Sample calculationfordifferentialrelays slideshare. Since current transformer is fundamentally a transformer, it translates the current from the pecondary side, rimary to the s inversely proportional to the turns so as to maintain the relationship, ip n is. Three good examples of the application of modern relays to. Calculation the rated current of the power transformer is. One set of motor leads are brought out on the line side u1, v1, w1 and the other set is brought. At that time, busbar differential protection against singlephasetoground faults, which used devices without a ferromagnetic core as instrument current transducers, demonstrated successful pilot operation 17, 18. Learn the basics of differential protection of transformers. Power transformer testing automatically measuring ratio and winding resistance of all. The differential protection of transformer has many advantages over other schemes of protection. 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. Current version can calculate values only for standard transformer core, thats w and u profile of core. Pdf complete software package for transformer design. First, the calculation of the actual burden of the ct, including connection wires and protection relay impedance, is presented. 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.
Transformer vector group and ct to relay connection. 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. Protection settings calculations for power transformers. Transformer design software integrated engineering software. Figure 1 simple diagram connection for differential power transformer protection. Transformer differential protection setting calculation. Such busbar differential protection was used for the first time in the usa in the 40s of the last century. The sel787 transformer protection relay is a versatile, twowinding current differential relay that protects industrial transformers. Download transformer calculator coils and wire thickness at. Ctdim is a software tool for current transformer ct and voltage potential transformer vt pt selection and dimensioning.
Through fault means a fault outside the zone of protection. The tool is standard, so it should be simple to use. In addition, the calculations may use a monthly model of ambient temperature, eliminating the need for external connections to the transformer and relay. Unit protection differential relays pouya software. The differential protection and setting calculation of the. A good resource presented in the sel387a instruction manual provides a straightforward calculation of the differential current pickup. Note that working frequency of all calculations is 50 hz you can use it for 60 hz too, in next release ill add ability to change that frequency. Sources of steadystate differential current steadystate differential current is not proportional to through current. This percentage is defined as bias setting of the relay. Pdf easy method for testing transformer differential relays. Current transformers ct are connected to the primary and secondary windings of the.
Transformer differential calculation linkedin slideshare. An excel spreadsheet has been developed by the ieee psrc for the purpose of easy. By optimizing the selection of ct or vt data with respect to technical requirements of power system protection andor metering, the engineering and production costs can be substantially reduced while maintaining. Therefore, how to estimate reliability of the differential during ct saturation. If you dont known anything about assembling transformers, please dont use calculations from this program for building your own transformer.
A differential transformer produces an electrical output voltage proportional to the displacement of the core. Especially under throughfault conditions with a high short circuit curre nt magnitude, the differential current may be very high too due to the current transf ormer. For 787 relay the calculations will be similar except for restraint current calculation. Transformer short circuit current calculation and solutions. The correct sizing of current transformers is required to ensure satisfactory operation of measuring instruments and protection relays. Dual slope differential relay as an effective technique. L has no effect on the differential calculation, it can be ignored, and. The spill current level for the relay is to just operate it. Software support blog about me my protection guide. Normally the differential setting for transformer is 0. The current transformer primary is connected in series with the device in which the current is to be measured.
Transformer differential protection scheme works by using two separate quantities calculated from the primary current iw1c and secondary current iw2c. Transformer calculator software for other platforms. The main purpose of a current transformer is to translate the primary current in a. Make sure you have knowledge of basics of transfomer. Percentage differential restraint settings harmonic blocking individual or common settings effect of residual flux transformer energization inrush current current transformer ct. Differential protection scheme basic and 5mva transformer. Current transformers are the very important aspect of. Selecting current transformers janitza electronics. The main purpose of a current transformer is to translate the primary current in a high voltage power system to single level that can be handled by delicate electromechanical or electronic device. Hybrid transformer are ordinarily small and under high load it can overheat.
Ct secondary current corresponding to lv side full load current 5857 3200 1. Most of these installations have a single set of secondary cts mounted as close to the transformer windings as physically possible. Oct 06, 2016 transformer differential calculation 1. Whilst measurement current transformers are intended to reach saturation point as quickly as possible once they exceed their operational current range expressed by the overcurrent factor fs in order to avoid an increase in the secondary current with a fault e. Percentage restrained differential, percentage of what. Relay settings calculations electrical engineering. Power transformer differential protection using current and. This must also be considered during testing and commissioning. Available software packages include electromagnetic. Several methods exist to size current transformers. Oct 02, 2016 3ph transformer differential protection through numerical relays. The current entering the transformer is more than the current leaving due to this increase in magnetizing current this causes the differential element to pick. Sep 20, 2018 published on sep 20, 2018 the ct calculation for generator protractionthe all types ct used calculation measuring ct,protraction ct, overall differential ct used to protraction to generator. The current transformers are not likely exactly matched to the transformer turns ratio so there will always be an unbalance currentin the operating coil of a transformer differential relay.
