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This paper presents a new index for fast and reliable protection of the synchronous generator (SG) against loss of field (LOF) incidence, focusing on the most important factors including operation time, reliability in clustering LOF and power system disturbance (PSD), and practical application. To this end, all allowable electrical parameters at SG...
Citations
... The last two methods show that the trip time is significantly reduced. The ratio of load angle derivative and reactive power is presented as a safe index of LOE detection in [25]. In [26], an LOE fault detection method based on the analysis of voltage and current waveforms is presented with the aim of improving performance in different situations. ...
... An evaluation of the efficiency of the mentioned approach versus the impedance-based approach when various LOEs occur at t = 1s is presented in this section. Based on investigations in [25,29] and simulations performed in this study, Table 3 summarizes these comparisons' results. LOE detection time is significantly reduced by the proposed strategy, as seen in Table 3. ...
One of the common methods to detect Loss of Excitation (LOE) is the impedance‐based technique. But it is too slow, and may show incorrect performance when faced with power system disturbances like stable power swings (SPS). To improve the aforementioned problems, a new index is introduced based on the change of transient states of the synchronous generator which are estimated by Extended Kalman filter (EKF). The principal idea of the proposed method is that the angle between the transient voltage and q‐axis internal voltage phasor will be increasing during LOE events. Therefore, this angle and its derivative are used. Estimation of the internal variables of the generator is used to achieve the angle between transient voltage and internal voltage phasor. To evaluate the efficiency of this algorithm, numerous simulations are performed on various networks and in different operating conditions. The simulation results of the method demonstrate that this approach both reduces the detection time in most cases and improves its security in the encounter of the other disturbances. Experimentally, the performance of the proposed method is evaluated by using a 5 kVA laboratory generator. Experimental studies show that the presented algorithm performed correctly detects LOE and SPS conditions.
... The reported results show that it has been able to correctly and effectively identify the simultaneous occurrence of LOE and PSD events. In some other researches such as [12,14], threshold-dependent methods have been proposed as effective methods to identify the LOE event. In [12], a new combination index is presented using the ratio of δ sg to Q sg , which despite proving its proper performance in conditions of complete LOE and PSD events, there are still the possibility of its wrong performance in SGs with various capacities, and serious need to update the operational threshold for each SG. ...
... In some other researches such as [12,14], threshold-dependent methods have been proposed as effective methods to identify the LOE event. In [12], a new combination index is presented using the ratio of δ sg to Q sg , which despite proving its proper performance in conditions of complete LOE and PSD events, there are still the possibility of its wrong performance in SGs with various capacities, and serious need to update the operational threshold for each SG. In [13], using the multiplication of the V sg and Q sg parameters and applying the derivative operator to it, a new LOE protection index is developed. ...
The most common disadvantages of loss of excitation (LOE) impedance relay are its improper operation in the conditions of power system disturbances (PSD) and its long operation time. In this regard, to solve the mentioned problems and as a result improve the accuracy and speed of detecting the LOE events, four key variables including active power (Psg), reactive power (Qsg), load angle (δsg), and terminal voltage (Vsg) are selected, on the basis of an in‐depth theoretical‐ and simulation studies. These variables have been implemented in a precise combinational logic. In the developed LOE detection logic of this paper, the dependent parameters of Vsg and Qsg as well as Psg and δsg parameters are examined simultaneously in an AND logic cluster. If both the defined combinations detect the occurrence of LOE, the generator trip command is issued. Otherwise, the normal operation of the under‐study machine will continue. The results of the performed simulations in MATLAB/Simulink environment (2017b) during the detailed scenarios of LOE and PSD events on the IEEE 39‐bus standard system confirm the efficiency of the outlined LOE protection model. Meanwhile, its superiority from the viewpoints of accuracy, swiftness, and simplicity and cost of implementation are comprehensively compared with the other schemes.
... Hence, to improve the performance of LOE protection detection, several studies have been performed in the literature. An index based on the rate of change of load angle on the reactive power is proposed in [15]. The possibility of the incorrect operation in the event of power stable oscillation is the main challenging problem of this method. ...
Flexible Alternating Current Transmission Systems (FACTS) connected to Transmission Lines (TLs) make systems more flexible, and optimize their operational capacity. Despite improvements in TL operational aspects, added FACTS can modify the amplitude, voltage, and current angles of the system wherein they are inserted and consequently the measured impedance, which can affect synchronous machine protections that are based on this feature. Firstly, this paper presents a set of computational simulations to evaluate possible changes in the synchronous machine protection connected to a TL with Static Var Compensator (SVC). Finally, is this context the traditional loss of excitation (LOE) protection is comparing with a proposed approach based on the use of a multilayer perceptron-type Artificial Neural Network (ANN). The simulation results show the effectiveness and robustness of the proposed ANN LOE protection to reach faster actuation time than the traditional LOE protection.
