KR20060111820A - Estimation method of the winding current of wye-delta or delta-wye transformer - Google Patents

Abstract

A method of estimating winding current of a wye-delta or delta-wye transformer is provided to accurately estimate winding current by using an induced voltage, which is calculated at a wye winding portion. A variable(sat_ind) is set to 0 before saturation(S15). Voltages and currents of primary and secondary windings are measured. Induced voltages(eA,eB,eC) at the primary winding are calculated by using the primary voltage and current, and a core loss current(icA) is measured by using a core loss resistance(S20). A non-circulating current and a circulating current(iDelta) are calculated(S22), and a winding current(iab) is calculated by using the non-circulating and circulating currents(S25). When it is determined that a transformer is not saturated(S30), a compensation difference current is calculated(S32). When the compensation difference current is smaller than a threshold value, the transformer is determined to operate normally(S34), and whether an error occurred is determined(S45) by using the compensation difference current. When the compensation difference current is greater than the threshold value, a magnetic flux at that timing is defined as an initial value(S34).

Description

ESTIMATION METHOD OF THE WINDING CURRENT OF WYE-DELTA OR DELTA-WYE TRANSFORMER}

FIG. 1A shows a three phase Y-delta (Y-Δ) transformer 40, the equivalent circuit of which is shown in FIG. 1B.

Figure 2 shows a preferred embodiment of the relay method to which the present invention is applied.

Figure 3 shows the process of obtaining the initial value of the magnetic flux at the iron core saturation through the magnetization curve.

4 shows a process of obtaining a magnetizing current from magnetic flux after iron core saturation.

5 shows a model used for the verification of the effects of the present invention.

6 is a test result in case 1, and shows a comparison of the case where the prior art (left) is applied with the case where the present invention is applied (right).

7 is a test result in case 2, and shows a comparison of the case of applying the prior art (left) and the case of applying the present invention (right).

8 is a test result in the case of Example 3, and shows the case of applying the prior art (left) and the case of applying the present invention (right).

FIG. 9 shows a three-phase delta-y (Δ-Y) transformer 50, the equivalent circuit of which is shown in FIG. 9b.

The present invention relates to a method for estimating a transformer winding current of a w-delta or delta-wy method, and more particularly, to provide a method of estimating a delta winding current using an induced voltage calculated on the wye connection side. will be.

The transformer protection relay shall be able to distinguish between other operating conditions and internal accidents. As the relay method to protect the transformer from internal accidents, the current differential method has been mainly used as in the case of generators and transmission lines. Here, the current differential method is a method of determining a difference between currents flowing through both terminals of a transformer (hereinafter, referred to as 'differential current' or 'differential current'), and determining an internal accident when the value becomes more than a certain value. Current differential relays can distinguish between external and internal accidents, but are likely to malfunction in the case of magnetic inrush or over-excitation. In order to prevent such a malfunction, when the excitation current is very large, the suppression or blocking signal estimated by the current or the magnetic flux value is used to stabilize the relay.

Conventional suppression or suppression methods are mainly based on harmonic components in the operating current. Einvall and Linders proposed a complex suppression function based on two- and five-harmonic components (CH Einvall, and JRLinders, "A Three-phase Differential Relay for Transformer Protection," IEEE Trans.on PAS , vol. 94, no 6, pp. 1971-1980, 1975). In this method, since the harmonic components are included in the primary side current during excitation, the differential current is the operating current for the operation of the relay, and the two harmonic components are used as the suppression current to distinguish between the internal accident and the excitation rush. In order to distinguish between internal accidents and over-excitation phenomena, 5 harmonic components are used as suppression currents. However, even with this method, the magnitude of each harmonic component may vary according to the residual magnetic flux in the iron core or the size of the iron core, and when the conditions such as the system condition and the transformer core material are changed, a large amount of two harmonic components may occur even during an internal accident. Due to the fact that it can be included, there is a limitation that it is practically difficult to distinguish between precise internal accidents and invasion of women. In addition, harmonic components exist in the transient period after the occurrence of an internal accident. Therefore, it takes some time until the harmonic component becomes zero, so it is very difficult to quickly determine the accident. In addition, the suppression and blocking method using such harmonics can prevent a certain amount of malfunction during excitation or over-excitation. However, when there are few harmonic components in the differential current, the malfunction cannot be prevented. As a result, this method can guarantee some stability during inrush or overexcitation, but there is a problem in that an internal accident causes a delay in relay operation time.

