JP3231415B2 - Differential relay - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential relay used for protecting a power system.

[0002]

2. Description of the Related Art FIG. 3 shows an example in which a ratio differential relay 1 is applied to a power transformer 2. Reference numeral 3 denotes a main current transformer, which is used to introduce a current at each terminal. FIG. 5 shows an example of the ratio characteristic of the ratio differential relay 1, and FIG. 6 shows an example of the second harmonic lock characteristic. To briefly explain the necessity of the second harmonic lock characteristic, the transformer inrush current flows from the power source side when the power is turned on when the power is turned on, as in the case of an accident inside the transformer. Therefore, the ratio differential relay may malfunction (operate without an accident). Therefore, it is necessary to distinguish between the inrush current and the current due to an actual accident. Since the excitation inrush current has a feature that a large amount of the second harmonic is included, the ratio of the second harmonic to the first harmonic is generally equal to or higher than a certain set value (generally, about 15% is often used). At times, it is often used to lock the ratio differential output to prevent malfunction of the relay.

FIG. 4 shows an example of a circuit of a conventional ratio differential relay for transformer protection. In FIG. 4, 4 is an input transformer,
6 is a vector sum generation circuit, 5 is a scalar sum generation circuit, 8
Is an addition circuit, 9 is a level detection circuit, 10 is an operation delay circuit, 13 is a second harmonic extraction filter circuit, 7 is a first harmonic extraction filter circuit, 14 and 15 are full-wave rectifier circuits, 16
Is an addition circuit, 17 is a smoothing circuit, 18 is a level detection circuit,
12 is a second harmonic content detection circuit, 19 is a NOT circuit, 1
1 is an AND circuit. In FIG. 4, the input currents I ₁ , I
₂ is introduced into a scalar sum creating circuit 5 and a vector sum creating circuit 6 through an input transformer 4 respectively. The vector sum generation circuit 6 derives the differential amount I _d = I ₁ + I ₂ , and the first harmonic extraction filter circuit 7 and the second harmonic content detection circuit 1
2 to the second harmonic extraction filter circuit 13. Together with the first harmonic extraction filter circuit 7 at the first harmonic differential amount is remove components other than the component I _d is a positive input to a summing circuit 8, the second harmonic content detection circuit 12 total is introduced into the wave rectifier circuit 14 (for a ratio differential element to prevent malfunction due to strain wave, a differential amount I _d is through the first harmonic extraction filter circuit 7).

On the other hand, the scalar sum generation circuit 5 controls the suppression amount I _r
= K (| I ₁ | + | I ₂ |) [where K is a constant], which is negatively input to the addition circuit 8. Therefore, the addition circuit 8
Outputs an operation amount (I _d -I _r). Level detection circuit 9
, The operation amount (I _d -I _r) is [here K4 Constant level detection value K ₁ outputs "1" larger output than. When the input is “1”, the operation-time delay circuit 10 outputs “1” after a predetermined period of time and is introduced into the AND circuit 11.

[0005] Next, the second extracted only the second harmonic component contained in the differential amount I _d at the second harmonic extraction filter circuit 13
The harmonic amount I _2f is full-wave rectified by the full-wave rectifier circuit 15 and is input to the adder circuit 16 in a positive manner. Also, the full-wave rectifier circuit 14
The first harmonic amount I _1f included in the differential amount I _d introduced into the adder 16 is subjected to full-wave rectification by the full-wave rectifier circuit 14, and becomes K ₂ · I _1f [where K ₂ is a constant] to the adder circuit 16. Negative input. Therefore, the adding circuit 16 outputs | I _2f | −K ₂ · | I _1f |, and the level detecting circuit 18 after smoothing by the smoothing circuit 17.
(In this circuit example, the full-wave rectified input is smoothed after addition, but the result is that each input is smoothed and added, that is,
_{| I 2f | - K 2 |} I 1f | which is the same as). Level detection circuit 18, input _{| I 2f | - K 2 |} I 1f | outputs "1" when the positive sign. The “1” output of the level detection circuit 18 is determined to be “0” by the NOT circuit 19 and the AND circuit 1
Introduced in 1. Therefore, the second harmonic content detection circuit 1
The operation of 2 locks the output of the ratio differential relay 1.

[0006]

In the second harmonic content detection circuit 12 of the conventional ratio differential relay 1, the filter characteristic of the second harmonic extraction filter circuit 13 is the selectivity of the second harmonic. , It is necessary to sufficiently attenuate the first harmonic (fundamental component) and the higher harmonic components than the third harmonic, and the transient response time of the filter is determined by the transient of the first harmonic extraction filter circuit 7. It has the property of being slower than the response time.

