JPS586374B2 - Differential relay device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a differential relay device for protecting power transmission lines.

First, we will consider harmonics that occur during power system accidents.

Harmonics during an accident occur as transient vibrations due to the capacitance and inductance of the power system.

Figure 1 shows an example of an accident in which harmonics are considered to be severe for the protective relay RY, where there is an overhead power transmission line near the cable transmission line and an accident occurs on the overhead power transmission line.

Cable power lines have a much larger capacitance than overhead power lines, so an accident near them will generate large harmonic currents.

In addition, since the overhead power transmission line has a larger inductance than the cable line, the resonance frequency with the capacitance of the cable line is relatively low, making it difficult to separate the fundamental wave and harmonics using a filter.

Furthermore, cable transmission lines are often located in heavy-duty areas in large cities, and it is rare for a large power source to be located on the cable line side, so that in the event of an accident, a large fundamental wave current is unlikely to flow from the cable line side.

When an accident occurs on an overhead power transmission line near the cable transmission line as shown in the figure, the protective relay RY on the cable line side from the accident point
As for the current introduced through the current transformer, the fundamental wave current is small, the harmonic transient oscillation current is large, and the harmonic frequency is not necessarily high.

Therefore, the relay RY is severely affected by harmonics.

The time constant of recent power transmission lines is often several tens of milliseconds or more even at IKHz or higher, and this time constant is longer than the operating time (several milliseconds) normally required of a protective relay device.

Therefore, it is necessary to prevent relays from malfunctioning due to the effects of harmonic transient vibrations.

FIG. 2 is an approximate equivalent circuit for considering the harmonic transient phenomenon that occurs in the accident shown in FIG.

L is the inductance of the overhead transmission line up to the fault point, C
is the capacitance expressed by centralizing the distributed capacitance of the cable transmission line portion, R is the resistance of both transmission line portions, and E is the instantaneous value of the voltage applied to the capacitance C immediately before the accident occurred.

S is a switch, and the transient phenomenon caused by the closing of S simulates the transient harmonic phenomenon at the time of an accident, and the current i indicates the current on the cable line side from the accident point.

The transient oscillating current i when the switch S is closed in FIG. 2 has the relationship R2<<4L/C in terms of power system constants, and this relationship also holds, so it is expressed as the following equation.

here Then, equation (1) becomes The magnitude of the current i is proportional to its angular velocity ωH.

If an accident occurs at the peak value of the grid voltage waveform,
In the above equation (3), the voltage E becomes the peak value EM of the grid voltage waveform, and considering the initial time t=o, the amplitude of the current i becomes the maximum, and the magnitude (effective value) of this maximum harmonic current is When IHl, it becomes.

(Hereinafter, the magnitude of current (effective value) will be expressed with the symbol 11 for absolute value.

) Here, if lIol is the constant effective fundamental wave charging current value for the capacitance C, then II01 is expressed by the following equation.

However, ω.

is the angular velocity of the power system fundamental wave. The following equation is obtained from equations (4) and (5).

As described above, the maximum harmonic current IIHl is the product of the constant fundamental wave charging current 1■o1 and the ratio ωH/ω0 of the harmonic angular velocity to the fundamental wave angular velocity.

FIG. 3 is a block diagram showing a configuration example of a differential relay device for power transmission line protection according to a conventional example and the present invention.

In the figure, LN is the protected section of the power transmission line, A and B are the terminals of the protected section LN, CTA and CTB are the current transformers installed at the A terminal and B terminal, respectively, and CBA and CBB are the current transformers installed at their respective terminals. It is a breaker.

TDA and TDB are input conversion devices provided at the A terminal and B terminal, respectively, SD is a transmitting device including a modulator NOD, and RD is a receiving device including a demodulator DEM.

Furthermore, DL is a delay device, and DET is a detector that functions as a differential relay element.

Secondary currents ■'A and ■'B of current transformers CTA and CTB corresponding to currents ■I and ■B flowing through terminals A and B of the transmission line are applied to input converters TDA and TDB, respectively, and outputs eA and generates eB.

The output eA is modulated by frequency modulation or otherwise by a modulator MOD in the transmitting device SD, and a modulated signal fA is sent to the terminal B.

This signal fA is received at the receiving device RD at terminal B and demodulated by the demodulator DEM to produce the output eA/.

Output eA/ is equal to output eA except that it is delayed by the transmission delay time between terminals A and B.

