Note that secondary ct currents, for such main ct connections as shown in figure 5b, have exactly the same phase angle relationship as the primary currents from the two power transformer sides see figure 4. Nov 28, 2015 background and history of differential protection of power transformer 11282015 14 the first solution to this problem was to introduce an intentional time delay in the differential relay by i. Modern power transformer is one of the most vital devices of the electric power system and its protection is critical. Power transformer differential protection through gradient of.
Power transformers differential protection using the pq. But the effect of even a rare fault may be very serious for a power transformer. Power transformers pt play an extremely important role on the reliability and energy supply continuity of electric power systems eps. We discuss each operating condition and its effect on the power transformer, and provide a solution in the protection scheme for each operating condition. Differential protection of a transformer the transformer is one of the major equipment in power system. Differential protection for shunt reactors and power.
One of the most effective transformer protection methods is the differential protection algorithm. Keywords symmetrical component, inrush current, internal fault, transformer protection i. Application of discrete stransform for differential. The power transformer nameplate in the pst mode of operation is given in 9. Power transformer is one of the most important components in power system, for which. Pdf a currentbased solution for transformer differential. Ii 0 correction provides full earth current sensitivity and correct phase selective fault type indication, however requires ct in the neutraltoearth connection of the transformer. The xd1t relay is a strict selective object protection for twowinding transformers. Currently, percentage differential protection is a common practice for power transformer protection. Second, we investigate harmonics restrain scheme and microprocessor basedprotection on power transformer differential protection. Energy is lost in the process of transmitting electricity long distances, such as during the journey from a power plant to. Setting procedures are only discussed in a general nature in the material to follow. Voltage transformers in our electric power systems windows.
The t35 performs automatic phase shift compensation for all types of transformer winding. Overcurrent protection devices such as fuses must be selected to allow this harmless inrush to pass. Zocholl, armando guzman, daqing hou schweitzer engineering laboratories, inc. Digital differential protection of power transformer using. Introduction 1power transformers are very expensive and vital components of electric power system. Introduction in general, the main concern with transformer protection is protecting the transformer against internal faults and ensuring security of. Later, when the transformer is reenergized, the core is likely to. In this type of protection the electrical quantities entering and leaving the protected zone or area are compared by current transformers c. Power transformer differential protection using current. Some of the power transformers are used in generating stations, substations and power transmission lines for either stepping down or stepping up the voltage. Differential relay is a type of protection relay protecitve relay, differential relay is very commonly used relay for protecting transformers and generators from localised faults. Apr 21, 2017 differential relay is a type of protection relay protecitve relay, differential relay is very commonly used relay for protecting transformers and generators from localised faults.
Figure 1 simple diagram connection for differential power transformer protection. Demagnetization of power transformers following a dc resistance testing g. 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. Modeling of power transformer for differential protection using pscad l. Problem statement article pdf available in ieee transactions on power delivery 164. Abstractthe differential protection of power transformer is a unit protection scheme. Pdf protection of power transformer using microcontroller. A currentbased solution for transformer differential protection part i. Introduction power system protection is one of the electrical engineering fields that relates to the electrical power systems protection and its duty is isolation of faulty parts from the rest of the. The information provided by the harmonic content of the differential active and reactive power components is used to detect winding insulation failures and to distinguish them from magnetizing inrush current transients. Differential protection for arbitrary 3ph power transformer. In the area of relay protection this means that a faster and sensitive protection is needed, while undesirable operation of the protection system is almost unacceptable 10.
