Abstractline current differential protection creates challenges for relay design and application. The differential protection used for power transformers is based on merzprize circulating current principle. Jun 08, 2019 the relays used in power system protection are of different types. The opposite polarity convention can also be used if it is applied to all cts in the differential zone. Bus protection considerations for various bus types.
If a through fault results in one set of current transformers saturating before another, the zone differential protection will see a false operate current and may false trip. Vectorial correction virtual interposing ct virtual interposing ct. Use the sel311l line current differential relay with integral fourzone distance backup for easytoapply, highspeed line protection. Line current differential protection relay electrical. Line differential protection substation automation protection and. The protection for internal fault in such type of transformer is to be provided by using differential protection system. Red650 line differential protection substation automation. This is simply a differential protection scheme applied to feeders. Modern line current differential protection solutions schweitzer.
A new approach to current differential protection for transmission lines m. Advanced differential offers a set of modules for testing differentialschemes. Current transformers in a differential scheme must be chosen to have nearidentical response to high overcurrents. Differential protection is based on kirchhoffs laws, stating that all current into a network node shall add up to 0 in an ideal system.
Pdf application of distance and line current differential relays in. Modern line current differential protection solutions. For generator differential protection, one set of current transformers ct are located on generator neutral side, whereas second set of ct is located on generator phase side. Principles of differential relaying my protection guide.
The relays used in power system protection are of different types. Among them differential relay is very commonly used relay for protecting transformers and generators from localised faults. From a design perspective, the distributed nature of the line cur. Line current differential protection current differential protection is based on kirchhoffs current law, which states that the sum of all measured currents that make up a protected zone must equal with zero,the protected zone being defined by the location of current transformers cts. Current comparison relays with associated communication media current differential line protection current differential relaying is a method of extending the benefits of differential protection as applied to transformers, buses or generators to the protection of transmission lines. A design scheme of line current differential protection. Current differential line protection applications current differential line protection is a fundamentally different scheme than the directional comparison line protection schemes, which brings with it both advantages and disadvantages. The increased use of current differential protection and developments in. Current differential line protection setting consideration. The difference in the current can operate the differential protection relay. Differential protection protection of transformer, motor. 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.
The relay is adapted for the protection of overhead. Line differential protection psl 6603u product guide. The relay also features current based protection functions for remote backup for downstream protection relays and local backup for the line differential main protection. This video outlines the basic principles behind differential protection and is a sample of the full 2. Under normal working condition, the two currents at both ends are equal and pilot wires do not carry any current, keeping relays inoperative. Pdf line protection in breakerandahalf configurations requires main protection functions to respond to the sum of the two currents. If a fault exists on the protected bus, the currents will add in the relays, but if.
An alternative principle for line protection that is quickly becoming the norm is differential protection. Partial differential relaying sums the currents entering or leaving a switchgear bus through main and tie breakers. Abstractparalleling current transformers cts is a common practice in differential or line protection applications where the number of cts exceeds the number of relay current inputs. It is assumed with these schemes that a certain degree of ct saturation is possible under throughfault conditions. Transmission line protection principles 9 time synchronized between the line ends for the differential calculation to be correct.
Fundamental overcurrent, distance and differential protection. The siprotec 7sd82 line differential protection has been designed particularly for the costoptimized and compact protection of lines in mediumvoltage and highvoltage systems. From a design perspective, the distributed nature of the line current differential system imposes limits on the amount of data that can be exchanged between the system terminals and calls for data. The aim of this this technical article is to cover the most important principles of four fundamental relay protections. Protection of power lines, differential protection, adaptive differential protection, incremental currents. Communications asymmetry leads to current differential protection relay misoperation by causing relays at either end of a power line to sample load current waveforms at different moments in time. Line current differential protection free download as powerpoint presentation. A practical approach to line current differential testing karl zimmerman and david costello, schweitzer engineering laboratories, inc. Abstract power line, a reliable decision can be made wheth the classical differential protection may maloperate during severe external faults due to the saturation of current transformers.
Pdf line current differential protection creates challenges for relay design and application. Abstractline current differential 87l protection of transmission lines is preferred because of its speed, sensitivity, security, and selectivity. Modern line current differential protection solutions ieee xplore. Differential relays are very sensitive to the faults occurred within the zone of protection but they are least sensitive to the faults. In order to apply the lcdp algorithm to a real project, the. Sep 08, 2016 general scheme of differential protection 6. Paralleling cts for line current differential applications. Provides line current faults and differential protection to power lines. In this type of protection the electrical quantities entering and leaving the protected zone or area are compared by current transformers c. The 87l function of the sel411l provides protection for any transmission line or cable with as many as three terminals over serial communications and as many as four ter minals over ethernet communications, in threepole or singlepole tripping modes.
Communications is an integral piece of a line differential relay, as the currents from one line terminal must be sent to relays at other line terminals to perform the differential calculation. As one of the core technologies of distributed feeder automation dfa, line current differential protection lcdp can locate faults quickly and accurately and have the ability to cope with multidirectional flow. Operation during internal and external fault conditions fig. In addition, this paper discusses protection applications for inline transformers where a transmission line terminates on a transformer and a single protection zone includes both the line and the transformer. When the communication channel is outofservice, the directional overcurrent or distance relays.
