Loss Of Excitation Relay Research Articles

STATCOM Impacts on Synchronous Generator LOE Protection: A Realistic Study Based on IEEE Standard C37. 102

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.

Improvement of loss of excitation protection of an alternator in the presence of shunt-FACTS – A comprehensive review

Among the different Loss of Excitation (LOE) relaying schemes in practice today, the most famous is the mho relay. During the loss of excitation, the impedance as seen by the relay enters the zones of protection that are set up according to the generator and system specifications. It then generates a trip signal to separate the affected alternator from the system in case the fault persists. Modern-day Power Systems incorporate FACTS devices to deal with certain tasks like voltage regulation, improvement of transient stability, prevention of voltage instability and damping Power oscillation. It has been shown that the reactive power injected by the shunt-FACTS devices prevents the terminal voltage of the alternator from dropping during LOE, which causes a delay in the operation of the LOE relay. Under certain conditions such as the event of partial LOE or during condenser mode of operation of an alternator, the presence of shunt-FACTS devices may lead to under-reach of the relay. This paper analyses the effects that shunt FACTS devices, such as Static VAR Compensators (SVCs) have on the loss of excitation (LOE) protection of an alternator. Simulations were carried out in the MATLAB/Simulink environment to simulate various LOE relay schemes during excitation system failures. The results give us an insight into the advantages and disadvantages of various LOE protection schemes and serve as a reference for selecting a particular scheme for any system.

A new protection scheme for loss of excitation detection in presence of FACTS devices

Loss of excitation (LOE) in synchronous generators can cause damage on both generators and power system. In the conventional method, LOE is detected by using mho negative offset. In this case, the speed of detection is low and also in some condition, a stable power swing can be detected by mistake. The mal-operation of conventional LOE relay can cause a blackout. Moreover, the presence of flexible alternating current transmission system (FACTS) devices change the impedance that measured by LOE relay, and hence it affects the performance of a LOE relay. In this paper, the validity of electrical and mechanical quantities is discussed. Therefore, some suitable electrical and mechanical features among the quantities are extracted. Then the classifier is employed and to evaluate the performance of the proposed scheme, some case of LOE, partial LOE (PLOE), and stable power swing (SPS) are simulated. The obtained results show that the proposed scheme is robust and secure to discriminate LOE from SPS. In addition, the proposed scheme is fast and adequate to detect LOE in the presence of FACTS devices due to delay time raised by compensation devices.

A Review of Generator Loss of Excitation Protection Schemes

Loss of excitation (LOE) on synchronous machine is an abnormal operating condition which, if not detected, can have severe consequence. This paper aims at providing an in-depth analysis of the phenomenon, factors and the impact of LOE. It discusses the various protection schemes and provides the basis for selection of settings. The philosophy for coordinating loss of excitation protection with generator capability and steady-state stability limits is discussed. The performance of impedance and admittance schemes is analysed with the help of simulation. A case where loss of excitation protection is prone to incorrect operation for stable power swings is studied, which suggests the importance of dynamic studies for setting loss of excitation relay. The results suggest the need for intelligent relaying techniques for improving the reliability of LOE protection schemes. Finally, it discusses the latest advancements in the area of LOE protection.

Flux linkage estimation based loss of excitation relay for synchronous generator

Loss of excitation (LOE) event threatens both the generator and power system stability. Numerous approaches have been proposed for LOE detection, most of which use the impedance trajectory. Such methods may maloperate under system disturbances, especially power swings. This study presents a new approach for LOE detection by estimating the field flux linkage participation (FFLP) in the stator flux linkage. Intrinsically, this newly defined index mainly depends on the generator excitation system and thus highly reduces when an LOE takes place. The FFLP parameter can easily be calculated using stator voltage and current signals. All kinds of LOE events cannot be studied using most available simulation software. To cover all of them, utilising state variables, a generator model connected to a power system is implemented. Performed simulation studies demonstrate that the proposed strategy not only considerably decreases the LOE relay operation time, but also improves the LOE relay security against system disturbances. In addition, the proposed approach is experimentally evaluated on a 10 kVA synchronous generator.

