The introduction of synchrophasor technology to the realm of power systems has presented a myriad of novel approaches to age-old problems. In this thesis, the questions of instrument transformer calibration and transmission line parameter estimation have been examined. With synchrophasors offering real-time data for analysis, a solution to each individual problem seems feasible. A quandary however arises due to the fact that calibration methods depend on accurate knowledge of line parameters, and estimation of these parameters depend on calibrated measurements. Traditional methods of determining the parameters may not be the most accurate due to a variety of fluctuations possible on the system, which is why real-time estimation could prove beneficial. This work analyzes each problem and a feasible solution and proposes a method to achieve transducer calibration as well as parameter estimation together, while employing synchronized phasor measurements. / Master of Science / Synchrophasor Measurement Units (PMUs) provide the magnitude and angle of the quantity being measured, along with GPS time synchronization. Voltage, current and frequency data can be sent to a central control centre at the rate of 30 or 60 times per second. With a sufficient number of PMUs deployed on the electric grid, system operators now have available essentially a ‘snapshot’ of the system, which aids to monitor the grid, predict abnormal conditions as well as quickly identify troubled areas and accordingly take remedial actions.
In order to facilitate the safe and reliable operation of the electric power grid, there are numerous devices that monitor quantities such as voltage, current, frequency etc. Most of these devices however are incapable of handling high levels of voltage and currents that are common to the power network. Instrument transformers (IT) are used to step down the measured quantities to much lower magnitudes that can then be analyzed by downstream devices. Each instrument transformer has a specified transformation ratio. For example, a voltage transformer with a transformation ratio of 100:1 would step down 500V to 5V. With time, these ITs may experience wear which might lead to degradation of its ratio, which would in turn be detrimental for applications relying on accurate measurements. Therefore routine calibration of ITs is desired. Traditional methods of calibration however involve taking the device out of service temporarily. As one can imagine, this is cost, labour and time intensive. With the availability of PMU data, it is now possible to perform calibration of these devices without having to take the device offline, provided we have accurate knowledge of the transmission line parameters.
The parameters of a transmission line include the resistance, reactance and susceptance of the line and depend on the type of conductor used, the length and ambient temperature. Therefore seasonal and daily temperature variations can cause changes in the line parameters. With PMU data, we now have the capability to estimate these parameters, so that we have the most accurate idea of the present parameters. However for this, calibrated voltages and currents are required.
Herein we face a quandary: we need to calibrate the ITs, which require accurate line parameters, but to estimate the current line parameters we need calibrated voltages and currents. This is the problem this thesis addresses. First, methods to perform both tasks, i.e. instrument transformer calibration as well as line parameter estimation using PMU measurements are analyzed. Finally an iterative method is proposed that can be applied to solve both problems together.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/77706 |
| Date | 23 May 2017 |
| Creators | Tauro, Yvonne Agnes Pearl |
| Contributors | Electrical and Computer Engineering, Centeno, Virgilio A., Phadke, Arun G., De La Ree, Jaime, Thorp, James S. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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