One of the cornerstones of a reliable transmission and distribution (T&D) grid operation is fully functional components that can operate robustly and with a low outage rate under all specified operating conditions. Dependable maintenance strategies are thus indispensable and are applied by grid operators around the world. One of the present key challenges in many countries with a widely developed T&D grid system is aging components that reach their anticipated end of life. Asset management faces the question of whether the lifetime of components could be prolonged and the replacement could be delayed. For this, the health of the components needs to be assessed and is ideally continuously monitored. In addition to this, the currently ongoing transition of the entire energy system leads to a change and increase of stress on the T&D equipment. The integration of new renewable energy sources on all voltage levels leads to bidirectional power flows and increased variability. The higher demand for electric power not only increases power-flow levels on average, but also in particular, peak flows. The result of this changed and increased stress on the equipment is an accelerated aging component and the need for maintenance strategies to be adopted for this new situation.

Voltage–current characteristics of free burning arcs in SF6 and air have been known for decades. As the demand for an SF6-free solution is increasing, there is an accompanying need to determine arc parameters in the alternative gases. An unblown arc experiment has been established to determine the voltage–current characteristics of SF6 alternative gases, which have not yet been thoroughly studied. In this experiment, free burning arc measurements were performed in a number of gases under consideration of SF6 alternatives, including CO2 and mixtures of CO2/O2 with and without C4F7N or C5F10O additives at the concentrations of up to 10 %. Measurements were also performed in air and SF6 for comparison. Arc voltage was measured in each gas at pressures ranging from 1- to 5-bar absolute, and electrode separations ranging from 20 to $95 \mathrm {~mm}$ . Voltage–current characteristic measurements for air and SF6 show good agreement with previously published results. A linear relationship of the arc voltage to the arc length is shown as well as the fourth root dependence of the arc voltage on the gas pressure. It was shown that neither the O2 nor the fluorinated additives to CO2 have any significant influence on the voltage–current characteristic. The minimum arc voltage in all measured gases was slightly higher than in SF6, but the arc in SF6 was the least stable and had the highest elongations resulting in high-voltage peaks. The arc voltage in air had a similar minimum value to the CO2-based gases, but the arc was much more stable, resulting in lower effective voltage, especially at low currents.

Circuit breakers (CBs) play an important role in modern society because they make the power transmission and distribution systems reliable and resilient. Therefore, it is important to maintain their reliability and to monitor their operation. A key to ensure a reliable operation of CBs is to monitor their condition. In this work, we performed an accelerated life testing for mechanical failures of a vacuum circuit breaker (VCB) by performing close-open operations continuously until failure. We recorded data for each operation and made the collected run-to-failure dataset publicly available. In our experiments, the VCB operated more than 26000 close-open operations without current load with the time span of five months. The run-to-failure long-term monitoring enables us to monitor the evolution of the VCB condition and the degradation over time. To monitor CB condition, closing time is one of the indicators, which is usually measured when the CB is taken out of operation and is completely disconnected from the network. We propose an algorithm that enables to infer the same information on the closing time from a non-intrusive sensor. By utilizing the short-time energy (STE) of the vibration signal, it is possible to identify the key moments when specific events happen including the time when the latch starts to move, and the closing time. The effectiveness of the proposed algorithm is evaluated on the VCB dataset and is also compared to the binary segmentation (BS) change point detection algorithm. This research highlights the potential for continuous online condition monitoring, which is the basis for applying future predictive maintenance strategies.

Abstract In recent years, significant achievements have been made with respect to the development of SF6-free gas insulated substations (GIS). In parallel, the interest in installing SF6-free GIS by utilities increased steadily and tenders for new substations or upgrades, which regularly also include alternative technologies. The excellent performance of SF6 was unequivocally accepted by all vendors and users so that the community became used to single technology solutions. This is no longer the case with alternative gas mixtures, and multiple technological solutions are available. However, from the present body of literature it is not possible to make a full and comparative evaluation of different alternative gas switchgear, i.e. circuit-breakers and disconnectors. Thus, the High-Voltage Laboratory of ETH Zürich started investigations and measurements of basic experiments that allow an unbiased comparison of properties of alternative gas mixtures relevant for switching. The two main purposes of these investigations are to define a set of measurements that allow an estimation and comparison of switching performance with different gas mixtures, independent of a specific interruption nozzle geometry, drive system, electrostatic design, and other design specific features, and to perform (some of) these measurements comparing pure SF6, with air, pure CO2, CO2/O2 mixture, and further specific gas mixtures that are currently proposed by manufacturers for SF6 replacement. The basic analysis behind the definition of measurements will be given in detail and the design principles of the chosen test devices and the derived test currents and diagnostics will be introduced. Test results themselves will not be given, rather they will be the subject of separate future publications.

