Prospective single and multi-phase short-circuit current levels in the Dutch transmission, sub-transmission and distribution grids

As elsewhere in the world, also in the Netherlands utilities face an increase in the actual and future short-circuit current levels at all voltages. This development is provoked by the required increase in transmission capacity as well as the concentration of power generation capacity. Large electricity production sites are moved to peripheral locations, thus overstressing the local transmission networks with respect to both the transmission capacity and the short-circuit power withstand capability. Dispersed power generation facilities, like windmills and co-generation plants for greenhouses, tend to appear in the same (optimal) neighborhoods, thus overstressing the local distribution and subtransmission networks. In the paper the development of short-circuit currents in the Dutch 400 kV-grid is illustrated. In addition, some particular aspects of the short-circuit currents will be addressed: three-phase and single phase fault currents, DC-time constants, peak values, contributions from transformers and distributed generators. Practical calculation guidelines on the actual short-circuit contribution from generators will be given. An example of design of a 400 kV station extension, emphasizing short-circuit current considerations is evaluated. National and international trends are addressed. More severe specifications of substation equipment lead to adapted designs and adequate testing procedures. Examples from testing of the consequences of short-circuit currents and fault arcs of 80 kA and above are highlighted

Towards Congestion Management in Distribution Networks:a Dutch Case Study on Increasing Heat Pump Hosting Capacity

The current high gas prices motivate end-users to replace their gas heating with electric heat pumps. This will likely cause frequent congestion issues in low-voltage (LV) distribution grids and slow down the heat pump adoption rate. To avoid or defer the expensive and complicated grid expansion, this study shares a solution approach of a Dutch Distribution System Operator (DSO) to enable the increasing adoption of heat pumps in existing dense housing areas. Data of the DSO and a local housing company have been combined to investigate the heat pump hosting capacity on a dense urban LV feeder, including realistic data of grid topology, load and heat dynamics, and practical operating characteristics of heat pumps. Our simulation compares two control strategies: (1) individual peak shaving and (2) central optimal power flow control. We show the central optimal power flow control with end-users' thermal comfort constraints and an objective function of minimizing losses can smoothen total grid loading and lead to flat voltage profiles. This allows the approach to be robust against baseload forecast errors, while the individual peak shaving is more prone to such errors. Moreover, by simulating the strategies on the worst-case scenarios where heat pumps are allocated to end-users at the end of the feeder, we determine the individual peak shaving strategy can slightly increase the heat pump hosting capacity from 49% where no control is imposed to 51%, while the central optimal power flow control allows 100% heat pump connections without causing grid congestion. Finally, recommendations to increase the heat pump hosting capacity are given based on simulation results

Rapamycin Does Not Act as a Dietary Restriction Mimetic in the Protection against Ischemia Reperfusion Injury

Introduction: Short-term fasting protects against renal ischemia reperfusion injury (IRI). mTOR signaling is downregulated and may be involved in its protective effect. Rapamycin is considered a possible mimetic as it inhibits the mTOR pathway. This study examines the effect of rapamycin on renal IRI. Material and Methods: Mice were divided into four groups: ad libitum (AL), fasted (F), AL treated with rapamycin (AL+R), and F treated with rapamycin (F+R). Rapamycin was administered intraperitoneally 24 h before bilateral renal IRI was induced. Survival was monitored for 7 days. Renal cell death, regeneration, and mTOR activity were determined 48 h after reperfusion. Oxidative stress resistance of human renal proximal tubular and human primary tubular epithelial cells after rapamycin treatment was determined. Results: All F and F+R mice survived the experiment. Although rapamycin substantially downregulated mTOR activity, survival in the AL+R group was similar to AL (10%). Renal regeneration was significantly reduced in AL+R but not in F+R. After IRI (48 h), pS6K/S6K ratio was lower in F, F+R, and AL+R groups compared to AL fed animals (p = 0.02). In vitro, rapamycin also significantly downregulated mTOR activity (p &lt; 0.001) but did not protect against oxidative stress. Conclusion: Rapamycin pretreatment does not protect against renal IRI. Thus, protection against renal IRI by fasting is not exclusively mediated through inhibition of mTOR activity but may involve preservation of regenerative mechanisms despite mTOR downregulation. Therefore, rapamycin cannot be used as a dietary mimetic to protect against renal IRI.</p

Review of Recent Developments in Technical Control Approaches for Voltage and Congestion Management in Distribution Networks

