Load Rejection Test Research Articles

Study on load rejection test of pumped storage units

Abstract The rise rate of rotating speed, the maximum inlet pressure of the spiral casing and the minimum inlet pressure of the draft tube cone of unit 2 in Jinzhai pumped storage power station were analyzed when 50% and 100% of the rated load were rejected in this paper. The low pass filtering method (cut off frequency is 0.2 times of the frequency) was used to process the pressure data at the inlet of the spiral casing and the draft tube cone to retain the trend term. The peak to peak values (97% confidence) of the pressure pulsation term under different data durations were studied, which provided technical support for rational and accurate calculation of the maximum inlet pressure of the spiral casing and the minimum inlet pressure of the draft tube cone, and provided an example reference for the load rejection test analysis of pumped storage units.

Effect of guide vane closing speed deviation on transition process in pumped storage power plant

Abstract The guide vane closing law is a crucial role in ensuring the hydraulic transients of pumped storage power plant. It is also essential for ensuring the safe operation of pumped storage power plant after long-term operation. Variations in the closing speed between simulated guide vane closing laws and on-site closing laws have been observed. This study first verifies the accuracy of the simulation model through load rejection tests conducted on two units. It then simulates the deviation in guide vane closing speed for these units. The deviation in guide vane closing speed does not impact the regulatory requirements for a single unit. However, variations in the closing speed between simulated guide vane closing laws and on-site closing laws have been observed. This study first verifies the accuracy of the simulation model through load rejection tests conducted on two units. It then simulates the deviation in guide vane closing speed for these units and proposes a reference range. The deviation in guide vane closing speed does not impact the regulatory requirements for a single unit. However, for two units in one pipe, opposite deviations in guide vane closing speed can result in key parameters failing to meet regulatory requirements.

Research on the Analysis Method of Measured Pressure Data during the Transient Process of Load Rejection in Hydropower Stations

Abstract This paper proposes a method to analyze the measured pressure data in the transition process of hydropower station. The method first separates the measured pressure data to the mean pressure and pressure fluctuation data, then divides the pressure fluctuation data into different time domain grids, and performs the confidence probability processing on the pressure fluctuation data in each time grid, and finally obtains the credible measured pressure data of transient process. In this paper, the specific implementation steps of the method are introduced by taking the results of a load rejection test of a pumped storage power station as an example.

Synchronous Generator Stability Characterization for Gas Power Plants Using Load Rejection Tests

For power grid operators, knowing the transient response of the synchronous generators (SGs) included in their grids is important in order to simulate and monitor faults and other contingencies. However, the time constant of the automatic voltage regulator (AVR) and speed governors of SGs are not fast enough to show their transient dynamics in the case of a fault in the grid. This paper presents a fieldwork carried out in more than 60 gas power plants, where the response of their controllers was studied. These power plants are running and supplying electricity to the Spanish grid. The study consists of recording some SG responses in different situations, varying the AVR or the speed governor setpoints while the generator is running at no-load conditions, and also performing load rejection tests, achieving a real fault emulation. Once all the data are gathered, a fitting of the SG parameters is performed by computer simulations using GENSAL, GAST and SEXS models replicating the performed field tests. This work allows us to build an accurate network model for the whole power system and check which plants are having trouble in the case of contingencies in the grid.

Design techniques for improving energy performance and S-shaped characteristics of a pump-turbine with splitter blades

The development of high-head pumped-storage projects presents various opportunities and challenges. One challenge is the operational stability of pumped-storage power plants, which is closely associated with the characteristics of pump-turbines. In this study, the design and experimental verification of the hydraulic performance of a pump-turbine runner with splitter blades are investigated. The effects of several main parameters on the performance curve and S-shaped characteristics of pump-turbines in turbine mode are examined via numerical simulation. Subsequently, model tests are conducted to validate the improvements in the performance curve, including a comparison of the S-shaped characteristic curve at a constant guide vane opening and under the same initial conditions. An emergency load rejection test based on the same guide vane closing scheme is performed to verify improvements in transient pressure in the spiral case, draft tube, and rotational speed. The results confirm the enhancement in the S-shaped characteristics and transient global parameters of the splitter blade design. Furthermore, a reduction in pressure pulsation intensity in the vaneless space during off-design conditions is confirmed.