FIG. 7 shows the response of the differential relay 1 when the transformer inrush current flows. Second for input current
The rise of the DC electric quantity | I _2f | for the harmonic component and the DC electric quantity K ₂ | I _1f | proportional to the first harmonic component are determined by the second harmonic extraction filter circuit 13 and the first harmonic extraction. K ₂ | I _1f | is larger than | I _2f |
Faster than. In the steady state after the transient state, the difference in the transient response time does not cause any particular problem, but the transformer inrush current is a transient input electric quantity, and the transient response time of each filter becomes a problem. . The smoothing circuit 17 is K ₂
When | I _1f |> | I _2f | (section in FIG. 7A), the quantity of electricity is negative, and when K ₂ | I _1f | <| I _2f | (section B in FIG. 7), the quantity is positive. And the output of the level detection circuit 18 (the output of the second harmonic content detection circuit 12) is output from the smoothing circuit 1.
7 is output on the positive side, that is, when | I _2f | <| I _1f | ≧ 0.

[0008] Therefore, the second
Despite the fact that the harmonic content is substantially constant above the operating value, the difference in the transient characteristics of each filter circuit results in an erroneous determination that the apparent content has changed. or,
Since the output of the level detection circuit 9 of the ratio differential element responds to the output of the first harmonic extraction filter circuit 7 irrespective of the second harmonic component, its operation time is reduced to the second harmonic content detection circuit 12.
Faster than the operation time. Therefore, in this state, a transient unnecessary output (malfunction) occurs as shown by a broken line in the relay output of FIG. In the conventional configuration, the second
Time coordination between the harmonic lock characteristic and the ratio differential characteristic (that is,
The operation delay circuit 10 is provided as a coordination timer on the side of the ratio differential circuit that can sufficiently ensure that the relay 1 does not malfunction due to the delay of the harmonic lock. For this reason, even in an accident where the lock by the second harmonic does not work,
There is a problem that the operation time of the ratio differential relay 1 is relatively long. Further, even if the transient characteristic of the first harmonic extraction filter circuit 7 is changed to match the second harmonic negative rise, the rise delay of the first harmonic will be longer than the operation time of the ratio differential element. The effect cannot be expected because it directly leads to the delay.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and does not require an operation delay circuit for time coordination of a ratio differential element even if an inrush current is input, so that the operation time can be reduced quickly. It is intended to provide a motion relay.

[0010]

In order to achieve the above object, according to the present invention, an electric quantity corresponding to a current flowing through each terminal of a transformer is input, and a differential amount obtained from each terminal input electric quantity is a predetermined value. A differential element that outputs when the above is greater than or equal to a second harmonic content that locks the output of the differential element when the ratio of the second harmonic to the fundamental in the differential amount is equal to or greater than a predetermined value. And a second harmonic content detecting element, wherein the second harmonic content detection element extracts a fundamental wave component included in the differential amount and performs full-wave rectification, and converts the full-wave rectified component into a fundamental wave. A circuit for extracting a proportional DC component, a circuit for extracting only a second harmonic component included in the differential amount, a circuit for full-wave rectifying the second harmonic component, and a DC component proportional to the fundamental wave. And a circuit for comparing the second harmonic with the full-wave rectified component of the second harmonic.

[0011]

The operation time delay circuit, which is a timer for time coordination of the ratio differential characteristic circuit, becomes unnecessary because the detection time of the second harmonic content detection element is shortened. Can provide a fast differential relay.

[0012]

An embodiment will be described below with reference to the drawings. FIG.
1 shows a configuration diagram of an embodiment of the differential relay according to the present invention, and the same parts as those in FIG.

In FIG. 1, reference numeral 20 denotes a smoothing circuit for smoothing the full-wave rectified input of the first harmonic, and reference numeral 21 denotes a continuous circuit for continuous intermittent output of the level detection circuit 18. The feature of this embodiment is that the smoothing circuit 17 and the operating delay circuit 10 are removed from the conventional configuration of FIG. 4, and the other configuration is the same as that of FIG. In the configuration of the present embodiment, the second harmonic component I that is full-wave rectified by the full-wave rectifier circuit 15 is used.
_2f and the first harmonic component K ₂ | I _1f smoothed by the smoothing circuit 20.
Is added to perform level detection, the output of the level detection circuit 18 is an intermittent output. Therefore, the continuation circuit 2
1 is used for continuation. Next, the operation will be described. Here, the response of the ratio differential relay 1 when the transformer inrush current flows is shown in FIG.

