JPS59191427A - Varying component detecting relay - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a change detection relay that detects at high speed the occurrence of an accident in a power system.

[Technical background of the invention]

Overcurrent relays are generally used to detect faults in power systems, but they are used to detect faults with high sensitivity when the fault current is small compared to the load current on heavy-load long-distance transmission lines. Therefore, in such cases, a change detection relay is used, which detects a failure when the current after the accident exceeds a certain value compared to the current before the accident.

Among such change detection relays, the operation of the 'm flow change detection relay will be explained with reference to FIG.

The current (2) obtained from the system is converted by a current transformer CT into a current (I) proportional to the current (1), and then converted into a stain pressure (2) by a resistor R1.

After that, the current 3 which is the output after passing through the bandpass filter BPFI and the current that does not pass through the bandpass filter,
Find the vector sum with vector synthesis circuit ■C.

Here, the absolute value of the current I, which is the vector sum of the current I and the current I3, is the bias amount K. , 1:υ, the level detection circuit LD operates and the output OUT PUT is obtained. Next, it will be explained why the change can be detected using the circuit configuration shown in FIG.

In Figure 1, the band-pass filter BPF l has an amplitude characteristic that resonates at the rated frequency of the input current generator, an input-to-output ratio of 1, and outputs in an opposite phase to the human power at the rated frequency. .

When the input current is at the rated frequency and its absolute value is constant, as shown in Figure 2, the current before the bandpass filter BPF 1O and the current after the current ■ are equal in magnitude and have opposite phases, so they are mutually exclusive. cancel each other out, the output current of the vector synthesis circuit remains zero, and the output of the level detection circuit LD also remains zero.

However, the input current ■ is at the rated frequency and its absolute value is at time 1. as shown in FIG. When it starts to change, bandpass filter B
A difference arises between the current I before PF] and the current 3 after it. This is generally referred to as the memory effect of a band-pass filter, and is called this because the output of the band-pass filter follows changes in the input with a certain time constant, and for this reason, the current I and A difference occurs in the current I3.

And the current is the difference current. The magnitude of is a predetermined value, that is, the bias amount K. When it becomes larger, time 1. as shown in FIG. The output 0 [JT PUT is obtained.

[Problems with background technology] The change detection relay described above has the following drawbacks.

(1) In principle, a bandpass filter is used, but the longer the storage time, the sharper the Q value, which indicates how well the filter resonates, and the narrower the passband becomes, resulting in better continuous characteristics when harmonics are included. However, conversely, even when the frequency fluctuates, an error occurs between the current I2 before the band-pass filter BFF1 and the current I3 after the band-pass filter BFFl, resulting in a TJJ possibility that malfunctions even though there is no level change.

(2) If the Q value, which indicates the quality of resonance, is large, the ability to follow changes in the input current is poor, so for example, the output O
Even if the input current I suddenly becomes zero while UT PtJT is present, the output OUT PUT will continue to be present for a certain period of time.

Therefore, since the recovery time becomes long, it may not be possible to coordinate the time with the protection and control equipment.

[Purpose of the invention]

The present invention detects the drawbacks of the conventional technology described above, and detects changes that are less likely to malfunction even when the system frequency fluctuates, and eliminates the need for severe adjustment by making the Q value of the bandpass filter smaller than that of conventional products. The purpose is to obtain a relay.

[Summary of the invention]

A transformer that converts the current or voltage obtained from the power grid into a predetermined value, a first bandpass filter with a resonant frequency that is an integer multiple of the fundamental frequency of the power grid, and a resonant frequency of one tones. a filter circuit in which second band-pass filters having a second band-pass filter ~ are connected in cascade; a vector synthesis circuit that takes a vector difference or a vector sum of the output of the filter circuit and the output of the transformer; 1. A change detection net ta device comprising a level detection circuit for detecting that the level of .

[Embodiments of the invention]

An embodiment according to the present invention will be described with reference to the circuit diagram of FIG.

The difference between FIG. 1 and FIG. 4 is that the band-pass filter in FIG. 1 is one stage, but the band-pass filter in FIG. 4 is two stages.

In Fig. 1, the bandpass filter BPFI is set to resonate with the fundamental frequency of the input current, but in Fig. 4, the bandpass filter BPF 1 and the bandpass filter BPF2 are The human power I is set to resonate at n times the fundamental frequency, and the other is set to resonate at ]/n times the fundamental frequency.

Here, the C1 coefficient n is a value larger than 0, and usually a value of 2 or less is selected.

As described above, in FIG. 4, if the fundamental frequency of the input current (1) is 50 Hz and, for example, the coefficient n is n = 2, then the resonance frequency f of the bandpass filter Bi)Fl. H is 100 Hz, and the resonance frequency f of the bandpass filter BP'F2. L is set to 25Hz.

In the circuit diagram of FIG. 4, a current 11 obtained from the grid is converted by a current transformer CT into a current I proportional to the current I,
Then, it is converted into a voltage by the resistor R1.

The current Is then passes through the bandpass filter BPF 1.
However, since the bandpass filter BPF l is adjusted to resonate at a frequency (100 [Hz)) higher than the fundamental frequency (5 o [Hz)] of the input current I, The currents 3' are equal in magnitude and lead in phase, but have opposite polarities.

Next, the current I3 passes through the bandpass filter BPF2 and is converted into the current ■3, but the bandpass filter np
Since p2 is adjusted to resonate at a frequency (25 (Hz)) lower than the fundamental frequency (50 [H2]) of input current I, current I is equal in magnitude to current I3. , the phase lags behind the current f, but has the opposite polarity and is in phase with the current I.

