JPH0124017B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a transformer protective relay device, and more particularly to a transformer protective relay device that can prevent malfunctions due to magnetic excitation inrush current of a transformer and is characterized by high-speed operation. Conventionally, transformer protection in the event of an abnormality such as a winding failure in a transformer has been carried out by extracting the current passing through each terminal of the protected transformer as an equivalent current signal corresponding to the transformation ratio using an AC converter. In many cases, current differential or current ratio differential is performed based on. However, in the current differential or current ratio differential method, in addition to the differential current generated when there is an internal fault in the transformer, the so-called differential current that occurs when the transformer is energized with no load or when the voltage is restored when an external fault is removed, etc. A differential current is also generated by the magnetizing inrush current. Therefore, in the past, malfunctions caused by the magnetizing inrush current have been prevented by focusing on the specificity of the magnetizing inrush current waveform. One method is to
Taking advantage of the fact that the proportion of harmonic components is higher than that in the fault current, when the proportion of second harmonic components in the differential current is above a certain value, it can be determined to be a magnetizing inrush current. A method is used in which the disconnector trip command is not output. However, as is well known, at least one cycle is required to detect the characteristic of the excitation inrush current that the proportion of the second harmonic component is high. Therefore, in this method, even in the event of an internal failure, the output of the breaker tripping command must be delayed for at least this amount of time (one cycle), which impedes high-speed operation. There is a problem. Furthermore, recently, cable systems have been widely used, and due to the increase in ground capacitance, the fault current when an internal failure occurs in a transformer tends to include many harmonic components. Depending on the system's ground capacitance, reactance, transformer impedance, etc., the secondary
May include lower harmonics near harmonics. In such a case, the above-mentioned conventional method causes a delay in the operation of the transformer protective relay device, which may lead to serious disasters such as destruction of the transformer tank due to malfunction. Another method to prevent malfunctions of transformer protective relay devices due to transformer excitation inrush current is to (1) sample and derive the primary and secondary voltages and currents of the transformer at the same time; (2) ) From the number of turns of the transformer, the exciting current I _p and the exciting current I _p
Find the transformer excitation magnetic flux Φ _M from a predetermined function of ) A digital method has been proposed that detects internal failures based on changes in this calculated value. However, as is well known, the relationship between the excitation current I _p of the transformer and the excitation magnetic flux Φ _M has a hysteresis characteristic, so the excitation magnetic flux Φ _M cannot be uniquely determined from the excitation current I _p . In particular, at the beginning of transformer excitation, the relationship between I _p and Φ _M varies greatly depending on the residual magnetic flux and the phase of the applied voltage. Therefore, in the conventional method described above, in order to prevent malfunctions due to excitation inrush current during transformer excitation, it is necessary to calculate the difference between Φ _M approximated from a predetermined function of I _p and the actual Φ _M
