Western boundary currents (WBC) influence the global ocean circulation and climate, whereas it locally reaches out differently the continental margins relief. This study analyses the response of WBC over their interactions with the corn of South America Margin. Particularly, the North and East sectors of Rio Grande do Norte (RN) on northeastern Brazil are investigated based upon bathymetry, in situ currents measurements, and simulations of oceanic currents using the CROCO model. The RN margin provides a critical pathway to the WBC along the East and North sectors, which are narrow and retracted shelves (up to 40 km offshore) with steep upper continental slopes (1:11). These sectors are separated by the shallower topography of the Touros High which extends 80 km offshore. The results reveal that the interactions of the Northern Brazilian Undercurrent (NBUC) with the RN northern margin physiography produces a recirculating current region forced by current shear. Eddies and meanders are explicit in February and August, with meander predominance in the latter month because of the increasing of wind intensity eastward. The accelerated core position of NBUC (> 1.0 m.s1) corresponds to the upper slope region of Touros High on both months, and confirms the constrain effect of the margin on the NBUC. The change of margin direction from the N-S to E-W leads to the decreasing of current velocity (~0.1m.s1) near the northern continental slope. This contrast produces an abrupt variation in the shear velocities forming vortices and meanders. Thus, the physiography of the Touros High, the margin directions, and the intensity of the winds control these features development on a regional scale. These oceanic events near the shelf slope affect the sedimentary and ecological system on Brazilian Equatorial continental shelves.

/pdf/dissertacao-de-mestrado-1dpvwmdg4g.pdf

Dissertação de Mestrado

The hysteresis loop of the core material in a test current transformer is simulated using the Jiles-Atherton theory. Comparisons are made between recorded and simulated waveforms and it is found necessary to replace the modified Langevin function used by Jiles and Atherton. Using an alternative function described in the paper, good agreement is achieved between test and simulated waveforms.

A current transformer model based on the Jiles-Atherton theory of ferromagnetic hysteresis

This paper reviews a number of mathematical models used to represent the nonlinear behavior of the magnetic core of in- strument transformers. Models of instrument transformers using these core representations are presented. The transient response of the instrument transformer is compared to actual test results recorded in the laboratory. The paper provides practical guidelines as to which of the physical elements of instrument transformers are important to model during transient studies and which elements could be ignored without sacrificing the accuracy of the simulation results. The electromagnetic transients program (EMTP) data files used to generate the models are also provided in the appendix to help new EMTP users model instrument transformers for evalua- tion of high-speed protective relaying systems.

Mathematical Models for Current, Voltage, and Coupling Capacitor Voltage Transformers Working Group C-5 of the Systems Protection Subcommittee of the IEEE Power System Relaying Committee,

This paper reviews a number of mathematical models used to represent the nonlinear behavior of the magnetic core of instrument transformers. Models of instrument transformers using these core representations are presented. The transient response of the instrument transformer is compared to actual test results recorded in the laboratory. The paper provides practical guidelines as to which of the physical elements of instrument transformers are important to model during transient studies and which elements could be ignored without sacrificing the accuracy of the simulation results. The electromagnetic transients program (EMTP) data files used to generate the models are also provided in the appendix to help new EMTP users model instrument transformers for evaluation of high-speed protective relaying systems.

http://smartgridcenter.tamu.edu/resume/pdf/per/Mathematical%20models%20for%20current,%20voltage,%20and%20coupling%20capacitor%20voltage%20transformers.pdf

Mathematical models for current, voltage, and coupling capacitor voltage transformers

Earlier work at Texas A&M University led to the development of transmission line fault location algorithms that were based on synchronized sampling of the voltage and current data from the two ends of the line. The line models used in the algorithms were based on lumped parameter models for electrically short lines, or lossless distributed parameter models for electrically long lines. In this paper, the lossless line model is modified to account for the series losses in the line. The line model equations are then solved in the time domain to accurately locate the fault. Testing of the modified algorithm is performed on a power system belonging to the Western Area Power Administration. Extensive EMTP based simulations are used to generate data that are supplied as inputs to the fault location algorithm. To make the testing as realistic as possible, detailed models of instrument transformers are used in the simulation of the various fault cases.

/pdf/fault-location-using-the-distributed-parameter-transmission-3o1g3uivh2.pdf

Fault location using the distributed parameter transmission line model

This paper describes an EPRI study of current transformer (CT) digital models intended for protective relay transient performance analysis. Experimental evaluation of CT models implemented using the Electromagnetic Transient Program (EMTP) was carried out. Two relaying CTs with 600/5 and 2000/5 ratios were used in the study. Experiments in a high power laboratory were performed to obtain transient responses. Simulation of the CT response to the same transient events was set up using three different CT models. They were implemented based on the saturable transformer and nonlinear reactor models available in an EMTP. Comparison of laboratory and simulation results indicates that CT models developed based on the EMTP program give satisfactory results for most of the cases. It has also been discovered that in some instances EMTP models need further improvements. >

Experimental evaluation of EMTP-based current transformer models for protective relay transient study

The authors describe the development by EPRI of digital coupling capacitor voltage transformer (CCVT) models that are intended for digital simulation of fault transients Experimental techniques for laboratory measurements of the CCVT parameters are outlined A sensitivity study was performed to identify the influence of various CCVT parameters on the transient behavior relevant for the relaying studies Digital models of three different CCVTs are given and their transient behavior is compared to the behavior of the actual transformers >

Digital models of coupling capacitor voltage transformers for protective relay transient studies

This paper reviews the past and present uses of relay models. It discusses the various types of models, what information is required to build such models and the model validation process. Examples of present and possible future use of software models are given.

/pdf/software-models-for-relays-2ugvr20koj.pdf

Software models for relays

This paper presents the results of an EPRI study on development of a new method for coupling capacitor voltage transformer (CCVT) frequency response measurements from the secondary side. The method is especially suitable for field measurements since it does not require any internal CCVT disassembly or access to its individual components. It has been verified by performing the field measurements on actual CCVTs installed in a substation. The results were compared with the results obtained by carrying out the CCVT frequency response measurements on the same type of CCVTs in a laboratory and using the method of frequency response measurement from the primary side. The proposed method is easy to use and gives accurate results. The method may be used for the EMTP-based CCVT model development and the CCVT performance analysis. >

L. Kojovic

Papers

Mathematical models for current, voltage, and coupling capacitor voltage transformers

Experimental evaluation of EMTP-based current transformer models for protective relay transient study

Digital models of coupling capacitor voltage transformers for protective relay transient studies

Software models for relays

A new method for the CCVT performance analysis using field measurements, signal processing and EMTP modeling