JPS6242456B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transformer protective relay device, particularly a second
The present invention relates to a protective relay device that prevents malfunctions in the event of an internal accident due to its harmonic suppression function.

As a conventional transformer protection relay system, a current differential system is adopted in which a differential output signal of the passing current of each winding of the transformer to be protected is detected and this is used as the operating force. On the other hand, as a measure to prevent malfunctions caused by the magnetizing inrush current of the transformer, the second
A method is adopted in which the harmonic component is used as a suppressing force and the trip command is locked when the amount exceeds a predetermined amount, for example, about 15% of the fundamental wave component. However, in the conventional system, if a current containing a large amount of second harmonics flows in due to an internal fault in the transformer, the relay output is locked and the relay malfunctions. A specific example of such a case is as follows. When a transformer has a power phasing capacitance (referred to as a stacon) as a load, when an accident occurs, an oscillating current is generated due to the inductance from the fault point to the stacon and the capacity of the stacon. As the frequency approaches the second harmonic, there is a risk that the current may be mistaken for an excitation inrush current, resulting in a malfunction resulting in non-operation.

Next, this phenomenon will be explained in detail with reference to FIG.

1 is a protected transformer; for example, primary, secondary
Next, consider a three-winding transformer with a tertiary winding. Here, the primary side is the symbol P, the secondary side is the symbol S,
The tertiary side will be indicated below by the subscript of the symbol T. The figure also shows a single line diagram of a three-phase AC transformer.

2 _P , 2 _S , and 2 _T are current transformers for deriving current signals passing through the respective windings, and their output signals are input to the protective relay device 4 .

3 _P , 3 _S , and 3 _T are shear disconnectors, respectively, and in the event of an accident, the protected transformer 1 is disconnected from the grid to 3 _P , 3 _S , and 3 _T by the shear disconnect command from the protective relay device 4 . Twist and separate. _6P and _6S are the power supplies behind each winding, and the presence of _{6P and 6S} may differ depending on the operating conditions of the system or the equipment. Therefore, _6P and _6S in the same figure can be considered as variable power supply terminals. In particular, the tertiary side is often used exclusively for load power supply within a substation or for connection to a starcon 5.
It is often operated as a non-power terminal. Here, for ease of explanation, the tertiary side is assumed to be a non-power terminal, and the influence of the resonant current with the internal impedance of the transformer 1 when the stator converter 5 is connected to this terminal will be explained.

Figure 2 shows the equivalent circuit in the event of an internal fault in the transformer.
As an example of an accident, the positive phase circuit at the time of a three-phase short circuit is shown.The symbols are the same as in Figure 1.
Figures and equivalents are shown.

In FIG. 2, Z _P ′, Z _S ′, and Z _T ′ are the back impedances outside the transformer, which are equivalent impedances of power transmission lines, generators, etc., and can almost be considered inductances. In Z _T ', the starcon is separated by symbol 5.

Furthermore, Z _P , Z _S , and Z _T indicate the internal impedance of each winding viewed from the fault point T.

Here, in the event of an accident, power supply 6 _P to _IP 6
I _S is energized from _S and becomes an input to the protective relay device 4 shown in FIG. 1 through current transformers 2 _P and 2 _S. I
Since _P and I _S are energized by a three-phase alternating current generator, depending on the phase in which the accident occurs, they can be considered to be commercial frequency currents with a transient DC component superimposed thereon. On the other hand, the current I _T flowing from the tertiary side is
ΔE is the voltage charged immediately before the accident, C is the capacitance of the stator capacitor, and Σ is the inductance of Z _T + Z _T ′.
Let L _T be I _T =ω _o CΔE ...(1).

however The current is _a frequency a determined by the inductance between the stacon and the short circuit point.

Here, for the purpose of explaining the principle, the resistance component is ignored in the explanation, but even in an actual transformer, the resistance component is quite small, for example, ΣL/resistance component is about 0.1. The operating time of a protective relay device is 1 to 2 cycles (based on commercial frequency), and the damped oscillating current due to the resistance component makes no difference to the protective relay even if the damping component is ignored; rather, it establishes the operating conditions. In order to achieve this, it is necessary to consider the case where the decay time constant is sufficiently large, and it is more appropriate to consider it using equations (1) and (2).

