Large Synchronous Condenser Research Articles

Diagnosis and Treatment of Oil Film Whirl Fault in the Bearing of Large Synchronous Condenser

The oil film vortex of a synchronous condenser rotor can cause an increase in bearing vibration. When the vibration amplitude exceeds the threshold value, it can cause the condenser to trip. The oil film vortex is related to many factors and often occurs during the start-up and acceleration process of the unit, as well as during the loading process of the unit. This article elaborates on the low-frequency oscillation accident of the bearing system caused by the oil film vortex fault of the rotor of a large synchronous condenser and its handling methods. This article presents a sudden low-frequency vibration of a large synchronous condenser. Based on the data collected on site and experimental test results, this condenser analyzes and diagnoses the low-frequency vibration incident, and ultimately determines it as an oil film vortex fault in the bearing system. The article combines the operation and maintenance plan of the synchronous condenser and conducts on-site dynamic balance tests on the synchronous condenser. After the dynamic balance test, the low-frequency vibration of the bearing system disappears and the fault is eliminated.

Study on the Fluid-Solid Coupling Heat Transfer in the Stator of Large Synchronous Condenser Considering Complex Transposition Structure

Study on the Fluid-Solid Coupling Heat Transfer in the Stator of Large Synchronous Condenser Considering Complex Transposition Structure

Heat Transfer Performance Analysis of End Structures of Large Synchronous Condenser Based on Deep Forest Prediction Model

This paper presents a three-dimensional fluid-solid coupling heat transfer model of the end domain of a synchronous condenser. The temperature of the end structures and the flow distribution of the cooling medium were analysed. The highest temperature point of the structural part was explored, and the influence rule of the properties of the cooling medium on the temperature of the end structures of the condenser were analysed in detail. Based on the deep forest prediction model (DFPM), an accurate prediction of the temperature of the copper shield, far finger plates, clamping plate and stator end winding insulation was obtained by selecting a cooling medium and a heat-conducting medium with different properties. Comparing the predicted temperature data of the end structural parts with the finite element simulation results, the difference is minor. In addition, by measuring the temperature of the inner edge of the copper shield, the simulation results are in agreement with the measurement results, confirming the accuracy of the proposed model. The presented model can replace the complex simulation and can be considered an interesting reference for selecting the cooling scheme.

Analysis of rotor winding interturn short circuits affected by the initial dynamic eccentricity in large synchronous condensers

To investigate the effect of initial dynamic eccentricity on the rotor winding turn-to-turn short circuit (RWISC) in a large synchronous condenser, this paper uses the study object of a 300 MVar dual water intercooler condenser. Firstly, the air gap flux density characteristics, unbalanced magnetic pull (UMP) and stator circulating current of the condenser under single and compound faults are derived theoretically. Then, a phase-modulated field-circuit coupling model is constructed using Anosoft software. It is used to simulate and analyse the condenser. Finally, the operation of the condenser was simulated with the SDF-9 experimental setup, and the correctness of the theoretical derivation and simulation analysis was verified. The results show that the initial dynamic eccentricity of the condenser has a cutting effect on the fault characteristics generated by the RWISC. The 2nd harmonic of air gap flux density and stator circulating current and the fundamental wave of UMP decrease and increase with eccentricity. This study can provide theoretical guidance to eliminate disturbing factors to improve the accuracy of RWISC diagnosis in large synchronous condensers.

Two-Level Surrogate-Assisted Transient Parameters Design Optimization of a Wound-Field Synchronous Machine

The rapid development of ultra-high voltage direct current transmission systems has placed greater demands on the design optimization of transient parameters for large wound-field synchronous machines (WFSMs) in power systems, such as large synchronous condenser for dynamic reactive power compensation. This paper proposes a novel two-level surrogate-assisted multi-objective optimization method for WFSMs that can optimize transient parameters including per-unit reactance and time constants rapidly and accurately. To facilitate the manufacture of a prototype for verification, the proposed method is applied to the optimization of a WFSM for scale-down generator application. This method is employed to deal with the excessive number of design parameters, issues of multi-objective evaluation and strong coupling between objectives that either result in inaccuracy or become time-consuming by using conventional methods. To generate the training set for the surrogate model efficiently by finite element analysis, an improved arbitrary rotor position standstill time response (SSTR) method is employed to identify all transient parameters simultaneously in a single test, while Latin hypercube design is used to capture data features. The optimal WFSM designed by using the proposed method is prototyped and measured. It confirms that the proposed method can achieve high validity and high optimization efficiency simultaneously.

