RU2244994C1 - Method for detecting power direction of current protective gear - Google Patents

Abstract

FIELD: phase-to-phase fault protection of double-ended or ring-circuit single-ended power transmission lines.

SUBSTANCE: proposed method includes continuous measurement of electrical installation current and its comparison with reference current, measurement of time equivalent of angle between current and shaped reference signal, and comparison with first and second values of angle equivalent; if current exceeds reference value, time equivalent of angle is higher than first and lower than second reference values of angle equivalent, then OFF-signal is supplied in a certain time delay to electrical installation; reference signal is shaped by memorizing length of preceding current cycle, and time equivalent of angle is found as increment between shaped reference signal and length of present cycle of current.

EFFECT: enlarged functional capabilities and enhanced reliability.

1 cl, 4 dwg

Description

The invention relates to the electric power industry, and in particular to the relay protection technique, and may find application for protecting power lines (power lines) with double-sided power supply or ring with single-sided power supply from phase-to-phase short circuits.

A known method of protecting electrical installations [1], in which the current value of the electrical installation is continuously measured and compared with a reference current value, each period determines the duration of the mismatch of current and voltage signals and is compared with the first and second reference values of the duration of the mismatch, if the current value is greater than the reference current value, the duration of the mismatch of the signals is greater than the first reference and less than the second reference value of the duration of the mismatch, then after a given delay time There is a signal to turn off the electrical installation.

The use of two analyzed electrical quantities - current and voltage - reduces the functionality of this method, reduces the reliability of devices created for the implementation of this method.

The closest in technical essence is the method implemented in the device [2], in which the electrical installation current is continuously measured and compared with the reference current value, each time period, the time equivalent of the angle between the current and the generated reference signal is determined and compared with the first and second reference angular values equivalent, if the current is greater than the reference current, the time equivalent of the angle is greater than the first reference and less than the second reference angular equivalent, then after a given the time delay sends a signal to turn off the electrical installation. In the device according to this method, the reference signal is also formed using voltage circuits, and to eliminate the dead zone at close faults (when the voltage of the damaged phase decreases to zero), the voltage vector is stored for a period of 1 to 10 periods of industrial frequency due to the time constant of the filter feeding from intact phases. Therefore, the storage of the voltage vector in some cases increases the reliability of devices implemented by this method.

However, when fuses blow in the voltage circuits of a device that implements this method, it becomes inoperative. Moreover, using this method, it is impossible to determine the direction of power in a three-phase short circuit, when the voltage of all phases decreases to zero, and also after more than 1-10 periods of industrial frequency. Therefore, the use of two analyzed electrical quantities - current and voltage - reduces the functionality of this method, reduces the reliability of devices created for the implementation of this method.

The objective of the invention is the expansion of functionality, increasing the reliability of current directional protection of electrical installations created to implement this method by reducing the number of analyzed values.

The problem is achieved in that the reference signal is formed by storing the duration of the previous current period, and the time equivalent of the angle is defined as the increment between the generated reference signal and the duration of the current current period.

The invention can be considered using diagrams showing the main modes of operation: figure 1 - operating mode, with a small increment of the load angle; figure 2 - operating mode, with a large increment of the load angle; figure 3 - short circuit mode in the protection zone, with a large increment of the angle; figure 4 - short-circuit mode outside the protection zone, with a large increment of the angle, where t _n-1 , t _n and t _{n + 1} - the duration of the previous, current and subsequent periods (time equivalent of the angle); Δt is the increment of the angle (increment of the temporal equivalent of the angle); t _e1 and t _e2 - the first and second reference values of the angular equivalent; I _L - line current; I _e - reference current value.

Moreover, a positive increment between the duration of the previous period and the current Δt = t _n-1 -t _n means the inclusion of inductive load, and the negative - capacitive. The conditions for the operation of the protection are: Δt> t _e1 , Δt <t _e2 , I _L > I _E. Based on the foregoing, consider the modes:

a) In this mode (Fig. 1), the increment between the duration of the previous period and the current is insignificant, that is, the increment of the time equivalent of the angle is less than the first and second reference values of the angular equivalent, while the line current does not increase and does not exceed the reference current value - the protection does not work:

Δt <t _E1 , Δt <t _E2 , I _L <I _E ;

b) The mode in figure 2 may occur, for example, when connecting a powerful inductive load, a change in power flows of power lines, etc. In this case, the time equivalent of the angle is greater than the first and less than the second reference values of the angular equivalents, but the current is less than the standard value of the current - the protection does not work:

Δt> t _E1 , Δt <t _E2 , I _L <I _E ;

c) In the mode shown in Fig. 3, the time equivalent of the angle is greater than the first and less than the second angular reference values, at the same time the current exceeds the current reference value - the operation condition is satisfied, the protection selectively works:

Δt> t _E1 , Δt <t _E2 , I _L > I _E ;

d) This is an emergency mode (figure 4), which can occur, for example, with a short circuit "behind" the protection on an adjacent power line. In this case, the current exceeds the reference current value, and the increment of the time equivalent of the angle is greater than the angular reference values (this is a condition of failure), therefore, the protection does not work:

Δt> t _E1 , Δt> t _E2 , I _L > I _E.

Thus, the current protections according to the proposed method respond to short-circuit in the protection zone, do not reliably work when short-circuit outside the protection zone and when the direction of power in the line changes in the operating mode.

SOURCES OF INFORMATION

1. Fedoseev A.M., Fedoseev M.A. Relay protection of electric power systems: Textbook. for universities. - 2nd ed., Revised. and add. - M .: Energoatomizdat, 1992 .-- 528 p.: Ill.

2. Molchanov VV, Golantsov E.B. Remote protection panels type PZ-5 (PE2105). - M.: Energoatomizdat, 1987 .-- 88 p.: Ill.

Claims (1)

The method for determining the direction of current protection power, which consists in continuously measuring the value of the current of the electrical installation and comparing it with the reference current value, each period determining the time equivalent of the angle between the current and the generated reference signal and comparing it with the first and second reference values of the angular equivalent, if the current value more than the reference current, the time equivalent of the angle is greater than the first reference and less than the second reference values of the angular equivalent, then after a given time delay apply a signal to turn off the electrical installation, characterized in that the reference signal is formed by storing the duration of the previous current period, and the time equivalent of the angle is defined as the increment between the generated reference signal and the duration of the current current period.

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