JPH0622440A - Ratio differential relay for transformer protection - Google Patents

Abstract

PURPOSE:To obtain a ratio differential relay for transformer protection in which a discrimination can be made accurately between internal fault current and excitation surge current when a transformer is thrown into a system by determining ' the content of second harmonic in the basic wave of excitation surge current accurately. CONSTITUTION:Only basic wave and second harmonic are passed through first to third filters 7-13 and subtractors 14, 15. A comparator 16 then calculates the content of second harmonic with respect to the basic wave thus making a decision whether it is an excitation surge current or not.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformer protection ratio differential relay used for transformer and bus protection.

[0002]

2. Description of the Related Art FIG. 3 shows, for example, JP-A-53-111451.
It is a circuit diagram which shows the conventional ratio differential relay with a 2nd harmonic suppression shown by the publication, 21 is a current transformer which inputs the difference current of the primary side electric current of a transformer, and a secondary side electric current. A differential circuit (hereinafter referred to as a CT differential circuit), 22 is an input transformer, and 23 is a second harmonic blocking filter composed of an inductance and a capacitor. 24a is an operating coil,
Reference numeral 24b is a suppression coil, 24 is a relay circuit composed of an operating coil 24a and a suppression coil 24b, and 25 is a second harmonic pass filter with fundamental wave blocking.

In general, when a transformer is put into a system, an exciting inrush current of ten times the rated current flows through the winding of the transformer. Since this exciting inrush current is similar to the internal fault current that flows when an internal fault occurs inside the transformer, it is possible that the differential relay may be mistaken for an internal fault and malfunction. Therefore, as in the device shown in FIG. 3, due to the difference in the content ratio of the second harmonic with respect to the fundamental wave of the exciting inrush current and the internal fault current (the internal fault current is about 6%, the exciting inrush current Is about 15 to 20%), and a device for determining whether it is an internal fault current or an exciting inrush current is considered.

Next, the operation will be described. When the internal fault current or the exciting inrush current is input to the CT differential circuit 21, the DC component in these differential currents is removed by the input transformer 22. After that, the component excluding the second harmonic is passed by the second harmonic blocking filter 23 and flows into the operating coil 24a. On the other hand, the second harmonic pass filter with fundamental wave blocker 25 blocks the fundamental wave in the differential current, passes higher harmonic components higher than the second harmonic wave, and passes them to the suppression coil 24b. From the current flowing through the operating coil 24a and the current flowing through the suppression coil 24b, the content rate of the second harmonic with respect to the fundamental wave is obtained, and it is determined from the content rate whether it is an internal fault current or an exciting inrush current. If it was judged to be an accident current, it tripped.

[0005]

Since the conventional ratio differential relay with second harmonic suppression is configured as described above, the normal calculation method of the content ratio of the second harmonic is (second harmonic). (Wave) / (fundamental wave) = (content of second harmonic), but the second case when a transformer is actually put into the system
For the calculation of the harmonic content, the generated harmonic components should be included and calculated as (2nd harmonic + higher harmonics of 3rd harmonic or higher) / (fundamental wave + 3rd harmonic or higher) In some cases, the calculation is performed for higher harmonics, which deteriorates the accuracy of the content rate calculation for the second harmonic, resulting in malfunction. For example, the content rate of the higher harmonics higher than the third harmonic to the fundamental wave is 20
%, Assuming that the content ratio of the second harmonic with respect to the fundamental wave is 10%, it should be actually 10%, but {(10% + 20
%) / (100% + 20%)} × 100 = 25%, and there was a problem that it was not possible to accurately determine whether it was an internal fault current or an exciting inrush current.

The present invention has been made to solve the above problems, and when a transformer is put into a system,
The purpose of the present invention is to obtain a transformer differential ratio relay that can accurately determine the content rate of the second harmonic with respect to the fundamental wave contained in the excitation inrush current and can accurately determine whether it is an internal fault current or an excitation inrush current. .

