The service reliability of an oilimmersed transformer therefore depends to a great extent on the quaiity of the oil. The principle of the differential protection, which is illustrated in fig. Figure 1 shows a simple differential protection scheme, also known as a. Unit ct value a t60 percent differential element per unit value refers to setting scaled to the identified unit ct. Traditionally, transformer protection methods that use its terminal behaviour are based on differential protection is considered as a most widely used technique to perform the protection function. A transformer has a turns ratio so the current in is not really equal to the current out. Transformer failure statistics 19831988 winding failures 37% tap changer failures 22% bushing failures 11% terminal board failures 3% core failures 1% miscellaneous failures 26% source. Setting procedures are only discussed in a general nature in the material to follow. Introduction transformer is a static device used to transform the electrical energy from one alternating current circuit to another without any change in frequency.
The faults occur in the transformer inside the insulating oil can be detected by buchholz relay. It is also an application that demands the relay be able to operate with unequal ct performance, since external fault magnitudes can be quite large. Medium voltage products technical guide protection. Differential protection protection of transformer, motor. The comprehensive transformer protection provided by multiple function protective relays is appropriate for critical transformers of all applications. Comparing current flowing into a line to the current flowing out of the same line allows for a simple protection scheme. Ret670 transformer protection substation automation. Hence, total current entering into a bus section is equal to total current leaving the bus section. This video outlines the basic principles behind differential protection and is a sample of the full 2.
The principle of differential busbar protection is very simple. Ass relays power transformer protection ago35005 e page 4 2. Digital differential protection of power transformer. Protection systems applied to these may be broadly classified as unit and nonunit protection systems. This system is operating in either of the two following principles. Current magnitude and phase angle difference compensation. Biased current differential protection is most commonly applied for transformer protection. However, if numerical differential protection for standard threephase power transformers is directly applied for differential protection of such converter transformer, it will not be possible to. Numerical differential protection algorithm for power. The differential protection function protects the zone between the main and additional current sensors. Pdf transformer differential protection relay service. The differential protection used for power transformers is based on merzprice circulating current principle. 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. This type of protection works on the basic theory of kirchhoffs current law, which states that the sum of the currents entering and exiting a node will equal zero.
Differential protection schemes are mainly used for protection against phasetophase fault and phase to earth faults. Similar to bus protections, transformers are protected by differential relays. Directional over current relayprotection of parallel linesdirectional over current protection duration. Ansi transformer connections daby or dy1 a b 2 1 1 2 b c 2 1 c a 2 1 a b c a a. Learn the basics of differential protection of transformers. Power transformer is a vital link in a power transmission system and distribution a power transformer is an expensive part of a power network. Product guide ret615 transformer protection and control. Differential current protection of transformer using.
Rel52504 p3t32, transformer protection relay with differential protection. The high impedance differential relay meets both requirements. 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. Analysis of modern digital differential protection for. T60 percent differential calculations 2 ge power management it is important for the user to understand the slope 1 and 2 percentage settings and the minimum pickup, break 1, and break 2 perunit values. Idv transformer differential protection complete and innovative solution for transformer bays and other machines idv relays include all protection, control and measurement functions for two or three winding transformers or autotransformers at any voltage level, with single or double breaker. Generally differential protection is provided in the electrical power transformer rated more than 5mva. It has very low requirements on the main cts, and no interposing cts are required.
Pdf differential protection for converter transformers. Introduction transformers are a critical and expensive component of the power system. Transformers are protected primarily against faults and overloads. Failure to detect these faults and quickly isolate the transformer may cause serious damage to the device. Description ret615 is a dedicated transformer protection and control relay for power transformers, unit and stepup transformers including power generator transformer blocks in utility and industry power distribution systems. Differential protection provides the best overall protection. Busbar protection busbar differential protection scheme. The siprotec 7ut85 transformer differential protection device has been designed specifically for the protection of twowinding transformers 2 sides.
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. Transformer differential protection siprotec 7ut85. The principles of differential protection you must. Bus protection is an application that demands many sets of cts be connected to the relays.
Differential protection for arbitrary 3ph power transformer. It is used here to protect transformers from a few mva to several tens of mva from internal faults inside the protected zone between the two sets of cts. Any fault existing in this protection zone is regarded as an internal fault, while any fault existing outside this protection zone is an external fault. The introduction of digital technology has led to further improvements in bus differential. Problem statement article pdf available in ieee transactions on power delivery 164. The differential protection used for power transformers is based on merzprize circulating current principle.