Modeling of pressure rise in SF6 GIS (Gas Insulated Switchgear) due to internal arc faults is a complex and challenging task, due to a large number of highly variable factors, which influence the whole process. This is especially the case in GIS with high rated short circuit currents, where the effects, such as material evaporation and erratic arc behavior, and consequently the pressure build-up rate, are much more pronounced. These severe conditions ultimately determine the design limits and must therefore be carefully investigated. The enhanced internal arc simulation model, presented in this paper, considers the impact of evaporation of different materials on gas properties and the pressure rise, as well as the dependence of released arc energy, thermal transfer and evaporation intensity on the state of gas. The experimental set-up and the test configuration, used to validate the calculation results, are evaluated and discussed. An evident finding, which is supported by measurements, is that the implemented improvements of the basic simulation model (introduced in the Technical Brochure 602 by the CIGRÉ working group A3.24) increase the prediction accuracy of GIS withstand performance during internal arc faults.

Nowadays, high voltage circuit breaker (CB) simulations are mostly based on Computational Fluid Dynamics (CFD) models. Such simulations require significant computer resources. An alternative approach is to use enthalpy flow models, which do not use space discretization of the interrupter unit chambers and valves. Gas flow is calculated based on state of gas in adjacent chambers and valve settings. However, the valve shape has significant influence on the effective flow cross section between chambers. Therefore, in order to ensure correct simulation results, it is necessary to determine the correct values of discharge coefficients for all valves in the interrupter unit of a circuit breaker. In this paper, the discharge coefficients were determined by combining a series of CFD and enthalpy flow simulations for each valve in the interrupter unit. After that, discharge coefficients are used as input for further simulations based on the enthalpy flow model. This way, benefits from both models are combined: more precise gas flow calculation and faster simulations. The proposed novel approach is validated in a high-power laboratory by pressure measurements on a 420 kV 63 kA self-blast circuit breaker.

Abstract This paper presents the design and development of a distributed measurement system for measuring pressure in high voltage circuit breakers (HV CB) and other switching apparatuses, during no-load operations. Instead of using traditional pressure transducers which require significant installation space, additional data acquisition cards and often demand for complex wiring, an in-house solution of pressure measurement is proposed. The system consists of miniature sensors, accompanied with a suitable amplifier, microcontroller unit and communication module, which may be distributed inside the interrupter unit in convenient locations. Due to the fact that the measurement values are transmitted digitally, measurement noise is significantly reduced while the wiring of the system is additionally simplified. The proposed measurement system is tested using two different interrupters (HV CB and a load break switch). The experimental results have demonstrated that the developed system is applicable, accurate, cost-effective, flexible and simple to use.

The self-blast type circuit breaker has been developed to reduce mechanical operation energy by building up the pressure of arc extinguishing gas flow from the heat of the arc itself. Unlike a puffer type, breaking performance for self-blast type are influenced and sensitive by various factors inside interrupter parts, such as the nozzle structure, chamber shape as well as amplitude of short circuit current. These days, particularly, it has been difficult to secure a low current breaking performance as the circuit breaker has been compacted. The currents for breaking test duties belong to from 10% to 30% of the rated breaking current in accordance with IEC standard. Although the arc energy for interruption is lower than the rated breaking current test duties, the breaking performance could be lower than the tests because the transient recovery voltage (TRV) after the current zero is relatively high. The capability of interruption is related to dielectric recovery after the arc quenching. Therefore, a complex analytical method is needed to secure the breaking performance for the current and to improve the performance by using the limited gas flow inside the interrupter parts. In this paper, it described the techniques to verify breaking performance such as hot gas flow analysis and dielectric analysis. And it has studied a method for improving the performance with various design parameters using computational fluid dynamics (CFD) programs and high power laboratory test. Finally, this paper shows us the improvement of dielectric recovery performance for the self-blast type circuit breaker.