Fast discrimination of stable power swing with synchronous generator loss of excitation

Fast and accurate discrimination between stable power swing (SPS) and synchronous generator loss of excitation (LOE) has been a great concern for power engineers. Since there is no unbalance during SPS condition, detecting this phenomenon is still a challenge. LOE detection methods are prone to interpret an SPS as a LOE event. Over the last decade, several techniques have been developed for LOE protection that most of them are based on the impedance trajectory as it enters into the protective zone. Such methods may not be able to discriminate between SPS and LOE. Therefore, assigning a time delay is usually utilised to overcome the possible maloperation of the LOE relay. However, merely providing the intentional time delay to avoid maloperation in this condition is not a perfect solution. This study presents a fast detection approach for this condition. The combined proposed method is based on the derivatives of the machine's external variables (i.e. output reactive power and terminal voltage) and the variation of the fast Fourier transform coefficient of the three-phase active power available at the location of the relay. The main advantage of this method is its speed, security and sensitivity to distinguish between SPS and LOE.

A PMU-Based LOE Protection of Synchronous Generator in the Presence of GIPFC

The existence of a generalized interline power-flow controller (GIPFC) in the transmission lines changes the voltage and current signals which are measured with the protection relays of power system dynamically. In this paper, the effects of the GIPFC on the measured impedance by the loss of excitation (LOE) relay of the synchronous generator are first investigated by analytical and computational methods for different operating modes of the power system. The results indicate that the presence of GIPFC causes a substantial delay on the operation of the LOE relay. It is also shown that when partial LOE occurs, the GIPFC causes to the LOE relay under-reaching. Consequently, to readjust the relay in the presence of the GIPFC, a new modified LOE protection algorithm on the basis of synchronized phasor measurements received from phasor measurement units is presented. The most important advantage of this modified algorithm is that it is a general algorithm which considers all voltage-source-converter-based flexible ac transmission systems controllers. Regarding the simulations results, it is concluded that using the modified algorithm for the LOE relay can sufficiently decrease the delay and prevent the relay from under-reaching. The impacts of the unified power-flow controller and interline power-flow controller on the LOE relay are also demonstrated.

Impact of STATCOM and SSSC on synchronous generator LOE protection

Loss of excitation (LOE) protection is one of the most important protections of synchronous generators. Nowadays, application of an impedance relay with two negative offset operation zones to protect LOE is prevalent; this relay measures the output voltage and current of generator to detect LOE. On the other hand, utilization of exible AC transmission systems (F ACTS) devices in power systems for different applications is soaring; these devices cause changes in voltage and current signals in the utilized power system. Therefore, this paper is dedicated to investigate the amounts of changes in the current and voltage signals measured by the LOE relay when the static synchronous compensator (STATCOM) and static synchronous series compensator (SSSC) are used. Research results show that the changes in the measured signals manipulate the operation of the relay. It is also shown that partial LOE culminates in an under-reach of the relay. In surveys conducted, various operational conditions of the power system and F ACTS devices are considered

Performance comparison of LOE protection of synchronous generator in the presence of UPFC

Generator loss of excitation (LOE) protection is a principal protection of power system which operate based on impedance measurement. This relay calculates impedance by measuring voltage and current at the generator terminal. On the other hand, the presence of unified power flow controller (UPFC) in transmission lines changes measured voltage and current signals during loss of excitation. In this paper, the impact of UPFC on the performance of LOE protection has been analytically investigated. Afterwards, using modeling results, it has been attained that the presence of UPFC leads to the drastic delay on the performance of LOE relay. This delay results to the overloading and damaging of armature winding of generator. It is also shown that in partial LOE presence of UPFC causes under-reach of the relay. Finally, the phasor measurement units (PMUs) based method has been proposed to reduce the effect of UPFC on the LOE protection. The results indicate that using this new method, the delay of LOE relay has been reduced. In the surveys conducted, various conditions of the power system have been considered.

