Reliable Analysis on Fast Valving of Ultra-Supercritical Unit Under Transient Fault Conditions

2017 ◽  
Author(s):  
Yu Cai ◽  
Wei Li ◽  
Bao Zhang ◽  
Wenjian Wu ◽  
Deren Sheng ◽  
...  
Keyword(s):  
Power System ◽  
Steam Turbine ◽  
Dynamic Model ◽  
Transient Stability ◽  
Power Grid ◽  
Load Shedding ◽  
Control Mode ◽  
Normal Operation ◽  
Transient Fault ◽  
The Stability

Fast valving of ultra-supercritical unit has great effects on over-speed prevention, load-shedding control, transient stability analysis of electrical system and other security problems. The purpose of fast valving is to maintain the stability of power system once fault or load shedding of unit occurs in the electric power system. Therefore, it is of great significance to study the reliability of fast valving for ultra-supercritical unit. In this paper, the KU ( short shedding) logic condition of SIEMENS T3000 system is analyzed as the research object of fast valving. The unit can be avoided over speed by monitoring the unit load and fast valving under faulty grid conditions based on the KU control. A series of measures will be taken after KU is triggered, for instance the governing valving will be closed quickly and the DEH (digital electro-hydraulic) control of the steam turbine will be switched to speeding control mode. On the other hand, the unit will return to normal operation if the transient fault of power grid disappears. The key contributions of this thesis include three parts: Firstly, based on the analysis of control characteristics of ultra-supercritical unit and protective logic and triggered conditions of KU function, a novel dynamic model by coupling the fast valving of steam turbine and the transient stability of generator is established by applying the PSCAD software. Then, the dynamic response process of ultra-supercritical unit is simulated and calculated by adopting the coupling dynamic model when KU function is triggered. Also the influence factors and reliability of fast valving are analyzed under transient fault conditions. Finally, two optimized measures by increasing the time delay and the speed of quantitative judgment are put forward to reduce risks and avoid the misoperation of signal distortion which may be caused by the power transmitter under transient fault conditions. The results of this study can not only help to evaluate the reliability of fast valving function scientifically in power grid transient fault, but also guide the technicians to analyze the stability of the power grid.

Research on Stability of Power System with Distributed Generation Synthesis Load Model

2013 ◽  
Vol 341-342 ◽  
pp. 1374-1379
Author(s):  
Yang Liu ◽  
Zhen An Zhang ◽  
Wei Liu ◽  
Ya Nan Wang
Keyword(s):  
Power System ◽  
Distributed Generation ◽  
Transient Stability ◽  
Power Grid ◽  
Stable Operation ◽  
Power Network ◽  
Small Hydropower ◽  
Large Power ◽  
Load Model ◽  
The Stability

With different element models and parameters in power system, the transient stability analysis results are also different, especially the model of generator and load. Based on the actual parameters of Hunan power grid, this paper builds the synthesis load model of the distribution network with small hydropower considered, and then the Hunan simulation network can also be got. Using PSASP, analyses the transient stability of Hunan power system with distributed small hydropower under different operation modes systematically and comprehensively. Through an overall check of the stability level in each Hunan area, and then compared with the analysis results of Hunan power grid based on the currently used load model , the influences of the distributed small hydropower on the safe and stable operation of the large power network are summarized.

Transient Stability by means of Generator Tripping, Under Frequency Load Shedding and a Hybrid Control Scheme

2018 ◽  
Vol 19 (1) ◽  
Author(s):  
P. F. Le Roux ◽  
R.C Bansal
Keyword(s):  
Power System ◽  
Transient Stability ◽  
Hybrid Control ◽  
Load Shedding ◽  
Electrical Network ◽  
Traditional Methods ◽  
Transient Fault ◽  
System A ◽  
Control Scheme ◽  
Hybrid Control Scheme

Abstract An electrical network constantly faces unforeseen events such as faults on lines, loss of generation, etc. Under Frequency Load Shedding (UFLS) and Generator Tripping are traditional methods used to stabilise a network when a transient fault occurs. These methods will prevent any network instability by shedding load or tripping the most critical generator at a calcultated time when required. By executing these methods, the network can be stabilised in terms of balancing the generation and the load of a power system. A hybrid control scheme is proposed where the traditional methods are combined to reduce the stress levels exerted on the network and to minimize the load to be shed.

scholarly journals A Three-Stage Procedure for Controlled Islanding to Prevent Wide-Area Blackouts

