SU1541535A1 - Filter of symmetric components - Google Patents

Abstract

The invention relates to electrical measuring equipment and can be used to simultaneously measure the voltage of the direct and inverse sequence of a three-phase network. The aim of the invention is to improve the accuracy when changing the frequency of the network by correcting the frequency errors of the RC circuits. The goal is achieved in that the filter is supplemented with a second and third inverters, two adders and an RC circuit connected to the second inverter. When the frequency of the input signal deviates from the nominal value, the voltage vectors supplied from the RC circuits to the adders do not change the amplitude and rotate in the same direction, which ensures the correction of frequency errors. 2 Il.

Description

The invention relates to electrical measuring equipment and can be used to simultaneously determine the voltages of forward U (and the reverse U2 of sequences in three-phase electrical networks.

The purpose of the invention is to improve the measurement accuracy when changing the frequency of the network.

Figure 1 presents the functional diagram of the proposed filter; Fig. 2 shows potential voltage diagrams for the direct (a) and reverse (b) sequences explaining its operation.

The filter consists of inverters 1–3, adders 4 and 5, and three RC circuits 6–7, 8–9, 10–11, and it is desirable to use 6, 8, 10 as resistors to effect the tuning of the filter.

series-connected resistor and potentiometer, which changes resistance in a small range. The filter is adjusted at the nominal frequency.

when serving

only the direct sequence (Fig. 2a). With the help of a resistor 10, they expose (ie / / ise) and find the position of the point E, on the potential diagram, E, with the help of the third inverter forms E. Using a resistor 6, they move D (as long as U U-p d + Ug A coincides with the input linear voltage UeA- With the help of resistor 8, they move D4 to the position inverse to point D ,,.

From the potential diagrams, it can be seen that, from the voltage of the direct sequence, U is formed, and

SL

four

cl

from cn

from the negative sequence voltages, a U 0. If both components are present at the corresponding filter outputs, U and U4 are separated.

If the frequency of the input voltage deviates from the nominal value of the points D, D, E, E for each of the pos. The roundings are moved around the circumference in the same direction, thereby providing compensation for the errors of one circuit of another.

Despite the different speeds of movement of the points D, D, E, E due to

R;

Where

Oi

V

when the frequency changes by 1 Hz

different ratios

 -L

Wc; - -

The error of measuring the voltage of the direct sequence is JjU (0.29%, and the voltage of the reverse sequence is 0.01%.

Claims (1)

Invention Formula Symmetrical component filter containing voltage converter five 0 five and two consecutive RC circuits connected between its input and output, and the resistor of the first RC circuit is connected to the input of the converter, which is the first input of the device, which is characterized by the fact that the converter is made in the form of a voltage inverter, and the filter further comprises a second and third voltage inverters, two two-input adders and a third RC circuit, which is connected between the input and output of the second inverter, and its resistor is connected to the input of the inverter The state second input of the device, the resistor of the second RC circuit is connected to the input of the first inverter, the third input of the device is a common bus, the midpoint of the direct RC-. the circuit is connected to the first input of the first adder, the second inputs of the first and second adders are connected to the midpoint of the third RC circuit, and the first input of the second adder is connected to the midpoint of the second RC circuit through the third inverter, the outputs of the device are the outputs of the adders. FIG. at 1C3 1 it ut eight