JPH0586128B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a differential relay used to protect a power transformer.

[Technical background of the invention and its problems]

FIG. 11 shows a typical application example of a differential relay. In Fig. 11, 1 is a power transformer, 2 _-1 ,
2 _-2 is a current transformer CT that extracts the terminal current of power transformer 1, and 3 is a differential relay that inputs the secondary current of current transformers 2 _-1 and 2 _-2 to differentially protect the transformer. , 4 is a breaker. FIG. 12 is a diagram showing an example of the characteristics of the differential relay 3 , in which the secondary currents of CT2 _-1 and CT2 _-2 based on the input current I ₁ ' and output current I ₂ ' of the power transformer 1 are expressed as I ₁ and _I2 . In the case where there is no fault inside the power transformer 1, the input current to the differential relay 3 is I ₁ =I ₂ , so the diagonal line in FIG. 12 is the area where the input currents I ₁ and I ₂ exist. However, in the case where there is a fault inside the power transformer 1, the input current becomes I ₁ ≠ I ₂ , so the differential current I _d = I ₁ + I ₂
≠0, and when the value of I _d becomes large, it enters the operating region of the ratio differential element DIF or the high setting overcurrent element HOC in FIG. to protect the power transformer 1. Here, the operating formulas of the ratio differential element DIF and the high-settling overcurrent element HOC are, for example, K ₁ (I ₁ + I ₂ )−K ₂ (|I ₁ |+|I ₂ |)≧K ₀ , I ₁
+I ₂ ≧K ₃ . However, K ₀ , K ₁ , K ₂ , and K ₃ are arbitrary constants. FIG. 13 is an example of a block diagram of the differential relay 3 . 5 _-1 and 5 _-2 are input transformers,
6 is an adder, 7 _-1 and 7 _-2 are rectifiers, 8 and 9 are adders, 10 and 11 are level detectors, 12 is a second harmonic current extraction circuit, 13 is a fundamental wave current extraction circuit, 14
1 is a comparator, and 15 is an inhibit circuit. Input currents I ₁ and I ₂ are introduced into an adder 6 through an input transformer 5, added together, and then input as a positive input into an adder 9. In addition, the input currents I ₁ and I ₂ are input to the input transformers 5 _-1 ,
The signals are also introduced into rectifiers 7 _-1 and 7 _-2 through 5 _-2 , and after being introduced into each, they are added up in an adder 8 and input as a negative input into an adder 9. The output of adder 9 is
K ₁ (I ₁ + I ₂ )−K ₂ (|I ₁ |+|I ₂ |), and the level detector 11 outputs K ₁ (I ₁ +I ₂ )−K ₂ (|I ₁ |+|I ₂ |). )≧
Produces output “1” when K ₀ , ratio differential element DIF
produces an output of

The output of the adder 6 is also input to the level detector 10, and the level detector 10 produces an output "1" when I ₁ +I ₂ ≧K ₃ , thereby producing the output of the high-settling current element HOC.

Furthermore, the output of the adder 6 is also introduced into the second harmonic current extraction circuit 12 and the fundamental wave current extraction circuit 13.
Each output is introduced into the comparator 14, and the ratio of the second harmonic current I _2f to the fundamental wave current I _1f is a predetermined value.
When the value exceeds K _e , that is, |I _2f |/|I _1f |≧K _e , the comparator 14 outputs an output, generating an inhibit input to the inhibit circuit 15, and detecting the level of the inhibited input input to the inhibit circuit. The output of the converter 11, ie, the output of the ratio differential element, is locked. For convenience of explanation, the circuit consisting of the second harmonic current extraction circuit 12, the fundamental wave current extraction circuit 13, and the comparator 14 will be referred to as an excitation inrush current detection circuit. If the output of comparator 14 is absent, the output of the ratiometric differential element will not be locked and the inhibit circuit will produce an output.

Next, the necessity of the excitation inrush current detection circuit 16 described in FIG. 13 will be explained. When the shield breaker 4 is turned on in FIG. 11, an excitation inrush current flows through the transformer 1, as is well known. 1st
Figure 4 shows an example of magnetizing inrush current. The magnitude of this magnetizing inrush current differs depending on the turning-on phase, residual magnetic flux, backing power supply, etc., but it produces a differential current I _d = I ₁ + I ₂ = I ₁ ≠ 0, as in the case of an internal fault in transformer 1, so it is Depending on the size, it may fall within the operating range of the ratio differential element DIF, so the differential relay 3 is connected to the transformer 1.
It may operate even though there is no accident. In order to prevent this unnecessary response, an excitation inrush current detection circuit 16 shown in FIG. 13 is used as an example. As shown in an example in FIG. 14, the excitation inrush current has a characteristic waveform containing a large amount of second harmonic components. Therefore, when the content rate of the second harmonic with respect to the fundamental wave exceeds a certain value, it is determined that it is an excitation inrush current, and the output of the ratio differential element DIF is locked to prevent unnecessary response of the differential relay 3 . This means that it is possible to do so. In addition, the high-settling overcurrent element
Regarding HOC, the above-mentioned countermeasures are not necessary because the excitation inrush current generally settles to a level that does not cause unnecessary response. As mentioned above, the second harmonic detection circuit has been used conventionally, but since the ratio differential element DIF is locked when the excitation inrush current occurs, if an internal fault occurs in the transformer at the same time, the Settling overcurrent element
We had no choice but to rely solely on HOC. Also, considering the time when magnetizing inrush current occurs, there is a case in which the high-settling overcurrent element HOC, which generally has a faster operating time than the ratio-differential element DIF, does not require high speed. Ratio differential elements can also be used in cases where the operating time is similar to that of elements.
Since DIF is locked when magnetizing inrush current occurs,
Unable to remove high settling overcurrent element HOC,
The circuit scale became large, and there were difficulties in terms of economy, miniaturization, etc.

