JPS6327929B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the protection of busbars in a double busbar configuration, and in particular, in the past, the opening/closing conditions of a disconnector were required to calculate the amount of differential, which was an obstacle to improving protection reliability. This invention relates to a highly reliable busbar protection method that eliminates the need for this.

FIG. 1 shows a well-known double busbar configuration in which there are four power transmission lines No. 1 to No. 4. In FIG. 1, A and B indicate respective busbars of a double busbar. CB ₁ to _{CB 7} are disconnectors, LS ₁ to _{LS 8} are disconnectors for switching the tangential bus of the power transmission line, C ₁
~ _C7 is a current transformer arranged in each part, and P _A and P _B are voltage transformers arranged in each bus bar.

FIG. 2 is for explaining means for protecting the double busbar shown in FIG. 1 using a conventional method. Now, in Figure 1, if transmission lines 1 and 3 are connected to A bus, and lines 2 and 4 are connected to B bus,
That is, LS ₁ , LS ₅ , LS ₄ , LS ₈ closed, LS ₂ , LS ₆ ,
This is the case when LS ₃ and LS ₇ are open. If an accident occurs on the A bus in this state, the accident will be detected when the differential amount of the A bus exceeds a certain value, and the breaker will be disconnected.
CB ₁ , CB ₂ , CB ₄ , and CB ₆ are cut off and only the accident bus is separated from the grid.

In such a conventional protection system, when calculating the differential amount ΣI _A of the A bus, for example, the current IL 1 of transmission line ₁
is linked to the opening/closing conditions of the disconnectors LS ₁ and LS ₂ and is taken into the arithmetic circuit S _A or S _B as shown in FIG. That is, in the above explanation, line 1 is connected to bus A, so LS ₁ is closed and LS ₂ is open, so auxiliary contact a ₁ linked to LS ₁ is closed, and auxiliary contact b ₁ linked to LS ₂ is opened. The current I _L1 of line 1 is taken into the arithmetic circuit S _A of ΣI _A. Similarly, the currents in line 2, line 3, and line 4 are also taken into arithmetic circuits S _A and S _B , respectively (2,
Lines 3 and 4 are not shown). In such conventional means, poor contact and welding of the auxiliary contacts a ₁ and b ₁ shown in FIG. 2 are a major cause of lowering the protection reliability.

As mentioned above, the present invention aims to provide a highly reliable busbar protection system that does not use auxiliary contacts linked to this disconnector. Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In Fig. 3, 1 detects the positive-sequence change △V and the zero-sequence change △Vo of the voltage obtained from the voltage transformers P _A and P _B arranged on each bus line A and B in Fig. 1. This is a voltage detection circuit. A judgment circuit 5 determines whether the changes △V and △Vo detected by the voltage detection circuit 1 exceed a certain value _K1 , and when they exceed a certain value, a judgment circuit 5 determines whether an accident has occurred inside or outside the bus. decision signal
YES is obtained, and when the value is below a certain value, a healthy state judgment signal NO is obtained. 2 is the differential amount of the A bus (ΣI _A )
It is an arithmetic circuit, which calculates the current I _T of transformer C ₁ and the current I L1 - I _L4 of selected transformers C ₄ - _{C 7} by taking the detected current I _SA of current transformer C ₂ as the total value or _subtracting or differential Find the quantity. Similarly, 3 is a differential amount (ΣI _B ) calculation circuit for the B bus, which uses the detected current I _SB of the transformer C ₃ as a total amount to calculate the current I _T of the transformer C ₁ and the selected transformer C ₄ ~ The differential amount is determined by subtracting the currents I _L1 to _{I L4} of _C7 . Here, transformer C ₄ ~
The selection of _C7 is based on the selection of the disconnector conditions from combinations that result in a differential amount calculation result close to zero in cooperation with the minimization circuits 12 and ₁₄ , which will be described later, without using the conditions of the disconnectors _LS1 to LS8. Changed and determined.

That is, when the judgment circuit 5 outputs NO, the calculation results of the calculation circuits 2 and 3 are as follows.
8 of logic circuits 7 to 10 shown as AND gates
and 10 gates are opened, and the minimization circuit 12,
14. Then, the minimization circuit 12,1
4 supplies the estimated control signal NO of the disconnector to the arithmetic circuits 2 and 3 from lines 29 and 30 until the respective differential amount inputs reach the minimum value.

