Flexible Operation of Electric Power Transmission Grids

In order to reduce carbon emissions and increase sustainability many countries in the world are switching to renewable sources of energy for electricity production. European Commission has set targets for its Member States to reduce such emissions and proposed share of renewables of around 30% in gross final energy consumption by 2030. Moreover, the electricity market is decentralized in Europe. As a result of decentralization and increased renewable penetration into the system, Transmission System Operators (TSOs) are faced with new challenges to operate their system securely. Some of the means of congestion management by the TSOs have become costly after decentralization. Moreover, variability associated with renewables can create congestion in a distant grid location which belongs to another TSO. Hence, TSOs are forced to find alternatives to operate their systems securely and in a cost effective manner. Inter-TSO coordination is one such non-costly alternative which requires increasing attention when more renewables are integrated into the system. The coordination (preventively and/or curatively) will help to operate the existing transmission grids more flexibly when more renewables integration demands transmission expansion, which is severely limited in Europe

Increasing wind penetration in Europe with the aid of controllable devices in the Benelux

status: publishe

An Approach for Optimal Placement of SVC to Minimize Load Curtailment

Modern electric power system is very complex and undergoes unforeseen rapid changes in terms of demand/generation patterns and trading activities that hinder the system security. For example, a steep rise in load or a certain critical line/equipment outage can cause line overload or undesirable voltage profile and such events can push the system towards instability and possibly even a black out. In order to cope with such situations, it is common practice to purchase the rights of asking for a reduction of load from certain customers. However, it is not an ideal situation from reliability perspective, financial as well as having critical load in the power system. Load curtailment is the collection of control strategies employed to reduce the electric power loading in the system and main aim is to push the disturbed system towards a new equilibrium state. Load curtailment may be required even when voltages at some buses are out of their safe operating limits, to prevent a possible voltage collapse. Flexible AC Transmission Systems (FACTS) controllers could be a suitable alternative to provide reactive power support at the load centres locally and hence keep the voltages within their safe operating limits. Due to high costs of FACTS devices, their proper location in the system must be ascertained. To deal with the above problem a new methodology has been proposed, in this thesis, in terms of sensitivity factors for the optimal location of Static Var Compensator (SVC) to minimize the system load curtailment requirements for maintaining the system security. In this work, SVC has been considered for the study to minimize the load curtailment. The effectiveness of the proposed method has been tested on IEEE 14-bus and practical 75-bus Indian systems. Optimal placement have been obtained for the base case loading and to verify its locations, an Optimal Power Flow (OPF) problem has been formulated with an objective to minimize the load curtailment and satisfying all operating constraints along with optimal settings of SVC which is used at suggested places from developed methodology. Moreover, the effects of SVC on load curtailment reduction, which are located at base case loading, have also been investigated for different operating conditions e.g., increased load or having different contractual obligation in the system

Increasing Transmission System Operation Flexibility using Power FlowControlling Devices

Managing the security of a power system poses a big challenge for the Transmission System Operators (TSOs) in the present days due to large amount of renewable energy source integration into the system. Congestion is now a frequent issue in a meshed power system like that in Europe, due to increased market competition after decentralization and high integration of renewables. This demands the existing transmission infrastructure to be expanded, but serious limitations are posed mainly due to the \enquote{not in my backyard} attitude. Another major aspect of congestion management is the incurred cost to the TSOs for generation re-dispatch in the decentralized environment. Hence, TSOs are forced to find other means of managing congestion, keeping the costly actions as their last means. Moreover, the existing grid has to be operated more flexibly in order to integrate more renewables, thereby diverting flows to non-congested areas in the system. Traditional N-1 principle for guaranteeing security of the power system will no longer be sufficient in the future due to enormous renewable integration into the system, as the cumulative forecast error can be significantly large. This, in turn, leads to serious challenges for the system operators to plan the operation of their systems day-ahead for real-time operation. Risk-based methods need to be developed in such a case in order to circumvent the limitation of the current approach of system security in the presence of increased renewables. Power flow controlling devices (PFCS) have gained increasing attention among the TSOs in Europe. Many of these devices are installed and operated mainly to limit loop flows and manage transit flows through their systems. These devices are also used to manage critical contingencies in the system, but their operation mainly lies on the operator expertise. These devices also have a critical impact on the neighboring interconnected system, as these devices can create congestion and endanger system security of the neighboring grids if not controlled in a coordinated manner. This thesis proposes algorithms to manage security and handle contingencies in the system with the help of already installed PFCs in a coordinated manner. It is also shown that operating the grid flexibly by these devices indeed helps integrating more renewables and handling more uncertainties in the system. A novel risk-based methodology is also developed in this thesis with which the system operators can learn the optimal operation point in their day-ahead operational planning, making maximum use of the system with a given confidence that the uncertainties present in the system due to renewables do not cause system overloads. It is also shown that the confidence can be significantly increased by a coordinated control of the PFCs.status: publishe