[0007]

SUMMARY OF THE INVENTION A transformer protection ratio differential relay according to the present invention is an internal accident judging circuit for judging whether or not an internal accident occurs based on a maximum current and a differential current from a current deriving circuit, and a difference between them. A first filter that passes the fundamental wave of the electric current, a second filter that passes only higher harmonics of the second harmonic or higher of the difference current, and a higher filter of the third harmonic or higher of the difference current A third filter that passes only harmonics and a first filter that outputs only the fundamental wave by subtracting higher-order higher harmonics than the second harmonic that has passed through the second filter from the current component that has passed through the first filter The subtractor and the higher harmonics of the second harmonic or higher that have passed through the second filter subtract the higher harmonics of the third harmonic or higher that have passed through the third filter, and only the second harmonic is output. Second subtractor and its fundamental and second harmonics Of the second harmonic with respect to the fundamental wave is calculated, and the comparison circuit that determines whether the current is an inrush current based on the calculated content rate, and the internal accident determination circuit determines that the current is an internal accident, and the comparison circuit determines the excitation inrush current. If it is determined that it is not, it is determined that it is an internal accident, and an AND circuit that outputs the result is provided.

[0008]

In the transformer differential ratio relay according to the present invention, the internal fault judgment circuit judges whether or not there is an internal fault based on the maximum current and the difference current of the primary side current and the secondary side current of the transformer. In addition, the first subtractor subtracts the higher harmonics of the second harmonic or higher of the difference current that has passed through the second filter from the current component of the difference current that has passed through the first filter to obtain the fundamental wave. Only output to the comparison circuit. Also,
The second subtractor subtracts the higher harmonics of the third harmonic or higher passed through the third filter from the higher harmonics of the second harmonic or higher passed through the second filter to obtain the second harmonic. Only the wave is output to the comparison circuit. Therefore, the calculation of the content rate of the second harmonic with respect to the fundamental wave by the comparison circuit is accurately performed,
Accurately determines whether or not the current is an inrush current. further,
When the AND circuit determines that the internal accident determination circuit is an internal accident and the comparison circuit determines that the inrush current is not an exciting current, it is determined to be an internal accident and is output.

[0009]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1a denotes a current transformer differential circuit (hereinafter referred to as CT differential circuit) which inputs a primary side current from a current transformer (not shown; hereinafter referred to as CT) provided on the primary winding side of a transformer. Reference numeral 1b is a CT differential circuit for inputting a secondary side current from a CT provided on the secondary winding side of the transformer. 2a, 2b
Is an input transformer for adjusting the primary side current and the secondary side current of the transformer input to the CT differential circuits 1a and 1b according to the turns ratio of the transformer, and 3 is an input transformer. 2a,
The suppression derivation circuit 4 receives the current from 2b and derives its maximum current, and 4 is a differential derivation circuit that similarly receives the currents from the input transformers 2a and 2b and derives the difference current between them. The differential derivation circuit 4 constitutes a current derivation circuit. Reference numeral 5 denotes a ratio differential detection circuit (internal accident determination circuit) that determines whether the internal accident or the external accident is based on the maximum current and the differential current, and sends an output signal when the internal accident occurs.

Reference numeral 6 is an exciting inrush current detection circuit for detecting an exciting inrush current when a transformer is applied to the system, and 7 is a bandpass filter (first filter) 8 having a fundamental frequency If ₁ as a resonance frequency. A band reject filter for blocking the fundamental wave If ₁ , 9 is a band pass filter having a second harmonic as a resonance frequency, and 10 is a first gain circuit for adjusting the gain of the current component passing through the band pass filter 9, The band reject filter 8, the band pass filter 9, and the first gain circuit 10 constitute a second filter. Reference numeral 11 is a band reject filter that blocks the second harmonic wave If ₂ , 12 is a band pass filter that has the third harmonic wave If ₃ as a resonance frequency, and 13 is a band pass filter 1.
2 is a second gain circuit that adjusts the gain of the current component that has passed through 2, and the bandpass filter 12, the band reject filters 8 and 11, and the second gain circuit 13 make a third gain circuit.
Configure the filter for.

