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.