It is necessary to prevent the transformer protective relay from operating when the calculated value changes corresponding to the difference between the two. That is, there is a problem in that the sensitivity for detecting internal failures decreases by this amount. In addition, focusing on the phenomenon that the approximation error of the excitation magnetic flux Φ _M is larger when the excitation current I _p is small, internal failure is determined based on the value obtained by multiplying the above calculated value by I _p , and the excitation inrush current A method has also been proposed to suppress malfunctions caused by However, since the residual magnetic flux, which is the most important factor for determining the excitation magnetic flux Φ _M that has an important influence on the calculated value of the above calculation formula, is unknown, from I _p to Φ _M
In the conventional method of approximating In addition, in the case of a transformer with a three-phase structure, such as a three-phase three-legged core or a three-phase five-legged core, there is magnetic coupling between the three phases, so the relationship between the excitation current I _p and the excitation magnetic flux Φ _M is not limited to only one phase. It is not fixed and is also affected by the excitation state of other phases. The residual magnetic flux of each core leg at the time of transformer excitation is uncertain, and even if the relational expression between the three phases is used, the above conventional method of approximating the excitation magnetic flux Φ _M from the excitation current I _p cannot detect an internal failure. It is extremely difficult to prevent malfunctions caused by magnetizing inrush current without reducing detection sensitivity. It is an object of the present invention to eliminate the drawbacks of the prior art described above, to detect internal failures of transformers with high sensitivity and perform high-speed protective operations, and to detect magnetizing inrush currents reliably at high speeds to provide a circuit breaker. It is an object of the present invention to provide a transformer protective relay device which prevents malfunctions by blocking the tripping command of the transformer and which can be applied regardless of the core structure and winding structure of the transformer. In order to achieve the above object, the present invention finds a relational expression that holds true only when a magnetizing inrush current is generated, and when it is determined by a predetermined calculation that this relational expression almost holds true, the difference The configuration is configured to suppress (or invalidate) the command to trip the shield breaker by the dynamic current detection relay element, and the predetermined calculation is performed when there is a possibility that a magnetizing inrush current is occurring ( In other words, it is executed only when the differential current exceeds a certain predetermined value. The main points of the present invention are as follows. (1) The method for detecting internal faults in a transformer is a current differential or current ratio differential method that uses the differential current obtained from each terminal current of the transformer. Occasionally, a breaker trip command is output. (2) As an electrical internal fault detection method, the method using differential current is the most direct and has high speed and high sensitivity. However, since differential current is also generated by magnetizing inrush current, the following (3) ), only the excitation inrush current is separately detected at high speed to prevent malfunction. (3) As a means of high-speed detection of only the magnetizing inrush current, it is possible to focus on the fact that the transformer core is magnetically saturated when the magnetizing inrush current is occurring, and to set the voltage and current at each terminal of the transformer to be the same. These values are sampled at time and used to perform a predetermined calculation based on a relational expression that holds true only when the core is magnetically saturated and there is no internal failure, and the result of this calculation is used to generate an excitation inrush current. Determine the presence or absence of. Note that the above-mentioned predetermined calculation is performed when there is a possibility that a magnetizing inrush current is occurring, in other words, when the differential current calculated from the terminal current of the protected transformer exceeds a certain predetermined value. Execute only. (4) When it is determined that the excitation inrush current has occurred based on the calculation results, a signal is output to prevent the shroud breaker tripping command. As will be described later, the output of the breaker tripping command prevention signal by the method of the present invention is as follows:
