Abstract
With longitudinal compensation of the reactance of the line, the problem of its protection against overcurrents arises from the point of view of relay protection. The problem is relevant with a greater degree of compensation. When compensating more than 50% of the reactance of the line, the protection of the power transmission line becomes practically impossible due to the failure or false operation of all existing types and forms of protection [1, 2]. Therefore, at present, the compensation of the line reactance is, as a rule, no more than 50% [3, 4], which does not allow the full potential of the line in terms of its transmission capacity to be revealed. The purpose of this study was to develop and test a new relay protection algorithm to be able to solve the above problem. The studies were carried out using modeling techniques in the PS CAD package, where a power transmission line with longitudinal compensation and an algorithm to protect it from internal damage were built. When carrying out the research, the work was carried out on the protection algorithm of the power transmission line with longitudinal compensation in the static mode without transferring electricity between substations and without the transmission mode along the active power line in both directions. It is shown that in order to determine the location of the damage, it is possible to use the criterion of the angle of the active component of the short-circuit current, which depends exclusively on the voltage angle and does not depend on the reactive parameters of the electrical network. The simulation result showed correct operation in all investigated modes. The algorithm described in the article showed quite satisfactory results, which makes it possible to protect the power transmission line with any degree of longitudinal compensation.
Highlights
In the power generating industry, there are several ways to increase the capacity of electric power transmission lines
This technical solution, in addition to advantages, has disadvantages: with a compensation coefficient of more than 50% of the line reactance, such phenomena are observed as: current inversion during a short circuit, voltage inversion during a short circuit, low-frequency oscillations after a short circuit clearance, etc. [7, 8]. These events lead to the impossibility of protecting the electrical power transmission line, since they lead to false operation or non-operation of relay protection in case of damage on the protected line [9, 10]
Current inversion at a short circuit on the line leads to the fact that the currents are not directed to the place of the short circuit, but as though in transit past it, as a result, the differential and phase-differential protection perceives this damage as external and does not work [11, 12]
Summary
In the power generating industry, there are several ways to increase the capacity of electric power transmission lines. One of the ways is to install a line of capacitors in sequence to compensate the reactive resistance of electrical power transmission lines [5, 6] This technical solution, in addition to advantages, has disadvantages: with a compensation coefficient of more than 50% of the line reactance, such phenomena are observed as: current inversion during a short circuit, voltage inversion during a short circuit, low-frequency oscillations after a short circuit clearance, etc. Current inversion at a short circuit on the line leads to the fact that the currents are not directed to the place of the short circuit (see Figure 1), but as though in transit past it (see Figure 2), as a result, the differential and phase-differential protection perceives this damage as external and does not work [11, 12] For this reason, at present, the degree of compensation for the reactance of the power transmission line does not exceed 50% [13]. The objective of the research is to develop a model of an electric power system containing an electrical power transmission line with a longitudinal compensation device; study of transient and steady-state processes in case of damage in the line and outside; development of an algorithm for differential relay protection, which allows to protect the electrical power transmission line with any degree of longitudinal compensation
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