JPS6132895B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides power system protection in which electrical quantities at remote points in a power system are transmitted via a signal transmission device by frequency modulation, and differential protection is performed using the transmitted signals. In a relay device, when a failure such as a momentary interruption or a deterioration of the S/N ratio occurs in the transmission system,
The present invention relates to a device that can prevent a protective relay device from malfunctioning due to this fault, and speed up the time required to restore the original function upon recovery from the fault.

FIG. 1 shows a conceptual diagram of a differential protection device. In other words, current transformers CT1 and CT2 are used to protect the power transmission line L between electric stations A and B, which are remote electric stations.
The secondary current is introduced into the relay device, level-converted, and then frequency-modulated through an appropriate V/F converter and transmitted from the transmitter to the destination electric station.

On the other hand, a signal that is frequency-modulated in the same way by the line current of the other electrical station is sent from the other electrical station, so this is received by the receiving section, and the relay is determined based on the demodulated signal and the signal at the own end. It is something.

FIG. 2 shows the details of a one-terminal relay section. The secondary output of the current transformer CT is converted to an appropriate size ν by the input converter TI, and then passed through the bias circuit BIAS(S) to Vo + ν, which is added with DC Vo.
After that, voltage-frequency conversion is performed by the V/F conversion circuit V/F, and then the signal is sent to the transmission device through the coupling transformer Ts. The purpose of adding bias Vo is to suppress the frequency band of the signal sent to the transmission device.If ν=ΔVsinωt, Vo+ν=Vo+ΔVsinωt Therefore, max|Vo+ν|=Vo+ΔV min|Vo+ν|=Vo−ΔV The voltage-frequency conversion coefficient is k( Hz/voit), then max = o + Δ = k (Vo + ΔV) min = o - Δ = k (Vo - ΔV) where ΔV; amplitude ω = 2π Angular velocity (: frequency) = kVo, Δ = kΔV In other words, Vo ± ΔV Max for DC input
It is possible to suppress the frequency to min. (ν=Δ
(As is well known, when modulating with a varying input like Vsinωt, sideband waves with high frequency components are generated.) On the other hand, the output of the input converter TI comes from the other end as a self-end signal before being guided to the relay judgment section. It is led to a delay circuit TD to compensate for signal transmission delays. This delay circuit delays the signal by an amount corresponding to the transmission delay time of the signal coming from the other end, and then passes the signal to the relay determination section 2 through the coordination filter 1 to match the transient characteristics with the FM demodulation section. A capacitor C1 is connected between them. This is to prevent DC drift from affecting the relay determination section. (This C ₁ forms a high-pass filter.) On the other hand, the signal from the other end guided through the transmission system passes through the coupling transformer _TR , and then undergoes frequency-voltage conversion by the F/V conversion circuit F/V.
V, and apply a bias -Vo to this output. This is done by BIAS (R), but by applying -Vo, [F/V output] -Vo = [Vo + ν] - Vo = ν In other words, the amount of electricity proportional to the input amount of electricity is Reproduced. Furthermore, this signal, whose excess harmonic components are removed by the demodulation filter 3, is led to the relay determination section 2 after the direct current component is removed by the capacitor _CR . C _R is inserted for the purpose of C ₁ . The part indicated by the overall code 4 is the FM demodulation section.

Generally, the relay determination unit 2 calculates a vector sum from the electric quantities obtained through C ₁ and _CR and uses this as the operation amount. For example, the well-known operation determination formula |Id|-k
Ratio differential is performed using _jΣ |Ij|>k _p (where |Id|: vector sum of electric quantities at each end, Ij: current at each end, k and k _p : constants).

