Figure 1 shows a simple differential protection scheme, also known as a merzprice scheme in this simple scheme, we can assume that under normal operating conditions, the current entering into the piece of equipment under protection is equal or in the case of a transformer, proportional to its exiting current. Differential protection is the best technique in protection. For the restricted earthfault protection using the biased differential protection principle, the following measurement quantities are used. Percentage differential protection electrical concepts. This document gives detail step by step procedure for the testing of above stability test. The protection for internal fault in such type of transformer is to be provided by using differential protection system. An alternative principle for line protection that is quickly becoming the norm is differential protection. The operation of the protection is based on the biased differential current principle, which is shown in fig. Cac1a01d2 relay contains a 3phase biased differential protection element and a 3phase differential overcurrent protection element. 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.
In this paper, we examine the degree of protection afforded by the various types of differential elements phase, negative, and zero sequence for stator winding faults. 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. Application and setting guide ref 542plus for this reason, it is necessary to stabilize the differential protection by means of a so called bias current. Differential protection is not supposed to operate for a through fault. Line differential protection substation automation. It is capable of providing all the protection and alarm functions for protecting a 2,3,4 or 5 winding transformer. Introduction the allenbradley 865 differential protection system includes all the essential protection functions needed to protect transformers for distribution networks of utilities, industry, power plants and offshore. Operate and restraint signals of a transformer differential relay. Scribd is the worlds largest social reading and publishing site. The differential relay works on the principle of comparison between the phase angle and magnitude of two or more similar electrical quantities. Differential protection of transformer differential. Biased differential protection is an older design of protection than high impedance circulating current. Aug 11, 2017 the presentation explains about the simple differential protection, biased differential protection and also the advanced numerical relay working in generator.
Jul 12, 2017 biased differential protection of two and three winding transformers. A currentbased solution for transformer differential. Differential relay protection settings low impedance differential protection systems typically have 3 to 5 settings required to properly define the restraint characteristic of the relay. Typically only used for ef schemes transformers but. 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. Figure 23 biased characteristics of biased differential relay for transformer protection. The faults occur in the transformer inside the insulating oil can be detected by buchholz relay. Differential protection is a unit scheme that compares the current on the primary side of a transformer with that on the secondary side. Scope this document introduces the application of the threephase differential protection in ref542plus. Where a difference exists other than that due to the voltage ratio it is assumed that the transformer has developed a fault and the plant is automatically disconnected by tripping the relevant circuit breakers. Us20090212857a1 dc selfbiased vacuum tube differential. Differential protection can be used to provide protection for zones with multiple terminals and can be used to protect lines, generators, motors, transformers, and other electrical plant. A single stage differential amplifier is disclosed as comprising a pair of vacuum tube triodes for amplifying two input signals and generating two output signals.
The differential protection used for power transformers is based on merzprize circulating current principle. Principles of differential relaying current balance high impedance ref is fast and sensitive more so than biased differential protection applied to transformer windings especially ones which have been impedance earthed. The relay is also adopted for threewinding power transformers provided that the power transformer is characterized by a unidirectional flow. Motor needs to have six winding leads brought outside to install either one set of three phase ct or two sets of three phase ct depending on the design. The user can select one or more of the functions listed below. In this type of protection the electrical quantities entering and leaving the protected zone or area are compared by current transformers c. To understand why and how windings fail, we need to know. Aug 30, 2018 the percentage biased differential relay comprises two restraint coils and one operating coil per phase. The relay performs a percentage biased differential protection of two windings. Current transformers in a differential scheme must be. Differential protection of generator or alternator electrical4u. The following are the classification of the differential protection relay. Low z differential relay protection settings engineering. This is designed to response to the differential current in the term of its fractional relation to the current flowing through.
