JP2003333744A - Ratio differential relay apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a ratio differential relay apparatus that can immediately cut off a transformer from a power system if an internal failure occurs, even in a power system with a large capacitance to the earth. <P>SOLUTION: When the attenuation factor of a DC component IDC is determined to have deviated from a prescribed range, a rip signal is outputted to cut off a transformer 1 from a power system. By this means, the transformer 1 may be cut off immediately from the power system if an internal failure FI (internal failure FI not containing the DC component IDC) comprising a large amount of a second harmonic components Id2 occurs; at the same time, the transformer 1 may be cut off immediately from the power system if an internal failure comprising the DC component IDC occurs. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ratio differential relay device which shuts off a transformer from a power system when a failure occurs in the power system.

[0002]

2. Description of the Related Art FIG. 12 is a system diagram showing a power system to which a conventional ratio differential relay device is applied. In the figure, 1 is a transformer and 2 is a cutoff installed on the primary side of the transformer 1. Bowl, 3
Is a circuit breaker installed on the secondary side of the transformer 1, and 4 is a transformer 1
A current transformer (hereinafter referred to as CT) that measures the primary current I ₁ (high-voltage side current) of the transformer 1 and a current transformer (hereinafter referred to as CT) that measures the secondary current I ₂ (low-voltage side current) of the transformer 1. ), 6 are ratio differential relays that disconnect the transformer 1 from the power system when an internal failure occurs in the power system.

FIG. 13 is a block diagram showing a conventional ratio differential relay device disclosed in, for example, Patent Document 1, in which 11 is a primary current I ₁ and C measured by CT4.
The secondary current I ₂ measured by T5 is compared, and the suppression current derivator that derives the larger current as the suppression current Ir, 12 is measured by CT5 and the primary current I ₁ measured by CT4. A differential current derivator that derives the vector difference of the secondary current I ₂ as a differential current Id, and 13 is a ratio differential device that outputs a trip signal when the ratio of the differential current Id to the suppression current Ir is a predetermined value or more. Is.

Reference numeral 14 denotes a fundamental wave component Id0 contained in the differential current Id derived by the differential current deriving device 12.
, 15 is a filter for extracting the second harmonic component Id2 contained in the differential current Id derived by the differential current deriving unit 12, and 16 is a differential current Id not less than a predetermined value. , An inrush determiner that outputs a non-lock signal by determining that the power system is not in the inrush state when the ratio of the second harmonic component Id2 to the fundamental wave component Id0 is less than or equal to a predetermined value, and 17 is the ratio differential unit 13 When the trip signal is output from the inrush determination unit 16 and the unlock signal is output from the inrush determination unit 16, it is a logical product circuit that disconnects the transformer 1 from the power system.

Next, the operation will be described. First, as shown in FIG. 12, the general function of the ratio differential relay 6 is to prevent the transformer 1 from being disconnected from the power system even if an external accident F0 occurs in the power system, but When the internal accident FI occurs, the transformer 1 is cut off from the power system in order to protect the transformer 1.

Specifically, first, the suppression current derivation device 11
Compares the primary current I ₁ measured by CT4 with the secondary current I ₂ measured by CT5, and derives the larger current as the suppression current Ir. In addition, the differential current deriving unit 12 derives a vector difference between the primary current I ₁ measured by CT4 and the secondary current I ₂ measured by CT5 as a differential current Id.

In general, the ratio differential unit 13 is highly likely to have an internal fault FI in the power system when the ratio of the differential current Id to the suppression current Ir is equal to or higher than a predetermined value. When the condition of is satisfied, a trip signal is output. Id> KF ₁ × Ir + KM where KF ₁ and KM are predetermined constants, while the filters 14 and 15 are the fundamental wave component Id 0 and the first wave component Id 0 included in the differential current Id derived by the differential current deriving unit 12, respectively. The second harmonic component Id2 is extracted.

When the power system is in the inrush state, the inrush deciding unit 16 generally changes the circuit breaker 2 from the open state to the inrush state when the circuit breaker 3 is in the open state. However, since the inrush current flows into the transformer 1, an internal accident FI occurs in the power system.
In some cases, the ratio differential unit 13 may output a trip signal due to the occurrence of a phenomenon similar to the case in which the internal fault FI has not occurred in the power system. Considering that it is necessary to prevent the device 1 from being disconnected from the power system, it is determined whether the power system is in the inrush state.

