Protective relays and trip units the term switchgear is used to describe coordinated devices used for control and protection of equipment such as generators, transformers, capacitor banks, motors, and distribution lines. The functions of electromechanical protection systems are now being replaced by microprocessorbased digital protective relays, sometimes. The program can handle the online calculations and make the decision accordingly. The micro51 operates from conventional 5a or 1a secondary current transformers. Microprocessor based protection relays, document number. This is the book protective relay principles, by anthony m. The third edition of protective relaying, principles and applications. Abb microprocessor based protective relays traditionally have control capabilities in forcing physical devices attached to the relay, but there was no method to force analog readings, to verify database mapping integrity. One can deduce that the execution order plays a significant role when designing logic in relays that provide multiple functions in a single relay. Lewis blackburn, the fourth edition retains the core concepts at the heart of power system analysis.
The logic dictates how the relay will perform its main duty of protecting the electrical system. Management, microprocessor relays, ied, protection and control. A unit can perform retransmission of several systems. In spite of the developments of complex algorithms for implementing protection functions the microprocessor based relays marketed in the 1980s did not incorporate them. Another important advantage of the microprocessor based relay is that a microprocessor unit can perform the retransmission operation of several systems. Ieee guide for protective relay applications to distribution lines ieee std c37. A big difference between conventional electromechanical and static relays is how the relays are wired.
Microprocessor relays are computer based and use programmable logic. The main advantage of this relay is that it is programmable. Protective relays work in concert with sensing and control devices to accomplish their function. Discusses alternative non microprocessor based protection relays, and problems related to international standards. Abstractphase and ground directional elements are relied on for fast and secure protection throughout the power system. The relay is selfpoered from the current, therefore, there is no continuous drain on. He is also the author of the relay testing handbook series and founder of valence electrical training services. Understanding microprocessor relay logic basic digital. The functions of electromechanical protection systems are now being replaced by microprocessorbased digital protective relays, sometimes called numeric relays. The digital protective relay is a protective relay that uses a microprocessor to analyze power system voltages, currents or other process quantities for the purpose of detection of faults in an electric power system or industrial process system. In digital relay microprocessors and micro controllers are used in replacement of analogue circuits used in static relays to implement relay functions. It is the goal of this paper to present the reader with some background material and discussions by which they can. However, during the past 1520 years, there has been a widespread displacement of emr by microprocessor based relay protection devices gurevich, 2012.
I have read the most popular book on the subject written j lewis blackburns book and it is ok. Tests of microprocessorbased relay protection devices. Types and revolution of electrical relays introduction. Microprocessorbased digital protection relays now emulate the original devices, as well. Continuing in the bestselling tradition of the previous editions by the late j. Useful for centrally coordinated backup protection. However i have read another book on the subject titled protective relay priciples written by anthony sleva and i have to say that this is the best that i. The present era with microprocessor based relays started in the beginning of the 1980s, where microprocessor performed the logics, but the filtering was analogue. Problems and solutions 337 examining the relay s reaction in supplying the signal to them. Protective relaying is a vital part of any electric power system. This is either programmable or fixed based on the relay. Microprocessorbased relays provide technical improvements and cost savings in several ways. This book contains information obtained from authentic and highly regarded sources. The mp4000 motor relay may be applied to any size motor at any voltage level.
Power system protection part power system protection. Novel applications of a digital relay with multiple setting groups. Microprocessor based distribution relays contribute to improved reliability and reduced costs on electric power systems. Protective relays, associated communication systems, voltage and current sensing devices, station batteries and dc control circuitry. On closer examination it turns out that the microprocessor based relay is a small computer in which the output circuits usually builtin ct or vt fig. This paper evaluates the performance of a transmission line protection scheme using microprocessor based protective and electromechanical relays using discrete components. In addition to customizing specific microprocessor based relay capabilities, skilled integration engineers can also help utilities and industrial facilities design their microprocessor based relay protection systems in such a way as to fully leverage the inherent benefits of the relays and maximize each relay s value. Time coordination curves tcc and coordination 73 chapter 3. Operation and maintenance of protective relays and associated. Microprocessor relays are computer based systems that utilize software based protection algorithms for the detection of electrical faults. Users have become accustomed to the electromechanical relays ability to last 50 plus years and this has strained the expectations of microprocessor based relays.
When microprocessor relays began to be applied in the. Schwartz, schweitzer engineering laboratories, inc. Positions currently this protective relay principles, by anthony m. In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker.