Phadeke and Thorp have also proposed a flux-suppressing current differential relay in which core flux is calculated using primary voltage values (AG Phadke, and JS Thorp, "A New Computer-Based Flux-Restrained Current-Differential"). Relay for Power Transformer Protection, " IEEE Trans. On PAS , vol. 102, no. 11, pp. 3624-3629). This technique assumes that in the case of excitation, the magnetization current and the magnetic flux follow the magnetization curve in the opening of the core, and in the case of an internal accident, the magnetic flux has a small slope value and is proportional to the magnetization current. However, due to the residual magnetic flux, the relationship between the magnetization current and the magnetic flux deviates from the magnetization curve described above. The above method calculates the slope of the magnetization curve, decrementing the counter when the slope is large, and increasing the counter when the slope is small. When the counter crosses the set point, it activates the trip signal. This technique assumes that the primary current is the magnetizing current. However, this method has a limitation in that it is difficult to apply in case of excitation to overload transformer or over-excitation.

In addition to the methods described above, numerical methods have been proposed that use the electromagnetic relationship of transformers (ie, transformer models) (MS Sachdev, TS Sidhu, and HC Wood, "A Digital Relaying Algorithm for Detecting Transformer Winding Faults,"). IEEE Trans.on PWRD , vol. 4, no. 3, pp. 16381648, 1989, YC Kang, BE Lee, SH Kang, and PA Crossley, "Transformer protection based on the increment of the flux linkages," IEE Proc. Gener Trans.Distr . , Vol. 151, no. 4, pp. 281289, May 2000). However, since this method requires both current and voltage data values across the transformer, a large amount of data must be measured, and there is a limitation that it is not suitable for a high-speed protection algorithm because of a large amount of calculation.

As mentioned above, the current differential relay operates by comparing the magnitudes of the primary and secondary winding currents with each other. However, in the case of excitation or over-excitation, the relay has a malfunction because the excitation current increases. Therefore, the present inventors estimate the excitation current including the iron loss current and the magnetizing current through the magnetization curve in the case of the Y-Wye transformer, thereby ensuring high accuracy while enabling rapid operation in the event of an internal accident, In particular, there has been proposed a compensated current differential relaying method that enables reliable protection even through the accurate estimation of the excitation current even in the presence of residual magnetic flux (refer to Korean Patent Application No. 10-2004-32762).

The relay by this method uses the same suppression current as the relay of the prior art. The operating current, however, has the difference that the excitation current calculates the compensated differential current. Before the core saturates, the relay calculates the iron loss current and uses it to compensate the measured differential current.When the transformer enters the saturation state, the instantaneous compensation differential current is substituted into the magnetizing current to obtain the core magnetic flux at that moment. . The obtained core magnetic flux is used as an initial value to calculate how the magnetic flux changes with time after saturation, and is used to estimate the magnetization current through the magnetization curve. Through such a method, the relay can accurately correct an internal accident, an inrush and an overexcitation by preventing a corrected differential current compensated for iron loss and magnetization current, thereby preventing malfunction.

However, the proposed method is for the Y-Wye transformer, which has a limitation in that it cannot be applied to the W-Delta or delta-Wy transformer because the winding current value is essential data. Unlike the W-Wye transformer, which is a structure in which the line current measured on the primary side and the secondary side is equal to the winding current, in the W-delta or W-delta transformer, the line current measured on the delta winding side shows the winding current. Because there is not. Therefore, in order to apply the above method to the wye-delta transformer, there is a problem in that the winding current of the secondary side of the delta connection must be known.

In addition, in order to actually measure the delta winding current, a method of installing a current transformer in the transformer is also used. However, since the current transformer must be installed in the transformer, the size of the transformer must be very large, resulting in an increase in the price of the transformer. do.