Here, the input current of the protective relay device is I _P , I _S is a combination of the commercial frequency component and the transient DC component, while the current I _T of the tertiary winding connected to the stator converter is
is the natural vibration _o in equation (2) determined by ΣL and C. In addition, when connecting the star controller to the power supply end,
The internal current further includes the above-mentioned harmonic components. In the conventional method described above, the current differential output ΣL=I _P +I _S +I _T ...(3) is detected as the operating amount, and the operating output is given when ΣL≠0, but even with the magnetizing inrush current of the protected transformer, ΣI≠0, and it is necessary to determine whether or not it is an excitation inrush current to distinguish between an internal fault and a transformer energization.

Conventionally, to detect magnetizing inrush current, depending on the amount of the second harmonic component contained in the input current, if it exceeds a predetermined amount, it is determined to be magnetizing inrush current, and the trip command output of the protective relay device is locked. was.

However, as shown in equation (2), it is possible for I _T to generate a natural oscillating current close to the second harmonic component even if there is an internal accident, and this tendency becomes especially strong as the capacity of C increases. . As a result, if the excitation inrush current and the possibility of an accident are determined simultaneously using equation (3), there is a risk that the transformer will not operate in the event of an internal accident.

The problem of malfunction in the event of an internal accident due to second harmonic suppression is caused by the second harmonic Generates an oscillating current with a frequency close to . It is also known that harmonics are generated by water turbine generators without damper windings, AC/DC or frequency converters. Therefore, in the following specification, these devices and the like will be collectively referred to as harmonic generation sources.

In view of the above, an object of the present invention is to provide a transformer protection relay system that can prevent malfunction due to harmonics in the event of an internal accident.

The present invention provides an effective solution when the harmonic generation source is connected to the non-power terminal.

Specifically, in the present invention, the operating force uses the vector sum ΣI of the passing currents of all the windings as in the past, but the suppressing force uses the current flowing in the winding connected to the non-power supply end that has a harmonic generation source. It is determined by the second harmonic component contained in the current flowing through the other windings.

In other words, if we take the above-mentioned three-winding transformer as an example, the detection of magnetizing inrush current focuses on the primary and secondary currents as a suppressing force since the tertiary side is the non-power supply end that has a harmonic generation source. .

The invention will be explained below based on FIG.
FIG. 3 shows the part 4 shown in FIG. 1.

31 _P , 31 _S , 31 _T are input currents I _P , I _S ,
This is an auxiliary transformer with an air-gap magnetic path for converting I _T to a voltage level and removing transient DC components. The output of 31 is applied as an input to operational amplifier _A1 via a resistor of _32P and _32S , and addition is performed in _A1 . The output of _A1 is a signal for detection of magnetizing inrush current. Here, as mentioned in the previous figure, the output of _31T is not added to _A1 because the tertiary side non-power supply terminal signal I _T is not required to detect the excitation inrush current. Of course, as a standard transformer protection device, the output of 31 _T is also connected to be added to A ₁ , and the connection is devised so that it is only disconnected when it is a non-power terminal that has a harmonic generation source. be done.

34 is an amplification resistor of _A1 , and 33 is a bias resistor, each of which is set in a stable region in consideration of the drift of the operational amplifier.

35 is a fundamental wave pass filter, and 36 is a rectifier circuit for deriving the absolute value of the output of 35, which includes a full-wave rectifier element and a smoothing filter.
37 is a filter for extracting the second harmonic component. 38 is a rectifier circuit for deriving the absolute value of the output of 37, and is equivalent to 36. 39 is a comparator which generates an inoperable output signal when the output of 38 is greater than a predetermined value with respect to the output of 36. The conventional detection ratio of magnetizing inrush current is 36 to 3.
An example of the predetermined amount is a value such that when 8 is 15% or more, 39 is an inactive output.

Next, the route containing operational amplifier _A2 is a circuit for detecting internal faults as before, and _A2 is an adder that constitutes a current differential circuit of I _P , I _S , and I _T . , external resistors 40 _P , 40 _S , 40 _T , and 41 and 42 are used in the same way as in the case of A ₁ . However, unlike in A ₁ , 40 _P , 40 _S , 40 _T
is a value determined by the change ratio of the main current transformers 2 _P , 2 _S , 2 _T and the transformers P, S, T so that the sum of the passing currents becomes zero when the transformer is healthy. 4
Reference numeral 3 denotes a low-pass filter, which is intended to make the fundamental wave (commercial frequency) component of the differential output current the operating amount. Reference numeral 44 includes a rectifier circuit and a waveform smoothing filter for the absolute value detection circuit of the output signal of 43. In short, this circuit provides an operating output when the total passing current ΣI≠0.

