JPS5910131B2 - Protective relay method - Google Patents

Description

[Detailed Description of the Invention] The present invention detects the magnitude of the difference in current obtained from the secondary sides of current transformers installed at both ends of the range to be protected in the event of a failure of a power transmission line, bus bar, etc. This invention relates to a protective relay method that performs protective operation.

Conventionally, power system protection and control were generally performed using analog quantities of voltage and current, but recently, transmission voltage and
Digital processing of current and voltage is effective for comprehensive protection and control using information from multiple electrical stations due to increased capacity and longer distances for power transmission, and there is a trend toward the realization of this digital processing.

Generally, power transmission line and busbar protection is carried out using a current differential method or a phase comparison method, but when the number of terminals increases, the current differential method becomes advantageous.

In view of the above points, it is an object of the present invention to provide a current differential type protective relay device using digital processing.

This will be explained below with reference to FIGS. 1 and 2.

FIG. 1 is a schematic diagram of the principle of a transmission line with two terminals, explaining an embodiment of the present invention, in which 1 is a current transformer installed at electric station A, and 2 is a current transformer installed at electric station B. , 3 indicates a power transmission line to be protected, and 15 indicates a power transmission line outside the protection range.

The protection operation when the currents obtained from the current transformers 1 and 2 are sampled three times in succession will be explained.

Now, if a fault occurs in part A of line 3 and currents IA and IB flow as shown in Figure 2 A, the difference current between A and B stations will be IA - IB, which is b. It becomes like this.

The currents IA and ■B each have a constant synchronized period △θ of 3
Since it has been sampled and converted into digital, the current values 11sl2, l3 at the three sampling points shown in b are digital quantities and correspond to their instantaneous values, and now i1-I Sin wi...・
・・・・・・・・・・・・・・・(1) R i =I Sin (wt 10△)・・・・・・・・・
・・・・・・・・・(2) 2 R (However, ■R is the effective value of the difference current.) Then, rearranging equation (2), 12=■FLSinwtCOs△θ+I RCOSW
(sin△θ=iCOS△θ+I IPIswi S
ln△θl From (1) and (3), that is, from ``1 t 12, as shown in equation (4), △θ is a predetermined value, so the effective value IR of the difference current can be found, and the effective value IR of the difference current can be found. It will look like C.

Similarly, using 12sl3, the effective value IR' of the differential current shown in FIG. 2d can be found from equation (5).

It goes without saying that R and R' are exactly equal if the differential current IA-IB is a sine wave.

That is, if the digital quantities of 11 and 12tl3 contain harmonic components or become erroneous values for some reason, IR and ■R' will not be equal.

? Since fault currents in power transmission lines generally contain many harmonics, ■R and ■R' are rarely equal.

However, if you remove harmonics by adding a Lylter etc. to the secondary side of each current transformer, the instantaneous value of the difference current 1) 12 + 13
can be seen as the instantaneous value of a waveform that is almost a sine wave.

Therefore, there is a certain tolerance ε that is the difference between the effective values ■R and ■R.
1, ε2, it can be seen that the sampled value has a waveform close to a sine wave.

In this way, if the digital amount of 11) 12tl3 is incorrect for any reason, such as surge input that cannot be removed by a filter, digital conversion, or when transmitting a digital amount, that digital amount will not be used and will be used next time. If the calculation is performed using sample values of , the protection function will not be lost due to an error in the digital quantity.

After confirming the above ε1, R1, R', and ε2, and determining that the obtained effective value is correct, compare the preset value K with the magnitude of either ■ or IR, and then
In the case of diagram A, I, I, > 0 or ■ Allowance > o, and it is determined that it is an internal accident and a protective action is taken.

Furthermore, if a failure occurs at the mouth of the line 15, as shown in FIG. 2B, I and IB will be in the same direction, and the difference current will be almost zero as shown in g.

In this case, as in the case where an accident occurs in the part A above, IR shown in h) IR shown in i by 11+12+13
Find IR,, IR' and find ε, <I R- I
,,'<62, then either effective value and IK
Compare with.

In this case, if IR-Ir is less than O and IB-IK is less than O, it is determined that an external accident has occurred, and no protective action is taken.

In addition, using the part of 61<IR-IR' in the above comparison of effective values ε1 × R-IR' and ε2, the desired result is IR
-■R'=o , IR-■*>o (when IR is large), IR-R'kuO (when IR' is large), the difference in effective value (IR-IR') becomes wavy. .

Assuming this, ε2 is considered as a positive determination level, and ε1 is considered as a negative determination level.

