Bus-bar Switching Research Articles

Online Preventive Control for Transmission Overload Relief Using Safe Reinforcement Learning With Enhanced Spatial-Temporal Awareness

The risk of transmission overload (TO) in power grids is increasing with the large-scale integration of intermittent renewable energy sources. An effective online preventive control schemes proves to be vital in safeguarding the security of power systems. In this paper, we formulate the online preventive control problem for TO alleviation as a constrained Markov decision process (CMDP), targeted to reduce the load rate of overloaded lines by implementing generation re-dispatch, transmission and busbar switching actions. The CMDP is solved with a state-of-the-art safe deep reinforcement learning method, based on the computationally efficient interior-point policy optimization (IPO), which facilitates desirable learning behavior towards constraint satisfaction and policy improvement simultaneously. The performance of IPO method is further improved with an enhanced perception of spatial-temporal correlations in power gird nodal and edge features, combining the strength of edge conditioned convolutional network and long short-term memory network, fostering more effective and robust preventive control policies to be devised. Case studies on a real-world system and a large-scale system validate the superior performance of the proposed method in TO alleviation, constraint handling, uncertainty adaptability and stability preservation, as well as its favorable computational performance, through benchmarking against both model-based and reinforcement learning-based baseline methods.

Transmission Congestion Management via Node-Breaker Topology Control

A novel topology control algorithm is proposed here to reduce congestion and overloads, thereby improving security margins in a power network. The proposed heuristic relies on normalized squares of the line currents as a direct indicator of transmission line loading. The sensitivity of this measure with respect to breaker positions forms the basis of the proposed heuristic to select switching actions for a reconfigured network topology that reduces the congestion and overloads while holding generation dispatch essentially fixed. While many prior works have examined this class of problem for line switching actions (i.e., topology changes that insert or remove branches), bus-bar switching actions (topology changes that merge or split nodes/buses) have received less research focus. Here, both line switching and bus-bar switching are implemented using a detailed node-breaker representation of the network. The algorithm adopts a novel form of the AC power flow that allows sparse calculation and reduced computation time. Case studies demonstrate that the proposed approach efficiently reduces congestion and overloads in the base case and in contingency situations.

Network topology optimisation based on dynamic thermal rating and battery storage systems for improved wind penetration and reliability

The nonflexible operations of transmission networks with high load demand and wind power increase the likelihood of power congestions and deteriorate grid reliability. This condition causes higher load curtailments and inhibits the penetrations of wind power, subsequently leading to higher dispatch cost because more expensive generators compensate for the loss of wind integrations. These unfavourable factors contribute to a higher total system operating cost, which should be reduced. This paper applies a network topology optimisation technique to optimise line and busbar switching for relieving network congestions and improving network flexibility. A dynamic thermal rating system is used to enhance overhead line ratings. A battery storage system is utilised to time shift wind power usage and avoid wind spillage. These methods are effective but they have been studied only in isolation. This paper presents an assessment framework that combines all the three methods in a single model to evaluate their synergistic effects on wind integration and network reliability. The proposed framework is generic and can be applied on any networks with changes only to the numerical results. The battery energy and power ratings required to maintain the prevailing security of supply standards in a large scale wind-integrated network are determined probabilistically. Case studies performed on a modified IEEE 24-bus reliability test system show that the proposed combination of methods reduces system dispatch, load curtailment and wind curtailment costs the most when compared to any combinations with fewer methods or using each method in isolation.

Incorporating Bus-Bar Switching Actions into AC OPF to Avoid Over-Current Status

This paper presents a new AC optimal power flow (AC OPF) model for sub-transmission networks. This model, which consists of sub-transmission and distribution bus-bar switching actions, can avoid undesirable over-current (OC) status and subsequent actions of OC relays. The proposed AC OPF optimizes the bus-bar switching actions along with optimizing sub-transmission control actions. Also, to consider the impact of OC relays’ actions in the proposed AC OPF, the cost of load shedding caused by these relay actions is included in the objective function and is minimized along with the sub-transmission operation cost. The bus-bar switching actions are modeled using binary decision variables. Therefore, the proposed AC OPF model is formulated as a Mixed Integer Non-linear Programming (MINLP) optimization problem. The effectiveness of the proposed model is illustrated on a real-world sub-transmission network of Iran’s power system.

