JP2885342B2 - Protection control device - Google Patents

Description

Description: Object of the Invention (Field of Industrial Application) The present invention relates to a protection control device, and more particularly to a protection control device for detecting a device failure that occurs discontinuously.

2. Description of the Related Art Conventionally, a protection control device, particularly a protection control device for a power system, has been required to have high reliability. For example, in the event that the protective relay device malfunctions, the effect is large, and in the worst case, it may lead to system collapse. In addition to the protection relay device, other protection control devices, such as a system stabilization device, an accident point locating device, and a system electric quantity observation device, also have responsibilities from the viewpoint of the operation of the power system. High reliability is still required.

Measures to improve the reliability of these protection control devices include improving the quality of the components used, multiplexing configuration, multi-sequence configuration, and applying automatic monitoring. In general, it is widely used.

On the other hand, in recent years, the practical application of a protection control device to which a microprocessor is applied has been rapidly advanced, and at the same time, the complexity of the device has been increased more than before. Therefore, the above-mentioned automatic monitoring function has also become more sophisticated in response to the development of such a device configuration.

As a typical protection control device in recent years, there is a digital protection relay device using a microcomputer. Hereinafter, the problems of the automatic monitoring function of the protection control device will be clarified by taking the automatic monitoring function of the digital protection relay device as an example.

The feature of the automatic monitoring function of the digital protection relay device (hereinafter referred to as digital relay) is that it can monitor most of the hardware that makes up the device by utilizing the processing function of the microprocessor. It is.

The following is an overview of typical monitoring performed by digital relays. FIG. 13 is a configuration diagram of a general digital relay.

In FIG. 13, the current / voltage amount of the transmission line 1 is input to an input converter 4 via a current transformer (CT) 2 and a voltage transformer (PT) 3.
, Where it is converted to a predetermined level. The output of the input converter 4 is converted into a stable signal via the analog filter 5, and the current / voltage amount taken into the sampling / hold circuit (S / H) 6 is converted into a DC amount and converted into a DC (multiplexer) (MPX) 7. And is taken into an A / D converter 8 for sequentially converting an analog amount into a digital amount. And A
The digital data of the current / voltage amount converted by the / D converter 8 is stored in a data memory (RAM) in the microcomputer 9.
9-1 are sequentially stored. On the other hand, program memory (RO
M) 9-2 stores a program instruction. According to the instruction, the central processing unit (CPU) 9-3 performs an operation using the data of the data memory (RAM) 9-1. A predetermined determination result or the like is output to the outside via an input / output interface (I / O) 9-4.

The digital relay having the above configuration realizes a plurality of protection characteristics by using current / voltage data obtained through the input converter 4.

As described above, the monitoring of each hardware unit constituting the digital relay is realized by utilizing the processing function of the CPU 9-3. According to the Electric Cooperative Research Vol. 41, No. 4, "Digital Relay", page 71
Monitoring of the degree of balance of each phase for monitoring the T circuits 2 and 3, monitoring of the zero-phase component for monitoring the input converter 4, analog filter 5, S / H6, multiplexer 7, etc., and monitoring for the accuracy of the A / D converter 8 / D accuracy monitoring, DI / DO monitoring for monitoring input / output interface (I / O) 9-4, read / write check for monitoring RAM9-1, invalid check for monitoring ROM9-2 (undefined instruction detection) Etc. As shown on page 71 of the above document, the timing of determining that a failure has occurred by monitoring this can be determined as instantaneous, or when a monitoring failure has occurred continuously for a predetermined number of times or for a predetermined time or more. There are times when you do. Considering the nature of the monitoring target, for the majority of monitoring,
A predetermined time continuous detection method is used. In general, the same monitoring is performed at a fixed cycle, and thus the method for detecting a predetermined number of times continuously can be said to be equivalent to the method for continuously detecting a predetermined time.
FIG. 14 shows a flowchart of a monitoring process by the predetermined time continuous detection method. This program is stored in the ROM 9-2 and executed by the CPU 9-3. When start is instructed in step S1-1, monitoring failure detection is performed in step S1-2. For example, A /
In the case of D accuracy monitoring, it is determined whether or not the value of the known DC voltage constantly applied to the sampling hold S / H6 falls within a predetermined range. Things. In step S1-3, according to the result of step S1-2, if no defect is detected, in step S1-4,
After resetting the detection timer T, the process proceeds to step S1-5. If a defect is detected, control is passed to step S1-6. In step S1-5, the fact that no trouble has occurred in the apparatus is output to the outside through the I / O 9-4.

