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An invasive diagnostic technique is proposed in this article for the detection and discrimination of turn-to-turn faults in the stator and rotor windings of synchronous machines during the startup period. For this purpose, search coils are installed in the machine to sense the rotational magnetic field along the air-gap circumference, while the difference in the related induced voltages (differential voltages) reveals its distortion, using it as a criterion for the detection of the faulty condition. Nevertheless, the rotor speed is a time-variant parameter, which changes from zero at the starting instant up to its rated value at a synchronous speed. Consequently, during the generator startup, the frequency of the induced voltages in the search coils needs to be updated continuously for obtaining reliable values for the differential voltages. A simple method is presented to achieve this goal by detecting the sequential zero crossing of the voltage waveforms. The proposed method is verified through simulation and experimental results. They show that the proposed diagnostic technique is capable of detecting and discriminating stator and rotor turn-to-turn faults during the machine startup period, both in generating and motoring conditions, with suitable accuracy and security. In addition, the region of stator turn-to-turn faults can be easily identified. [ABSTRACT FROM AUTHOR]

The impacts of the static synchronous compensator (STATCOM) on the traditional loss of excitation (LOE) protection are investigated in this article. To do a comprehensive study, a common and realistic excitation system is developed for the generator by employing the phase-domain model of the synchronous generator accessible in the real-time digital simulator. Using such a model, the LOE phenomenon is realistically studied in accordance with IEEE Standard C37. 102-2016, while the generator dynamics along with the LOE relay performance are investigated through different types of partial and complete LOE events. It is shown that in the presence of STATCOM, two major impacts on the generator and its LOE protection can be expected: 1) it imposes an additional time delay on the relay to detect the LOE failures, which depends on the generator initial loading and the type of LOE failure and 2) it might lead the generator to reach a new stable operating point without experiencing a loss of synchronism condition, during an improper changeover from automatic voltage regulator to manual voltage regulator operating mode. The related consequences for both of the impacts are discussed in this article, and some solutions are suggested to deal with the probable negative aspects. [ABSTRACT FROM AUTHOR]

A portable flux probe is proposed and investigated in this article to detect turn-to-turn fault in the rotor poles of the high rated salient pole synchronous machines. The rotor circuit is fed by a low amplitude sinusoidal voltage source with a fixed voltage amplitude which has a frequency more than a few hundred Hz to achieve the higher reaction of the shorted turns on the faulty pole, which results in a significant reduction of the magnetic flux in the air-gap. Numerous simulations and experimental tests are carried out to investigate the proposed probe and the related technique performance to specify the faulty pole versus the number of shorted turns, applied frequency and probable eccentricity in the rotor position. The obtained test results show that all stable turn to turn faults (weak or heavy ones) can be specified easily by applying a portable sinusoidal voltage source with the frequency in the range of more than a few hundred Hz. The experimental test results validate that the flux density can be reduced to about zero in the faulty pole face, even in the case of one shorted turn in the sample machine. [ABSTRACT FROM AUTHOR]

A new approach for generator loss of field (LOF) protection is proposed by estimating the field current based on the generator measurable parameters. The main idea of the proposed approach is that a significant difference will be created between the measured excitation and the estimated field currents during LOF occurrence. A differential index is introduced to monitor such difference and consequently to detect LOF failures. A detailed and realistic field circuit is considered for the generator by using the phase-domain model of the generator in the real-time digital simulator, while different types of LOF events can be simulated through such model as well. The obtained results show that the presented technique can detect various types of LOF events much faster than the conventional impedance-based scheme. Moreover, it exhibits more security than the conventional technique in the face of power system disturbances (e.g., stable power swing and out-of-step conditions). [ABSTRACT FROM AUTHOR]