In other words, the inrush deciding device 16 determines that the ratio differential 1 is provided only when the power system is not in the inrush condition.
In order to validate the trip signal output by 3, the differential current I
When d is equal to or larger than a predetermined value and the ratio of the second harmonic component Id2 to the fundamental wave component Id0 is equal to or smaller than the predetermined value, it is determined that the power system is not in the inrush state, and the unlock signal is output. Id2 <KF ₂ × Id0 where KF ₂ is a predetermined constant, where the second harmonic component Id with respect to the fundamental wave component Id0.
The reason for determining the ratio of 2 is that the inrush current generally contains more second harmonic component Id2 than the fault current.

The AND circuit 17 is provided for the ratio differential unit 1
When the trip signal is output from 3 and the unlock signal is output from the inrush determination unit 16, it is determined that the internal accident FI has occurred in the power system, and the transformer 1 is disconnected from the power system. A series of processing ends. Note that FIG.
4 is a table showing the output of each component under no load (including in-rush state, internal failure), under load (including sound and external failure, internal failure) In this example, the AND circuit 17 disconnects the transformer 1 from the power system only when an internal fault FI (internal accident in which the content of the second harmonic component Id2 is small) occurs in the power system. Is shown.

[0011]

[Patent Document 1] JP-A-53-111451

[0012]

Since the conventional ratio differential relay is constructed as described above, the internal fault FI having a small content rate of the second harmonic component Id2 in the power system.
Is generated, the transformer 1 can be cut off from the power system, but in a power system with a large ground capacity,
Many second harmonic components Id2 in the accident current even when there is an internal failure
Therefore, until the ratio of the second harmonic component Id2 is attenuated to a predetermined level, the unlock signal is not output from the inrush deciding unit 16, and the transformer 1 cannot be promptly cut off from the power system. There was a problem.

The present invention has been made to solve the above problems, and even in a power system having a large ground capacity, a ratio differential which can immediately disconnect the transformer from the power system when an internal failure occurs. The purpose is to obtain a relay device.

[0014]

According to another aspect of the present invention, there is provided a differential differential relay device according to the present invention, wherein when the attenuation rate determining means determines that the attenuation rate of a DC component is out of a predetermined range, When the trip signal is output, the transformer is cut off from the power system.

In the ratio differential relay device according to the present invention, when the attenuation rate of the DC component contained in the differential current is smaller than the minimum attenuation rate of the DC component contained in the inrush current, the difference therebetween. It is determined that the attenuation rate of the DC component included in the dynamic current is out of the predetermined range.

In the ratio differential relay device according to the present invention, when the attenuation rate of the DC component contained in the differential current is larger than the maximum attenuation rate of the DC component contained in the inrush current, the difference therebetween. It is determined that the attenuation rate of the DC component included in the dynamic current is out of the predetermined range.

In the ratio differential relay device according to the present invention, when the content ratio of the direct current component to the fundamental wave component included in the differential current derived by the current deriving means is equal to or more than a predetermined value, the transformer The equipment is designed so as not to be cut off from the power system.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below. Embodiment 1. 1 is a system diagram showing a power system to which a ratio differential relay device according to a first embodiment of the present invention is applied. In the figure, 1 is a transformer and 2 is a primary side of a transformer 1. A circuit breaker, 3 is a circuit breaker installed on the secondary side of the transformer 1, 4 is a current transformer (hereinafter referred to as CT) for measuring the primary current I ₁ (high-voltage side current) of the transformer ₁ , and 5 is a transformer. Current transformer (secondary current I ₂ (low-voltage side current))
Reference numeral 20 is a ratio differential relay device that disconnects the transformer 1 from the power system when an internal failure occurs in the power system.

FIG. 2 is a block diagram showing a ratio differential relay device according to Embodiment 1 of the present invention.
Reference numeral 11 is a suppression current derivation device (current derivation means) that compares the primary current I ₁ measured by CT4 with the secondary current I ₂ measured by CT5 and derives the larger current as the suppression current Ir. Reference numeral 12 is a differential current deriving device (current deriving means) for deriving a vector difference between the primary current I ₁ measured by CT4 and the secondary current I ₂ measured by CT5 as a differential current Id, and 13 is for the suppression current Ir. It is a ratio differential device (ratio differential means) that outputs a trip signal when the ratio of the differential current Id is a predetermined value or more.