Hereinafter, the same repetitive processing as described above is performed. This repetition process is generally executed at a fixed period (a multiple of the sampling period) ΔT.

On the other hand, when a defect is detected and the process proceeds to step S1-6, ΔT is added to the detection timer T to update the timer value. In step S1-7, it is determined whether or not this value is equal to or greater than a predetermined value T _K. If the value is less than T _K , the process proceeds to step S1-4 to take action for no defect. The following is performed as described above. Conversely, the detection timer T is if equal to or more than T _K, determines that a malfunction has occurred in the apparatus, through the I / O9-4, alarm, display, and outputs the control signal or the like at the time of failure. Thereby, measures such as operation stop of the apparatus are taken automatically or by a human system. Thereafter, the process returns to step S1-2, and thereafter, the same repetitive processing as described above is performed. FIG. 15 shows the above processing represented by logical symbols. That is, the on-delay timer of the time period T _K corresponds to the monitoring failure detection timer described above. Although FIG. 14 shows a method of realizing the detection timer by software processing, it is well known that the on-delay timer of FIG. 15 can also be realized by hardware. (A realization method is omitted.) FIG. 16 (a) is a time chart expressing the function of the monitoring failure detection timer. If the monitoring failure continues for the continuous _TK time, a failure occurrence signal is output, indicating that the failure occurrence signal is restored at the same time as the monitoring failure is recovered.

The above is the monitoring detection processing conventionally performed. In the conventional processing, a monitoring failure that does not occur continuously, that is, a monitoring failure that occurs intermittently, may not be detected as a failure occurrence. This is shown in FIG. 16 (b). That is, T _K
Even if a failure in which the monitoring failure does not continue for a longer period of time occurs intermittently, it cannot be detected as a failure.

Conventionally, the above-described continuous detection method for a predetermined time has been adopted. However, this is because a monitoring failure occurs due to a single cause such as noise, thereby instantaneously determining that there is a failure in the apparatus, and Taking measures such as stopping the operation also leads to a decrease in the operation rate of the device, which is not preferable. That is, by confirming for a predetermined period of time, a single failure due to noise or the like (a failure that is not expected to reoccur) is distinguished from a failure of the original monitoring target (a failure that is expected to reoccur thereafter). You can expect that.

(Problems to be Solved by the Invention) On the other hand, considering the aspect of the occurrence of the monitoring failure, the failure is not always continued for a predetermined time or more, and the failure occurs intermittently as shown in FIG. 16 (b). It can be said that there are times when it does.
That is, it is considered that the failure occurrence mode mainly depends on the deterioration of the hardware constituting the monitoring target part and the surrounding environment. However, when the causes of occurrence are complicatedly affected, the occurrence modes, that is, occurrence frequency, occurrence interval, It can be said that the occurrence duration time and the like are various. Therefore, in the conventional method for continuous detection for a predetermined time as described above, there is a problem in that even if a monitoring failure of an aspect having a problem in the function of the device occurs, it may not be possible to determine the failure. In particular, even if the failure continues at a high frequency, if the failure is recovered within a predetermined time, the device will be operated despite the long-time failure state as the accumulated time, It can be said that normal operation of the device cannot be expected for a long time. As a countermeasure against this, a predetermined time
A method of shortening T _K is also conceivable, but as described above,
It is not a good idea to reduce the operation rate as a result of a single failure such as noise.

In the above, the description has been made with respect to the failure of the components in the protection control device. However, the same applies to the failure detection outside the device. As an example of failure detection outside the device, in a digital relay, the above-described phase balance monitoring for monitoring the PCT circuit can be cited. This is monitoring for detecting a failure such as disconnection of the PT and CT circuits, and is essential for the protection function to operate normally. Therefore, detection of a defect in a component inside the apparatus and detection of a defect in a specific portion outside the apparatus are equally important, and both can be said to have similar problems in the conventional method.

The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a protection control device capable of detecting an intermittent monitoring failure and obtaining a failure occurrence output.