... In recent years, many valuable works have been done to overcome the raised weaknesses of the impedance-relay which are divided into different categories and discussed below. Threshold-based schemes: The provided schemes in [9][10][11][12] exploit the internal voltage, the combination of derivative of terminal voltage and reactive power, rate of change of load angle over reactive power, and rate of change of power factor, respectively. Although, these threshold-based schemes could identify the happened events with a minimum time delay, the threshold value adjustment to reliable clustering of the various events is a challenging issue. ...
... Since the reactive power of SG unit (Qsg) is considered as one of the most remarkable and key index in many LOE studies such as [10,11,15,23], it has also been considered here and defined as below. ...
... As seen, the impedance relay has failed during the selected NLOE events and detects the LOE events with a noticeable time delay, while the offered LOEDI reveals all events properly and quickly. Unlike the threshold-based protection schemes in [9][10][11][12] which require an exact threshold value for reliable clustering of the various events, the proposed scheme of this paper can detect all events without any threshold amount. Despite the setting-free approaches in [13][14][15] which fail during the happening of the hybrid event, the provided scheme is quite reliable for detecting such a condition. ...
In this paper an improved setting-free loss of excitation (LOE) protection is developed for fast and reliable classification of various events. In the proposed scheme, the internal voltage and reactive power of the synchronous generator (SG) have been exploited to fulfill the condition of no needing the threshold amount. Because, they are directly dependent on the rotor field and continuously reduced during the LOE, leading to having a negative polarity of variation. However, due to slow dynamic variation during the LOE condition, they are multiplied to accelerate and highlight the reduction changes, giving rise to increasing the detection speed. Meanwhile, owing to the considerable difference between the value of internal voltage and reactive power and to highlight the effect of multiplication function, an adaptive gain on the basis of steady-state parameters of SG is suggested. Furthermore, given that the negative polarity of the multiplied parameters can be affected during the hybrid events, the limited integral function is implemented to eliminate the happened swings, resulting in keeping the negative polarity and thus clustering the hybrid events reliably. The performed simulations on the IEEE 9-bus and 39-bus test systems prove that, the provided setting-free protection can detect all types of the events reliably and quickly than other schemes.
... In [19], a new LOF/SPS detection approach is provided based on differential of current of the under study PPSG. The suggested scheme in [20] implements the ratio of derivation of the load angle and reactive power as a suitable index to preserve the PPSG during LOF fault and secure detection of the SPS events. The provided approach in [21], in spite of the existing LOF protection schemes in the literature that use the various parameters of the PPSG, suggests the dynamic state estimation of the PPSG to classify the LOF/SPS cases. ...
... The most remarkable drawbacks [9,10] Possibility of wrong detection of both LOF/SPS events during some conditions [11] Non-detection of the LOF event under hybrid happening the SPS/LOF events [12] Impossibility of measuring the load angle parameter directly [13,14] Impossibility of direct measurement of parameters and need to use some sensors and/or estimation [15] Impossibility of direct measurement of the load angle and challenge of threshold-setting [16] Possibility of wrongful tripping of the PPSG thorough some SPS events [17] Possibility of wrongful operation under poor training of the algorithm [18] Complexity in implementation and false tripping throughout some SPS accidents [19] Possibility of wrongful operation through both LOF/SPS events [20] Impossibility of direct measurement of the load angle parameter [21] Possibility of failure during poor estimation of the dynamic states [22] Possibility of interference with the PSS and requirement of exact coordination ...
... Therefore, to cope with this problem and complete the accuracy and reliability, using the arithmetic mean value as (8) and analysis of the ZRBF after a time delay are suggested. Based on the available works such as [9,11,20,22], entrance time of TOZ to the Z-relay zones (T z ) is much more than 1 s during the LOF, hybrid and some few SPS cases, while it will be lesser than 1 s during some other SPS events. Therefore, observation time of ZRBF for event classification is considered as follows. ...
The conventional impedance (Z)-based relay which is the well-known relay to preserve the power plant’s synchronous generator (PPSG) against loss of field (LOF) accident may fail during some stable power swing (SPS), on the other hand, most of the previously introduced schemes may fail during the happening of hybrid events. In this paper to overcome the raised problems, a straightforward index is developed for reliable detection of the hybrid events, and it is combined in an AND-logic cluster with the Z-relay to avoid its spurious trip during SPS events. The reactive power (QSG) of the faulty PPSG is continuously decreased during LOF, while it oscillates under both SPS and hybrid events, leading to non-detection of the hybrid event. Hence, using the integral operator and arithmetic mean value are suggested to eliminate the swinging variations of QSG as a Z-relay blocking function (ZRBF). Thus, QSG decreases during both LOF and hybrid events and does not decrease under SPS events. Therefore, by combination of ZRBF with the Z-relay, the PPSG is properly tripped out during the both LOF and hybrid events, and wrong tripping under SPS is reliably hindered. The reliable performance of developed scheme is completely approved thorough performed simulation studies.