It can be generated at extremely high speeds. In the present invention, since the means to detect only the excitation inrush current at high speed is the most important, the relationship is established only when the transformer core is magnetically saturated and there is no internal failure such as a partial short circuit in the transformer winding. For simplicity, the equation will be explained using FIG. 1, taking a single-phase two-winding transformer as an example. Figure 1 is a schematic diagram of a two-winding transformer, where 1 is the iron core,
21 and 22 are primary and secondary windings, respectively.
In addition, the symbols in the diagram, such as V ₁ , V ₂ , I ₁ , I ₂ , R ₁ , R ₂ , T ₁ , T _2, etc., represent the terminal voltage, terminal current, and winding resistance on the primary and secondary sides, respectively. , indicates the number of turns. Primary and secondary when iron core 1 is magnetically saturated
The self-inductance of the next winding is L ₁₁ and L ₂₂ respectively.
Let the mutual inductance between the primary and secondary windings be L ₁₂ =L ₂₁ . The differential permeability of the iron core when it is magnetically saturated is the same as that of air or transformer oil. Therefore, these inductance values are approximately equal to those without an iron core, and are uniquely determined by the winding structure of the transformer. When the iron core is magnetically saturated, as in the case of two coils with normal mutual magnetic coupling, (1)
The two relational expressions shown in Eq. Here, take the inverse matrix of the inductance matrix consisting of the self and mutual inductances in equation (1), By multiplying this from the left side of equation (1), equation (2) is obtained. Here, each voltage, current, and resistance can be set to any standard number of turns.
If the values converted to T _p are v _k , i _k , r _k (k=1, 2), then V _k = T _k /T _p v _k I _k = T _p /T _k i _k R _k = (T From the relationship _k /T _p ) ² r _k , equation (2) is transformed into equation (3). However, by adding and rearranging the two equations expressed by _equation ( ³ ) _, equation ₍ 4 _{) is} obtained. A ₁ (v ₁ − _{r 1} i ₁ ) + A ₂ (v ₂ − r ₂ i ₂ ) −d/dt (i ₁ + i ₂ )=0 ...(4) A ₁ = y ₁₁ + y ₂₁ A ₂ = y ₁₂ + y _22As is clear from the above explanation, equations (1) to (4) only hold true when the transformer core is magnetically saturated and there is no internal failure such as a winding short circuit. , will not hold when the transformer core is healthy and not magnetically saturated or when there is an internal failure. In addition, each coefficient or coefficient matrix in equations (1) to (4) is the winding resistance of each winding of the transformer, the number of turns, and the self and mutual inductance when the iron core is magnetically saturated, or the self and mutual inductance matrix. It is a constant determined by the inverse matrix. In other words, since these constants can be set in advance, Equations (1) to (4) do not include any uncertain elements such as the excitation magnetic flux, and the iron core magnetic saturation, that is, the excitation It can be used as a complete relational expression for determining the presence or absence of inrush current. The relational expressions explained above using a two-winding transformer as an example can be easily extended to transformers having three or more windings, so this will be explained next. For any N-winding transformer, the voltage at each terminal,
Express current etc. as a matrix as follows. Uppercase letters indicate values in the actual circuit, and lowercase letters indicate values converted to an arbitrary standard number of turns T _p . [V], [v]; Column vector of terminal voltage [I], [i]; Terminal current [R], [r]; Winding resistance matrix [L]; Inductance matrix consisting of self and mutual inductance [I] ] ^T , [r] ^T ; transposed matrix of [I] or [i] By the above expression, (1) for a two-winding transformer
Deriving the relational expressions for an N-winding transformer corresponding to Equations (3) to Equations (5) to (7) are obtained. [V] - [R] [I] ^T - [L] d/dt [I] = [0
] ...(5) [Y] {[V]-[R][I] ^T } -d/dt[I]=