The focus of this paper is percentage restrained differential protection as applied to a power transformer. In order to enhance the security, the operating region of the characteristic is divided into two areas figure 6 having diverse operating modes. The biased beam relay also called percentage differential relay is designed to respond to the differential current in terms of its fractional relation to the current flowing through the protected section. The differential protection is designed to protect power transformers or high. Percentage restrained differential, percentage of what. Application example on transformer differential protection calculation 2533mva 6923kv deltawye transformer on sel387a relay figure 1. A stepbystep transformer differential protection calculation for a 2533mva deltawye transformer using sel387a transformer differential protection relay. Generator and motor diff are included where applicable.
The differential protection relay is used for the protection of the generator, transformer, feeder, large motor, busbars etc. Protection relays differential relays b high impedance differential protection. The differential scheme creates a welldefined protection zone, encompassing everything between the two current transformers. Differential protection for standard power transformers has been used for decades. Biaseddifferential protection is an older design of protection than high impedance circulating current. There are three styles of motor differential protection. Pdf a currentbased solution for transformer differential. Jul 07, 2019 differential protective relay is a protective relay that functions on a percentage or phase angle or other quantitative difference of two currents.
Basic transformer differential protection calculation. Differential protection is therefore suited as fast main protection for all important plant items. In order to correctly applytransformer differential protection the following compensations shall be provided. Basic transformer differential protection calculation pac.
This analysis will focus primarily on differential protection. Jun 01, 2019 commonly, differential protection is used for large 2000hp medium voltage motors or large motors that are very critical or expensive. Until the advent of the highimpedance design, it was also applied to busbar protection, although the last few years have witnessed a. Percentage restrained differential protection is one of the oldest forms of adaptive protection algorithms. The operation of removing the zero sequence component is necessary also for a delta. A differential scheme should therefore be able to respond to the. Differential relay spad 330 c service and legacy product.
Differential protection of generator or alternator. Jun 24, 2018 the biased beam relay also called percentage differential relay is designed to respond to the differential current in terms of its fractional relation to the current flowing through the protected section. Differential relay current differential relay biased. Detailed discussion of types b and c occupies most of this chapter. If the net difference equal zero, it means no fault exist. Under normal working condition, the two currents at both ends are equal and pilot wires do not carry any current, keeping relays inoperative. 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. Protection and control thermal model biased with rtd and negative sequence current feedback start supervision and inhibit mechanical jam voltage compensated acceleration undervoltage, overvoltage underfrequency stator differential protection thermal overload overtemperature protection. In the relay, the torque produced by operating coil tends to close the relay contacts for instantaneous tripping of circuit breakers but at the same time the torque produced by the restraint coils prevents to close the relay contacts as restraint coils torque is directed opposite of the.
Introduction transformers are a critical and expensive component of the power system. Principles of differential relaying my protection guide. Principles of differential relaying the restraint characteristic suppose further that there is 0. It is based on ampereturnbalance of all windings mounted on the same magnetic core lag. In this article we have discuss the basics of transformer protection systems such as over current protection, differential protection, differential relays,buchholz relay protection and transformer lighting protection. May 15, 2018 generally differential protection is provided in the electrical power transformer rated more than 5mva. The differential amplifier has dc selfbiasing ability and gridtocathode overvoltage protection for directly coupling from the outputs of another differential amplifier. The principles of differential protection you must. Early forms of biased differential protection for busbars. This video outlines the basic principles behind differential protection and is a sample of the full 2. The presentation explains about the simple differential protection, biased differential protection and also the advanced numerical relay working in generator. It is capable of providing all the protection and alarm functions for. Universal testing method for power transformer differential.
Protection is commonly referred to as percentage biased differential protection. The principles of differential protection you must understand. The percentage biased differential relay comprises two restraint coils and one operating coil per phase. Bus protection fundamentals terrence smith ge grid solutions. Testing numerical transformer differential relays commissioning. One set of motor leads are brought out on the line side u1, v1, w1 and the other set is brought. The differential relay spad 330 c is designed to be used as a fast interwinding shortcircuit and interturn fault protection for twowinding power transformers and power plant generatortransformer units. The highimpedance input is created by an internal impedance, typically resistive, of 2000 ohms or higher. Trip circuit supervision arc fault protection option disturbance. The mib202 is microcontroller based numerical biased differential protection relay with inbuild current amplitude and vector group compensation features and also with instantaneous differential highset element for two winding power transformer and autotransformers.
