JPH0546769B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a protective relay that uses a digital computer to determine the operating state of a power system and protect equipment.

[Conventional technology]

FIG. 5 is a principle diagram showing a conventional protective relay disclosed in, for example, Japanese Unexamined Patent Publication No. 55-23779. In the figure, 21 is a rectifying and smoothing element that rectifies and smoothes the amount of current in the system, and 22 is a rectifying and smoothing element for rectifying and smoothing the amount of current in the system. 23 is a scalar addition element that adds each of the rectified and smoothed current amounts as a vector,
24 is a rectification and smoothing element that rectifies and smoothes the vector addition amount, 25 is a comparison judgment element that compares and judges the vector addition amount (operation amount) and the scalar addition amount (suppression amount), and 26 outputs the above judgment result. It is an output element.

Next, the operating principle of FIG. 5 is shown using equations (1) and (2).

‖ 〓 ⁱ I ^t _i ‖≧K ₁ × ( 〓 ⁱ ‖I ^t _i ‖)＋K ₀ (1) (‖I ^t ‖=｜I ^t ｜+｜I ^t-3 ｜+K ₂ ×‖I ^t ｜− ｜I ^t-3 ‖)
(2) Here, I _i ^t is the amount of current sampled at time t, and the subscript i is the terminal number. Also, 〓 ⁱ I _i ^t means vector addition, ‖I ^t ‖ means rectification smoothing, 〓 ⁱ ‖I _i ^t ‖ means scalar addition, and K ₀ , K ₁ , and K ₂ are constants. In addition, in the above example, the sampling frequency is set to the grid frequency.
12 times (30° sampling).

Next, the operation shown in FIG. 5 will be explained. In other words, the amount of current in each sampled power system
I _i ^t is rectified and smoothed by the rectification and smoothing element 21 as shown in equation (2) to become ‖I _i ^t ‖, and the scalar addition element 23
The scalars are added by 〓 ⁱ ‖I _i ^t ‖. In addition, each of the above current amounts I _i ^t is the vector addition element 2
2, and is further rectified and smoothed by the rectification and smoothing element 24 to obtain ‖ 〓 ⁱ I _i ^t ‖.

In the comparison judgment element 25, the above scalar addition amount 2
The output 〓 ⁱ ‖I _i ^t ‖ of step 3 is multiplied by an appropriate constant, and the equation (1) is determined together with the output 〓 〓 ⁱ I _i ^t ‖ of the rectifying and smoothing element 24. As a result, if formula (1) holds, then
An operation signal is output from the comparison/judgment element 25. The output element 26 gives the above operation signal an appropriate time limit and outputs it as a final operation signal.

In the above equation, K ₀ in equation (1) is the minimum operating value,
Since we are trying to obtain the differential characteristics shown by the solid line A in the operating characteristics of a general differential protective relay in Figure 6 using K ₁ as a ratio, simply rectifying the instantaneous value will result in pulsation, and depending on the sampling phase, Since variations occur in the operating characteristics, it is necessary to perform rectification and smoothing as shown in equation (2), for example. By calculating this equation (2), a form similar to four-phase rectification is obtained, the operating value error can be reduced, and the variation due to the sampling phase of the differential characteristics can be reduced.

[Problem that the invention seeks to solve]

Since the conventional protective relay is configured as described above, when handling multi-terminal information such as bus bar protection, the calculation process of equation (2) takes an enormous amount of time. In addition, in order to avoid malfunctions due to CT saturation, etc., measures are taken such as automatically changing the constants K ₀ and K ₁ depending on the amount of current, and greatly changing the slope of the differential characteristics in the large current region. Although,
It is not perfect; for example, in a case where the CT of one terminal is completely saturated and the CT secondary current instantaneously becomes 0, there is a possibility of malfunction, and this process also takes a considerable amount of time, making it difficult for the computer to process. There were problems such as severe restrictions on ability.

This invention was made to solve the above-mentioned problems, and aims to provide a protective relay that is easy to process, responds quickly, and is stable against CT saturation.

[Means for solving problems]

The protective relay according to the present invention uses the following formula (3) as a principle formula, and uses the output of the first comparison and determination element that determines formula (3) to determine the following formula (4). The arithmetic circuit is configured so that the final output is obtained by inhibiting the output of It is configured to perform equation (3).