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 3066 ◽  
Author(s):  
Hongbo Shao ◽  
Yubin Mao ◽  
Yongmin Liu ◽  
Wanxun Liu ◽  
Sipei Sun ◽  
...  
Keyword(s):  
Power System ◽  
Dynamic Stability ◽  
Power Flow ◽  
Transient Stability ◽  
Load Shedding ◽  
Area Measurement ◽  
Wide Area ◽  
Measurement Systems ◽  
Controlled Islanding ◽  
Three Stages

Controlled islanding has been proposed as a last resort action to stop blackouts from happening when all standard methods have failed. Successful controlled islanding has to deal with three important issues: when, and where to island, and the evaluation of the dynamic stability in each island after islanding. This paper provides a framework for preventing wide-area blackouts using wide area measurement systems (WAMS), which consists of three stages to execute a successful islanding strategy. Normally, power system collapses and blackouts occur shortly after a cascading outage stage. Using such circumstances, an adapted single machine equivalent (SIME) method was used online to determine transient stability before blackout was imminent, and was then employed to determine when to island based on transient instability. In addition, SIME was adopted to assess the dynamic stability in each island after islanding, and to confirm that the chosen candidate island cutsets were stable before controlled islanding was undertaken. To decide where to island, all possible islanding cutsets were provided using the power flow (PF) tracing method. SIME helped to find the best candidate islanding cutset with the minimal PF imbalance, which is also a transiently stable islanding strategy. In case no possible island cutset existed, corresponding corrective actions such as load shedding and critical generator tripping, were performed in each formed island. Finally, an IEEE 39-bus power system with 10 units was employed to test this framework for a three-stage controlled islanding strategy to prevent imminent blackouts.

scholarly journals Transient stability control by means of under-frequency load shedding and a hybrid control scheme

2017 ◽  
Vol 28 (4) ◽  
Author(s):  
P. F. Le Roux ◽  
R.C. Bansal
Keyword(s):  
Transient Stability ◽  
Hybrid Control ◽  
Stability Control ◽  
Load Shedding ◽  
Electrical Network ◽  
Traditional Methods ◽  
Transient Fault ◽  
System A ◽  
Control Scheme ◽  
Hybrid Control Scheme

An electrical network constantly faces unforeseen events such as faults on lines, loss of load and loss of generation. Under-frequency load shedding and generator tripping are traditional methods used to stabilise a network when a transient fault occurs. These methods will prevent any network instability by shedding load or tripping the most critical generator at a calculated time when required. By executing these methods, the network can be stabilised in terms of balancing the generation and the load of a power system. A hybrid control scheme is proposed where the traditional methods are combined to reduce the stress levels exerted on the network and to minimise the load to be shed.

Mid-Term Stability Assessment of Jiangxi Power Grid

2013 ◽  
Vol 732-733 ◽  
pp. 882-887
Author(s):  
Yong Chun Su ◽  
Hao Wei Jia
Keyword(s):  
Power System ◽  
Power Grid ◽  
Assessment Method ◽  
Control Measures ◽  
Assessment Process ◽  
Jiangxi Province ◽  
Stable Operation ◽  
Stability Assessment ◽  
Term Stability ◽  
The Stability

Mid-term stability assessment is an important work to support power system operation in a province power grid of China every year. The stability assessment method and process was introduced in this paper. As an example, the stability of Jiangxi province power system was evaluated in the following two years. Weak area and weak transmission line were found out in each power supply area. Prevention and control measures were proposed. According to problems among the assessment process and using the state monitoring data, an approach was discussed to increase the assessment result accuracy. The analysis conclusion provides the reference to the safe and stable operation of Jiangxi power system.

Analysis and Stability Enhancement of DG Sourced Power System with Modified AVR and PSS

2013 ◽  
Vol 768 ◽  
pp. 313-316
Author(s):  
P. Sivakumar ◽  
C. Birindha
Keyword(s):  
Power System ◽  
Distribution System ◽  
Transient Stability ◽  
Probabilistic Approach ◽  
Small Signal Stability ◽  
Signal Stability ◽  
The Stability ◽  
System Stabilizer ◽  
Stability Issues ◽  
Stability Enhancement

Distribution system is facing stability issues with integration of distributed generators and controllers. This proposed method presents the stability of renewable energy based distribution system with varying energy source considering intermittent nature of wind and solar energy using probabilistic approach. The system is supplied by conventional and distributed generating sources like PV and wind. Monte Carlo approach is used for predicting the wind and solar power uncertainties. Proposed work explains both small signal stability and transient stability enhancement of DG sourced power system with power system stabilizer and automatic voltage regulator .It is carried out in is 4 machine 10 bus system. The initial simulation has been carried out using MATLAB/SIMULINK.