Research on Electromagnetic Field, Eddy Current Loss and Heat Transfer in the End Region of Synchronous Condenser with Different End Structures and Material Properties

Aiming at the problem of end structure heating caused by the excessive eddy current loss of large synchronous condensers used in ultra-high voltage (UHV) power transmission, combined with the actual operation characteristics of the synchronous condenser, a three-dimensional transient electromagnetic field physical model is established, and three schemes for adjusting the end structure of the condenser under rated condition are researched. The original structure has a copper shield and a steel clamping plate. Scheme 1 has no copper shield but has a steel clamping plate. Scheme 2 has no copper shield but has an aluminum clamping plate. By constructing a three-dimensional fluid–solid coupling heat transfer model in the end of the synchronous condenser, and giving the basic assumptions and boundary conditions, the eddy current loss of the structure calculated by the three schemes is applied to the end region of the synchronous condenser as the heat source, and the velocity distribution of the cooling medium and the temperature distribution of each structure under the three different schemes are obtained. In order to verify the rationality of the numerical analysis model and the effectiveness of the calculation method, the temperature of the inner edge of the copper shield in the end of the synchronous condenser is measured, and the temperature calculation results are consistent with the temperature measurement results, which provides a theoretical basis for the electromagnetic design, structural optimization, ventilation and cooling of the synchronous condenser.

Highly reliable Coordinated Control Strategy for Static Frequency Converters applied to Large Synchronous Condensers

A large synchronous condenser can quickly and flexibly implement various functions such as dynamic change in load tracking, realization of peak reduction and valley filling, emergency reserve, frequency modulation, and phase modulation. This type of condenser is typically started using a static frequency converter (SFC). Based on the analysis of the working principle of SFCs, this paper proposes a highly reliable coordinated control method with resynchronization criterion for an SFC. An auxiliary loop is introduced for voltage control at the SFC to realize feedforward of the trigger angle of the rectifier. This method can effectively improve the success rate of grid synchronization of the synchronous condenser and shorten the start-up time. Moreover, when the AC voltage on the grid side drops, the auxiliary ring can automatically reduce the terminal voltage to maintain a stable operation. A comparative experiment was conducted on an RTDS to verify the feasibility and effectiveness of the proposed method.

Fault diagnosis of vibration signal of synchronous condenser based on wavelet model

A large synchronous condenser has a complex structure and many parts, which is very prone to failure. However, the regular electrical quantity generally does not change significantly at the initial stage of failure, and may not reflect the fault characteristics. Some non-electrical quantities, such as vibration characteristics, can be used to diagnose and predict faults in a timely manner. Based on this, a multilayer-perceptron based wavelet model is proposed for fault diagnosis. Vibration signals are taken in real time at different positions on the surface of the condenser, and the energy eigenvalues are calculated by fast Fourier transform of the data, and the wavelet neural network model is input for training to obtain the nonlinear mapping relationship between the vibration signals and the fault types of the condenser, so as to realize the fault diagnosis of the condenser. Experimental results show that this method can effectively detect and diagnose the fault of the synchronous condenser in the early stage.

Research and application of key commissioning technologies for new generation of 300Mvar large synchronous condenser

As the new generation of 300 Mvar large synchronous condensers have gradually been produced and installed in China, research on the commissioning technologies before being formally put into operation is particularly important. This paper mainly takes the view of the difference between synchronous condenser and the traditional large generator especially in the following respects of startup mode, over-excitation performance, and grid-connection mode. The commissioning technologies of electrical system, oil system, chemical system and monitoring system are put forward in detail. Furthermore, innovative achievements such as the optimization design of protection configuration and hot water flow method for checking the water circuit within the stator winding, along with the new type of apparatus for magnetization test of stator core are present. The commissioning technologies have been applied in Yi’nan converter station, which all successfully went into pre-operation after the commissioning work been completed, contributing a lot to the security of regional power grid.

