P.H. Schavemaker

Phase shifting transformers: principles and applications

The purpose of this paper is to give a short overview of existing technologies regarding phase shifting transformers (PSTs). A classification is made based on the symmetrical or asymmetrical and on the direct or indirect character of the PST. As a case-study, the PSTs in Meeden, The Netherlands are studied more profoundly. Furthermore, a model is developed on a real-time digital simulator (RTDS) in order to demonstrate the capabilities of the PST

Impacts of distributed generation penetration levels on power systems transient stability

Concerns on environmental and economical issues drive the increasing developments that support small scale generators to be connected close to distribution networks, i.e. distributed generation (DG). When connected in small amounts, the impact of DG on the power system transient stability will be negligible, however, when the penetration of DG increases, its impact is no longer restricted to the distribution network but starts to influence the whole system, including the transmission system transient stability. In this paper, the transmission system transient stability is investigated when a fault is applied in all possible branches (regarding the N-1 security analysis). In this studie the penetration level of DG implementation is raised in two ways: (1) a load increase is covered by DG implementation (with a constant centralized generation) or increased CG output, and (2) a reduction of centralized generation is covered by DG (with a constant load).

Investigating impacts of distributed generation on transmission system stability

Driven by the increasing environmental concerns and the increasing amount of new generation technologies, it is expected that many new generation technologies, including renewable generation, will be connected to the electrical power system. A lot of these new technologies will be connected at the distribution level. When the penetration of this distributed/dispersed generation (DG) is low, the impacts of the DC on the transmission system transient stability may be neglected. However, when the penetration of DG strongly increases, its impact is no longer restricted to the distribution network but begins to influence the whole system. In this paper the impact of DG on the transmission system transient stability is investigated by considering different types of DG technologies and various penetration levels. It is observed that both the types of DG technologies and the penetration levels of DG in the power system have a strong influence on the transmission system transient stability.

Analytical Approach to Grid Operation With Phase Shifting Transformers

Analytical expressions are derived to gain insight in the operating principles of phase shifting transformers (PSTs) in a highly meshed grid. To this extent, the dc load flow algorithm is adapted to account for such devices. This leads to a linear expression for the relation between PST settings and the active power flow in the lines. Based on these equations, the total transfer capacity (TTC) can be described mathematically, which allows for optimization. Furthermore, the linear least squares method is used to distribute a cross-border transport evenly over the interconnectors.

Digital testing of high-voltage circuit breakers

The functionality of high-voltage circuit breakers is tested in high-power laboratories. Due to the necessary power and the physical size of the equipment, testing is rather expensive and time consuming. The steps followed so far by the authors in order to enable the digital testing of HV circuit breakers are described in this paper. At the end of the article, examples of digital testing are also presented.

On a hysteresis model for transient analysis

The letter describes an approach to a representation of transient behavior due to switching off complex nonlinear circuits. For this purpose the widely known Jiles model (JM) was implemented into the Alternative-Transient-Program (ATP). Calculations have been made on simplified transformer single-phase and three-phase circuits.

Border-Flow Control by means of Phase Shifting Transformers

In this paper, a control scheme is demonstrated that regulates multiple phase shifting transformers (PSTs) to equally load the interconnectors of a border. A crucial step in the development of the control scheme is the derivation of phase shifter distribution factors (PSDFs), which indicate the influence of a PST on the active power flow on a certain line. Based on these PSDFs, the Linear Least Squares (LLS) method is used to calculate the optimal PST settings. The degree to which an even repartition can be obtained, depends on the number of PSTs in relation to the number of interconnectors. As a case- study, simulations are performed involving the Dutch and Belgian interconnectors.

Impact of Stochastic Generation in Power Systems Contingency Analysis

A new methodology is proposed for the contingency analysis of power systems with a high penetration of stochastic generation. The essence of the proposed technique is the use of a probabilistic risk measure for the security assessment of the N subsystems deriving from the application of the N-1 criterion. This measure, namely the stochastic stress of the system, corresponds to the concurrent behavior of the stochastic system inputs (loads and stochastic generators) that are situated in the lower voltage levels of the system. In the context of Monte Carlo simulation, this problem is equivalent to the sampling of a large number of non-trivial dependent random variables (stochastic power injections). The modeling procedure is split in two independent tasks: modeling the marginal distributions and modeling the stochastic dependence structure. The second part is the most cumbersome modeling problem. For this, a two-step method is used. First, clusters of positively correlated variables are defined and are modeled based on the concepts of perfect correlation (comonotonicity). Then, the exact correlations between these clusters are modeled based on the joint normal transform methodology. This powerful computational method can be easily applied to large systems with a high number of stochastic generators. The application of the method for the contingency analysis of the 5-bus/7-branch test system (Hale network) with a high penetration of wind generation is presented in the paper

Probabilistic power flow methodology for the modeling of horizontally-operated power systems

Stochastic generation is expected to take a large share of the energy production in future power systems. Two basic features of this type of generation distinguish it from the traditional centralized, conventional generation: it is highly distributed (large number of small-scale generators) and non-dispatchable (use of an uncontrolled prime mover). The incorporation of such power sources in the lower system levels leads to a new horizontal structure of the power system, where the distribution networks contain both uncertain stochastic generation and load. For the analysis of such systems, the use of a probabilistic approach is necessary. There are two basic problems with the probabilistic formulation of this problem: the large number of random variables involved in the analysis and the presence of complex dependencies between the system inputs. In this contribution, a two-step method is presented for the stochastic modeling of the system: first, clusters of positively correlated variables are defined and modeled based on the concepts of perfect correlation (comonotonicity), and then the exact correlations between these clusters are modeled based on a new proposed technique, the joint normal transform methodology. This powerful computational method can be easily applied to large systems with a high number of stochastic generators. The proposed method has been implemented and applied for the 5-bus/7-branch test system (Hale network) with a high penetration of wind generation. The results are presented in the paper

Real-time simulation to study the impact of renewable energy in power systems

A real-time simulation tool, in our case a real-time digital simulator (RTDS), gives the opportunity to study the impact of renewable energy in power systems on a real-time base, driven by actual solar and wind data. In the first part of this paper, the real-time digital simulator (RTDS) is briefly introduced. The application of this analyzing tool is first demonstrated on a detailed model of a wind energy conversion system (WECS) whereas secondly the application on an autonomous power system is shown. Both applications demonstrate the capabilities of this simulator and the added value for power system analysis