The Study of Chopper in the LVRT of Direct-Drive Wind Energy Generation System

2014 ◽  
Vol 950 ◽  
pp. 314-320 ◽  
Author(s):  
Jun Jia ◽  
Xin Xin Hu ◽  
Ping Ping Han ◽  
Yan Ping Hu
Keyword(s):  
Power System ◽  
Wind Power ◽  
Wind Turbines ◽  
Reactive Power ◽  
Power Grid ◽  
Synchronous Generator ◽  
Direct Drive ◽  
Fault Ride Through ◽  
Wind Power System ◽  
The Stability

With the scale of wind farm continuously increasing, when grid fault, the influences of the wind turbines connected to the grid on the stability of the power grid can never be ignored. Therefore, there are higher standards of the wind turbines’ abilities of fault ride-through (FRT) and producing reactive power. This paper studies the direct-drive wind power system, and the main point is the fault ride-through (FRT) of the permanent magnetic synchronous generator (PMSG) with Chopper. By establishing the dynamic model of PMSG under the environment of DigSILENT, this paper simulates the fault ride-through (FRT) of the direct-drive wind power system connecting into power grid. During the research, we focus on the stability of voltage about the Chopper to the DC bus under faults. What’s more, in this paper, we analysis the data about how the Chopper help the DC bus to improve its stability. The simulation results show that: when there is a fault on the point of common coupling, the permanent magnetic synchronous generator has the capability of fault ride-through (FRT). Especially when there is a voltage dip on the grid side, the permanent magnetic synchronous generator could produce reactive power for power grid, effectively preventing the system voltage from declining seriously, so as to improve the system stability under faults.

The Summary of HVDC Commutation Failure and Example Analysis

2013 ◽  
Vol 446-447 ◽  
pp. 853-857
Author(s):  
Qian Jin Wu ◽  
Xue Zhi Wang
Keyword(s):  
Power System ◽  
Preventive Measures ◽  
Power Grid ◽  
Large Area ◽  
Hvdc System ◽  
Identification Method ◽  
Commutation Failure ◽  
The Common ◽  
The Stability

Commutation Failure is the common fault of HVDC, continuous commutation failure may lead to HVDC block and affect the stability of the power system. Especially in southern power grid, china, its special that the end of four HVDC system are all in Guangzhou. If the AC system occurs serious fault, all of the HVDC system may occur commutation Failure, HVDC block, even occurs large area blackout. So how to avoid continuous commutation failure and restore the stability of HVDC is important for AC and DC parallel power system. This paper based on the mechanism of commutation failure, analyze the reason of commutation failure and identification method, preventive measures. At last, this paper uses actual recorded wave to analyze the diversification of system after commutation failure.

scholarly journals Event-Based Under-Frequency Load Shedding Scheme in a Standalone Power System

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5659
Author(s):  
Ying-Yi Hong ◽  
Chih-Yang Hsiao
Keyword(s):  
Power System ◽  
Power Grid ◽  
Peak Load ◽  
Low Frequency ◽  
Computation Time ◽  
Load Shedding ◽  
Power Generators ◽  
Cascading Outages ◽  
Event Based ◽  
Wind Power Generators

Under-frequency load shedding (UFLS) prevents a power grid from a blackout when a severe contingency occurs. UFLS schemes can be classified into two categories—event-based and response-driven. A response-driven scheme utilizes 81L relays with pre-determined settings while an event-based scheme develops a pre-specified look-up table. In this work, an event-based UFLS scheme is presented for use in an offshore standalone power grid with renewables to avoid cascading outages due to low frequency protection of wind power generators and photovoltaic arrays. Possible “N-1” and “N-2” forced outages for peak and off-peak load scenarios in summer and winter are investigated. For each forced outage event, the total shed load is minimized and the frequency nadir is maximized using particle swarm optimization (PSO). In order to reduce the computation time, initialization and parallel computing are implemented using MATLAB/Simulink because all forced outage events and all particles in PSO are mutually independent. A standalone 38-bus power grid with two wind turbines of 2 × 2 MW and photovoltaics of 7.563 MW was studied. For each event, the proposed method generally obtains a result with a smaller shed load and a smaller overshoot frequency than the utility and existing methods. These simulation results verify that the proposed method is practically applicable in a standalone power system with penetration of renewables.

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