L. Kojovic

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

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.

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

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. >

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

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. >

Software models for relays

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.

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

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. >

DYNA-TEST simulator for relay testing. I. Design characteristics

The authors describe a new digital dynamic testing (DYNA-TEST) simulator developed for protection relay applications. This simulator is capable of producing voltage and current transients that correspond to actual fault events in the power systems. Fault transients are generated either by simulating power system faults using an electromagnetic transient program or by replaying records of fault signals captured in substations by digital fault recorders. These signals are used to test protection relays. Such an approach to relay testing represents a major improvement over steady-state testing. >

DYNA-TEST simulator for relay testing. II. Performance evaluation

For pt.I see ibid., vol.6, no.4, p.1427 (1991). Evaluation steps undertaken in the analysis of the DYNA-TEST simulator performance are described. The evaluation assumes comparison of the simulator output waveforms obtained using simulated data with the reference waveforms obtained through recording of an actual fault event. Tests are done using specific utility data. Particular attention is given to the system and instrument transformer modeling as well as to the D/A (digital-to-analog) conversion signal reconstruction subsystem characteristics. Particular reference is made to the Houston Lighting and Power (HL&P) system modeling approach. >

Discussion of "Mathematical models for current, voltage, and coupling capacitor voltage transformers" and closure

G. Swift comments on the paper by Working Group C-5 of the Systems Protection Subcommittee of the IEEE Power System Relaying Committee (see ibid., vol.15, no.1, 2000). The author points out an error in the article. The Working Group reply to the comments.