The delta winding current is divided into two components, the cyclic component and the acyclic component. The latter can be estimated directly from the line current, but the former is not. Therefore, in order to apply a modified differential current relay for W-delta or delta-W transformer protection, it is necessary to estimate the cyclic component of the delta winding current.

The present invention is to solve such a problem, to provide a method for estimating the delta winding current in the case of a w-delta transformer or a delta-y transformer.

In order to achieve this object, a method for estimating the delta winding current of a w-delta or a delta-w transformer according to a feature of the present invention includes a voltage and a line current on the wire connection side of each phase and a line voltage on the delta connection side. And sampling the line current; Obtaining an induced voltage of the wire connection side using the wire phase voltage and the wire current; Obtaining a cyclic component of a delta winding current using the wire connection side induced voltage; Obtaining a delta winding current from the delta winding current circulation component and the delta side line current.

인 관계를 이용한다.Preferably, the step of obtaining the induced wire induced voltage,

Use relationship

의 관계를 이용하며, 여기서 상기 좌변의 값은, 상기 미리 구하여진 와이 결선측 유기 전압으로부터 권선비를 고려하여 추정하는 것이 가능하다.And the step of obtaining the delta winding current circulating current component,

Where the value of the left side can be estimated in consideration of the winding ratio from the obtained wire connection side induced voltage.

및

의 관계를 이용하여 델타 권선 전류의 추정이 가능하다.In the step of obtaining the delta winding current, since the delta connection,

And

Using the relationship of, we can estimate the delta winding current.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1. Three-phase Y-delta (Y- △) transformer:

FIG. 1A shows a three-phase Y-delta (Y-Δ) transformer 40, the equivalent circuit of which is shown in FIG. 1B. Here, the symbols used in the drawings are as follows.

v _A , v _B , v _C : primary terminal voltage of each phase;

i _A , i _B , i _C : primary current of each phase;

v _ab , v _bc , v _ca : secondary line voltage;

i _a , i _b , i _c : secondary line current;

i _ab , i _bc , i _ca : secondary winding current;

i _pa , i _pb , i _pc : acyclic current component;

i _Δ : cyclic current component;

R _A , R _B , R _C : primary winding resistance;

L _{l A} , L _{l B} , L _{l C} : primary leakage inductance;

R _a , R _b , R _c : secondary winding resistance;

L _{l a} , L _{l b} , L _{l c} : secondary leakage inductance;

e _A , e _B , e _C : primary induced voltage;

e _ab , e _bc , e _ca : secondary induced voltage;

R _{c A} , R _{c B} , R _{c C} : iron loss resistance;

L _mA , L _{m B} , L _{m C} : magnetization inductance;

i _{e A} , i _{e B} , i _{e C} : excitation current;

i _{c A} , i _{c B} , i _{c C} : iron loss current;

i _{m A} , i _{m B} , i _{m C} : magnetization current;

N ₁ , N ₂ : primary and secondary windings

_{Here, R A ~R B ~R C =} R 1, L lA ~L lB ~L lC = L l 1, R ab ~R bc ~R ca = R 2, and L = L _lab ~L _lbc ~L _lca Assume _{l 2} . At this time, if there is no internal accident, the primary voltage and the secondary voltage may be represented by Equations 1 and 2, respectively.

In the A phase of such a w-delta transformer, in the current differential relay method of the prior art, the magnitude I _dA of the difference current fundamental wave is calculated as in Equation 3 below.

Where a = N ₂ / N ₁ , that is, the turns ratio. In addition, the fundamental wave component I _rA of the suppression current for suppressing relay operation is calculated as in Equation 4.

In addition, the operating characteristics of the current differential relay is shown in equation (5).

I _offset is the minimum current setpoint for the operation of the relay (e.g. 15A), and K is the sensitivity of the relay and can be set arbitrarily. The following data is data obtained by setting the sensitivity of the relay to 0.3.