Standstill Time-Domain Response Parameter Estimation of the Large Synchronous Condenser in Arbitrary Rotor Position

The necessity to align the rotor with the d-q magnetic axes is the main obstacle for the wide application of synchronous machine standstill parameter tests, especially for the high-power units. This paper presents an arbitrary rotor position parameter estimation method for standstill time-domain response (SSTRs) tests and applied on a 300 MVar, 20 kV large synchronous condenser, a DC step voltage signal is selected as the input signal. Firstly, a frequency-domain Dalton-Cameron transformation is demonstrated and used to simultaneously obtain both axes' operational inductances in an arbitrary rotor position, thus eliminating the need for the rotor prepositioning process. Then, a novel analytical parameter estimation method combined with an I/T transformation is proposed, all the parameters of both axes are determined without extra tests, the mutual leakage flux between the field winding and the d-axis damper winding is also taken in account. To validate the proposed method, this test is carried out and its parameter estimation results are compared against that of the three-phase sudden short-circuit test and the traditional SSTR test. Estimation results are given in the form of I-type and T-type circuits, the maximum relative error no more than 6% and 10%, respectively.

Analysis of Rotor Grounding Protection Action of Large Synchronous Condensers

Rotor Grounding protection of synchronous condensers in a converter station of Jiangsu province acted on September 24, 2018. The burning loss of primary side of synchronous transformer was found by accident investigation. Based on the theory of rotor grounding protection and fault cause, the correctness of rotor grounding protection of injection is verified. Meanwhile, the unstable grounding fault caused by the synchronous transformer was further studied. Based on the analysis of fault recording waveform of converter station, this paper proposes an improved scheme for the rotor grounding protection logic. Compared with the traditional rotor grounding protection logic, it can avoid the situation that the fault cannot be removed in time because of the unstable grounding fault. It can provide a reference for the protection of the excitation system of the new large-capacity synchronous condensers.

Application of the New Generation Large Capacity Synchronous Condenser in HVDC System

The AC dynamic reactive power compensation in high voltage direct current (HVDC) still remains an unsolved problem. Owing to its flexible and rapid reactive power output, synchronous condenser (SC) has a broad application prospect on sending and receiving ends of HVDC transmission system. Firstly, the system structure of a new large capacity SC is introduced. Secondly, reactive power dynamic characteristics of SC in sub-transient and transient are studied theoretically. Then its supporting effect on low bus voltage is analyzed and verified. On this basis, the reactive power application requirements of SC in DC system are studied. An actual transmission system model is established by PSCAD/EMTDC. The simulation verifies the suppression effect of SC on commutation failure and bus transient overvoltage, which provides a theoretical basis for the application of SC in HVDC system.

Study on the Blockage and Temperature Distribution of Stator Bar Strands in Water-cooled Large Synchronous Condensers

Study on the Blockage and Temperature Distribution of Stator Bar Strands in Water-cooled Large Synchronous Condensers

Simulation of Sensorless Control for the Start-up of Large-Scale Synchronous Condenser Using Static Frequency Converter

In this paper, the structural characteristics of large synchronous condensers and the working principle of static frequency converter are studied firstly. Intermittent commutation and natural commutation are adopted by the inverter on the machine side in low-speed and high-speed stage respectively. Second, methods of sensorless control in different conditions are proposed. The initial rotor position is estimated through two methods, the terminal voltage method and the rotor-flux-oriented method. And similar methods are used in low-speed stage. Besides, phase-locked loop is used in high-speed. Finally, simulation models are established in PSCAD/EMDTC. The rotor-flux-oriented method used in standstill condition and low-speed stage shows better accuracy. And the phase-locked loop is also effective in high-speed stage. Therefore, the sensorless control methods are feasible.