For example, in differential amount calculation circuits 2 and 3, it is unclear which bus line power transmission lines 1, 2, 3, and 4 shown in Figure 1 are connected to in this method, which does not use disconnector conditions. It is. Therefore, the initial conditions for calculating the differential amount are arbitrarily set in advance, and the calculation is started (an electronic computer is suitable for the calculation). Now, suppose that ΣI _A and ΣI _B are determined by setting the conditions as follows.

ΣI _A = I _SA + I _T + I _L1 + I _L3 …(1) ΣI _B = I _SB + I _T +I _L2 + I _L4 …(2) (Each current represents a vector quantity) In equations (1) and (2), I _SA , I _SB , and _IT are always used to calculate the differential amount. I _L1 to I _L4 are determined by the minimization circuits 12 and 14. If there is no accident on the inside or outside of the bus, the output of the determination circuit 5 becomes NO, and the differential amounts of equations (1) and (2) are input to the minimization circuits 12 and 14.

The minimization circuits 12 and 14 determine whether ΣI _A and ΣI _B are extremely close to zero, and if they are not zero, they control the NO in order to change the estimation of the disconnector condition to the differential amount calculation circuit. Signals are provided from lines 29 and 30. For example, when ΣI _A ≠0, the minimization circuit provides a control signal to the operation amount (ΣI _A ) calculation circuit 2 to replace I _L1 in equation (1) with I _L2 . At this time, 2 performs the following calculation.

ΣI _A = I _SA + I _T + I _L2 + I _L3 ...(3) The result of equation (3) is judged by the minimization circuit 12. If it is still not zero, the minimization circuit 12 instructs the arithmetic circuit 2 to set I _L2. Give a control signal to switch to I _L4 . In this way, the minimization circuit has the function of determining whether the differential amount has become the minimum and controlling the estimation of the disconnector conditions, and the arithmetic circuit performs all combinations of calculations until the differential amount becomes zero. 2 and 3 to find the disconnector conditions under which ΣI _A ≈0 is determined.

Next, when the minimization circuits 12 and 14 respectively find the disconnector conditions under which the differential amount approaches zero, these conditions are taken into the singularity determination circuits 16 and 18, respectively. These singular determination circuits 16 and 18 determine whether ΣI _A ≈0 is established under a single disconnector condition or under a plurality of disconnector conditions. For example, the judgment of the minimization circuit 12 is satisfied under the following two conditions: ΣI _A = I _SA + I _T + I _L1 + I _L2 ≒0...(4) ΣI _A = I _SA + I _T +I _L1 + I _L4 ≒0...(5) Suppose we did. In this case, I _L2 and I _L4 are obviously equal. Such conditions can often occur on parallel two-circuit transmission lines.
In this case, the singular determination circuit 16 outputs a NO signal and detects that the differential amount ΣI _A ≈0 is established based on the estimation of the plurality of disconnector conditions. On the other hand, YES
If the signal is output, it is determined that a single condition is met.

Minimization according to the above single condition ΣI _A ≒0, ΣI _B ≒
When 0 is determined, that is, singularity determination circuit 1
When the outputs of 6 and 18 become YES, the transmission lines connected to the A bus and B bus are determined as a single disconnector condition, and the differential amounts ΣI _A and ΣI _B
This means that the differential amounts of the lines actually connected to the bus lines A and B are calculated.

The shearing judgment circuit 20 is a single judgment circuit 16,1.
When both judgment outputs of 8 become YES, ΣI _A and ΣI _B of differential amount calculation circuits 2 and 3 are newly taken in with the power transmission line connected under these conditions, and these differential amounts become above a certain value. Occasionally, a command to cut off the busbars A and B is issued. This signal is the AND gate 17 described later.
When the detection output of the occurrence of an accident is given, it is taken out from the AND gates 26 and 27 as an actual shearing command.

Next, the minimization circuits 13 and 15 are connected to an AND gate logic circuit 7 whose gate is opened when the determination circuit 5 outputs a YES signal indicating that an accident has occurred.
The differential amounts ΣI _A and ΣI _B as the calculation results are taken in from the differential amount calculation circuits 2 and 3 through the differential amount calculation circuit 9, respectively, and a minimum value is determined for these differential amounts. This process is performed in the same manner as the minimum value determination in the minimization circuits 12 and 14 described above,
The disconnector conditions at that time are also determined, but the condition is that the singular determination circuits 16 and 18 are each generating a NO signal. That is, singularity determination circuit 1
If the outputs of 6 and 18 are NO, it is determined that it is impossible to determine the connection state of the power transmission line in the loaded state, and the system waits to determine the connection state of the power transmission line based on the internal and external fault currents. .