Sel311l line current differential protection and automation. Consider the comparison of the input and output current of the transmission line. In differential protection, cts are oriented so that a line drawn from the polarity mark to the protected equipment passes through the ct. Partial differential relaying powell industries, inc. Built on the industryleading ur platform, the multilin l30 transmission protection relay is a costeffective line current differential protection relay intended for subtransmission and medium voltage lines and cables providing reliable and secure operation even under the worst case power system conditions. Line differential protection siprotec 5 siemens siemens. Current balance differential protection voltage balanced differential protection 1. Jul 09, 2018 this video outlines the basic principles behind differential protection and is a sample of the full 2. It features line current differential operation as its main protection, with absolute selectivity, extremely high sensitivity and high operation speed. Siprotec protection relays figure 1 shows a simple differential protection scheme, also known as a merzprice scheme. Transmission line protection principles ge grid solutions. A failure in the line current differential hardware does not impact backup protection. The l90 line differential relay and the l60 line phase comparison.
The siprotec 7sd828687 line differential protection have been designed particularly for the selective protection of overhead lines and cables with singleended and multiended infeed in mediumvoltage and highvoltage systems. Alexander ge corporate ge power management research and development malvern, pa schenectady, ny updated and presented by subhash c. Principles of differential relaying current balance high impedance also known as unbiased differential protection only one actuating relay quantity current required for operation. A sensitive current element in series with the highimpedance element is calibrated in volts based on the voltage drop across the internal impedance. Synchronization errors show up as phase angle offset, where identical currents produce phasors with different phase angles, and transient errors, where changes. Product guide red615 line differential protection and control. The communication system and its impacts on line current. Conventional current differential protection needs to be set above ich to avoid tripping for 5060hz line charging current modern relays can extract ich to allow more sensitive current settings to be applied protection of transformer feeders. Also, if used, it should be noted that the line differential backup protection schemes are subject to the same type of complexities.
Application considerations when protecting lines with. Standard configurations d and e include directional overcurrent and voltage based protection functions. Sample specification, line differential protection red650 english pdf technical specification kema report of performance, function tests, 670 and 650 series version 2. The principles of differential protection you must understand. A practical approach to line current differential testing. Digital current differential relays power line carrier figure 1. With its flexibility and the powerful digsi 5 engineering tool, the siprotec 7sd82 device offers futureoriented system solutions with high investment security and low. 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. This is especially true of line current differential applications applied to breakerandahalf and ringbus configurations.
Use single or dual differential channels for reliability. Line current differential protection creates challenges for relay design and application. The principles of differential protection you must. If the magnitude of the input current of the transmission line is more than that of output current that means the additional current flows through it because of the fault. Abstractcurrent differential relay plays a very important role in transmission line protection because of its absolute selectivity for isolating the failure equipment.
Differential protection is based on kirchhoffs laws, stating that all current into a. Relay are both phasesegregated, current only relays. Differential protection schemes are mainly used for protection against phasetophase fault and phase to earth faults. Mohammed tawfeeq alzuhairi 321 differential protection differential protection is the best technique in protection. However, lcdp algorithm has high requirements for communication speed, and is sensitive to communication quality. Line differential protection substation automation. Patel ge power management malvern, pa presented at the electric council of new england. The highimpedance input is created by an internal impedance, typically resistive, of 2000 ohms or higher. Figure 1 shows a simple differential protection scheme, also known as a merzprice scheme. Apply subcycle current differential protection with included fourzone distance and directional overcurrent backup. Pdf sel311l line current differential protection and. Current differential line protection current differential relaying is a method of extending the benefits of differential protection as applied to transformers, buses or generators to the protection of transmission lines.
A new approach to current differential protection for. As a unit protection having its zone delimited by location of current transformers cts, the differential protection principle is considered superior. Pdf line current differential protection automation and. Line current differential relay response to a direct. Although nowadays differential protection is achieved numerically, in order to understand the principles of differential protection it is useful to analyze the ubiquitous electromechanical relay. Pdf on feb 16, 2018, hank miller and others published modern line current differential protection solutions find, read and cite all the research you need on researchgate. A collection of technical papers representing modern solutions normann fischer on. Line current differential protection automation and control system. In this simple scheme, we can assume that under normal operating conditions, the current entering into the piece of equipment under protection is equal. There are two basic types of differential protection.
Differential protection what goes in must come out. Jun 23, 20 in differential protection scheme, the current entering at one end of the line and leaving from other end of the line is compared. This paper discusses a unique new approach to numerical current differential line protection that offers improved performance over the conventional percentage. Protective relays, associated communication systems, voltage and current sensing devices. Line current differential protectionapply single or threepole subcycle differential protection. Differential protection electrical impedance relay. Transformers and compensating coils in the protection range are also possible.
Pdf modern line current differential protection solutions. A new method of line differential protection enhanced by. Protection relays differential relays b high impedance differential protection. A vector ratio of the local and remote phase and sequence currents provides highspeed protection independent of line loading, ct saturation, or tapped load. The principles of differential protection you must understand on photo. L to limit current through relay to line may affect line current differential protection schemes if outfeed conditions occur during internal line faults. Overcoming asymmetrical communication delays in line. Channels traditionally used for line current differential. The protection system should be set to operate in the presence of the outfeed condition. The sel311l relay implements line current differential protection using communications interfaces, a processor, and contact outputs separate from those used for backup protection and control. This book addresses the design and application of line current differential 87l protection, communications. Protection functions bias differential protection 87 harmonic restraint protection over fluxing i.
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