Application examples of overcurrent protection circuit. Phasetoground line distance protection testing 451. Simple percent differential 87 element testing 247 1. Overcurrent protection fundamentals r ced engineering.
Point list manual, iec 608705103 english pdf manual line differential protection and control red615 5. The course provides basic guidelines for overcurrent device coordination in radial systems. Numerical distance protection relay commissioning and. An overcurrent relay is a type of protective relay which operates when the load current exceeds a pickup value. Distance protection, line differential protection, and overcurrent protection for 3pole tripping, manual 3 c53000g5040c0109, edition 07. Phase distance protection function 21 distance protection to provide backup protection for system faults that have not been cleared by transmission system circuit breakers via their relays. Phasetophase line distance protection testing 425 6. Wells engineering has provided power system protection engineering for power system generation, transmission, distribution, and utilization levels. Assume the fault is a standard fault meaning voltage at fault point is zero. Introduction transformers are a critical and expensive component of the power system. Line differential protection modeling with co mposite current and volt age hamzah eteruddin 61 the relay commanded the breaker to trip at an equal period of time i. Alexander general electric co malvern, pa introduction distance functions have been in use for many years and have progressed from the original electromechanical types thr ough analog types and now up to digital types of functions. Nov 01, 2016 a differential relay is defined as the relay that operates when the phase difference of two or more identical electrical quantities exceeds a predetermined amount. Principles and characteristics of distance protection.
Power plant and transmission system protection coordination. The transformer energization resembles the condition of an internal fault. If the net difference equal zero, it means no fault exist. Distance protection, in its basic form, is a nonunit system of protection offering considerable economic and technical advantages. Note that this is a doubleended substation, with two main breakers and a tie breaker. The addition of directionality extends the application of overcurrent protection to looped lines. Distance protection relay is the name given to the protection, whose action depends on the distance of the feeding point to the fault. Unlike phase and neutral overcurrent protection, the key advantage of distance protection is that its fault coverage of the protected circuit.
Differential relays, 63 see also percentagedifferential relays directionalcomparison relaying, for bus protection, 277 principle of operation, 106 see also line protection with pilot relays directional control, of electromagnetic relays, 23 of singlequantity induction relays, 32,57,310,3 directionalovercurrent relay, 57. This video outlines the basic principles behind differential protection and is a sample of the full 2. The operating manual describes the basic principles and procedures for operating and assembling the. Line differential protection substation automation. The numerical distance protection relay used is rel 5112. Principles of differential relaying the restraint characteristic what needs to be realised is that the first one is properly termed the restraint characteristic rc whilst the latter is an operating characteristic. Generator differential protection function 87g and overall differential protection function 87u protection measures difference current in its associated zone. The time of operation of such protection is a function of the ratio of voltage and current, i.
Numerical relays protection and control products for power. To improve reliability, the generating plants, transmission lines, and substations of a highvoltage power system are interconnected to form a network. Overcurrent protection is when the fault current in the circuit reaches the action value of the current relay, the current of the current relay is set according to the requirements of the line selectivity. The magnetizing inrush current has significant 2nd harmonic content. An alternative principle for line protection that is quickly becoming the norm is differential protection. Differential protection, frame leakage protection the systems in which selectivity is relative are nonunit systems. The current differential relay compares the local currents with the remote currents to determine that the fault is inside the protection zone or not. Prot 403 provides an overview of the principles, schemes, and devices for protecting mediumvoltage distribution feeders and buses. A differential relay is defined as the relay that operates when the phase difference of two or more identical electrical quantities exceeds a predetermined amount. Numerical relays are based on the use of microprocessors. In a typical feeder oc protection scheme, what does the residual relay measure. Fundamental overcurrent, distance and differential. Voltage sag transient stability issues shock and arcflash hazards.
Tips and tricks to overcome common obstacles 209 chapter 10. As the oc elements are built as separate units, we may implement the overcurrent protection principles using. Residual neutral instantaneous overcurrent protection 209 6. Distance protection, line differential protection, and overcurrent protection for 3pole. Numerical distance protection relay commissioning and testing. The aim of this technical article is to cover the most important principles of four fundamental relay protections.
The advantages of the current differential protection scheme are. Differential protection is based on kirchhoffs laws, stating that all current into a network node shall add up to 0 in an ideal system. Understand basic protection principles overcurrent 50, 51, 50n, 51n directional overcurrent 67, 67n distance 21, 21n differential 87. Jun 01, 2019 overcurrent earth fault protection earthfault protection can be provided with normal overcurrent relays, if the minimum earthfault current is sufficient in magnitude. Why are sealin and 52a contacts used in the dc control scheme. Is there a typical standard on when to use distance protection as opposed to overcurrent protection. Overcurrent relay protection is given at b, c, d and e, that is, at the infeed position of each part of the electrical power system. The differential relay works on the principle of comparison between the phase angle. It also covers the application of negativesequence overcurrent and directional overcurrent protection in distribution systems. A differential protection relay is defined as the relay that operates when the phase difference of two or more identical electrical quantities exceeds a predetermined amount. Principle and applicaions of overcurrent protection circuit.