In other words, the current 3 is smaller in size and has the same phase as the current 1.

Then, the vector difference between current 1 and current 2 is determined by a vector synthesis circuit VC, and the absolute value of current 1, which is the vector difference, is the bias amount I. When it becomes larger, the level detection circuit LD operates and the output OUT'PtJT is obtained.

The aforementioned bandpass filters BPFI and BPF
To explain the response of No. 2 mathematically, the transfer function T(jω) of the bandpass filter is expressed as generally known. From this, the shooting width characteristic] raw IT (jω)1 and phase characteristic l
T(jω) is IT(jω) 1−−−−−1−−− 1〆+Q2(!−ri2 ω. ω −IT(jω) =−, an−1((n GJ,−)
ω. becomes ω.

Next, the response shown in FIG. 4 will be explained for the case where the fundamental frequency of the system is 50 Hz.

As a condition, the bandpass filter BPF 1 is Q=2
, 1o=100Hz, K=3.16, and the bandpass filter BPF 2 is Q=2, f6=2514.
Let z, K = 3.16.

Table]: Response of RPF1 Table 2: Response of BPF2 From the above table, it can be seen that the band-pass filters BPFI and BPF2 have the same output size relative to the input, and the phases are opposite to each other.

From this, in Fig. 4, for the current ■, the current T,
It can be seen that they have the same size and the same phase.

The amplitude characteristics and phase characteristics of these bandpass filters are shown in FIGS. 5 and 6.

In the present invention, two band-pass filters are used to avoid the influence of frequency fluctuations, but a comparison with the case where one band-pass filter is used will be described below.

For comparison, the bandpass and pass filter is 50H2.
It is adjusted to respond to K and the frequency is 45H2 to 5.
The table below shows how the 4th stream ■4 changes when the frequency changes up to 5 Hz.

(F margin below) Table 3: Differences between the conventional method and the present method As described above, it can be seen that according to the method of the present invention, there is little change in amplitude and phase with respect to frequency fluctuations.

Note that FIGS. 7 and 8 show changes in the amplitude characteristics and phase customization of the method of the present invention with respect to frequency fluctuations. These figures are the fifth
It can be easily estimated from the figure and the 61st threshold.

[Other Examples]

In the present invention, one stage each of a band pass filter having a resonant frequency of n j tones and a band pass filter having a co-local wave number of 11 tones for the basic IKI wave number are provided; It is not something that should be determined by one person at a time.

In other words, the purpose is to make it less susceptible to the effects of frequency fluctuations by providing two or more stages of band-pass filters in a part of the filter, which conventionally had one stage.

An example is shown in FIG.

If the configuration shown in FIG. 9 is implemented, the circuit will be less susceptible to frequency fluctuations than the circuit configuration shown in FIG. 4, in which part of the filter is formed by two stages of bandpass 1 black filters.

The part of the filter shown in FIG.
1 and BPF2.

This method is less susceptible to wide frequency fluctuations than the circuit configuration shown in Figure 4, as explained in Figure 4. From the fact that is almost constant, it can be seen in FIG. 9 that the amplitude is almost constant even in the frequency band up to the fundamental frequency 675) and up to n force λ up to 2n. Furthermore, it is easily inferred that if the number of stages of the band-pass filter is increased, K becomes even less susceptible to frequency fluctuations.

[Effects of the Invention] According to the present invention, it is possible to provide a change detection relay that can reduce errors even in a system with frequency fluctuations, and does not require changing the resonance frequency of a band-pass filter even if the rated frequency changes. I can do it. Furthermore, since the Q value, which indicates the quality of resonance, can be reduced, a change detection relay with a shorter return time than the conventional system can be created.

[Brief explanation of drawings]

Figure 11.4 is a block diagram showing the configuration of a change detection relay according to the conventional method, Figure 2 is a diagram showing the response of each part when a certain input is given in the conventional method, and Figure 3 is a diagram showing the response of each part in the conventional method. Figure 4 is a block diagram showing the structure of the change detection relay according to the present invention, and Figure 5 is a diagram showing the response of the valley when there is a change in the input that causes the change detection relay to operate. Amplitude % of each of the two bandpass filters according to the invention
Figure 6 shows the phase characteristics of two band-pass filters according to the present invention, and Figure 7 shows the amplitude characteristics when two band-pass filters according to the present invention are connected in series. FIG. 8 is a diagram showing phase characteristics when two band-pass filters according to the present invention are connected in cascade, and FIG. 9 is a diagram showing another embodiment of the present invention. CT...Transformer BPFl, BPF2 Bandpass filter VC...
Vector synthesis circuit LD, level detection circuit agent Patent attorney Kensuke Chika (and 1 other person) No.
1 Figure 4 Figure 2 Figure O□ Figure 3 Figure 5 Figure 6゜

Claims (1)

[Claims] (1) A transformer that converts the current or voltage obtained from the power grid into a predetermined amount, a first bandpass filter that has a resonant frequency n times the fundamental frequency of the power grid, and a resonant frequency that is 1 times the fundamental frequency of the power grid. a filter circuit in which second band-pass filters are connected in cascade; a vector synthesis circuit that takes a vector difference or a vector sum between the output of the filter circuit and the output of the transformer; A change detection relay characterized by comprising a level detection circuit that detects a change in level. (2. In the item described in claim (1), a band-pass filter having a resonance layer 1 wave number n times and 2n times as large as the fundamental frequency, and a resonance frequency that is - times and h times as high as the fundamental frequency. A change detection relay consisting of a filter circuit connected in cascade with a band-pass filter.