Distance relay or impedance relay working principle types. Application notes for kcgg high impedance protection. I want to know how a high impedance differential scheme. It is noteworthy here that in electrical engineering, the term impedance can be applied to resistance alone or reactance alone, or a combination of the two. You should read that post first before we dig deep into the calculations and considerations that explain how high impedance busbar differential schemes function. Connect your testset voltage channel across the relay ac input. Considerations for using highimpedance or low impedance relays for bus differential protection ken behrendt. These relays are known as distance relay or impedance relay. This relay consists of two units an overcurrent element and a currentvoltage directional element. High impedance bus differential relays are used on most of the busses in north america. Considerations for using highimpedance or lowimpedance. This principle is applied to bus protection in power system networks. There is one type of relay which functions depending upon the distance of fault in the line.
High impedance differential relaying ge grid solutions online store. Suitable relay settings and the selection of current transformers are. This can create extra time between the fault inception and the relay operation that doesnt happen with a solidstate, or singlefeature high impedance differential relay. Minnesota power prefeimpedance bus differential rs high87z protection systems.
Current transformers cts are installed to monitor all currents entering and leaving a bus. Practical considerations for high impedance restricted earth. Circulating current high impedance differential protection using 7sj8. The operation of the conventional over current relays either direction or non directional, depend on the magnitude of current or power in the protected circuit, where as the distance protection relay operate on the principle of the ratio of applied voltage to current in that circuit. Many relays use an electromagnet to mechanically operate a switch, but other operating principles are also used, such as solidstate relays. The operating level of the high impedance relay is to be set to the lowest value not giving operation caused by faults outside the zone. Impedance relay is protection relay which functions depending upon the distance of fault in the line. Applying highimpedance differential busbar protection. Application notes for kcgg high impedance protection introduction the application of the kcgg numerical overcurrent relay as differential protection for machines, power transformers and busbar installations is based on the high impedance differential principle, offering stability for any type of fault occurring outside the protected zone. The relay whose working depends on the distance between the impedance of the faulty section and the position on which relay installed is known as the impedance relay or distance relay. Oct, 2016 as relay sees only summation of current hence we normally employ an overcurrent element in high impedance differential protection. Apr 22, 2017 impedance relay is protection relay which functions depending upon the distance of fault in the line. This paper summarizes the operating principle of a high impedance protection unit, its relay sensitivity, related ct requirements, importance of. High impedance differential relay applications may be one of the few instances where you might be better off installing the simplest relay possible.
It is clear from the characteristics that if the impedance seen by the relay lies within the circle then the relay shall operate else it wont operate. The protection consists of instantaneousdefinite time overcurrent elements 8750 and. Comparison between high impedance and low impedance bus. Principles and protection applications of low impedance bus differential relay high speed selective bus protection can do much towards limiting the effects of a busbar fault on the system. This is the main difference between a high impedance and low impedance differential protection. Bus protection must provide fast operation for all bus faults and high security for. The setting for a ref relay is a voltage level, which is the resistor value multiplied by the operating current level. Simple fastoperating relays would have a low safety factor constant in the stability equation, as discussed in first section stability. If all the cts maintain the same nominal ratio for all external faults the assumed scheme is perfectly valid since no current can flow in the relay coil. High impedance principle means that protective relay has a such a large series impedance that even the largest through fault current occuring during transient condition does not. Mib high impedance differential protection relay mib 0ce000 00 application 1 1 winding transf. From this basic method, the graded overcurrent relay protection system, a discriminative short circuit protection, has been formulated. High performance, including high speed, high sensitivity, and high security.
Current transformers cts are installed to monitor all currents. High impedance restricted earth fault protection siemens. Circulating current high impedance differential protection using 7sj8 siprotec 5 application note sip5apn030 edition 1 1 circulating current high impedance differential using multifunctional relay 7sj8 1. More specifically, the relay operates depending upon the impedance between the point of fault. Sep 01, 2018 there is one type of relay which functions depending upon the distance of fault in the line. Instantaneous attracted armature relays or numeric relays that mimic the high impedance function are used. This document introduces the application of restricted earthfault protection in. Distance relays, also known as impedance relay, differ in principle from other forms of protection in that their performance is not governed by the magnitude of the current or voltage in the protected circuit but rather on the ratio of these two quantities. The current transformers are replaced in the diagram by ideal current transformers feeding an equivalent circuit that represents the magnetizing. Redundant bus protection using highimpedance differential relays. High impedance differential relays are some of the easiest relays to test. For the impedance z as shown in figure, the current is lagging behind the voltage by angle o. The current element developed positive torque and a currentvoltage developed directional element which opposes the current element depending on the phase angle between current and voltage.
