SELF HEALING

INTRODUCTION

Smart Grid is sophisticated, digitally enhanced power systems where the use of modern communications and control technologies allows much greater robustness, efficiency and flexibility than today’s power systems.
The American Electric Power Research Institute (EPRI), an advocator of building the smart grid, gave this grid a definition with self-healing, security, integration, collaborative, forecast, optimization and interaction. While European commission define it as : A grid which could support distributed and renewable energy access, supply more reliable and secure electricity, have a service-oriented architecture and flexible grid applications, possess an advanced automation and distributed intelligent, be able to local interact the load and the power, adhere to customer centric.
Obviously, these definitions has been formulated for the future of power industry mainly focusing on world today’s energy generation, transmission, distribution limitation & changing consumer trends. Recently world has observed a series of blackout, partial power failure and this compelled the world’s nations to go for an ideal grid system that is smart enough to face such kind of challenges. This has resulted the unification of power system with the information technology & modren telecommunition setup. And SELF HEALING become the key component of smart grid, as smart grid should possess an intelligent control funtion, which could rapidly isolate and self recover the fault, prevent the occurance of balckout and improve the reliability of grid operation with minimum human intervention & consume distributed generation too.

Background:

An especially illuminating event occurred in 1879 when Thomos Edison invented what is considered to be the precursor of modern light bulb. Three years later, in 1882, he flipped the first switch on the first electric grid in lower Manhattan. In less than 100 years, electricity became widely available. It is now delivered by means of expensive electrical grids on every continent on Earth, and is integral to various satellites that orbit her.
In the decades following this tremendous achievement, however, much of the electrical grid has grown old and outdated. Sadly, Edison would recognize much of the today’s installation. Too often, we find ourselves looking ahead toward the next technological evolution while our infrastructure is more than a century old.
This over exhausted and inefficient electrical grid has left the world susceptible to security threats; inhibited alternative energy/ conservation goals; and contributed to reliability goals such as power quality disturbances and blackouts. Smart grid is the solution we desperately need to solve many global energy problems. It is changing the way we think about and interact with our electrical grid.

Current Status:

Transmission
Today’s transmission grid was designed with many self-healing features. Auto‐reclosing and auto sectionalizing are common techniques employed to maintain service under adverse conditions. The mesh network design of the transmission system is inherently self‐healing due to its built‐in redundancy and such protective relaying features as high‐speed reclosing and single‐phase tripping.
System planners have historically modeled the transmission system to verify that, under a normal system configuration, assumed loads could be met even during expected peak conditions. In addition, planners ensured that these same loads could be met even with the failure of single, and in some cases, multiple lines or components.
Sophisticated protective relaying schemes are in place to monitor system conditions and take corrective action should specific parameters exceed limits. Transmission lines and equipment are relayed out (opened) when conditions require. Most loads normally are not impacted by a single transmission line fault because the system can tolerate such a contingency. Substation automation and new intelligent electronic devices have taken transmission protection to the next level. Some of today’s special protection systems and remedial action schemes (SPS/RAS) are obvious precursors of the intelligent agents that will be deployed throughout the grid. Their effectiveness is expected to be improved by frequent tuning from a higher level, as well as through better local analyses.
The design of the current transmission system has actually incorporated the notion of self‐healing for many years by implementing new technologies, processes, and techniques as they became available. Significant advances in digital control, protection, and communications technologies, correctly applied, will continue to improve this self‐healing capability.

Distribution:

At the distribution level, new distribution automation (DA) technologies are being deployed to increase reliability and efficiency. DA applications improve the efficiency of system operations, reconfigure the system after disturbances, improve reliability and power quality, and identify and resolve system problems. Many DA applications can also be extended to coordinate with new customer applications, such as demand response (DR), and distributed energy resources (DER). In addition, distribution systems that include feeder‐to‐feeder backup allow enhanced DA functionality. These new approaches are directionally consistent with the vision of the self‐healing characteristic of the smart grid.
However, from a self-healing perspective, the current distribution system has been limited by a significant lack of distributed resources and intelligent networking capabilities. Today most DA and substation automation (SA) systems are applied at a local level, using local information for decisionmaking. While the basic design of the integrated transmission grid—many geographically diverse generation sources feeding a high‐voltage, switchable, networked transmission system—is conducive to self‐healing, the fundamental design of today’s distribution systems does not accommodate a comparable depth of self‐healing.

Future with Self healing Technology in Smart Grid

The self-healing characteristic of the smart grid, at both the transmission and distribution level, will move beyond its current state by integrating enhanced capabilities that include the following features: Look-Ahead Features 1. Analytical computer programs, using many new and timelier system measurements, will identify challenges to the system, both actual and predicted, and take immediate automatic action to prevent or mitigate problems. Where appropriate, and when time allows, these algorithms will also provide options for the system operator to manually address such challenges. 2. Probabilistic risk analysis will identify threats to the system under projected normal operating conditions, single failures, double failures, and out‐of‐service maintenance periods. 3. Load forecasting will be greatly improved. These models will cover various time horizons—minutes, hours, and days in support of operations; monthly, quarterly, and annually to support operations and maintenance (O&M) planning activities; and longer range to support investment decisions. 4. Fast simulation & modeling (FSM) will enable look‐ahead capabilities to anticipate power system disturbances, while continually optimizing grid performance. FSM will: * Provide faster‐than‐real‐time simulations to avert previously unforeseen disturbances * Perform what‐if analysis for large‐region power systems * Integrate market, policy, and risk analysis into system models, and quantify their effects on system security and reliability.
Monitoring Features 1. Numerous intelligent sensors and communication devices will be integrated with power system control. Real‐time data acquisition, employing advances in communication technology and new, lower‐cost smart sensors, will provide a significantly larger volume and new categories of data, such as wide‐area phasor measurement information. This dramatic increase in the volume of real‐time data, combined with advanced data processing and visualization techniques, will give system operators a rapid grasp of the power delivery system’s health. Advanced metering infrastructure (AMI) systems will provide an additional new source of relevant distribution status information, including loadings, voltage profiles, harmonics, and outage conditions. 2. By analyzing equipment condition data, such as high‐frequency emission signatures, condition monitoring technologies will provide additional perspectives on the probability and consequences of potential equipment failures. 3. System state estimators will take advantage of advanced measurement and data acquisition technologies and powerful computers will enable them to solve problems in seconds or less. The availability of phasor information will make state estimators faster and more accurate. 4. Command and control centers at the regional level for transmission operations, and at more local levels for distribution operations, will serve as hubs for many new self‐healing features.

