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Abstract Reliable and dedicated protection of the transformer is the main requirement in the power system due to the supervision of a highly expensive equipment transformer. Non‐linear characteristics of the transformer give mysterious behaviour for the period of inrush and Current transformer saturation conditions. As a stagnant and electro‐magnet...
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A transformer is the heart of the entire power system and power is the heartbeat of the entire nation for the growth of the manufacturing, production, and industrial aspects. All terms are directly concerned with the Direct Foreign Investment (FDI) of the nation. Mostly, all types of businesses depend on the reliability and continuity of electricity. So, the “without power no business” slogan proves its usefulness. Power system protection is very crucial and complex due to having huge numbers of nodes. The contingency of various tactics is involved in the system and if it is done randomly then the mis-operation of the protective schemes occurs. Nowadays, the deregulation of the power network involves the malfunctioning of several system parameters. As far as a concern with the reliability of the power network, it is directly apprehension to the growth of the nation. As a key component in the power system, the protection of the power transformer has remarkable importance. Power transformer designing has many complexities like nonlinearity of its core, higher power rating, different voltage and current ratios, different phase angles in primary and secondary, and connection class. Having numerous complexity and different operating characteristics of power transformers, protection also becomes multifarious. Also, unwanted tripping of power transformer generates issues not only for consumer or industry but it gives an effect for the ecosystem of society, economy, political scenarios, and the entire nation. Different power transformer failure analysis is carried out by focusing on the failure of protective schemes (Rajurkar et al. in 16th National power systems conference, pp 180–185 [1]). Even, in the international market, different failure analyses with recent trends and involvement of further scope for the protection are analyzed in depth (Binder in Transformers-magazine, vol 1, no 1, pp 30–33 [2]).
Modern-day unit-type transformer protection required a special performance that can adapt to any situation carefully with flexibility in all functions. It should cover all the abnormalities and discrimination ability against small internal faults with caution. Many possibilities of inter-turn fault, CT saturation under fault conditions, core saturation of transformer, magnetizing inrush, etc., are considered individually or with a different combination. This chapter exemplifies all the above-said conditions with combinations under unit-type protection. A smart relay is developed with the multifunctioning condition to operate under faulty conditions in the internal area of the device. An algorithm is validated in PSCAD™ software and a laboratory environment. Detection of inrush in transformer core to avoid malfunctioning in unit-type protection, itself a very crucial condition. The second derivative of differential current is elaborated here to evaluate the inrush current successfully. CT saturation conditions also cause severely misguided tools in protection. Here, in this chapter, adaptive algorithm is developed based on the saturation index. If saturation is detected in the CT, then percentage-biased characteristics shifted adaptively and avoid malfunctioning under such abnormality. Sometimes over-fluxing conditions are generated due to the amplification of system parameters. Times for over-fluxing are normally momentary or very small under starting of the transformer for a few cycles. Mostly, fifth and seventh harmonics are predominant under over-fluxing conditions. So, based on the fifth and seventh harmonic levels, detection techniques are also incorporated into the proposed algorithm to overcome this abnormality. So, here in this chapter inrush, CT saturation, and over-fluxing conditions are incorporated with discrimination of internal fault and other abnormal conditions to avoid the unnecessary operation of percentage-biased differential protection of the power transformer. A trip signal is generated as per the suggested algorithm when an internal fault or severe abnormality arises in a transformer. The considered power system diagram is simulated in PSCAD™ software. Voltage and current data are captured through the CT & PT of PSCAD™ and analyzed by the Modified Full Cycle DFT (MFCDFT) algorithm in MATLAB software. The hardware setup is developed in the laboratory environment considering the physical three-phase transformer with tap facilities on both windings. Various abnormal and fault conditions are generated and real-time testing has been performed on a developed algorithm. The suggested algorithm runs successfully on software and hardware with result analysis and proved its acceptability in a real field of power systems.
The unit protection method is universally accepted as the chief protective scheme for transformers. In conditions such as transitory over-fluxing, the universally accepted unit type of protection may mal-operate. Higher voltage level side and lower voltage level side currents become unequal in the transformer, because of core saturation. This chapter depicts the recognition of such conditions compared to the condition like interior fault, because of the fifth harmonic content of difference current. By identifying the amount of fifth harmonic w.r.t. the primary constituent of the difference current, the operational setting of the percentage bias feature is customized to evade false actions. When this type of circumstance is recognized, the presented algorithm triggers time delayed V/f relaying scheme to save the equipment. Here, the projected scheme is authorized on the PSCADTM platform, and post to that these collected data are exported to a MATLAB-based program, and then it is used for additional corroboration. The projected scheme is certified by testing various test circumstances like normal loading conditions, exterior fault, interior fault, as well as excessive fluxing in the core. One can say that the presented algorithm truthfully spots the interior fault condition inside of the transformer or can obstruct the triggering of relay operation under momentary over-fluxing (temporary excessive fluxing) circumstances. More on these, to evaluate the proficiency of the projected scheme, an experimental evaluation is checked on a one-phase transformer. Data received from diverse test conditions are recorded using DSO, the captured data then transfer to the computer to export it to the algorithm to check its proficiency. After examining the entire outcome, it can be clearly stated that the projected algorithm could never prevent the transformer separation during the occurrence of temporary excessive fluxing.
A trustworthy and devoted defensive system for a transformer is a prime necessity in power structure because of an extremely pricey and dependable apparatus. Nonlinearity feature of this device offers puzzling characteristics during inrush as well as CTs’ saturation states. Being an electrical-magnetic machine, it is mostly inducted by a heavy rush of current known as inrush. The behavior of the core becomes a significant case which may be an obstruction to discriminating the faults. Here, in this chapter, the impact of the inrush condition, precedent study performed to distinguish inrush from fault state, and a distinct technique for identification of it are explained. Around 50 research articles, a variety of books along with research theory are meticulously referred to evaluate the existing classifier methods. A relative investigation is performed to propose to filter out the pros and cons of different methodologies. Additionally, the average derivative angle of differential current-based resolution is presented to pick out the inrush case from faults and abnormalities. A detailed software simulation is performed to check the feasibility of the suggested scheme. The obtained outcome demonstrates the impact of inrush as well as the identification of faults. It is to be observed from the results that the scheme is capable of discriminating inrush and all kinds of faulty conditions within the considered transformer.
