SU616682A1 - Method of limiting overvoltage at automatic three-phase repeated switching-on of electric transmission lines with shunting controllable reactors - Google Patents

Description

(54) METHOD FOR LIMITING OVERSTRAINS

: AT THREE-PHASE AUTOMATIC

Reclosing TRANSMISSION LINES WITH .SHUNTIRUYUSCHIMI controlled reactor disadvantage of this method is not justified puff pause TAPV IE-a large beat period at the terminals vzhpyuchatep that adversely skazyvaets on maintaining stability LEP posle.tsikpa TAPV. The aim of the invention is to improve the reliability of power transmission by reducing the current-free pause before re-enabling the line. This is achieved by the fact that, according to the proposed method, the inductance of the controlled reactor is adjusted to the inductance of the controlled reactor prior to re-activation of the line. The natural frequency of the line can be determined by measuring the free current of the reactor, passing it through a maximum can reduce the inductance of the reactor and let it pass current through zero - increase this inductance. The frequency of the voltage beats at the contacts of the spinner is compared with a given beat frequency and is changed by changing the biasing of the reactor. When the power is turned off, the bias is removed from the controlled reactors. FIG. 1 is a schematic diagram of a power transmission line with controlled reactors — FIG. 2 is a circuit for replacing power transmission lines in the dead time; in fig. 3 - curves of change of inductance and current of the reactor during a blank pause, where a is the rectangular modulation of the inductance of the reactor; b — harmonic modulation of the inductance of the reactor (increase in oscillations) j c — harmonic modulation of inductance (oscillation damping); in fig. 4 is a schematic diagram of a power transmission line with corrective devices; FIG. 5 - wills current characteristics of controlled reactor. Transmission line 1 is connected via switches 2.3 to 4.5 power systems. Controlled reactors 6.7 are used as transverse compensation devices on the line. During a dead-end pause at TAPV, line 1 disconnected from power systems 4 and 5 with controlled reactors 6.7 is a high-quality oscillating circuit (see Fig. 2, where n is the inductance of the controlled reactor, C is the line capacitor, R is the active line resistor and reactor). In this circuit, for a few seconds, slow-fading collars may continue at a frequency close to 50 Hz. Frequency and period of beating of contact voltage. The disconnected switches 2 and 3 and the position of the minimum of the envelope determine the frequency irregularity ui - | 3 t 211 1ГГ: de Tjj- “the period of the beating of voltage on the contacts of the switch J UJ-industrial frequency energy HCTeMij P is the natural frequency of the oscillating circuit. When an intact line is disconnected, the natural oscillations have a frequency that is approximately equal to: ViTpC where p is the inductance of shunt reactors; C - line capacitor. With a constant reactor inductance L p, the beat period can be so long that it will lead to the need to increase the best of time. The principle of change (modulation) of the inductance is explained; FIG. 3, where L, (- t) curves of inductance changes of reactors, 4 (- b) - curves of free currents of reactors.; Let the reactor inductance bH) change according to the following law: at those times when the oscillating free current reaches a positive or negative maximum (13), the reactor inductance increases very rapidly from the value of L to the value of L 2, and then when the current passes through its zero value (i О), inductance also returns very quickly, to its previous value b (Fig. 3a). While an increase in inductance by an amount is accompanied by an increase in the electromagnetic reserve energy of the circuit by a value equal to (Lg-b) m, the decrease in inductance does not cause a change in the electromagnetic anergy reserve of the circuit, since this decrease occurs at ("0. For every half the period of current change, i.e., over the period of inductance change, the energy dissipated in the active resistance of the circuit is approximately equal (if the current attenuation during the specified time is neglected) -g R where Tr is the inductance change period. atelno contour energy does not decrease, that is not considered oscillation is damped if i -.. (

Given the inertia of the reactor, its inductance practically does not change in jumps, but according to the following law:

UUV-L - | - mcos (), UV.

LO)

where U is the average inductance:

fn - induction modulation guubin

Sj. - inductance modulation frequency

 - initial phase inductance. During the current-free pause TAPV in the circuit appears the free component of the current frequency | b - defined by the equation)

V i4: l-r3 e Cos (p,), (4)

where V is the decay rate

V-initial phase of current.

The frequency | i is much less than the frequency j defined by equation (2), therefore the period of the beating and the time of idle pause for the change in inductance. the reactor is drastically reduced.

More tggo, a correctly selected law of inductance variation allows to quickly quench all oscillations on the line and thereby effectively reduce the magnitude of the overvoltage during the TLV (Fig. 3b, c).

