Projects:2016s1-122 A Complete Model for a Synchronous Machine
A Dynamic Model for a Synchronous Machine
Supervisor:
Dr Andrew Allison
Co-supervisor:
David Vowles
Project Members:
Leng Wai Kit Teng, Praveen De Silva, Thomas Klopf, Samuel Conlin
Aim:
To find a model for the Dynamic Characteristics of a synchronous machine. Then the model will be validated through a series of tests on an actual machine. The test procedures will be standardized and documents for use with other synchronous machines.
Motivation:
The steady state characteristics of the synchronous machines in the power labs at the University of Adelaide are already well documented, however information about the dynamic characteristics of these machines haven't been documented much. If a model and standardized test procedure to find the synchronous machines dynamic characteristics could be found, more information about the machines could be documented for future use by students and academics who wish to use them.
EES Steady State Testing:
Steady state tests for the synchronous machine involved three different test procedures as directed by the EES practical notes, each procedure determined a different machine operation condition. The tests completed were the open circuit, short circuit and slip test.
Through the use of the EES Synchronous Machine Experiment we were able to accurately find several important steady state synchronous machine parameters including Xd and Xq. It was found that the value for Xd = 33.33 ohms = 1.46 pu and the value for Xq = 10.41 ohms and .456 pu.
Synchronous Machine Saturation Model:
A saturation model is a non-linear model which is required to describe the behavior of a power system.[9]Therefore it was essential that as a part of the project a saturation model of the synchronous machine was found. The open circuit tests from the EES Synchronous Machines experiment were used with the methods to find a saturation model found in “Small-signal stability, control and dynamic performance of power systems” [9]
The synchronous machine saturation model was found to be S(φ)=(0.5φ^5.0694)/φ. Figure 1 shows the found Saturation Model.
Steady State Capability Testing:
Steady state capability testing is an essential testing procedure required to find synchronous machine parameters such as XL In order to complete the steady state capability test, testing procedures were required to be designed and developed. The testing procedures were also run to find the synchronous machine parameters. Several hurdles were encountered through this testing procedure due to the lack of documentation on the machine set. In the steady state capability test, the synchronous machine will be synchronized and connected to the mains. Once connected to the mains, its field current will be measured for multiple combinations of real and reactive power which are varied through the use of the DC machine rheostat and the synchronous machine excitation. The results found in the Steady State Capability testing can be seen in Figure 2.
Figure 3 was created using the data found in Figure 2 and a suite of Matlab functions authored by David Vowles. [10] The suite of Matlab functions authored by David Vowles was used to compute the synchronous machine field current from the results found in steady state capability tests and the EES Synchronous Machine Experiment. The code compares and plots the relative error as a percentage for the measured and calculated values of field current. This graph can be seen as Figure 3.
An accurate estimate of XL (leakage reactance) is a required to find parameters which are used for both steady state and dynamic modelling of a synchronous machine.[9] Unfortunately XL cannot be directly measured using testing procedures. In order to achieve an accurate estimate for the value of XL the results found in the Steady State Capability Tests were required to be run through software provided by David Vowles. [10] an accurate estimate for XL was found. XL=0.1037pu=2.37Ω. The software also recalculated the calculated field current for this value of XL. The new calculated value of field current was plotted against the measured value of field current found in the steady state capability tests. This graph can been seen as Figure 4.
Load Rejection Testing:
Load rejection testing is an essential testing procedure required to find the dynamic parameters of the synchronous machine. In order to complete the load rejection test, testing procedures were required to be designed and developed. The testing procedures were also run to find the synchronous machine dynamic parameters. Several hurdles were encountered through this testing procedure due to the lack of documentation on the machine set. In the load rejection test the synchronous machine was synchronized to the mains. Once the machine was synchronised the synchronous machine will be disconnected from the mains. When the disconnection occurs the phase to neutral voltages and field current data will be captured for 2.5 second intervals on an oscilloscope.