Reference numeral 14 is a first subtractor for subtracting the current component passing through the first gain circuit 10 from the current component passing through the bandpass filter 7, and 15 is the first subtractor from the current component passing through the first gain circuit 10. A second subtractor for subtracting the current component that has passed through the second gain circuit 13, and 16 is a second harmonic wave with respect to the fundamental wave If ₁ from the current component input from the first subtractor 14 and the second subtractor 15. This is a comparator (comparison circuit) that calculates the content rate of If ₂ and determines whether the current is an inrush current based on the calculated content rate.

Reference numeral 17 is an inhibit circuit (logical product circuit) between the input signal from the ratio differential detection circuit 5 and the input signal from the comparison circuit 16, and 18 is an internal serious accident due to a difference current from the differential derivation circuit 4. If it is an internal serious accident, it is an overcurrent relay that sends an output signal, and 19 is an OR circuit.

Next, the operation will be described. The circuit diagram shown in FIG. 1 is for protecting one of three phases of a two-winding transformer. The primary side current and the secondary side current are input from the CTs provided on the primary winding side and the secondary winding side of the transformer to the CT differential circuits 1a and 1b, and the input transformers 2a and 2 are input.
By b, the primary side current and the secondary side current are adjusted according to the turns ratio of the transformer so that they become equal. Further, the primary side current and the secondary side current of the transformer include a direct current component I, a fundamental wave If ₁ , a second harmonic wave If ₂ , a third harmonic wave If ₃ , ....
, If _n as a component flow, the DC component I of the current is removed by the input transformers 2a and 2b.

The suppression derivation circuit 3 and the differential derivation circuit 4 receive the currents from the input transformers 2a and 2b, derive the maximum current and the difference current, and output them to the ratio differential detection circuit 5. The ratio differential detection circuit 5 determines whether it is an internal accident or an external accident and a normal state based on the maximum current and the difference current, and when it is an internal accident, the inhibit circuit 1
The judgment output of internal accident is output to 7.

In the exciting inrush current detection circuit 6 for detecting the exciting inrush current, the bandpass filter 7 for inputting the output current of the differential derivation circuit 4 and passing the fundamental wave If ₁ has the above-mentioned current (fundamental wave If ₁ , Second harmonic If ₂ , third harmonic I
f _3, ···, If _n) from the gain of the frequency characteristics of the band-pass filter _{7 (If a1, If a2,} If a3, ···, I
a current as a component (f _an ). Further, the band reject filter 8 blocks the fundamental wave If _1, and the gain of the frequency characteristic of the band reject filter 8 becomes (If _b2 , I
f _b3 , ..., If _bn ) pass a current. Similarly, the band-pass filter 9 that passes the second harmonic passes the current having the (If _c2 , If _c3 , ..., If _cn ) component, and the gain adjustment of the first gain circuit 10 causes (I _c
, af _a2 , If _a3 , ..., If _an ).
Then, the bandpass filter 7 is processed by the first subtractor 14.
(If _a1 , If _a2 , If _a3 , ..., If _an )
The current as the component (If _a2 , If _a3 , ..., If _an ) that has passed through the first gain circuit 10 is subtracted from the current as the component to obtain only the fundamental wave If _a1 .

The second harmonic the If ₂ band-reject filter 11 to prevent the passing through the band-reject filter _{8 (If b2, If b3,} ···, If bn) from current to component (If _d3, ··· , If _dn ), and the bandpass filter 12 passes (If _e3 , ..., If _en ), and the gain adjustment of the second gain circuit 13 causes (I
f _a3 , ..., If _an ) current is used as the component. afterwards,
The second subtractor 15 passes through the first gain circuit 10 and passes through the second gain circuit 13 (If _a2 , If _a3 , ..., If _an ) from the current (If _a3 , ... .., I
subtracting the current to f _an,) component, to obtain only the second harmonic the If _2.

