SU418933A1 - METHOD OF PROTECTING ELECTRICAL TRANSMISSION LINES OF LARGE EXTENSION AGAINST BETWEEN PHASE SHUTCHES - Google Patents

Description

one

This method relates to the field of electric power industry and can be used to perform protection of lines whose reactive parameters noticeably prevail over active ones, i.e.

- LO, Co, Go - the primary parameters of the line, / - its length, ZG - the characteristic impedance of the line without loss.

The known remote method of relay protection is based on measuring the value of equivalent resistance to a short circuit point. According to the principle of operation, a method of controlling the values of the steady state is known. The free component of the transient is a hindrance to it.

In the proposed method, in order to increase speed, three voltages are formed, the first of which is proportional to the instantaneous value of the linear voltage, and the second and third are the differences of the instantaneous values of the linear currents, with the ratio of the proportional coefficients of the first and second and, respectively, first and third voltages pa. clearly the sum and difference of the wave resistance and half of the active resistance of the protected line; The first load is added to the second and subtracted.

from the third; the delay time of the total voltage relative to the differential voltage is compared with the time of the setpoint and, if the delay is less than the specified one, produced

protection operation. In order to increase the noise immunity, the time for the accumulation of the total voltage relative to the differential voltage is determined twice: by the moments of zero crossing of the voltages themselves and by the moments

the zero crossing of their derivatives, in addition, determines the ratio of the differential voltage to the total voltage and does not activate the protection if this ratio is less than a specified value.

By the magnitude of the time shift of the voltage f () with respect to the voltage f (/), it is possible to establish at what distance from the place of installation of the protection a short circuit occurred. The simplest way to determine the shift of two voltages in time is to measure the time interval between the moments of passage of these voltages through zero. In order to increase the reliability of measurement, it is produced at a certain sign.

Derivatives - f (t) and (p (t). If you additionally measure the time between the moments of passing through zero, the derivatives -f (i) and fp (t), which is also equal to 2х, the reliability of protection will increase. If the measurements show,

that 2 tons is shorter than the set time, this means that a short circuit occurred in the protection zone. The magnitude of the transient resistance at the point of the short circuit does not play a special role, since the protection in principle works at any value. This inequality can be satisfied at the end of the line under supernatural loads. Therefore, to improve the detuning from the operating modes, it is advisable for values of 2ix close to 2%. It is most convenient to control the value of / (/) at the moments when the derivative f passes through zero (t so that for small negative values - reflection coefficient from the point of short circuit.

According to this method, two stresses are formed:

and o - kaU, Ut kii,

where ku and ki are real coefficients, and.

Subtracting the first voltage from the second and folding them, get two new voltages

U Ui-Uu + Ua.

The magnitude of the time lag of the voltage 7+ from the voltage f / is determined. If this lag is less than the setpoint value, the protection is triggered.

In a three-phase circuit, for protection against interphase faults, a linear voltage must be used as voltage IJi, and the difference between the corresponding linear currents as current tl.

If the protection is turned on for the voltage and current of the P-sequence, then it will act in the same way as in the two-wire line.

Protection against single-phase closures is unequivocally constructed. If the transformer neutral on the receiving side is not grounded or is grounded through a resistance, so that T | the transformer does not shun the zero-sequence circuit, then the ao-sequence circuits are connected in cascade, i.e.

In this case, protection against single-phase short-circuits can be switched on for a voltage

u, uj, - and,

and for current 4 - U - th and the setting parameter is equal to the sum

+ year

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In the general case, protection of single-phase circuits is switched on for phase voltage and linear current, adjusting the values of ZG and t so that they meet the conditions of the passage of the phase-to-earth wave.

Subject invention

Claims (2)

1. A method of protecting long-distance power lines against phase-to-phase short circuits, based on measuring the time lag of voltage waves, characterized in that, in order to increase speed, three voltages are generated, the first of which is proportional to the instantaneous value of the linear voltage, and the second and third are the differences of the instantaneous values of the linear currents, and the ratio of the proportionality coefficients of the first and second and first and third voltages is equal to the sum and the difference in resistance and half the active resistance of the protected line, after which the first voltage is added to the second and subtracted from the third, and the lag time is determined by zero crossing of the total voltage relative to the difference, the lag time is compared with the set time and if the lag time is less than settings, turn off the line. 2. A method according to claim 1, characterized in that, in order to improve noise immunity, the lag time is determined twice - according to the moments of zero crossing voltages, as well as their derivatives, and the line is not disconnected if the ratio of the differential voltage to total less than a given value.