In this prior art current differential relay method, the excitation current is not considered. Therefore, at the time of excitation or over-excitation, the difference current I _dA exceeds the threshold value, and the relay may malfunction. In the relay method of the present invention, the delta winding current is estimated in a Y-delta or a delta-Wy transformer, and applied to the method of the aforementioned patent application No. 10-2004-32762 for the Y-Wy transformer, The differential current compensated for the magnetization current is estimated.

In the schematic description of the relaying method proposed in Patent Application No. 10-2004-32762, first, the iron loss current is calculated from the iron loss resistance and the induced voltage, and the magnetized difference current compensated for the iron loss current at the initial saturation start of the iron core. Substituting the curve, the magnetic flux at that moment is calculated, and the magnetic flux at every instant after saturation is obtained by using this magnetic flux as the initial value. The magnetic flux calculated in this way is substituted into the corresponding section of the magnetization curve to estimate the magnetization current corresponding to the magnetic flux. Subsequently, the magnetized current and iron loss current obtained as described above are subtracted from the primary current, and the corrected differential current obtained by subtracting the secondary current multiplied by the turns ratio is obtained, and the internal accident is determined based on this.

However, the method proposed in the above-mentioned patent application No. 10-2004-32762 is for the Y-Wye transformer, there is a problem that can not be applied to the Y-delta transformer as it is. As shown in Fig. 1A, the line currents i _a , i _b , i _c on the secondary side of the phase current delta connection are different from the winding currents i _ab , i _bc and i _ca , and the excitation inrush and To consider the problem of the excitation, the winding currents i _ab , i _bc and i _ca have practical significance. Therefore, as in the prior art W-delta transformer relay method, the relay method using the differential current based on the measurement of the line currents i _a , i _b , i _c of Equation 3 above is used in the inrush or over-excitation time. Cannot guarantee accuracy.

Therefore, in the present invention, the differential current of the w-delta transformer is defined using the following equation.

To find the delta winding current i _ab , follow the steps below.

The secondary winding current may be divided into two components as shown in Equation 7 below. That is, it is a cyclic component and an acyclic component.

It is known that the acyclic component can be represented by the following Equation (8).

Therefore, when the circulating component is obtained, the winding current can be obtained. In the present invention, the following algorithm is proposed to obtain a circulating current.

First, by the above Equation 1 expressing the wire connection side, the following equation 9 can be obtained.

In addition, by modifying Equation 2 representing the delta connection side, a relationship as shown in Equation 10 below may be obtained.

_{Here, R A ~R B ~R C =} R 1, L lA ~L lB ~L lC = L l 1, R ab ~R bc ~R ca = R 2, and L = L _lab ~L _lbc ~L _lca Assuming _{l 2} , we obtain

)를 고려하여, 상술한 수학식 9에 의해 구해지는 1차 유기 전압으로부터 추정이 가능하다. 따라서 순환 전류(i_△)는 수학식 11의 미분 방정식의 수치 해석에 의하여 얻어질 수 있다(예를 들어, backward Euler method 등의 방법이 바람직하다). 위와 같이 비순환 전류와 순환 전류를 구하면, 수학식 7을 통해 권선 전류를 추정할 수 있게 된다.The left side of Equation 11 above is the turn ratio of the primary side and the secondary side (

), It is possible to estimate from the primary induced voltage obtained by the above equation (9). Therefore, the circulating current i _Δ can be obtained by numerical analysis of the differential equation of Equation 11 (for example, a method such as the backward Euler method is preferable). When the acyclic current and the circulating current are obtained as described above, the winding current can be estimated through Equation 7.

The circulating current i _Δ can also be obtained as follows. The relation of the A phase of Equation 4 is summarized as follows for the first and second induced voltages.

By substituting Equations 7 and 8, the following relation is obtained.

의 관계가 성립한다. 따라서 수학식 13의 좌변은 1차 A상의 유기전압 e_A(t)와 변압기 1, 2차 권선비를 이용하여 구할 수 있기 때문에, 순환전류(i_△)는 수학식 13으로부터 구할 수 있다. If no internal accident occurs, between the induced voltages of each of the primary and secondary phases.

