JPH0447545B2 - - 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 the protective relay device disclosed in, for example, Japanese Patent Application Laid-Open 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 the above-mentioned rectifying and smoothing element. 23 is a vector addition element that adds vectors of each amount of current in the system; 23 is a scalar addition element that adds each amount of current that has been rectified and smoothed; 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 is an output that outputs the above judgment result. is an element.

Next, the principle of operation shown in FIG. 4 will be 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. Furthermore, _〓I ^{t ‖} means vector addition, ‖I ^t ‖ means rectification smoothing, 〓 ⁱ ‖I ^t ‖ means scalar addition, and K ₀ , K ₁ , and K ₂ are constants.
Furthermore, in the above example, the sampling frequency is set to 12 times the system frequency (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 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 ‖. Further, the above-mentioned respective current amounts I _i ^t are vector-added by the vector addition element 22, and further rectified and smoothed by the rectification smoothing element 24.
It is rectified and smoothed by ‖ 〓 ⁱ I _i ^t ‖. In the comparison judgment element 25, the output of the scalar addition element 23 ‖ 〓 ⁱ
I _i ^t ‖ 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 equation (1) is established, an operation signal is output from the comparison/judgment element 25. The output element 26 gives the above operation signal a suitable time limit and outputs it as a final operation output signal.

In the above calculation equation, K ₀ in equation (1) is the minimum operating value, K ₁ is the ratio, and the differential characteristic shown by the solid line (A) in the operating characteristics of a general differential protective relay in Figure 5 is calculated. Therefore, simply rectifying the instantaneous value will result in pulsations and variations in operating characteristics will occur depending on the sampling phase, so it is necessary to perform rectification and smoothing calculations as shown in equation (2), for example. The calculation of equation (2) creates a form similar to four-phase rectification, which reduces operating value errors and reduces variations in differential characteristics due to sampling phases.

[Problem that the invention seeks to solve]

Conventional protective relays are configured as described above, so when handling multi-terminal information such as that applied to bus bar protection, it takes a huge amount of time to calculate equation (2), and CT In order to avoid malfunctions due to saturation, etc., it is necessary to automatically change the constants K ₀ , K ₁ , etc. depending on the amount of current, and greatly change the slope of the differential characteristics in the large current region. There were problems such as time constraints and strong constraints on computer processing power.

This invention was made to solve the above-mentioned problems, and its purpose is to provide a protective relay that is easy to process, responds quickly, and operates stably even when CT is saturated. do.

[Means to solve the problem]

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 to produce the final output by inhibiting the output.

M a ix | 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 represent the sampling amount before the time I _i ^t-ta . (Hereinafter, the first comparison and judgment element will be referred to as the ratio lock element, and the second comparison and judgment element will be referred to as the differential element.) [Operation] By using this principle equation, the ratio lock can be theoretically determined using the instantaneous value of the grid current. The element (first comparison/determination element) becomes capable of a determination operation.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First, in Fig. 1, 1 is a rectifier element that rectifies the current sampled from multiple systems, and 2 is a rectifier element that selects the one with the maximum absolute value of the instantaneous value (suppression amount) among the currents sampled from multiple systems. 2 is a maximum value derivation element (maximum value derivation element), 3 is a vector addition element that vector adds the instantaneous values of currents sampled from multiple systems, and 4 is a vector addition element that adds the absolute value of the vector addition amount to vector addition element 3. A rectifying element 5 is a storage element 6 that stores the amount of vector addition added to the vector addition element 3.
compares the absolute value of the addition amount of the current sampling vector added to the vector addition element amount 3 with the absolute value of the addition amount of the previous sampling stored in storage element 5, and selects the larger one (differential amount). 1st
7 is the first maximum value derivation element 6
8 is a first determination element that determines lock/non-lock based on the ratio between the differential amount selected in 2 and the suppression amount selected in second maximum value derivation element 2; If there is a fact that the first judgment element 7 has determined lock in the previous sampling), a return timer element that forcibly locks the lock even if the first judgment element 7 has determined non-lock this time. , 12 is a first comparison judgment element composed of a first maximum value derivation element 6, a first judgment element 7, and a return timer element 8; 9 is an addition amount of the current sampling vector-added by the vector addition element 3; An effective value calculation element 10 calculates the square sum of the absolute value of the absolute value of the addition amount of the previous sampling stored in the storage element 5, and 10 compares the square sum of the effective value calculation element 9 with the reference value and calculates the magnitude. 13 is a second determination element that determines operation/non-operation based on the relationship;
11 is the first comparison and judgment element 12
This is an inhibiting element that outputs an operating signal only when the lock is not locked and the second comparison judgment element 13 is operating.