A new approach to parameter identification of generation unit equipped with brushless exciter using estimated field voltage

Parameter estimation of power plants is one of the main challenges of power system studies. Among different components of a power plant, excitation system (EXS) has great importance because of its effect on dynamic stability of power systems. Thus, it is vital to have accurate models of EXSs for power system dynamic studies. Since the field voltage and current are not accessible in brushless EXSs, parameter estimation of them is more difficult and challenging. Therefore, a new method is proposed in this paper to estimate field voltage signal using other measurements of the synchronous generator (SG). The proposed method is carried out through three stages; 1) parameter estimation of the SG using load rejection tests, 2) field voltage estimation, and 3) parameter estimation of EXS. The proposed method is applied to a 147 MVA industrial gas unit. The estimated model outputs are compared to the experimental results to show the accuracy and effectiveness of the proposed method.

Real machine Test inversion research of J Pumped Storage Power Station

Accurate prediction of transition process is an important issue in the design and operation of pumped storage power station. In this paper, combined with load rejection test of J Pumped-storage Power Station, the basic equation of water flow motion and the element matrix equation of the turbine were established first, and the calculation model was established through HYSIM software. Then for the 100% load rejection control condition, the inversion calculation and analysis of actual load rejection test under the same boundary condition were carried out. According to the comparison process line between numerical simulation and measured data of the surge-chamber water level, a comprehensive combination calculation was used to calibrate the impedance coefficient of surge-chamber. Finally, based on the calibrated impedance coefficient, a new calculation model was established, and the inversion calculation was carried out again. By comparing the numerical simulation and measured data of volute and tail pipe pressure, the pressure pulsation characteristics of the characteristic parameters of the unit were obtained, and the correction value of pressure pulsation was obtained. The calibration method and pressure pulsation correction method adopted in this paper can provide a reference for the inversion analysis of load rejection test in similar power stations.

Inversion calculation and prediction of extreme conditions by in-situ test of real machine in a hydropower station

The in-situ test of the real engine in hydropower station is a necessary test before the unit is put into operation. During the test, the problems in the test process can be found through the auxiliary inversion calculation, and the calculation and analysis of extreme conditions can provide important support for the unit’s permanent operation. First of all, this paper analyzes the problem that the maximum pressure of the spiral shell and the increase rate of the unit speed in the load rejection test of the hydropower station exceed the control standard. Through inversion calculation, it is found that the closing law of the guide vane of the unit is different from the set closing law, and the robustness of the closing law is poor; then, combined with the test situation, the closing law of the guide vane of the unit was optimized. While the adjusted load rejection test was simulated under the same boundary conditions, and the measured data and numerical calculation results were compared and analyzed to obtain the modified values of the characteristic parameters. Finally, the extreme conditions in the transition process of large fluctuations are predicted and calculated by numerical simulation. This research idea provides reference and guidance experience for similar projects.

New Method for Synchronous Generator Parameters Estimation Using Load Rejection Tests Data Considering Operational Limitations

Load rejection (LR) test, recommended by different standards including IEEE Std.115., is considered as one of the most popular methods for parameter estimation of the synchronous generator (SG). However, parameter identification using this method has demonstrated no acceptable results for experimental data. Therefore, the present study aims to analyze common LR test operational limitations and to suggest a new method for parameter estimation based on LR test results which overcome the shortcomings of the previous method. To this end, a new approach is proposed for SG parameter estimation using LR test data. Using the proposed method, parameter estimation covers both salient pole and round rotor SGs. In both d and q axes, the effects of limitations are considered, and finally, parameters are estimated by fitting curve to experimental data based on the non-linear least square method and the genetic algorithm (GA). The proposed method is applied to the 200 MVA gas unit of a combined cycle power plant, and the results are discussed accordingly.

Ground Saturation Response During First Filling of Lined Pressure Tunnels: A Case Study

The Neelum–Jhelum Hydropower Project, commissioned in April 2018 and located in the Azad Kashmir region of northeast Pakistan, is one of the most challenging and technically complex projects in the region. The project’s 28.6 km headrace tunnels are constructed in a highly mountainous region with relatively complex geology that includes various sedimentary rocks of Murree formation. The hydro-mechanical behavior of the deep headrace tunnels with a maximum overburden of 2000 m and underground powerhouse at a depth of 450 m are of particular interest. The project generates electricity by diverting water from the Neelum River to an underground powerhouse through a tunnel system crossing beneath the Jhelum River. The pressurization of the hydraulic tunnels was an important milestone and necessitated intentional planning down to the smallest detail for the first filling. Successful filling was a governing criterion for proper functioning of the tunnel lining that was supplemented by monitoring instruments, a drainage system, and ground treatments during construction of the project. Ground re-saturation during the first filling of the concrete and shotcrete-lined waterways constructed in the diversified rock mass is interesting to study. The rock mass in this area is sheared and fractured, with open fissures. In this study, we investigated the ground re-saturation and water leakages in adits, plugs, and surface outflow after the first filling of the headrace tunnel. A load rejection test was conducted to evaluate overall fitness of the power waterways, plant, and to study any change in leakages due to sudden oscillation in the waterway tunnels. Surfer3D software was used to analyze the data collected from the piezometers, which showed abnormal water pressure built up in a localized zone between penstocks three and four. This study was also supported with two-dimensional finite element modeling of the project, at a location where the tunnel has minimum rock cover susceptible to hydrojacking. Numerical analysis results were compared with field data results during the first filling process and both showed close proximity.