Reference numeral 32 is a direct current derivator (attenuation rate determining means) for deriving a direct current component IDC contained in the differential current Id derived by the differential current derivation device 12, and 33 is a direct current derivation device 3.
Attenuation rate of DC component IDC derived from 2 ΔIDC /
When Δt is equal to or greater than the set value KH, a high change rate detector (attenuation rate determination means) that outputs a detection signal indicating that, 34
Is a low change rate detector (attenuation rate determination means) that outputs a detection signal indicating that when the attenuation rate ΔIDC / Δt of the DC component IDC derived by the DC derivator 32 is less than or equal to a set value KL, Reference numeral 35 is a logical sum circuit (attenuation rate determination means) that outputs a non-lock signal when a detection signal is output from either the high change rate detector 33 or the low change rate detector 34, and 36 is from the ratio differential unit 13. When the trip signal is output and the unlock signal is output from the OR circuit 35, the transformer 1
Is a logical product circuit (control means) for cutting off the power supply from the power system.

Next, the operation will be described. First, as shown in FIG. 1, the general function of the ratio differential relay 20 is to prevent the transformer 1 from being disconnected from the power system even if an external accident F0 occurs in the power system. When the internal accident FI occurs, the transformer 1 is cut off from the power system in order to protect the transformer 1.

Specifically, first, the suppression current derivation device 11
Compares the primary current I ₁ measured by CT4 with the secondary current I ₂ measured by CT5, and derives the larger current as the suppression current Ir. In addition, the differential current deriving unit 12 derives a vector difference between the primary current I ₁ measured by CT4 and the secondary current I ₂ measured by CT5 as a differential current Id.

In general, the ratio differential unit 13 is highly likely to have an internal fault FI in the power system when the ratio of the differential current Id to the suppression current Ir is equal to or higher than a predetermined value. When the condition of is satisfied, a trip signal is output. Id> KF ₁ × Ir + KM where KF ₁ and KM are predetermined constant DC derivation devices 32, and the differential current derivation device 12 is a differential current Id.
Is derived, a DC component IDC included in the differential current Id is derived.

When the DC deriving unit 32 derives the DC component IDC, the high change rate detector 33 sets the attenuation rate ΔIDC / Δt of the DC component IDC to the set value K as shown below.
It is determined whether or not it is H or more, and if the attenuation rate ΔIDC / Δt of the DC component IDC is the set value KH or more, a detection signal indicating that is output (see FIG. 3). ΔIDC / Δt = {(IDC−90 °) −IDC} / Δ
t> KH where IDC is the current DC component IDC-90 ° is an electrical angle 90 ° before the DC component Δt is a time corresponding to 90 ° in electrical angle

Thus, the attenuation rate ΔI of the DC component IDC
Whether or not DC / Δt is equal to or greater than the set value KH is determined by determining that the attenuation rate of the DC component IDC included in the fault current is included in the inrush current as shown in FIG. This is because the DC component IDC is larger than the attenuation rate, and therefore, by comparing the attenuation rates, it is possible to determine whether a failure has occurred in the power system or whether the power system is in the inrush state.
The set value KH is the maximum attenuation rate of the DC component IDC included in the inrush current, that is, the DC component IDC.
Is a value that is set in consideration of the case where the attenuation rate is the largest (time constant is about 0.2 seconds).

ΔIDC / Δt = {(IDC-90 °)-
IDC} / Δt <KL where DCC is the current DC component IDC-90 ° is an electrical angle of 90 ° and the DC component Δt is a time corresponding to 90 ° in electrical angle.

Thus, the attenuation rate ΔI of the DC component IDC
Whether or not DC / Δt is less than or equal to the set value KL is determined in some cases because the DC component IDC is not included in the fault current. In such a case, the low change rate detector 34 detects the DC component. Since the DC component IDC attenuation rate ΔIDC / Δt is substantially zero, it is smaller than the DC component IDC attenuation rate contained in the inrush current. If the attenuation rates are compared, a failure occurs in the power system. This is because it can be determined whether the power system is in the inrush state. In addition,
The set value KL is a value set in consideration of the minimum attenuation rate of the DC component IDC included in the inrush current, that is, the case where the attenuation rate of the DC component IDC is the smallest (in terms of time constant conversion, About 30 seconds).

When the detection signal is output from either the high change rate detector 33 or the low change rate detector 34, the OR circuit 35 determines that a failure has occurred in the power system and unlocks the system. Output a signal. Then, the AND circuit 36
When the trip signal is output from the ratio differential unit 13 and the unlock signal is output from the OR circuit 35,
When it is determined that the internal accident FI has occurred in the electric power system, the transformer 1 is cut off from the electric power system, and the series of processing ends.

