Static Excitation System Research Articles

Research on AC Excitation Regulation Control System for Synchronous Generators

Although there are many methods for classifying the excitation systems of synchronous motors, there are three types of excitation systems for synchronous motors based on the numerous methods of providing excitation power to synchronous generators. One is a DC excitation system, the second is an AC excitation system, and the other is a static excitation system. This paper mainly studies the AC excitation system. The rotor speed of AC excited generators is variable and has excellent characteristics such as improving power system stability, allowing for deep operation without losing step. AC excitation generators not only have variable speed and constant frequency power, but also have independent adjustment functions for speed, reactive power, and effective power. The use of high-performance variable frequency excitation power supplies and appropriate excitation control methods can maximize the reliability, operational flexibility, and exceptional adjustment performance of AC excitation generators. The excitation system is an important part of synchronous generator operation. A good excitation system not only ensures the stable and reliable operation of the generator, but also greatly improves the stability of the motor and power system.

Performance Evaluation of Excitation Systems in Stability Enhancement of Power Systems

This paper involves the characterization and the performance evaluation of various types of synchronous generator excitation systems in the transient stability enhancement of power systems. The Investigations are carried out by modelling the typical DC, AC and static excitation systems represented by IEEE types DC1A, DC2A, AC4A, AC5A, ST1A and ST2A attached with a generator connected to the infinite bus. The performance evaluation of these excitation systems is performed in terms of their response ratio and ceiling voltage together with the system settling time and the critical clearing time following a sudden three-phase short-circuit in the system. Each excitation system together with its power system stabilizer is considered in the analysis. 4th order Runge Kutta method is utilized for transient stability analysis of the power system with the 3rd order model for synchronous generator representation. The investigations reveal that the IEEE ST2A Excitation System is better than the other types of excitation systems.

Design Improvement and Tuning of Excitation System ST5B With PSS3B and Coordinated OEL in Hydropower Plant

The article analyzes and suggests the tuning and design improvement in the excitation system for the 1400 MW Tehri–Koteshwar hydropower plant (HPP) to mitigate the severe issues of active power oscillations leading to tripping of generating units. The static excitation system model ST5B, power system stabilizer model PSS3B, and over excitation limiter (OEL) are designed for each synchronous machine in the power plant. The coordination of ST5B, PSS3B, and OEL during critical transient operating conditions is analyzed. The proper coordination of these components of excitation system provides better transient and voltage stability. A new thermal-based OEL and modified power system stabilizer (PSS) designs are implemented to enhance the system's voltage and transient stability. The advantage of improved transient response by using different transient gain reduction (TGR) blocks formed by the lead-lag filter in ST5B during normal and limiting excitation operating conditions is presented. The ST5B and PSS3B dynamic analysis and tuning are performed using bode frequency response in offline mode. The robustness of the modified excitation system and limiters together with the added advantage of different TGR blocks in ST5B are verified using real-time digital simulator. A PSS-improved design and thermal-based OEL implemented for this HPP offer better transient and voltage stability as compared to the existing excitation system.

Perturbation estimation based nonlinear adaptive control of VSC flexible excitation system

A new type of flexible excitation system (FES) is proposed by using fully-controlled power electronic devices such as IGBTs to replace the half controlled devices in the conventional static excitation system, which has the merit of independent control of rotor angle and terminal voltage of the synchronous generator. This paper proposes nonlinear adaptive control (NAC) strategies for synchronous generator with FES in a single machine infinite bus system. External disturbances and the uncertainties of all parameters as well as modelling are defined as lumped perturbation terms and estimated by perturbation observers or state and perturbation observer. The estimated perturbation terms are used to compensate the real perturbations and achieve a model-independent and robust NAC. Merits of the FES against the conventional static excitation system and effectiveness of the proposed NAC scheme against the accurate model based multi-variable feedback linearisation control are verified via small-signal stability analysis and simulation studies. The simulation results have shown that the proposed NAC can achieve superior control performance with less states feedback during a three-phase short circuit and better robustness against parameter uncertainties, compared with linear control and multi-variable feedback linearisation control.

