E. Janeček

Probabilistic Extension of the Backward/Forward Load Flow Analysis Method

The environmental need to curb distribution network losses and utilize renewable energy sources has created new challenges in estimation. High fidelity estimates are required even in the presence of significant uncertainty. Herein, we develop a new analytical probabilistic load flow method that, unlike existing analytical methods, is not based on a Taylor series approximation of the power equations. The method is exact for a set of distributions that includes the multivariate normal distribution. The method implementation is made scalable by casting all formulas into the framework of the popular backward/forward algorithm. The advantages of this approach are illustrated on a radial IEEE 32-bus test system. Significant improvements are observed in the presence of large power uncertainties and near the network power limits. Uniformly better estimation of power losses is achieved.

Transmission line identification using PMUs

The paper is devoted to the identification of transmission lines from synchronized measurements of current and voltage phasors provided by the phasor measurement units (PMUs). The series and shunt line parameters are recursively estimated using the extended Kalman filter (EKF). Actual line temperature and reference resistance are estimated instead of actual series resistance, which is then computed from these estimates. This approach can accommodate more information and, therefore, produce better estimates of the line resistance than the traditional approaches based on the weighted least squares method. Two case studies based on data from South Moravia and East Bohemia are presented to demonstrate the effectiveness of the proposed approach.

A New Approach to Modelling of Electricity Transmission System Operation

One of basic system services that an electricity transmission system operator guarantees is power balance maintenance. The aim of this service is to keep power export/import to/from surrounding interconnected electricity systems at a proposed value. This implies that the amplitude of a power balance deviation has to be kept in specified boundaries. The operator uses so called ancillary services for this purpose. In order to perform the overall volume and structure optimization of the ancillary services it is needed to know the magnitude and dynamics of the deviation that will be decayed. For this reason a deviation balance model has been designed and is presented in the paper. It describes electricity transmission system operation

Risk limiting dispatch with optimal curtailing in active distribution networks

Renewable energy sources often provide intermittent power at distributed locations in transmission and distribution networks. Efficient utilization of these sources must consider economics, computation, and reliability in managing network resources. A new computational tool for efficient dispatch of intermittent sources is developed using the risk limiting operational paradigm. Optimal dispatch of regulation and load following ancillary services is computed using current estimates of future random energy production. Substitution of intermittent power with firm power through a curtailment strategy is used to avoid regulation costs in excess of current firm power prices. The underlying mathematical framework is a non-convex optimal power flow problem, which is shown to have an exact convex relaxation under a set of realistic assumptions. The methodology is successfully tested on an IEEE 30-bus test system. Several operational effects of source uncertainty are captured. For instance, optimal solutions are shown to create power flows that mutually compensate intermittencies from different sources to minimize regulation requirements.

Criteria for evaluation of power balance control performance in UCTE transmission grid

In this paper two criteria for evaluation of power balance control performance in control areas of the UCTE interconnection are proposed: the mean value of Area Control Error (ACE) and the standard deviation of ACE. A methodology for assigning fair values of the two criteria to individual control areas is presented. This methodology ensures that the UCTE grid is operated in a safe manner and no area performs control at the expense of other areas. Since the fair values of the ACE standard deviation depend on a chosen model of ACEs coincidence, two cases were investigated: a model with no coincidence (optimistic one) and a model with full coincidence (pessimistic one).

Computing Intervals of Secure Power Injection

Abstract Existing tools used in many power system operations evaluate individual scenarios for power injection and network configuration but fail to consider nearby regions in the operating space. Such tools may lead to market transactions, preventive actions, or corrective actions that are nominally efficient but poor in general. Herein the foundations of an interval method are introduced. The presented results include an algorithm defined within a tractable optimisation framework that computes maximal power injection sets containing power injection profiles that are necessarily secure. The method is demonstrated on a simple 4 bus test system as well as on a medium sized IEEE 30 bus test system.

Backward/forward probabilistic network state estimation tool and its real world validation

Increasing penetration of renewable energy sources into conventional power networks causes increase of the uncertainty level which reveals new research and technological challenges. High fidelity network state estimation in environment with significant share of intermittent energy sources is required for planning and operation activities performed by system operators. Probabilistic load flow methods stand for promising estimation techniques which can be applicable for environment with strong presence of uncertainty. Paper describes an estimation tool based on probabilistic backward/forward method. Special emphasis is given to the description of particular components of the estimation tool. Reliability and robustness of the tool is demonstrated on the results from real world validation.

On-line Ampacity Monitoring from Phasor Measurements

Abstract The knowledge of transmission line parameters involving series impedance and shunt admittance is crucial to power system analysis and power system state estimation. Particularly in areas of power systems protection it is critical to have accurate values of these parameters to determine the line ampacity. The line parameters change according to the load level and weather conditions, so it is necessary to identify the line parameters in real time. The paper deals with the on-line parameter identification of transmission lines from synchronized measurements of current and voltage phasors provided by the phasor measurement units. The series and shunt line parameters are recursively estimated from the phasor measurements and weather conditions using the extended Kalman filter. Contrary to the other works, an actual line temperature and reference resistance are estimated, which makes possible to monitor the actual state of the transmission line in order to determine an actual reserve or prediction of future transmission capacity. A case study based on data measured from a 110kV overhead transmission line is presented to demonstrate the effectiveness of the proposed approach.

Optimal scheduling of a pumped-storage hydro power plant operation

The paper presents an optimization technique for scheduling of pumped-storage power plant operation up to one year horizon. A pumped-storage power plant is an energy source with fast time response consisting of upper and lower reservoir, which has ability to store excess electric energy in the upper reservoir in form of potential energy of water, which is pumped from the lower reservoir. Its importance increases as a tool for transmission system operator to control of power system stability, load balancing and frequency control due to the increase of amount of power generated from renewable energy sources characterized by the fluctuation of power output such as photovoltaic and wind power sources. Usually, it has part of capacity reserved for needs of transmission system operator and the remaining capacity can be used by the plant operator in commercial manner to increase of profit. The aim of the paper is to propose fast algorithm based on dynamic programming to optimize free capacity while complying with all the technical and operational restrictions.

Modular algorithms for computing Intervals of Secure Power Injection

New market tools and distributed energy sources in present day transmission systems necessitate innovation in supporting information technologies. Existing tools used for power system operation evaluate individual power system snapshots but do not fully consider nearby regions in the operating space. Such tools may lead to market transactions, preventive actions, or corrective actions that are nominally efficient but poor in general. The Intervals of Secure Power Injection (ISI) method provides an alternative set based approach. Herein the ISI method is reformulated to allow fast recomputation of the interval sets under marginal changes in network topology. This method can be potentially applied in short term reconfiguration planning and in contingency analysis. Computation efficiency of proposed modular algorithms was tested on IEEE and real transmission system models.