Madson C. de Almeida

Evaluation of the impact of distributed generation on power losses by using a sensitivity-based method

The connection of generators on distribution feeders may cause significant impact on the steady-state performance of the network. Quantification of the impacts on power losses, in a systematic way, is a difficult task due to the complexity of network operation since generators can operate with different lead and lag power factors and, occasionally, can inject variable active power on the network. This paper evaluates the impact of distributed generators on the active and reactive power losses of the system by using a sensitivity-based method. From one base case power flow solution it is possible to estimate the active and reactive power losses for a new generator installed at any bus of the system, for any combination of active power injection, and also for any operating power factor. The effects of varying the location, generation level and operating mode of the generators can be easily assessed by using the analytical method. Moreover, a numerical index to quantify the impact of multi-distributed generators on power losses is also proposed. The method is applied to a 70-bus distribution network. The simulations results are compared with those obtained by the repetitive power flow solutions in order to validate the results obtained by the sensitivity-based method.

Increasing the PV hosting capacity with OLTC technology and PV VAr absorption in a MV/LV rural Brazilian distribution system

Distributed Generation (DG) can provide multiple benefits in MV/LV distribution networks. However, high penetration levels may cause technical issues to the grid, as already observed in some countries. Thus, Distribution Network Operators (DNOs) have to consider alternative solutions to guarantee normal operation, even under high penetration levels. In this paper, a time-series based probabilistic methodology is used to estimate the maximum PV hosting capacity of LV distribution networks. The proposed method is applied to assess a real rural Brazilian distribution system. According to the obtained results, voltage regulation and overloads in distribution transformers limit the PV hosting capacity. Therefore, aiming to increase this capacity, the use of PV VAr absorption and OLTC transformers was technically evaluated.

Analysis of bad data detection in power system State Estimators considering PMUs

This paper investigates the bad data detection issues in power system state estimation considering SCADA and PMU measurements. The traditional State Estimator (SE) containing only SCADA measurements, two One Phase SEs and one Two Phase SE are evaluated. The SEs are assessed by considering measurements containing gross and gaussian errors and two classical methods for measurement standard deviations specification. The bad data detection is realized with the classical Largest Normalized Residual approach. The main found is that the One Phase SEs are, in general, more accurate and, therefore, the bad data detection approach works better with these SEs. Besides, the performance of bad data detection approach is strongly deteriorated, even for SCADA measurements, when classical standard deviation methods are adopted with the Two Phase SE. In general, considering all evaluated SEs and the classical standard deviation methods the bad data detection presented inadequate performance for PMU measurements. Therefore, it can be concluded that some improvements are required in this topic. Test results on the IEEE-14 bus system are presented.

A Numerical Method for Finding Spanning Trees in Power System State Estimation

This paper presents a simple and robust numerical method to find non-redundant sets of measurements that form spanning trees. This can be useful to the observability analysis of power system state estimation. The proposed method is based on the triangular factorization of the Gram matrix constructed considering the rows of the measurement Jacobian matrix as vectors. The method is robust and suitable to be used in realtime applications. Numerical examples to show the performance of the method are presented.

An approach to fault location in HVDC lines using mathematical morphology

This paper presents an approach to fault location in HVDC transmission lines. A superimposed signal calculated from voltages and currents sampled in the same terminal is processed by a morphological filter in order to highlight the wavefronts and allow the fault location. The morphological filter was adopted due to its simplicity and low computational cost. A suitable combination of superimposed signal, morphological filter and Structuring Element (SE) enabled developing a simple algorithm to detect the correct wavefronts and, consequently, estimate the fault position. The results were obtained considering data sampled in one or two terminals. The influence of the main fault parameters as well as the approach parameters were evaluated and the results are promising.

Load Monitoring Using Distributed Voltage Sensors and Current Estimation Algorithms

A major feature of the smart grid is its diverse load management opportunities for customers, which calls for innovative techniques for load monitoring. This paper presents a method to monitor loads in commercial and small industrial facilities using a set of distributed voltage sensors and current estimation algorithms. The technique is especially suited for facilities where it is difficult to measure loads directly but the load voltages can be sensed. A state-estimation-like current estimation algorithm is proposed to estimate the load currents using the voltages sensed at the terminals of the loads. Currents and powers collected from a limited number of panels are also utilized to provide redundancy for the estimation. Case studies have shown that the proposed method represents a promising alternative measurement strategy for load monitoring.

A transmission line two-end fault location approach based on mathematical morphology

This paper presents a fault location method for transmission lines. The proposed approach is based on voltage traveling waves sampled in both line terminals. A morphological filter called Simplified Multi-resolution Morphological Gradient (SMMG) is proposed. Because of its simplicity and low computational load, the SMMG is suitable for real time applications. The SMMG is used to detect the instant of arrival of the first wave front at the line terminals. Using these instants and the waves propagation speed, obtained from line parameters, the fault location is calculated. Tests based on a real transmission line show the robustness and the good precision of the proposed approach.

An Improved Three-Phase AMB Distribution System State Estimator

State estimators (SEs) are required to enable the evolving and increasingly important role of communications and control in smart distribution systems. In this context, this paper presents an improved three-phase admittance matrix-based (AMB) SE for medium voltage systems to tackle issues related to zero injections, consistency, and the inclusion of voltage measurements. Here, the state variables are the real and imaginary parts of the complex bus voltages, while power and voltage measurements are converted into equivalent currents and voltages, respectively. The key improvements include: 1) considering zero injections through a linear nonweighted procedure, 2) using phasor rotation for calculation of the equivalent voltage measurements, and 3) including the covariance between real and imaginary parts of equivalent current measurements. Despite these new characteristics, the proposed improved AMB SE (ISE) features constant coefficient matrices, thus resulting in reduced computational times. The performance of the ISE is assessed considering a real UK medium voltage system. Its consistency is assessed via a Monte Carlo analysis. Comparisons with other AMB SEs demonstrate that the proposed three-phase ISE is more robust, statistically more consistent, and computationally very competitive.

Assessing the statistical consistency of the AMB State Estimator in distribution systems

In this paper the statistical consistency of the single-phase Admittance Matrix-Based State Estimator (AMB SE) originally proposed for distribution systems is for the first time assessed and compared to that of the widely used Traditional SE (TSE). The AMB SE is an interesting alternative for distribution systems given the use of a constant Gain matrix, thus simplifying its implementation and significantly reducing the computational time. However, it is crucial to statistically assess its consistency so as to ensure estimated values and variances (outputs) are in agreement with the specified measurements and variances (inputs). This is carried out using a Monte Carlo analysis and a generic 16-bus UK distribution system. Despite the conversion from actual to equivalent measurements required by the AMB SE, as well as the approximations regarding the variances of the equivalent measurements, the results demonstrate that the single-phase AMB SE is as consistent and precise as the TSE.

Fault location in power distribution systems using a learning approach based on decision trees

This paper presents a learning-based strategy that uses decision trees for locating faults in radial power systems, which is aimed to improve the power quality as demanded by the deregulated electrical markets. The proposed method first subdivides the power system into several regions, and then, a classification technique based on decision trees is trained using a fault database. The obtained decision trees are used to assign a faulted zone to a new fault event, which reduces the restoration time and as a consequence helps to maintain good quality indices. The proposed method is validated in the IEEE 34-node test feeder considering several operating conditions, such as variations in load, substation voltage, line length and fault resistances. The obtained results prove the good performance of the proposed fault location method. Finally, the implementation of this method on real power distribution systems helps to maintain good power continuity indices, with a low investment.