The relationship is established. Therefore, since the left side of the equation (13) can be obtained using the induced voltage e _A (t) of the primary A phase and the transformer primary and secondary winding ratios, the circulating current i _Δ can be obtained from the equation (13).

2 shows a preferred embodiment in which the present invention is applied to the relaying method of No. 10-2004-32762. As shown, in the state before saturation, the sat_ind variable is first set to 0 (S15).

The primary voltage and current, the secondary voltage and the line current are respectively measured (S15). Through the measured primary voltage and current, the primary induced voltages (e _A , e _B , e _C ) are obtained according to Equation 9 above, and the iron loss current i _cA is obtained using the iron loss resistance values (S20). . Here, it is assumed that the iron loss current i _cA satisfies the following relationship with the iron loss resistance as on the equivalent circuit shown in FIG. 1B. Iron loss resistance can be provided by measurement.

).In addition, the acyclic current and the circulating current i _Δ are obtained according to Equations 8 and 11, respectively (S22), and the winding current i _ab is obtained by using Equation 7 using these values (S25). If it is determined that the sat-ind value is before saturation (that is, sat_ind = 0) (S30), a compensation difference current is obtained by using Equation 6 (S32). Here, before saturation, the magnetizing current (i _mA ) is very small and therefore ignored (i.e.

).

If the obtained compensation difference current value is less than or equal to a predetermined threshold value, since it is a normal operating state before saturation, the process proceeds to the next step (S34), and the accident determination is performed based on the obtained compensation difference current value (S45). If the compensation difference current value exceeds a predetermined threshold value, it is determined as a saturation moment and the magnetic flux at that moment is defined as an initial value (S34). 3 schematically shows a magnetization curve, and assumes that the compensation difference current value at the instant when the compensation difference current value exceeds the threshold is the magnetization current. Substituting the compensating differential current value (i _m ) at the instant of exceeding the threshold value into the data of the magnetization curve, the magnetic flux (λ _A (t 0)) at the saturation start is obtained, and sat-ind is 1 to indicate that the saturation is started. (S37).

The threshold for determining the instant of saturation start is preferably selected to be greater than the saturation point current value on the magnetization curve of the iron core. For example, a value that is twice the saturation point current can be used as the threshold.

From the next sampling moment, since the start of saturation (sat_ind = 1), the excitation current becomes very large and cannot be ignored. Therefore, using the excitation current value obtained using Equation 9 above and the initial magnetic flux value obtained above, the instantaneous magnetic flux value λ _A is obtained as follows.

The magnetization current i _mA at that moment is estimated using the data of the magnetization curve as shown in FIG. 4 using the magnetic flux value λ _A at that moment obtained above (S35). By substituting the magnetization current obtained through the above process into Equation 6, it is possible to obtain the compensation difference current compensated for the iron loss current and the magnetization current, and it is possible to accurately determine the accident without the malfunction of the relay even during inrush or over-excitation. .

In order to verify the effectiveness of the proposed method, after modeling the Y-delta transformer using EMTP, after generating excitation, internal accident, overexcitation, and external accident data under various conditions, existing current The results were compared with the differential relay method.

The model of the system used for verification is shown in FIG. 5. Here, two-phase three-phase W-delta transformers (154kV / 13kV, 55 MVA) were modeled using EMTP, and the sampling rate was 64 samples per cycle.

Type-96 devices were used to model the hysteresis characteristics of transformer cores, and saturation points (40A, 334Vs) were used for HYSDAT. The low pass filter designed a Butterworth secondary filter with a stopband cutoff frequency of 1920 Hz, allowing all voltages and currents to pass through. The threshold for determining the saturation start time was selected as twice the saturation point current, that is, 80A.

The test results are shown only for phase A. The effects of the present invention were verified by comparing the current differential relay method of the prior art and the method of the present invention in the case of excitation, internal accident, overexcitation, external accident, and the like.

In case of woman rush

Since the magnitude of the excitation current varies with the input phase angle, the residual magnetic flux, and the load, various excitation intrusions are simulated by changing three parameters.

