JPS6412163B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protective relay for protecting an electric power system, and particularly to a protective relay constructed using a digital processing device such as a microcomputer.

In recent years, with advances in semiconductor technology, so-called digital protective relay devices configured using digital processing devices such as microcomputers are being put into practical use as protective relay devices for protecting power systems. Furthermore, conventionally, protective relay devices have been composed of two different types of protective relays. One of them is a protective relay, commonly called a main relay, that detects only accidents that occur within the protection range of the protective relay device among accidents that occur in the power system. This main relay needs to identify only accidents within the protection range from complex power system accident phenomena, and its determination section requires advanced arithmetic processing functions. The other type is what is called a fail-safe relay, and its responsibility is to prevent errors or disconnections in the power system due to malfunction of the main relay when the power system is normal. As long as it can reliably detect at least an accident that occurs within the protection range of the main relay, a strict accident identification ability is not required. Therefore, the determining section does not require a very sophisticated arithmetic processing function. Further, such fail-safe relays are the final element to prevent malfunctions of the protective relay device, and are required to have high reliability.

By the way, when trying to convert a protective relay device consisting of a main relay and a fail-safe relay into a digital relay, one of the characteristics of a digital relay is "hardware standardization".
A possible method is to take advantage of this and apply the same hardware to the main relay and fail-safe relay. However, such a method means that hardware that originally has a sophisticated arithmetic processing function is applied to a fail-safe relay that only needs a relatively simple arithmetic processing function. In other words, this not only results in wasted use of arithmetic processing functions, but also impedes miniaturization of the device, increases the cost of the device, and is economically disadvantageous.

The present invention was made in view of the above-mentioned circumstances, and its purpose is to configure a relay that does not require advanced arithmetic processing functions, such as a fail-safe relay, with simple hardware, and to make the arithmetic processing functions effective. It is an object of the present invention to provide a protective relay which can be used to reduce the size of the device and improve its reliability, and which is also economically advantageous. In order to achieve the above object, the protective relay according to the present invention has a selection circuit that receives a plurality of electrical quantities corresponding to the current and voltage of the power system and selects whether the input electrical quantities are "on" or "off". a variable gain circuit that can vary the magnitude of at least one of the plurality of electrical quantities selected by the selection circuit; and a variable gain circuit that calculates the sum or difference between the output from the variable gain circuit and other electrical quantities. A calculation unit that outputs a reference quantity of electricity for operation judgment, a reference quantity generation circuit that generates a reference quantity of electricity for operation judgment, a reference quantity of electricity from the reference quantity generation circuit and an output from the computing unit, and calculates the magnitude relationship between the two. A comparator that sends out an output according to
and a digital arithmetic processing section having means.

(A) Means for controlling “on” and “off” of the selection circuit, (B)
means for controlling the gain of the variable gain circuit, (C) means for setting the reference amount of the reference amount generation circuit, (D) means for detecting the zero point of the output of the arithmetic unit, and (E) means for detecting the zero point. Means for determining whether the output of the arithmetic unit after a predetermined period of time is larger or smaller than a predetermined value, using the zero point as a reference.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows in block form an example of the construction of a protective relay according to the present invention. In Figure 1,
1 inputs electrical quantities I and V corresponding to the current and voltage of a power system (not shown), and switches SW ₁ , which selects each input electrical quantity I and V based on a control signal S ₁
This is a selection circuit that selects and sends out switching by turning SW ₂ on or off. 2 is the switch of the selection circuit 1 above.
This is a variable gain circuit that receives as input the amount of current and electricity I that is switched and sent out by _SW1 , and can vary the gain of this amount of current and electricity I based on the gain control signal _S2 . Further, reference numeral 3 denotes an arithmetic unit that calculates the difference (V-I) between the voltage electricity quantity V switched and sent out by the switch SW ₂ of the selection circuit 1 and the output electricity quantity I of the variable gain circuit 2. 4 is the output electricity quantity e _x of this computing unit 3
and the reference electric quantity e _r which is the output of the reference quantity generating circuit 5.
This is a comparator that compares the size with. Furthermore,
Reference numeral 6 denotes a digital arithmetic processing section which receives the output _S3 of the comparator 4 as an input and sends out a protection output _S4 based on the result of arithmetic processing, the details of which will be described later. Further, this digital arithmetic processing unit 6 controls the selection control signal S ₁ that controls switching of each switch SW ₁ and SW ₂ in the selection circuit 1 to “ON or OFF”, and the gain in the variable gain circuit 2. gain control signal S ₂ ,
and a selection control signal _S5 for selecting the magnitude of the reference electric quantity _er , respectively, at a timely manner.

