Pdf easy method for testing transformer differential relays. 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. 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. Fault current flowing through saturated ct and associated wiring generates a voltage across the relay rscombination. Percentage restrained differential relays measure the individual branch currents and quantify the through current in the zone of protection. The differential relays normally response to those faults which occur in side the differential protection zone of. The differential protection and setting calculation of the newtype converter transformer abstract. Setting procedures are only discussed in a general nature in the material to follow. The overcurrent relay is set to prevent operation on the maximum voltage expected across the thyrite for an external fault. Biased differential protection theory and application on.
This is the value of current, expressed as a percentage of the chosen current rating, at which the relay will operate with zero bias current. Ret670 optimized for transmission applications ret670 ieds provide customized or preconfigured protection solutions for any type of transformer and shunt reactor application. Indication for blocked relay is given with yellow led. Cts having the same ratio are installed in all the connections to the.
Abstract the second harmonic inrush restraint function of transformer differential relays maintains security of the differential protection during transformer inrush events. Please share some relay setting calculations excels, pdf or doble or rio test kit calculation files if you have any so that we could purchase it on this website. Protective relaying philosophy and design guidelines. These settings may be revaluated during the commissioning, according to actual and measured values. Setting calculation based on the relay type, relay function is a major concern for utilities and understanding each setting and basis for setting helps in arriving at right settings. The presentation explains about the simple differential protection, biased differential protection and also the advanced numerical relay working in generator. Differential relays can detect such type of faults. The relays used in power system protection are of different types. 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. Principles of differential relaying setting a low z diff relay. Ret670 transformer protection substation automation.
We will set this value or digital relays calculate. Transformer differential protection scheme with internal faults detection algorithm using second harmonics restrain and fifth harmonics blocking logic. Differential relaying provides selectivity by providing a zone of protection with a circuit of interconnected cts. Index terms current differential protection, power transformer, protection relay, single phase i. A series resistor rs can be inserted in series with the relay so that the current. Idaux, differential current induced by the useof an auxiliary winding on the transformer. Differential protective relay is a protective relay that functions on a percentage or phase angle or other quantitative difference of two currents. Protection relays differential relays 1 using stabilizing resistor. This interval is measured between relays in serie s eithe r at the instantaneous setting of the load sid e feeder circuit breaker relay or the maximum shortcircuit current, which can flow through both dev ices simultaneously, whichever is the lower value of current. Calculation of idmt over current relay settings 505150n51n calculation model for thermal relay siemens 7sj64. Siprotec 4 7ut6 differential protection relay for transformers, generators, motors and busbars 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. The differential relay minimum pickup setting need to be adjusted to detect faults on as much of the. S setting is the combination of differential pick up and turning point differential setting.
Current differential line protection setting consideration. Differential protection of transformer differential relays. Dependin g on the sensitivity of the setting of the basic differential protection solution, i. Digital and numerical distance relays may have up to five zones, some set to measure in the reverse direction. The differential protection is designed to protect power transformers or highvoltage motors. Protection selectivity is partly considered in this report, and could be also revaluated.
Unit ct value a t60 percent differential element per unit value refers to setting scaled to the identified unit ct. Further, the document deals with differential protection of threewinding power. The calculations with illustrative examples apply to twowinding power transformer applications. Moreover buchholz relay is provided in transformer for detecting any internal fault in the transformer but differential protection scheme detects the same in more faster way. For reliable protection and control of all types of power transformers and reactors. Further the guide lines help not only in carrying out the setting calculations, but also help in future, if. The term biased differential or percentage differential is based on the fact that the operating threshold increases with the through current.
These spreadsheets below will make your endless calculations much more easier. Pdf optimizing differential protection settings for. Thus the relay current equals the difference of the respective magnetisation currents. We calculated that the voltage across the nonsaturated ct, when another ct saturates, is 83. Differential protection scheme basic and 5mva transformer. Principles of differential relaying current balance high impedance determine worst case throughfault current. Differential relays are very sensitive to the faults occurred within the zone of protection but they are least sensitive to the faults that occur outside the protected zone. Tutorial on protection of three singlephase transformers. Protective relaying philosophy and design guidelines pjm. High impedance busbar differential protection valence. Operating time, sensitivity, dependability and security requirements are examined for typical applications. These configurations allow for greatly reduced settings for many line configurations, with or without potential transformers.
Generator protection setting calculations generator protection sample relay setting calculations the sample calculations shown here illustrate steps involved in calculating the relay settings for generator protection. Practical experience in setting transformer differential inrush restraint 63 1. This paper presents an improved methodology to optimize the differential relay settings. After presenting a definition of unit protection, the principle introduction. Typical settings for three forwardlooking zones of basic distance protection are given in the following subsections. Relay settings calculations electrical engineering. The application of the high impedance differential relay is based on all of the cts being set to the same ratio. High impedance busbar differential protection minimum allowable ct saturation voltage calculation. When primary current both ends are the same, have identical turns ratios and no saturation then, i21p i21q. The typical setpoint for the second harmonic restraint is the relay manufacturers default. Biaseddifferential protection theory and application eep. Among them differential relay is very commonly used relay for protecting transformers and generators from localised faults. Thus, it can be quite tricky to test a numerical transformer differential relay by secondary injection in order to verify that the relay is set properly to protect transformer in a particular. Typical reach and time settings for a 3zone distance protection are shown in figure 11.
The operation is based on the biased differential protection principle with a fourfold tripping characteristic. Current transformers application calculation of transformer differential relay setting relay busbar protection abb earth busbar calculation rk 646 differential relay calculation of transformer differential relay relay rd3 diode unit rloe 100 text. In this situation a solid generatorterminal fault creates roughly 100% of rated current. High impedance busbar differential protection will not work properly if the cts are not sized correctly for the connected circuit. It is always advisable to plot the curves of relays and other protection devices, such as fuses, that are to operate in series, on a common scale. Under external fault condition, the protection must remain stable and should not operate, even if one c. Optimizing differential protection settings for power transformers. Practical experience in setting transformer differential. Low voltage breaker fuse coordination requires a minimum 0. Overcurrent coordination page 3 qualtech engineers, inc. Percentage restrained differential, percentage of what. The relay is provided with triple slope characteristics. Overcurrent relay setting model for effective substation.
I op is 1is 2 the equivalent current in the restrain windings are proportional to. The differential current in the operating coil is proportional to is 1is 2. Ret 670 required data ratings of the power and current transformers mva voltage ratio rated voltage in kv hv side rated voltage in kv lv side. This document introduces the application of the threephase differential protection in ref542plus. Mohammed tawfeeq alzuhairi 311 at normal conditions. This paper offers a selection and setting guide for ground fault detection on noncompensated overhead power lines. The calculation of the vector group compensation is shown in table 3. Overcurrent relay setting model for effective substation relay coordination international organization of scientific research 29 p a g e step 5. Investigation of recent trippings of power transformer on harmonics in differential relay for taking corrective action to prevent further trippings. Medium voltage products technical guide protection. Detailed calculations of differential relay for meeting operational requirement and preventing unwanted tripping on the account of harmonics. It helps you to shape up your technical skills in your. Because of that, comparison of upstream and downstream currents in the same phases is not convenient for transformer differential protection. 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.
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