High impedance bus differential relays are used on most of the busses in north. Virtually no limit on the number of branch circuits connected to the bus. A range of metrosil varistors, primarily based on 150mm diameter discs, has been developed to limit this voltage to a safe level. High voltage busbar protection the protection arrangement for an electrical system should cover the whole system against all possible faults. Applying highimpedance differential busbar protection scheme. This paper summarizes the operating principle of a high impedance protection unit, its relay sensitivity, related ct requirements, importance of a reliable. Lowimpedanceref protectionis so named because the differential relay current inputs have low impedance to the.
In some applications of high impedance relays for protection and control duties, the maximum internal fault current can develop high voltages that can damage the relay insulation. Applying highimpedance differential busbar protection scheme eep. Many integrated relays perform ct ratio compensation eliminating the need for matching cts. The popularity can be explained by the good performance of this scheme in relation to ct saturation and the. Figure 21 ac connections restricted balanced earth fault 3. Overcurrent protection fundamentals r ced engineering. Applying high impedance differential protection with ied 670. We calculated that the voltage across the nonsaturated ct, when another ct saturates, is 83. Apr 14, 2016 the operating characteristic of impedance relay is shown below. High impedance busbar differential protection will not work properly if the cts are not sized correctly for the connected circuit.
More specifically, the relay operates depending upon the impedance between the point of fault and the point where relay is installed. This is principle applied to bus protection in power system networks. Isolate the relay from the trip circuit and voltage inputs. The differential protection principal for high and low impedance differential. Numerical high impedance relay with ct supervision dad n numerical high impedance relay with ct supervision description the overall differential protection uses the high impedance circulating current principle. Pdf high impedance restricted earth fault protection. High impedance restricted earth fault protection researchgate. I want to know how a high impedance differential scheme works. Power utility 2v73 high impedance differential relay mors smitt. High impedance busbar differential protection valence.
Principles of differential relaying current balance high impedance determine worst case throughfault current. Calculation of stabilizing resistor in high impedance. This paper summarizes the operating principle of a high impedance protection unit, its relay. Principles and protection applications of lowimpedance bus. This document described the high impedance differential protection and such applications with 670 series products. In such implementations, a lowimpedance principle is used for ref protection to complement differential protection in detecting transformer earth faults 2. Many integrated relays perform ct ratio compensation eliminating the need for matching. We covered the basic operating principles of high impedance busbar differential protection in our previous post, i want to know how a high impedance differential scheme works. Low impedance bus differential relay operation the low impedance bus differential relay vectorially sums the normalized currents from all ct inputs to detect the difference current resulting from an internal fault i. Restricted earth fault relay principle pdf performance of restricted earth fault ref relays. Review of principles and approaches page 4 of 14 for highspeed tripping. Overcurrent protection fundamentals relay protection against high current was the earliest relay protection mechanism to develop. Distance relays are actually double actuating quantity relays with one coil energized by. What is restricted earth fault relay 5 ct explanation.
Connect your testset sensing input to the relay trip output. Since the terms low and high depend on context to some extent, it is possible in principle for some high impedance nodes to be described as low impedance in one context, and high impedance in another. Line protection concepts, such as overcurrent and distance arrangements, satisfy this requirement, even though short circuits in the busbar zone are cleared after certain time delay. The principle of the high impedance ref scheme is applied, and to do so the following. High impedance busbar differential protection minimum allowable ct saturation voltage calculation. The popularity can be explained by the good performance of this scheme in relation to ct saturation and the low cost, if used on a simple bus system. Fault current flowing through saturated ct and associated wiring generates a voltage across the relay rscombination. Energized primary conductor contacts quasiinsulating object, eg.
Siprotec 5 application note circulating current high. This principle became really attractive with the advent of microprocessorbased relays because of the following. In protective relaying terminology, however, an impedance relay has a characteristic that is different from that of a relay responding to any component of impedance and therefore, the. High impedance restricted earth fault protection academia. This paper summarizes the operating principle of a high impedance protection unit, its relay sensitivity, related ct requirements, importance of a reliable protection, and the necessary setting. The induc tion principle makes this relay less responsive to the dc and harmonic components of the false differential current resulting from ct errors due to. Free electrical calculator for android best android app for electrical engineer and eee student in this restricted earth faulty relay video, i have explained 5 ct explanation. Applying high impedance differential protection with ied 670 1.