Protection and Control Features 1. Advanced relaying will be employed to communicate with central systems and adapt to realtime conditions. Line current differential relaying, enabled by high speed communications between high voltage (HV) stations, will increasingly replace older impedance schemes, providing more secure and reliable protection of transmission lines 2. Due to their “uncontrolled” nature, real and reactive power flows are often smaller than can be thermally accommodated, reflecting an underutilization of some transmission paths. Power transfer is governed by line impedance, voltage magnitude, and phase angle difference across a transmission corridor. Improved utilization of transmission lines will be realized through the broad deployment and dispatching of flexible AC transmission systems (FACTS) devices that can control each of these steady state flow parameters. 3. High‐speed switching, throttling, modulating, and fault‐limiting devices will dynamically reconfigure the grid. This will include faster isolation and sectionalization, as well as rapid control of power flows in response to dynamic system challenges. 4. Intelligent control devices, such as grid‐friendly appliances, will modulate load requirements in response to changing grid conditions. 5. Broadband communications between stations and from stations to control centers will allow wider areas to be protected as an integral unit. System integrity protection systems (SIPS), remedial action systems (RAS), and other wide area protection and control (WAPC) concepts will be more widely deployed as integral features of the new transmission smart grid. In particular, extensive phasor monitoring will provide cycle by cycle assessment of the grid’s dynamic performance. 6. The computing and communication systems of the self‐healing grid will employ a multitude of embedded processors scattered throughout the system that will communicate via standardized interfaces. They will employ control cycles that match relevant power system time constants.
Distribution Technology Features 1. Two‐way power flow at the distribution level will be made possible by new communications, protection, and control technology. Two‐way power flow is an essential feature of the distributed energy resource applications that help make a distribution circuit more robust. 2. Distribution management systems (DMS) will have the features that help operators process and analyze extensive new data streams and develop/implement optimal distribution control strategies:

These advances together will create a sophisticated self-healing capability that will dramatically improve overall reliability, efficiency, and safety and will also enhance resistance to a security attack. Barriers & Challenges

Major change usually faces substantial barriers for achieving a self-healing grid. 1. Financial Resources—The business case for a self‐healing grid is good, particularly if it includes societal benefits. But regulators will require extensive proof before authorizing major investments based heavily on societal benefits. Also, concerns about rapidly changing technology that may become obsolete within a few years can cause some regulators to hesitate to approve such investments. 2. Government Support—The industry may not have the financial capacity to fund new technologies without the aid of government programs to provide incentives. Smart grid funding in US is from the American Recovery and Reinvestment Act of 2009 (ARRA). 3. Compatible Equipment—Some older equipment must be replaced as it cannot be retrofitted to be compatible with the requirements of the self‐healing characteristic. This may present a problem for utilities and regulators, since keeping equipment beyond its depreciated life minimizes the capital cost to consumers. Early retirement of equipment may become an issue. 4. Speed of Technology Development—Specific areas that will need to be accelerated include the following: o An integrated, secure, reliable high‐speed communications platform; o Intelligent electronic devices (both front‐end sensors and back‐end control devices); o Distribution automation schemes to provide distribution‐level self‐healing capabilities that will accommodate all forms of DER and act as an asset to the transmission system; o Cost‐effective, environmentally‐acceptable DER, including micro grids and energy storage devices capable of existing among residential populations; o DR systems using real‐time pricing; o Advanced transmission protection schemes that provide rapid area‐wide response to system threats; o Tools to accommodate two‐way flow on existing distribution circuits; and o Advanced analytical tools. 5. Policy and Regulation—A new regulatory model should be considered that decouples delivery company profits from sales volume. Instead, a model that rewards achievement of the principal characteristics would accelerate smart grid progress, particularly in the area of self healing.

In Pakistan, power sector esp. distribution utilities have so for been neglected and politicized, resulting in a variety of system failures like:

• Poorly planned distribution networks
• Overloading of system components
• Lack of reactive power support and regulation services
• Low metering efficiency and bill collection
• Power theft These problems need to be solved for the economic growth of country. Regulatory changes are required for reduction in Aggregated Technical and Commercial Loss, improvement in Power Quality, Reliability of Power Supply, Improvement in Customer Satisfaction and rationalization of electricity tariff. Also financial frailty, coupled with public ownership of utilities and the related bureaucratic slowness, has made it very difficult for investors to take interest in Pakistan’s grid.

References:

1- Anticipates and Responds to System Disturbances (Self Heals) v2.0 2- Smart Grid—Building on the Grid (www.nema.org/smartgrid). 3- IEEE papers(The Application of Self-healing Technology in smart grid & The Self-healing Technologies of Smart Distribution Grid ) 4- http://www.oe.energy.gov/eac.htm 5- IEEE paper smart grid initiative for power distribution utility in India.