FIG. 5 shows the output of each component under no load (including the inrush state and internal failure) and under load (including sound and external failure and internal failure). It is a table shown, but in this example, not only at the time of an internal failure having a small content of the second harmonic component Id2 but also at the time of an internal failure having a large content of the second harmonic component Id2 and an internal failure having a DC component. Also, in the figure, the AND circuit 36 indicates that the transformer 1 is cut off from the power system.

As is clear from the above, the first embodiment
According to this, when it is determined that the attenuation rate of the DC component IDC deviates from the predetermined range, the transformer 1 is cut off from the power system when the trip signal is output.
When an internal fault FI containing a large amount of harmonic components Id2 (an internal fault FI not containing a DC component IDC) occurs, the transformer 1 can be immediately disconnected from the power system, and an internal fault FI containing a DC component IDC is generated. Even if it occurs, the transformer 1 can be immediately shut off from the power system.

Incidentally, in FIG. 4, topCHH1 is the operating time of the high change rate detector 33 (generally, 15 ms).
The time is about ec (0.75 on a 50-cycle basis)
Cycle)), and treCHH1 is the return time of the high change rate detector 33 (generally about 25 msec (1.25 cycles on the basis of 50 cycles)). Also,
topCHL1 is the operating time of the low change rate detector 34 (generally about 15 msec (0.75 cycles on the basis of 50 cycles)), and treCHL1 is the return time of the low change rate detector 34 (generally, 15msec
It is about a time (0.75 cycle on a 50 cycle basis). The recovery time tr of the high change rate detector 33 is
If CHH1 is set to be long and the operation time topCHL1 of the low change rate detector 34 is set to be short, once the failure occurs, the unlock signal of the OR circuit 35 can be continuously output.

Embodiment 2. FIG. 6 is a configuration diagram showing a ratio differential relay device according to a second embodiment of the present invention. In the figure, the same reference numerals as those in FIG. Reference numeral 37 is a high change rate detector (attenuation rate determination means) that outputs a detection signal indicating that when the attenuation rate ΔIDC / Δt of the DC component IDC derived by the DC derivator 32 is less than or equal to a set value KH. , 38 are attenuation rates ΔI of the DC component IDC derived by the DC derivator 32.
When DC / Δt is greater than or equal to the set value KL, a low change rate detector (attenuation rate determination means) that outputs a detection signal indicating that, 39 is a high change rate detector 37 and a low change rate detector 3
A logical product circuit (attenuation rate determination means) that outputs a lock signal when the detection signals are output from both 8 and a trip signal is output from the ratio differential unit 13 at 40 and an AND circuit 3
This is an inhibit circuit (control means) that shuts off the transformer 1 from the power system when the lock signal is not output from 9.

Next, the operation will be described. In the first embodiment, the high change rate detector 33 or the low change rate detector 34 is used.
When a detection signal is output from any of the above, a non-lock signal is output (a non-lock signal is output when the attenuation rate of the DC component IDC is in the shaded portion of FIG. 3), and the control means is the AND circuit 36. However, as shown in FIG. 6, when a detection signal is output from both the high change rate detector 37 and the low change rate detector 38, a lock signal is output (DC component When the attenuation rate of the IDC is in the shaded area in FIG. 7, a lock signal is output), and even if the control means is configured by using the inhibit circuit 40, the same principle as that of the above-described first embodiment causes an internal failure ( Power is supplied to the transformer 1 not only at the time of an internal failure in which the content of the second harmonic component Id2 is small but also in the case of an internal failure in which the content of the second harmonic component Id2 is large and the internal failure in which the DC component IDC is included. Cut off from the grid Rukoto can, it is possible to obtain the same advantages as the first embodiment.

FIG. 9 shows the output of each component under no load (including the inrush state and internal failure) and under load (including sound and external failure and internal failure). It is a table shown, but in this example, not only at the time of an internal failure having a small content of the second harmonic component Id2 but also at the time of an internal failure having a large content of the second harmonic component Id2 and an internal failure having a DC component. Inhibit circuit 40
Indicates that the transformer 1 is cut off from the power system.

