JPH0224091B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a protective relay device, and particularly to a protective relay device that detects an asymmetric waveform current caused by an excitation inrush current of a transformer or the like.

[Technical background of the invention]

When a transformer, reactor, etc. changes from a non-excited state to a voltage applied state due to the closing of a circuit breaker, etc.
It is well known that a half-wave rectified wave-like magnetizing inrush current as shown in FIG. 1 occurs. Since this excitation inrush current causes malfunction of current differential relays or distance relays used in transformers, various countermeasures have been taken in the past. For example, a current differential relay is designed to lock its operation when the second harmonic component contained in the input current has a high content ratio with respect to the fundamental wave.

This can be seen from the fact that when the waveform in Figure 1 is expanded into a Fourier series, i=A/π+A/2sinωt−2A/3πsin2ωt −……−2A/πcos2nωt/4n ² −1 …(1) This method focuses on the fact that the excitation inrush current contains many second harmonic components.

On the other hand, in the case of distance relays, we focused on the fact that the current on one wave side (the negative wave side in Figure 1) becomes extremely small, and the operation judgment circuits on each side of the positive wave and negative wave both generate operational outputs. Efforts have been made to treat it as an action only after it has been completed.

[Problems with the background art] In recent years, due to changes in the iron core material and design technology of transformers, the zero interval of the magnetizing inrush current has become shorter, and there has been a strong tendency for the magnetizing inrush current to become closer to a sine wave. That is, a typical waveform is as shown in FIG. Therefore, in the method of detecting the excitation inrush current based on the content rate of the second harmonic, the content rate drops significantly, so it is necessary to use a filter for detecting the fundamental wave or the second harmonic with steep characteristics. Attempts have been made to detect low content rates using a filter, but sufficient accuracy and stability have not been achieved, and the operation time delay due to the steep characteristics of the filter is difficult to achieve in differential relays, which often require high-speed operation. This is unacceptable and has become a major problem.

In addition, distance relays are equipped with a high-pass filter in the current circuit to remove the effects of transient DC components included in the current when a system failure occurs.
In response to excitation inrush current as shown in Figure 2, there is an increased chance that the device will operate on both the positive and negative wave sides, and in particular,
If such a malfunction were to occur in a distance relay used for remote backup protection, it could cause a power outage over a wide area, and the emergence of a fundamental solution has been eagerly awaited.

[Purpose of the invention]

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide a protective relay device that can detect magnetizing inrush current accurately and at high speed.

[Summary of the invention]

In the present invention, a square wave is formed by removing the DC component from the asymmetric waveform generated as the excitation inrush current, and the difference between the period T _P of the positive half wave and the period T _N of the negative half wave due to this square wave is set. If the current is greater than this value, it is determined to be an excitation inrush current, and the output is used to lock differential relays and the like.

[Embodiments of the invention]

Examples will be described below with reference to the drawings. Third
The figure is a configuration diagram of an embodiment of a protective relay device according to the present invention. In FIG. 3, 11 is a high-pass filter that removes DC components from the system current i.
12 is a square wave conversion circuit which converts the current waveform after removing the DC component into a square wave using the current waveform. Reference numeral 13 denotes an up-down counter, which inputs the output from the square wave conversion circuit 12 as a control input, and the output from the square wave conversion circuit ₁₂ is applied to the input terminal P2 of the microprocessor 16. on the other hand,
14 is an oscillator, the output of which is directly applied to the clock terminal CLK of the microprocessor 16 and serves as a reference signal for running the microprocessor, and at the same time is divided into an appropriate size by a frequency divider circuit 15. A pulse train is applied to the counting input terminal. The counting result by the up-down counter 13 is sent to the microprocessor ₁₆ via the terminal P1.
and a terminal of the microprocessor 16
The counting result is cleared by the control signal from _P3 . The determination result is output from terminal _P4 of the microprocessor 16.

