Sjef Cobben

Harmonic current interaction at a low voltage customer's installation

The increased use of power electronics and switching devices in the electricity network have changed the operational environment of the power system. These devices have non-linear voltage-current characteristics and produce harmonic currents, and consequently distort the voltage waveform. A low voltage domestic customer can have mixed loads that consist of linear and non-linear loads such as home appliances and lighting devices. In the PQ laboratory of TU/Eindhoven, the harmonic fingerprints of various household devices are measured. A LV household customers installation, consisting of various home appliances, is simulated in the network analysis tool ‘Power Factory’. The measured harmonic fingerprints of the connected devices are fed in to this software to perform harmonic simulations. The simulation results give the total harmonic current distortion level at the installation and the combined harmonic current interaction effects of different household devices. Furthermore, a case study is done to evaluate the total current harmonic distortion level at a customers installation when the grid voltage is polluted with a specific order of harmonic (such as the 5th harmonic). This is expected to be a typical futuristic scenario when many non-linear devices would be connected in the network and would distort the supply voltage.

Gaussian Mixture Based Probabilistic Load Flow For LV-Network Planning

Due the many uncertainties present in the evolution of loads and distributed generation, the use of probabilistic load flow in low voltage (LV) networks is essential for the evaluation of the robustness of these networks from a planning perspective. The main challenge with the assessment of LV-networks is the sheer number of networks which need to be analyzed. Moreover, most loads in the LV-network have a volatile nature and are hard to approximate using conventional probability distributions. This can be overcome by the use of a Gaussian mixture distribution in load modeling. Taking advantage of its radial nature and high R/X ratios, the LV-network can be analyzed more efficiently from a computation viewpoint. By the application of simplifications defined in this paper, the backward–forward load flow can be solved analytically. This allows for the direct computation of the load flow equations with a Gaussian mixture distribution as load. When using this new approach, the required calculation time for small networks can be decreased to 3% of the time it takes to generate a similar accuracy with a Monte Carlo approach. The practical application of this load flow calculation method is illustrated with a case study on PV penetration.

Estimation of the planning levels for flicker in the Dutch networks

The electricity grid operator should supply a voltage at a customers installation according to the requirements of the standard EN50160 or national grid code. In contrast, no present grid codes specify clearly the responsibility of the customers regarding power quality (PQ) at their installations. The voltage flicker is one of the most irritating PQ problems on which the Dutch grid operators get many complaints. It often happens that flicker is generated because of the customers own or neighboring customers loads. Therefore, the standard should specify a limit for the customers about the flicker emission at their installations. The new technical report IEC/TR 61000-3-14 indicates a method to estimate the flicker emission limit for various customers in the low voltage (LV) network. In this paper, an analysis is done on a model Dutch network to estimate a LV customers maximum share of flicker emission into the network. Also, the most appropriate planning level value of flicker at different voltage levels in the Netherlands is suggested.

An application of a decision-making algorithm for an intelligent distribution substation

In this paper, the expected functionality and the operational priority of an intelligent distribution MV/LV substation is evaluated. The analytic hierarchy process is applied as a multi-criteria decision-making tool for evaluation based on a survey of expectations among expert responders. The results are presented in terms of the priority ranked criteria as well as the available alternatives, such that the alternatives are ranked based on their fulfillment of the expected criteria and functionality.

Demand response of medical freezers in a business park microgrid

This paper presents a demand response (DR) framework that utilizes the flexibility inherent to the thermodynamic behavior of four groups of independently-controlled medical freezers in a privately-owned business park microgrid that contains rooftop photovoltaics (PV). The optimization objectives may be chosen from the following 3 options: minimizing electricity exchanges with the public grid; minimizing costs by considering prices and RES availability; and minimizing peak load. The proposed DR framework combines thermodynamic models with automated, genetic-algorithm-based optimization, resulting in demonstrable benefits in terms of cost, energy efficiency, and peak power reduction for the consumer, local energy producer, and grid operator. The resulting optimal DR schedules of the freezers are compared against unoptimized, business-as-usual scenarios with- and without PV. Results show that flexibility can be harnessed from the thermal mass of the freezers and their contents, improving the cost- and energy performance of the system with respect to the business-as-usual scenarios.

6MW solar plant integration feasibility study: Bonaire island case study

The power supply on Bonaire is characterized by a high penetration of wind energy. Currently 5 diesel generators (total capacity 14MW) and 12 wind turbines (total capacity 10.8MW) operated by ContourGlobal generate electricity for Water and Electricity Bonaire (WEB). To meet future power demand increase, WEB has the ambition to connect a 6MW centralized solar plant to their system, thereby further increasing their renewable power generation in the islands energy mix. This paper studies the system impact of adding a 6MW centralized solar plant on the existing system and highlights the associated operational constraints.