Output eB is applied to delay DL to yield eB/.

Output eBl is equal to output eB except that it lags by a time equal to the time that output eA/ lags eA.

The output eA/ is applied to a detector DET where eB/ functions as a differential relay element.

This detector DET operates when both forces eA/ and eBl are under the following conditions.

However, K1 and K2 are positive constants. The input conversion devices TDA and TDB each have the same configuration, each having a single tuning filter that passes the fundamental wave as a component, and the output is expressed by the following equation.

However, K3 is a constant, α1 is an attenuation constant, and ■' is the input current ■κ
or IB/, e is the output eA or eB of the input converter TDA or TDB, and ω is the angular velocity of the input current 1'.

With the above configuration, the demodulator output eA/ and the delayer output eB/
has the same proportional relationship with the currents ■κ and ■Bl, that is, eAl/■A11 eBl/■Bl, so (
7) Equation is converted as shown below.

However, K4 is a positive constant.

Equation (9) is a well-known equation as the operating condition equation for a known ratio differential relay, and for normal fundamental wave current phenomena, the detector DET operates only when there is an internal fault in the protected section LN. , otherwise it doesn't work.

However, when a harmonic current as shown in equation (6) passes due to an external accident, the detector DET may malfunction.

This will be explained. Figure 3 shows the delay of the demodulator output eA/ with respect to the input converter output eA and the delay output eBl.
Although the delay with respect to the output eH of the input conversion device is compensated by the delay device DL, this compensation necessarily involves an error.

This error becomes a phase error, and the error angle θ6 is becomes.

Figure 9 is a diagram for explaining phase errors, where waveform A shows the output eA/(or eBl) when there is a compensation error, and waveform opening shows the output eA/(or 6Bz) when there is no compensation error.
shows.

If an external accident causes an error of +θ5 in the transmission delay of output eA/ and -θ6 in the delay of output eB/ when the relationship between outputs eA and eH is eA - eH, outputs eA/ and eB
The magnitude of the output eεl due to the error in the phase eAt+eBt of / is 1eA/1 - leA1, leBi, ignoring the amplitude error.
If =leB1, then the following is obtained.

FIG. 10 is a vector diagram for explaining this equation (1l).

The vector indicated by the broken line in the figure is the output eA/ when there is no error.
and −eB/.

Now, assuming that the compensation time error is a value that normally occurs, for example, 0.1 milliseconds, a harmonic current of frequency fH passes through the protected section, and the outputs eA and -eB at this time are eH, then equation (10) is obtained. From formula (11).

The output due to error is 2eH when fH is 2500Hz, 8
At 33 Hz, it is eH, and below 833 Hz, it is approximately proportional to the frequency.

On the other hand, the harmonic current at the time of an external fault is expressed by equation (6), and the output eA or eB is expressed by equation (8).

If the outputs eA and eB when the harmonic current ■H in equation (6) flows are eH, then ωH of eH is ω.

If it is sufficiently larger than Equation (8), then However ■.

l is the fundamental wave charging current■. is the current transformer secondary current when flowing through the primary side of current transformer CTA or CTB, and the magnitude (effective value) of eH is constant regardless of frequency.

Since the error output eEl is 2eH at worst, the error output e5
The magnitude (effective value) of the maximum value eE/maX of l is as follows.

As a result of the recent increase in cable systems, the fundamental wave charging current ■.

It is also possible that the current is 4000 amperes or more.

On the other hand, the sensitivity of the differential relay is required to operate at a fundamental wave fault current of about 2000 amperes, in consideration of cases where the resistance at the fault point is large or when a large power supply is disconnected.

The outputs eA and eB of the input converter when the fundamental wave current flows are ω-ω in equation (8).

If the currents ■A' and ■B/ are fundamental wave currents and their sum is IF/, then the sum of the outputs eA and eH will be, and if errors are ignored, both the outputs of the detector DET will be eA/
This is also the effective value of the sum of and eB/.

Using equation (16) to select the minimum sensitivity of the detector DET to operate at a fundamental wave fault current of 2000 amperes, we get:
It will operate according to the following equation (17) (where K4 is the current transformation ratio of current transformers CTA and CTB), and the fundamental wave charging current ■.

When is 4000 amperes, eAl+eB/
The maximum error output that occurs is given by equation ([4)].

The error output of equation (18) is set to 1/2 of the minimum sensitivity of equation (17).
In other words, when trying to do so, the attenuation constant α1 becomes 1/8.