Transformer protection 1 of 12 section i introduction the primary objective of the transformer protection is to detect internal faults in the transformer with a high degree of sensitivity and cause subsequent deenergisation and, at the same time be immune to faults external to the transformer i. It is therefore of crucial importance the development of new transformer protection. Protecting power transformers from common adverse conditions. If the overcurrent protection is on the source end of the 3 km feeder, and is set low enough to see all transformer faults, and there is no problem with tripping other feeder loads for a transformer fault, then this is probably enough for a 500 kva transformer. Main 1 differential protection features the main 1 i. Generally differential protection is provided in the electrical power transformer rated more than 5mva. Power transformer differential protection using current and. Causes of this phenomena, such as winding dc resistance testing, and consequence of the remanent flux are described. Differential protection of transformer differential relays. Transformers sometimes called voltage transformers are devices used in electrical circuits to change the voltage of electricity flowing in the circuit.
One major problem is that power is lost between the power plant and the consumers because currents use some of the power to heat the transmission lines. By using this method differential protection for arbitrary power transformers will be ideally balanced for all symmetrical and nonsymmetrical throughload conditions and external faults. Transformer modeling as applied to differential protection stanley e. Demagnetization of power transformers following a dc. The current ratio is used to discriminate between inrush and fault conditions. The differential protection then bases on matching the primary and secondary current of the trnasformer for ideal operation. Interwinding faults short circuits and ground faults within power transformers can be detected by this protection scheme. The rogowski coil applications for relay protection presented here include differential protection of power transformers, busbars, generators, and large motors. The continuous monitoring of power transformer can provide early warning of electrical failure and could prevent catastrophic losses. Protection of power transformer using microcontrollerbased relay.
This paper describes the application of the pq power theory to the differential protection of power transformers. The differential relay works on the principle of comparison between the phase angle. Transformers can be used either to increase the voltage called stepping up or decrease the voltage step down. International journal of engineering research and general. Differential protection for special power transformers with ret 670 sa2007000028 page 7 7 4. The trainer contains two sets of three singlephase transformers to demonstrate threephase transformer bank configurations such as wyewye, deltadelta, closed. Tech, department of electrical engineering, nit patna, india 1professor, department of electrical engineering, nit patna, india. New general method for differential protection of phase. Power transformers are classified as one of the most valuable equipments in a power system, hence their protection is of very high importance.
This paper will point out some key bullets of similarities and differences for the differential protection applied to a shunt reactor 87r or a power transformer 87t. The problem associate with these methods is the need to design neural networks or fuzzy lows, which require a huge number of training patterns produced by simulations of various cases m. Identifying inrush currents from internal faults using. The faults occur in the transformer inside the insulating oil can be detected by buchholz relay. This paper presents a new methodology for identifying internal faults and inrush currents in power transformers based on the gradient of the differential current. Differential elements compare an operating current with a restraining current. On transformers connected to long, overhead power transmission lines, induced currents due to geomagnetic disturbances during solar storms can cause saturation of the core and operation of transformer protection devices. A new approach in power transformer differential protection. Digital differential protection of power transformer. In this case the protection setting may be at a level that does not pose a threat to the transformer but does indicate a grid problem. It is a static device, totally enclosed and usually oil immersed, and therefore the fault occurs on them are usually rare. The power transformer differential protection using.
The technique is to calculate the angle of the gradient vector along the curve of the differential current in the data window and through waveforms recognition techniques to identify the type of occurrence. However, nonlinearities in the transformer core, the current transformer ct core or in both, cause a substantial differential. International journal of engineering research and general science volume 2. The method is independent of individual transformer winding connection details i. The differential current signals are infected by noise and the robustness of the algorithm under noisy conditions is investigated. Pullman, washington abstract this paper presents a power transformer model to evaluate differential element performance. The t35 transformer protection system is a threephase transformer relay designed to protect power transformers with up to six windingsrestraints. Mar 23, 2016 differential protection setting calculations transformer size mva rating voltage taps no load transformer connection current transformer ratios current transformer connection voltage transformer ratios voltage transformer connections lg or ll ltc tap information calculating differential set points and system setup 87t sample. It is therefore of crucial importance the development of. Types of faults there are two types of faults 1 external fault 2 internal fault the faults that occur within the transformer protection zone are internal fault. As per standard protection practice, these two differential relays have been set to be ideally balanced for the power transformer oltc midtap position. Power transformer differential protection through gradient.