In this way, when the singular determination circuits 16 and 18 are in the NO signal generation state, if an accident occurs inside or outside the bus, the output of the determination circuit 5 becomes YES,
The minimization circuits 13 and 15 are now ready to start determination. At this time, the differential amount calculation circuits 2 and 3 receive the current in the fault state, estimate a certain arbitrary disconnector condition, and start calculation, even though the connection state of the power transmission line is unknown.

Here, depending on the load current, ΣI _A ≒0 or ΣI _B ≒0
When two or more conditions occur, the problem is whether or not the conditions can be narrowed down to a single one due to a fault current generated near the bus bar.

In the load current state, as shown in equations (4) and (5) above,
IL ₂ and IL ₄ are exactly the same and there are multiple judgments, but for example, if an accident occurs on line ₂ (this is a transmission line accident and an accident outside the bus _line ) The inflow directions are different, and in such a case, the differential amount obviously includes the fault current, so even if multiple conditions hold for the load current, it can be reduced to a single fault current. That is, the minimization circuit 1
When 3 or 15 becomes YES, it can be determined that only a single condition is true.

In addition, if an accident occurs on a transmission line other than the No. 2 or No. 4 transmission line, the same I _L2
It is possible that I L4 and I _L4 are the same. However, while the current under load is determined mostly by the load impedance, in the event of a fault, the fault current flows depending on the impedance specific to the transmission line. Therefore, even if there are two parallel lines, the phase arrangement is different (Line 1 has phases a, b, c from the top of the steel plate, and line 2 has phases c, b, c from the top,
Differences in fault current occur due to differences in transmission line constants due to non-strength (order of A-phase) and non-strengthened transmission lines. Therefore, it is possible to narrow down to a single condition that I _L2 ≠ I _L4 , ΣI _A ≒0, and ΣI _B ≒0.

Furthermore, if an internal accident occurs on either the A bus or the B bus, a single condition under which either ΣI _A or ΣI _B becomes zero can be found in the same manner as described above.

As mentioned above, when a single disconnector condition is determined, the minimization circuit 13 or 15 outputs YES, and the disconnection circuit 22 again calculates ΣI _A based on the clear transmission line connection state. , ΣI _B is calculated, and when this differential amount exceeds a certain value, the output line A of 22
Alternatively, a signal indicating bus line breakage or B bus line breakage is obtained at B, respectively.

Even if the circuits 13 and 15 for minimizing the differential amount due to fault current estimate all the disconnector conditions and control the differential amount calculation circuit 2 or 3, ΣI _A ≒0 or ΣI _B ≒0
If the condition does not hold, the unsatisfied condition detection circuits 17 and 19 output a detection signal indicating that the minimization is not satisfied, and inform the constraint judgment circuit 21 that the minimization condition does not hold. The shear failure determination circuit 21 obtains a shear failure signal for the output lines A and B in order to shear both the A bus line and the B bus line on the condition that both outputs 17 and 19 are present. If either the A bus or the B bus has an internal fault, an output is obtained from either of the failure condition detection circuits 17 and 19, but in this case the sheath failure determination circuit 21 does not issue a failure signal. Detection circuit 17,1
9 are both detected and output when an accident occurs on both the A bus and B bus, or when trying to switch the connection of the transmission line of line 1 from A to B in Figure 1, for example, LS ₁ and LS ₂ are both closed and an accident occurs on one of the busbars. In such a case, both the A bus line and the B bus line are naturally cut off by the determination circuit 21.

Reference numeral 4 in FIG. 3 is a differential amount calculation circuit that calculates the differential amount of the A and B bus lines at once, and a determination circuit 6 determines whether or not this differential amount is equal to or greater than a certain value. If the value exceeds a certain value, it is determined that there is an accident on either bus A or B, and the AND gate 11 with the above-mentioned output for determining whether the bus is inside or outside the bus is used as a condition for a bus accident to occur. Bus bar protection relays have a particularly large impact on the system when they malfunction, and it is common to include such differential conditions and voltage change conditions in order to improve the reliability of malfunctions. When the output of the AND gate 11 is obtained, the shear failure judgment circuit 20 mentioned earlier,
OR if either 21 or 22 has a power failure signal
Gates 23, 24, 25, AND gates 26, 2
7 or 28, the appropriate busbar is selected and disconnected.