Max i｜I _i ^t ｜−m ₀ ×Max(｜ 〓 ⁱ I _i ^t ｜, ｜ 〓 ⁱ I _i ^t-ta ｜)≧0 ……(3) ‖ 〓 ⁱ I _i ^t ‖≧K ₀ …… (4) However, m ₀ and K ₀ are constants, and I _i ^t-ta represents the sampling amount before time t _a . (Hereinafter, the first comparison and judgment element will be referred to as a ratio lock element, and the second comparison and judgment element will be referred to as a differential element.) [Operation] The ratio lock element (first comparison and judgment element) in this invention is, in principle, a By making it possible to perform judgment calculations using the instantaneous current value, CT saturation in the event of an external fault can be instantly detected and locked to prevent malfunction.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a rectifying element that rectifies the current amount of the sampled system, 2 is a second maximum value deriving element that selects the instantaneous maximum value (suppression value) of the rectified current amount, and 3 is the above-mentioned maximum value deriving element. A vector addition element for vector addition of each sampled current amount; 4 is a rectification element for rectifying the above vector addition amount; 6 is an addition of the rectified vector addition amount and several samples before stored in storage element 5. A first maximum value deriving element 7 selects the maximum value of the amount (differential amount), and a first determining element 7 compares and determines the magnitude relationship between the suppression amount and the differential amount.

Reference numeral 8 denotes an operation number detection element that outputs an operation signal when the operation output of the first determination element 7 exceeds a predetermined number of times within a predetermined time; and 9 detects whether the suppression amount is greater than or equal to a predetermined reference value. Second judgment element to be judged, 1
0 is an inhibiting element that inhibits the AND condition of the output of the first determining element 7 and the output of the second determining element 9 with the output of the number of operation detection element 8, and 11 is the output of the first determining element 7. , is an AND element that outputs an AND condition of the output of the second determination element 9 and the output of the operation count detection element 8.

12 is a first operation timer that outputs an operation when the output of the inhibit element 10 continues to be active a predetermined number of times, and 13 is a first operation timer that outputs an operation when the output of the AND element 11 is greater than the operation timer 12 for a predetermined number of times. The second output that outputs the operation by continuing
The operation timer 14 is the output of the first operation timer 12 and the output of the second operation timer 13.
The OR element 15 that outputs the OR condition is a return timer.

16 is an effective value calculation element that calculates the sum of the squares of the rectified vector addition amount and the addition amount of several samples before stored in the storage element 5; 17 compares the above-mentioned square sum with a reference value and calculates the magnitude thereof; 18 is an inhibiting element that locks the output of the determining element 17 with the output of the recovery timer 15; 19 is a ratio locking element (the first 20 is a differential element (second comparison/judgment element) that performs the judgment based on the above-mentioned principle formula (4).

Next, the operation shown in FIG. 1 will be explained. First, when the block diagram of FIG. 1 is realized by a program using a digital computer, the flowchart of FIG. 2 is obtained. That is, in step 1, the current amount I _i ^t of the system is sampled at time t and the quantized current amount is added by the vector addition element 3 to calculate E _D ^t .

In step 2, the maximum value E _R ^t (suppression amount) of the absolute value of each of the current amounts I _i ^t is calculated using the maximum value deriving element 2, and then in step 3, the vector addition amount
Maximum value of vector addition amount E _D ^t-ta before time E _D ^t and t _a
E _D ′ ^t (differential amount) is calculated using the maximum value deriving element 6.

Next, in step 4, the judgment element 9 compares the magnitude of the suppression amount E _R ^t and the constant K ₁ , and if the former is greater or equal, the process proceeds to step 5, and if the latter is large, the ratio lock element is momentarily disabled and the process proceeds to step 4. Proceed to 9.

In step 5, the differential amount E _D ' ^t is multiplied by m ₀ and the magnitude relationship with the suppression amount E _R ^t is compared by the determination element 7.
When the former is greater, the comparison lock element is instantaneously inoperative and the process proceeds to step 9; when the latter is greater or equal, the ratio lock element is instantaneously active and the process proceeds to step 6.