[Purpose of the invention]

The present invention has been made to solve the above problems, and an object of the present invention is to provide a differential relay for protecting a power transformer that is excellent in terms of reliability, economy, and miniaturization.

[Summary of the invention]

The present invention locks the ratio differential element even when detecting magnetizing inrush current by reducing the sensitivity of the ratio differential element to a characteristic equivalent to that of a high-settling overcurrent element or an arbitrary predetermined characteristic when detecting magnetizing inrush current. The purpose of the present invention is to realize a differential relay for protecting power transformers which is superior in terms of reliability, economy, and miniaturization.

[Embodiments of the invention]

<Configuration of Embodiment> An embodiment of the present invention will be described below using FIG. 1.

In FIG. 1, parts corresponding to those in FIG. 13 are given the same reference numerals, and redundant explanation will be omitted. In FIG. 1, the output of the adder 8 is introduced into the adder 9 through the variable amplifier 17, and the output of the adder 9 is level detected by the variable level detector 18, and the output of the variable level detector 18 is input to the ratio differential element DIF. The output is Further, the output of the comparator 14 is introduced as a control signal to the variable amplifier 17 and the variable level detector 18, respectively.

<Operation of the Embodiment> In FIG. 1, when there is no magnetizing inrush current, the magnetizing inrush current detection circuit 16 does not operate, so the comparator 14 outputs "0". When the output of the comparator 14 is "0", the gain of the variable amplifier 17 is 1, the level detection value of the level detector 18 is K ₀ /K ₁ , and the operating formula of the ratio differential element DIF is the 13th The operating formula K ₁ (I ₁ + I ₂ )−K ₂ (|
I ₁ |+|I ₂ |)≧K ₀ , and its characteristics are also similar to those shown in FIG. When the magnetizing inrush current exists, the magnetizing inrush current detection circuit 16 operates, so the comparator 14 outputs "1". When the output of the comparator 14 is "1", the gain of the variable amplifier 17 is 0, and the level detection value of the level detector 18 is
K ₃ , and the operating formula of the ratio differential element DIF is the same as that of the high-settling overcurrent element HOC: I ₁ +I ₂ ≧K ₃ , and its characteristics are also the same as that of the high-settling overcurrent element in Figure 12.
It has the same characteristics as HOC. FIG. 2 shows the pattern of changes in the characteristics of the ratio differential element DIF when detecting this excitation inrush current. In this way, when the excitation inrush current is detected, the characteristics of the ratio differential element DIF are reduced in sensitivity to the characteristics of the high-settling overcurrent element HOC, so the ratio differential element DIF does not react unnecessarily. Furthermore, since the same operating range as the high-settling overcurrent element HOC is secured, it is possible to perform the fail-safe function of the high-settling overcurrent element, improving reliability. In addition, if the operating time of the high-settling overcurrent element HOC is the same as that of the ratio differential element DIF, it is possible to eliminate the need for the high-settling overcurrent element HOC, resulting in economic efficiency, circuit miniaturization, etc. It becomes possible to provide a differential relay that is excellent in this respect.

<Effects of Examples> As described above, by using the present invention, it is possible to obtain a differential relay that is highly reliable, economical, compact, etc., and the effects are significant.

<Other Embodiments> (i) In the embodiment shown in FIG. 1, the characteristics after changing the ratio differential element DIF are the same as those of the high-settling overcurrent element HOC, but the gain of the variable amplifier 17 can be set to an arbitrary value K〓,
Set the level detection value of the level detector 18 to an arbitrary value.
K〓 may also be used, and the operating formula in that case is K ₁ (I ₁ +
I ₂ )−K〓(|I ₁ |+|I ₂ |)≧K〓, and an example of its characteristics is shown in FIG.

(ii) In the example of FIG. 1, an example of ratio differential element DIF self-phase control was described during magnetizing inrush current detection, but as shown in FIG. Ratio differential elements of ratio differential relays
It may be possible to control all DIFs. In FIG. 4, 19 is an OR circuit.

(iii) Furthermore, as shown in FIG. 5, the two-phase excitation inrush current detection circuit 16 may control all the ratio differential elements DIF of the ratio differential relays of each phase during operation. In FIG. 5, 20 is an AND circuit;
1 is an OR circuit.

