System Switching Operations Research Articles

Design and Application of Multiple Adaptability Evaluation Algorithms Based on UHVDC Digital Simulation Operating System

The digitally simulated UHVDC system provides an all-round, full-process, and full-scenario high-fidelity training and teaching platform for the switching operation of the UHVDC system, which can fully meet the training requirements of the operation and maintenance personnel of the converter station. In order to solve the problem of inaccurate evaluation due to the existence of multiple operation procedures for an operation target, an improved digital simulation system based on multiple adaptive evaluation algorithms was designed: the teacher uses a modular combination method to generate a standard operating procedure as the main line, and then uses the trainee’s simulated operating procedure as a supplement to jointly form a standard answer to adapt to the different operating procedures of the same operating task for the trainees. Based on this system, it can solve the problem of inaccurate evaluation caused by millions of answers in the simulation operation evaluation process. It provides fast, efficient and accurate evaluation results for the digital simulated UHVDC system switching operation procedure.

Performance evaluation of online transformer internal fault detection based on transient overvoltage signals

Winding deformation is a critical power transformer issue that needs to be detected as soon as it emerges due to its progressive nature and severe consequences it may lead to. Frequency response analysis (FRA) is the only reliable technique currently used to detect such deformation. However, the technique is conducted offline that may cause interruption to the electricity grid when taking an operating transformer out of service for testing. Moreover, as the current FRA technique is only conducted on suspected units, a mechanical fault may emerge and progress before the utility becomes aware of. To overcome these limitations, this paper presents a practical feasibility study to detect transformer winding deformations online. The technique relies on utilizing transient overvoltage signals that a transformer is subjected to during its normal operation as a natural variable frequency excitation source. The feasibility of utilizing various transient overvoltage signals as excitation source for transformer FRA signature measurement is firstly investigated and optimum signal parameters are recommended based on signal voltage and energy spectrum analyses. Secondly, the proposed technique is verified through simulation analysis by comparing the transformer frequency response signatures when transient overvoltage and conventional sweep frequency voltage are used as excitation sources. Also, experimental testing is conducted to assess the feasibility of the proposed technique to identify various winding deformations such as radial buckling, telescoping and short circuit turns. Custom-made capacitive voltage divider is developed to accurately detect the response of transient overvoltage signals generated due to environmental conditions or power system switching operations. The proposed technique along with the developed capacitive voltage divider is implemented on a 3-phase Wye-Delta, 50 Hz, 31.5 MVA, 110/10.5 kV power transformer to measure the frequency response signatures of the high voltage winding.

An investigation to identify possible sources of electromagnetic field transients responsible for exposures reported in recent epidemiological studies

The possible link between occupational exposure to high-frequency short-duration electromagnetic field transients and the health of utility workers has been discussed in two epidemiological studies. Questions have been raised, however, on the sources responsible for the exposures reported in these studies. A thorough investigation has therefore been carried out, in the laboratory as well as in the utility work environment. The results indicate that the instrument used in these epidemiological studies is typically responding to the use of hand-held walkie-talkies and mobile radio-communication devices rather than power system switching operations.

Status of Evaluating the Fatigue of Large Steam Turbine-Generators Caused by Electrical Disturbances

The torsional fatigue impact of different and successive electrical transients on the shafts of nearby turbine-generators is explained and quantitatively compared for various fault conditions and system switching operations. The basis for evaluating fatigue is explained and the many contributory factors are discussed. Results of measurements of the damping of shaft torsional oscillations are presented. The operating principle of the newly developed Torsional Stress Analyzer is described. The necessity for close cooperation between operating utilities and turbine-generator manufacturers in obtaining more data on the behavior of large machine shafts in response to electrical disturbances is emphasized.

Torsional Fatigue of Turbine-Generator Shafts Caused by Different Electrical System Faults and Switching Operations

The torsional stresses that occur in large steam turbine- generator shafts due to both planned and unplanned system switching operations are discussed. These operations include routine line switching, reclosing line-to-ground faults by either triple-pole or single-pole breaker operation, reclosing line-to-line and three-phase faults, malsynchronization and load rejection. The calculation of cumulative fatigue of individual turbine-generator shafts from computer-plotted torsional swing traces is explained. The benefits of single-pole breaker operation and of dividing the output of large generators between different electrical systems are briefly mentioned.

Switching Surges on Northern States Power Company's 345-kV Circuits

This paper reports the results of field tests conducted on the Northern States Power Company's 345-kV transmission system which investigated the effects of various system switching operations on transient overvoltages. Following the field tests a transient network analyzer was used to duplicate the field tests and then explore the maximum switching transients which system parameters could produce.