[0] ...(6) Takashi, [Y] = [L] ^-1 [y] {[v] - [r] [i] ^T } -d/dt [i] =

[0] ...(7) Here, when each voltage, current, and coefficient are expressed with subscripts, the relational expression corresponding to equation (4) becomes equation (8). _N 〓 ^k=1 {A _k (v _k r _k i _k )}−d/dt ( _N 〓 ^k=1 i _k )=0 ……(8) Then, A _k = _N 〓 ^j=1 y _jk (k=1 to N) As is well known, the integral form is often more convenient than the differential form for processing the above-mentioned relational expressions. Therefore, by converting the above equations (5) to (8) into integral form, equations (9) to (12) are obtained. ∫[V]dt-[R]∫[I] ^T dt-[L]∫d[I]=

[0] ...(9) [Y] {∫[V]dt−[R]∫[I] ^T dt} −∫d[I]=

[0] ...(10) [y] {∫[v]dt−[r]∫[i] ^T dt} −∫d[i]=

[0] ...(11) _N 〓 ^k=1 {A _k (∫v _k dt−r _k ∫i _k dt)}−∫d ( _N 〓 ^k=1 i _k )=0
...(12) When digitally calculating the relational expressions for any N-winding transformer shown above, differential calculations in equations (5) to (8) and integral calculations in equations (9) to (12) are performed. As will be described later, each voltage and current are discretely performed at appropriate sampling intervals. However, in order to make the relational expressions in the integral form of equations (9) to (12) hold true when the iron core is magnetically saturated, the integration must be started from the moment the iron core becomes magnetically saturated. . The first method for this is to clear each integral calculation in equations (9) to (12) above when the differential current exceeds a predetermined error current value due to the current transformation ratio error of the current transformer, etc. It is to be. As described above, the differential current exceeds a predetermined value when a magnetizing inrush current occurs or when an internal failure occurs. When a magnetizing inrush current is generated, in the present invention,
It is detected that the above formulas (9) to (12) are satisfied, and as a result, while the core is magnetically saturated, a signal is output that prevents the disconnection command from being issued as described later. Ru. In the case of an internal failure, the integral calculations of equations (9) to (12) are cleared, but after the integral calculations are started again, the equations (9) to (12) become invalid within a very short time. Therefore, as will be described later, a signal to prevent the command to trip the shingle breaker is not output, or even if it is output, it is canceled immediately. Therefore, a command to trip the breaker using a current differential method or a current ratio differential method is output. A second method is to start the integration or calculation when the differential current exceeds a predetermined error current, and end it when the differential current falls below the predetermined error current. While calculations are not being performed, a signal is output that prevents a command to trip the cutter or disconnector. With this, as in the first method, the excitation inrush current can be determined without any problems. In addition,
In this case, by clearing the integration memory at the end of the integration calculation, the next integration can be executed without delay. With any of the above methods, even in the case of integral calculations, it is possible to perform highly accurate calculations that eliminate uncertain elements such as excitation magnetic flux. Even when using the relational expressions in the differential form of Equations (5) to (8), it is not healthy to execute these calculations only when the differential current exceeds a predetermined error current. ) is effective in terms of preventing malfunctions caused by unnecessary calculations and noise. Furthermore, not only is the influence of passing current caused by an external failure reduced, but also calculations become simpler. Therefore, overall, it is possible to improve the discrimination performance between the excitation inrush current and the internal fault current. Furthermore, when the arithmetic computer is used, its load can be reduced. Also, in the above relational expression, equation (8) or (12) is Σi _k ,
That is, since differential current is used, it has the characteristic that it is not easily affected by passing current in the event of an external failure. Furthermore, the term r _k i _k or r _k ∫i _k dt in these equations is
Usually, it is much smaller than the term v _k or ∫v _k dt, so
The proportion contributing to the establishment of equation (8) or (12) is small. That is, in general, the winding resistance of a transformer is very small, and even if it is ignored, it often does not have a substantial effect on the relational expression between the voltage and current of the transformer. In order to shorten calculation time, it is desirable to avoid performing unnecessary calculations. In equations (5) to (12) above, the relational expressions when winding resistance is ignored are shown in equations (13) to (20). [V]-[L]d/dt[I]≒

[0] ...(13) [Y] [V] - d/dt [I]≒

[0]……(14) [y] [v] - d/dt [i]≒

[0]……(15) _N 〓 ^k=1 {A _k v _k }−d/dt( _N 〓 ^k=1 i _k )≒0……(16) ∫[V]dt−[L]∫d [I]≒

