of CT in the Presence of Harmonic Distortion

Current transformers (CTs) are extensively used for the measurement of electrical energy, and hence they play a crucial role in the revenue generation for power distribution utilities. The novelty of this paper is that it presents artificial neural network (ANN) application for the ratio and phase angle error corrections of CTs in the presence of harmonic distortions. In this paper, the behaviors of silicon iron alloy and nanocrystalline alloy CTs are examined by the means of a number of experimental tests under the sinusoidal and distorted waveform conditions. The relation between the nature of CTs secondary current waveforms (CTSwf) with their metrological properties, connected burdens, and nature of load currents (linear or nonlinear) is established. The training data are obtained by the nature of CTSwf in terms of amplitude errors, time shifts, and deviations caused by different harmonic contents between input and output quantities. The ANN is trained for various operating conditions. The implementation of the error correction system and data acquisition is done using dSPACE 1104 software. The experimental results illustrate that the proposed technique can be used for error compensation in case of sinusoidal and the distorted waveform composed of fundamental and many harmonics.

Current Transformer Selection Techniques for Low-Voltage Motor Control Centers

This paper provides a clear set of procedures and equations to follow in optimal current transformer selection for low-voltage motor control centers. Methods of using protective relay settings to minimize current transformer cost and size are also shared. The selection criteria are explained from the fundamental principles of operation of a current transformer and a protective relaying device. This paper shows how the current transformer ratio, voltage knee points, and relay protection elements can be selected together simultaneously to provide a low-cost, high-performance system. This paper describes a case study in which the authors developed a simplified set of current transformer selection criteria for compact IEC low-voltage motor-control center drawers at a large oil and gas field in Central Asia.

Final report EURAMET.EM-S30 on EURAMET Project 1081: Supplementary comparison of measurements of current transformers

The supplementary comparison was carried out between CMI, Czech Republic and BIM, NCM Bulgaria in the field of current transformer ratio measurements. The current errors and phase displacement of the traveling standards, current transformers: Tettex 4720, CLA 2.2, CLA 2.2, CLA 3.2, CLB 10, I 523 were determined at 50 Hz, 5 VA burden at unity power factor at ratios: primary (4000, 2000, 1000, 500, 100, 5, 1 and 0.5) A/secondary 5 A. Both participants used their own standard measurement method.The obtained results show good agreement for all of the current ratio error measurements (except for the measurements at 2 kA) and for the current phase displacement measurements (the agreement on several measurement points is marginal). The aim of the comparison was to demonstrate the improvement and extension of the calibration and measurement capabilities (CMCs) of BIM in this working field and to support the improved CMCs in Appendix C of the CIPM Mutual Recognition Arrangement (MRA).Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by EURAMET, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

On the Use of the Ultimate Current Transformer Ratio in Design and Analysis of the Behavior of Differential Protections of Transformers

A reduced ultimate ratio is used as a generalized parameter for describing current transformers (CT). This parameter is used to formulate the requirements to CT under steady state and transient operating conditions. It is shown that the performance of differential protections under transient conditions of short circuits in the protected zone can be considerably increased by increasing the values of the reduced ultimate ratio of CT. This will also reduce the transient imbalance currents at low through currents that appear, for example, upon startup of a powerful engine.

Simple absolute method for current transformer calibration

A simple mains-frequency current transformer ratio build-up scheme has been developed which enables calibration by absolute means of ratios from 5 A:5 A to 500 A:5 A with uncertainties of 0.03 parts in 10/sup 6/ and 0.05 /spl mu/rad. The build-up is based on series-parallel interchange of primary windings of two-stage transformers with magnetically shielded second stages.

An algorithm for compensating secondary currents of current transformers

Current transformer (CT) saturation may cause power system relays to malfunction. The conventional method used to deal with the problem is overdimensioning of the transformer core so that CTs can carry up to 20 times the rated current without exceeding 10% ratio correction. However, this not only reduces the sensitivity of power system relays, but also increases the CT core size. This paper presents a technique of estimating the secondary current corresponding to the CT ratio under CT saturation. The proposed algorithm can improve the sensitivity of relays to low level internal faults, minimize the instability of relays for external faults, and might ultimately assist in reducing the dimension of the required CT core cross-section.