The approach is particularly based on the ct errors and voltage ratio variation of the power transformer load tapchanger. The limiting values stated in the document must not be exceeded. The impact of currenttransformer saturation on transformerdifferential protection article pdf available in ieee transactions on power delivery 303. Aiming at the special winding connection of the newtype converting transformer, its connecting scheme of differential protection is proposed based on the establishment of the current transform equations. The distribution transformer calculations can help you to calculate the natural ventilation for transformer room, current protection rating, and so much more. Differential protection of induction motors provides very sensitive protection against internal phase phase and internal phaseground faults. Out put of soft ware includes a lot of information about details of transformer that may be quoted to customer.
The main source of steadystate differential current is the magnetizing branch of the transformer equivalent circuit. Sel351a transformer hv over current pickup setting 51pp for phase fault element 51gp for. Differential protection of transformer differential relays. Dec 18, 2017 calculation of inrush current in any terminal with depended parameters such as damping time, pick and effective current in any switching angle, etc. This paper describes how to provide universal, current based, differential protection for any threephase power transformer, including phaseshifting transformers with variable phase angle shift. Download transformer calculator coils and wire thickness. Lets consider an example transformer differential protection system with sel 387587 relays.
Ct winding arrangements, and software phase compensation are to be made. Assuming an ideal transformer, determine a the primary and secondary fullload currents, b the transformer turns ratio. Auto analyze windings connection to create desired vector group and define best choose for position of end leads of windings. Using the labvolt power supply, a labvolt faultable transformer, and a sel787 relay. Current differential line protection setting consideration. We will start the transformer differential protection calculation with the identification of the transformer. The foremost interface device between the power system and the protective relaying is the ubiquitous current transformer. Pdf the impact of currenttransformer saturation on. Differential protection of transformer differential.
We are going to design a 50 va step down transformer of 230v to 12v. Digital differential protection of power transformer using. Current transformer basics and the current transformer. Modeling of power transformer for differential protection. Ct matching factor in transformer differential protection. The faults occur in the transformer inside the insulating oil can be detected by buchholz relay. After sorting, the best design can be choice by user as final design. Substations sitemap test formats manuals softwares. Current transformer design tool assists design engineers in choosing the most appropriate core material and size for a number of current transformer ct topologies. Itotis commonly called the restraint current but in reality the restraint current is derived from it. Published on sep 20, 2018 the ct calculation for generator protractionthe all types ct used calculation measuring ct,protraction ct, overall differential ct used to protraction to generator. Yd30, yy0, dd0, yz30 and dz30 here, y stands for a wye win d ing, d for a delta winding and z for a zigzag winding, capital letters denote hv side. Introduction the following questions arise while applying a differential relay for transformer protection. In order to accurately detect arc faults in a lowvoltage alternating current ac system, a novel differential highfrequency current transformer dhfct sensor for collecting highfrequency arc currents was proposed.
Transformer protection and control ret615 iec compact and versatile solution for utility and industrial power distribution systems ret615 is a dedicated transformer protection and control relay for protection, control, measurement and supervision of power transformers, unit and stepup transformers, including power generator transformer blocks. Percentage differential protection slope in differential. The most important protection principle for transformers is differential protection. Differential relay modelling using matlab simulation procedure. Differential current that is transient in nature transient. I d is proportional to the fault current for internal faults and approaches zero for any other operating ideal. Differential protection of generator or alternator.
A transformer differential protection scheme based on current ratio and voltage ratio between difference and sum of fundamental components of line currents and power transformer terminal voltages, respectively, is proposed in this paper. Implementation of noiseimmune rogowski coils for busbar. Differential protection is not supposed to operate for a through fault. Table 1 table 2 for better understandings, go through the following steps for calculations. For this logic coordination 0,1 no trip signal is released. Developers recommend the transformer calculator software only for professional who have experience in assembly transformers. Itotis also a measure of the loading of the primary system.
May 15, 2018 at maximum through fault current, the spill output produced by the small percentage unbalance may be substantial. Restraint current calculation in 387587 uses average of winding currents whereas the 787 the calculation is straight addition. Transformer differential protection voltage disturbance. Digital current differential relays power line carrier figure 1. The information for the different mva transformer loads can be obtained. The operating current also called differential current, i d, can be obtained from the phasor sum of the currents entering the protected element. Principle of differential protection scheme is one simple conceptual technique.
