SU536558A1 - Starting body lock when swinging x distance protection - Google Patents

Description

one

The invention relates to devices for relay protection and automation of power systems, in particular, devices for blocking remote protection of high-voltage power lines in the electrical system.

The starting blocking device for oscillations should primarily satisfy the requirements of high sensitivity, speed, reliable detuning from oscillations with a small period and large equalizing currents. These requirements are particularly important for starting blocking organs when the superhigh voltage lines are protected, when high sensitivity and speed are required, provided that the load currents can be greater than the damage currents.

The triggering bodies of interlocks in the swings of remote protections, used to prevent false operation of protections during oscillations in power systems 1, are known.

The closest in technical essence to the proposed is the creep blocking body when the distance protection swings, containing a reverse sequence current filter (voltage) connected to the primary winding of the transformer with two secondary windings, to one of which is connected through an inertial element and a rectifying bridge reacting authority 2.

This organ has a rather high sensitivity, since it responds to the vector increment (D / 2), i.e., to a relatively rapid change in the / 72 vector (/ 2) in absolute value or in phase.

However, this organ is characterized by insufficient detuning from oscillations with a short period and large balance currents. In this mode, since the output of the negative sequence filter contains components of frequencies that differ from the frequency of tuning the delay line, there is a significant imbalance at the input of the rectifier bridge, sufficient to trigger the level detector. The detuning from the indicated unbalance by the rudeness of the level detector makes it possible to ensure the necessary sensitivity of the organ and may ruin the triggering organ. Another disadvantage of the prototype is the need to use a delay line, which requires fine tuning of its constituent elements and has considerable dimensions due to its implementation at the industrial frequency. The aim of the invention is to increase

sensitivity of the starting organ and detuning from the swing with large equalizing currents and small periods.

This is achieved by the fact that the secondary windings of the transformer are turned on, the LC filter of the fundamental frequency is applied as an inertial element, and a differentiating element is connected between the rectifying bridge and the reacting body, made on the basis of a bridge circuit with a differentiating RC circuit in adjacent arms which included a diode and a resistor connected in series.

FIG. 1 shows the block diagram of the proposed starting body; in fig. 2 and 3 are diagrams for his work.

In the drawing, the following symbols are used; F is a current (voltage) reverse sequence filter, TN is an intermediate transformer, RI, L1, C1 are elements forming a resonant LC filter, R2 is a potentiometer, VM is a rectifying bridge, C2, R3, R4, Rb, RQ, D1, D2 elements that form a differentiating bridge circuit, RE is a reacting element that operates at a certain polarity and signal size, C / IJ2 is the voltage across the output of the LC filter and potentiometer in the established pre-emergency mode, Ui (t) is the voltage at the output of the LC filter in transient, (O - voltage: at the input of the VM bridge in transient mode.

In the LC filter tuned to resonance at the industrial frequency, the output voltage Ui coincides in phase with the input voltage in a steady state. The polarities of switching on the secondary windings of the intermediate transformer TH are different, therefore the voltage Uz is in antiphase with the voltage Ui, and the potentiometer R2 is set in such a position that the total voltage 0 applied to the input of the bridge VM is close to the bullet. If the frequency of the mains voltage is different from the nominal and when the voltage swells f / | and f / 2 do not coincide in phase and the differential voltage at the input of the bridge is not equal to zero, the reacting element of the OM also does not work in the specified steady state. The capacitor C2 in this case is charged almost to the full value of the rectified voltage at the output of the bridge, therefore the potential of point 1 is greater than the potential of point 2 and the diode D2 is locked.

Thus, the circuit is rebuilt from significant unbalances at the output of the reverse sequence filter and from unbalances due to the detuning of HC-F1Pltra caused by the frequency deviation from the nominal frequency in the normal mode and in the swing mode.

When a short circuit is accompanied by a change in the current vector (voltage) of the reverse sequence in magnitude or phase, a relatively rapid change in the phase and magnitude of the signal at the output of the reverse sequence F filter occurs. At the same time, the voltage: t / 2 at the output of the K.2 potentiometer varies from Uz to U2, and the voltage L / i (t) at the output of the LC filter changes with a sufficiently good filter corresponding to

j (l) lJl - () e-

where b is the filter decay constant.

Taking into account that in the established post-failure mode, we obtain the value of the voltage U3 (t) on the input of the VM bridge in the transient mode

U, () :: U2-lj, (i).

Using an LC filter instead of a delay line reduces the dependence of the current (voltage) of the response on the phase of the damage. This is due to the fact that a decaying sinusoidal voltage Uy, (t) with duration and amplitude envelope, not depending on the turn-on phase with a sufficiently good filter, appears at the input of the VM (Figs. 2 and 3). This provides a fairly wide impulse at the input of the bridge circuit and its high-quality operation during any switching phase. Applying a filter also simplifies the layout and its configuration.

Thus, at the output of the VM bridge, an abrupt increase in voltage occurs (see Fig. 3), at which for some time, until capacitor C2 had time to charge, the potential of point 2 becomes greater than the potential of point 1, diode D2 opens and the EM it works.

The constant charge of capacitor C2 is determined by the relatively small resistance formed by the parallel connection of resistors 3 and RQ, since diode D is open when the capacitor is charged. The constant discharge of capacitor C2 is much larger, since diode D1 is closed and the resistor R & choose a large resistor R.

As a result, the conditions for the detuning of the circuit from the variable component at the output of the VM bridge with a small swing period are improved, since the potential of point 1 rises relatively quickly and is kept at a high level, preventing RE operation. In the actual scheme, a small smoothing co-detector is included in parallel with the OM for noise and harmonics tuning.

The proposed triggering body has improved technical characteristics and allows expanding the range of ratios between the maximum possible currents and frequencies of oscillations and the minimum response current. Such a triggering organ has a sensitivity of L / 2 0.04A and at the same time provides a detuning from oscillations with currents at a difference in the frequency of the systems at the ends of the Hz transmission, accompanied by an asymmetry of at least 20%, and is used in a prototype of distance protection of 750 kV line voltage.

Claims (2)

1.Chernobrovov N.V. “Relena protection,“ Energie, M., 1974, p. 418-427. 2. USSR author's certificate number 187872, M. Kl.2 N 02N 3/40 (prototype).