Estimation of power network parameters based on real-time measured operation quantities using phasor measurement units placed with the help of genetic algorithm

Power Electrical Engineering Master Thesis

Power Orientation

Abstract

Network development planning, operation planning and finding solutions to improve the security and economic performance of the system Power all require system studies. The most necessary step in conducting these studies is network modeling, which itself requires detailed information about the impedance parameters of lines and transformers. These parameters can change under the working and environmental conditions or the life of the equipment. Therefore, we will need to estimate network parameters in a timely manner. In recent years, real-time estimation of network parameters based on operational quantity information is an issue that has been noticed by using phasor measurement units. In this thesis, the proposed method is able to estimate the parameters of those two lines as well as the middle bus voltage by using 3 times of measurement of voltage and current quantities at the beginning of two consecutive lines. With this algorithm, it is possible to simultaneously estimate state variables and network impedance parameters. The advantage of this method compared to other methods is that it requires less number of measuring devices. In this thesis, the state-parameter estimation algorithm will be introduced first, and then the optimal placement of phasor measurement units will be discussed according to the presented algorithm. In the end, the optimal placement of the phasor measurement units and the proposed state-parameter estimation algorithm have been implemented on the IEEE 39-bus network as a test network. state estimation; exploitation quantities; phasor measurement units; Optimal placement of PMU

1-1-Introduction

Network development planning, operation planning and finding solutions to improve the security and economic performance of the power system all require system studies. The most necessary step in conducting these studies is network modeling, which itself requires detailed information about the impedance parameters of lines and transformers. Estimation of network parameters in real-time based on quantitative information of operation is a subject that has been considered by using phasor measurement units.

Parameter estimation [1] is a process in which one or more network parameters whose correctness is not known are estimated. The correct values ??of the parameters are required for the safe and economical operation of the power system. Most economic and security applications of the network require precise values ??of the network parameters. However, databases often have imprecise parameters. The parameter error may be due to the following reasons:

Inaccurate information provided by the equipment manufacturer to the customer.

Changes in the network that have not been reported to the database operators.

Network performance in conditions different from the ideal assumptions assumed for mathematical calculations.

Inaccuracy of measuring devices

Power equipment manufacturers conduct tests on their equipment. With these tests, they obtain the equivalent circuit parameters of their equipment and provide them to the customer. It should be noted that these parameters have errors for various reasons. If these parameters are recorded in the database without correction, they may cause errors in the results of system studies. The power grid is constantly changing. The operation of relays during fault and disconnection of lines, removal of power equipment such as transformers and lines due to repairs, entry and exit of production and consumption units and changes in the tap of transformers are among the changes that are occurring frequently in the power system. In the meantime, some of these changes may not be recorded in the database for various reasons. So it is necessary to identify these changes. In addition to this, the models presented for the system will include non-linear equations.. In order to increase the speed and simplify the calculations, linearization is often done in the equations, which will reduce the accuracy of the calculations and, as a result, reduce the accuracy of the estimated parameters; Therefore, for the correct operation of the power system, the database must be able to continuously update the parameters.

Network security applications require accurate information from the network. As mentioned, the recorded values ??for the parameters may be wrong for various reasons. In the protection of power systems, various protection algorithms such as the distance relay protection algorithm require access to the exact parameters of the network to set the relays and locate them in case of an error; Therefore, we need access to the exact parameters of each line.

This is also very important in network operation. By measuring effective parameters such as voltages, currents and line power, the condition of transmission lines and their parameters, the condition of switches, frequency, production power of units, tap transformers and so on. will be checked This information is sent to various software such as system state estimator software to make the overall system state available. The information obtained from these activities should be carefully examined so that the results of these examinations can be accurately provided to the network operator so that the operator can take the necessary actions with sufficient speed to prevent major disruptions. In measurement systems, there are always factors such as noise and errors in calibrating measuring devices, which will reduce the accuracy of measurement and consequently reduce the accuracy of parameter estimation ][i][. In the past, power system parameters were measured by traditional measurement systems. These systems did not have proper accuracy. Another problem of these systems was that their performance was not simultaneous. In a subsystem that works separately, synchronization in the broad sense will not make sense; Because a pulse signal can synchronize all measurements; But when the measurement parameters are obtained from different areas, we need to use a suitable system to synchronize these parameters and increase the measurement accuracy as much as possible and consequently the estimation accuracy.

In this thesis, the principles of the proposed algorithm for estimating network parameters and bus voltage are based on the classification of network lines into packages consisting of two consecutive lines. The combination of both consecutive lines and their three busbars has formed a parameter estimation package, where the phasor measurement unit [2] is placed at the beginning of the two lines and by measuring the voltage and current at the beginning of the lines during several measurement samples, they will be able to estimate the parameters of the two lines and the bus voltage between them. It requires optimization calculations. The general process of the proposed algorithm for estimating parameters and system state can be divided into two general stages. In the first stage, considering all the possible combinations for the binary packages of the lines, based on an optimization method such as the genetic algorithm, the installation locations of the phasor measurement units are located in the network. Optimization is based on minimizing the number of phasor measurement units for visibility and estimation of all lines and bus voltages. After the optimal placement of the phasor measurement units on the network buses, the combination of the double packages of the lines to estimate the network parameters is specified, which can estimate the parameters of the lines and bus voltage by implementing the state-parameter estimation algorithm on each package. For this purpose, at least 3 measured samples of the voltage and current quantities at the beginning of the lines should be prepared. Among the features of this algorithm, we can mention the large reduction in the number of measuring devices and the independent performance of the proposed estimator for each pair of network lines. At the end, to check the performance of the proposed algorithm, the IEEE 39-bus network has been selected. In this network, the optimal placement of the measuring devices will be done first, and then the performance of the estimation-parameter algorithm will be investigated.