Analysis of voltage dips in future networks
Roozbeh Torkzadeh defended his PhD thesis at the Department of Electrical Engineering on September 6th.
The global shift towards renewable energy sources, such as wind and solar power, is a key strategy towards combatting climate change. This transition from conventional fossil fuel-based power generation to such energy sources will help reduce carbon emissions but will also impact power quality. A good power quality is required to guarantee the proper and long-term operation of connected parties' installations. An important aspect for the network operators and connected parties to address is how energy transition impacts their voltage quality. For his PhD research, Roozbeh Torkzadeh explored these challenges, focusing on voltage dips, which are short-term reductions in voltage levels below a predefined threshold.
The Dutch grid code includes a legal framework for power quality assessment. Despite the major changes in the system, such as a weaker and alternative usage of the grid, the proper quality of the supply must be ensured.
At the heart of the Dutch energy transition are two major change drivers which are shaping the future of the electric system. First is the phase-out or less frequent dispatch of conventional power generation units and shift toward higher penetration levels of renewable energy sources (RES). The second one is the grid reinforcements and reconfigurations facilitating the energy transition at the generation side and demand side, i.e., electrification in various sectors such as mobility.
Voltage quality and dips
An important point for network operators and related parties to answer relates to what extent the energy impacts voltage quality.
For his PhD research, Roozbeh Torkzadeh explores these challenges, focusing on voltage dips. These dips, or sags, are short-term reductions in voltage levels below a predefined threshold.
Voltage dips are recognized as a critical power quality issue as they can cause severe societal and financial impacts. Such drops are usually caused by a short-circuit in the network and can disrupt connected processes, resulting in, for example, a loss of production. Voltage dips can propagate throughout the grid and impact many connected parties.
Impact of voltage dips
Torkzadeh鈥檚 research addresses the impact of the energy transition on voltage dips by analyzing how the earlier-mentioned changes can affect the voltage dips. As the disturbances for connected parties are mostly caused by 3 phase faults, these are used as an indicator to analyze future changes.
Torkzadeh confirmed this by analyzing voltage dips that occurred over a period of 3 years. Analysis of measured data from actual events was used to validate the used network model. Given that voltage dips occur randomly, a typical moment/hour was chosen for the analysis to obtain insight into future changes. Finally, impacts were quantified based on several representative cases. This allowed for comparison of the voltage dips in the current situation with the future situation for the same event.
Key findings
The key findings from the research of Torkzadeh can be summarized as follows.
The total impact of all changes within the Dutch electric grid is location- and time-dependent. Depending on the location of the event, which causes a voltage dip, and the location of the fault with respect to the connected party, can lead to a positive (+) or negative (-) impact on the energy transition in general.
Grid reinforcements and reconfigurations are essential for diminishing network congestion and facilitating the energy transition. They can impact the voltage dips in future networks positively or negatively.
Grid reinforcement, such as the establishment of new transmission lines, new substations, and adding more transformers to increase the capacity of downstream networks, will strengthen the grid, which can be translated into less severe voltage dips (+). However, a more interconnected power system also means lower 鈥渆lectrical distances鈥� between the nodes. Thus, voltage dips can propagate further and impact more connected parties (-).
Reconfigurations, such as operation in pockets as a solution to the network congestion in the high-voltage grid, can limit the propagation area of the voltage dips and lower the number of the impacted connected parties (+). Within an operational pocket, the connected parties may experience deeper voltage dips, especially if they are located at the boundaries of a pocket (-). This can also increase the number of connected parties inside a pocket that experience a severe voltage dip. Mitigation measures have been considered for one area.
A shift toward RES power generation and decommissioning/less frequent dispatch of central conventional generation has a negative impact on system strength and voltage dips by deepening the dips (-). This impact is limited to the adjacent nodes of the phased-out generation facility. However, the extra short-circuit contribution from the RES generation facilities in the medium-voltage grids shows a small increase in the short-circuit power in some areas where the grid is currently weak. This can be translated to slightly shallower dips (+).
Title of PhD thesis: . Supervisors: Sjef Cobben, V. Cuk, and Jeroen van Waes.