FIG. 2 is a flowchart showing an example of the arithmetic processing functions of the digital arithmetic processing section 6 in FIG. 1. In other words, the first
Step a (second means) is a step in which the gain of the variable gain circuit 2 is determined to be, for example, Z by the gain control signal _S2 . The second step (first means) b includes selecting the selection circuit ₁ by the selection control signal S1.
In this step, switch SW ₁ is turned on and switch SW ₂ is turned off. (As a result, "ZI" and "0" are applied to the input of the calculator 3, and "-ZI"
is output. ) Third step (third means)
c is a selection control signal S ₅ to the reference amount generating circuit 5;
This is the step of setting the reference quantity of electricity _er to zero. The fourth step (fourth means) d reads the output _S3 of the comparator 4 at high speed, and as a result of the change in the output S3, the output _ex of the arithmetic unit ₃ , that is, "-"
This is the step of detecting the zero point of ZI.
After detecting the zero point of "-ZI" in step d (fourth means), the next fifth step (first means)
Step e is a step in which the selection control signal _S1 controls the switch _SW1 in the selection circuit 1 to be "off" and the switch _SW2 to be "on". (As a result, "0" and "V" are applied to the input of the arithmetic unit 3, and "V" is output.) The sixth step (third means) f is
This is a step in which the reference electric quantity _er is set to a predetermined value by the selection control signal _S5 to the reference quantity generating circuit 5. The seventh step (fifth means) g is based on the zero point of "-ZI" detected in the fourth step (fourth means) d, and the comparison after a predetermined period of time including immediately after the zero point. The magnitude relationship (e _x −er) between the input of the calculator 4, that is, the output e _x =V of the calculator 3, and the reference electric quantity e _r set in the sixth step (third means) _f is expressed as follows: In this step, the determination is made by reading the output _S3 of the comparator 4. Then, the above-mentioned sixth and seventh steps (third and fifth means)
f, g and the fifth step (first means) e
is repeated as many times as necessary to obtain predetermined relay characteristics. The final eighth step (sixth means) h selects the output _S4 of the digital arithmetic processing unit 6 as a protection output according to the determination result in the seventh step (fifth means) g. This is the step to send to the outside. Incidentally, in the above, the fifth step (first means) e may control both the switches SW ₁ and SW ₂ in the selection circuit 1 to be turned on by the selection control signal S ₁ . In this case, “ZI” and “V” are applied to the input of the calculator 3, and e _x =
"V-ZI" is output, and in the seventh step (fifth means) g, after a predetermined period of time has elapsed based on the zero point of "-ZI" detected in the fourth step (fourth means) d. Input e _x =V−ZI of comparator 4 at
The output of the comparator 4 determines the magnitude relationship with the reference electric quantity e _r set in the sixth step (third means) f.
Determine by reading S ₃ .

Next, the action of the protective relay with such a configuration will be explained in the third section.
An example will be described in which the relay characteristics shown in the figure are realized. It is assumed here that the input electrical quantities I and V in FIG. 1 are electrical quantities corresponding to the electric power system's current I _p and voltage V _p , respectively, and have the following correspondence relationship.