Study on the Key Problems of UHVAC/DC Power Grids with New Generation Large Synchronous Condenser

In order to cope with the great pressure caused by the gradually exhaustion of fossil energy and environmental protection and climate warming, the development and application of the renewable energy has become an important foundation and development direction in the field of energy. However, due to the impact of energy and resource endowment, China’s load center and renewable energy base into the characteristics of long-range reverse distribution, the use of long-distance large-capacity transmission potential is necessary. With the “strong DC system and weak AC system” problem of the company power grid is increasingly prominent, the higher demand of dynamic reactive power support is put forward in the UHV DC power transmission project. Then, the large-capacity dynamic reactive power of new generation synchronous condenser is large-scale built up in the UHV DC/AC power system. Due to the high requirement of response speed and capacity in the UHV DC power transmission, the structure, dynamic characteristics, excitation control and relay protection and other aspects of the large synchronous condenser are different from generators and traditional synchronous condenser. Based on this, the dynamic reactive power demand of UHV DC power system is analyzed in this paper. Then, the main situation of large synchronous condenser is considered. In addition, the key points of the excitation control system and protection system are also discussed in this paper. There are important theoretical and practical significance for the safe and reliable operation of the UHV DC/AC power system.

General approaches to efficient d-q simulation and model translation for synchronous machines: a recap

This paper summarizes some recent findings in the area of synchronous machine modeling by means of equivalent circuits of arbitrary order. This allows us to propose a concise analytical expression to be derived for the admittance matrix and yields a structure of the state matrices which facilitates their numerical evaluation. By organizing the parameters into two structured vectors, we show how to calculate the state matrices and admittance matrix of generalized models of machine by means of MATLAB programs. The techniques are proposed for passing from the equivalent circuits to the operational impedances and vice-versa. Lastly, we transpose the conventional electromechanical state equations into our generalized modeling framework and derive new formulas for the matrices used in the eigenvalue analysis of synchronous motors and generators. Besides conventional stability studies, the present approaches along with the MATLAB toolbox could be useful for machine-converter system optimization, motor starting problems, digital TNA implementation and machine models identification. The latter application is investigated in particular with a view to enhancing current methods used to analyse short-circuit oscillograms recorded during the commissioning of large utility grade generators and synchronous condensers.

Starting of Large Synchronous Motor Using Static Frequency Converter

This paper deals with the synchronous starting of a large synchronous motor, using a static thyristor frequency converter system. This method, in the following called, Converter Starting, is described. Special inverter questions are treated and the results of analytical and computer studies of the system and of a field test are presented. Potential applications of the method are dewatered starting in the pumping mode of reversible pumped-storage generator/motors and the starting of large synchronous condensers. The same equipment can also be used for braking the machines.

345 MVA Fully Water-Cooled Synchronous Condenser for Dumont Station Part I. Application Considerations

A brief historical review of the use of static capacitors and synchronous condensers for regulating power system voltage is made. Comparative costs are shown which demonstrate that the large synchronous condenser has a place on the large EHV power system. Application of the 345 mva fully water-cooled synchronous condenser on the American Electric Power System is described.

The Development of Modern Excitation Systems for Synchronous Condensers and Generators

DURING the past 15 years and particularly in the past ten years, there have been many major developments in excitation systems for synchronous condensers and generators. These changes and improvements were stimulated in 1928 by the introduction of the hydrogen-cooled synchronous condenser which necessitated a reconsideration of the excitation arrangement and brought about a change from a direct-connected exciter to separate excitation. This, together with the desire to obtain maximum speed of response and to eliminate maintenance caused by moving parts associated with rotating exciters and with mechanical regulators, led to the trial of electronic applications on the systems of the American Gas and Electric Company A development program along these lines was carried on over a period of approximately 15 years and included specifically 15 exciter applications on large generators and condensers. About six years ago a review of the performance and operating experience on the machines involved in this plan resulted in the design and trial of a system using a direct-connected exciter with amplidyne control for excitation of a large synchronous condenser. Following this, four similar installations were provided. Thus there has been obtained a wide variety of experience with excitation systems and associated equipment. It is the purpose of this paper to recount these developments, describe typical installations, and discuss the operating results obtained with them.

Automatic control of large synchronous condensers

Automatic control of large synchronous condensers