45 _P , 45 _S , and 45 _T are rectifier circuits for deriving the absolute values of passing currents I _P , _IS , and _IT in order to suppress passing currents, that is, to obtain ratio differential characteristics with scalar sum suppression, and each includes a smoothing filter. have. 46
_P , 46 _S , 46 _T are scalar sums Σ of _A3 operational amplifiers
The calculation resistors 47 _and 48 for deriving |I|=|I _P |+|I _S |+| _IT It is used for. The output of A ₃ is the scalar sum suppression amount, and the output of A ₂ is the operation amount based on the vector sum. Comparator 49 compares the output of A ₂ and the output of A ₃ .
When the output of _A2 exceeds a preset level compared to the output of _A3 , the output of 49 generates an internal fault detection operation signal.

50 is a coincidence gate, which outputs the output of 39, that is, the difference current detection output which is not the excitation inrush current, and the output of 49.
By matching the operating conditions of both differential outputs,
yielding the final output of the invention.

To explain how the method of the present invention described above can respond correctly in various cases, first, as before, the comparator 49 provides a trip permissible output when the vector sum of all terminal currents exceeds the scalar sum; Reference numeral 39 provides a tripping prevention output when the second harmonic content of all terminal currents excluding the non-power terminal current is greater than a predetermined amount.

First, considering internal accidents, the comparator 49 provides a tripping allowable output as in the conventional device, and the comparator 39
are the input currents I _P of the primary and secondary terminals,
Since I _S contains a small amount of second harmonic components, no tripping prevention output is given. Therefore, the breaker is tripped correctly.

Second, in the event of an external accident, since the comparator 49 does not provide a tripping permissible output like the conventional device, tripping is correctly prevented without considering the response of the comparator 39.

Thirdly, when looking at the influence of the excitation inrush current when closing each terminal or turning on the circuit breaker to start the transformer, it can be divided into two cases. One of these is the closing of the breaker at the non-power end. First, because the comparator 39 does not monitor the terminal current I _T at the non-power end, the second harmonic content is small, and the breaker is actively triggered. Unable to provide removal prevention output. At this time, comparator 4
9, the vector sum is always zero (output of 44)
increases due to the excitation inrush current I _T . However, the terminal current I _T at the non-power supply end is sufficiently small compared to the other currents I _P and I _S , so the vector sum cannot be larger than the scalar sum (output of operational amplifier _A3 ). , 49 do not provide a trip permission signal.
As a result, the breaker is not tripped correctly. It goes without saying that the circuit that calculates the vector sum and the scalar sum and compares them is adjusted so as not to respond to minute currents at the non-power supply end.

In the case where the primary and secondary circuit breakers are closed, the monitoring inputs I _P and I _S contain sufficient second harmonics, and the comparator 39 provides an output to prevent circuit breakers from tripping.
Therefore, regardless of the presence or absence of the output of the comparator 49, tripping can be prevented and a correct response can be performed.

As described above, according to the present invention, correct responses are made in all possible cases. Finally, to explain the reason why the present invention is effective only when the harmonic generation source is located at the non-power supply end, when the harmonic generation source is located at the power supply end, it is possible to This will result in the device being tripped. Since the current at this power supply terminal is not subject to second harmonic content monitoring, the comparator 39 does not provide a trip prevention signal when the power supply terminal is closed or when the circuit breaker is turned on. On the other hand, due to the excessive current flowing from the power supply terminal upon turning on, the vector sum becomes sufficiently larger than the scalar sum, and the comparator 49 provides a trip-permissible output.

According to the embodiments of the present invention, it is possible to reliably detect a fault even in the case of waveform distortion of fault current caused by an internal fault, without causing malfunction due to excitation inrush current. In particular, when a large-capacity harmonic generation source is connected to the non-power supply end of the transformer, protection performance can be improved. Incidentally, as a modification or application example of the above-described present invention, the following may be used.