Case 1: input phase angle 0 degree, residual flux 0%, no load

FIG. 6 compares the results of the method of the present invention with the prior art current differential method (left) for Case 1 above. The transformer was turned on at 29.2 ms. In this case, since the input phase angle is 0 degrees, the iron core is severely saturated, and according to the conventional method, the relay enters the operating region (left side of FIG. 6), and a trip signal is generated at 5.4 ms after the input. However, in the method of the present invention, the saturation start instant was detected at 34.1 ms, and 347.7 Vs was calculated as the initial magnetic flux. From the next moment, λ ( t ) calculated using Equation 15 was substituted into the magnetization curve to magnetize the magnetization curve. The current i _mA was estimated to obtain a compensation differential current as shown in Equation 6. Since the value of the compensation differential current obtained is very small, the relay did not enter the operating area (right side of FIG. 6), and no trip signal occurred, so that the case of excitation incidence was accurately distinguished from the accident.

Case 2: input phase angle 0 degree, residual flux 80%, no load

Fig. 7 shows the results of applying the prior art current differential method (left) and the method (right) of the present invention to Example 2. Since the input phase angle is 0 degrees and the residual magnetic flux is 80%, the primary current becomes larger than in the case 1 above. Therefore, in the current differential method of the prior art, a high differential current of 2300 A is detected, the relay quickly enters the operating region, and a trip signal is generated at 3.1 ms after the input (left of FIG. 7). However, in the method of the present invention, the saturation start instant was detected at 31.5 ms, and the initial magnetic flux was calculated to be 342 Vs. Using the calculated iron loss current and the magnetizing current, the compensation difference current of Equation 6 was obtained. Since the value of the compensation difference current is very small, the relay did not enter the operating area (right side of FIG. 7), and the trip signal was Did not occur.

In case of internal accident

An internal accident was simulated on the A phase of the primary winding to compare and test the prior art method with the method of the present invention.

1) Case 3: Zero-degree ground fault 80% from neutral

8 shows the test results of the prior art current differential method (left) and the method (right) of the present invention for Example 3. FIG. The accident occurred on phase A of the primary winding at 29.2 ms. In the case of the prior art method, the relay enters the operating area at 2.8 ms after the occurrence of an accident, causing a trip signal (left of FIG. 8).

On the other hand, in the method of the present invention, the saturation start instant was detected at 30.2 ms, and the initial magnetic flux was calculated to be 346.0 Vs. Therefore, even when the method of the present invention is applied, a trip signal is generated at 2.8 ms after the occurrence of an accident, and thus the relay operation in the event of an accident is normally performed.

As described above, the method of the present invention not only can operate accurately regardless of the residual magnetic flux, but also eliminates the disadvantages of delaying the operation speed in the prior art method because no blocking or suppression signal is required. have.

2. Three-Phase Delta-Wye (△ -Y) Transformers:

The following describes a method of estimating a circulating current in the case of a three-phase delta-y transformer.

FIG. 9A shows a schematic circuit diagram of a three-phase delta-y transformer 50, and FIG. 9B shows an equivalent circuit thereof. Reference numerals used in the drawings and the following description are as follows.

v _AB , v _BC , v _CA : Primary terminal voltage of each phase

v _a , v _b , v _c : secondary terminal voltage of each phase

i _A , i _B , i _C : Primary line current of each phase

i _CA , i _BC , i _CA : Primary winding current of each phase

ia, ib, ic : secondary current of each phase

e _AB , e _BC , e _CA , e _a , e _b , e _c : Induced voltage of each of the primary and secondary phases

R _A , R _B , R _C , R _a , R _b , R _c : winding resistance of primary and secondary phase

L _lA , L _lB , L _lC , L _la , L _lb , L _lc : Leakage inductance of primary and secondary phases

R _cA , R _cB , R _cC : _Iron loss resistance of each phase

L _mA , L _mB , L _mc : Magnetization inductance of each phase

N ₁ , N ₂ : primary and secondary windings

i _eA , i _eB , i _eC : _Excitation current of each phase

i _cA , i _cB , i _cC , i _mA , i _mB , i _mC : _Iron loss current and magnetization current of each phase

The primary and secondary terminal voltages of each phase of the transformer at each moment are:

The primary winding currents i _AB ( t ) , i _BC ( t ) and i _CA ( t ) can be divided into two parts. One part is the non-circulating current component i _pA ( t ) , i _pB ( t ) , i _pC ( t ) and the other part is the circulating current component i _Δ ( t ). That is, it is represented as follows.