A flux-based technique is proposed for the on-line detection, localization and discrimination of stator and rotor turn-to-turn faults in synchronous generators, using the measured air-gap rotational magnetic field. Simple magnetic field sensors (MFSs) are installed in the stator slots at different regions, and the corresponding induced voltages are measured. Several differential voltages are then obtained to give a picture of the rotational magnetic field symmetricity, whose distortions indicate the presence of the stator or rotor faults. The proposed diagnostic technique is presented in detail and validated initially by simulation results obtained with a finite element simulation package and afterwards through the experimental tests. The obtained results demonstrate that the proposed technique can be used to detect and discriminate stator and rotor turn-to-turn faults with appropriate sensitivity. In addition, the region of the stator turn-to-turn faults can be identified as well. [ABSTRACT FROM AUTHOR]

This paper presents a novel technique for the online detection of broken rotor bar(s) (BRBs) in induction motors, based on the analysis of the air-gap rotational magnetic field (RMF), being it indirectly sensed using the voltages induced in dual search coils installed in several stator regions. The induced voltages allow obtaining three differential voltages which reveal the symmetricity level of the mentioned field along the stator circumference. Under the presence of the broken bar(s), the RMF is disturbed by the rotor magneto-motive force, being these disturbances detected through the fundamental components of the differential voltages using a new time-domain analysis technique. The proposed diagnostic approach is verified by finite-element analysis and also by several experimental tests. A high sensitivity, robustness in the face of unbalanced voltage sources and motor load level variations are the main advantages of the proposed technique. Moreover, it is a secure method for BRB detection, easily implementable in low-cost digital signal processing units. [ABSTRACT FROM AUTHOR]

A real-time realistic framework for synchronous generator loss of field (LOF) protection studies is suggested in this paper by using the real-time digital simulator, which allows the user to realistically model the generator field supply circuit. By using such framework, the performance of LOF protection algorithms can be comprehensively evaluated in the face of the various LOF events including the short circuit and two types of the open circuit events, while the open circuit occurrence cannot be studied in the conventional simulation programs. The obtained results demonstrate that the generator dynamics are significantly different in the face of various LOF failures and then all of them must be regarded to develop the new LOF protection algorithms. By using the suggested framework, the performance of some recently proposed schemes along with the conventional impedance and the admittance relays are comprehensively evaluated. The obtained results from applying the various LOF failures show that, against the conventional relays, the new schemes cannot detect all types of LOF failures and so, they do not have enough reliability. [ABSTRACT FROM AUTHOR]

A new air-gap flux-based technique is proposed in this paper for turn-to-turn fault (TTF) detection and defective region identification, which is implemented in line-connected and inverter-fed induction motors. Some search coils (SCs) are used to measure the magnetic flux in various air-gap regions of the mentioned motor. The induced voltages in the SCs reveal the configuration of the rotational magnetic field (RMF) along the stator inner circumference to assess the symmetricity level of the flux distribution at each time instant. The RMF asymmetric distribution can be detected by comparing the induced voltages in various dual SCs (which under healthy conditions must sense identical magnetic flux) to detect TTFs and identify the faulty region as well. The proposed method is verified through finite element simulations and also by carrying out several experimental tests. Despite the fact that the proposed method is an invasive diagnostic technique, significant sensitivity and robustness in the face of unbalanced voltage sources and/or loading level are compelling evidence to use it for TTF detection at an incipient stage. The capability of the proposed technique to identify the faulty phase and the related region in the stator is another advantage of this invasive method, which cannot be ignored. [ABSTRACT FROM AUTHOR]

Power transformer, as one of the most important apparatus in power system, must be protected against the turn-to-turn faults. Although the various methods based on the terminal currents and/or voltages have been presented for transformer protection, the flux-based methods can be used to achieve the more accurate, sensitive, and secure results. Since the symmetrical form of the magnetic flux distribution will be disturbed due to any fault occurrence in the transformer windings, it can be considered as an appropriate criterion to achieve a suitable protection algorithm, which can detect the fault occurrence and identify the faulty phase/region. In this paper, a new leakage flux sensor is introduced and then a flux-based technique is proposed to detect and identify the faulty phase in transformers to apply in online conditions. By using the proposed technique, the faulty region can be identified in offline conditions, as well. The experimental results (which are done on a distribution transformer) show that this technique is secure in the face of overfluxing and transformer energizing conditions and can detect turn-to-turn faults with high sensitivity. Moreover, tap changer operation, imbalanced loads, and/or unsymmetrical voltage sources cannot influence the proposed technique security. [ABSTRACT FROM PUBLISHER]