Analisis Pengaruh Pengaturan Sudut Penyalaan Thyristor Pada Tegangan Eksitasi Terhadap Keluaran Daya Reaktif Generator di PT.PJB PLTU Gresik Unit 3

The process of changing mechanical energy into electrical energy is carried out by a synchronous generator using an excitation system that functions to supply a DC source to the generator field winding. In this study, the excitation system used is a static excitation system that uses a transformer and several thyristors connected in a bridge configuration. The excitation system is then implemented on a generator with a capacity of 200 MVA / 15 kV using the MATLAB Simulink R2017b simulation. By using the above circuit, the thyristor ignition angle setting can be adjusted so that it can adjust the excitation voltage and obtain the appropriate excitation current to maintain the stability of the generator output voltage. The simulation was carried out with variations in generator load and using 2 different types of excitation settings. The first setting is to set the thyristor ignition angle to 30° with t=10 ms, at this setting the generator can maintain a stable V out value with a voltage regulation limit of ±5% and the reactive power that can be generated by the generator is +50 MVAr and - 40 MVAr. When given a constant excitation at an angle of 35° with t=1 ms, the value of Vout exceeds the expected regulatory limit and the resulting reactive power limit is between +60 MVAr and -100 MVAR where the reactive power does not match the load requirements. This can have an impact on the interconnection system, namely when the reactive power of the generator is greater than the load requirement, the generator with a smaller reactive power will absorb reactive power in the interconnection system and can disrupt the stability of the interconnection network.

Diagnosis of the Static Excitation Systems of Synchronous Generators with the Use of Hardware-In-the-Loop Technologies

In this paper, testing and diagnosis methods for the static excitation systems of power plant synchronous generators using Hardware-In-the-Loop technology are described. These methods allow a physical excitation system to be connected to a real-time model of a power plant unit. A feature of a static excitation system is the presence of generator self-excitation—that is, when the input voltages of the excitation system are defined by a synchronous generator. These voltages are determining by the digital model, which creates additional difficulties with combining a digital model with a real excitation system. Various ways to solve this problem are described in this article; in particular, we focus on the option in which the gate-impulses of a thyristor converter are applied to the digital model by a real static excitation system. The real-time models are based on the method of average voltages in the integration step. This method is effective for providing numerical stability for the models of power schemes and their functioning in real time mode over a long period. A synchronization method for the calculation time of the model with real time is described. The adequacy of the described method is proved by the results of the static excitation system of synchronous generators testing in operating and fault modes.

Self-Excited Synchronous Machine Using Airgap Harmonics

This article introduces a self-excitation technology for field wound synchronous machines (FWSMs) to eliminate conventional components required by brushless and brushed static excitation systems. This technology is based on the utilization of pre-existing airgap flux harmonics, so no exciter or brush is required. The energy of these airgap harmonics at the slotting frequency is captured using rotor-mounted harvesting coils. A power electronic converter is then used to rectify the induced harvesting coil voltage and regulate the field winding current of the FWSM. Simulation results are presented showing the efficacy of the proposed method for a prototype FWSM under various loading conditions. For demonstration, a full-scale 5.4-MVA synchronous generator is used for design and validation.

Reduction of Induced Shaft Voltage and Bearing Current in Turbo Generators: Modeling, Compensation, and Practical Test

The static excitation system of a turbo generator, supplied by a rectifier, can cause induced voltages on the generator's shaft. This article proposes a complete distributed model of a turbo generator, regulated by a static excitation system, to investigate the shaft voltage and bearing current. The complete modeling of all components is proposed by considering the couplings between them in a static excitation system. When shaft voltages exceed the dielectric breakdown voltage of the lubricating oil film in journal bearings, electrical discharge current flows through the bearings. This will further reduce the life expectancy of the dielectric gradually. Two different approaches are explained and discussed in detail to keep the shaft voltages within the safe region: a passive filter and a dc–dc converter solution. Both methods along with the initial system are simulated and compared accordingly. Additionally, frequency-domain analysis has been performed for evaluating the compensating solutions. Moreover, experimental tests were carried out on a 200-MVA turbo generator, and results of the suggested passive filter with those of the proposed compensation method are compared. Both experiments and simulations confirm the mentioned issue and show the effectiveness of the proposed compensation approaches in this regard.

Reduction of the Induced Voltage in the Synchronous Generator Shaft Using Active AC / DC Converter

Today, synchronous generators are broadly employed in the industry. The thyristor rectifier in the static excitation system of synchronous generators is responsible for supplying the DC voltage of the excitation winding. In these rectifiers, a high-frequency component is generated at the output of the DC voltage, during turning on and off of the thyristor. These high-frequency components charge the generator’s parasitic capacitors. The voltage induced in these capacitors induces the voltage in the synchronous generator shaft. In this paper, the induced voltage analysis in the generator shaft is performed. Then, modeling, simulation, and experimental laboratory results of pulse width modulation are performed in the static generator excitation system. The induced voltage of the generator shaft is examined by applying this rectifier and it is compared and analyzed with the results of the thyristor rectifier. The hiring of a pulse width modulation rectifier has had a great impact on reducing the induced shaft voltage.