[0] ...(17) [Y]∫[V]dt−∫d[I]≒

[0] ...(18) [y]∫[v]dt−∫d[i]≒

[0] ...(19) _N 〓 ^k=1 {A _k ∫v _k dt}−∫d( _N 〓 ^k=1 i _k )≒0 ...(20) Among these equations, especially (16 ) or (20) uses only a differential current as the current, so it is not affected by passing current and has the feature that the excitation inrush current can be determined by simple calculations. Next, a specific calculation method for determining whether the above relational expression holds true will be described. As an embodiment of the present invention, when a digital system is adopted, the differential or integral calculations in equations (5) to (20) are performed by discretizing each voltage and current at appropriate sampling intervals. As an example, an example of a calculation method when determining the occurrence of magnetizing inrush current using the relational expression (12) will be shown below. In equation (12), the sampling values of each voltage and current at time t are v _k (t) and i _k (t), and
For example, when the sampling interval is Δt and the integral interval is mΔt, the time t when applying the trapezoidal formula
Letting the calculation result in δ ₁ (t), equation (21) is obtained. δ ₁ (t)=A(t)-B(t)-C(t)...(21) Then, A(t)= _N 〓 ^k=1 [A _k ×Δt/2× _n 〓 ^{j =1} {v _k (t−jΔt)+v _k (t−(j−1)Δt)}] B(t)= _N 〓 ^k=1 [A _k ×Δt/2× _n 〓 ^j=1 {i _k (t-jΔt)+i _k (t-(j-1)Δt)}] C(t)=i _p (t) i _p (t-mΔt) i _p (t)= _N 〓 ^k=1 i _k ( t) As mentioned above, if we start the integral calculation at the moment the differential current is detected, then (1) In the case of magnetizing inrush current, while the iron core is magnetically saturated, the equation (21) is The calculation result δ ₁ (t) is almost zero, and (2) in the case of an internal failure, the calculation result δ ₁ (t) becomes a large value immediately after starting the integral calculation. Therefore, if the setting error that allows transformation errors due to voltage and current transformers is ε, then when the formula (222) |δ ₁ (t) | < ε ...(22) holds, it is determined that it is a magnetizing inrush current. be able to. Also, like normal ratio differential relay elements,
Letting the ratio setting value be K, δ ₂ (t)=|A(t)-B(t)-C(t)|-K
{|A(t)−B(t)|+|C(t)|}...(23) is calculated, and when |δ ₂ (t)|<ε...(24), the excitation inrush current and It is also possible to judge. When it is healthy, no differential current is detected, so there is no need to perform the calculation itself. Even if the differential current is temporarily detected due to noise or the like and a signal is erroneously output to start calculation and block the circuit breaker tripping command, there will be no actual harm. In the above specific calculation example, B(t)=0
It is clear that this is a specific example of using the relational expression (20) that ignores the winding resistance. Next, one embodiment of the present invention will be described. FIG. 2 is a schematic diagram showing an example of application of the present invention to a two-winding transformer. In this figure, 21 and 22 are the primary and secondary windings of the transformer to be protected, 31 and 32 are the primary and secondary side current transformers, 41 and 42 are the primary and secondary side voltage transformers, and 51 , 52 are primary and secondary side shear breakers. Further, 6 is a differential current detection relay element that receives the outputs of the current transformers 31 and 32, detects a differential current, and outputs a shingle breaker tripping command. 7 samples the outputs of the current transformers 31 and 32 and the voltage transformers 41 and 42 at the same time, and calculates at least one of the above formulas to detect the magnetic saturation state of the transformer core. However, in the case of magnetic saturation, it is a magnetic saturation detection relay element that outputs a signal that prevents the disconnection command from being issued. 8 is an inhibit circuit having two inputs, the output of the differential current detection relay element 6 and the inverted output of the magnetic saturation detection relay element 7; 9 is the inhibit circuit 8;
This is a timer that stretches out the output signal from. In this embodiment, the timing for starting calculation in the magnetic saturation detection relay element 7 is calculated and determined within itself using the outputs of the primary and secondary current transformers 31 and 32. Can be done. Alternatively, a control signal line 10 as shown by the dotted line in FIG. A signal for starting the magnetic saturation detection relay element 7 may be transmitted from the differential current relay element 6 to the magnetic saturation detection relay element 7. Since the calculation method for determining the core magnetic saturation in the magnetic saturation detection relay element 7, which is a feature of the present invention, has already been described in detail, its explanation will be omitted here. In addition, when performing these calculations digitally, the magnetic saturation detection relay element 7 must be comprised of a sample hold circuit, an analog-to-digital conversion circuit, an arithmetic device, and the like. Of course, if the outputs of the current transformers 31, 32, voltage transformers 41, 42, etc. are digital quantities,
An analog-to-digital conversion circuit becomes unnecessary. Next, the operation of the embodiment of the present invention shown in FIG. 2 will be explained with reference to FIGS. 3 and 4. FIG. 3 shows an operation time chart when an excitation inrush current occurs. The excitation inrush current is detected as a differential current, so waveform 3 in the figure