Loss-of-field (LOF) phenomenon in synchronous generators may cause equipment damage and voltage drop in the power system, which can be terminated to a blackout. Conventional schemes, which detect LOF on the basis of the measured impedance from the generator terminal viewpoint, have some major drawbacks such as low speed, complicated setting procedure, and unsecure performance in the face of similar phenomena, e.g., stable power swing. In this paper, different electrical quantities of the generator including terminal voltage (V), current (I ), active (P) and reactive power (Q), and power angle (δ) variations are studied to achieve a secure technique for LOF protection in synchronous generators. Comprehensive studies show that a simple criterion based on polarities of V, Q, and δ variations is accessible to achieve this goal, which does not need a complicated procedure to set it. To evaluate the performance of the proposed algorithm, some cases are simulated on sample power systems under various operating conditions. Also, superiority of the proposed algorithm in comparison with the other schemes is proven by the obtained results, as well. Moreover, the proposed technique is experimentally tested by using some 2-kVA laboratory generators to detect LOF. [ABSTRACT FROM AUTHOR]

Among the various techniques for transformer protection, more accurate, sensitive, and secure results can be achieved by the flux-based ones. The symmetrical form of the magnetic flux distribution will be disturbed due to any fault occurrence in the transformer windings. So, it seems that this is an appropriate criterion to achieve a suitable protection algorithm, while it can be used to detect faults as well as identify the faulty phase/region. In this paper, a miniature sensor is proposed consisting of simple planar magnetic flux sub-sensors and located in the existing space between the transformer core and the first insulating layer to sense the leakage flux distribution. Comparing the induced voltages in symmetrical sub-sensors for each phase exhibits asymmetrical configuration of the leakage flux distribution and identifies the faulty region in that phase. Appropriate fine and tiny construction of the proposed sensors provides them a good choice to install in the transformer core vicinity. Then, the leakage flux can be sensed in the origin regions during turn-to-turn faults. Experimental results show that such sensors have high sensitivity to detect leakage flux that ejects from the core or comes back to it. [ABSTRACT FROM PUBLISHER]

Analyzing of detected partial discharge (PD) signals is a reliable technique to assess the electrical insulation in power transformers. In order to detect and locate the PD sources in power transformers, some distributed simple fine sensors are proposed and used, which are made by a few turns of thin enameled copper wire wrapped around the transformer core. They are distributed sensors, which sense PD voltage signals through capacitive coupling with the transformer windings. Two methods, including broadband and limited-band PD signal analyzing, are considered to identify defective phase and/or region on that phase through the proposed distributed sensors outputs. Transfer functions of these sensors are obtained and it is experimentally shown that although defective phase can be diagnosed, the expected priority to identify defective region is not regarded in broadband analysis, while a suitable limited frequency band can be found to achieve this aim. The idea is implemented on a sample transformer by injecting artificial PD signals to different high-voltage winding sections. The results show that not only PD signals can be detected through the mentioned sensors with high sensitivity, but also defective phase can be diagnosed using broadband analysis. Moreover, defective region can be accurately identified by limited-band analysis. [ABSTRACT FROM PUBLISHER]

Current-transformer (CT) saturation phenomenon impacts the performance of the current-based protective relays and leads them to malfunction; so detecting and resolving such phenomenon are important issues in power system protection. This paper provides a modification for two well-established algorithms: 1) least square error and 2) artificial neural network to compensate and reconstruct CT's distorted secondary current waveform (CTDISCW). The effectiveness of an online algorithm is its operating capability in noisy environments and in the presence of travelling waves generated by any event. In addition, this algorithm must be stable against any normal variation in network structure. Then, both mentioned methods need to be modified to present proper results with an acceptable error in online conditions. In this paper, a real CT is considered to simulate, and a section of the Iranian power network is selected to generate CTDISCWs using the modeled CT, and to evaluate the proposed algorithms’ performance. [ABSTRACT FROM AUTHOR]