The load rejection data was inputted into software authored by Andrew Allison. The software utilized filters to smooth and estimate the amplitude of the synchronous machine field current and phase to neutral voltage. The result can be seen as Figure 5.
Conclusion:
Over the course of the project the team has been able to create a significant amount of documentation for the machine set found in the Machines Labs, NG06, located at The University of Adelaide. As a result this project report will be valuable for all future academics and students who wish to expand their knowledge on the machine set and in particular the synchronous machine. This report also has to potential to increase the use of a currently underutilized resource. Several significant outcomes are evident as a result of the project. These outcomes include a; accurate calculation of the steady state parameters Xd, Xq and Xl, saturation model, DC machine operational procedure, steady state capability testing procedures, load rejection testing procedure and a project risk analysis. Through the use of the EES Synchronous Machine Experiment we were able to accurately find the value of Xd was 33.33ohms = 1.46 pu and the value for Xq was 10.41ohms and .456pu. Using methods found in “Small-signal stability, control and dynamic performance of power systems” [9] and the open circuit results found the EES Synchronous Machine Experiment the team found the synchronous machine saturation model was S(φ)=(0.5φ^5.0694)/φ. Through investigation the project team were able to create a detailed operation procedures for the DC machine found on machine set two. Using this DC operation procedure a steady state capability test procedure was designed, tested and redesigned in order to find values of synchronous machine field current for varying values of real and reactive power. The results found from the steady state capability were used to find an accurate estimate of XL, which was found to be 0.1037pu for the project synchronous machine. Again through investigation the project team were able to create a detailed operational procedure for a load rejection test. The test methods were designed and tested by the team in order to find the transient behaviour of the project synchronous machine and hence could be used to find the dynamic parameters of the machine.
References: [1]F. P. D. Mello et al, “Derivation of synchronous machine parameters from tests”, IEEE Power Tech. Inc., Schenectady, NY, Rep. 4, 1977. [2]J. P. Bartlett, “The practical application of optimal control techniques to synchronous generator excitation”, The University of Adelaide, Adelaide, SA, 1972. [3]. Kundur, Power system stability and control, New York, McGraw Hill, 1994. [4]T. Wildi, Electrical machines, drives, and power systems, 5th edition, New Jersey, Pearson Education Inc, 2006.
[5]The Institute of Electrical and Electronics Engineers, IEEE Guide for Test Procedures for Synchronous Machines, New York, 2010. [6]"Synchronous Generator as a Wind Power Generator", Alternative Energy Tutorials, 2016. [Online]. Available: http://www.alternative-energy-tutorials.com/wind-energy/synchronous-generator.html. [Accessed: 17- Apr- 2016]. [7]"Permanent magnet synchronous motor with sinusoidal fluxdistribution - MATLAB",Au.mathworks.com, 2016. [Online]. Available: http://au.mathworks.com/help/physmod/sps/ref/permanentmagnetsynchronousmotor.html. [Accessed: 17- Apr- 2016]. [8]"Risk Management Process - ISO 14971 - Risk Assessment - Risk Control", TSQuality.ch, 2016. [Online]. Available: http://tsquality.ch/risk-management-process/. [Accessed: 31- May- 2016]. [9]D. Vowles, P. Pourbeik and M. Gibbard, “Small-signal stability, control and dynamic performance of power systems”. University of Adelaide Press, 2015.
[10] D.J. Vowles, Suite of Matlab functions for steady-state analysis and parameter identification of synchronous machines, May 2016. A copy of the software is given in Appendix C and D
[11]W. Soong and A. Allison, "EES lecture Note Package", 2016. [12]K. Daware, "Basic construction and working of a DC Generator.", Electricaleasy.com, 2016. [Online]. Available: http://www.electricaleasy.com/2012/12/basic-construction-and-working-of-dc.html. [Accessed: 17- Oct- 2016]. [13]"Synchronous Motor Excitation | Electrical4u", Electrical4u.com, 2016. [Online]. Available: http://www.electrical4u.com/synchronous-motor-excitation/. [Accessed: 19- Oct- 2016].