The comparator 16 calculates the content rate of the second harmonic with respect to the fundamental wave from the fundamental wave If _a1 input from the first subtractor 14 and the second harmonic wave If _a2 input from the second subtractor 15. Based on the calculated content rate, it is determined whether the current is an exciting inrush current, and if it is the exciting inrush current, a determination output is made. Further, the inhibit circuit 17 determines that the internal fault occurs only when the ratio differential detection circuit 5 determines that it is an internal fault and the comparator 16 determines that it is not the exciting inrush current, and outputs an output signal. Moreover, the overcurrent relay 1 which is judged by the OR circuit 19 to be an internal serious accident due to the difference current from the differential derivation circuit 4
Trip output is performed with the logical sum of 8 output signals.

Example 2. In the first embodiment described above, the case where the third harmonic or higher harmonics cannot be ignored has been described. However, when the harmonics can be ignored depending on the system, the exciting inrush current detection circuit 20 for detecting the exciting inrush current can be simplified as shown in FIG. Good.
In this case, from the configuration of the first embodiment, the band reject filter 11, the band pass filter 12, the second gain circuit 1
3, the second subtractor 15 can be omitted.

In the above embodiment, the first filter,
Although the band-pass filter and the band-reject filter are used as the second filter and the third filter, for example, a low-pass filter may be used in place of the band-pass filter and a high-pass filter may be used in place of the band-reject filter.

Further, in the above-mentioned embodiment, it is judged whether or not the inrush current is the exciting current based on the content rate of the second harmonic with respect to the fundamental wave. However, when it is easier to judge other harmonics depending on the system, for example, , Other harmonics with respect to the fundamental wave, or other harmonics with respect to other harmonics.

[0021]

As described above, according to the present invention, only the fundamental wave and the second harmonic wave are passed by the first to third filters, and the fundamental wave and the second harmonic wave are changed from the fundamental wave to the fundamental wave. Since the content ratio of the second harmonic is calculated and it is determined whether or not it is the exciting inrush current, when the transformer is put into the system, the second harmonic with respect to the fundamental wave included in the exciting inrush current. The content rate of is accurately obtained, and it is possible to accurately determine the internal fault current and the excitation inrush current.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a ratio differential relay for protecting a transformer according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a transformer protection ratio differential relay according to another embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional ratio differential relay with second harmonic suppression.

[Explanation of symbols]

3 Suppression derivation circuit (current derivation circuit) 4 Differential derivation circuit (current derivation circuit) 5 Ratio differential detection circuit (internal accident determination circuit) 7 Bandpass filter (first filter) 8 Band reject filter (second filter) , Third
Filter) 9 bandpass filter (second filter) 10 first gain circuit (second filter) 11 band reject filter (third filter) 12 bandpass filter (third filter) 13 second gain Circuit (third filter) 14 First subtractor 15 Second subtractor 16 Comparator (comparator circuit) 17 Inhibit circuit (logical product circuit)

Claims (1)

[Claims] 1. A current derivation for inputting a primary side current and a secondary side current of the transformer, which are evenly adjusted according to the turns ratio of the transformer, deriving a maximum current thereof and deriving a difference current thereof. A circuit, an internal accident determination circuit that determines whether there is an internal accident based on the maximum current and the difference current, a first filter that allows the fundamental wave of the difference current to pass, and a second harmonic higher than the second current of the difference current. A second filter that passes only the next higher harmonic wave, a third filter that passes only higher-order higher harmonic waves than the third higher harmonic wave of the difference current, and a second component from the current component that has passed the first filter. First subtractor that subtracts the higher harmonics of the second harmonic or higher that have passed through the filter and outputs only the fundamental wave, and the higher harmonics of the second harmonic or higher that has passed through the second filter Higher than the 3rd harmonic passing through the 3rd filter from Second subtractor for subtracting the second harmonic of the above and outputting only the second harmonic, and the second harmonic with respect to the fundamental wave from the fundamental wave and the second harmonic input from the first subtractor and the second subtractor A comparison circuit that determines the content rate of the wave and determines whether it is an exciting inrush current based on the calculated content rate, and if the comparison circuit determines that the internal failure determination circuit determines that it is an internal failure and is not an exciting inrush current, A ratio differential relay for transformer protection, which includes an AND circuit that determines that an internal accident has occurred and outputs the result.