Hydro generators are considered as an essential component in power generation system as it transforms turbine's mechanical energy into electrical power. The main focus of this paper is based on inter- turn fault in salient pole rotor that mostly occurs in standard synchronous generators. Most of the synchronous generators come across with winding short circuit failures. It is mandatory to detect fault at an early stage and take appropriate diagnosis methods to overcome it. From the literature survey conducted, it is observed that there are number of techniques proposed by various researchers to detect the faults in hydro generators. These techniques were able to assess fault position, detect fault at an early stage, and to cope up with rotor intern-turn. Furthermore, less research has been done by researchers on various dependences factors of fault detection and in future there is a great scope of development of various decision modeling approaches for online fault detection.
A loss in speed produces generator physical size and cost for a definite value of power [3]. Furthermore, the hydro generators are classified into four categories as shown in figure1.1. Vertical Shaft
Generators
PIT Type Generators
Motor Generators
Variable Speed
MotorGenerators Vertical Shaft Generators: The turbines with Vertical shaft especially in hydro are connected to vertical shaft generator with outputs ranging up to 840 MVA. Vertical generators for Pelton, Kaplan, and Francis turbines have been used in the past for a wide variety of outcomes and speeds. PIT type Generators: PIT generators have been used in low-head implementations and that is the reason it is connected to the horizontal turbine shaft by use of step-up gear. PIT implementations are a cost-effective alternative for hydropower stations with low head and lower ratings (typically up to 17 MVA). PIT generators are known for their solid design and ability to withstand the high runaway speeds needed by hydropower plants.
Motor Generators: To operate pump turbines and produce electricity, pumped storage plants utilize motor generators. With novel adaptive speed and one or two rotation directions, motorized generators for the implementation of pumped storage. It could exceed up to 360 Million VoltAmps.
Variable Speed Motor-Generators: To maintain synchrony with the grid frequency, the turbine and generator’s rotational speeds should be constant in traditional plants. The grid's capacity to provide ancillary services is constrained under these conditions. Furthermore, at a constant speed, the pumped-storage plants prevent the pumping power from being adjusted, therefore restricting the most efficient usage surplus electricity [4].
Any enterprise or process's overall economy is highly dependent on fault detection. Vibrationsignal-, knowledge-, and Model-based methods are currently three types of approaches that are based on HGU's fault diagnosis [5]. Researchers have studied a wide variety of system defects, such as uneven stator plus rotor, eccentricity in addition to bearing faults with split rotor bars. Generator breakdown can cause significant economic losses for the HGU. Fault identification, study and control are therefore very critical activities to be considered in order to prevent significant economic losses. This will reduce unexpected faults, downtime repairs and operating costs. It could also be avoided to operate electrical equipment in dangerous conditions. 1.1.
Rotor inter-turn short circuit fault is a type of synchronous generator failure. Synchronous generators have complicated structure, high voltage and high workload characteristics. Moreover, the generator rotor is under rotary vibration for a long period and can lead to failure. The rotor windings failure of the inter-turn short circuit is more prevalent [6]. Most synchronous generators occurred with an excitement winding short circuit failure or were defective [7, 8]. The rotor winding short-circuit result into increased excitation and intensifying rotor vibration in the broad synchronous generator [9, 10]. The fault features of inter-turn winding are too small to be effectively established in the initial stage. If a short circuit fault is not resolved, the rotor winding inter-circuit may result in a major mishap and pose a considerable risk to the safe operation of the generator and the power system. The safe, consistent operation of the synchronous generator is critical to ensuring that the power supply of the electrical system is safe, and the synchronous generator rotor winding inter-turn failure in the early stage needs to be established.
As discussed in the previous section that the rotorinter turn short circuit may result for major accident and many other impacts, therefore it is mandatory to early detection of such faults and takes appropriate precautions to overcome it. There are number of techniques those are proposed by researcher for detection as well as for diagnosis purpose. This section presentsa literature survey of various short circuits related fault detection and prevention approach. Following this review, a tabular comparison for these techniques is also mentioned. Finally, a conclusion and future scope of research in given.Yong-gang Li, et al. [11], presented the reverse calculation approach for the no-load curve and used just electrical parameters like active, reactive, voltage, and current. A. Ur Rehman et al., [12], proposes a method for detection of inter-turn short circuit faults in rotor winding relied on fundamental electrical characteristics. C. Wei, et al. [13], proposed a failure diagnostics technique to deal mostly with rotor windings which were utilized for online fault control, inter-turn short circuit fault those are found in synchronous condenser. W. Shuting and T. Haixia, [14],the parallel linked branches of the stator, which circulate current features, due to the inter-turn failure of the rotor winding were examined. Also, a system is designed for fault diagnoses using virtual instruments. H. Sabir, et al. [15], developed a combined technique based on CSA (Current Signature Analysis) and TSA (Time Synchronous Averaging) to boost the wind turbine control system and the DFIG down time S. E. Zouzou, et al. [16], proposed to employ the PRI (Partial Relative Indexes) as fault indicators to enhance the fault detection process.L. Yonggang et al. [17], evaluated the variations in electromagnetic characteristics, electrical parameters as well as the defect specifications which maximize the field current and reduce reactive power after failure to propose a new online methodology for analyzing the rotor inter-turn failure of the brushless excitation synchronous generator. F. Sun, et al. [18], an RSO approach was developed to assess the fault position of the inter-turn short circuit by examining the signal propagation time, winding symmetry and fault function database.T. D. Razafimahefaet al. [19], designed a turnaround short circuit in the induction machine's stator and rotor windings as well as the identification of a defect in startup.S. S. S. R. Sarathbabu Duvvuri, et al. [20], developed an induction motor models with reference framework theory. The diagnostic significance for the short-speed rotor turn-to - turn faults of these SRIM models was studied.
Proposed a failure diagnostics technique to deal mostly with rotor windings which were utilized for online fault control, interturn short circuit fault those are found in synchronous condenser.
T. D.
et al. [19] S. S. R.
SarathbabuDuv vuri et al. [20] 2007 2018 2010 2016 2019 2015 2018
turn failure in the brushless excitation synchronous generators.
inter-turn short circuit by examining time of the signal propagation , winding symmetry and fault function database
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This article provides an overview to hydro power generators and detail description of the inter turn short circuit fault. From the literature survey, it is observed that hydro generator rotor fault detection techniques are inaccessible or complicated. For detection as well as for diagnosis purpose, a large number of techniques were proposed by researchers. In addition to this, various methods were proposed by researchers to deal with rotor inter-turn fault short circuit. After analyzing various papers based on intern-turn fault short circuit we find that there is a scope of improvements in these methods to detect fault at an early stage. Furthermore, various decision modeling approaches could be made using dependences factors of online fault detection.
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