Differential protection is applicable to all parts of the power system. Pdf optimizing differential protection settings for power. Differential protection of yy and connected power transformer mayurdhvajsinh p. Principles of differential relaying the restraint characteristic suppose further that there is 0. Switchgear and protective devices 2015 8 p a g e risk of synchronous motors in large industrial premises falling out of step and tripping out. It is based on ampereturnbalance of all windings mounted on the same magnetic core lag. Principle of differential protection by the small percentage unbalance may be substantial.
The highimpedance input is created by an internal impedance, typically resistive, of 2000 ohms or higher. The differential protection of power transformer is a unit protection scheme. A currentbased solution for transformer differential protection part i. Within the limits of the accuracy of the cts and the relays, true bus differential relaying will detect all faults on the protected bus. True bus differential relaying compares all currents entering and leaving a switchgear bus. The differential protection of transformer has many advantages over other schemes of protection. Strictly speaking the rc tells us how much current a relay will use to restrain based on the currents. The differential protection function protects the zone between the main and additional current sensors. Differential protection falls into one of the following three. Partial differential relaying powell industries, inc. Jan 14, 2017 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.
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. 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. For power transformers, it is recommended that percentage differential protection be provided for transformers rated kva and above if circuit breakers are provided for each winding into which power can flow when an internal fault occurs, and for all. The percentage restraint characteristic requires that the differential current be greater than a percentage of the through restraint current. Within a very short time this relay detects faults occuring within the zone to be protected by. 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.
Differential protection for arbitrary 3ph power transformer. Pdf a currentbased solution for transformer differential. L to limit current through relay to may 15, 2018 generally differential protection is provided in the electrical power transformer rated more than 5mva. This system gives protection against phase to phase faults and phase to ground faults to the power transformers. Protection relays differential relays b high impedance differential protection.
The percentage differential relay is defined as the relay that operates on the phase difference of two or more similar electrical quantities. This paper carries the idea of selection of dual slope differential relay parameters for various faulty conditions on the system. The slope characteristic provides high sensitivity when low levels of current. Line differential protection is a strict selective object protection. A sensitive current element in series with the highimpedance element is calibrated in volts based on the voltage drop across the internal impedance. Protection devices for electrical systems minimize fault damages, assist in maintaining power system stability and help to limit supply interruptions to consumers. Evaluating the impact of increasing system fault currents on. Pdf high impedance restricted earth fault protection. Pdf easy method for testing transformer differential relays. When the relay is correctly set, one screw must be in the lower row of holes at the correct tap value and the other must be in the hole directly above. The percentage differential protection or merzprice protection based on the circulating current pronciple can also be used for the transformers. The differential protection relay will pick up if magnitude of differential current is more than a fixed percentage of the restraining current. Bus protection, automatic reclosing, 292 by backup relays, 275, 291 circuitbreaker bypsasing, 292 combined power transformer and bus, 287 current differential with overcurrent relays, 278 current differential with overvoltage relays, 288 current differential with percentage relays, 284 directional comparison, 277 fault bus, 275 grounding.
Type ca percentage differential relay for transformer. To determine the correct tap setting, calculate the currents delivered to the relay at full load on the trans. The following are the classification of the differential protection relay. Jun 08, 2019 the relays used in power system protection are of different types. Figure 6basic relay connections one phase for fixed percentage restraint. Modern line current differential protection solutions. Patel ge power management malvern, pa presented at the electric council of new england. Setting procedures are only discussed in a general nature in the material to follow. Abstractpercentage restrained differential protection is one of the oldest forms of adaptive protection algorithms.
The type ca percentage differential relay for trans former protection is designed for the protection of power transformer. Percentage differential protection slope in differential. Percentage restrained differential relays measure the individual branch currents and quantify the through current in the zone of protection. Comparing current flowing into a line to the current flowing out of the same line allows for a simple protection scheme. The differential relay actually compares between primary therefore. With the differential protection relaying, the cts at both end of the stator windings must be same. Scope this document introduces the application of the threephase differential protection in ref542plus. The differential protection is designed to protect power transformers or highvoltage motors. Differential protection of a transformer the transformer is one of the major equipment in power system. Among them differential relay is very commonly used relay for protecting transformers and generators from localised faults. Micro processor based advanced bus protection scheme using iec 61850 process bus 92 sampled values k. Modified differential ground fault protection keywords.
A new approach to current differential protection for transmission lines m. Micro processor based advanced bus protection scheme using. Principle of percentage restrained differential protection. In percentage differential protection, we provide a slope feature to the differential protection relay. Differential protection symposium belo horizontenovember 2005 g. Generator stator protection, underover voltage, under over. Protection functions bias differential protection 87 harmonic restraint protection over fluxing i.
Type ca percentage differential relay for transformer protection. Percentage restrained differential, percentage of what. In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected 4 the first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as overcurrent, overvoltage, reverse power flow, overfrequency, and underfrequency. Let for differential protection to operate, id should be greater than the x% of ib. Sep 08, 2016 general scheme of differential protection 6. Transformer differential protection percentage restraint differential protective relays have. Problems for the differential protection caused by transformer inrush currents are discussed. In modern numerical differential protection relay two.
Mdgf, ground fault, modified differential ground fault protection, created date. Problem statement article pdf available in ieee transactions on power delivery 164. Thus this scheme provides protection to the greater percentage of the stator winding. It is a static device, totally enclosed and usually oil immersed, and. The percentage differential relay is defined as the relay that operates on the phase difference of two or more similar electrical quantities exceeds a predetermined amount. This popular scheme is known as biased differential protection or merzprice protection. Basic percentage differential protection scheme for. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. Percentage differential protection free download as word doc. The following safety and common symbols may be used in this manual and on. Percentage differential protection for transformers your. Abstractpercentage restrained differential protection is one of.
Pickup value id slope k1 slope k2 with footing point ir0 ires. Percentage differential protection slope transformer scribd. Abstractline current differential protection creates challenges for relay design and application. Jul 06, 2016 to prevent the differential protection scheme from picking up under such conditions, a percentage differential protection scheme is used. Ziegler, 102005 page 19 id ir0 k1 k2 iop ires digital differential protection. Thompson, schweitzer engineering laboratories, inc. A new approach to current differential protection for. Differential protection for standard power transformers has been used for decades. The faults occur in the transformer inside the insulating oil can be detected by buchholz relay. Pdf differential protection of power transformer in substation. The only difference between them is the restraining coil. Current differential line protection setting consideration. Differential relays are very sensitive to the faults occurred within the zone of protection but they are least sensitive to the faults. The mathematical relationship between differential protection and directional protection is derived.
759 342 1130 895 1435 1607 45 557 341 1158 718 1544 342 1569 144 757 1001 460 1541 32 1026 780 261 801 75 962 623 396 1344 1308 993