In step 6, the combination of instantaneous operation and instantaneous return of the ratio lock element is performed once, and the number of times the combination occurs per predetermined time is determined by the operation number detection element 8. If the number of times is equal to or greater than the predetermined number N, step 8
If the result is below, proceed to step 7.

In step 7 and step 8, the operation timers 12 and 13 set different times T ₁ and T ₂ (T ₁
<T ₂ ) As the operation output continues, the ratio lock element is activated and the process proceeds to step 9.

In step 9, the operation count detection element 8 counts the number of times the above-described combination of instantaneous operation and instantaneous return of the ratio locking element occurs. Note that the operation number detection element 8 is reset again a predetermined time after the start of counting the number of occurrences of the combination.

In step 10, the return timer calculation is performed by the return timer 15 to output the operation result as is when the result of the determination in steps 7 and 8 indicates operation, and to continue outputting operation for an appropriate time when it is not operation.

Next, in step 11, the above vector addition amounts E _D ^t and t _b
The square sum E _D ″ ^t of the vector addition amount E _D ^t-tb before the time is calculated by the effective value calculation element 16, and the above 2 is calculated in step 12.
The determination element 17 compares the magnitude relationship between the multiplicative sum E _D ″ ^t and the constant K ₀ ² , and when the former is greater or equal, the differential element is operated, and at other times, the differential element is disabled. Make a judgment.

In step 13, based on the judgment results of steps 4 to 12, only when the ratio lock element is inactive and the differential element is active, the overall operation is performed, and the inhibit element 18 is activated to output the final output. The final output is determined as total inoperation or total recovery.

Note that the order of steps 1 and 2, steps 2 and 3, and steps 4 to 10 and steps 11 and 12 may be reversed. Also, the amount of current I _i ^t in the grid
When changes temporally in a sinusoidal manner, it is already clear that if the time t _b is set appropriately, the above sum of squares E _D ″ ^t becomes the square of the effective value, so the explanation is omitted here. do.

When t _b = 90°, (E _D ^t ) ² + (E _D ^t-tb ) ² = |E _D | ² (sin ² ωt + cos ² ωt) = |E _D | ² .

Further, the determining section at step 12 in FIG. 2 can perform verification multiple times (description will be omitted as it is self-evident) as a measure for stabilizing the characteristics.

According to this invention, by determining the solid line A in FIG. 6 using the above-mentioned principle equation (3) and determining the dotted line A in FIG. is obtained, and since the principle formula (3) is determined only by the ratio of the differential amount E _D ′ ^t and the suppression amount E _R ^t , it can be determined using an instantaneous value.

In addition, line A in Figure 6 is a straight line passing through the origin, so if an internal accident occurs while the power flow is passing through the system, the judgment element 9 is set so that the return timer division time of the ratio lock element is not delayed. and K ₁
The value of is set larger than the tidal current so that the ratio lock element does not operate when the tidal current is constantly passing through.

As shown in Figure 3 ^, when the terminal currents are not in the same phase _or out of phase, ^the time domain ( _3rd By compensating for the area (shaded area in the figure) with the stored vector addition amount, this area is eliminated and the operating range is prevented from being instantaneously narrowed due to the phase characteristics.

The above _compensation method is other than the method in step 3 ^.
It is also possible to adjust the operating limit angle of the phase characteristic by multiplying ^ta by an appropriate constant and taking the maximum value.

Furthermore, in the event of an external accident, excessive current will pass through the outflow side.
Current concentrates on the CT, saturating the CT, and causing an apparent differential error. However, before saturation occurs, the ratio lock element that determines the principle formula (3) operates, and the operating signal is converted into a differential error. By prolonging the period during which the relay occurs, the lock state continues and malfunction of the relay is prevented. However, if an extremely large fault current passes through the relay, the CT will become saturated in a very short period of time and the ratio locking element will not be sufficient. There may be cases where it cannot be detected.

However, as shown in the signal waveform diagram in Fig. 4, according to the present invention, in the case of extremely severe CT saturation, the period in which the CT is not saturated is the shortest at the beginning of an accident, and gradually becomes longer. (Because the DC component of the fault current gradually attenuates), at the beginning of the accident, the ratio lock is detected by the operation timer 12 for a short time (instantaneous is also possible), and after the accident occurs, the ratio lock is detected. By detecting the ratio lock using the long-time operation timer 13, it is possible to detect CT saturation at high speed and respond stably to other system phenomena.