If the attenuation constant of a single-tuned filter is set to 1/8, a small error in the component constants will cause a large phase error when inputting the fundamental wave, causing malfunctions in the event of an external fault, and the delay in the output relative to the input will become significant, resulting in poor response. It has the disadvantage of slowing down.

An object of the present invention is to provide a differential relay device that solves the above problems.

The schematic structure of the differential relay device according to the present invention is as shown in FIG. 3, similar to the conventional example.

However, the internal configurations of the input conversion devices TDA and TDB are quite different, and the output is expressed by the following expression instead of expression (8).

However, α2 and α3 are attenuation constants.

An input conversion device having such characteristics can be realized, for example, by the configuration shown in FIG.

In the figure, TAP, , TAP2 are input terminals, TAP3,
TAP4 is an output terminal.

L1, L2 are reactors, CI, C2 are content length, R
,,R2 are resistors.

These are input/output terminals TAP1, TAP2, TAP3, T
It is connected between AP4 as shown in the figure, and generates an output voltage e based on an input current ■'.

Reactor L2 and capacitor C2, which are connected in series with each other.
and the impedance of resistor R2 are the same as those of reactor L1, capacitor C1, and resistor R2, which are connected in parallel with each other.
, shall be sufficiently large for each impedance.

Further, the inductances L, L2 of each reactor and the capacitances CI, C2 of the capacitors are set to be respectively.

With this configuration, almost all of the input current ■' flows through the parallel circuit of the reactor L1, the capacitor C1, and the resistor R1, and the indicated voltage V becomes .

This voltage V is applied to a series circuit of reactor L2, capacitor C2 and resistor R2 to produce an output voltage e.

The output e becomes.

(211, in formula (22), R1=K3, Then, the output e is expressed as equation (19).

In equation (19), ω1ω.

Then, the output e is e=K3I'・1...
(23), and at other frequencies the value of e is smaller than the equation (23).

ω is ω. When it is thick enough for , the value of output e is Therefore, the attenuation is approximately inversely proportional to the square of the frequency.

From equations (6) and (24), the effective value of the output eH when the harmonic current of equation (6) flows is ωH.

when it is large enough for and is inversely proportional to the harmonic frequency.

The effect of setting the outputs of the input conversion devices TDA and TDB to the equations (19) will be explained using the same numerical values as those described for the conventional device using the equation (8).

Compensation time error ±0.1 ms, fundamental charging current I.

is 4000 amperes, α2 and α3 in equation (19)
Assuming that both are 2, the output e5l due to the error in the output sum (eAl 〇Bl) when the harmonic current IH in equation (6) passes through the protection interval is expressed by the curve I in Figure 5 on a logarithmic scale. becomes.

In other words, the secondary currents of current transformers CTA and CTB ■A/, ■B
The size of y is the value obtained by dividing the value of equation (6) by the current transformation ratio K4, and when this is set as ω - ωH and substituted for ■' in equation ([9)], the absolute value of the output e is is the magnitude le. of the outputs eA and eH when the angular velocity is ωH. It becomes 1.

Output 1e obtained by substituting this 1eH1 into equation 02),
When l1 passes harmonic current IH, output (eA/+e
The magnitude of the output is due to the error of B/), and the following equation is obtained.

In equation (26), IO=400OA, α2-α3-2, ω.

The solid line portion of curve A in FIG. 5 is obtained by calculating 1e5l1 when fH is 100 to 2500 Hz as -2π×50.

At 2500 Hz or higher, sin θ when the compensation time error is 0.1 ms, that is, sin (360° x 0.
000]XfH) becomes smaller than 1, but the compensation time error is reduced to 0. ] milliseconds or less, the maximum value of sin θ is 1, so in this case, the magnitude of the output due to the error is expressed by the following equation.

However, ωH>2πX2500 The range shown by equation (27) is the broken line portion of curve A in FIG.

When the input conversion device is a conventional device whose output is expressed by equation (8), the outputs 1e,'l due to errors are expressed as (26) and (
It is equivalent to replacing the denominator of equation (27) with the denominator of equation (8).

■About this thing. =400OA, α, = 1/8, ω
If o=2π×50 and the outputs 1e, 11 due to the error are determined, the curved line in FIG. 5 is obtained.

Similar to curve A, the portion where the harmonic frequency fH is 2500 Hz or more is indicated by a broken line.

