RU2510115C1 - Method to connect three-phase transmission line - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: first phase is connected, voltage is measured on the second and third phases, it is checked how the first reference value exceeds each of the measured voltages, and if the check results are positive, they connect the second phase, measure voltage on the third phase, inspect how the second reference voltage value exceeds the voltage measured in the third phase, and if the result of the check is positive, they connect the third phase, and in case of negative check result in the first reference value exceeding voltages measured in the second and third phases, and the second reference value exceeding the voltage measured in the third phase, subsequent phases are not connected, and the ones connected previously are disconnected. When a signal is received on availability of an earth fault in the first phase during its connection, it is disconnected, and subsequent phases are not connected, after connection of the second and third phases they compare modules |U₁₂₍₁₃₎| of vector difference of voltages in the first and second phases |U₁₂| and the first and third phases |U₁₃| with low reference value 0.1|U pn|, where |U pn| - nominal phase voltage, and if the condition |U₁₂₍₁₃₎|<0.1 IU pn| is met, they fix the closure of accordingly the first and second and the first and third phases to each other, afterwards they disconnect the first and second and the third phases, accordingly.

EFFECT: expanded area of application and higher safety.

Description

The invention relates to the electric power industry and can be used to control the inclusion of a three-phase power line with automatic restart after an emergency shutdown of the power line or when putting it into operation.

There is a method based on the use of a power line model, which consists in the fact that for the network with an isolated neutral, an equivalent circuit is drawn up, according to which, for all lines, transient parameters are calculated, setting the distance to the place of damage along the entire length of the line in steps of 10 meters and for various transient resistances in the place of damage with a step of 10 Ohms, the eigenfrequencies of the transient process calculated in this way are stored in a computer database, and if damage occurs the damaged line and the actual natural frequency of the transient are fixed at the substation, compared with the calculated parameters recorded in the database, and the distance to the place of damage is determined with the accuracy determined by the step of setting the distance to the place of damage [RU 2308731 C1, G01R 31/08, 20.10. 2007].

The disadvantage of this method is the relatively narrow scope, since the known method allows the line to determine the place of a single-phase earth fault of the power line, but does not allow for the safe inclusion of a three-phase power line.

There is also a method according to which the state of the insulation of the network and the zero sequence currents in the outgoing lines are monitored, while the insulation level of the network is reduced, a circuit is formed for the short-term flow of the double-fault current to the ground, while the change in the zero sequence currents in the outgoing lines is controlled, and if the moment of flow of the double-fault current to earth, a zero-sequence current changes in one of the outgoing lines, a signal is generated to turn off this line upon the fact of its closure to the ground [RU 2308731 C1, G01R 31/08, 10.20.2007].

The disadvantage of this method is also a relatively narrow scope, since it allows you to protect three-phase networks with isolated neutral from single-phase earth faults, but does not allow protection from other undesirable factors, for example, short-circuits between phases when three-phase power lines are turned on.

The closest in technical essence to the proposed one is a method of switching on a three-phase power line, characterized in that the first phase is turned on, the voltages in the second and third phases are measured, the excess of the first control value of each of the measured voltages is checked, and if the checks are positive, the second phase is turned on, the voltage is measured in the third phase, check the excess of the second control value of the voltage measured in the third phase, and if the test is positive, turn on the review phase, and if any of the checks is negative or the relay protection signal is turned off to turn off the on phase, the subsequent phases do not turn on, and previously turned on phases turn off [RU 2358368 C1, H02H 3/06, 06/10/2009].

The disadvantage of this method is the relatively narrow scope and relatively low security of switching on three-phase power lines, due, in particular, to the fact that as a result of the procedures (private operations) of the checks, the fact of the closure of the second and / or third phases with the first phase is not revealed.

The required technical result is to expand the scope and increase the safety of the inclusion of three-phase power lines.

