With the growing number of severe system disturbances and blackouts around the world, controlled system separation is becoming an increasingly important system integrity protection scheme (SIPS) to save the electric power system from a complete or partial disintegration. A successful controlled splitting approach should at least tackle the following two well-known and interrelated problems: 'when to split?' and 'where to split?'. Multiple previous publications consider these problems separately, and even those pursuing a combined approach propose solutions with limited applicability. In this article, we are proposing a novel PMU-based detector of loss of synchronism that utilizes generator PMU data to promptly detect rotor angle instabilities over a wide area. Moreover, we are showing how our loss of synchronism detection principle can be coupled with the known controlled splitting techniques to form an integrated defense scheme against unintentional loss of synchronism. The performance of this wide-area SIPS is demonstrated on the IEEE 39-bus test power system for various types of unstable conditions.

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This paper presents a new formulation for intentional controlled islanding (ICI) of power transmission grids based on mixed-integer linear programming (MILP) DC optimal power flow (OPF) model. We highlight several deficiencies of the most well-known formulation for this problem and propose new enhancements for their improvement. In particular, we propose a new alternative optimization objective that may be more suitable for ICI than the minimization of load shedding, a new set of island connectivity constraints, and a new set of constraints for DC OPF with switching, and a new MILP heuristic to find initial feasible solutions for ICI. It is shown that the proposed improvements help to reduce the final optimality gaps as compared to the benchmark model on several test instances.

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The last decade has seen an immense growth in renewable energy sources such as solar photovoltaic (PV) plants due to environmental concerns. Due to this rapid growth, solar PV plants are starting to have a larger influence on power system stability and thus their dynamic behavior cannot be ignored in stability studies. The lack of well-established models and parameter sets is the primary reason solar PV plants are not modeled with dynamic characteristics. This paper presents a method to define a standard parameter set for representing large-scale and aggregated solar PV plants in stability studies from the perspective of the transmission system operator (TSO). The method takes into account primarily the conditions provided in the grid connection requirements; for illustrative purposes, the connection requirements of the Netherlands are used. Additionally, a relationship defined as short-circuit current (SCC) PV ratio is proposed to estimate the effect of solar PV plants on transient stability. To illustrate the workings of the proposed ratio, the transmission network of the TenneT TSO B.V. in the Netherlands is used. The analysis demonstrated that high values of SCC PV ratio are an indicator that solar PV plants affect the transient stability while low values of SCC PV ratio showed that solar PV plants have minimal effect on the transient stability. Additionally, methods to improve the transient stability are provided which include limiting the operation regions of critical generators, increasing short-circuit ratio by adding a synchronous condenser or static compensator (STATCOM) and decreasing the reactance between the critical synchronous generator and faulted bus.@en

Switching operations in power systems can produce significant overvoltages under specific circumstances. With the increasing application of underground cables in transmission systems, the statistical distribution of energization overvoltages is expected to change substantially due to the different electrical characteristics of cables and OHLs. Therefore, it is crucial to perform an insulation coordination study by analysis of the statistical distribution of energization overvoltages. This paper presents a statistical switching analysis on a hybrid OHL-Cable circuit to investigate how such hybrid circuits can affect the distribution of overvoltages. The literature has addressed the distribution of energization overvoltages only for OHLs or cables, but such an study is not available for hybrid systems consisting of OHLs and cables combined. The study is carried out for different cable lengths in the case study to identify how an increasing cable share in the circuit influences the overvoltages distribution due to no-load energization. Moreover, the impact of symmetrical and asymmetrical circuit structures is also addressed. The study is carried out on a distributed frequency-dependent parameter model of the Dutch 380 kV grid in PSCAD/EMTDC.@en

Zero-missing is a phenomenon in shunt compensated cable systems in which the current through the line breaker does not cross the zero point for several cycles. This paper deals with a thorough investigation on countermeasures of the zero-missing phenomenon in transmission systems and determines the requirements, benefits, and risks of applying each method. The effectiveness of countermeasures is studied on a simulated cable project with different cable lengths in an actual grid model of the Dutch 380 kV transmission system. Results are analyzed based on three criteria related to the IEC standards and the Dutch grid code. In addition, the switching sequence of circuit-breakers is specified to maximize the effectiveness of the countermeasures. A statistical switching analysis is performed for the insulation coordination study since the application of some countermeasures increases the probability of high transient switching overvoltages. Moreover, the closing variation threshold of circuit-breakers is calculated as a function of the circuit impedance and the shunt compensation degree.

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Energization overvoltages are among the severest overvoltages stressing insulations of EHV power system components. Since these overvoltages have a statistical nature, the insulation level should be determined with the use of a statistical approach by which the distribution of overvoltages is calculated. Literature has properly studied the distribution of energization overvoltages in purely OHL or cable systems, but such a study is not available for hybrid systems consisting of both OHLs and cables. It is expected that the overvoltage distributions change substantially when both OHLs and cables are used in a transmission line. This paper tackles this issue by analyzing the overvoltage distributions due to the energization of a 380 kV hybrid OHL-Cable circuit, in which the cable length is variable. The study includes various sensitivity analyses to find out the impact of system parameters and topology on overvoltages. By the statistical analysis, it has been discovered that energization overvoltages of a hybrid OHL-Cable circuit are higher than those of a fully-cable circuit and very likely lower than those of a fully-OHL circuit with the same transmission lengths.