An approach for managing switchings of controllable devices in the Benelux to integrate more renewable sources

The augmented importance of using renewable energy sources to produce electricity and their integration with the transmission grid leads to a significant increase in loop flows in the transmission network. The uncertainty of wind energy, one such renewable energy source, and its stochastic nature leads to variable energy and cross border flows through the transmission corridors of different countries in Europe. Hence congestion occurs in the system. The opening of the electricity market has also led to additional difficulty for the Transmission System Operators (TSO) to manage the loop flows and cross border energy flows in their network. Power flow controlling devices, such as phase shifting transformers, can redirect power flows, thereby minimizing congestion in the system. The current day-ahead scheduling of power system operation in the Benelux grid does not take the phase shifting transformers fully into account. Moreover there is insufficient coordination in the phase shifting transformers installed in the system. This paper describes the current operation of the phase shifting transformers in the Benelux grid. A methodology to include phase shifting transformers in the 24 hours day-ahead scheduling process is proposed in this paper. The main objective in the scheduling process is to resolve congestion in the system taking into account minimum number of operator interventions caused by switching of the phase shifting transformers for the 24 hours schedule. © 2011 IEEE.status: publishe

An Approach for Optimal Placement of SVC to Minimize Load Curtailment

Modern electric power system is very complex and undergoes unforeseen rapid changes in terms of demand/generation patterns and trading activities that hinder the system security. For example, a steep rise in load or a certain critical line/equipment outage can cause line overload or undesirable voltage profile and such events can push the system towards instability and possibly even a black out. In order to cope with such situations, it is common practice to purchase the rights of asking for a reduction of load from certain customers. However, it is not an ideal situation from reliability perspective, financial as well as having critical load in the power system. Load curtailment is the collection of control strategies employed to reduce the electric power loading in the system and main aim is to push the disturbed system towards a new equilibrium state. Load curtailment may be required even when voltages at some buses are out of their safe operating limits, to prevent a possible voltage collapse. Flexible AC Transmission Systems (FACTS) controllers could be a suitable alternative to provide reactive power support at the load centres locally and hence keep the voltages within their safe operating limits. Due to high costs of FACTS devices, their proper location in the system must be ascertained. To deal with the above problem a new methodology has been proposed, in this thesis, in terms of sensitivity factors for the optimal location of Static Var Compensator (SVC) to minimize the system load curtailment requirements for maintaining the system security. In this work, SVC has been considered for the study to minimize the load curtailment. The effectiveness of the proposed method has been tested on IEEE 14-bus and practical 75-bus Indian systems. Optimal placement have been obtained for the base case loading and to verify its locations, an Optimal Power Flow (OPF) problem has been formulated with an objective to minimize the load curtailment and satisfying all operating constraints along with optimal settings of SVC which is used at suggested places from developed methodology. Moreover, the effects of SVC on load curtailment reduction, which are located at base case loading, have also been investigated for different operating conditions e.g., increased load or having different contractual obligation in the system

Grid-forming requirements based on stability assessment for 100% converter-based Irish power system

The fault response of a 100% converter-based system can be significantly different to that of a synchronous generator-based system, considering the lower capacity headroom, but flexible control capability, of power electronic converters. The system response is investigated for an Irish grid under balanced three-phase faults comprising of 100% converter-based generation: grid-forming (GF) and grid-following (GL). Electro-magnetic transient (EMT) simulations show that a system consisting only of GF converters (all droop control, all dispatchable virtual oscillator control, or a mix of both) is robust against three-phase faults, with little variation in performance, despite the fault location or choice of GF control methods. However, the rating and location of GF converters are critical to operating the grid securely in the presence of both GF and GL converters. Assuming that individual converter bus nodes are either GF or GL, a minimum GF requirement (by capacity) is found to be 37–40%, with these GF converters located close to the major load centres. Assuming instead that individual generation nodes consist of a mix of GF and GL converters, it is found that the GF requirement can be relaxed by 8–10%.European Commission Horizon 2020Science Foundation Irelan