In Fig. 3, input auxiliary transformers 31 _P , 31 _S , 31
Although _T is a transformer with a gap, it is not necessarily necessary to have a gap because each of 35, 37, and 43 has a filter.

In this case, the filter 43 is not a low-pass filter, but a fundamental wave band-pass filter is effective.

Further, the excitation inrush current detection means in FIG.
By vector calculation of _P and I _S , the ratio of the second harmonic component to the fundamental component is calculated from the output.
Further, as a modification/application example, there is a method shown in FIG. Figure a shows a method for detecting the second harmonic for each of the primary current I _P and the secondary current I _S , 51 is a circuit for deriving the absolute value of the fundamental wave component of I _P , and 52 is a circuit for deriving the absolute value of the fundamental wave component of I _P . This is a circuit that derives the absolute value of the second harmonic component. 53 is a comparator that generates a lock signal when the output of 52 is larger than the output of 51 by a predetermined amount; 54 is a fundamental wave component absolute value detection circuit for I _S like 51; and 55 is an I _S
This is a second harmonic component absolute value detection circuit. 56 is a comparator, which outputs a lock output when the output of 55 is larger than the output of 54 by a predetermined amount. 5
Reference numeral 7 is a NAND gate, and both 53 and 56 generate an operating signal only when there is no lock signal, and the output of 57 corresponds to the signal 39 in FIG. 3. According to this embodiment, since the detection level of the excitation inrush current can be set for each line current, there is an effect that it can be set variably depending on the structure of the transformer.

In Fig. 4b, only the fundamental wave component of the tertiary passing current I _T is derived by the filter 61, the operating amount is derived by the vector sum absolute value detection circuit 62, and the second harmonic component of the tertiary passing current I T is derived by the absolute value detection circuit 62. By the absolute value detection circuit, I _P ,
Find the composite value of the second harmonic component included in I _S ,
Using this as the suppression amount, 66 comparison circuits calculate 6
66 generates an operating output when the operating amount of 2 is greater than the suppression amount of 65 by a predetermined amount. Similar to the signal 39 in FIG. 3, the signal 66 will be input to the coincidence gate 50 in FIG. 3 below. According to this embodiment, since a current differential output is obtained in which the fundamental wave component of the tertiary winding is used as the operating amount, it is possible to detect the excitation inrush current with high sensitivity even when there is a tertiary load current. Further, although 65 in FIG. 4B is an adder, it may be a maximum value addition that detects the maximum value of 63 and 64.

Although the above explanation is a detailed explanation of the protective relay system for a three-phase, three-winding transformer, the present invention is a method for detecting magnetizing inrush current, which detects the flow of magnetizing inrush current that is easily mistaken for an internal fault current. The purpose is to use at least all of the current at the terminal (that is, the power supply terminal) obtained, and not to use the current at the terminal that is a non-power supply terminal and has a harmonic generation source.

As described above in detail, according to the present invention, even when a non-power supply terminal having a harmonic generation source is provided, malfunction due to an internal accident of the transformer can be completely prevented.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a power system having a transformer that is the subject of the present invention, and FIG. 2 is a diagram for explaining that an oscillating current flows through a non-power supply end having a starcon.
FIG. 3 is a diagram showing a specific embodiment of the present invention,
FIG. 4 is a diagram showing a modification/application example of the present invention. 31...Auxiliary transformer, 32, 33, 34, 4
0, 41, 42, 46, 47, 48...Resistance, 3
6, 38, 44, 45... Rectifier circuit, A ₁ , A ₂ ,
A ₃ ... operational amplifier, 35, 37, 43 ... filter, 39, 49 ... comparator, 50 ... coincidence gate.

Claims (1)

[Claims] 1. In a protective relaying system for a transformer that connects a non-power end that has a harmonic generation source to a part of the winding, the vector sum and scalar sum are calculated from the currents flowing through all the windings of the transformer, and by comparing them, the transformer is determined. A first means for giving an output in the direction of cutting off the device, the second harmonic contained in the current flowing through all the windings except for the winding connected to the non-power supply end having the harmonic generation source. a second means for deriving the second harmonic component and providing an output in a direction to prevent the transformer from breaking according to the second harmonic component; A transformer protective relay system comprising: third means for determining.