Gurunath Gurrala

Reliable Implementation of Robust Adaptive Topology Control

The topology (transmission line) switching to achieve economic and reliability gains in the power grid has been proposed some time ago. This approach did not gain much attention until recently when large penetration of renewable generation created incentives to use transmission line switching to control sudden changes in power flows and mitigate contingencies caused by the generation variability. This paper explores implementation issues related to circuit breaker (CB) monitoring, relay setting coordination and detection of relay misoperations in the context of the topology switching sequence implementation. The paper covers risk-based assessment of CB status needed for determination of reliable switching sequences; it indicates how relay settings may be changed due to switching actions; it also provides an on-line algorithm for detection of relay misoperations, which identifies the lines that may be switched back to service after being trip erroneously by a relay.

Security-based circuit breaker maintenance management

Circuit breakers play a vital role in maintaining system security since their malfunctioning could result in further component outages and may lead to the insecure operating conditions. This paper proposes a new approach for identifying the most risky circuit breakers using the condition-based monitoring data and security-based impact evaluations. For a given substation configuration, those circuit breakers which cause line outages due to mal-operation during contacts opening are identified and analyzed. The security oriented risk indices taking into account both voltage violations and overloading conditions as the consequence of circuit breaker mal-operations are proposed. A new breaker maintenance prioritization scheme based on the risk factors is elaborated. The proposed security-based risk framework is deemed to be an efficient approach in both breaker maintenance planning and identification of the breakers which are unreliable for reconfiguration plans. The presented methodology is investigated and verified on the IEEE 14-bus test system.

Assessing circuit breaker life cycle using condition-based data

How to make decisions to optimally allocate the resources by deciding when to perform maintenance on power apparatus is a critical issue, especially with present economic scenario in power industry. This paper proposes a new approach to assess the circuit breakers life cycle or deterioration stages using its control circuit data. In this approach, the “classical” healthy, minor and major deterioration stages have been mathematically defined by setting up the limits of various performance indices. The model can be automatically updated as the new real-time condition-based data become available to assess the CBs operation performance using probability distributions. The methodology may also be used to quantify the effect of maintenance making use of the defined performance indices, which further helps in developing system-wide risk-based decision approaches for maintenance optimization. Case studies using field data recorded at different times during operations of circuit breaker are presented at the end.

Novel approach for the design of state feedback power system stabilizers

Several researchers have shown in the literature that the state feedback power system stabilizers possess superior control capabilities when compared to the conventional lead-lag power system stabilizers. However, power system state variables are generally not measurable, especially the generator rotor angle measurement is not available in most of the power plants. In multi machine systems full state feedback controllers require feedback of other machine states as well. This makes the state feedback designs impractical. This paper utilizes the recently proposed modified Heffron Phillips model, which is derived by taking the secondary bus voltage of the step-up transformer as reference instead of the infinite bus, for the design of state feedback controllers so as to eliminate the drawbacks of existing state feedback designs. Here a linear quadratic regulator has been designed as state feedback controller. The performance of the proposed controller has been evaluated on a single machine infinite bus system over a wide range of system and operating conditions. It has been observed that the performance of the proposed controller is much better than the conventional PSS.

Parareal in Time for Fast Power System Dynamic Simulations

Recent advancements in high-performance parallel computing platforms and parallel algorithms have significantly enhanced the opportunities for real-time power system protection and control. This paper investigates application of Parareal in time algorithm for fast dynamic simulations. Parareal algorithm belongs to the class of temporal decomposition methods which divide the time interval into sub-intervals and solve them concurrently. Time-parallel algorithms face the difficulty of providing correct initial conditions for all the sub-intervals which impact the convergence rates. Parareal overcomes this difficulty by using an approximate trajectory. It has become popular in recent years for long transient simulations (e.g., molecular dynamics, fusion, reacting flows). This paper presents an approach for reliable implementation of Parareal with detailed models of power systems including saturation. Windowing approach is proposed for improving the convergence. Parareal is compared with the Newton-based time-parallel method. Effectiveness of the algorithm is analyzed by parallel emulation using extensive case studies on 10-generator 39-bus system and 327-generator 2383-bus system for various disturbances. Parareal with simulation windows of 1 s have shown convergence in 1 to 3 iterations for majority of the simulated cases, irrespective of the size of the system and nature of the disturbance. All the cases tested have converged with the proposed implementation.

New approach for the design of pole placement power system stabilizers

Pole placement power system stabilizers (PSS) are well known for their superior performance when compared to the conventional lead-lag stabilizers. They require feedback of all the state variables which are generally not measurable. In multi machine systems pole placement designs require feedback of other machine states as well. This paper proposes a new approach for the pole placement based PSS. In this paper, recently proposed modified Heffron Phillips model is used for the PSS design. It is derived by taking the secondary bus voltage of the step-up transformer as reference instead of infinite bus. State variables of this model are locally measurable, which makes the pole placement design decentralized. The performance of the proposed controller is evaluated on a single machine infinite bus system over a wide range of operating conditions. The proposed PSS performance is found to be better than the conventional PSS.

Application of Adomian Decomposition for multi-machine power system simulation

In this paper, the merits of Adomian Decomposition Method (ADM) have been investigated for the time domain simulation of multi-machine power systems. ADM is an analytical approximation method for the solution of linear, nonlinear, deterministic and stochastic operator equations. It approximates the nonlinearities in the equations using Adomian polynomial series and that can form a rapidly convergent sequence of analytic functions. We apply the ADM approach for simulation of differential algebraic equations representing the detailed multi-machine power system. The ADM approach has been applied on the widely used IEEE 3 generator 9 bus system and IEEE 10 generator 39 bus system for 3 - φ fault simulations. In our simulations we found that the ADM approach is faster than the standard trapezoidal time integration method for the comparable accuracy.

Power system stability enhancement using a STATCOM with ESS

This paper describes the use of a STATCOM with Energy Storage System (ESS) to improve the small signal stability of power systems. The ESS considered is a wind farm based Permanent Magnet Synchronous Generator (PMSG) along with an AC/DC converter that is connected to a standard STATCOM. With this configuration of STATCOM/ESS extremely effective control strategies for modulation of reactive and active powers can be devised to improve transient and dynamic stability limits of the system. In this paper this is demonstrated by computer simulation studies on a SMIB model equipped with a STATCOM-ESS combination.

Power System Stability enhancement by Single Network Adaptive Critic Stabilizers

This paper proposes a Single Network Adaptive Critic (SNAC) based Power System Stabilizer (PSS) for enhancing the small-signal stability of power systems over a wide range of operating conditions. SNAC uses only a single critic neural network instead of the action-critic dual network architecture of typical adaptive critic designs. SNAC eliminates the iterative training loops between the action and critic networks and greatly simplifies the training procedure. The performance of the proposed PSS has been tested on a Single Machine Infinite Bus test system for various system and loading conditions. The proposed stabilizer, which is relatively easier to synthesize, consistently outperformed stabilizers based on conventional lead-lag and linear quadratic regulator designs.