Here, the non-cyclic current component is represented as follows.

Substituting the estimated non-cyclic current component of Equation 19 into Equation 18 is as follows.

The induced voltage of the secondary angle phase can be obtained from Equation 21 above. Further, by adding three equations of Equation 16 and substituting Equation 20, the following relational expression can be obtained.

At this time, if the internal accident does not occur, the following relationship is always established between the induced voltages of the first and second phases.

Therefore, since the left side of the equation (22) can be obtained from the equation (21) using the relationship of the equation (23), the circulating current component i _Δ ( t ) can be obtained from the equation (22).

Alternatively, the circulating current component i _Δ ( t ) can also be obtained by the following method.

The equations for the A phase primary and secondary induced voltages of Equations 16 and 17 are summarized as follows.

Substituting the current value of Equation 20 into Equation 24 and arranging it is as follows.

If no internal accident has occurred, the relation of Equation 23 above always holds. Therefore, since the left side of the above Equation 25 can be known from the A phase induced voltage e _a (t) and the transformer primary and secondary winding ratios, that is, Equations 21 and 23, the circulating current component i _Δ ( t ) is You can get it using 25.

The winding current estimation method of the delta-y or the w-delta transformer according to the present invention can be modified and applied in various forms within the scope of the technical idea of the present invention and is not limited to the above preferred embodiment. The embodiments and drawings are merely for the purpose of describing the contents of the invention in detail, and are not intended to limit the scope of the technical idea of the invention, the present invention described above has a general knowledge in the technical field to which the present invention belongs Various substitutions, modifications, and changes are possible in the present invention without departing from the spirit of the present invention, but are not limited to the embodiments and the accompanying drawings, as well as the appended claims and equivalents. It should be judged including the scope.

According to the present invention, in the case of a wa-delta or a delta-w transformer, the current differential relay system for transformer protection can be accurately and precisely protected by estimating the delta winding current, and even in the presence of residual magnetic flux. Or a wide range of applications to various other electrical devices.

Claims (4)

In the relay method for the protection of the Y-delta or delta-Y transformer, Sampling the wye phase voltage and line current, the delta side line voltage and line current of each phase; Obtaining a Wai-side induced voltage using the Wei-side phase voltage and line current; Obtaining a cyclic component of a delta winding current using the wye-side induced voltage; Obtaining a delta winding current from the circulating component of the delta winding current and the delta line current. The method of claim 1, Obtaining the first induced voltage,

Using the relationship, where v _A , v _B , v _C : primary terminal voltage of each phase, i _A , i _B , i _C : primary current of each phase, v _ab , v _bc , v _ca : secondary line voltage, R ₁ : primary winding resistance, L _l1 : Compensated current differential relaying method for the protection of a wye-delta transformer with primary leakage inductance. The method of claim 1, Obtaining the delta winding current circulation component,

Where e _ab , e _bc , e _ca : secondary induced voltage, i _A , i _B , i _C : primary current of each phase, v _ab , v _bc , v _ca : secondary line voltage, R ₂ : 2 Secondary winding resistance, L _l2 : secondary leakage inductance, i ??: secondary circulating current component), And estimating the cyclic component of the delta winding current of the transformer of the y-delta or delta-y method, wherein the value of the left side is estimated in consideration of the turns ratio from the previously obtained wye-side induced voltage. The method of claim 1, Obtaining the delta winding current,

And

Where i _a , i _b , i _c : secondary line current, i _ab , i _bc , i _ca : secondary winding current, i _pa , i _pb , i _pc : acyclic current component, i _?? : circulating current Compensated current differential relaying method for Y-delta transformer protection using the

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