[Configuration of the invention]

(Means for Solving the Problems) FIG. 1 is a functional block diagram showing a basic concept of the present invention, and the present invention relates to at least one of a monitoring target 1 inside a protection control device and a monitoring target 2 outside a device. Monitoring failure detecting means 11 for detecting one or more failures, and observing at least one of an occurrence time, an occurrence frequency, an occurrence interval, and an occurrence continuation time of the monitoring failure detected by the means 11 for a predetermined period; A failure occurrence determining means 12 for determining whether or not a monitoring target failure has occurred;
It is composed of

(Operation) The operation of the above configuration will be described. First, failure detection of a monitoring target is performed by a predetermined method. The occurrence of the monitoring failure obtained after the implementation is observed for a predetermined period, and based on the result, the presence or absence of a failure is determined, and a failure determination output is obtained.
Measures such as alarms, displays, and stoppage of operation of the device are performed inside and outside the device.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. The hardware configuration of this embodiment is equivalent to that of a digital relay, and details are the same as those in FIG. Therefore, description is omitted. The functions constituting the present invention are realized by executing a program stored in the ROM 9-2 in FIG. 13 by the CPU 9-3.

A feature of the present invention is that it is possible to detect an intermittent failure that could not be determined as a failure in the conventional method. calculating a cumulative value a monitoring failure time is compared with a predetermined value T _K, provided with a function determines the presence or absence of defect occurrence.

(1), during the predetermined period L, the cumulative value of the monitoring failure time is equal to or greater than T _K shows that determines that a malfunction occurs Yes. An example in which the equation (1) is realized by the above program is shown in the flowchart of FIG. Here, the integral of the expression (1) is approximated by the expression (2) which is the addition of k · ΔT in the ΔT cycle.

Here, if ΔT → 0, the approximate value of the expression (2) approaches the expression (1) without limit. First, in step S2-1, the program is started, and in step S2-2, the period calculation value t and the accumulated value A are initialized.

Next, in step S2-3, a monitoring failure is detected. This processing corresponds to the monitoring failure detecting means 11 described above,
Also, it is the same as step S1-2 in FIG. 14 described in the description of the conventional method. Next, in step S2-4, the presence or absence of defect detection is determined,
If there is, in step S2-5, the cycle ΔT of this program is added to the accumulated value A, and the value of A is updated. This processing corresponds to the above equation (2). Next, in step S2-6, the accumulated value A is
If it is equal to or more than the predetermined value T _K, it is determined that there is a defect in step S2-7, and a signal for performing measures such as alarm, display, and operation stop is output. On the other hand, if A is less than T _K , step S2-8
Then, it is determined that there is no failure, and a return command such as an alarm is output. Next, in step S2-9, the period calculation value t is updated. The point in time when t exceeds L is determined in step S2-10, and step S2-11
Initializes t and A. By repeating the above with a period of ΔT, the expression (1) can be realized.

Next, the operation of the present embodiment is shown in FIG. As shown in FIG. 3, even when the monitoring failure occurs intermittently, according to the above embodiment, if the cumulative value A of the occurrence time in any section L becomes equal to or greater than T _K , Since a failure occurs, reliable determination can be expected. According to this embodiment,
Intermittent failures, which were impossible with the conventional method, can be reliably detected and determined to be defective. T _K
For example, assuming that the probability of expecting a normal operation is P, the value of A and A may be determined by T _K / A = P. According to this, it can be said that a monitoring method that is more compatible with the operation of the apparatus can be realized as compared with the conventional method.

In the above embodiment, the predetermined period L is set to L as shown in FIG.
Although it is set so as to be shifted at intervals, the same effect can be expected even if the interval is set shorter. FIG. 4 shows a flowchart in this case. The embodiment shown in FIG. 4 is a method in which a predetermined section L is shifted at intervals of ΔT. First, step S3
The program is started at -1 and the accumulated value A is initialized at step S3-2. Step S3-3 is the same as S2-3 described above. If no defect is detected in step S3-4, step S3
At -5, the current addition value ΔT _{I is set} to 0. If a defect is detected, the program cycle ΔT is substituted for ΔT _I. In step S3-7, ΔT _I is added to A. In step S3-8, it subtracts the L time before the addition value [Delta] T _M. ΔT _M is ΔT _I L hours before and is stored in the RAM 9-1. Next, in step S3-9, ΔT _I is stored. This is L
After a time, it is used as ΔT _M. In step S3-10, A is compared with a predetermined value T _K , and in steps S3-11, S3-12, respectively.
Then, the output processing is performed with or without a defect.

