Abstract:
The operation state assessment can evaluate and analyze the real-time and historical operation state of the power grid, and predict the future power grid operation situation, screen the weak link of the power grid, and eliminate the power grid stealth fault in the bud, which is one of the important means to improve the power supply reliability of the power grid. In current urban and rural low-voltage distribution network, due to the lack of graphics and model data, small measurement configuration and poor data quality, it is of great practical significance to use the widely configured low-voltage user smart meter as far as possible to realize the operation state evaluation of the low-voltage distribution network. Each smart meter forms a loop through the live line, neutral line, T-connected line, load and distribution transformer. The impedance of the load varies according to the quantity and power of the electrical equipment. However, the loop resistance formed by the live line, the neutral line, the T-connected line, and the distribution transformer in the upstream of the smart meter does not change in a short time. If the loop resistance is abrupt, it indicates that the operating state of the loop is abnormal. According to this principle, the operating state of the low-voltage distribution network can be evaluated. When the voltage value of the equivalent power supply in the upper main network of the distribution transformer is almost invariable or cannot be collected, the loop resistance can be approximately determined by the change rate of the voltage and current measured by the smart meter. The demand side real-time voltage data matrix is set up to record the real-time voltage measurement information collected by the smart meters on the low-voltage demand side of a distribution transformer. The demand side real-time current data matrix is set up to record the real-time current measurement information collected by the smart meters on the low-voltage demand side of a distribution transformer. The demand side real-time loop resistance data matrix is set up to record the real-time loop resistance information of all low-voltage demand side smart meters on the distribution transformer. The method of generating the demand side real-time loop resistance data matrix from the demand side real-time voltage data matrix and the demand side real-time current data matrix are discussed in detail. Finally, the evaluation method of the operating state of the low-voltage distribution network is discussed in detail based on the loop resistance data matrix. Many cases such as line broken line, line fault blackout, line plan blackout, load unstarted, user uninhabited, electricity stealing, smart meter damage, line aging alarm and line aging fault were analyzed in detail. The feasibility of the proposed method was analyzed by taking a low-voltage distribution network with four smart meters as an example. The maximum error of the approximate value and the actual value of the low-voltage loop resistance of each smart meter was not more than 81%, the minimum error was not more than 11%, and the average error was not more than 22%. The error was far less than the set line aging alarm limit LA and line aging fault limit LB. Therefore, in the actual calculation, when the power supply voltage of the main network upstream of the distribution transformer is not changed or cannot be obtained, the approximate value of the loop resistance can be used to express the change trend of the upstream loop resistance of the smart meter. The method proposed in this paper can meet the actual needs of field engineering.