Differential protection relay vamp 265 the flexible protection functions, many communication protocols and various auxiliary functions make the vamp 265 perfect for differential protection of transformers, generators and motors. The percentage differential relay is defined as the relay that operates on the. Review of principles and approaches page 6 of 14 the differential protection function uses a doubleslope doublebreakpoint characteristic. Differential protection protection of transformer, motor. Differential relaying provides selectivity by providing a zone of protection with a circuit of interconnected cts. Jul 26, 2017 differential protection relay 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. Micom p63x required data ratings of the power and current transformers mva voltage ratio rated voltage in kv hv side rated voltage in kv lv side vector group ct ratio hv side ct hv side vector group ct ratio lv side ct lv side vector group. How to determine the effectiveness of generator differential.
Differnet types of electrical transformer protection. Transformer vector group and ct to relay connection. In this example we will assume that the entry and exit currents are equal. Differential protection is applicable to all parts of the power system. The differential relay works on the principle of comparison between the phase angle.
Differential protection is based on kirchhoffs laws, stating that all current into a network node shall add up to 0 in an ideal system. Differential relay current differential relay biased beam. As discussed in the post transformer differential protection, differential protection is supposed to operate for the internal faults or for the zone of protection it is intended for. A sensitive current element in series with the highimpedance element is calibrated in volts based on the voltage drop across the internal impedance. Index termsdifferential protection, power transformer pro. Cts having the same ratio are installed in all the connections to the. Pdf easy method for testing transformer differential relays. Abstractdifferential protection is often touted as being the protection for generator stator windings. The differential protection is designed to protect power transformers or highvoltage motors. Mohammed tawfeeq alzuhairi 321 differential protection differential protection is the best technique in protection. Pdf differential protection of power transformer in substation.
Biaseddifferential protection theory and application eep. A multifunction digital threepole percentage biased differential protection relay for transformer or generator transformer unit is installed wrongly for application of generator differential protection. Generally differential protection is provided in the electrical power transformer rated more than 5mva. Biased differential protection of two and three winding transformers. The differential protection of transformer has many advantages over other schemes of protection. Types of differential relay the differential protection relay is mainly classified into three categories. By possessing these unique features, this differential. Differential protection relay 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 transformer protection relay duobias m numerical transformer protection relay description the duobiasm has an established history as a transformer protection relay, its roots going back to the fundamental development of biased differential transformer protection. In differential protection scheme, the current entering at one end of the line and leaving from other end of the line is compared. We will start the transformer differential protection calculation with the identification of the transformer vector group. Protection of reconfigurable busbars becomes easy as the dynamic bus. Differential protection schemes are mainly used for protection against phasetophase fault and phase to earth faults.
It is widely applied to twowinding transformers except those connected to the lower distribution voltages. The main protection function is a current differential with load bias and second harmonic restraining characteristic. Mib202 relay, which can be used to operate for internal faults, like. Differential protection of induction motors provides very sensitive protection against internal phase phase and internal phaseground faults. Transformer protection principles ge grid solutions. Differential protection of transformer differential relays. Differential protective relay is a protective relay that functions on a percentage or phase angle or other quantitative difference of two currents. Through fault means a fault outside the zone of protection. Operate and restraint signals of a transformer differential relay page 4 of 24 emulating the delta connection of the cts for all the wyeconnected windings of a protected transformer, or by calculating and subtracting the zero sequence cu rrent explicitly. The ensuing discussion will mainly focus on differential protection for power transformers. The differential protection is designed to protect power transformers or high voltage motors.
1279 1601 16 1264 957 178 808 122 1106 99 1343 1616 1186 334 1398 44 889 1121 14 839 211 990 1555 1565 591 730 257 339 139 1122 181 90 13 650 424 614 1035 116 469