Since the second harmonic extraction filter circuit 13 has a high selectivity for the second harmonic as in the prior art, its transient response time is the transient response time of the first harmonic extraction filter circuit 7. It has the property of being slower than that. For this reason, it is impossible to shorten the transient response time of the second harmonic extraction filter circuit, so the output of the second harmonic extraction filter circuit is used as it is as a full-wave rectified wave, and the first harmonic extraction filter is used. After full-wave rectification of only the output of the circuit 7, a DC component is extracted through the smoothing circuit 20, and the comparison is performed. Here, the rise (time constant) of the DC component of the smoothing circuit 20 is selected so as to be equal to the difference between the transient response time of the first harmonic extraction filter circuit and the transient response time of the second harmonic extraction filter circuit. Then, the rise of the first harmonic (the output of the first harmonic extraction filter circuit + smoothing circuit) during the transition is equal to the rise of the second harmonic (the output of the second harmonic extraction filter circuit). The characteristics are as follows. Thus, the ratio of the first harmonic to the second harmonic to be detected by the second harmonic content detection circuit (the content of the second harmonic with respect to the first harmonic) from the point in time when the excitation inrush current is input. Rate) does not change, and accurate operation determination can be performed, and the output of the second harmonic content detection circuit is "1" earlier than in the conventional circuit. Since the comparison between the full-wave rectified input and the smoothed input is performed, the output is a continuous wave. Accordingly, the output is made continuous by the return delay circuit 21 to be continuous "1" output, and then introduced into the NOT circuit 19, whereby the output of the ratio differential element is locked. As the operation time of the second harmonic content detection element 12 is shortened, the time coordination with the output of the ratio differential element level detection circuit 9 is sufficiently ensured. Therefore, the operation time delay circuit 10 for time coordination shown in FIG. It becomes unnecessary.

According to the above embodiment, there is no output delay of the second harmonic content detection circuit due to the difference between the rising edges of the first and second harmonic extraction filter circuits, and the operating time delay for time coordination. A circuit is unnecessary, and a differential relay having a short operation time when an accident to operate can be obtained. In the above embodiment, the description has been made of the differential relay for protecting the two-winding transformer. However, the present invention can be applied to a differential relay for protecting the transformer having three or more windings.

[0016]

As described above, according to the present invention, there is no delay in the output of the second harmonic content detection circuit, and no time delay circuit for time coordination is required. And the transformer can be protected with sufficient time.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of one embodiment of a differential relay according to the present invention.

FIG. 2 is a time chart for explaining the operation.

FIG. 3 is a diagram illustrating an example of application of a ratio differential relay to a power transformer.

FIG. 4 is a configuration example diagram of a conventional transformer protection ratio differential relay.

FIG. 5 is a diagram showing an example of ratio characteristics of a ratio differential relay.

FIG. 6 is a diagram showing an example of a second harmonic lock characteristic.

FIG. 7 is a time chart of a conventional ratio differential relay.

[Description of Signs] 1 Ratio Differential Relay 2 Power Transformer 3 Main Current Transformer 4 Input Transformer 5 Scalar Sum Creation Circuit 6 Vector Sum Creation Circuit 8,16 Addition Circuit 9,18 Level Detection Circuit 10 Operating Delay Circuit 11, 19 logic circuit 12 second harmonic content detection circuit 13 second harmonic extraction circuit 7 first harmonic extraction circuit 14, 15 full-wave rectifier circuit 17, 20 smoothing circuit 21 return delay circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02H 3/28 H02H 7/045

Claims (1)

(57) [Claims] 1. A differential element for inputting an electric quantity corresponding to a current flowing through each terminal of a transformer and outputting when a differential amount obtained from each terminal input electric quantity is equal to or more than a predetermined value; A second harmonic content element that locks the output of the differential element when the ratio of the second harmonic component to the fundamental component in the quantity is greater than or equal to a predetermined value. The content detection element includes a circuit that extracts only the fundamental wave component included in the differential amount and performs full-wave rectification, a circuit that extracts a DC component proportional to the fundamental wave from the full-wave rectified component, A circuit for extracting only the second harmonic component included in the signal, a circuit for full-wave rectification of the second harmonic component, a DC component proportional to the fundamental wave, and a full-wave rectification component for the second harmonic. A differential relay comprising: