Harsha V. Padullaparti

Advances in volt-var control approaches in utility distribution systems

In recent years, voltage and reactive power control in distribution systems is becoming increasingly complex with the growing penetration levels of distributed energy resources (DER), electric vehicle loads, and new requirements like conservation voltage reduction (CVR). Traditional approaches of voltage control rely on slow acting electromechanical devices installed on the primary feeder. These approaches are not suitable for handling the changing paradigm in the distribution systems towards smart grid. Advanced volt-var control technologies like smart inverters and other distributed secondary-side voltage regulation devices are perceived to be the key enabling technologies to meet the requirements of future smart grid such as effective voltage control and ability for seamless integration of DER. This paper reviews existing and emerging volt-var control techniques in the distribution systems with DER.

Analytical Approach to Estimate Feeder Accommodation Limits Based on Protection Criteria

Widespread deployment of large-scale photovoltaics (PVs) and energy storage systems (ESSs) in distribution networks necessitates the development of methods to assess their possible system impacts. One of the primary concerns related to the integration of these systems is short-circuit overcurrent protection problems. Present techniques use simulations of full and detailed distribution circuit models with a large number of scenarios to estimate the PV and ESS sizes a distribution feeder can accommodate without causing adverse impacts. As this process requires considerable time and effort, this paper develops a practical and simplified analytical approach to conservatively estimate a utility distribution feeders accommodation limits without causing protection problems. Sympathetic tripping and relay insensitivity problems are considered in this paper under both symmetrical and unsymmetrical fault conditions. Using the analysis presented, the factors influencing these protection problems are determined to provide insights into relay settings. The feeder accommodation limits obtained using the proposed analytical approach are compared with those obtained using simulations of an actual detailed distribution circuit model. The findings show that the proposed approach is accurate in estimating the feeders accommodation limits for integrating large-scale PV and ESS.

Model-based relaying supervision for mitigation of cascading outages

Several major outages have been traced to the failure of remote backup protection elements in distance relays. Experience has shown that coordination of remote backup zones in stepped-distance protection can be vulnerable during stressed conditions. Furthermore, relay settings are typically biased for high dependability, resulting in lower security especially when several unexpected events coincide. An incorrect response by a relay during such a condition can trigger or propagate the disturbance. Therefore, a new framework for Model-Based Relaying is introduced to supervise and secure the operation of remote backup protection elements, such as Zone 3. The framework utilizes the fact that while a single relay can observe a 3-phase fault or stressed system condition with similar apparent impedances, other system parameters will be significantly different. Therefore, the framework proposes to include the capability in relays to quickly run circuit model simulations at the relay level. The proposed method aims to work in parallel with and supervise the conventional distance relays zone 3 for discrimination between 3-phase faults and stressed conditions using the output of local circuit model simulations. Several case studies are evaluated to demonstrate that dependability is not degraded for true fault conditions and security is enhanced for stressed system conditions.

Visualization of time-sequential simulation for large power distribution systems

Many graphical alternatives are useful to demonstrate critical characteristics of distribution systems such as voltage regulation or power flow. The visualization of electrical variables can also be an effective approach to analyze, compare and evaluate large-scale systems. However, visual analysis of large power distribution systems is increasing in complexity for operational and research purposes. In this paper, we show a proposed approach to take advantage of the statistical inference to visualize complex behaviors in time-sequential simulations. This method provides a meaningful representation to millions of simulation results that can be used for analysis and validation of smart grid strategies and devices. The visual examples show a fast identification of electrical phenomena obtained from the OpenDSS simulation of the EPRI Ckt24 test circuit. This approach can be applied to the volt-var control, topological reconfiguration, distributed generation management, storage control, and operation assessment among others.

Optimal placement of edge-of-grid low-voltage SVCs in real-world distribution circuits

This paper proposes a method to determine optimal locations to deploy edge-of-grid low-voltage static var compensator (SVC) devices in large real-world distribution circuits. The SVC device operation, characteristics, and modeling are also discussed. The optimization problem formulation developed in this work has the objective of mitigating undervoltage violations in the circuit using the minimum number of SVCs while improving the traditional voltage regulation device operations and circuit losses. Undervoltage area criterion is used to identify effective candidate locations and the binary particle swarm optimization (BPSO) algorithm with quasi-static time series (QSTS) simulations are used to determine the optimal SVC locations. The results show that the proposed method is effective in identifying the optimal SVC locations in large distribution circuits.

Supervision of power swing blocking using model-based distributed intelligence relaying framework

The power swing phenomenon is characterized by oscillations in power flow between two areas of a power system due to an abrupt imbalance in mechanical and electrical power. Unintentional operation of distance relays during power swings can propagate a disturbance and result in a cascading outage. It is therefore critical that relays operate securely under such conditions. Modern distance relays can provide a function for power swing blocking (PSB). However, the PSB settings can be difficult to calculate without extensive stability studies and may fail to block if the slip frequency is too fast. In this work, we investigate the application of a model-based relaying framework applied to power swing blocking. The framework is named Model-Based Distributed Intelligence (MBDI) because it integrates, at the relay level, real-time knowledge of the network structure and system state in the form of simulation circuit models. We investigate the efficacy of a relay equipped with MBDI to supervise PSB operation during power swing and fault scenarios.

Analytical approach to estimate distribution circuit's energy storage accommodation capacity

In the past few years, the integration of energy storage (ES) systems into power distribution networks has rapidly increased. Before deploying ES systems, it is imperative to estimate the largest ES capacity a given circuit can accommodate without resulting in any undesirable impacts on system operations. The obtained ES size is called circuits ES accommodation capacity. Since calculating ES accommodation capacity requires evaluating a large number of scenarios for multiple grid integration issues, simple analytical methods are called for. This paper develops circuit analysis based analytical methods to determine distribution systems ES accommodation capacities. The results obtained using the proposed approach are validated against those obtained using detailed three-phase distribution system simulations. We conclude that the proposed method accurately estimates ES accommodation limits. Moreover, since the approach is based on analytical calculations, it is easily scalable to larger distribution systems.