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This paper investigates the transient stability issues that may occur when long underground cables are added to EHV transmission systems. Dynamic behaviour of generators and terminal voltages with respect to various disturbances like cable disconnection/connection and fault currents are studied. Simulations are performed for the 2020 model of the Dutch transmission grid. The effects of partial undergrounding in two case studies with the total transmission length of 280 km are investigated. This work proposes criteria for accurate sizing of cable shunt compensation for dynamic simulation purposes based on grid voltages, generator reactive powers and power exchange with neighbouring grids. Moreover, a comparison between the dynamic behaviour of system variables for three different shunt compensation arrangements including line-end compensation, line-end middle compensation, and cable-end compensation is performed. Finally, a specific switching sequence for line disconnection/connection to improve voltage profiles and generator behaviours is introduced. The simulations are performed in PSS^®E environment.@en

This paper deals with the shunt compensation design of long 380kV-50Hz XLPE cables by simulating a double-circuit partially cabled connection with the transmission length of 80km in the Dutch transmission system. The proposed procedure for shunt compensation sizing is fully elaborated in this paper. Four sizing criteria are used to find the minimum required size of compensation. All simulations are performed for different cable lengths. Moreover, different compensation arrangements including line-end and distributed arrangements are compared in terms of minimum required compensation size. Finally, the influence of mixed-line configuration, i.e. the number and the location of cable sections, on the minimum required compensation size is investigated by simulating five mixed-line configurations. All simulations are performed for two load-flow scenarios representing two extreme situations in the future planning of the Dutch transmission grid. @en

The worldwide demand for electricity, which is steadily increasing, leads to a continuous need for developing and extending the electrical transmission networks. However, the installation of new overhead lines (OHL) faces many challenges due to societal and environmental reasons. One solution that gains widespread public support is the installation of EHV AC XLPE underground cables (UGC). Although this development is quite encouraging from a societal perspective, new challenges might arise, mainly from a technical perspective. This is due to different electrical characteristics of underground cables compared to OHL as well as long repair time in the case of failure in cable systems. These aspects highlight the necessity of investigating power system technical performance issues related to application of EHV cables to prevent any unwanted condition in partially cabled grids. This paper, among various system operation issues, investigates optimum shunt compensation sizing, reliability analysis, and condition monitoring of EHV cable systems. Reactive power compensation by means of shunt reactors should be allocated for long cables to consume their reactive power surplus. It is crucial to have sufficient size of shunt compensation because both undercompensation and overcompensation can lead to undesirable system operation like overvoltage and zero-missing phenomenon. In this work, the shunt compensation sizing of a 80 km double-circuit connection in the Dutch transmission system consisting of series connected OHL and cable sections is studied. The sizing is performed for two load-flow scenarios and based on four sizing criteria and different cable lengths in the case study. Moreover, the most decisive sizing criterion in each case is determined too. The next studied issue is the reliability analysis of partially cabled EHV grids. The additional components of UGC (joints and terminations) together with a significantly larger repair time (compared to OHL), reduce the reliability of the whole system. In this work, a reliability assessment approach is developed in order to examine how the installation of EHV UGC in transmission networks impacts the overall reliability level. A contingency analysis regarding failures of 380 kV OHL and UGC is performed through state enumeration. Reliability indicators are calculated by performing a dc load-flow calculation and applying remedial actions (if necessary) to relieve overloads. Varying cable length is installed in three connections in the Dutch network, the probability of load curtailment is calculated and the main factors that influence the probability of overload with EHV UGC are explored. The third studied aspect is the condition monitoring of cable systems. An advanced real time Condition Monitoring System (CMS) was installed in the Dutch 380 kV grid and its goal is to monitor the status of the cable connection and its impact on the 380 kV electricity transmission network. In this paper, a first comparison between measurement and simulation results, in both time and frequency domain, is presented. In this way a first validation of the simulation models is performed and the reasons of possible deviations are discussed. @en

Application of long EHV XLPE underground cables has divers effects on the transient behavior of transmission grids, mainly due to their large capacitive shunt impedance. Low-order resonance frequencies are one of the features of long cables that deserve special attention. This paper investigates the
resonance behavior of partial cable-based EHV networks by simulating a 380 kV double-circuit mixed OHL-cable connection in the future Dutch transmission system. The Sweep Frequency Response Analysis (SFRA) is performed for the distributed frequency-dependent parameter model of the whole Dutch 380
kV grid with and without cables in the case study project. The analysis is carried out for different cabling scenarios (i.e. different cable lengths) and for several sensitivity analyses including the influence of shunt compensation size, shunt
compensation location, and mixed-line configuration on the resonance behavior of the grid. The results are compared in terms of order of first harmonic resonance frequency and number of resonance frequencies. The EMT studies are carried out in the PSCAD environment.@en

Integration of long EHV XLPE underground cables in traditionally OHL-based transmission systems can result in abnormal transients caused by large cable shunt capacitance. Transients associated with switching of long cables may result in severe temporary or transient overvoltages. This paper investigates energization transients related to the installation of long 380 kV cables in transmission systems. Voltages and currents at multiple locations were analyzed in the time-domain after energization of different cable lengths in a 80 km mixed OHL-cable connection in the future Dutch 380 kV grid. Moreover, zero-missing phenomenon, as one of the likely events during energization transients of shunt compensated cables, and its countermeasures are discussed. The study comprises time-domain simulations in PSCAD/EMTDC environment,
where an accurate distributed frequency-dependent parameter model of the complete Dutch 380 kV grid is developed.@en