Practical Power Distribution for Industry (Jan de Kock and Cobus Strauss) better appreciation of the role played by power system protection systems. Fundamentals of Power System Protection Y.G. Paithankar Formerly High- Frequency Trading: A Practical Guide to Algorithmic Strategies and Trading. Presents. Practical Power Systems Protection for. Engineers and Technicians. Revision Website: billpercompzulbe.cf E-mail: [email protected]
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Introduction to Practical Power System Protection. 7. Reliability. Above all else, relays must be reliable, both dependable and secure. This definition of reliability. Description. Plant operators, electricians, field technicians and engineers will gain a practical understanding of the role and workings of power system protection. emphasis throughout the book is on giving the reader an understanding of power system protection principles. The numerous practical details of relay system.
For parts of a distribution system, fuses are capable of both sensing and disconnecting faults. Failures may occur in each part, such as insulation failure, fallen or broken transmission lines, incorrect operation of circuit breakers, short circuits and open circuits.
Protection devices are installed with the aims of protection of assets, and ensure continued supply of energy. Switchgear is a combination of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment.
Switches are safe to open under normal load current, while protective devices are safe to open under fault current. A single such device can replace many single-function electromechanical relays, and provides self-testing and communication functions. Protective relays control the tripping of the circuit breakers surrounding the faulted part of the network Automatic operation, such as auto-re-closing or system restart Monitoring equipment which collects data on the system for post event analysis While the operating quality of these devices, and especially of protective relays, is always critical, different strategies are considered for protecting the different parts of the system.
Very important equipment may have completely redundant and independent protective systems, while a minor branch distribution line may have very simple low-cost protection.
There are three parts of protective devices: Instrument transformer : current or potential CT or VT Circuit breaker Advantages of protected devices with these three basic components include safety, economy, and accuracy. Economy: Relays are able to be simpler, smaller, and cheaper given lower-level relay inputs.
Accuracy: Power system voltages and currents are accurately reproduced by instrument transformers over large operating ranges. Types of protection High-voltage transmission network Protection on the transmission and distribution serves two functions: Protection of plant and protection of the public including employees. At a basic level, protection looks to disconnect equipment which experience an overload or a short to earth.
Some items in substations such as transformers might require additional protection based on temperature or gas pressure, among others. Generator sets In a power plant, the protective relays are intended to prevent damage to alternators or to the transformers in case of abnormal conditions of operation, due to internal failures, as well as insulating failures or regulation malfunctions.
Such failures are unusual, so the protective relays have to operate very rarely.
If a protective relay fails to detect a fault, the resulting damage to the alternator or to the transformer might require costly equipment repairs or replacement, as well as income loss from the inability to produce and sell energy.
Overload and back-up for distance overcurrent Overload protection requires a current transformer which simply measures the current in a circuit.
There are two types of overload protection: instantaneous overcurrent and time overcurrent TOC. Instantaneous overcurrent requires that the current exceeds a predetermined level for the circuit breaker to operate.
TOC protection operates based on a current vs time curve. Based on this curve if the measured current exceeds a given level for the preset amount of time, the circuit breaker or fuse will operate. Earth fault "ground fault" in the United States Earth fault protection again requires current transformers and senses an imbalance in a three-phase circuit.
Furthermore, it serves as a reference guide for solving application problems. For the new edition all contents have been revised, extended and updated to the latest state-of-the-art of protective relaying. Understanding how protection functions is crucial not only for equipment developers and manufacturers, but also for their users who need to install, set and operate the protection devices in an appropriate manner. After introductory chapters related to protection technology and functions, Digital Signal Processing in Power System Protection and Control presents the digital algorithms for signal filtering, followed by measurement algorithms of the most commonly-used protection criteria values and decision-making methods in protective relays.
A large part of the book is devoted to the basic theory and applications of artificial intelligence techniques for protection and control. Fuzzy logic based schemes, artificial neural networks, expert systems and genetic algorithms with their advantages and drawbacks are discussed.
