JPH023372B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protective relay that protects equipment in a voltage system such as a transformer through which a large current flows when turned on.

Conventionally, there has been a relay of this type as shown in FIG. In Figure 1, 1 is the so-called differential input (signal) detected from the current related to the equipment to be protected in the power system, 2 is the so-called suppression input (signal) detected from the current, and 3 is from the differential input 1. A derivation circuit that derives only the fundamental wave component If ₁ through a filter, 4 a derivation circuit that derives only the second harmonic component If ₂ from the differential input 1 through the filter, and 5 a derivation circuit that derives only the fundamental wave component If ₁ from the differential input 1 through the filter. 6 is a detection circuit that outputs a signal 5a when the ratio becomes larger than a predetermined ratio, and 6 inputs the fundamental wave component If ₁ and the second harmonic component If ₂ from the derivation circuits 3 and 4, and also has a bias of a predetermined value. Input Vb, If ₂ + Vd＞kIf ₁ , i.e.
If ₂ +Vb/If ₁ > k (k is a constant), the detection circuit outputs the signal a, 7 is the ratio detection circuit 5
The logical product of the signal 5a and the inverted logic of the signal a is taken, and a signal 7a for operating the relay is output. It is a logic circuit. That is, the relay in FIG. 1 constitutes a ratio differential relay.

FIG. 2 is a waveform diagram illustrating the operation of the circuit shown in FIG. 1. Now, if a transformer is connected to the power system, an excitation inrush current is generated from time t ₀ , a fundamental wave component If ₁ and a second harmonic component If ₂ rise, and a differential input 1 is generated. Since the sharpness Q of the derivation circuit 4 is made larger than the sharpness Q of the derivation circuit 3,
The rise of the harmonic component If ₂ is slower than the rise of the fundamental wave component If ₁ . Here, Vb=0, K=
1, the detection circuit 6 outputs the signal a at time t ₁ when If ₂ > If ₁ . On the other hand, Vb<0, i.e.
If Vb ^- , then lf ₂ +Vb ^- > If ₁ at time t ₂ , and signal a' is output. Further, if Vb>0, that is, Vb ⁺ , then If ₂ +Vb ⁺ >If ₁ at time t ₀ and a signal a'' is output. Here, the signal a is a signal that locks the relay operating signal 7a.

That is, when a magnetizing inrush current is generated due to the input of the transformer into the power system, the ratio detection circuit 5 inputs the fundamental wave component If ₁ and the suppression input 2 of the derivation circuit 3,
Although the signal 5a is generated, it is not caused by an accident, so if the relay is operated by the signal 5a, it will malfunction. Therefore, the second harmonic component that occurs when a magnetizing inrush current occurs, but rarely occurs during an accident.
If ₂ is introduced and it is determined that an excitation inrush current is generated, the detection circuit 6 generates a signal a and inhibits the signal 5a.

Therefore, the signal from the detection circuit 6 needs to be generated earlier than the signal 5a from the ratio detection circuit 5, so as is clear from FIG. 3, the bias Vb is set to Vb ⁺ . It is common that

By the way, the formula for If ₂ +Vb ^- >kIf ₁ is If ₂ /If ₁
+Vb ^- /If ₁ >k, and as If ₁ becomes larger, it approaches k. Similarly, If ₂ +Vb ⁺ >kIf ₁ also approaches k as If ₁ increases,
This relationship is shown by the magnitude of If ₁ and If ₂ /If ₁
FIG. 3 shows the relationship between the bias Vb and the bias Vb as a parameter.

In addition, FIG. 4 shows the excitation inrush current I at the differential input 1.
and energization angle θ when used as suppression input 2.
It is a graph showing the relationship between If ₂ /If ₁ and implicitly shows the relationship between the magnitude of magnetizing inrush current I and If ₂ /If ₁ . That is, since the fundamental wave component of the excitation inrush current also increases or decreases as θ increases or decreases, θ in FIG. 4 can be regarded as If ₁ .

Since the excitation inrush current I is generally generated by the saturation of the magnetic flux of the transformer, it has a waveform biased toward a positive wave or a negative wave, as shown in FIG. This waveform is a waveform that takes only the positive or negative side of the sine wave + DC waveform, as described in, for example, Protective Relay Engineering, published by the Institute of Electrical Engineers of Japan, pages 62 and 63. Generally known.

Therefore, in conventional protective relays, the magnetizing inrush current I
If ₂ / If ₁ at the maximum of (At this time, If ₂ / If ₁ is the minimum value)
The characteristics of the output signal a of the detection circuit 6 are set to be lower than the characteristics of the output signal a (part of FIG. 4).