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 value Ii ^t obtained by sampling and quantizing the amount of current in the system at time t is applied to the vector addition element 3 and added to calculate E _D ^t . In step 2, the absolute value of each of the above-mentioned current amounts Ii ^t is The maximum value E _R ^t (suppression amount) is calculated by maximum value derivation element 2, and then in step 3, the maximum value E _D of the vector addition amount E _D ^t and the vector addition amount E _D ^t- ta before time ta is calculated. ′ ^t (differential amount) is calculated using the maximum value deriving element 6, and in step 4, the differential amount E _D ′ ^t is calculated.
m is multiplied by ₀ , and the magnitude relationship with the suppression amount E _R ^t is compared with the determination element 7. If the latter is larger or equal, the ratio lock element 12 is set to lock; otherwise, the ratio lock element 12 is set to lock. is determined to be unlocked. In step 5, step 4
If the judgment result is lock, a lock signal is output as is, and if it is non-lock, a lock signal is output if there is a fact that lock has been determined several samplings ago, otherwise a non-lock signal is output. The return timer element 8 performs the return timer calculation such as output. Next, in step 6, the sum of the squares of the vector addition amount E _D ^t and the vector addition amount E _D ^{t - tb before time tb is} calculated using the effective _value calculation element 9.
In step 7, calculate E _D ″ ^t of the above sum of squares and a constant.
The determination element 10 compares the magnitude relationship of K ² ₀ , and when the former is greater or equal, it is determined that the differential element is operated, and otherwise, it is determined that the differential element is inoperative. In step 8, based on the judgment results of step 4 and step 7, the inhibit element 11 operates as a total operation and outputs the final output only when the ratio lock element is inactive and the differential element is active, and in other cases, the overall operation is performed. The final output is determined as non-operation or comprehensive recovery. Note that the order of steps 1 and 2, steps 2 and 3, steps 2-5 and steps 6-7 may be reversed. Also, when the current amount I _i ^t of the grid changes in a positive wave over time, if the tb time is set appropriately,
Since it is already clear that the sum of squares E _D ″ ^t is the square of the effective value, the explanation will be omitted here.

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

Further, in FIG. 2, each determination unit can perform verification multiple times (description will be omitted since it is obvious) 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. can get. In addition, since the above-mentioned 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 based on the instantaneous value, and the solid line A in Fig. 5 is a straight line passing through the origin. It has the feature that the minimum operating value K ₀ and the ratio m ₀ can be set independently. In addition, as shown in Figure 3, when the phases of the terminal currents are not in the same phase or opposite phases, the suppression amount E _R ^t instantaneously increases despite the operating range.
The vector addition amount stored in the time domain (shaded area in Figure 3) in which exceeds the vector addition amount E _D ^t
By compensating with E _D ^t-ta , this region is eliminated and the phase characteristic prevents the operating range from becoming narrower due to instantaneous calculation. Here, in Figure 3, the phase of the two-terminal current is
It shows the waveform of each calculation amount in the case of 120°. Furthermore, in the event of an external accident, excessive current will pass through the outflow side CT.
When the CT secondary current is saturated, the CT secondary current instantaneously decreases and an excessive differential current appears to occur. However, according to the present invention, the ratio lock element that determines the principle equation (3) before saturation occurs. is operating, the recovery timer covers the period in which an excessive differential amount occurs, and the lock state continues and malfunction does not occur.

In addition, in the above embodiment, 2
Although a sum of multiplication operation is used, since it is basically a level judgment, the rectification and smoothing operation of equation (2) explained in the conventional embodiment, or the integral operation number of equation (5) may also be used. , the same effect as the above embodiment is achieved.

‖ 〓 ⁱ I _i ^t ‖= 〓 ⁱ ｜ 〓 ⁱ I _i ｜ ^t-t1 =｜ 〓 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, the arithmetic circuit is configured in such a way that it is theoretically possible to make arithmetic judgments based on the instantaneous value of the system current. When there is a large amount of The burden of
Furthermore, it has the effect of reliably obtaining extremely stable characteristics even against CT saturation phenomenon during external accidents.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the operating principle of a protective relay for a system according to an embodiment of the present invention, FIG. 2 is a flowchart of FIG. 1, FIG. 3 is a diagram of the principle of guaranteeing phase characteristics of the present invention, and The figure is a block diagram of the operating principle of a conventional protective relay, and FIG. 5 is a diagram of the operating characteristics of a general differential protective relay. In the figure, 1 is a rectification element, 2 is a second maximum value derivation element, 3 is a vector addition element, 4 is a rectification element, 5 is a storage element, 6 is a first maximum value derivation element,
7 is a first determination element, 8 is a return timer element, 9
is an effective value calculation element, 10 is a second judgment element, 11
is an inhibit element, 12 is a ratio lock element (first comparison judgment element), and 13 is a differential element (second comparison judgment element).

Claims (1)

[Scope of Claims] 1. A vector addition element that vector adds instantaneous values of currents sampled from a plurality of systems, a rectification element that takes the absolute value of the addition amount vector-added to the vector addition element, and a rectification element that takes the absolute value of the addition amount added to the vector addition element, and a storage element that stores an output; a maximum value derivation element that selects a current sampled from the plurality of systems with a maximum absolute value of instantaneous values and outputs the maximum absolute value as a suppression amount; The absolute value of the addition amount of the current sampling vector-added to the vector addition element and the absolute value of the addition amount of the previous sampling stored in the storage element are compared, the larger one is selected as the differential amount, and the differential amount is Lock or non-lock is determined based on the ratio between the amount and the suppression amount output from the maximum value derivation element, but if there is a fact that lock has been determined several samplings ago, it is forcibly set to lock. Operation/non-operation is determined based on the first comparison judgment element, the absolute value of the addition amount of the current sampling vector added to the vector addition element, and the absolute value of the addition amount of the previous sampling stored in the storage element. Second to do
A protective relay comprising: a comparison determination element; and an inhibiting element that outputs an operation signal only when the first comparison determination element is non-locked and the second comparison determination element is activated. 2. As a circuit configuration of the first comparison and determination element,
a first maximum value deriving element that takes in the outputs of the rectifying element and the storage element; and a second maximum value that selects the instantaneous maximum value of the absolute value of the output of the first maximum value deriving element and the amount of current in the system. Claim 1, characterized by comprising: a first determination element that compares the output of the value derivation element; and a return timer element that causes the output signal of the first determination element to have a predetermined delay time. The protective relay described in item 1. 3 The configuration of the second comparison and determination element includes an effective value calculation element that takes in the outputs of the rectification element and the storage element, and a second element that determines the level of the output of the effective value calculation element as a predetermined constant value. 2. The protective relay according to claim 1, further comprising: a determining element.