On the Rotor Angle and Voltage Dynamics Decoupling in Synchronous Generators with Nonlinear AVR

In this paper, rotor angle and voltage dynamics decoupling in a synchronous generator connected to an infinite bus using a partial feedback linearization-based nonlinear voltage regulator (FBLAVR) is described. It is well known that the fast voltage regulation using static excitation system introduces negative damping in the system. If this coupling can be eliminated then one can simultaneously achieve fast voltage regulation and desired damping performance. This paper identifies such a decoupling behavior using an FBLAVR and shows that the damping with the FBLAVR only depends on the inherent damping of the machine. The necessity of a power system stabilizer (PSS) is identified even with the FBLAVR, if the natural damping is not sufficient. Thus motivated, an FBLAVR + PSS control scheme is proposed and compared with a linear automatic voltage regulator (AVR) + PSS control scheme. It is shown that the generator-exciter-power system [GEP(s)] characteristics with FBLAVR does not change with the system operating conditions. The superiority of the proposed control scheme is validated over a wide range of operating conditions on a single machine infinite bus (SMIB) power system.

Self-Excitation of a Synchronous Generator During Power System Restoration

This paper analyzes synchronous generator self-excitation during power system restoration, caused by a large capacitive load and the impact of generator voltage control on the voltage rise. The paper analyzes measurements from a recent self-excitation incident in the Finnish 400-kV transmission system, models the system using an electromagnetic transient model and a linear d -axis generator model, validates the models using the measurements and analyzes the impact of generator voltage control during self-excitation. Self-excitation is rare during a normal system operation but may occur in a weak system during system restoration after a blackout. Since high voltages caused by the self-excitation may delay the restoration or even damage the equipment, self-excitation should be taken into account in restoration planning. This paper shows that the voltage controller and especially the under-excitation limiter settings of the generator have significant impact on the voltage during self-excitation. This paper also shows that details in the excitation system response influence the simulations significantly and reference measurements from the specific generator are required for detailed modeling. However, all measured incidents with digital static excitation systems are important references for simulations. In addition, special attention should be given to protection relays during the restoration.

Logic Control of Static Excitation System in Power Alternators using PLC

Logic control of Static Excitation System (SES) in Power Alternators deals with the use of PLC to control the terminal output voltage of the Alternator in a more simplified and efficient manner using a closed loop system. A closed loop control with negative feedback is designed, which involves AVR, Pulse Generator, Pulse Amplifier, Limiters, Power System Stabilizers with an Auto and a Manual channel. Disruption in the terminal voltage is caused by faults. These faults were rectified earlier by Electro Mechanical relays. Now we are at a major technological Change of Analog to Digital control. It reduces the complexity of the control system, and eliminates the need of wide range of contactors and coils to energies the relay. The best way to maintain the stability of the system is to identify the need and rectify it. This paper proposes an easy and an efficient design for fault detection and elimination using PLC based excitation system in power alternators.

Simulasi Pemodelan Sistem Eksitasi Statis pada Generator Sinkron terhadap Perubahan Beban

Excitation system is one of the most important parts of synchronous generators, where the system functions to provide dc power to the field generator coil. Iin this study, a static excitation system consisting of transformers and connected thyristors in bridge configuration has been implemented in synchronous machines that operate as 206,1 mva capacity generators, 16,5 kv using the help of matlab simulink r2017b software. By adjusting the load given to the generator, variations in excitation currents can affect the amount of output voltage generated by the generator so that it can increase and decrease the induced voltage. In full load conditions, namely p = 175 mw, q = 100 mvar, the results of the study show that when the simulation is run at alpha 0 °, it is known that the average value of dc voltage is 496,4 v, excitation current is 1057 a and voltage generator output has increased beyond its nominal voltage of 16,72 kv. in this case, to maintain the terminal voltage, the excitation current must be reduced by increasing the angle of shooting of the thyristor to an alpha angle of 45 °, so that the average dc voltage can be reduced to 479,3 v, as well as the excitation current to 985,9 a. the generator output voltage at the alpha 45 ° angle is obtained according to its nominal value of 1,.5 kv.

