Damásio Fernandes

An Approach for Controlled Reclosing of Shunt-Compensated Transmission Lines

An approach for controlled reclosing of transmission lines with shunt reactive compensation is proposed here to reduce switching surge overvoltages. It consists on applying Karrenbauers transformation as a matrix operator for the analysis of voltage signals required to control switching operations. The procedure also determines the arc extinction time for single and double-phase to ground faults which may avoid unsuccessful reclosing. A device to control the line reclosing was implemented and evaluated through real time simulations. An offline version was implemented for parametric and sensitivity analysis through the EMTP using actual parameters from the Brazilian Power System Grid. Several field oscillographic data, obtained from Brazilian power transmission lines with different transposition schemes were used to validate the proposed approach and the results attest its efficiency.

Transients detection in EHV transmission lines using park's transformation

Among various algorithms used to diagnose electrical disturbances, the transient detection is considered one of the most important functions. The objective of this paper is to present the Parks transformation (Tdq0) as a simple and efficient tool to detect transients in EHV transmission lines. The evaluation of such technique is performed with actual records from a Brazilian power system utility. The results reveal that the Tdq0 can detect accurately the transient occurrence and, thus, may be used to give support to various protective applications based on the detection of travelling waves.

A transient based approach to diagnose high impedance faults on smart distribution networks

This paper presents a transient based approach to diagnose high impedance faults (HIFs) on smart distribution grids. The algorithm does not require the knowledge of the feeder parameters and uses the discrete wavelet transform (DWT) to monitor fault-induced transients at strategic points of the power system, taking advantages of available Smart Grid communication channels. It allows the HIF detection and then the identification of the area in which the fault occurred. The proposed methodology is evaluated through Electromagnetic Transients Program (EMTP) simulations of HIFs in a 13.8 kV system, which was modeled using actual data of a Brazilian distribution network. Obtained results show that the method is able to detect HIFs practically at the disturbance inception as well as to provide a great reduction of the fault search field using a small computational burden.

Device to limit Transient Recovery Voltage

This paper summarizes the main results about design and evaluation of a device to reduce Transient Recovery Voltage (TRV) magnitude in medium voltage switching equipments. Zinc Oxide (ZnO) devices are modeled in an Electromagnetic Transients Program (EMTP), being applied as an alternative to limit TRV peaks in circuit breakers and reclosers of 15 kV and 72.5 kV voltage class. The assessment of device effectiveness in elimination of three-phase ungrounded and kilometric faults is performed with the purpose of providing information for testing and future deployment. Laboratory conditions are reproduced digitally describing the absorved energy by the device as a function of fault current and TRV frequency. The most severe cases allow the use of ZnO varistors commercially available, giving feasibility to achieve limiter devices. Results obtained in studies presented good agreement, showing that operations preliminarily qualified as unsafe can become permissive. Financial support usually used to replace equipment by another with higher voltage class can be reduced.

Tuning CCVT Frequency Response Data for Improvement of Numerical Distance Protection

A new method to numerically estimate the primary voltage waveform of coupling capacitor voltage transformers is presented. The outcome is a simple digital filter suitable for the frequency range from 10 to 60 Hz, enabling us to recover the transformer primary voltage waveform from its secondary voltage waveform. Unlike the techniques reported in the literature, the method does not depend directly on the transformer topology nor on the operational characteristics of the protected system, once only the coupling capacitor voltage transformer frequency response is required as input. The evaluation of the technique is performed through digital simulations using the Alternative Transients Program and transmission-line data from the Brazilian National Power System Grid. Frequency- and time-domain analysis of two coupling capacitor voltage transformers with different topologies and voltage levels are presented. It is shown that the proposed method is effective for the dynamic correction of low-frequency disturbances that may improve the speed, reliability, and security of the numerical distance relay.

A TDQ-based fault detector for digital power system relaying

In this paper, a fault detector (FD) based on Parks transformation (TDQ) for digital power system relaying application is presented. It detects faults by identifying decaying DC components and phase unbalance in current signals and, therefore, it does not require high sampling rates. To improve the FD reliability, a self-adaptive threshold is used, what overcomes the need of manual calibrations and minimizes problems due to electrical noises. The TDQ-based FD performance was compared against those of four fault detection algorithms available in the literature. In order to do so, Electromagnetic Transients Program (EMTP) simulations of faults in a 230 kV power system were carried out, through which the influence of the fault features and signal-to-noise ratio (SNR) was analyzed. The obtained results indicate that the TDQ-based FD is reliable, robust to noises and able to detect faults within a very few samples after its inception.

An approach for controlled reclosing of shunt compensated transmission lines

An approach for controlled reclosing of transmission lines with shunt reactive compensation is proposed here to reduce switching surge overvoltages. It consists of applying Karrenbauers transformation as a matrix operator for the analysis of voltage signals required to control switching operations. The procedure also determines the arc extinction time for single and double-phase-to-ground faults which may avoid unsuccessful reclosing. A device to control the line reclosing was implemented and evaluated through real-time simulations. An offline version was implemented for parametric and sensitivity analysis through the Electromagnetic Transients Program using actual parameters from the Brazilian Power System Grid. Several field oscillographic data, obtained from Brazilian power transmission lines with different transposition schemes, were used to validate the proposed approach, and the results attest its efficiency.

Design and performance of a ZnO device to reduce transient Recovery Voltage peaks

With the continued growth of power systems, it is possible that Transient Recovery Voltage (TRV) requirements lead circuit breakers to failure. In the medium voltage networks, studies have been made to evaluate the design and performance of a device which can reduce TRV peaks. The basic cell and its structure are presented and modeled in an Electromagnetic Transients Program (EMTP). The device is composed by Zinc Oxide (ZnO) varistors and its non linear characteristic allows reducing TRV magnitude when used across the breakers during interruption of three-phase ungrounded and kilometric faults. Data from the Northeast Brazilian Power System Grid of ENERGISA are used in the case studies. Simulations are carried out with ATP (Alternative Transients Program). Important aspects of planning are addressed to ensure a correct TRV diagnosis, which may come up with saving investments that would be used to replace circuit breakers or reclosers by others equipments with higher voltage class.

Chaveamento controlado de linhas de transmissão: uma abordagem em tempo real via RTDS

The goal of this work is to present a method for controlled switching of transmission line circuit-breakers and to develop a device to control the closing of its contacts. The switching strategy consists on finding a suitable circuit breaker making instant and it is based on a very simple zero crossing algorithm. For the first time, the method is evaluated in real time using a RTDSTM (Real Time Digital Simulator) and its implementation is accomplished in two ways: first, it is used the CBuilder tool of the RTDSTM and second, a DSP (Digital Signal Processor) is used as a control device. Data from the CHESF power system are used to produce case studies. Different line switching events are analyzed: closing and re-closing of shunt compensated lines taking into account trapped charge effects. The performance of the proposed method is compared to the pre-insertion resistors method. The simulations attest the efficiency of the controlled switching, which is economically more attractive.