Differential protection of power transformers figure 5 shows a traditional power transformer differential protection based on conventional cts. Principles of differential relaying my protection guide. Mar 26, 20 this paper presents a new methodology for identifying internal faults and inrush currents in power transformers based on the gradient of the differential current. In this paper we use the decision tree method to offline differential protect of the power transformer which is. A power transformer is a very expensive electrical device, and its operation directly affects the performance of. Differential protection of eaf transformers rogowski coil. The differential protection of transformer has many advantages over other schemes of protection. This paper presents the use of ann as a pattern classifier for differential protection of power transformer, which makes the discrimination among normal, magnetizing.
Jun 27, 2016 in differential protection of transformer ct matching is an important thing to care care else differential protection wont be efficient and reliable. 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. Adaptive differential protection 18 and also decision tree 19 are used to protect the transformer. Introduction transformers are a critical and expensive component of the power system. Voltage transformers in our electric power systems. Second, we investigate harmonics restrain scheme and microprocessor based protection on power transformer differential protection. Differential protection of transformer differential. When a transformer is switched off, its core generally retains some residual flux. Mohammed tawfeeq alzuhairi 321 differential protection differential protection is the best technique in protection. Casper labuschagne, schweitzer engineering laboratories, inc.
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. Background and history of differential protection of power transformer 11282015 14 the first solution to this problem was to introduce an intentional time delay in the differential relay by i. Application of discrete wavelet transform for differential. 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. Distribution transformer trainer labvolt series by festo. In differential protection of transformer ct matching is an important thing to care care else differential protection wont be efficient and reliable. International journal of engineering research and general science volume 2, issue 4, junejuly, 2014. The transformer differential protection provides fast tripping in case of a fault before severe damage spreads out. For this reason, the protection of power transformers has taken an important consideration by the researchers. Similar to bus protections, transformers are protected by differential relays. The protective scheme for power the protective scheme for power transformer should operate only for the internal fault, and it must be insensitive for any fault outside the zone of protection. It also provides an extra investigation on how the differential protection is affected by switching in a shunt reactor and a power transformer. Universal testing method for power transformer differential. Transformer performs a great job in the power system to change voltage and current level so proper protection for the transformer is important to maintain reliability in the system.
The operating current also called differential current, i d, can be obtained from the phasor sum of the currents entering the protected element. Application of discrete wavelet transform for differential protection of power transformers. Numerical differential protection of power transformer using ga trained ann neha gupta, harish balaga, d. By using stepup power transformer, the voltage level in the transmission line is increased, thereby low current flows through the line. In order for the electrical power distribution network to function, voltages must be stepped up before power is transmitted great distances over power lines. Principles of differential relaying introduction power systems divided into zones of protection e. May 15, 2018 generally differential protection is provided in the electrical power transformer rated more than 5mva. Transformer differential protection electrical concepts. Fault, inrush current,protection stransform transformer. The distribution transformer trainer is a portable, handson trainer designed to allow students to develop the skills required to connect single and threephase transformers similar to those found in north american ac power networks. Numerical differential protection of power transformer using walsh hadamard transform and block pulse function based algorithm kumari rashmi1, dr. Internal faults transformer can be divided into two types. Abstract power transformers of various size and configura tion are applied throughout the power system. Once the phase angle relationship between the two ct secondary currents is known.
Differential protection setting calculations transformer size mva rating voltage taps no load transformer connection current transformer ratios current transformer connection voltage transformer ratios voltage transformer connections lg or ll ltc tap information calculating differential set points and system setup 87t sample. Under frequency protection on a power transformer may be a form of load shedding to assist the system to recover from overloads. To develop a new monitoring procedure for power transformer. The t35 provides for automatic or userdefinable magnitude reference winding selection for ct ratio matching. Raka levi dv power, sweden abstract this paper discusses several methods for removal of remanent magnetism from power transformers.