양수발전소의 수력학적 과도현상에 관한 연구(Ⅰ)

This field test was conducted to investigate the hydraulic transient at a pumped storage power plant with four 250 MW pump turbines. The occurrence of a hydraulic transient may be a problem related to the water hammer that occurs during the pump start and pump input power shutoff or turbine start and turbine load rejection, which affects the hydraulic pressure change, flow-rate change, and rotational speed change of the pump turbine caused by the water hammer of the penstock and tailrace. The water hammer was field tested to investigate such hydraulic transients. Accordingly, the main factors in the field test must be determined to analyze the water hammer. We monitored the main sensors attached to the pump turbine and those attached to the inlet valve. The result after the field study confirmed that the occurrence of the water hammer during the pump start and pump stop under a normal operation of the pump turbines was not problematic. Moreover, during the load rejection test, an upsurge occurred in the penstock under the rapid closing of the upper and lower wicket gates, while a downsurge occurred in the draft tube and spread to both the upstream and the lower stream. As a result, the pressure rose in the penstock, and the pressure rapidly fell in the draft tube. Subsequent to the full close of the upper wicket gate, the water hammer repeatedly rose and fell in the tailrace between the pump storage power plant and the lower reservoir. Moreover, the pressure in the draft tube rose, and surging occurred in every 2 minutes.

Optimization of Closure Law of Guide Vanes for an Operational Hydropower Plant of Nepal

This paper addresses the optimization of two-stage closure law of guide vanes in an operational hydropower plant of Nepal. The mathematical model has been established in commercial software Bentley Hammer, whose correctness has been validated by comparing the results with the data of experimental load rejection test. The validated mathematical model has been employed to find the parameters of optimum closure pattern, which minimizes the non-linear objective function of maximum water pressure and maximum rotational speed of turbine.

Temperature analysis of the HTR-10 after full load rejection

The HTR-10 is a small modular high-temperature reactor located in Tsinghua University, in China. After the reactor ran continuously for 72 h at full power in the commissioning stage, a full load rejection test was conducted by manually disconnecting the generator from the grid. In this study, reactor transients were analyzed using the THERMIX model. Some of the important thermal–fluid phenomena that occurred after the test initiation are discussed here, including the natural convection of helium in the core and the temperature redistribution in the reactor. Temperatures reproduced for the measuring points arranged in the internals were in agreement with the test data. This demonstrated that the code and calculation model are suitable for posttest analysis applications. Regarding the safety features of the reactor, there was a large margin between the predicted maximum fuel temperature of 997 °C and the safety limit of 1620 °C.

Detailed Derivation and Experimental Validation of a Method for Obtaining Load Conditions for Salient Pole Synchronous Machine Quadrature Axis Parameters Determination

In this paper, a method to determine load conditions under which the armature current of a salient pole synchronous machine is on the q -axis is described. The proposed method allows the determination of a locus in the $P-Q$ space in which the armature current is completely on the q -axis. The derivation of these conditions simplifies the determination of the machine q -axis parameters during load rejection tests, since it eliminates the necessity for trial and error procedures or power angle estimation. The method was tested in a 100 MVA, 13.8 kV, 60 Hz, 40 poles salient pole synchronous machine installed in a hydro power plant. Tests results show that loads calculated with the proposed method are in fact points where the armature current is on the q -axis.

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.

Optimization of Closure Law of Guide Vanes for an Operational Hydropower Plant of Nepal

This paper addresses the optimization of twostage closure law of guide vanes in an operational hydropower plant of Nepal. The mathematical model has been established in commercial software Bentley Hammer, whose correctness has been validated by comparing the results with the data of experimental load rejection test. The validated mathematical model has been employed to find the parameters of optimum closure pattern, which minimizes the non-linear objective function of maximum water pressure and maximum rotational speed of turbine.