Circuit implementation of power converter for high-speed switching operations

Recently, high di/dt and dv/dt switching operations of power converter circuits has been discussed for realizing a high-efficiency power converter circuit. In this case, parasitic inductances of the bus bar between a DC capacitor and power devices may cause issues of overshoot voltage and electromagnetic interference(EMI) noise. Therefore, it is necessary to design the bus bar geometry while considering the minimization and optimization of the parasitic inductance of bus bar. This paper discusses a relationship between bus bar geometry and switching characteristics. In addition, the bus bar analysis is based on the PEEC method, and the bus bar geometry is designed by considering the stray inductance with using an inductance-map method. Moreover, this paper also presents a design procedure of acceptable stray inductance based on a standardization method. It should be noted that the stray inductance is designed not for minimization, but optimization, and it is shown not as an absolute value(H), but as a percentage value(%). Finally, the oscillation waveforms under turn-off operation will be discussed depending on the bus bar geometry.

Corrective Switching Algorithm for Relieving Overloads and Voltage Violations

It is widely known that corrective switching, including transmission line switching, bus-bar switching, and shunt element switching, may change the states of the power systems, and consequently, affect the distribution of power flows, transmission losses, short circuit currents, voltage profiles as well as transient stability of power systems. In this paper, a new algorithm is developed to find the best line and bus-bar switching action for relieving overloads and voltage violations caused by system contingencies based on a sparse inverse technique and fast decoupled power flow with limited iteration count. A general model of bus-bar switching action is also presented such that the new algorithm can simulate any kind of complicated bus-bar switching action. Furthermore, on the basis of a newly proposed voltage distribution factor by multiple iterations in power flow calculation, a novel algorithm for corrective voltage control by shunt switching is developed. These two algorithms are then integrated into a corrective switching algorithm. Simulation results on the WECC 179-bus system indicate that the new corrective switching algorithm proposed in this paper can effectively solve certain problems of line overloads and voltage violations. The computation time required is also satisfactory.

An expert system for Switching Operations for Blackout restoration—Line, bus-bar and feeder switching

An expert system has been developed for switching operations of network restoration of power systems. The proposed method restores the blackout area in a power system by using sensitivity analysis and heuristic rules. The rules are categorized into flow-control rules, energization rules, line and bus-bar switching rules, and load-shedding rules. The switching (opening/closing) operations of transmission lines, transformers, substation feeders and bus-bars are used for the network restoration described in this paper. A new model for bus-bar switching in a substation is also proposed. The representation of the power-system equipment has hierarchical data structures for the real-time recognition of a network topology.

Practical experience with corrective switching algorithm for on-line applications

The objective of the corrective switching algorithm (CSA) is to identify switching candidates to eliminate or reduce power system overloads. This paper describes the implementation of the CSA for online contingency analysis. The developed program searches for the best switching candidates from a user specified list, which normally includes all branches in the study area and most typical switching operations (openings and closings) at main substations. The developed algorithm has the unique ability to process complicated substation busbar switching scenarios, including multiple switching scenarios per any substation. The selection algorithm is based on a linearized DC model, but all selected candidates are verified using AC load flows. The program has been used as part of the security analysis program at Public Service Electric and Gas Company (PSE&G) since Summer 1994 and has proved its reliability and efficiency.

Verification of the electromechanical transients program setpos by means of comprehensive power‐station measurements

AbstractMost electrical power engineers involved with the planning and designing of power station auxiliary power supply systems are faced with the problem of credibility of the electromechanical transients programs offered as supplementary aid in fulfilling their jobs. These programs contain a variety of mathematical models of electrical power system components, which can be combined to constitute the electrical system being analysed. Most simulation programs have been tested on a number of theoretical cases and the results compared to those of other similar computer programs. This is due to the general lack of‐ and difficulties in achieving ‐ field measurements of reproducible electromechanical transients in fully known power subsystems. Such field measurements of a slow busbar switching in the auxiliary system of a modern power station unit are presented and compared to the computational results obtained by simulating the incident using the SETPOS electromechanical transients program.

Corrective Control of Power System Flows by Line and Bus-Bar Switching

Corrective Control of Power System Flows by Line and Bus-Bar Switching

Corrective Control of Power System Flows by Line and Bus-Bar Switching

A fast algorithm is developed for automatic selection and ranking all possible circuits for corrective control by network switching to relieve system overloads. The non-iterative DC approximate model for a power system is used to generate linear sensitivity factors. These factors are calculated using relevant elements of the sparse bus impedance matrix and branch reactances. Special treatment of substation circuit breakers makes it possible to use bus-bar splitting for corrective action. The method was tested on two systems. Test results show the reliability and effectiveness of the method in selecting lines and circuit breakers for corrective overload control.