By repeating the above processing, the predetermined section L is set to ΔT
It is possible to calculate the accumulated value A by shifting each time.
FIG. 5 shows the operation of this processing.
As shown in the figure, if the faulty output is not reset every L time, and if the monitoring failure tends to continue, there is an advantage that the faulty output also has a continuing direction.

In the above embodiment, the example in which the cumulative value of the monitoring failure occurrence time is observed is shown. However, as the failure occurrence determination means, the cumulative value A of the monitoring failure occurrence frequency (the number of occurrences) in a predetermined period is calculated by the following equation. There is also a method of comparing with a predetermined value K to determine whether or not a failure has occurred.

However, the monitoring failure occurrence time is not included in the monitoring failure occurrence continuation time. Here, the integral of the equation (3) is ΔT
It can be approximated by equation (4), which is the addition of k in the cycle.

Here, if ΔT → 0, the approximate value of equation (4) is given by (3)
Approach the ceremony. In order to realize the above equation (4), steps S2-4, S2-5, and S2-6 in FIG.
4, S2'-5 and S2'-6.

Here, as a specific method of judging the point of occurrence of a failure in S2'-4, there is a method of judging the point of occurrence of a defect if the time before ΔT is normal and the current point of time is defective. FIG. 7 shows the operation of this embodiment. In the example of FIG. 7, K = 4, indicating that a monitoring failure has occurred four or more times during the predetermined period L, and that a failure has occurred. In consideration of the degradation characteristics of the monitoring target, it may be more appropriate to count the cumulative occurrence frequency than the above-described cumulative occurrence time, and this embodiment can be expected to be effective in such a case.

In the above embodiment, an example in which the occurrence time or occurrence frequency is observed has been described.
By observing the change in the monitoring failure occurrence interval for a predetermined period,
There is also a method of determining whether or not a failure has occurred.

If T ₁ > T ₂ > T ₃ …> T _n-1 > T _n then a problem has occurred (5) −
(A) T ₁ <Mu _{T 2 <T 3 ... <T} n-1 <T n If a problem occurs (5) -
(B) where n: the number of occurrences of monitoring failures occurring during a predetermined period T _i : intervals at which monitoring failures occur during a predetermined period (i = 1 to n) In general, the failure occurrence aspect of the monitoring target is: It is considered that there is a tendency to shift from an intermittent state to a continuous state due to the deterioration characteristics. Therefore, in the failure occurrence state, the monitoring failure occurrence interval tends to be shorter in an arbitrary period, as shown in Expressions (5) to (a). Conversely, when the monitoring failure is restored from the monitoring failure state to the normal state again due to a change in the surrounding environment, the monitoring failure occurs at an arbitrary interval (5)-
As shown in equation (b), the length is in the direction of becoming longer. Therefore,
The presence / absence of a failure can be determined by the equations (5)-(a) and (5)-(b).

FIG. 8 shows a program for realizing this embodiment. First, in step S4-1, the present process is started, and in step S4
At -2, the predetermined period calculation value t is initialized. Then step
In S4-3, it is determined whether a predetermined period L has elapsed. t
If L is equal to or smaller than L, monitoring failure detection processing is performed in step S4-4. This is a process equivalent to step S3-3 described above. Next, in step S4-5, the occurrence of a defect is determined. If it is determined that the failure occurred, performing the calculation of the monitoring failure interval T _i in step S4-6. _Ti is the previous monitoring failure (i-1)
Is calculated by calculating the time from the occurrence of the current failure to the occurrence of the current failure i. In step S4-7, t is updated, and the process returns to step S4-3. Hereinafter repeated, the processing is performed, at step S4-3, when it is determined that t is greater than L, and the in step S4-8, the relationship to the calculated T ₁ through T _n is described above (5) - (a) It is checked that the expression is satisfied. If the expression is satisfied, in step S4-9, a process equivalent to that of the previous embodiment is performed as occurrence of a failure. Also step
In S4-10, T _i is (5) - (b) Checks satisfies the equation, if satisfied, at step S4-11, processing a bug-free. Thus, the processing in the predetermined section L is completed, and the process returns to step S4-2 again, initializes t, and repeats the above processing. The operation of this embodiment is shown in FIG.
FIG. 7A shows a case where a failure occurs, and FIG.
This shows a case where the defect recovers. In this embodiment,
Observing the transition of the failure state is equivalent to predicting in advance that a permanent failure will be caused or recovered.

