JPH0546768B2 - - 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. 4 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. 4 is shown using equations (1) and (2).

‖ 〓 ⁱ I _i ^t ‖≧K ₁ × ( 〓 ⁱ ‖I _i ^t ‖)＋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. Also, in the above example, the sampling frequency is set to the grid frequency.
12 times (30° sampling).

Next, the operation shown in FIG. 4 will be explained. In other words, the amount of current in each sampled power system
I _i ^t is rectified and smoothed by the rectifying and smoothing element 21 as shown in equation (2 ⁾ , and is scalar-added by _the scalar addition element 23 to become 〓 ⁱ ‖I _i ^t ‖. Further, each of the above-mentioned current amounts I _i ^t is vector-added by the vector addition element 22, and further, the rectification smoothing element 24
It is rectified and smoothed by ‖ 〓 ⁱ I _i ^t ‖.

In the comparison judgment element 25, the above scalar addition amount 2
The three outputs 〓 ⁱ ‖I _i ^t ‖ are 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 equation (1) is established, an operation signal is output from the comparative example determining 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 5 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,
For example, if the CT of one terminal is completely saturated and the CT secondary current instantaneously becomes 0, malfunction may occur. Also, this process takes a considerable amount of time and is difficult for computers. There were problems such as strong restrictions on processing capacity.

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 composed of

Max i｜I _i ^t ｜−m ₀ ×Max(｜ 〓 ⁱ I _i ^t ｜, ｜ 〓 ⁱ I _i ^t-ta ｜)≧0 ……(3) ‖ 〓 ⁱ iI _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, it is possible to instantly detect CT saturation in the event of an external accident and prevent malfunctions.

〔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 selects the maximum value of the amount (differential amount), 7 is a first determination element that compares and determines the magnitude relationship between the suppression amount and the differential amount, and 8 indicates that the suppression amount is a predetermined value. a second determination element that determines whether it is below the reference value;
Reference numeral 9 denotes a third determination element that determines the level of the suppression amount at a level different from that of the determination element 8, and 10 outputs an AND condition of the output of the second determination element 8 and the output of the first determination element 7. AND element, 11 is an AND element that outputs the AND condition of the output of the third judgment element 9 and the output of the first judgment element 7, 12 is the above
a first operation timer that outputs an operation when the output of the AND element 10 continues on the operation side a predetermined number of times;
13 is a second operation timer that outputs an operation when the output of the AND element 11 continues on the operation side for a predetermined number of times greater than the operation timer 12;
4 outputs the OR condition of the output of the first operation timer 12 and the output of the second operation timer 13.
OR element, 15 is a return timer, 16 is an effective value calculation element that calculates the square sum of the rectified vector addition amount and the addition amount several samples ago stored in storage element 5, and 17 is the square sum of the above squared sum. a fourth determination element that compares with a reference value and outputs a determination based on the magnitude relationship;
18 is an inhibiting element that locks the output of the determination element 17 with the output of the recovery timer 15; 19 is a ratio locking element (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
The maximum value between E _D ^t and vector addition amount E _D ^t-ta before time t _a
E _D ^t (differential amount) is calculated using maximum value derivation element 6.

Next, in step 4, the determination element 8 compares the suppression amount E _K ^t with the constant K ₁ , and if the former is greater or equal, the process proceeds to step 5, and if the latter is greater, the process proceeds to step 4'. In step 4', the magnitude of the suppression amount E _R ^t and the constant K ₂ (however, K ₁ > K ₂ ) is compared using the judgment element 9. If the former is large, the process proceeds to step 5. If the latter is large, the ratio locking element is instantaneous. Make it inactive and proceed to step 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 using the determination element 7.
When the former is large, the comparison lock element is instantaneously inoperative and the process proceeds to step 9; when the latter is large or equal, the ratio lock element is instantaneously active and the process proceeds to step 7.