The curve of change in inductance of the reactor as a function of time and the curve of change of the considered component of the free current for the case L0 is shown in FIG. 3 b (V jj x 0) ..

As can be seen from equations (3) and (4), the inductance of the reactor increases with the greatest speed when the current reaches a positive or negative maximum (Fig. 36). Accordingly, with the highest rate of ins (the activity decreases when the current passes through its zero value.

As in the previous case, when the inductance changes abruptly only at the instants of current passing through the maximum igr through zero, in this case energy can also be accumulated as a result of a periodic change in the parameter. In this case, the amplitude of free oscillations can increase without limit if the energy introduced into the circuit as a result of a change in the parameter increases.

However, with a different value of the initial phase, the current; a change in the parameter may not lead to a decrease, but to an increase in attenuation. Indeed, as can be seen from FIG. Zv, at) oL - ft the fastest rate of decrease of a parameter coincides with the moment of current passing through a maximum, and the highest rate of increase of a parameter — with passing a current through zero.

; Thus, harmonic modulation not only changes the frequency of self-oscillations and leads to a decrease in the period of beating of the voltage at the contacts of the switch, but also reduces the amplitude of the oscillations, which increases the efficiency of the TPV and increases the reliability of the transmission.

The reduction in the current-free pause is achieved by measuring the frequency of the beating voltage at the contacts of the switch, comparing with a given frequency of beats and

5 by changing it by changing the natural frequency of the line, for example, by changing the biasing of the controlled reactor. Power line 1 is connected through switches

0 2 and 3 to power systems 4 and 5 and has shunt controlled reactors 6.7 to each of which corrective devices 8 and 9 are connected. During the current pause, when TPV is disconnected from energy 25 systems 4 and 5, line 1 with controlled

reactors 6,7 is a high-quality oscillatory circuit, in which: slowly damped oscillations can continue for a few seconds

0. A frequency close to 50 Hz. The frequency and period of the voltage beating on the contacts disconnected, switches 2 and 3 and, consequently, the position of the minimum envelope is determined by the difference in the frequency oy-Ya535 according to formula (1).

Thus, by influencing the inductance of the controlled reactor, it is possible to change the natural frequency of the line and, accordingly, the period of the beating of the voltage at the contacts of the switch from which the charge-. hangs the value of the dead time at TAPV.

The inductance of controlled reactors can be varied in various ways. One way is to control

S {magnitude of the bias current, carried out with the help of corrections of 8 and 9, to the inputs of which two frequencies are simultaneously supplied — the reference and real, measured from the contacts

 key switch The reference frequency can be preselected as the minimum frequency for the sake of reliable preservation of the stability of power transmission lines after the TAPV. When the real beat frequency is turned off from the reference one, the reactor control current value and, accordingly, the reactor inductance change.

The simplest way to change the inductance of controlled reactors is by removing the bias from controlled reactors. At the same time, the operating point on the current characteristics of the reactor (Fig. 5 jumps from curve I to curve f. Curve 1 corresponds to the curve-current characteristic of the reactor in the presence of nofr magnetization, curve 5, with clear removal, transition from the curve. To K1 Willow1 will bring about a drastic change in the reactor inductance.At the same time, the voltage beating period at the contacts will be reduced and therefore the current-free pause may be reduced at the TAPV time relay. Invention. NIN 1. The method of limiting overvoltages with three-phase automatic re-activation of the power transmission lines with shunting controlled reactors by re-activating the power transmission line to the minimum of the beating of the voltage on the contacts of the disconnected switch, from and off, in order to ensure the reliability of the transmission, in order to ensure reliable transmission. pauses before re-activation of the line, adjust the inductance of the controlled reactor depending on the natural frequency of the line. 2. The method according to claim 1, dt p and h a l and h and s, since the line natural frequency is determined by measuring the free current of the reactor and passing it through a maximum, reduce the inductance of the reactor and increase the current through this inductance. 3. A method according to claim 1, characterized in that the frequency of the voltage beating at the contacts of the switch is compared with the given frequency of the beat and changing its value by changing the magnetisation of the reactor. 4. The method according to claim 3, that is, with the fact that when the line is disconnected, the bias is removed from the controlled reactors. Sources of information taken into account in the examination; l.ceepicJi.Ructistuhe Q, V anA / CJnieuense of stiun-tf eactops on sv / itctiingf svpiges lEEEjTrctnSjOn PoMver App und ig70, p. B9, L / 28, p.p1727 - f736. 2. Belkov, H.H., Rashkes, V.S., Method of limiting overvoltages during repeated switching on of power lines, Electricity, f9 2, 1975.

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