I∝I _p <φ … V∝V _p … In other words, the electric current I is proportional to the electric current I _p of the power system advanced by an angle (in electrical angle) I _p <φ, and the voltage electric quantity I V is also the system voltage V _p
It is proportional to .

On the other hand, the relay characteristics shown in Figure 3 are as follows:
This is an undervoltage relay with directionality based on I _p , which operates when voltage and electrical quantity V enters the hatched area in the diagram, and is used as an accident detection relay on power transmission lines.

Next, the specific response of the device will be described. First, in the digital arithmetic processing section 6, each (arithmetic) process is sequentially performed based on the first to third steps a, b, and c shown in FIG.
The output _S3 of the comparator 4 in the figure is the reference amount e _r =0 of the reference amount generating circuit 5 and the output e _x =- of the arithmetic unit 3.
An output is obtained according to the magnitude relationship of ZI, that is, whether (−ZI)−0=“−ZI” is “positive or negative”. Therefore,
By periodically reading the output signal S ₃ of the comparator 4 in the digital arithmetic processing unit 6, the signal S ₃ .
(e _x ) “−ZI” changes from “positive” to “negative” or “negative”
In the fourth step d, the point in time when the value changes from to "positive", that is, the zero point of the output "-ZI" of the arithmetic unit 3, is detected. (Here, the response when a zero point is detected where the signal "-ZI" changes from "negative" to "positive" will be described below.) As a result, first, in the fourth step d, the signal "-ZI" changes from "negative" to "positive". If a zero point from “negative” to “positive” is detected, the input e _x of comparator 4
, the signal V is output from the arithmetic unit 3 through the processing in the fifth step e, and the following judgments are immediately made in the sixth and seventh steps f and g.

VK ₁ ... V-K ₃ ... Here, K ₁ and K ₃ are the values shown on the relay characteristics in Fig. 3 above, and the magnitude of the reference electrical quantity e _r set in the sixth step f. It shows that.

Also, after detecting the zero point of the above signal “-ZI”, the electrical angle
At the lapse of time T (π/2) corresponding to 90°, the following determinations are made in the sixth and seventh steps f and g in the same manner as above.

VK ₂ ...Next, in the process of the fifth step e, (V-ZI) is output from the arithmetic unit 3 as the input e _x of the comparator 4, and the following judgment is made in the same way as above and seventh steps f and g.

(V-ZI)K ₄ ... In this case, the fact that all of the above conditional expressions ~ holds true means that the voltage and electricity quantity V exists in the hatched area in the relay characteristic diagram shown in Figure 3 above. It is. Therefore, in the next eighth step h, if all of the above conditional expressions ~ are satisfied, the digital arithmetic processing section 6 sends out a protection output as its output _S4 , and the above conditional expressions ~ are satisfied. If any one of the following does not hold true, the output _S4 is not sent out. After performing the above processing, the first or second
Return to step a or b.

On the other hand, in the first to fourth processing steps a to d,
The same is true when a zero point from "positive" to "negative" of the signal "-ZI" is detected. Immediately after this zero point is detected, the following equation is determined: VK ₁ ... VK ₃ ... Time T equivalent to 90° electrical angle after detection
When (π/2) has elapsed, determinations as shown in the following equation are made in the sixth and seventh steps f, g and the fifth step e.

VK ₂ ... V-ZIK ₄ ... As a result, when all of the above conditional expressions ~ are satisfied, the output S ₄ as a protection output is sent out in the eighth step in the same way as above, and the above ~
If any one of the conditional expressions does not hold true, the output _S4 is not sent out.

Note that the present invention is not limited to the above embodiments, but can also be implemented as follows.

(1) In the above embodiment, ~ or ~
In the above description, the output _S4 is sent on the condition that all of the conditional expressions are satisfied, but the combination of these conditional expressions is not limited to this, and may be, for example, the conditional expressions - or. In other words, all the conditional expressions of ~ hold true,
Alternatively, even if the output _S4 is sent out when all the conditional expressions are satisfied, the relay characteristics as shown in FIG. 3 can be obtained.