Each relay protection device comprises a definitetime delay overcurrent protection relay in which the trip of the current sensitive element starts the time delay device. The differential relay works on the principle of comparison between the phase angle and magnitude of two or. Impedance measurement derived from the quotient of generator terminal voltage divided by generator stator current. The differential relay works on the principle of comparison between the phase angle and magnitude of two or more similar electrical quantities. Modern line current differential protection solutions. What is the difference between overcurrent and distance. Strictly speaking the rc tells us how much current a relay will use to restrain based on the currents. This impedance between the relay and the fault depends on the electrical distance between them.
For example, a relay including function 51 would be a timed overcurrent protective relay. Overcurrent earth fault protection principle equation. We perform a series of endtoend tests on a normal transmission line with standard line distance protection and compare the results to a pott scheme to. Overcurrent relay protection can no longer be used because coordinating the relays becomes a difficult, if not impossible, task. Medium voltage products technical guide protection. Protection systems applied to these may be broadly classified as unit and nonunit protection systems.
Name two protective devices for what purpose is ieee device 52 is used. At wells engineering, we take pride in having the ability to provide highlevel problemsolving skills that render solutionbased results. The magnitude of earthfault current is usually low compared to the phasefault currents because the fault impedance is much higher for earthfaults than for phasefaults. Provides highspeed phase fault protection for the generator zone 87g and unit overall zone 87u coordination concerns none except to ensure overlaps are done correctly. L to limit current through relay to jul 09, 2018 this video outlines the basic principles behind differential protection and is a sample of the full 2. Overcurrent protection has found widespread use in distribution utility and industrial systems. Protection engineering consultants power system design. Fundamental overcurrent, distance and differential protection. Figure 1 advantages of distance over overcurrent protection. Partial differential relaying is a form of overcurrent relaying frequently used to detect main bus overcurrent faults and to back up feeder overcurrent relaying. Due to the long lead time for repair of and replacement of transformers, a major goal of transformer protection is limiting the damage to a faulted transformer. In distance protection, there are protection zones. Partial differential relaying powell industries, inc. Using distance protection vs overcurrent protection.
Overcurrent earth fault protection earthfault protection can be provided with normal overcurrent relays, if the minimum earthfault current is sufficient in magnitude. The suite of overcurrent elements 51, section 8 is generally considered backup transformer protection, or for protection of the bus and backup protection for the feeder relays. Abstractline current differential protection creates challenges for relay design and application. A big difference between conventional electromechanical and static relays is how the relays are wired. Home technical articles fundamental overcurrent, distance and differential protection principles essential protection principles the aim of this technical article is to cover the most important principles of four fundamental relay protections. Differential and overcurrent protection do not provide adequate protection for wyeconnected windings with grounded neutrals. When the vt returns to normal condition, the blocking of the distance protection will be deactivated, i. Numerical relays protection and control products for. Electromechanical and static relays have fixed wiring and the setting is manual. Differential protection is the best technique in protection. Im looking at a protection scheme in a 69kv switchyard and i notice that all of the outgoing 69kv transmission lines use distance protection but some of the outgoing lower voltage 12. Pdf line differential protection modeling with composite.
While setting parameters will differ depending on the type of current differential relay, the setting principles and system conditions to consider remain largely the same. Distance protection is comparatively simple to apply and it can be fast in operation for faults located along most of a protected circuit. This includes fundamentals of measuring distance to fault based on electrical signals from one end of the circuit. Current differential line protection setting consideration. Unlike phase and neutral overcurrent protection, the key advantage of distance protection is that its fault coverage of the protected circuit is virtually independent of source impedance variations. This relay testing book is our core handbook and is used by large organizations across north america in their training programs. Jan 04, 2015 we perform a series of endtoend tests on a normal transmission line with standard line distance protection and compare the results to a pott scheme to see how standard distance protection is. Fundamental overcurrent, distance and differential protection principles published on february 24, 2017 february 24, 2017 22 likes 1 comments. If no inhibiting mechanism is provided, the differential element will trip. Modern line current differential protection solutions hank miller and john burger, american electric power normann fischer and bogdan kasztenny, schweitzer engineering laboratories, inc. Distance protection v1, application note and setting guide english pdf. Differential pilot 87 overcurrent protection, the simplest and most economical of these principles, is limited to radial lines. It can also provide both primary and remote backup functions in a single scheme.
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