As shown in the figure, from the differential current detection relay element 6,
A breaker tripping signal shown by waveform 6 is output. On the other hand, from the magnetic saturation detection relay element 7, it is clear from the explanation of the calculation contents, and the waveform 7 in the same figure
As shown in , even if a differential current is detected, a signal that prevents the disconnection command from being issued continues to be output. Therefore, the inhibit circuit 8 and timer 9 do not output the breaker tripping signal. FIG. 4 shows an operating time chart of the present invention when an internal failure of the transformer occurs. When the differential current shown by waveform 3 exceeds a certain value, the differential current detection relay element 6 outputs a breaker trip signal shown by waveform 6. On the other hand, immediately after the differential current exceeds the predetermined error current and the calculation is started, the calculation result becomes greater than the predetermined value, so during this period, as shown by waveform 7, the signal from the magnetic saturation detection relay element 7 Output is aborted. Therefore, the inhibit circuit 8 outputs an intermittent signal as shown by waveform 8 in the figure. timer 9
extends the signal of the inhibit circuit 8 and outputs a stable breaker tripping command as shown in waveform 9 in the figure. As a result of the above, it is possible to trip the disconnector at high speed after an internal failure occurs. In addition, in the transformer circuit illustrated in FIG.
Even if an internal fault current and an excitation inrush current occur simultaneously, each of the above relational expressions does not hold, so the fourth
As shown in the figure, the breaker can be operated at high speed. Moreover, since malfunctions due to excitation inrush current can be reliably prevented, according to the present invention, the internal failure detection sensitivity of the differential current detection relay element 6 can be made extremely high compared to the conventional system. When implementing the present invention by digital calculation, in order to simplify the calculation circuit, the differential current detection relay element 6, the magnetic saturation detection relay element 7, and the inhibitor described in the embodiment of FIG. It goes without saying that the circuit 8 and the calculation, determination or control circuits such as the timer 9 may be combined and executed by a single calculation device. It goes without saying that the present invention is applicable not only to the transformer having the separate winding structure described in the embodiments, but also to a transformer having a common winding portion, such as an autotransformer. In addition, in the case of a transformer having a tap winding, correcting the voltage and current coefficients or coefficient matrices in each of the above calculation formulas each time the tap winding is switched is as follows:
This is effective for further enhancing the effects of the present invention. As described in detail above, according to the present invention, it is possible to detect internal failures in a transformer with extremely high sensitivity and high speed, and also to reliably prevent malfunctions caused by magnetizing inrush current. This can greatly contribute to increasing the reliability of equipment and preventing the spread of serious disasters in the event of internal breakdowns in transformers.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a two-winding transformer for explaining the principle of the present invention, Fig. 2 is a schematic diagram showing an embodiment of the present invention, and Figs. 3 and 4 are schematic diagrams of a two-winding transformer. 2 is a time chart for explaining the operation of the embodiment. DESCRIPTION OF SYMBOLS 1... Iron core, 21, 22... Winding wire, 31, 32... Current transformer, 41, 42... Voltage transformer, 51, 52... Shrink breaker, 6... Differential current detection relay element, 7... Magnetic saturation Detection relay element, 8... Inhibit circuit, 9... Timer.

Claims (1)

[Scope of Claims] 1. A differential current detection relay element that detects the differential current of the terminal currents of each winding of the transformer to be protected and outputs a command to trip the insulation breaker; and each winding of the transformer. means for detecting a terminal voltage and a terminal current of a line; and generating an output when a differential current obtained from the terminal current does not exceed a predetermined value; and when the differential current exceeds the predetermined value, each winding Determining whether or not a relational expression is established in which the terminal voltage and terminal current of the line or the differential current are variables and the winding inductance or the reciprocal of the inductance at the time of magnetic saturation of the transformer core holds as a coefficient, A magnetic saturation detection relay element that generates an output when the relational expression is substantially satisfied, and means for prohibiting output of a tripping command for the shield breaker based on the output of the magnetic saturation detection relay element. A transformer protection relay device characterized by: 2. The transformer protection relay device according to claim 1, wherein the value of the coefficient included in the relational expression is changed in response to tap switching information of the transformer to be protected.