As described above, the present invention performs the first and second minimization detections that are obtained by changing the disconnector conditions from the current differential amount depending on the presence or absence of a bus fault, and makes single or plural determinations on the disconnector conditions. In the single case, the busbar disconnection signal is obtained when the differential amount exceeds a certain value, and in the plural case, when an accident occurs, the disconnector condition is determined from the second minimization,
In the case of single judgment, the busbar disconnection signal is obtained when the differential amount exceeds a certain value, so the opening/closing conditions of the disconnector, which conventionally had problems in terms of reliability, are not used for relay judgment, and the conventional This eliminates erroneous protection operations due to abnormalities in the auxiliary contacts that determine the opening/closing conditions, and makes it possible to reliably select and disconnect the faulty busbar, resulting in an extremely reliable busbar protection method. In particular, the present invention determines whether the disconnector condition is singular or plural even when minimizing detection, and when there are multiple determinations, it is assumed that it is impossible to estimate the disconnector condition under load, and when an accident occurs, minimizing detection is performed. In order to estimate the disconnector conditions, it is possible to accurately determine faults on bus A and B even when there are lines with almost the same current. Also, the differential amount ΣI _A , ΣI _B
The condition for which is close to zero is true for multiple disconnector conditions when there is a load on two parallel circuits or a remote external short circuit, and when it is true for a single line, it is true for a single line transmission line under load or in the event of an external fault. By providing a single determination means, it is possible to reliably determine the connection state of the disconnector in a load state or an external accident state.

In addition, this method uses the instantaneous values of current and voltage input at intervals of about 2 to 3 ms, which can be calculated digitally using microcomputers, which have been particularly rapidly developed in recent years. Calculations for one circuit condition can be executed at a high speed of 1.5 μs, so even if the number of power transmission lines increases, the operating time of the relay will hardly be affected.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a double bus bar for explaining the present method and the conventional method, Fig. 2 is a schematic diagram of the use of disconnector conditions for explaining the conventional method, and Fig. 3 is an example of an embodiment of the present invention. FIG. 1... Voltage detection circuit, 2, 3... Differential amount calculation circuit,
4... Differential amount batch calculation circuit, 5, 6... Judgment circuit, 1
2 to 15... Minimization judgment circuit, 16, 18... Singularity judgment circuit, 17, 19... Unsatisfied condition detection circuit, 2
0, 21, 22...Shrinkage judgment circuit.

Claims (1)

[Claims] 1. In protecting double busbars consisting of two buses using the current differential method, one of the busbars,
accident determination means 1 and 5 for determining the presence or absence of an accident;
From this determination, the first minimization detection means 2, 3, 8, 10, 1 obtains by changing the disconnector conditions so that the differential amount calculation result of each bus becomes close to zero when there is no accident.
2, 14, singularity determination means 16, 18 for determining whether or not the disconnector condition determined by the detection means is a single disconnector condition; A first shear breakage determination means 20 that obtains a shear breakage signal for each bus bar when the value exceeds a certain value; Second minimization detection means 2, 3, 7, 9, 13, 1 which changes the disconnector conditions so that the quantity calculation result is close to zero.
5, a second shear failure determination means 22 for obtaining a bus line shear failure signal in which the differential amount is equal to or greater than a certain value when the differential amount is minimized on one side by this detection means;
When the amount of differential calculated for the two buses collectively is equal to or greater than a certain value, the accident determining means determines that an accident has occurred, and when the bus line breakage signal and the bus breakage signal are established simultaneously, the selection of both buses is obtained. Selection means 4, 6, 11, 26,
27, and from the calculation of the differential amount of both buses when arbitrarily estimating and giving which bus the transmission line is connected to, the condition that the differential amount of each of the two buses is the minimum is determined by the transmission line. A busbar protection system characterized by determining load conditions and internal and external fault conditions of the busbar, and selecting and disconnecting faulty busbars by determining whether the conditions are single or multiple.