Impact of Fixed Series Capacitors and SSSC on the LOE Protection of Synchronous Generator

Loss of excitation (LOE) relay is prevalently used to protect synchronous generator. The widely used method for synchronous generator LOE protection is a negative offset mho relay with two zones. The basis of this relay is identical to mho impedance relay. In other words, this relay calculates impedance by measuring voltage and current at the generator terminal. On the other hand, the presence of series compensation, changes measured voltage and current signals during loss of excitation. This paper reveals that the presence of series compensators such as fixed series capacitors (FSCs) and static synchronous series compensator (SSSC) causes a significant delay on the performance of generator LOE relay. It is also shown that the presence of SSSC causes the LOE relay to be under-reached. Different operating modes of the power system, the SSSC and also different percentages of series capacitive compensations have been considered in the modeling. All the detailed simulations are carried out in the MATLAB/Simulink environment using the SimPowerSystems toolbox.

A Novel Approach to Detect the Synchronous Generator Loss of Excitation

The loss-of-excitation (LOE) event threatens the generator and power system stability. Several methods have been proposed for LOE detection, most of which are based on the impedance trajectory. These approaches may not be able to distinguish between LOE and the stable generator swing (SGS). Thus, allocating an operation time delay is usually used to overcome the LOE relay misoperation due to SGS. This paper presents a new approach for the LOE relay. The proposed strategy exploits a combined scheme based on the derivative of the terminal voltage and the output reactive power of the generator. Comprehensive simulation studies are accomplished for various generator conditions and system disturbances to determine the relay setting and to evaluate its performance. The performed studies demonstrate that the proposed strategy enhances security and operation time of the LOE relay, compared with some existing methods.

Operation of synchronous generator LOE protection in the presence of shunt-FACTS

This paper deals with the impact of shunt-FACTS devices on the synchronous generator loss of excitation (LOE) protection. Considered shunt-FACTS devices in this paper include the static VAR compensator (SVC) and static synchronous compensator (STATCOM). The SVC has been modeled by thyristor switched capacitor (TSC) and thyristor controlled reactor (TCR) branches. Also, 48-pulsed converter is used to model STATCOM. The LOE relay considered in this paper is a negative offset mho distance relay containing two zones. It has been shown that injected reactive power of by shunt-FACTS devices prevents from the generator voltage drop during LOE, which causes the operation of LOE relay to be delayed. It has been also shown that when an incomplete LOE occurs, the presence of shunt-FACTS devices leads to under-reach of the relay. In this paper, various operational conditions of the power system and shunt-FACTS devices have been surveyed to authenticate the results.

A novel method to prevent incorrect operation of synchronous generator loss of excitation relay during and after different external faults

Summary This paper presents a novel method for synchronous generator loss of excitation (LOE) protection during and after different external faults. This method is based on the variation of the magnetic flux linkage in the air gap combined with negative sequence current. Extensive simulations show that the proposed method has various distinct features that are advantageous over existing schemes. Speed and sensitivity are the main points featured in the proposed technique. Also, the distinctive feature is that the proposed method prevent of LOE relay incorrect operation during and after external faults. The effectiveness of the proposed protection is demonstrated by comparing it with the conventional LOE protection. Copyright © 2014 John Wiley & Sons, Ltd.

Seen impedance by impedance type relays during power system sequential disturbances

The trajectory of the seen impedance by distance type relays during sequential disturbances was investigated. For transmission systems, distance relays are known to be the main protection. For generator protection, loss of field relays present a major element of the protection systems. These two impedance type relays are considered. A case study of the seen impedance by the healthy phases during single-phase autoreclose (SPAR) following earth faults and the seen impedance by the loss of excitation relay during simultaneous faults, an earth fault in the external system triggering another fault in the generator excitation system, were investigated using phase coordinate analysis with full machine and system representation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>