FIG. 4 is a waveform diagram, and the operation of the embodiment having the above configuration will be explained with reference to this diagram. In FIG. 4, 1 is the waveform of the excitation inrush current i (corresponding to the waveform in FIG. 2) with a short zero interval, and this is the input to the high-pass filter 11. Here, if the excitation inrush current i is a perfect sine wave as shown by the dotted line in FIG. However, since a waveform without the dotted line portion is actually given as input, the OV line becomes a solid line b.

Therefore, when this waveform is converted into a square wave by the square wave conversion circuit 12, the period of "1" becomes the period of the positive half wave T _P and the period of "0" becomes the period of the negative half wave. A square wave equal to T _N (see FIG. 4, 2) is obtained respectively. This square wave becomes the control input of the up-down counter 13, and in the up-down counter 13, the output of the frequency dividing circuit 15 (see FIG. 4, 3) is up-counted during the T _P period, and _T
It will be counted down during this period.

On the other hand, the square wave is applied to the terminal _P2 of the microprocessor 16, and when the square wave changes from "0" to "1", the up-down counter 1
3 to the terminal _P1 of the microprocessor 16, and at the same time
A clear signal for the up-down counter 13 is sent via _P3 . Therefore, if the change in the count value of the up-down counter 13 is illustrated, it will be as shown in FIG. The absolute value ΔT of the difference in the period of is a value corresponding to ΔT=|T _P −T _N |...(2). At the same time as this ΔT is read into the microprocessor 16 (more precisely, immediately after it is read), the up-down counter 13 is reset and starts a new up-count. Then, in the microprocessor 16, when the above-mentioned ΔT is larger than a predetermined value ε, that is, when the inequality ΔT>ε...(3) is satisfied, the input i is determined to be the excitation inrush current, and the input is outputted from the terminal _P4 . Outputs an operation signal. Therefore,
By locking a distance relay, a current differential relay, etc. using this operating signal, it is possible to obtain a relay device that does not generate any unnecessary response. Moreover, in this embodiment, since a circuit such as a steep band filter for detecting only the second harmonic with high precision is not used, the detection of the magnetizing inrush current is extremely fast, and therefore the distance relay Even if a current differential relay or the like is used based on the principle of detecting system failures at high speed, there is no risk of malfunction due to magnetizing inrush current. Here, in Fig. 4, the output 3 of the frequency dividing circuit 15 is actually a pulse train of a much higher frequency than that shown in the figure in order to reduce the counting error, but it is shown as shown in the figure for ease of understanding. .

FIG. 5 is a block diagram illustrating the locking mechanism of the protective relay. In FIG. 5, 21 is the protective relay device for detecting the excitation inrush current described above;
3 is a protective relay such as a current differential relay. 22
is a prohibition circuit, and is configured to introduce the output of a protective relay device for detecting excitation inrush current as a prohibition input with respect to the output from the protective relay 23 described above. In other words, the output of the protective relay 23 such as a current differential relay is derived only when there is no output (signal from terminal _P4 of the microprocessor 16) from the protective relay device 21 for detecting magnetizing inrush current. It is something to do.

The above explanation was about the waveform shown in Figure 2, but if it is the waveform shown in Figure 1, the period T _P of the positive half wave and the negative half wave in the waveform after the DC component has been removed. The difference between T N and the period T _N further increases,
More reliable detection is possible. In addition, in the case of a normal system failure, even if the waveform has a superimposed transient DC component, the waveform after removing the DC component is symmetrical between positive and negative, so T _P ≒ T _N ...(4), and the current There is no risk of interfering with the operation of differential relays, etc.

FIG. 6 is a block diagram of another embodiment of the protective relay device according to the present invention. In Figure 6, the number 1 in the diagram
1, 13 to 15 correspond to FIG. 3
1 and 32 are positive and negative level detection circuits,
When the output of each high-pass filter 11 exceeds a predetermined positive or negative level, it outputs "1".
In other words, in the case of protective relay devices using current differential relays, distance relays, etc., the control is often performed so that the protective operation is performed only when the magnitude of the input current exceeds a predetermined value. In this example, these functions are also provided, simplifying the device and
This is to improve reliability. The outputs of the two level detection circuits described above are logically summed by a logical sum circuit 33, and then outputted from the oscillator 1 by a logical product circuit 34.
The signal from 4 is logically ANDed with the output via the frequency dividing circuit 15 and is input to the up-down counter 13.