In step 6, the same judgment as in step 5 is made, and if the former is large, the ratio lock element is assumed to be instantaneously inoperable, and the process proceeds to step 9. If the latter is large, the ratio lock element is considered to be instantaneously activated, and the process proceeds to step 8.
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, a return timer calculation is performed using the return timer 15, so that when the judgment results of steps 7 and 8 indicate operation, the operation result is output as is, and when it is non-operation, the operation result is continuously output for an appropriate period of time. .

Next, in step 10, the above vector addition amount E _D ^t and
The square sum E _D ″ ^t of the vector addition amount E _D ^t-ta before time t _b is calculated by the effective value calculation element 16, and in step 11, the above 2 is calculated.
The determination element 17 compares the magnitude relationship between the multiplicative sum E _D ″ ^t and the constant K ² ₀ , and when the former is greater or equal, the differential element is activated, and at other times, the differential element is inactivated. Make a judgment.

In step 12, based on the judgment results of steps 4 to 11, 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 9 and steps 10 and 11 may be reversed. Furthermore, when the amount of current I _i ^t in the grid changes over time in a sinusoidal manner, it is already clear that if the time t _b is set appropriately, the sum of squares E _D ″ ^t will be the square of the effective value. Therefore, the explanation will be omitted here.

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. 5 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, since line A in Figure 5 is a straight line passing through the origin, if an internal accident occurs while normal power flow is passing through the system, the judgment element is used so that the return timer division time of the ratio lock element is not delayed. 9 is established,
The value of K ₂ 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 Fig. 3 ^, when the phases of the terminal currents are not the same phase ^or opposite _phases , the time domain (the _phase By compensating for the shaded area in FIG. 3 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 is occurring, the lock state continues and malfunction of the relay is prevented. However, if a very 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 become saturated. There may be cases where sufficient detection is not possible.

However, according to the present invention, the determination element 8 and the operation timer 12 are provided, and the magnitude of the suppression amount is determined ( _K1 is set in the excessive current region) when the CT is extremely saturated. timer 12
This allows instant detection and prevents malfunctions. It is assumed that 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 it may be a rectification smoothing operation as in equation (2) explained in the conventional embodiment, or an integral operation as in equation (5). , the same effect as the above embodiment is achieved.

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

‖ 〓 ⁱ I _i ^t _i ‖=〓｜ 〓 ⁱ I _i ｜ ^tt =｜ 〓 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, since calculation can be performed using instantaneous values in principle, the processing time is short and operation judgment can be made at high speed.
This has the effect of providing protection performance that enables a reliable and high-speed correct response to CT saturation phenomena during extreme accidents that are unique to multi-terminal system protection such as busbar protection.

[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, FIG. 3 is a diagram of the compensation principle of phase characteristics of the present invention, and FIG. 4 5 is a block diagram of the operating principle of a conventional protective relay, and FIG. 5 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 a second determination element, 9 is a third determination element, 12 is a first operation timer, 13 is a second operation timer, 15 is a recovery timer, 16 is an effective value calculation element, 17 is a fourth determination element, and 19 is a ratio lock element ( 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; 2
The amount of current derived by the maximum value derivation element is the first
a second determination element for determining whether or not the current amount is greater than or equal to a reference value; and the amount of current derived by the second maximum value derivation element is greater than or equal to a second reference value that is smaller than the first reference value. a third determination element that determines whether the current amount is greater than or equal to a predetermined multiple of the vector addition amount; a first operation timer that outputs a lock signal for a predetermined period of time when the amount of current is determined to be equal to or greater than the first reference value; a second operation of outputting a lock signal for a time longer than the predetermined time when it is determined that the current amount is equal to or greater than the second reference value and the third determination element determines that the current amount is equal to or greater than the second reference value; a timer; and a second step that calculates the square sum of the vector addition amount rectified by the rectifying element and the vector addition amount several samplings ago stored by the storage element, and determines whether the sum of squares is equal to or greater than a reference value. When the sum of squares is determined to be equal to or greater than the reference value by the comparison determination element No. 2 and the second comparison determination element, and a lock signal is not output from either the first or second operation timer, A protective relay equipped with an inhibit element that outputs an operation command.