... In [17], the use of rate of change of the reactive power parameter is presented, which makes the possibility of wrong operation in the case of PSD under different power factors. In [18], a fast and simple index based on the rate of change of load angle on reactive power is proposed, which the possibility of incorrect operation in the event of PSD is the main challenging problem of it. Finally, some of the latest research works in the field of LOE protection such as methods in [19,20,21] suggest the reactive power increment of SG and checking the variations of the voltage, dynamic state stimation, and rate of change of phase angle of the faulty SG, respectively. ...
... A typical test system shown in Fig. 3 including two parallel SGs connected to the main grid, whose all key information are presented in [18]. To provide an in-depth analysis on performance of the extended LOE protection strategy, some key LOE conditions during various loading status and PSD events are simulated at t=3 sec and the obtained results have been reported in detail. ...
The main weaknesses of the impedance-based loss of excitation (LOE) relay are its mal-operation during the power system disturbances (PSD) and its long detection time during LOE events. In this paper, to rectify the mentioned problems, a new LOE protection scheme is presented based on the load angle (δ) variation of the parallel synchronous generators (SGs) connected to a point of connection (POC). It will be shown that during a PSD, the variation of δ for all parallel SGs is similar such that their δ increases or decreases simultaneously. However, it will be shown that when the LOE happens in one of the parallel SGs, the δ of faulty SG increases while other SGs will experience a reduction in their δ. Hence, when more than one SG is connected to a POC, the LOE condition can be discriminated from PSDs by the proposed LOE relay. However, when one SG is connected to the POC, the conventional impedance-based relay is employed to detect LOE/PSD. Since in real conditions, the outage rate of the parallel-connected SGs in a power plant is very low on a yearly basis, therefore, the contribution of the conventional impedance relay in the detection of LOE/PSD is quite limited to some special instances. Simulation studies on a typical power prove the high efficiency of the proposed algorithm.
The main weaknesses of impedance-based loss of excitation (LOE) relay are its mal-operation during the power system disturbances (PSD) and its long detection time during LOE events. In this paper, to tackle the mentioned problems, a new LOE protection scheme is proposed based on load angle (δ) variation of parallel synchronous generators (SGs) connected to a point of connection (POC). It will be shown that during a PSD, the variation of δ for all parallel SGs is similar such that their δ increases or decreases simultaneously. However, it will be shown that when the LOE occurs for one of the parallel SGs, the δ of faulty SG increases while other SGs will experience reduction in their δ. Hence, when more than one SG is connected to a POC, the LOE event can be discriminated from PSDs. In the proposed scheme, when one SG is connected to the grid, the impedance-based relay is employed to enable the developed method to detect LOE/PSD. Since in a real-world application, the outage rate of the parallel SGs in a power plant during the emergency situations, periodic services, etc. is very low on a yearly basis, the contribution of the impedance relay in the proposed scheme is quite limited to some special circumstances. Comprehensive simulation studies have been conducted in MATLAB/Simulink environment (R2017b); the results prove high efficiency of the proposed scheme.
This paper deals with an innovative Loss of Field Protection Scheme (LoFPS), in which, some key supplementary features are provided to avoid spurious trip of the Conventional Impedance-Based Relay (CIBR) during Stable Power Swing (SPS). The proposed algorithm is developed for two conditions of the multiple-parallel-synchronous generator (SG) and single-SG in service. Entrance time (ti) of Z-trajectory to the CIBR zones is utilized for single-SG in service owing to the different dynamic responses of the SG to the LoF/SPS events. Meanwhile, for the multiple-parallel-SGs condition, the average value of the variation of the output reactive current of SG (ΔIRSG¯) is selected to analyze the dynamic behavior of the faulty- and healthy-parallel-SGs. The ΔIRSG¯ for all the parallel-SGs during both normal and SPS conditions has a similar polarity, whereas during LoF incidence in one SG, its polarity is different for the faulty and healthy-parallel SGs. Therefore, the nuisance trip of the CIBR can be easily avoided by implementing the selected features. Widespread simulation studies in MATLAB/Simulink environment on the IEEE 9-bus test system affirm the superiority, higher reliability, and easy implementation of the developed LoFPS than other schemes, especially the CIBR ones.