Recently, the self-blast principle of extinguishing the arc by the blast pressure which is generated by the arc itself has been widely applied to the high voltage circuit breaker. In the self-blast principle, the pressure relief valve fitted on the piston is opened to release excessive pressure in the compression volume during high current interruption. The design of the pressure relief valve operation is important for the performance of self-blast interrupter. Practically, the pressure relief valve is actuated by spring force and designed to open when the overpressure becomes greater than the designated operating pressure difference. In this paper, the actual pressure measurement result of the compression volume to understand the movement of the pressure relief valve are presented. The analytic model which describes the movement of the pressure relief valve are proposed, and the effects of different pressure relief valve models are analyzed by gas flow simulation tools.

Superior characteristics of SF6 gas have enabled its successful use as the interruption media in high voltage circuit breakers. Unique combination of physical properties considers high dielectric strength, high thermal interruption capability and high heat transfer performance. However, having in mind its high global warming potential (GWP), long term use of SF6 gas in the future should be called into question. Considering that CO2 has much lower GWP than the SF6, it represents a promising alternative, but still with known inferior breaking performance. Therefore, careful investigation of the CO2 gas behavior should be obtained. In the present work, pressure rise in a high voltage circuit breaker during no-load operation has been simulated and measured for SF6 and CO2 gas, followed with the results comparison. For simulation of high voltage circuit breakers operation, computer program HV CB Simulation, which takes into consideration interaction between the interrupting unit and the driving mechanism is used. Thermodynamic properties of gases are calculated using highly accurate equations of state explicit in Helmholtz free energy.

Special attention needs to be given to the processes that occur in alternating current arcs at the instant when the current naturally passes through a zero. The short interval of time around current zero, named the "interaction period" [1], is of crucial importance for arc-quenching, when it is decided whether the interruption will be definite or whether arc reignition will occur. As a matter of fact, regardless of the SF6 circuit breaker working principle, its rated voltage and history of the short circuit current interruption process, there is a critical value of arc extinction voltage peak which must be reached to make a successful interruption possible [2]. The arc extinction voltage peak can be increased by elongating the arc (in other words by increasing the distance between arcing contacts) and/or by increasing the pressure of SF6 gas inside the thermal chamber around current zero instant. This means that it is possible to find a critical value of distance between arcing contacts and a critical value of SF6 gas pressure inside the thermal chamber at current zero instant as criteria for successful short circuit current interruption. Based on the results of type tests in high power laboratory (including current zero measurement - CZM) and the calculation results of the software HV CB Simulation, these criteria for short circuit current interruption are successfully established for a real SF6 circuit breaker 245 kV 40/50 kA.

High voltage SF6 circuit breaker simulations based on an integral-physical enthalpy flow arc model are very powerful tool in designing and optimization of high voltage SF6 circuit breakers. This is especially important in case when full correlation between the electric arc, interrupter unit and operating mechanism parameters is needed. This paper presents computer simulations of an improved operating mechanism proven on a 123/145kV 31.5/40 kA GIS circuit breaker and verified using experimentally obtained data. The optimum value of the opening energy for rated short-circuit current interruption of the analyzed circuit breaker is estimated by using an improved operating mechanism model. In addition, several analyses have been made in order to investigate how some interrupter parameters affect the contact travel and breaking performance.

The interruption of capacitive currents is a very common switching case, unlike the breaking of short-circuit currents. The current involved is quite small and therefore easy to interrupt. However, a recovery voltage higher than 2 per unit appears across the contacts half a cycle after current zero. This circumstance inevitably increases the risk of restrikes, which may have rather undesirable effects, such as voltage escalation. Combined electric field and flow field simulations are widely used as a tool for evaluation of the dielectric performance of high voltage SF6 circuit breakers in these conditions. The computational fluid dynamics (CFD) simulation starts from the completely closed contact positions and, therefore, it takes CPU time of several hours running a workstation. In this paper, in order to shorten the calculation time to several minutes, a new numerical method for calculating the coupled fields has been developed. The new method uses simulation software for HV SF6 circuit breakers based on an integral-physical enthalpy flow arc model to obtain boundary conditions for CFD simulation. This way, a higher precision CFD simulation combined with electric field calculations can start at any given moment during recovery voltage after the current reaches zero and cover only a short interval of time proximate to an increased risk of restrikes. The new approach additionally provides a full correlation between all design parameters of the circuit breaker (including its operating mechanism) and estimated breakdown voltage during the interruption of capacitive currents.