Development and hardware implementation of a compensating algorithm for the secondary current of current transformers

The conventional method of dealing with current-transformer (CT) saturation is overdimensioning of the core so that CTs can reproduce up to 20 times the rated current without exceeding 10% ratio correction. However, this not only reduces the sensitivity of relays, as some errors may still be present in the secondary current when a severe fault occurs, but also increases the CT size. An algorithm is described for estimating the secondary current corresponding to the CT ratio under CT saturation using the flux/current (λ/i) curve, and the results of hardware implementation of the algorithm using a digital signal processor are also presented. The main advantage of the algorithm is that it can improve the sensitivity of relays to low-level internal faults, maximise the stability of relays for external faults, and reduce the required CT-core cross-section significantly.

An adaptive scheme for digital protection of power transformers

The development of an adaptive scheme for digital differential protection of power transformers is described. The transformer status is monitored to decide if the transformer is disconnected or is in normal operating condition. When the transformer is energized, a two-state Kalman filter model monitors the transformer during normal operating conditions. The current transformer ratios and tap values are included in the algorithm to obtain an adaptive percentage differential characteristic. This adaptive scheme was tested on data obtained in the laboratory and proved to be highly accurate and fast. >

Interactive relay coordination using microcomputer graphics

A computer procedure is presented which enables the power system designer to interactively determine tap and time dial settings of overcurrent relays for the protection of industrial power systems. The user enters data about the power system, and a fault analysis is performed. Current transformer ratios, relay types, and load currents are then input to the program and the user selects tripping times or coordinating time intervals. Computer graphics techniques are then used to display the coordination curves and settings may be changed, if necessary, until the desired protection characteristics are achieved. An example of protection design for a sample industrial power system is provided to show the procedures for program use and demonstrate its capabilities.

Evaluation of the permeability of cores and the turns ratio of current transformers

1. For the calculation of permeability of cores filled with a mixture of ferromagnetic and nonmagnetic powders it is recommended to use formula (4). 2. The true transformer ratio of the toroidal current transformers both air-cored and with dust cores can be evaluated from formula (6).

The testing of current transformers

A method of testing the phase angle and ratio of current transformers using a polyphase wattmeter and phase shifter is described. Results of tests are given showing the effect, on the accuracy of a transformer, of allowing it to be run with the secondary open-circuited.

Some applications of the A.C. potentiometer

There are described certain applications of the A.C. potentiometer for which the Tinsley-Gall type is especially suitable. These include the measurement of the magnetic properties of laminated steel, values of inductance and effective resistance, the magnitude of current transformer ratio and phase angle errors, the amplification factors of audio-frequency amplifiers, and finally the use of the potentiometer for magnetic analysis.

Some Applications of the AC Potentiometer*

There are described certain applications of the ac potentiometer for which the Tinsley-Gall type is especially suitable. These include the measurement of the magnetic properties of laminated steel, values of inductance and effective resistance, the magnitude of current transformer ratio and phase angle errors, the amplification factors of audio frequency amplifiers, and finally the use of the potentiometer for magnetic analysis.

Current transformer ratio and phase error by test ring method

This method of testing may be indicated briefly as follows: A special current transformer or test ring is connected with its primary and secondary respectively in series with the primary and secondary of the current transformer under test. The number of turns in the secondary coil of the special current transformer is varied until the primary and secondary ampere turns of the special current transformer or test ring are equal to each other and show a balance. Then the ratio of turns in the special current transformer is the current ratio of the transformer under test. Of course, the primary and secondary ampere turns can never actually balance, because they are not exactly in step or opposition, but a point can be found where the vector difference between them is at right angles to one of them and this point is taken as the balance point. This actual minimum value of vector difference gives a measure of the phase difference between primary and reversed secondary amperes.