Comparing the curve A and the mouth in Fig. 5, the error output ie, l
When the maximum value of I is high, the stability against malfunctions when harmonic current passes during an accident is almost the same.

FIG. 6 shows the attenuation characteristics of each of the above input conversion devices on a logarithmic scale.

In FIG. 6, the characteristics A and D correspond to those of A and A in FIG. 5, respectively, and are asymptotic to the straight lines A' and B.

In the straight line A', the output is inversely proportional to the square of the frequency, and in the straight line A'
In this case, the output is inversely proportional to the frequency.

The characteristic of the conventional system has a significantly narrower passband than the characteristic of the present invention.

Those with extremely narrow passband characteristics have significant output fluctuations due to component errors.

That is, the constants of the parts change due to errors, and ω in equation (8).

If K3 changes by a factor of 1.02, the output when the fundamental wave is input becomes α, -1/8, which causes an error of about 30% with respect to the original output K3'.

On the other hand, the characteristic (a) with a wide pass band causes little output fluctuation even when component errors occur.

That is, as in the previous case, ω in equation (19).

If it changes by a factor of 102, the output in the case of the fundamental wave input will be α2 - α3-2, and the error is only 4%.

In the event of an external accident, large fundamental wave currents often pass through.
In this case, for the characteristics (mouth), even a small component error will cause a large error as described above, and this error will be the output sum eA/+e
Since it occurs as Bl, it is very likely to malfunction.

On the other hand, for characteristic (a), the error is extremely small;
There is much less risk of malfunction.

As described above, in this embodiment, the input conversion device of the differential relay device is configured so that the output for an input of the same level is approximately inversely proportional to the square of the frequency in a sufficiently high frequency band with respect to the fundamental frequency. It is something.

As a result, the magnitude of the output of the input converter when a harmonic current at the time of an accident whose magnitude is proportional to the frequency is applied is approximately inversely proportional to the frequency, so that if the output of the input converter is If the magnitude is the same regardless of the frequency at the time of an external accident, the higher the frequency, the more severe the risk of malfunction during an external accident can be eliminated, and a differential relay device that can respond stably can be obtained.

Additionally, as a result of the above, it is possible to use an input conversion device with a sufficiently wide pass band near the fundamental wave compared to conventional devices, so there is less delay in the output of the input conversion device with respect to the fundamental wave current due to an internal fault.
This also has the advantage of enabling high-speed protection.

The configuration of the input conversion device is not limited to the embodiment shown in FIG. 4, but various configurations can be used.

FIG. 7 is a diagram showing an example thereof, and the same parts as in FIG. 4 are indicated by the same symbols.

In the figure, R3 is a resistor and C3 is a capacitor, and the impedance of a series circuit of both is sufficiently larger than the impedance of a parallel circuit consisting of a reactor L1, a capacitor C1, and a resistor R.

The illustrated connections provide an output voltage e.

In the figure, the voltage V is shown in the CD formula as in the case of Figure 4,
The output e is expressed by the following equation.

The output e in FIG. 7 is the same as the equation (19) except that the equation (22) is replaced with the equation (30), and is expressed by the following equation.

In equation (32), ω is ω.

When it is sufficiently large, the output e becomes 2 of the frequency.
Approximately inversely proportional to the power of

As a result, as in the case of the input conversion device shown in Figure 4, the output for harmonic current in the event of an accident is approximately inversely proportional to the frequency, eliminating the risk of malfunction in the event of an external fault, and providing a stable response to the differential relay. You can get the equipment.

FIG. 8 is a diagram showing still another embodiment of the input conversion device.

In the figure, T is a current transformer whose primary winding is connected between a pair of input terminals TAP, TAP2, R4 is a resistor connected to the secondary winding of current transformer T, and F, F2, F3 are It's a filter.

A current proportional to the input current ■' flows through resistor R4 and the voltage V
produces i.

A voltage Vi is applied to the cascade of filters F1, F2, F3, and an output e3 is produced between terminals TAP3 and TAP4.

Each filter FI, F2 is a single tuning filter that passes the fundamental wave.
F3 is a resistance filter, and the outputs e, , e2, and e3 are expressed by the following equations.

However, α5, α6, and α7 are attenuation constants.

Each of these filters can be easily obtained using known techniques.

The output e3 is expressed as: When the frequency is sufficiently higher than the fundamental frequency, the output is approximately inversely proportional to the cube of the frequency.