Therefore, there is an advantage that a failure can be detected before a fatal failure occurs, and monitoring with excellent selectivity becomes possible.

In the above embodiment has been observed change in monitoring failure interval, as defect generation means, according to the following equation by observing the monitor changes in failure duration T _i of a predetermined time period, the method determines the presence or absence of defect occurrence There is also.

If T ₁ <T ₂ ... <T _n-1 <T _n , a problem has occurred (6)-(a)
_{T 1> T 2 ...> T} n-1> T Mu _n If a problem occurs (6) - (b)
Here, n: the number of occurrences of monitoring failures occurring during the predetermined period T _i : the duration of monitoring failures occurring during the predetermined period (i = 1
~ N) In general, the duration of a monitoring failure tends to be longer before a permanent failure occurs (i.e., a permanent failure),
Conversely, when recovering from a permanent failure, it tends to be shorter. Therefore, the presence or absence of a defect can be determined by the equations (6)-(a) and (b). The realization method of this embodiment is the same as that of FIG. 8 of the above embodiment, and the steps S4-5, S4-6, S4-8, S4-
10 can be changed. That is, in step S4-5, detects that the failure is recovered, in step S4-6, get bad duration T _i by calculating the time until the failure recovery than during failure. In steps S4-8 and S4-10, it is determined whether the expressions (6)-(a) and (6)-(b) are satisfied.

FIG. 10 shows the operation of the present embodiment. This embodiment has an advantage that a failure state can be predicted as in the above-described embodiment.

As another embodiment, there is also a method of observing a change in the cumulative value of the monitoring failure occurrence time during a predetermined period and determining whether or not a failure has occurred, using the following equation as the failure occurrence determination means.

If f ₁ (A _i , A _i−1 ,..., A ₁ ) <A _i <f ₂ (A _i , A _i−1 ,... A ₁ ), a problem occurs (7) − (a) g ₁ (A _i , A _i-1 ,... A ₁ ) <A _i <g ₂ (A _i , A _i−1 ,... A ₁ ), no failure occurs (7) − (b) f ₁ , f ₂ , g ₁ , g ₂ are functions or constant values dependent on at least _one of the past cumulative values A _i ,... A _1. Generally, the monitoring failure occurrence time cumulative value A _i is It can be said that a certain tendency is taken before reaching a permanent failure, and that when recovering from a permanent failure, it changes in another tendency. Therefore, any
Focusing on A _i , it is possible to determine the presence / absence of a failure by (7)-(a) when a failure occurs and by (7)-(b) when recovering.

There is also a method in which the occurrence time is changed to the occurrence frequency in the above-described embodiment, and the change in the cumulative value of the monitoring failure occurrence frequency for a predetermined period is observed by the following equation to determine whether or not a failure has occurred. The effect in this case is the same as that of the above embodiment.

If f ₁ (A _i , A _i−1 ,... A ₁ ) <A _i <f ₂ (A _i , A _i−1 ,... A ₁ ), there is a problem (8) − (a) g ₁ (A _i , A _i-1 ,... A ₁ ) <A _i <g ₂ (A _i , A _i−1 ,... A ₁ ), no failure occurs (8) − (b) f ₁ , f ₂ , g ₁ , g ₂ are functions or constant values dependent on at least _one of the past accumulated values A _i ,... A _{1 In} the above embodiments, the occurrence time and occurrence frequency are arbitrary. It was determined that the function value or the constant value was within a certain range. However, when the occurrence time and the occurrence frequency changed, the occurrence interval indicated by the expression (9) was used, or the occurrence continuation time indicated by the expression (10) was used. In this case, the same effect can be expected. In equation (9),
FIG. 11 shows a defect detection area when the interval of occurrence becomes exponentially shorter and leads to a defect. According to the present embodiment, if the failure occurrence mode up to the failure of the monitoring target is known, extremely high-precision monitoring can be performed by setting a function value corresponding to this.