In addition, in the above, the time T (π/2) corresponding to an electrical angle of 90° with the zero point of the signal “-ZI” as a reference
The judgment timing of the conditional expression after the elapsed time is
This is determined by a counter, a register, etc. included inside the digital arithmetic processing section 6 in FIG. Further, it goes without saying that a microcomputer or the like may be applied to the digital arithmetic processing section 3 for digital arithmetic processing as shown in FIG.

(2) In the above embodiment, the configuration of the reference amount generation circuit 5 was not described in detail, but the reference amount generation circuit 5 is usually configured as a digital/
An analog converter (D/A converter) is used, and an example of its configuration is shown in FIG. 4A. D/A
Since the converter converts the encoded digital signal into a corresponding analog quantity as is well known, it can be easily connected to the data bus of the digital arithmetic processing unit 6 in FIG. 1 or to the digital output circuit. For example, if the digital processing unit 6 is an 8-bit microcomputer, an 8-bit D/A converter with a latch can be connected to its data bus (corresponding to S5 in FIG. _4a ). ⁸ = 256 levels of reference electrical quantity can be generated.

On the other hand, in FIG. 4b, the reference amount generating circuit 5 is connected to a resistor.
This shows an example in which R _i (i=1 to 4), an inverting circuit 7 using an operational amplifier, and a multiplexer 8 are connected to a digital output circuit of a digital arithmetic processing section 6. In other words,
The voltage divided by the resistor R _i is K ₁ ~ K ₄ , −
K ₁ to −K ₄ and 0 are introduced into the multiplexer 8, respectively, and are input to the digital arithmetic processing unit 6.
The reference electrical quantity is selected by the digital output S ₅ of
It is input to comparator 4 as e _r .

(3) Furthermore, a general digital/analog converter (D/A converter) can be similarly used for the variable gain circuit 2 in the above embodiment. A normal D/A converter has a reference voltage input terminal V _REF and can obtain a voltage output obtained by multiplying a value given by a digital code by the reference voltage input. Therefore, for example, as shown in FIG. 5, the reference voltage input terminal V _REF and the selection circuit 1 are connected, and the output terminal OUT and the arithmetic unit 3 are connected, respectively, and the gain control signal S ₂ is connected from the latch input. If you input the constant Z, D/A
The converter will function as a variable gain circuit.

(4) In the above embodiment, it goes without saying that if the determination of the conditional expressions of and is omitted, the relay characteristics as shown in FIG. 6 can be obtained.

(5) In the above embodiment, only two quantities, current, voltage, and electrical quantities I and V are input to the device. Electrical quantities corresponding to the current and voltage may be introduced, respectively. An example of the configuration of the input circuit in this case is shown in FIG. In FIG. 7, the difference from the input circuit in FIG. 1 is that the selection circuit 1 is composed of switches SW ₁ to _{SW 6} , and the number of selection control signals S ₁ to the selection circuit 1 is accordingly changed. This is the only point where . Also,
The processing in the digital calculation unit 6 in this case is as follows:
The processing of the flowchart shown in FIG. 2 may be performed by processing the R, S, and T3 phases using well-known time-sharing processing.

(6) In the above embodiment, the digital calculation processing unit 6
The processing in is not limited to the flow chart shown in FIG. For example, it goes without saying that processing functions for improving reliability, such as automatic monitoring, automatic inspection, and self-diagnosis, can be added using free time in each step.

(7) In the above embodiment, the magnitude of the reference electric quantity e _r (K ₁ to K ₄ , −K ₁ to −K ₄ ), the gain Z of the variable gain circuit 2, etc. are all determined in advance. As mentioned above, each of these values determines the relay characteristics, and may need to be able to be varied or set externally. In such a case, external settling becomes possible by, for example, a configuration as shown in FIG. That is, FIG. 8 shows a configuration in which a numerical value setter 9 such as a digital switch is provided on the data bus _S5 of the digital arithmetic processing section 6 in FIG. After reading each numerical value set in the device 9 via the data bus _S5 , the set value is outputted to the D/A converter as the reference generation circuit 5 again via the data bus _S5 , and gain control is performed. Variable gain circuit 2 via signal S ₂
This is to set the gain of . With this configuration, the relay characteristics shown in FIG. 3 can be arbitrarily set from the outside.