By the way, FIG. 3 shows the situation when noise is superimposed on the transmission system in this device. For clarity, the input current is shown as zero.
Figure 3 A shows the FM wave when a single noise enters the transmission system and causes disturbance to the FM wave.
The demodulated wave corresponding to this, that is, the waveform at the point in FIG. 2, is as shown by the solid line in FIG. 3. Also, the waveform at the point in Figure 2 is like the dotted line in Figure 3, because the charge stored in _CR is discharged at a certain time constant.
The waveform has a backshoot (arrow portion in FIG. 3). The one-dot chain line in the figure is the detection level of the relay, and when the absolute value exceeds this detection level, an output "1" is produced as shown in C in FIG. 3 correspondingly. On the other hand, D in FIG. 3 is the output of the noise detector 5, and while this output is "1", the output of the relay is locked. Therefore, as is clear from FIG. 3, the determination section 2 of the relay does not malfunction due to noise superimposition.

Next, FIG. 4 shows the situation when single-shot noises are continuously mixed. The case of FIG. 4 is also shown in a state where the input current is zero for the sake of clarity. What happens when one-shot noise continuously enters the transmission system?
The FM waveform is shown in Figure 4 A. The demodulated wave corresponding to this, that is, the waveform at the point in FIG. 2, becomes like the solid line in FIG. 4. Also, the waveform at the point in Figure 2 is the 4th waveform.
As shown by the dotted line in the figure, the amount of charge stored in the capacitor C _R increases over time, and the backshout also increases accordingly. Depending on the frequency of the noise and the relay time, the backshout exceeds the detection level, as shown in FIG. The output of the level detector in response to the input indicated by the dotted line in FIG. 4A is shown in FIG. 4C. The discharge time constant of the backshut is selected to be long (about several hundred meters) in order to reduce attenuation at the commercial frequency, so the level detection output corresponding to the backshout is quite long, and the noise detector 5 shown in Figure 4 (d) The relay cannot be locked with the output of , and the relay malfunctions as shown in FIG. If an attempt is made to prevent malfunction of the relay by extending the output of the noise detector 5, if noise is superimposed on the occurrence of an internal fault in the system, a problem will occur in which the relay will lock for a long time, resulting in a delay in tripping or a false alarm. There is a possibility that this could be an action.

Therefore, an object of the present invention is to eliminate the need for the relay judgment unit to stop functioning when signal disturbances such as S/N deterioration occur when transmitting a waveform with FM modulation. To provide a conveyance protection relay device capable of preventing malfunction of a relay without increasing its length.

FIG. 5 is a block diagram showing one embodiment of the present invention. In FIG. 5, parts that are the same as those in FIG. 2 have the same functions indicated by the same symbols. Also, after the coordination filter 1 and the demodulation filter 3, the b contact of the auxiliary relay is connected.
b ₁ and b ₂ are connected, but these b contacts are always closed, and when noise is detected, the noise detector 5
The circuit is simultaneously opened by the output of , and the own terminal signal and the demodulated signal are cut off.

In addition, b ₁ and b ₂ are configured to open at the same time in response to the output of the noise detector, but this is because there is a possibility of malfunction due to current if there is a time difference when opening the own terminal signal and the other terminal signal. However, this is to eliminate this possibility.

FIG. 6 is a waveform chart for explaining the operation of the device shown in FIG. For the sake of clarity, FIG. 6 is also shown in a state where the input current is zero. A in FIG. 6 shows the demodulated output when single-shot noise is continuously superimposed, that is, the waveform at the point in FIG. Also, B in Figure 6 shows the output of the noise detection circuit 5. While the output of the noise detection circuit 5 is "1", the b contact of the auxiliary relay is open, so no charge is stored in the capacitor _CR . . Therefore, the waveform at the point in FIG. 5 becomes as shown in FIG. 6C, and does not exceed the detection level indicated by the dashed line. Therefore, the output of the relay will be as shown in Figure 6 (D) and will not malfunction. Moreover, as is clear from FIG. 6, almost at the same time as the noise component disappears, the output of the noise detection circuit 5 becomes "0" and the original function of the relay is promptly restored.

The above explanation deals with the case where single-shot noise is mixed continuously, but even instantaneous interruptions or deterioration of the S/N ratio can be completely eliminated by controlling the demodulated wave according to the present invention when such disturbances are detected. Similar effects can be expected.