The required technical result is achieved by the fact that, according to the method based on switching on the first phase, measuring the voltage in the second and third phases, checking if the first control value exceeds each of the measured voltages, and if the switching on of the second phase is checking positive, measuring the voltage on the third phase, checking exceeding the second control value of the voltage measured in the third phase, and with a positive result of checking the inclusion of the third phase, and with a negative result of checking The subsequent phases do not turn on the first control voltage value measured in the second and third phases and exceed the second control voltage value measured in the third phase, and previously switched on - turn off when a signal is received about the presence of a short circuit to ground of the first phase when it is turned on it is turned off and the subsequent phases are not turned on; after switching on the second and third phases, the modules | U _{12 (13)} | the vector voltage difference of the phases of the first and second | U ₁₂ | and the first and third | U ₁₃ | with a small control value of 0.1 | U fn |, where | U fn | is the nominal phase voltage, and when the condition | U _{12 (13)} | <0.1 | U fn | fix the closure, respectively, of the first and second and first and third phases to each other, after which the first and second and third phases are disconnected, respectively.

The sequence of operations of the method is as follows.

When switching on three-phase power lines after it has been switched off or when putting it into operation, it is necessary to exclude cases of switching on an interphase short circuit (short circuit), and also to detect the presence of a two-phase short circuit before turning on the third phase. This can be achieved by sequentially switching phases with monitoring the network status.

We assume that the first one turns on any of the phases A, B and C, which below will be conventionally designated as 1 (first), 2 (second) and 3 (third) phases.

If there is a short circuit to ground at the first switched phase (for example, phase A), then the switched phase is disconnected from the action of relay protection and the process of switching on the power line ends.

If there is no short circuit to ground at the first switched phase (for example, phase A), then it remains switched on and the voltage is monitored at the other two unconnected phases of the line - phases (B and C).

If the module | U _{AB (AC)} | the vector voltage difference between phases A and B (A and C) is close to zero | U _{AB (AC)} | <| 0.1U _fn | (| U _fn | is the nominal phase voltage), which means the closure of phases A and B (or phases A and C) between themselves, phase A is turned off, and the switching on process stops.

If the voltage in phase B (or phase C) induced from the switched on phase A is close to zero | U _{B (c)} | <| 0.1U _fn |, then it is obvious that phase B (or phase C) is shorted to ground. Then phase A is turned off and the switching on process is terminated.

If the voltages induced in phases B and C are significant in magnitude | U _{B (C)} |> | (0.1-0.15) U _fn , then there is no short circuit to ground of phases B and C.

However, to determine the presence / absence of a short circuit between these phases (B and C), it is necessary to turn on the second phase (for example, phase B or phase C) after switching on the first phase (A).

If, after (0.1-0.2) s after switching on the second phase (for example, phase B), the voltage Uc induced now from the two phases B and A is such that the modulus of the vector voltage difference between the phases B and C | U _{B (c)} | <| 0,1U _fn |, then phases B and C are closed to each other, but if | U _{B (C)} |> | (0,1-0,15) U _fn |, then there is no closure between phases B and C , i.e. after (0.1-0.2) s, you can turn on the third phase (phase C), which completes the process of alternating phases.

It is easy to see that the total turn-on time of a three-phase power line with automatic alternating connection of phases will not exceed 0.5 s.

Thus, due to the improvement of the known method by using additional operations of the method, the required technical result is achieved regarding the expansion of the scope and increase the safety of switching on three-phase power lines, due, in particular, to the fact that as a result of the procedures (private operations) of the checks, the fact that the second and / or third phases with a first phase.

Claims (1)

The way to turn on a three-phase power line, based on switching on the first phase, measuring the voltage in the second and third phases, checking if the first control value exceeds each of the measured voltages and, if the test is positive, turning on the second phase, measuring voltage on the third phase, checking if the second control voltage exceeds measured in the third phase, and with a positive result of checking the inclusion of the third phase, and with a negative result of checking the excess of the first counter subsequent voltage phases measured in the second and third phases, and the excess of the second control voltage value measured in the third phase, the subsequent phases do not turn on, and previously turned on - turn off, characterized in that when a signal is generated about the presence of a short circuit to ground of the first phase at turning it on, turning it off and the subsequent phases do not turn it on, after turning on the second and third phases, the modules | U _{12 (13)} | the vector voltage difference of the phases of the first and second | U ₁₂ | and the first and third | U ₁₃ | with a small control value of 0.1 | U _fn |, where | U _fn | is the nominal phase voltage, and when the condition | U _{12 (13)} | <0.1 | U _fn | fix the closure, respectively, of the first and second and first and third phases to each other, after which the first and second and third phases are disconnected, respectively.