Static Excitation System of Generator in Hydropower Station

Static Excitation System of Generator in Hydropower Station

Controlled Brushless De-Excitation Structure for Synchronous Generators

The main weakness of the brushless excitation system in a synchronous generator (SG) is the slow de-excitation response obtained during a load rejection. That is why voltage overshoots may be observed on the generator terminals. This behavior is mainly due to the exciter machine response time and the rotating diode bridge which is not able to quickly de-excite the generator by negative excitation voltages. This paper presents a new brushless de-excitation structure able to perform a quick de-excitation of the generator by providing controlled negative excitation voltage to the generator main field winding. The proposed structure is based on a new brushless de-excitation machine, called a control machine, and mounted on the same shaft of the generator and the brushless exciter. The brushless control machine is a low power one and used to transfer the orders from the voltage regulator to the discharge system located on the rotor side of the main generator. The dynamic performance of the proposed de-excitation system is evaluated in terms of system stability, voltage regulation response times and voltage overshoots during different load rejection tests. The proposed system is compared to the conventional brushless excitation system without the proposed de-excitation structure. In addition, a comparison is done with the static excitation system. The simulation tests are realized on an experimentally validated model of 11kVA synchronous generator developed in Matlab/Simulink.

A Control Strategy for Damping Subsynchronous Oscillation Based on Voltage Source Converter Excitation System

As the traditional thyristor static excitation system is widely applied in the power system, the electrical damping of the system is weakening, and that makes the system facing the risk of subsynchronous oscillation(SSO). Although some research on Flexible AC Transmission Systems(FACTS) for damping SSO has been proposed, the applying of the FACTS is not economic enough. The Voltage Source Converter(VSC) Excitation system is a kind of excitation system using full-controlled power switches. There is no research on damping SSO based on the VSC excitation system. By analyzing the characteristics of the VSC excitation systems, a control strategy for damping SSO based on phase compensation method is proposed.

Lyapunov Stability Based Wide Area Control Systems for Excitation Boosters in Synchronous Generators

Excitation boosters (EBs) are aimed to improve fault ride through capability of synchronous generators equipped with bus fed static excitation systems by means of adding a supplementary voltage or current source to the rectifier. However, this paper shows that EBs governed by local on–off controls may result in adverse effects in case of remote faults from generators that may occur in multi-machine systems. To sort this problem out, a novel EB Wide Area Control System (WACS) that modulates the EB voltage using the generator speed deviation with respect to the speed of the center of inertia (COI) is proposed. The speed of the COI is obtained using a Wide Area Measurement System (WAMS), whereas the control laws are deduced from the Lyapunov stability theory. Results show that transient stability of multi-machine systems can be enhanced using EB WACS.

A WACS exploiting generator Excitation Boosters for power system transient stability enhancement

Excitation Boosters (EB) are designed to improve transient stability of synchronous generators equipped with bus fed static excitation systems. They can be controlled using either local or remote signals following a disturbance. This paper explores how critical clearing times (CCT) can be improved by EBs controlled using remote signals. Particularly, Pseudo Center of Inertia (PCOI) and Dominant Interarea Path (DIP) signals derived from Phasor Measurement Units (PMU) within a Wide Area Control System (WACS) are used. Prototype controllers are tested by means of a Real Time (RT) Hardware-in-the-Loop (HIL) experimental setup.

A static exciter with interleaved buck converter for synchronous generators

In this study, an interleaved buck converter based static excitation system is proposed for large-scale synchronous generators where thyristor controlled systems are widely used. The proposed system removes the slow response drawback of the thyristor controlled systems even for dynamic load conditions. The finite element analysis based model of the synchronous generator's electromagnetic system is obtained and co-simulations of the modeled generator and proposed interleaved buck converter are performed. Results obtained from simulation results show that, the proposed system offers better performance in terms of step response and inductor current ripple. The simulation results are validated with experimental studies. All measurement, monitoring and control processes have been performed with field programmable gate array called NI CompactRIO platform and LabVIEW software.

Optimal design of voltage regulators for static excitation system in synchronous generator to reduce shaft-induced voltage

Long-term shaft-induced voltage could harm synchronous generators, specifically their bearings and insulators. This paper investigates the reduction of shaft-induced voltage using both a passive filter and an active voltage regulator. An RLC circuit is used as a passive filter, and a DC-DC buck converter is used as an active voltage regulator. As a result, they remove high-frequency spikes, leading to the reduction of shaft-induced voltage. Buck converters show minimum-phase behavior and can pose as stable-casual converters. A 5 kW synchronous generator was considered for the laboratory setup in which a static excitation system using a 6-pulse thyristor rectifier supplies the rotor winding. Active and passive filters were placed between the rectifier and the excitation winding of the synchronous generator. Both simulations and experiments show that the suggested filters are capable of efficiently removing the parasitic capacitance, significantly mitigating shaft-induced voltage. However, the active voltage regulator performs better than the passive filter in reducing shaft-induced voltage. This reduction can increase the lifespan of bearings in a generator.