In FIG. 5, the auxiliary relay contact is used to open and close the circuit, but it is not limited to this, and any type of contact may be used as long as it can open and close the circuit without time delay. For example, it may be a well-known electronic switch realized by a semiconductor circuit such as a transistor, and in that case, faster operation can be expected than when opening/closing by electromagnetic means.

In Fig. 5, the auxiliary relay is controlled by the noise detection signal, and both input signals to the relay determination section 2 are controlled to zero (for convenience, this is referred to as input zero control), but from the point of view of preventing malfunction. As a redundant design, a function of locking the relay output using a noise detection signal may be added as shown in FIG.

In the above explanation, the case where the power system has two terminals has been explained, but it can also be applied to a multi-terminal protective relay device having three or more terminals without any problem. An example of a three-terminal protective relay device is shown in FIG.

As mentioned above, the capacitors C _R and C ₁ are used to prevent drift effects including carrier drift that always exist in the transmission system from reaching the relay determination section. This function can also be realized by a coupling transformer other than a capacitor, for example. Even in this case, depending on the state of the disturbance in the transmission system, a large DC-like transient waveform may occur in the FM demodulation circuit, which may cause problems such as deterioration of the excitation characteristics of the coupling transformer. Even in that case, it goes without saying that the above-mentioned disadvantages can be overcome by controlling the front stage of the transformer using the method of the present invention. An example is shown in FIG.

In FIG. 5, the b contact of the auxiliary relay is connected before the capacitors C _R and C ₁ , and the auxiliary relay is controlled by the noise detection signal. However, the present invention is not limited to this. Capacitor C
Even if you connect the b contact of the auxiliary relay after _R and C ₁ ,
Similar effects can be expected. An example is shown in FIG.

In Fig. 5, the b contact of the auxiliary relay is connected in front of the capacitors _CR and _C1 , and the auxiliary relay is controlled by the noise detection signal to cut the own terminal signal and the demodulated signal. However, the present invention is not limited to this, but the A contacts a ₁ and a ₂ of the auxiliary relay are connected between the signal line and OV as shown in FIG. 11 in front of the capacitors C _R and C ₁ to output the noise detection signal. Therefore, the same effect can be expected even with a configuration in which the own terminal signal and the demodulated signal are bypassed by these a contacts.

As described above, according to the present invention, when signal disturbance such as S/N ratio deterioration occurs during FM modulation and transmission of a waveform, input zero control is applied to the own terminal signal and demodulated signal input to the relay determination section. As a result, it is possible to obtain a conveyance protection relay device that can appropriately prevent malfunction of the relay and quickly restore the function of the relay body upon recovery from disturbance.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of the differential protection system, Fig. 2 is a block diagram of a conventional device, Figs. 3 and 4 are waveform diagrams of various parts, and Fig. 5 is a block diagram showing an embodiment of the present invention. FIG. 6 is a waveform diagram of each part, and FIGS. 7 to 11 are block diagrams showing other embodiments of the present invention. C ₁ , _CR , _CR ′...Capacitor, b ₁ , b ₂ , b ₂ ′...
...Auxiliary relay normally closed contact, 5...Noise detection circuit,
Tc...Coupling transformer, _a1 , _a2 ...Auxiliary relay normally open contacts.

Claims (1)

[Claims] 1 Frequency modulation of a carrier wave with a signal obtained from each electric station in the power system, and transmitting this modulated wave to an opposing electric station via a signal channel,
In a device in which at least one of the plurality of electric stations inputs a signal obtained at its own terminal and a demodulated signal of a received signal from another terminal to a relay determination section to determine an accident section, the relay When an electric station having a determination unit detects disturbance in the received signal from another electric station, the detection signal causes the demodulated signal introduced into the relay determination unit and the own terminal signal to become substantially zero at the same time. A transport protection relay device characterized in that it is controlled so that. 2. The conveyance protection relay device according to claim 1, which simultaneously cuts the demodulated signal and the own terminal signal based on the disturbance detection signal, and controls the signal input to the relay determination section to zero. . 3. The transport protection relay device according to claim 1, wherein the disturbance detection signal bypasses the demodulated signal and the own terminal signal, and controls the signal input to the relay determination section to zero.