AI techniques are compared and it is also shown how they can be combined to eliminate the disadvantages and magnify the useful features of particular techniques. The information provided in Digital Signal Processing in Power System Protection and Control can be useful for protection engineers working in utilities at various levels of the electricity network, as well as for students of electrical engineering, especially electrical power engineering.
It may also be helpful for other readers who want to get acquainted with and to apply the filtering, measuring and decision-making algorithms for purposes other than protection and control, everywhere fast and on-line signal analysis is needed for proper functioning of the apparatus. Fundamentals of Power System Protection by Y. Paithankar The electrical power system is a highly complex dynamic entity.
One malfunction or a careless set relay can jeopardize the entire grid. Power system protection as a subject offers all the elements of intrigue, drama, and suspense while handling fault conditions in real life. Anderson, a noted expert on power systems, presents an analytical and technical approach to power system protection.
His discussion shows how abnormal system behavior can be detected before damage occurs, and points to effective control action to limit system outages.
This essential reference work provides new and advanced concepts for understanding system performance. Power System Protection. Voltage amplitude quality takes into account persistent RMS value, flicker, and intermittent dips and peaks, as well as momentary and long-term outages. Frequency changes at most a few hundredths of a hertz, unless the power system has lost generation control. Induction motors have the most sensitivity to power system frequency.
Waveform purity is largely a function of harmonic content and is predominantly influenced by load. The quality of electrical power is an issue for loads that are sensitive to momentary outages and harmonics.
In the past, when loads were primarily resistive and inductive, harmonics were either inconsequential or nonexistent. Also, momentary outages had little effect on residential Introduction to Practical Power System Protection 4 customers. Commercial and industrial customers compensated for momentary outages either with multiple feeds from the utility power sources or with local generation. Today, every residential customer knows that there was an outage whether she or he was home to experience it.
Outages affect home computers and the digital clocks on VCRs, microwave ovens, and other numerous appliances. Although the inconvenience may seem trivial to the relay engineer and perhaps the actual number of outages is even less than in years past, the customer may perceive that the power system is not as reliable today. Good relay selectivity is key to reducing the number of outages and faster relaying minimizes the duration of power dips.
Hence a substantial component of poer quality is not tripping unnecessarily. Instrumentation distortion is usually caused by saturation from excessive inputs or remnant flux. Breaker failures or faults in the dc controls can cause control failures. Relay equipment reliability depends on design and manufacturing processes. In addition to overlapping zones of protection, both redundant and backup protection increase reliability for critical applications. Improper settings render relay systems useless.
Hence protection systems designers must know which relay is best suited for a particular application and how to set the relay parameters to obtain the proper selectivity and sensitivity. Proper relay application is the single most important factor in the quality of power system protection. Continuous Improvement Power systems are not static networks. Transmission lines and generators are continuously put into or taken out of service. Each change in the network potentially affects the operations of protective relays.
Protection engineers must decide how to alter the relay settings to compensate for a change in the power network configuration. Many modern computer based relays allow multiple setting which can be automatically selected depending on system conditions.
Analysis of Data Each fault tests the power system relays in the vicinity of the fault and presents an opportunity to analyze the behavior of the entire protection system.
The fault location, type of fault, fault impedance, and relay sensitivity determine which relays respond to the fault. Relays either operate correctly including in a timely manner or incorrectly including too slowly or too quickly. Microprocessor-based relays can now report information that provides the data to determine just how correct the operations were.
Prior to microprocessor-based relays, oscillographs and sequential events recorders were used to determine the correctness of operations. Chapter 6 provides examples of this type of analysis.
Economics of Protection Plant equipment represents a significant investment to electric utilities. Figures from a representative utility that has a significant amount of hydro-based generation show that 50 percent of the plant investment is allocated to production, 14 percent to transmission, and Introduction to Practical Power System Protection 5 27 percent to distribution.
In actual year dollars for a moderately sized utility, the investment in transmission and distribution alone is over one billion dollars. The cost of protection equipment is but a very small part of this investment. If the relaying scheme includes pilot protection, the cost of the communications is an additional expense.