Arithmetic sum hence, slope 1 so, let slope k170% under the normal operating condition at any time the differential current is not increasing beyond1 a. Preface 6 siprotec 5, transformer differential protection, manual c53000g5040c0169, edition 06. Because current transformers always have a certain inherent error, the differential current is never zero, once load current is flowing. Thus, it can be quite tricky to test a numerical transformer differential relay by. The main source of false differential current is ct saturation. This software creates transformer designs from 2mva till 600mva in single and 1800mva in three phases and 0. Sel787 and sel 387587 transformer differential relay is used for this discussion. A novel differential highfrequency current transformer. Differential protection scheme basic and 5mva transformer oltc protection calculation published on may 15, 2018 may 15, 2018 125 likes 6 comments. The differential relay actually compares between primary current and secondary current of power transformer, if any unbalance found in between primary and secondary currents the relay will actuate and inter trip both the primary and secondary circuit breaker of the transformer. Ctdim current and voltage transformer selection, dimensioning. The current ratio is used to discriminate between inrush and fault conditions.
We often get requests to add differential protection in industrial unit substations transformer secondary switchgear. False differential current is differential current that does not exist in the primary circuits. We will start the transformer differential protection calculation with the identification of the transformer vector group. A 50 kva singlephase transformer has a 4000 v primary, and a 400 v secondary. Generally differential protection is provided in the electrical power transformer rated more than 5mva. Modeling differential protections of power transformers and their. If you have some experience in assembling transformers, then this program is perfect for you. Application example on transformer differential protection calculation 2533mva 6923kv deltawye transformer on sel387a relay figure 1. Calculation of the current transformer 1mrs 755481 accuracy limit factor 1. The current measured by the differential relay will be fairly linear due to the presence of load current, and may result in low levels of second harmonic current. Transformer calculation software electronic circuits. The break 1 setting is based on the previously defined pu value of the full load transformer current. With twophase faults outside of the transformer, an additional phase shift will introduce a differential current in the nonfaulty phase.
Accurate power transformer modeling and proper current transformer selection lead us to improved transformer protection. Sizing current transformers for line protection applications. Testing numerical transformer differential relays commissioning. Therefore, differential protection of transformer should be provided with a proportional bias of an amount which exceeds in effect the maximum ratio deviation.
The standard current transformer secondary winding is rated at 5a as per ansi standards. Commissioning and testing of differential protection for. Usually, the nerds have the experience in making accurate calculations. Performannce analysis of traditional and improved transformer differential protective relays. The dc offset in the primary current can cause the flux in the iron core of the ct to build up in one direction until it. Transformer calculator kva calculator full load amps. Key words transformer, inrush, excitation, differential. Differential current pickup settingbias setting of the relay is adopted based on the maximum percentage of allowable mismatch adding some safety margin. Ctdim is a software tool for current transformer ct and voltage potential. The highfrequency noise of the arc current is one of the typical arc characteristics of almost all loads. There will be a small current flow in the transformer primary even if the secondary is open circuited.
An additional phaseshift has to be considered by the differential protection to fulfill the requirements for selectivity. Thus the differential current under the considered full load condition 1. 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. Traditional, often line frequency current transformers, hall effect current transformers and switchmode power supply smps current transformers are examined in depth. Transformer protection and control ret615 iec transformer. A current based solution for transformer differential protection part 1. If you dont know anything about assembling transformers, please dont use calculations from this program for building your own transformer. Sel787 transformer differential protection differential pickup slope1 setting slope2 setting differential unrestrained u87p unrestrained differential pickup 2nd harmonic 5th harmonic. Kbch relay offers biased differential current, restricted earth fault ref and.
Scope this document describes the calculation of the actual accuracy limit factor f a for protectiontype p current transformers ct. Monitor transformer health with cumulative throughfault current recording, and for the first time in the industry, automatically check and generate differential compensation settings with the commissioning assistant software. It is used to measure motion and to sense displacements. Diff current 1 pu note on ct polarity dots through current. Overall differential protection, transformer, generator protection needs ps class ct. Calculation of the current transformer accuracy limit factor. In this case the harmonic calculation part released logic 0 but the amplitude comparator showed in fig. Apr 19, 2020 transformer calculation is program for calculating number of coils and wire thickness at transformer. The differential protection and setting calculation of the newtype converter transformer abstract. Current transformers reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the. Differential transformer article about differential. This note will look at several methods, with particular attention being paid to protection class cts sized in iec 60044, which is adopted internationally. Or the harmonic analyzer tool in the relay software can be used to identify the. Usually, wrong calculations are dangerous because they not only damage the device.
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