The increasing installation of distributed energy resources in residential households is causing frequent voltage and congestion issues in low- and medium-voltage electrical networks. To defer or avoid the costly and complicated grid expansion, technical, pricing-based, and market-based approaches have been proposed in the literature. These approaches can help distribution system operators (DSOs) exploit flexible resources to manage their grids. This study focuses on technical control approaches, which are easier to implement, and provides an up-to-date review of their developments in modeling, solution approaches, and innovative applications facilitating indirect control from DSOs. Challenges and future research directions are also discussed

Flexpower3: Significant increase in grid hosting capacity without comfort loss, by smart charging based on clustering and non-firm capacity

Summary: A novel Smart Charging strategy, based on low base allowances per charger combined with 1. clustering of chargers on the same part of the grid and 2. dynamic non guaranteed allowance, is presented in this paper. This manner of Smart Charging will allow more than 3 times the amount of chargers to be installed in the existing grid, even when the grid is already congested. The system also improves the usage of available flexibility in EV charging compared to other Smart Charging strategies. The required algorithms are tested on public chargers in Amsterdam, in some of the most intensely used parts of the Dutch grid

Techno-economic analysis of low-temperature electrolysis’ waste-heat utilization

Low temperature electrolysis will be an indispensable system integration asset in future low-carbon energy systems but is known for its inefficiency and associated waste-heat production. Low temperature electrolysis' waste-heat could be used in e.g. 4th or 5th generation district heating systems. However, its economical feasibility is uncertain due to spatial, temporal and temperature imbalances between waste-heat supply and heat demand. Therefore, this study proposes a model that addresses these hurdles and is able to calculate, under varying circumstances, the distance between low temperature electrolyzers and district heating systems at which waste-heat utilization is still profitable. The model contains a detailed description of the waste-heat extraction system, an electrochemical and thermodynamic model of an alkaline water electrolyzer, and an optimal dispatch strategy of the electrolyzer based on electricity and hydrogen prices. Results show that the economically feasible distance between electrolyzers and district heating system increases with the electrolyzer's capacity and stack temperature. The model can be used to strategically site electrolyzers by private owners or system operators

Prospective single and multi-phase short-circuit current levels in the Dutch transmission, sub-transmission and distribution grids

As elsewhere in the world, also in the Netherlands utilities face an increase in the actual and future short-circuit current levels at all voltages. This development is provoked by the required increase in transmission capacity as well as the concentration of power generation capacity. Large electricity production sites are moved to peripheral locations, thus overstressing the local transmission networks with respect to both the transmission capacity and the short-circuit power withstand capability. Dispersed power generation facilities, like windmills and co-generation plants for greenhouses, tend to appear in the same (optimal) neighborhoods, thus overstressing the local distribution and subtransmission networks. In the paper the development of short-circuit currents in the Dutch 400 kV-grid is illustrated. In addition, some particular aspects of the short-circuit currents will be addressed: three-phase and single phase fault currents, DC-time constants, peak values, contributions from transformers and distributed generators. Practical calculation guidelines on the actual short-circuit contribution from generators will be given. An example of design of a 400 kV station extension, emphasizing short-circuit current considerations is evaluated. National and international trends are addressed. More severe specifications of substation equipment lead to adapted designs and adequate testing procedures. Examples from testing of the consequences of short-circuit currents and fault arcs of 80 kA and above are highlighted

Combined MV-LV Power Grid Operation: Comparing Sequential, Integrated, and Decentralized Control Architectures

The increasing connection of distributed energy resources (DERs) to low-voltage (LV) power grids challenges the operation of both connected LV grids and upstream medium-voltage (MV) grids, through power flow via the MV/LV transformers. Handling the coupling between MV and LV grids calls for combined MV-LV network operation models. This study develops various optimization-based models, built respectively on sequential, integrated, and decentralized control architectures. A new objective function is also designed to attain fairer DER curtailment strategies. For the decentralized architecture, this study explores the generalized Benders decomposition (GBD) and two augmented Lagrangian relaxation (ALR)-based approaches: the alternating direction method of multipliers (ADMM) and the auxiliary problem principle (APP). Computational results based on open-source Simbench networks show reduced power curtailment from the integrated architecture compared to the sequential one. For decentralization, GBD already shows superior convergence performance compared to ADMM and APP under moderate accuracy requirements. Under higher accuracy requirements, GBD maintains fast convergence, while ADMM and APP fail to converge in a reasonable number of iterations