Incidentally, in FIG. 8, topCHH2 is the operating time of the high change rate detector 37 (generally 15 ms.
The time is about ec (0.75 on a 50-cycle basis)
Cycle)), and treCHH2 is the return time of the high change rate detector 37 (generally about 25 msec (1.25 cycles based on 50 cycles)). Also,
topCHL2 is the operating time of the low change rate detector 38 (generally about 15 msec (0.75 cycles on the basis of 50 cycles)), and treCHL2 is the return time of the low change rate detector 37 (generally, 15msec
It is about a time (0.75 cycle on a 50 cycle basis).

Embodiment 3. FIG. 10 is a configuration diagram showing a ratio differential relay device according to a third embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 41 is a differential current deriving device 12
A filter (content rate determining means) for extracting the fundamental wave component Id0 included in the differential current Id derived by
When the content rate of the DC component IDC with respect to the fundamental wave component Id0 extracted by the filter 41 is a predetermined value KG or more, a content rate detector (content rate determining means) that outputs a detection signal to that effect, and 43 is high. A logical product circuit (attenuation rate determination means, content rate determination means) 44 that outputs a lock signal when detection signals are output from all of the rate-of-change detector 37, the low rate-of-change detector 38, and the content rate detector 42, Ratio differential 13
When the trip signal is output from the AND circuit and the lock signal is not output from the AND circuit 43, the inhibit circuit (control means) shuts off the transformer 1 from the power system.

Next, the operation will be described. Filter 4
1, except for the content rate detector 42, the logical product circuit 43, and the inhibit circuit 44, the description is omitted because they are the same as those in the second embodiment. First, as in the second embodiment, when the differential current deriving unit 12 derives the differential current Id, the filter 41 extracts the fundamental wave component Id0 included in the differential current Id.

Then, the content rate detector 42 uses the filter 4
1 extracts the fundamental wave component Id0, the fundamental wave component Id0
It is determined whether or not the content rate of the DC component IDC is above a predetermined value KG, and when the content rate of the DC component IDC is above the predetermined value KG with respect to the fundamental wave component Id0, a detection signal indicating that is detected. Output. Here, the fundamental wave component I
Whether or not the content rate of the DC component IDC with respect to d0 is greater than or equal to a predetermined value KG is determined by an internal fault FI containing a large amount of the second harmonic component Id2 (internal fault FI not including the DC component IDC). This is because it is necessary to surely disconnect the transformer 1 from the power system in the case of doing so.

When the detection signals are output from all of the high change rate detector 37, the low change rate detector 38, and the content rate detector 42, the logical product circuit 43 has no failure in the power system. It is determined that the lock signal is output. Then, when the trip signal is output from the ratio differential unit 13 and the lock signal is not output from the AND circuit 43, the inhibit circuit 44 determines that an internal fault FI has occurred in the power system, 1 is cut off from the electric power system, and a series of processing ends.

FIG. 11 shows the output of each component under no load (including the inrush state and internal failure) and under load (including sound and external failure and internal failure). Although it is a table shown, in this example, the second harmonic component Id2 is not limited to the internal failure and the second harmonic component Id2
The inhibit circuit 4 can be used even during an internal failure with a large content of the harmonic component Id2 and during an internal failure with a DC component.
4 indicates that the transformer 1 is cut off from the power system.

As is clear from the above, the third embodiment
According to this, the fundamental wave component Id included in the differential current Id
Since the transformer 1 is cut off from the power system on the condition that the content rate of the DC component IDC with respect to 0 is equal to or less than a predetermined value, the second harmonic wave is generated more than in the first and second embodiments. Internal fault FI containing a large amount of component Id2
When the (internal failure FI not including the DC component IDC) occurs, the transformer 1 can be reliably cut off from the power system.

[0042]

As described above, according to the present invention, when the attenuation rate determining means determines that the attenuation rate of the DC component is out of the predetermined range, the ratio differential means outputs a trip signal. Then, since the transformer is configured to be disconnected from the power system, even in a power system with a large ground capacity,
There is an effect that the transformer can be immediately disconnected from the power system when an internal failure occurs, and the transformer can be immediately disconnected from the power system even when the internal failure including the DC component occurs.

According to the present invention, when the attenuation rate of the DC component included in the differential current is smaller than the minimum attenuation rate of the DC component included in the inrush current, it is included in the differential current. Since it is configured to judge that the attenuation rate of the direct current component that is out of the specified range, it is possible to reliably judge whether there is an accident in the power system or whether the power system is in the inrush state. There is an effect that can be.

