Microsoft powerpoint electrical protection module 4. The relay can perform the protection functions listed below. 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. View and download powerpoint presentations on protection of transformer ppt. High impedance busbar differential protection will not work properly if the cts are not sized correctly for the connected circuit. Introduction transformers are a critical and expensive component of the power system. Transformer differential 87t protection instantaneous phase overcurrent 50 protection instantaneous ground overcurrent 50n protection phase. With static or electromechanical 87t relays, external interposing current transformers are used in order to compensate for.
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. Currently, percentage differential protection is a common practice for power transformer protection. Improved differential relay for bus bar protection scheme. The vector group of the protected autotransformer is ynautod5, thus the 220kv positive sequence, noload voltage component is in phase with 400kv positive sequence, noload voltage component. However, the voltage and the current in both the primary and secondary sides are different depending on. Power system protection college of engineering and. Differential protection schemes for auto transformers. Key words transformer, inrush, excitation, differential. Power transformer differential protection using current. A transformer has a turns ratio so the current in is not really equal to the current out. Differential protection schemes and techniques for power transformers educational aspects chapter pdf available december 2016 with 807 reads how we measure reads.
Thus, a new standardized testing methodology for transformer differential protection relay from any manufacturer will be presented. Power transformer differential protection 87t has been used for decades. View and download powerpoint presentations on transformer protection ppt. Move a tapchanger in a transformer human intervention. The differential protection of transformer has many advantages over other schemes of protection. Calculation for transformer differential protection given details. In this example we will assume that the entry and exit currents are equal. Ret670 transformer protection substation automation. These differences are a direct result of three characteristics or a transformer. Siprotec 4 7ut6 differential protection relay for transformers connection of transformer differential protection with high impedance ref i7 and neutral. The 11 work on fuzzyneuro techniques in order to ensures relay stability against sympathetic inrush, external faults, magnetizing inrush over excitation conditions and its action on internal faults. Transformer protection principles ge grid solutions. The faults occur in the transformer inside the insulating oil can be detected by buchholz relay.
Principles of differential relaying my protection guide. Differential protection for a generator phase winding. In differential protection of transformer ct matching is an important thing to care care else differential protection wont be efficient and reliable. Power transformer protection rishi tandon assistant manager wwo wind world india limited. Percentage restrained differential, percentage of what. Application of discrete wavelet transform for differential. Differential protection, frame leakage protection the systems in which selectivity is relative are nonunit systems. However, nonlinearities in the transformer core, the current transformer ct core or in both, cause a substantial differential current to flow when there is no fault. Transformer protection l instantaneous l differential lgas l thermal overload. The function of the module is to digitize the three phase currents supplied by the secondary windings of a conventional current transformer ct. 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. Accurate power transformer modeling and proper current transformer selection lead us to improved transformer protection.
Advances in bus and transformer differential protection brought to life highperformance products. Transformer differential protection electrical concepts. Simulation of a power transformer differential protective. Three basic things of any protective system measure the parameter compare the parameter control the abnormal condition by activating circuit breaker to measure the current of the power transformer we.
Transformer protection powerpoint presentation, free download. The differential protection relay is used for the protection of the generator, transformer, feeder, large motor, busbars etc. High impedance busbar differential protection minimum allowable ct saturation voltage calculation. Ppt on protection of power transformers slideshare. The protection for internal fault in such type of transformer is to be provided by using differential protection system. The differential relay works on the principle of comparison between the phase angle. Bus bar protection is considered as the most important part of power system protection because if any incorrect operation occurs, it will lead to disconnecting healthy circuits connected to the bus bar. Find powerpoint presentations and slides using the power of, find free presentations research about transformer protection ppt.
We calculated that the voltage across the nonsaturated ct, when another ct saturates, is 83. Watch one of the weekly webinars showcasing easypower power analysis software. Downloading a fault record from the protective relay. Therefore, for such differential protection scheme the transformer. High impedance busbar differential protection valence. The transformer model simulates current signals for different operating and fault conditions, these signals are. The differential protection used for power transformers is based on merzprize circulating current principle. Differential protection of transformer differential. The numerical differential protective relay is a powerutility grade, numerical protective relay siemens siprotec 5 series mounted in a tabletop enclosure.
Digital differential protection of power transformer using. This pertains to speed of operation, sensitivity, and immunity to ct saturation. Differential protection i 1p i 1s ct1 20005 a i 2p i 2s bus ct2 20005 a h1 x y i i 1s i 2s i i 1s i 2s. Transformer modeling accurate modeling of the power transformer is very necessary to evaluate protective relay performance and leads to the transformer protection improvement. Transformer differential protection electric power. Differential protection for power transformers repositorio digital. Digital differential protection of power transformer. Differential protection is a unittype protection for a specified zone or piece of equipment. Limitation of fault energy injected into a distribution transformer limited by current. Test results with an actual transformer validate the model. Ppt on protection of power transformers linkedin slideshare. An alternative principle for line protection that is quickly becoming the norm is differential protection.
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. For reliable protection and control of all types of power transformers and reactors. As soon as the load crosses 15% of the rated current, the transformer trips on differential protection. Due to the long lead time for repair of and replacement of transformers, a major goal of transformer protection is limiting the damage to. Generally differential protection is provided in the electrical power transformer rated more than 5mva. Ppt transformer protection powerpoint presentation. Digital transformer protection current adaptation, example 2 page 209 200708. Ret670 optimized for transmission applications ret670 ieds provide customized or preconfigured protection solutions for any type of transformer and shunt reactor application. Protection summary the power system must be protected. Principles of differential relaying introduction power systems divided into zones of protection e. It is based on the fact that it is only in the case of faults internal to the zone that the differential current difference between input and output currents will be high however, the differential current can sometimes be substantial even without an internal fault. Modern line current differential protection solutions.
Setting procedures are only discussed in a general nature in the material to follow. Maloperation of the protection is prevented by the loadproportional stabilizing current i s. Transformer protection transformer which our relays protect are mainly used in the lv and medium voltage distribution network of the power system. Differential protection schemes are mainly used for protection against phasetophase fault and phase to earth faults. Percentage restrained differential protection is one of the oldest forms of adaptive protection algorithms. The current ratio is used to discriminate between inrush and fault conditions. Differential protection for arbitrary 3ph power transformer. Pdf differential protection schemes and techniques for.
The paper includes a guide for properly selecting current transformers for differential protection applications. Principle of percentage restrained differential protection. The focus of this paper is percentage restrained differential protection as applied to a power transformer. In power transformers, the input power is equal to the output power.
Differential protection is based on kirchhoffs laws, stating that all current into a network node shall add up to 0 in an ideal system. Ct saturation reduces the secondary output current from the ct, and causes a false differential current to appear to the relay. The principles of differential protection you must. Using the labvolt power supply, a labvolt faultable transformer, and a sel787 relay. 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. Limitations of differential protection of transformer. Scribd is the worlds largest social reading and publishing site. 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.
Line differential protection substation automation. Protection when selecting transformer protective relaying schemes, it is important to recognize the potential impact of a transformer failure. These improvements were possible because of the availability of highperformance microprocessors, highspeed sampling. Pdf differential protection for converter transformers.
1535 1450 1475 886 966 1017 902 1603 1422 883 526 150 492 535 759 424 1045 799 936 941 683 543 181 77 1561 720 451 21 215 1638 367 1333 1338 1326 759 1110 797 1193 132 947 761 890 193 1347