Further, the setting time of the operation timer 13 is set to an appropriate time so that the operating range of the phase characteristic does not become narrow.

In addition, in the above embodiment, 2
Although the explanation has been made using a multiplication-sum operation, in principle it is a level judgment, so even if it is a rectification smoothing operation of equation (2) explained in the conventional embodiment or an integral operation such as the following equation (5), In many cases, the same effects as in the above embodiment can be achieved.

Further, at this time, since the calculation only needs to be performed on the vector addition amount E ^t _D , there is no problem with the processing time.

‖ 〓 ⁱ I _i ^t ‖= 〓 ^j ｜ 〓 ⁱ I _i ｜ ^t-tj =｜ 〓 ⁱ I _i ^t ｜＋｜ 〓 ⁱ I _i ^t-t1 ｜＋｜ 〓 ⁱ I _i ^t-t2 ｜＋ …… (5) [Effects of the Invention] As described above, according to the present invention, calculations can be made using instantaneous values in principle, so operation can be determined at high speed with less processing time. In the event of an extreme accident specific to multi-terminal system protection such as
This has the effect of providing protection performance that enables a reliable and high-speed correct response to CT saturation phenomena.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the operating principle of a protective relay according to an embodiment of the present invention, FIG. 2 is a flowchart explaining the operation of this protective relay, and FIG. 3 is a diagram of the compensation principle of phase characteristics of the present invention. 4 is a signal waveform diagram of each part of FIG. 1, FIG. 5 is a block diagram of the operating principle of a conventional protective relay, and FIG. 6 is a diagram of operating characteristics of a general differential protective relay. In the figure, 2 is a second maximum value derivation element, 3 is a vector addition element, 5 is a storage element, 6 is a first maximum value derivation element, 7 is a first determination element, 8 is an operation number detection element, 9 is the second determination element, 12 is the first operation timer, 13 is the second operation timer, 15
16 is a return timer, 16 is an effective value calculation element, 17 is a third judgment element, 19 is a ratio lock element (first comparison judgment element), and 20 is a differential element (second comparison judgment element). In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A vector addition element that takes in instantaneous values of current amounts from multiple systems and adds the vectors, a rectification element that rectifies the vector addition amount vector-added by the vector addition element, and a vector addition amount rectified by the rectification element. and a first maximum value derivation that compares the magnitude relationship between the vector addition amount rectified by the rectification element and the vector addition amount before several samplings stored by the storage element and derives the larger one. a rectifying element that rectifies the amount of current taken in from the plurality of systems, a second maximum value deriving element that derives the largest amount of current from among the amounts of current of each system rectified by the rectifying element; a first determination element that determines whether the amount of current derived by the second maximum value derivation element is equal to or greater than a predetermined multiple of the vector addition amount derived by the first maximum value derivation element; 1
an operation number detection element that outputs an operation signal when the number of times the current amount is determined to be at least a predetermined multiple of the vector addition amount by the determination element becomes equal to or more than a predetermined number within a predetermined time; a second determination element that determines whether the current amount derived by the second maximum value derivation element is equal to or greater than a reference value; and a second determination element that determines whether the current amount derived by the second maximum value derivation element is a predetermined times the vector addition amount. It is determined that the value is greater than or equal to the value, and
When the second determination element determines that the current amount is equal to or greater than the reference value, and the operation number detection element does not output an operation signal,
a first operation timer that outputs a lock signal for a predetermined period of time; the first determination element determines that the current amount is equal to or greater than a predetermined multiple of the vector addition amount; and the second determination element determines that the a second operation timer that outputs a lock signal for a time longer than the predetermined time when the amount of current is determined to be equal to or greater than the reference value and the operation number detection element outputs an operation signal; and the rectification element. a second comparison determination element that calculates the square sum of the vector addition amount rectified by the vector addition amount and the vector addition amount several samplings ago stored in the storage element, and determines whether the sum of squares is equal to or greater than a reference value; , the sum of squares is determined to be greater than or equal to the reference value by the second comparison determination element;
and an inhibit element that outputs an operation command when neither the first nor second operation timer outputs a lock signal.