As a result, compared to the case where an input conversion device whose output is inversely proportional to the square of the frequency is used, the higher the frequency, the greater the attenuation, and there is no possibility of the differential relay device malfunctioning in the event of an external fault.

As mentioned above, when the frequency is sufficiently higher than the fundamental frequency, the input conversion device not only makes the output approximately inversely proportional to the square of the frequency, but also approximately inversely proportional to the cube of the frequency. A similar effect can be achieved.

This effect is the same even when the multiplier is raised not only to the third power but also to the fourth power or higher.

That is, when the input conversion device has a sufficiently high frequency with respect to the fundamental frequency, the same effect as described above can be achieved by making the output inversely proportional to the frequency raised to the power of two or more.

In the above embodiments, the differential relay device was explained as having the configuration of formula (7), but the present invention can be applied to differential relay devices with various other configurations and have exactly the same effect. be.

As these differential relay devices, those having the following operating principle are known.

Further, the present invention is not limited to the above two-terminal differential relay device,
The same effect can be obtained when applied to a multi-terminal differential relay device having three or more terminals.

Note that the power system configuration in the above embodiment is a case in which a cable transmission line is connected outside the protected section LN, but the present invention uses a static capacitor for power factor improvement and voltage adjustment instead of the cable transmission line. Even if they are connected, protection can be provided in the same way as above.

As detailed above, when the present invention is applied to a system that generates excessive harmonic transient oscillating current in the event of an accident, it is possible to provide a differential relay device that provides a significantly more stable response than conventional devices. be.

[Brief explanation of drawings]

Figure 1 is a system diagram showing an example of an accident in which harmonic transient vibration is considered severe, Figure 2 is a diagram showing an approximate equivalent circuit for harmonic transient vibration of the system in Figure 1, and Figure 3 is a differential coupling diagram. 4 is a circuit diagram showing an embodiment of the input conversion device of the present invention, and FIG. 5 is a differential relay device operation caused by an error when a harmonic transient oscillating current flows during an external fault. FIG. 6 is a diagram showing the attenuation characteristics of the input conversion device, FIG. 7 and FIG. 8 are diagrams showing other embodiments of the input conversion device, and FIG. 9 is a diagram showing the frequency characteristics of the input conversion device. FIG. 10 is a diagram for explaining the phase error, and FIG. 10 is a diagram for explaining equation (11). TDA, TDB... Single power conversion device, MOD...
...Modulator, DEM...Demodulator, DL...
-...Delay device, DET...Modulator, F,,F
2, F3... Filter.

Claims (1)

[Claims] 1. An input conversion device that inputs a current obtained at each terminal of a power transmission line and outputs an amount of electricity corresponding to this current, and an input conversion device that inputs an amount of electricity output from this input conversion device, A transmitting device that transmits a signal corresponding to this input amount of electricity, a receiving device that receives the signal transmitted from this transmitting device and outputs an amount of electricity corresponding to this received signal, and an output amount of electricity from this receiving device. and the output electricity amount of the input conversion device,
The input conversion device is composed of a differential relay element that operates when the sum of both input electric quantities exceeds a predetermined condition, and the input conversion device adjusts the ratio of the output to the input at a frequency sufficiently higher than the fundamental frequency of the transmission line current. A differential relay device characterized in that the differential relay device is approximately inversely proportional to the power of two or more. 2. In the device described in claim 1, the input conversion device has a resistor R1, a capacitor CI, and a reactor L1 connected in parallel between a pair of input terminals, and a reactor L2 and a capacitor C2 for this parallel circuit. and a resistor R2 were connected in parallel, and output terminals were derived from both terminals of the resistor R2, so that the following relationship was established between the reactors L, L2 and the capacitors C, C2. A differential relay device characterized by: However, ω0: angular velocity of the power system fundamental wave. 3. In the item set forth in claim 1, the input conversion device has a resistor R1, a capacitor CI, and a reactor L1 connected in parallel between a pair of input terminals, and a resistor R3 and a reactor L1 connected to the parallel circuit. A series circuit consisting of a capacitor C3 is connected in parallel, an output terminal is derived from both terminals of this capacitor C3, and the impedance of the series circuit consisting of a resistor R3 and a capacitor C3 is changed to a series circuit consisting of a resistor R1, a capacitor C1, and a reactor L1. A differential relay device characterized by having a sufficiently large impedance compared to the impedance of a parallel circuit.