SYSTEM OPERATIONS &
PLANNING
A METHOD FOR TUNING MODELS IN
DIgSILENT POWERFACTORY, WITH
REFERENCE TO A TGOV5 GOVERNOR
TUNING EXAMPLE
Rev. 0
TABLE OF CONTENTS
Contents
Page
no.
1. Introduction ... 3
2. Methodology ... 3
3. Results and Interpretation... 7
4. Conclusion ... 8
List of Tables and Figures
Figure 1: Plant model frame used for Governor tuning...3Figure 2: Measurement block properties...4
Figure 3: Test grid used for TGOV5 tuning...5
1. Introduction
Models are important for dynamic studies as they are mathematical representations of real systems in the power grid. This report explains a method for tuning dynamic models within DIgSILENT. A TGOV5 governor model is tuned using frequency event data as an example of this method. The event data is extracted from a PMU recording of frequency from the Under Frequency Load Shedding (UFLS) event that occurred on 27 December 2009 at 17:06 in the Eskom network.
2. Methodology
The best way to tune any model is to excite it with a measured input and compare the simulated output with the actual output. In the case of governors, the input signals are frequency (or speed), and electrical power; the output signal is turbine power.
Measurements ElmFile y1 0 1 vco slot ElmVco* vuel voel ur;ui ut spare1 spare2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 1 2 pcu Slot ElmPcu* fe psco pturb spare1 spare2 pturb spare1 spare2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 sym Slot ElmSym*,IntRe.. xmdm psie 0 1 2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pss slot ElmPss* dfedt spare1 spare2 0 1 2 3 4 5 6 7 8 9 10 11 w1 cosn Wf xme pt xmt phiui upss fe u qg pg pgt ir;ii curgn curex ve
By editing the plant model frame in DIgSILENT, the governor model can be excited by an external signal. Figure 1 shows the plant model frame used for governor tuning. It was adapted from the IEEE Frame and is different only because of the Measurements input block which is used to provide the event frequency. The measured frequency is input into the governor block (PCU) instead of speed (w) which is normally fed back from the generator block (SYM). This is acceptable provided that the frequency is in per unit. The measurement block uses the ElmFile type which allows data to be imported from an external file (.txt file type). Figure 2 shows the measurement block properties which illustrate its connection to the ElmFile type.
Figure 2: Measurement block properties
A simple network must be modeled for these tests because the governor uses electrical power as an input. The electrical power is fed back from the generator model block and is dependant on the network. The network model that was used is shown in Figure 3. An infinite bus is used to represent the rest of the Eskom network, this is necessary to compensate for any deficit in power between the generated power and load demand.
Station2/LV 22.00 1.00 4.08 Station1/HV 400.00 1.00 0.00 General Load 520.00 0.00 G ~ Kendal Gen 498.00 17.74 61.52 External Grid 22.00 MW 17.74 .. 0.78 2-Winding.. -498.00 17.74 71.19 498.00 17.74 71.19
Figure 3: Test grid used for TGOV5 tuning
The plant model frame slots are populated with the relevant controller blocks. The slot configuration is shown in Figure 4.
Figure 4: Slot configuration for the TGOV5 tuning plant model
It is important to note that the Measurements block points to a file object which is created in the Data Manager. To create a file object the following steps must be followed:
Open the Data Manager and select either the active system stage or grid. Select the New Object button:
Configure the Element Selection window as shown below:
Browse for the file containing the measurement data and change the file name.
The file must be saved as a .txt and should be in the format shown below:
The first column always contains the time data. This does not have to be of equal intervals because DIgSILENT uses interpolation to correct for missing
data. The remaining columns contain all the other data and the first row shows the number of columns excluding the time column.
The data object will now appear under the system stage or grid folder and this can be selected as a slot. In order to plot the file’s data, a variable set must be created by right-clicking on it in the Data Manager.
Once this is completed, simulations can be run. The resultant power can then be compared to the measured power by plotting each on the same graph. To view the measured power signal, an ElmFile object must be created in the same way as mentioned above.
3. Results and Interpretation
Figure 5 shows the results of the governing tuning example in the form of several plots. The top plot shows the input frequency which was recorded from the power system using PMUs. This is the signal that is input in to the governor model. The bottom plot shows four different signals on the same axes. All of these signals represent the electrical power output from the Kendal machines, however, the smoother plots show simulated data whereas the noisy plots show measured data. The red and blue plots represent the measured power out of two separate Kendal machines and the brown and purple lines represent the simulated response using two different sets of parameters. From observing these graphs whilst changing the model parameters, one can determine the optimal values required for a certain response. For example, the difference between the purple and brown lines is evident, this provides a better understanding of the effects that the changed parameter has on the overall response.
400.00 319.98 239.96 159.94 79.920 -0.1000 [s] 1.010 1.005 1.000 0.995 0.990 0.985 0.980
Freq: Measurement value 2
400.00 319.98 239.96 159.94 79.920 -0.1000 [s] 575.00 550.00 525.00 500.00 475.00 450.00
Kendal Gen: Positive-Sequence, Active Power in MW KendalMW: Measurement value 2
KendalMW: Measurement value 1 Kendal Gen: 2010-02-25 Parameters Kendal Gen: 2010-03-12 Parameters
DIgSILENT
Figure 5: Measured response versus simulated response for the TGOV5 model at Kendal
4. Conclusion
A method for tuning dynamic models in DIgSILENT was presented. This method reduces errors because tuning is done on the same model that is used during the dynamic
studies. The method is explained in detail with use of a TGOV5 governor tuning example. The benefits of this approach are evident from the results of the tuning example which are presented.