However, due to changes in the iron core of transformers in recent years, the magnetizing inrush current If ₁ has tended to increase, and therefore the minimum If ₂ /If ₁ has tended to decrease. As a countermeasure for this,
The characteristics of the output current a have to be lowered. However, lowering the characteristics of the output current a means that second harmonics may be generated even in the event of an accident, making it more likely that erroneous locking will occur in the event of an accident, lowering the operational reliability of the protective relay.

In this invention, if the bias Vb is Vb ^- , the detector _is
Focusing on the fact that If ₂ /If ₁ shows the characteristic of decreasing as Vb ⁺ detector and ^Vb-
When the excitation inrush current is generated, the ratio detection circuit signal is inhibited by the fast-acting Vb ⁺ detector, and when the fundamental wave component becomes large after the excitation inrush current is generated, the Vb It is an object of ^the present invention to provide a protective relay in which inhibition is applied by a Vb ^- detector before inhibition can no longer be applied by a + detector, and a highly reliable response can be obtained.

An embodiment of the present invention will be described below with reference to the drawings. In Fig. 6, the same symbols as in Fig. 1 indicate the same parts, and 8 indicates the fundamental wave component If ₁ and the second harmonic component.
If ₂ and bias Vb ^- (however, Vb ^- <0.Vb ⁺ >0)
If ₂ +Vb ^- >kIf ₁ , that is, If ₂ +Vb ^- /If ₁ >k, the detection circuit outputs the signal b. 9 is the signal 5a of the detection circuit 5, the inverted logic of the signal a, and the inverted logic of the signal b. This is an AND gate that performs a logical product of inverted logic and outputs an operation signal 9a for protecting a protection target.

Next, the operation will be explained. Here, the fundamental wave component If ₁ and the second harmonic component If ₂ as shown in FIG.
are output from the derivation circuits 3 and 4.
As explained in FIG. 1, the detection circuit 6 detects If ₂ +
Signal a is output when the condition of Vb ⁺ >kIf ₁ is satisfied.

Further, the detection circuit 8 outputs the signal b when the condition of If ₂ +Vb ^- >kIf ₁ is satisfied. and·
Even if the gate 9 outputs the signal 5a from the detection circuit 5, if the signal a or (logical sum) b is output,
It is prohibited and cannot be opened.

FIG. 7 shows the detection circuit 6 in the circuit shown in FIG.
The output signals a and b of 8 are the magnitude of If ₁ .
It is a graph showing a state that changes depending on the relationship with If ₂ /If ₁ .

As is clear from the illustration, the graph of the output signal b after crossing the graph of the output signal a is
This shows a similar trend to the graph shown in the figure.

That is, as If ₁ increases, the output signal b becomes
It has a characteristic that If ₂ /If ₁ decreases, and it is possible to inhibit even a transformer with a large If ₁ . Further, when an excitation inrush current is generated, the output signal a can be inhibited earlier than the signal 5a of the ratio detection circuit 5.

In the above embodiments, a case has been described in which a detection output is generated when the sum of all inputs is equal to or greater than zero, but the bias application method, including its polarity, is not limited to the above embodiments.

As described above, according to the present invention, the bias
By using the logical sum of the outputs of two detection circuits where Vb is Vb ⁺ and Vb ^- , the output of the operating signal of the relay, which performs a protective operation when a transformer excitation inrush current occurs, is prohibited, so there is no malfunction and reliability. This has the effect of providing a highly protective action.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional protective relay, FIG. 2 is a waveform diagram of the operation of the protective relay shown in FIG. 1, and FIGS. 3 and 4 are graphs showing the characteristics of the protective relay shown in FIG. 1. Figure 5 is a waveform diagram of magnetizing inrush current, Figure 6
The figure is a circuit diagram of a protective relay according to an embodiment of the present invention, and FIG. 7 is a graph showing the characteristics of the protective relay shown in FIG. 6. 3, 4... Derivation circuit, 5, 6, 8... Detection circuit, 7, 9... AND gate. In addition, in the figures, the same reference numerals indicate the same parts.

Claims (1)

[Claims] 1. A first derivation circuit that introduces a differential input detected from a current related to a protection target in a power system and derives a fundamental wave component from this differential input, and a first derivation circuit that derives a second harmonic component from the differential input. a second derivation circuit; and a first detection device that outputs a signal when the fundamental wave component derived from the first derivation circuit becomes larger than the suppression input detected from the current by a predetermined ratio. circuit, the second harmonic component derived from the second derivation circuit, and a first harmonic component of a predetermined value.
A second circuit that outputs a signal when the sum of the bias and the bias becomes larger than the product of the fundamental wave component and a predetermined constant value.
The sum of the second harmonic component derived from the detection circuit and the second derivation circuit and the second bias having the opposite polarity to the first bias is the sum of the fundamental wave component and the predetermined constant value. a third detection circuit that outputs a signal when the product is greater than the product; A protective relay comprising a logic circuit that outputs a signal to protect the above-mentioned object to be protected.