Reactors and capacitors there are two basic types of differential protection. An overall view of the economic impact of a transformer failure and what can be done to reduce the risk, including. Second, we investigate harmonics restrain scheme and microprocessor basedprotection on power transformer differential protection. This ensures the stability of the standard transformer differential relay which is actually set to protect the power transformer having standard dd0 vector group. One of the important protections against internal transformer faults, such as winding turns shortcircuit, is the differential protection. Another common form of protection for apparatus such as transformers, generators, busses and power lines is current differential. Electrical technology and industrial practice 3,445 views 8. The additional protection functions can also be used as backup protection for. Such protection provides protection against internal phasetophase and phasetoearth faults and is generally used for transformers of rating exceeding 2 mva. The direct economic impact of repairing or replacing the transformer. It is a static device, totally enclosed and usually oil immersed, and therefore the fault occurs on them are usually rare. This transformer protection ied is designed to operate correctly over a wide frequency range in order to accommodate power system frequency variations during disturbances and generator startup and shutdown.
In many ways pilot protection is analogous to differential protection of buses, transformers and machines. Differential protection installation on the 24pulse drive for the oil industry is given in figure 3. A currentbased solution for transformer differential protection part i. The use of standard transformer differential protection for. The protection of transformers is critical on phenomenon. Differential protection is based on the fact that any fault within electrical equipment will result into the difference in current entering it and the current leaving it. For transformers the differential protection figure 1 is basically the same as that for a bus but there are certain differences that we will look more closely at.
Transformer differential protection electrical concepts. Power transformer is the key element in electrical power system. The use of channel to compare conditions at the terminals of a power line, provides the only selective means of highspeed clearing of end zone faults. Interwinding faults short circuits and ground faults within power transformers can be detected by this protection scheme. Williams, firstenergy corporation ariana hargrave, matthew watkins, and vinod k.
Proper protection is needed for economical and safe operation of electrical power system. Transformer protection overview the type of protection for the transformers varies depending on the application and the importance of the transformer. Sel487e transformer differential relay threephase transformer protection, automation, and control system major features and benefits the sel487e transformer differential relay provides threephase differential protection for transformer applications with up to five threephase restraint current inputs. The protection for internal fault in such type of transformer is to be provided by using differential protection system. Current differential line protection setting consideration. Thus by comparing the two currents either in magnitude or in phase or both we can determine a fault and issue a trip decision if the difference exceeds a predetermined set value. If the net difference equal zero, it means no fault exist. The differential scheme creates a welldefined protection zone, encompassing everything between the two current transformers.
There are various protection relays and those are used for protection against a wide variety of conditions. This paper presents the analysis of digital differential protection for three phase power transformers. A differential scheme should therefore be able to respond to the. The siprotec 7ut6 differential protection relays are used for fast and selective fault clearing of shortcircuits in transformers of all voltage levels and also in rotating electric machines like motors and generators, for short lines and busbars. It is the main protection for the trans former and contains many other protection and monitoring functions. The scheme of busbar protection, involves, kirchoffs current law, which states that, total current entering an electrical node is exactly equal to total current leaving the node. In this type of protection the electrical quantities entering and leaving the protected zone or area are compared by current transformers c. Differential protection of a transformer the transformer is one of the major equipment in power system. But if any fault occurs in the transformer but not in oil then it can not be detected by buchholz. A currentbased solution for transformer differential. However, special industrial transformers, such as 24pulse converter transformers, could not typically be protected easily with the.
Principles of differential relaying my protection guide. Power transformer differential protection has been used for decades on standard threephase power transformers. Transformer protection application guide this guide focuses primarily on application of protective relays for the protection of power transformers, with an emphasis on the most prevalent protection schemes and transformers. This course covers generator protection concepts and theory. The unit protection responds to internal faults only. Protective devices that are described in this course can be used in multiple generator protection configurations. Differential protection is the best technique in protection.
1220 718 1041 1303 368 1287 61 933 463 1537 357 416 898 1441 1495 1545 1313 1294 403 790 1375 1308 146 953 587 1251 1347 1028 1223 117 1313 1058 26 823 54 1274 305 1459 715