According to the present invention, when the attenuation rate of the DC component contained in the differential current is larger than the maximum attenuation rate of the DC component contained in the inrush current, it is included in the differential current. Since it is configured to judge that the attenuation rate of the direct current component that is out of the specified range, it is possible to reliably judge whether there is an accident in the power system or whether the power system is in the inrush state. There is an effect that can be.

According to the present invention, the transformer is removed from the power system on condition that the content rate of the direct current component with respect to the fundamental wave component contained in the differential current derived by the current deriving means is equal to or less than a predetermined value. Since it is configured to cut off, there is an effect that the transformer can be surely cut off from the power system when an internal failure including a large amount of the second harmonic component (internal failure not including the DC component) occurs. .

[Brief description of drawings]

FIG. 1 is a system diagram showing a power system to which a ratio differential relay device according to a first embodiment of the present invention is applied.

FIG. 2 is a configuration diagram showing a ratio differential relay device according to a first embodiment of the present invention.

FIG. 3 is a waveform diagram illustrating an attenuation rate of a DC component included in a differential current.

FIG. 4 is a waveform diagram showing waveforms of various signals.

FIG. 5 is a table showing the output of each component under no load and under load.

FIG. 6 is a configuration diagram showing a ratio differential relay device according to a second embodiment of the present invention.

FIG. 7 is a waveform diagram illustrating an attenuation rate of a DC component included in a differential current.

FIG. 8 is a waveform diagram showing waveforms of various signals.

FIG. 9 is a table showing the output of each component under no load and under load.

FIG. 10 is a configuration diagram showing a ratio differential relay device according to a third embodiment of the present invention.

FIG. 11 is a table showing the output of each component under no load and under load.

FIG. 12 is a system diagram showing a power system to which a conventional ratio differential relay device is applied.

FIG. 13 is a configuration diagram showing a conventional ratio differential relay device.

FIG. 14 is a table showing the output of each component under no load and under load.

[Explanation of symbols]

1 transformer, 2, 3 circuit breaker, 4, 5 current transformer, 11
Suppressing current deriving device (current deriving device), 12 Differential current deriving device (current deriving device), 13 Ratio differential device (ratio differential device), 20 Ratio differential relay device, 32 DC deriving device (attenuation rate determination) Means), 33 high change rate detector (attenuation rate determination means), 34 low change rate detector (attenuation rate determination means), 35
OR circuit (attenuation rate determination means), 36 AND circuit (control means), 37 High change rate detector (attenuation rate determination means), 38 Low change rate detector (attenuation rate determination means), 39
AND circuit (attenuation rate determination means), 40 inhibit circuit (control means), 41 filter (content rate determination means), 42 content rate detector (content rate determination means), 43
AND circuit (attenuation rate determination means, content rate determination means), 44
Inhibit circuit (control means).

Claims (4)

[Claims] 1. A current derivation means for deriving a suppression current and a differential current from a primary current and a secondary current of a transformer, and a suppression current and a differential current derived by the current derivation means satisfy a predetermined relationship. Ratio differential means for outputting a trip signal, and attenuation rate determination means for determining whether or not the attenuation rate of the DC component contained in the differential current derived by the current derivation means deviates from a predetermined range. A control means for shutting off the transformer from the power system when a trip signal is output from the ratio differential means when the attenuation rate determination means determines that the attenuation rate of the DC component is out of a predetermined range. Ratio differential relay with and. 2. The attenuation factor determining means includes the DC component included in the differential current when the attenuation factor of the DC component is smaller than the minimum attenuation factor of the DC component included in the inrush current. 2. The ratio differential relay device according to claim 1, wherein it is determined that the attenuation rate of the DC component that is present exceeds a predetermined range. 3. The attenuation rate determining means includes the DC component included in the differential current when the attenuation rate of the DC component is larger than the maximum attenuation rate of the DC component included in the inrush current. 2. The ratio differential relay device according to claim 1, wherein it is determined that the attenuation rate of the DC component that is present exceeds a predetermined range. 4. A content rate determining means for determining whether the content rate of the direct current component with respect to the fundamental wave component contained in the differential current derived by the current deriving means is equal to or more than a predetermined value, and the control means is provided. When the content rate determining means determines that the content rate of the direct current component with respect to the fundamental wave component is equal to or more than a predetermined value, the transformer is not shut off from the power system. The ratio differential relay according to any one of 1.