Pressure fluctuation analysis and extreme pressure prediction in the transient processes of pumped storage power station

The analysis of hydraulic transient process is very important for the design and operation of pumped storage power (PSP) station. The one-dimensional mathematical model is often used in the transient process calculation, by which the maximum value at the spiral case inlet and minimum value at the draft tube inlet can be obtained. However, the one-dimensional mathematical model only provides cross section pressure trends at spiral case inlet and draft tube inlet, and the pressure fluctuation in load rejection cannot be revealed. But the pressure fluctuation amplitude of pump turbine in load rejection process is proved to be huge by test on site. In load rejection test, the measured pressure signals obtained from one or two taps, and the measured pressures affected by tap locations, and polluted by noise. So there exists great difference between the measured extreme values and numerical extreme values. To improve the accuracy of theoretical prediction, analysing the measured data and extracting the pressure fluctuation required in computed results are needed. This paper analyses the load rejection test results in generating mode and pumping mode of a PSP plant using empirical mode decomposition (EMD) method. The measured results at spiral case inlet and draft tube inlet are successfully separated to the trend terms and pulsation terms. Comparison between the measured trends and theoretical calculated results are also performed. The pressure fluctuation value superposed in the transition process calculated result of extreme pressure is recommended, which is of great significance for the safe operation of the PSP station.

Improving Synchronous Generator Parameters Estimation Using <inline-formula> <tex-math notation="LaTeX"> $d- q$</tex-math> </inline-formula> Axes Tests and Considering Saturation Effect

Fundamentals of parameter estimation of synchronous generator (SG) have already been presented in different standards such as IEEE Std. 115. The first proposed methods require short circuit tests and/or some tests for which the synchronous generator should be out of service. In recent reports, however, to avoid the shortcomings of former methods, partial load rejection tests on $d- q$ axes have been recommended to estimate the electrical parameters of SG such as different reactances and time constants. In this paper, it is first shown that the standard well-known methods are valid when there is no saturation effect. Therefore, a new method is proposed to improve SG parameters estimation taking into account the saturation effect. The proposed method uses saturation curve parameters, rotor angle, and analytical equations of the SG alongside the load rejection tests results. To show the accuracy and precision of the proposed method, it is applied to experimental data of an 80 MVA gas turbine unit, and the results are discussed.

Effective estimation of angular speed of synchronous generator based on stator voltage measurement

Estimation of the parameters of the power generators are important part of a power system modeling and simulation. A reliable estimation of a synchronous generator parameters can be done using waveforms measured directly on the terminals of the machine. The waveforms are recorded during a carefully chosen disturbance tests of the generating unit. One of the quantities necessary to determine the generator parameters is the deviation of the generator angular speed. However, because of the safety reasons, it is very difficult to get access to the direct measurement of this quantity on a operating generating unit. Angular speed estimation based on a generator stator voltage seems to be an alternative solution to the problem.The aim of the paper is to find a computationally efficient and accurate method of indirect angular speed estimation of a synchronous generator which is based on the recording of its stator voltage during a load rejection test. The algorithms evaluated in the paper are based on Prony’s estimator, zero-crossing detection, least-square data fitting and layer recurrent neural network. Paper contains literature survey, mathematical model of the considered generator, analysis of its stator voltage recorded in a power plant, description of the selected algorithms and results of the algorithms estimation using a signal with known frequency variation. Performed algorithms evaluation allows to choose the best solution in terms of accuracy and computational effort.

Load Rejection Test for 600 MW Unit with the Improvement of DEH System

本文开展了DEH系统改造后的600 WM机组甩负荷试验，计算了改造后机组的各项动态特性参数，确定了其良好的动态调节特性；结合改造前后数据的对比发现，改造后机组的转子飞升时间常数变小，在甩负荷后可能出现动态超速难易控制的情况，蒸汽容积时间常数也变小，这可能与汽门严密性试验不合格有关。进而提出了相关甩负荷试验进行时需注意的几个问题。 Load rejection test for 600 MW unit with the improvement of DEH system was made. Based on the calculation of various parameters, the good dynamic regulation characteristic was identified. After the comparison of data before and after system transformation, the constant Ta decreased, which leaded to a difficult control of over speed problem after load rejection test probably. And the constant Tv was also decreased obviously due to the failed valve tightness. Finally, several important problems were proposed, which should be paid more attentions when the load rejection test was carried out.