(iv) In the example shown in Fig. 1, the magnetizing inrush current detection circuit 16 that detects the magnetizing inrush current detects the magnetizing inrush current based on the ratio of the second harmonic current I _2f and the fundamental wave current I _1f in the self-phase differential current I _d . However, as shown in Fig. 6, the second harmonic current I _2f in the differential current I _d of each phase is
The sum of harmonic currents | I _2fa | + | I _2fb | + | I _2fc | may be used. In this case, the detection formula for the a-phase relay is |I _2fa |+|I _2fb |+|I _2fc |/|I _1fa
｜≧ K _e b-phase relay is ｜I _2fa ｜+｜I _2fb ｜+｜I _2fc ｜/｜I _1fb
｜≧ K _e c-phase relay is ｜I _2fa ｜+｜I _2fb ｜+｜I _2fc ｜/｜I _1fc
｜≧K _e .

In FIG. 6, 22 is an adder.

(v) Furthermore, as shown in Figure 7, the fundamental wave current of the own phase
Instead of I _1f , the sum of the fundamental wave currents in the differential current I _d of each phase may be |I _1fa |+|I _1fb |+|I _1fc |.
In this case, the detection formula for each phase relay is |I _2fa | + | I _2fb | + | I _2fc | / | I _1fa | + | I _1fb | +
｜I _1fc ｜≧K _e . In FIG. 7, 23 and 24 are adders.

(vi) Furthermore, as shown in Figure 8, the maximum fundamental wave current of each phase is used as the fundamental wave current.
Max [|I _1fa |, |I _1fb |, |I _1fc |] may be used.
In this case, the detection formula for each phase relay is |I _2fa |+|I _2fb |+|I _2fc |/Max[|I _1fa |, |I _1f
b |, |I _1fc |]≧K _e .

In FIG. 8, 23 is an adder and 25 is a maximum value extraction circuit.

(vii) In the embodiment shown in Fig. 1, the sum of each terminal current |I ₁ | is used as the suppression amount that determines the ratio characteristics of the ratio differential relay.
+|I ₂ | is used, but the maximum value of each terminal current Max [|I ₁ |, |I ₂ |] may also be used as shown in FIG. The operating formula in this case is K ₁ (I ₁ + I ₂ )−K ₂・
Max [|I ₁ |, |I ₂ |]≧K ₀ . In FIG. 9, 26 is a maximum value extraction circuit.

(viii) Although the example in Figure 1 shows a ratio differential relay for protection of a power transformer with two windings, it can be similarly applied to a ratio differential relay for protection of a power transformer with three or more windings. As an example, the case of a ratio differential relay for protection of a three-winding transformer is
As shown in the figure. In this case, the operating formula of the relay is that the ratio differential element DIF is K ₁ (I ₁ + I ₂ + I ₃ ) − K ₂ (|I ₁ | + | I ₂ |
＋｜I ₃ ｜)≧K ₀ , the high settling overcurrent element is I ₁ + I ₂ + I ₃
≧ _K3 . In FIG. 10, 27 and 28 are adders.

(ix) High setting overcurrent elements for protection of power transformers
If the operating time of the HOC is the same as that of the ratio differential element DIF, the high-settling overcurrent element circuit 29 can be omitted. In this case, the circuit scale becomes small, and the relay can be made smaller and lower in cost.

〔Effect of the invention〕

By using the present invention, the ratio differential element of the ratio differential relay is not locked when magnetizing inrush current is detected, and there is no need to rely on the operation of only the high-settling overcurrent element, greatly increasing the reliability of the ratio differential relay. improve. In addition, if the operating time of the high-settling overcurrent element is comparable to that of a ratio differential element, the high-settling overcurrent element can be eliminated, making it possible to significantly reduce the size and cost of the relay, and to increase its effectiveness. It is noticeable in large areas.

[Brief explanation of the drawing]

FIG. 1 is an example of a block diagram of the differential relay of the present invention.
Figures 2 and 3 are diagrams showing characteristic examples of the differential relay of the present invention, Figures 4 to 10 are block diagrams of other embodiments of the present invention, and Figure 11 is an example of application of the differential relay. 12 is a diagram showing an example of the characteristics of a differential relay, FIG. 13 is a block diagram of a conventional differential relay, and FIG. 14 is a waveform diagram of an excitation inrush current. DESCRIPTION OF SYMBOLS 1...Power transformer, 2...Current transformer, 3 ...Differential relay, 4...Shipping breaker, 16...Magnetizing inrush current detection circuit.

Claims (1)

[Claims] 1 A ratio differential that inputs the amount of electricity corresponding to the current flowing through each terminal of the transformer to create the operating amount and suppression amount, and operates and produces an output when the operating amount, suppression amount, and level detection value meet the predetermined relationship. In the differential relay device for protecting a transformer, the magnetizing inrush current detection means operates when the ratio of the fundamental wave to the second harmonic is equal to or higher than a predetermined value based on the quantity of electricity, and the magnetizing inrush current detection means operates. and a characteristic changing means for changing at least one of the suppression amount or the level detection value of the ratio differential characteristic to shift the characteristic to a lower sensitivity side when Device.