However, such technology will be completely superseded within the next five years by numerical relays. Microprocessor based relays, also called digital relays, have a proven track record of reliability, with over 100,000 relay years of field experience. The digital processing by microprocessor gives several abilities to the protective system such as combinational logic, use of online processing of variables, programmable features etc. For example, if a fault is detected, the protective relay will. Thus various advantages of microprocessor based relay are. The cutlerhammer mp4000 motor protection relay by eaton corporation is a multifunctional microprocessor based protective relay for the protection of threephase ac motors. Integral to microprocessor based relay tc2 cc in1 breaker status input in2 trip circuit monitor input optional tc1 breaker trip coil 1 tc2 breaker trip coil 2 cc breaker close coil out1 protective relay trip contact out2 protective relay. Protective relay principles focuses on probable power system failure modes and the important characteristics of the protective relays used to detect these postulated failures. It is most commonly used on large, medium voltage threephase induction motors.
Sel products, systems, services, and training make electric power safer, more reliable, and more economical. Life expectancy of microprocessor based protective relays ied krisys electrical 14 feb 18 06. Mohamad tawfeeq types of relays the main types of protective relays are summaries in the following diagram. Principles and applications has been the goto text for gaining proficiency in the technological fundamentals of power system protection. Attracted armature solid computerized state digital relays plunger type magnetic induction. Protective relays are of three different technology eras, electro mechanical, electronic and microprocessor based electromechanical relays installed up to 1983 with a 30 year life expectancy electronic relays installed 1980 through 1995 with 15 to 20 year life expectancy. The increased growth of power system both in size and complexity has brought about the need for fast and reliable relays. Micro51 microprocessorbased overcurrent relays are used for phase and ground overcurrent protection in utility, industrial and commercial electrical power systems. Understanding microprocessor relay logic basic digital logic. A digital protective relay may also be called a numeric protective relay.
Pdf microprocessorbased overcurrent relays researchgate. The analog readings are stored in the modbus protocol. Abstract microprocessor based protective relays have been widely used to. Numerical relays protection and control products for. Ieee guide for protective relay applications to power transformers. Sel provides complete power system protection, control, monitoring, automation, and integration for utilities and industries worldwide. In practice it has turned out that most mpds simply do not sense the substitution of the whole printed board of one kind for the board of other kind which is not compatible with relay current settings. Digital relays are the functional replacements for electromechanical protective relays and may include many protection functions in a single unit, as well as providing metering, communication, and selftest. The worlds first commercially available digital protective relay was introduced to the power industry in 1984. The question arises if the microprocessor based protection device is a relay in the full sense of the word. This transition from the electromechanical to the numerical relays can be justified by the large flexibility and the wonderful features such as. Operation and maintenance of protective relays and associated circuits previously titled. This video discusses how you can convert the digital relay logic found in microprocessor based relays and translate that. Microprocessorbased protective relays applications in.
The book presents useful new concepts in a way that is easier to understand because they are equally relevant to older, electromechanical and solidstate relays, and. Abstractthis report covers issues concerning the security of electronic communication paths to protective relays. This paper describes a novel design of an electrical protection relay using microprocessor. For microprocessor based relays, the cycle time is how frequently a function is performed or executed. A proposed scheme of overcurrent relays dealing with programming of the singleboard microcomputer tk85, built by nec around intels 8bit 8085 microprocessor, is described. With the development of economical, powerful and sophisticated microprocessor, there is a growing interest in developing microprocessor based protective relays which are more flexible because of. Microprocessorbased protective relays deliver more. Excerpts from masons book the art and science of protective relays. Discussions in this book are based on indian standards mentioned here in under.
Microprocessorbased distribution relay applications. Numerical relays are based on the use of microprocessors. Relay information type, part number, style, and instruction manual. Now, microprocessor based digital relays are becoming the norm for new installations and many replacements, because of their improved protective capabilities, reliability, and additional features. Ieee buff book ieee recommended practice for protection and.
The relays use programmable logic to reduce and simplify wiring. Fundamentals and improvements for directional relays. Life expectancy of microprocessorbased protective relays. Commissioning microprocessor based ied communication. Siprotec 7sj61, 62, and 63 are microprocessor based protective relays designed to provide. Download pdf protective relay principles, by anthony m. Operation and maintenance of protective relays and. Under normal power system operation, a protective relay remains idle and serves no active function. In addition, microprocessor based relays have a builtin feature for measuring phase angles and computing the busbar frequency from the. The relays provide protection for bus faults, breaker failure, and highside transformer blown fuse detection at. Life cycle considerations for microprocessor relays. The function of protective relaying is to cause the prompt removal from service of an element of a. Focusing on practical solutions, this book explains how to correctly choose digital relays and ensure their proper use while avoiding the. It also covers power system, transformer protection and zone of protection.
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