On the other hand, the output of the positive level detection circuit 31 is also introduced as the control input of the up-down counter 13 and the _P2 input of the microprocessor 16, similar to the output of the square wave conversion circuit 12 in FIG.
The other configurations are the same as in FIG. 3.

Figure 7 is a waveform diagram, and while referring to it,
The operation of the illustrated embodiment will be explained. FIG. 7 1 is the same as FIG. 4 1, but the detection levels of the positive wave and negative wave level detection circuits 31 and 32 are indicated by dashed-dotted lines p and n, respectively.
It is expressed as Therefore, each detection level p,
The time exceeding n can be expressed as T′ _P and T′ _N.
The outputs of the positive wave and negative wave level detection circuits are 2 and 3, and either 2 or 3 is "1".
When , the output of the frequency dividing circuit 15 becomes the count input of the up-down counter 13, so the count input becomes 4.

On the other hand, the up-down counter 13 is controlled by the output of the positive wave level detection circuit 31 (see FIG. 7, 2), and if this is "1", the up-down counter 13 is
Also, if it is " ₀ ", a down count is performed, so as in the case of _{FIG .} When ΔT' is equal to or greater than a predetermined value, an excitation inrush current occurs.

In the above description, a high-pass filter is used to remove the DC component of the input current, but a band-pass filter may be used as long as the DC component can be removed. In recent years, a bandpass filter is often used in the input section to remove the influence of transient harmonics that occur during a system failure, but this filter can also be used.

〔Effect of the invention〕

As explained above, according to the present invention, the DC component is removed from the grid current to form a square wave, and when the difference between the positive polarity period and the negative polarity period of this square wave is greater than or equal to a predetermined value, the magnetization is activated. Since the configuration is such that the relay output is locked upon determining that it is an inrush current, detection of the excitation inrush current can be achieved at high speed and with high reliability, and moreover, with a simple configuration.

[Brief explanation of drawings]

1 and 2 are typical waveform diagrams of magnetizing inrush current, FIG. 3 is a configuration diagram of an embodiment of the protective relay device according to the present invention, and FIG. 4 is a waveform diagram for explaining operation.
FIG. 5 is a block diagram for explaining the locking mechanism of the protective relay, FIG. 6 is a block diagram of another embodiment of the protective relay device according to the present invention, and FIG. 7 is a waveform diagram for explaining the operation. 11...High-pass filter, 12...Square wave conversion circuit, 13...Up-down counter, 14...
... Oscillator, 15 ... Frequency dividing circuit, 16 ... Microprocessor, 21 ... Protective relay device for excitation inrush current, 22 ... Prohibition circuit, 23 ... Protective relay, 3
1, 32... Level detection circuit, 33... OR circuit, 34... AND circuit.

Claims (1)

[Scope of Claims] 1. In a protective relay device that prevents malfunction of a relay by discriminating excitation inrush current contained in an input current from a power system, a DC component in the input current is filtered by a filter circuit. After removing and converting into a square wave, the period of positive half wave of said square wave T _P
and a negative polarity half-wave period _TN , and determines that an excitation inrush current exists when these _TP and _TN satisfy a predetermined relationship. 2. In a protective relay device that prevents malfunction of a relay by discriminating the excitation inrush current contained in the input current from the power system, the DC component in the input current is removed by a filter circuit and then the level is detected. Introduced into a circuit and derived as an output above a predetermined positive or negative level, converting the output above the predetermined level into a square wave, and the time it takes to exceed the predetermined positive level
It is characterized by detecting T′ _P and the time T′ _N during which it falls below a predetermined negative level, and determining that it is a magnetizing inrush current when these T′ _P and T′ _N satisfy a predetermined relationship. Protective relay device. 3. The protective relay device according to claim 1 or 2, characterized in that the filter circuit is a bandpass filter capable of simultaneously removing unnecessary harmonic components.