Therefore, considering IIR-IR'l<ε2, ε1
Of course, IR-R' becomes unnecessary.

FIG. 3 is a block diagram showing an embodiment of the present invention based on this theory.

3 is the power transmission line to be protected, 1 and 2 are current transformers installed at each electric station, 4 and 5 are Anaguchi digital converters that convert analog quantities to digital, and 13 is a synchronous sampling oscillator, which is currently used in A Electric. To explain the locations, the digital amount of current sampled at electrical station A and the digital amount of current from electrical station B are transmitted to electrical station A through a transmission line, for example, the micro transmission line 11, and are then processed by the difference current calculation circuit 6. Differential currents 11 v 12 , 13 . . . are obtained.

14.15 is a memory unit for delaying the output for a certain period of time; if the difference current at the current sampling point is i3, the memory unit 14 is for outputting the difference current 11 two samplings ago; outputs the difference current 12 before l sampling.

Then, in the effective value calculation circuit 7, the effective value IR is determined by equation (4) using the first two consecutive sampling values 11 g 12 of the difference current.

Next, the effective value arithmetic circuit 8 calculates the effective value ■R' based on the following two consecutive sampling values 12el3 based on equation (5).

Each of the effective values IR and ■R' is outputted to an effective value comparison circuit 9, and the comparison circuit 9 checks whether there is any error in the converted digital quantity and each circuit.

This check is performed by comparing IR and ■R'. If both data do not match, it is determined that there is no error in the data and is output to the operation judgment circuit 10. However, if they do not match, the data is removed and the next data IR, ■
Waits for input of R'.

The operation determination circuit 10 has a comparison determination section for comparing the input IR or IR' with a determination constant K and a drive section for driving an output relay (not shown), and has a drive section for driving an output relay (not shown), and has an error-free input data. (or IR') and a constant K.

As a result of the comparison, when IR-K>0, it is determined that there is an internal accident (within the protection zone) and a trip signal for the circuit breaker is outputted via the drive unit.

Note that these 6 to 10 and 14.15 constitute a calculation/judgment section, and a similar one is also provided at the B electric station.

At electric station B, the digital amount of current from electric station A is transmitted by the microtransmission circuit 11, etc., and a circuit similar to that at electric station A determines whether the electric current is in operation or not.

As described above, the present invention determines the effective value from the first two sampling values and the last two sampling values of three consecutive samplings of the difference current, and by comparing the results, confirms the correctness of the digital value, and then confirms the correctness of the digital value. Since the operation is determined, an extremely reliable protection device can be obtained for high-speed protection.

Although the above explanation was made using 3 consecutive samplings, errors in digital quantities can be confirmed by calculating and comparing the effective values two or more times with constant synchronized two-sampled data values. It goes without saying that a similar protective operation can be achieved by comparing with the set value.

[Brief explanation of drawings]

Figure 1 is a power transmission line principle diagram for explaining the principle of the present invention.
FIG. 2 is a waveform diagram for explanation, and FIG. 3 is a block diagram showing one embodiment of the present invention. 1 and 2 are current transformers, 4 and 5 are Anaguchi digital converters, 6 is a difference current calculation circuit, 7 and 8 are effective value calculation circuits, 9
10 is an effective value comparison circuit, 10 is an operation determination circuit, and 13 is a synchronous sampling oscillation device.

Claims (1)

[Claims] 1 Current transformers are installed at both ends of the power transmission lines and busbars in the protected area, and the amount of current detected by each current transformer is introduced into an analog-to-digital converter, and each is synchronized with a fixed sampling period. is converted into a digital quantity, and the calculation is performed based on the converted current amount at the own end and the current amount at the other end transmitted via the transmission line. Difference current calculation means that calculates and outputs the difference in the amount of current between the same sampling points detected respectively, and the first two consecutive sampling values and the last two sampling values among the three consecutive sampling values with the outputted difference current. Or an effective value calculation means that calculates and outputs the effective value twice or more with two sampling values of a constant period, and the difference between each effective value calculated by each effective value calculation means is within a predetermined fixed tolerance range. an effective value comparing means which compares whether the sampled value is within a certain tolerance range and outputs the sampled value by determining that there is no error when it falls within a certain tolerance range; An operation determination unit is configured with an operation determination unit that performs a protective operation by determining whether or not it is inside or outside a protection range by comparing the magnitude with a preset current value, and this calculation determination unit is connected to each of the analog-to-digital converters. A protective relay system that is characterized by being provided on the output side of each.