(8) In the above embodiment, a switch SW is used as the selection circuit 1 that turns input on and off.
may be either mechanical or electronic. Further, as still another embodiment, an example constructed using a variable gain circuit 2 is shown in FIG. In FIG. 9, the variable gain circuit 2 can make its output zero by setting its gain to zero, and can obtain an output equal to its input by setting its gain to "1". Therefore, this variable gain circuit 2 can also function as a selection circuit 1 that switches input between "on and off."

In addition, the present invention can be modified and implemented in various ways without changing the gist thereof. Therefore, as described above, the protective relay with this configuration can be used as a fail-safe relay or an accident detection relay that simply detects the presence or absence of an accident in the power system, which has relay characteristics that do not require advanced calculation processing functions. As is clear from the above, when implemented as a digital relay, the device can be configured with an extremely small number of parts, which greatly contributes to the miniaturization, higher reliability, and lower cost of protective relay devices. It is something that can be done. In addition, the present invention has the general merit of digital relays that it is possible to standardize the hardware (various relay characteristics can be realized without changing the hardware), as well as automatic inspection and automatic monitoring functions. This makes it possible to obtain an excellent protective relay that is extremely easy to add.

As explained above, according to the present invention, relays such as fail-safe relays that do not require advanced arithmetic processing functions are configured with simple hardware, and the arithmetic processing functions are effectively used to reduce the size of the device. Reliability can be improved. Furthermore, it is possible to provide a protective relay that is extremely economically advantageous.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing one embodiment of the present invention;
Figure 2 is a flowchart showing the processing functions of the digital arithmetic processing section in Figure 1, Figure 3 is a diagram showing an example of relay characteristics realized by the present invention, Figures 4, 5, 7, 8, and 9. 6 is a schematic configuration diagram showing another embodiment of the present invention, and FIG. 6 is a diagram showing other relay characteristics realized by the present invention. 1... Selection circuit, 2... Variable gain circuit, 3...
Arithmetic unit, 4...Comparator, 5...Reference amount generation circuit,
6...Digital arithmetic processing section, 7...Inversion circuit, 8
...Multiplexer, R ₁ ~ R ₄ ... Resistor, SW ₁ ~
SW ₆ ...Switch.

Claims (1)

[Scope of Claims] 1. A selection circuit which inputs a plurality of electric quantities corresponding to the current and voltage of the power system and selects whether the input electric quantities are "on" or "off"; a variable gain circuit capable of varying the magnitude of at least one of the plurality of electrical quantities, which calculates and outputs the sum or difference between the output from the variable gain circuit and the other electrical quantities; a computing unit; a reference quantity generating circuit that generates a reference quantity of electricity for operation determination; inputting the reference quantity of electricity from the reference quantity generating circuit and the output from the computing unit; a comparator that sends out an output from the comparator; and a digital arithmetic processing unit that receives the output from the comparator and has at least the following means (A) to (E). . (A) Means for controlling "on" and "off" of the selection circuit. (B) means for controlling the gain of the variable gain circuit; (C) means for setting the reference amount of the reference amount generation circuit; (D) means for detecting the zero point of the output of the arithmetic unit; (E) Means for determining whether the output of the arithmetic unit after a predetermined period of time is larger or smaller than a predetermined value, using the zero point detected by the zero point detecting means as a reference. 2. The protective relay according to claim 1, wherein at least one of the plurality of electrical quantities is phased by a predetermined electrical angle. 3. Claim 1, in which at least one of the variable gain circuit and the reference amount generation circuit is constructed using a digital/analog converter.
Protective relay as described.