If f ₁ (T _i , T _i−1 ,... T ₁ ) <T _i <f ₂ (T _i , T _i−1 ,... T ₁ ), a problem occurs (9) − (a) g ₁ (T _i , T _i−1 ,... T ₁ ) <T _i <g ₂ (T _i , T _i−1 ,... T ₁ ), no failure occurs (9) − (b) where f ₁ , f ₂ , g ₁ and g ₂ are functions dependent on at least one or more of the past occurrence continuation times T _i ... T ₁ or constant values T _i . If the duration f ₁ (T _i , T _i−1 ,..., T ₁ ) <T _i <f ₂ (T _i , T _i−1 ,..., T ₁ ), a problem occurs (10) − (a) g ₁ If (T _i , T _i−1 ,... T ₁ ) <T _i <g ₂ (T _i , T _i−1 ,... T ₁ ), no failure occurs (10) − (b) where f ₁ , f ₂ , g ₁ and g ₂ are functions that depend on at least one or more past occurrence intervals T _i ... T ₁ or constant values T _i (i = 1 to n) of monitoring failures occurring during a predetermined period. Occurrence interval In the embodiment described above, a problem occurs in software. Has been described how to achieve a constant means, but it is naturally also feasible in hardware, the effect is equally. In particular, problems that reduce the reliability of software (for example, RAM
Failure, ROM failure, CPU failure, etc.), detection by hardware is effective. FIG. 12 shows an implementation example in this case. The cumulative counter in the figure is realized by hardware, and the I / O
Upon receiving a signal indicating the occurrence of a monitoring failure from the interface, counting is cumulatively performed. The accumulative counter is a means for realizing the equation (2), and its concrete circuit configuration is well known, so that the explanation is omitted. Instead of the accumulation counter, there is also a method of realizing the equation (1) by using an integrating circuit composed of a resistor and a capacitor and a level detecting circuit composed of a transistor and the like.

Although a single monitoring failure has been described in the above embodiment, a plurality of monitoring target parts are generally provided in one apparatus, and different monitoring is performed. Therefore, a failure occurrence determination means is provided for each monitoring part. The operation and effect in this case are also the same as those of the embodiment described above.

〔The invention's effect〕

As described above, according to the present invention, the occurrence of a monitoring failure is monitored for a predetermined period, and the failure is determined in consideration of the occurrence, so that an intermittent failure that has been impossible in the past can be detected. Further, it is possible to provide a protection control device having highly accurate and flexible monitoring means corresponding to the generation mode and operation mode.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing the basic concept of the protection control device according to the present invention, FIG. 2 is a flowchart showing the processing of one embodiment, FIG. 3 is a time chart for explaining the operation of the embodiment, and FIG. Flowchart showing another embodiment, FIG. 5 is a time chart for explaining the same operation, FIGS. 6 to 9 are flowcharts showing another embodiment, FIG. 10 is a time chart of another embodiment, FIG. Is a graph illustrating the operation of another embodiment, FIG. 12 is a configuration diagram illustrating another embodiment, FIG.
FIG. 1 is a diagram showing a configuration example of a conventional protection control device, FIG. 14 is a flowchart showing a conventional method, FIG. 15 is a logic circuit diagram showing the conventional method, and FIG. 16 is a time chart thereof. 10: protection control device, 11: monitoring failure detection means 12: failure occurrence determination means

Claims (3)

(57) [Claims] In a monitoring method of a protection control device, a monitoring failure detection means for detecting failures of a plurality of monitoring target items of an internal circuit of the protection control device at a predetermined detection cycle, and the monitoring for each monitoring target item The failure detection detected by the failure detection means is counted on the condition that no failure has been detected in the previous detection cycle, and the cumulative value A of the number of monitoring failure occurrences during a predetermined period is defined as the monitoring failure occurrence frequency by the following equation. A cumulative value calculating means for calculating, and a failure occurrence determining means for comparing the cumulative value calculated by the cumulative value calculating means with a predetermined value T _K and determining that a failure has occurred if the cumulative value is larger than the predetermined value. A protection control device characterized by the above-mentioned. 2. A monitoring method for a protection control device, comprising: monitoring failure detection means for detecting failures of a plurality of monitoring target items in an internal circuit of the protection control device; and monitoring failure detection means for each monitoring target item. Failure occurrence interval calculation means for calculating the occurrence interval of monitoring failures for a predetermined period that is periodic,
If the occurrence interval of the monitoring failure during the predetermined period calculated by the failure occurrence interval calculating means is sequentially shortened, it is determined that a failure has occurred and a determination signal is output, and the occurrence interval of the monitoring failure during the predetermined period is sequentially increased. A protection control device comprising: a failure occurrence determination unit that determines that no failure has occurred if it is, and restores the determination signal. 3. A monitoring method for a protection control device, comprising: a monitoring failure detecting means for detecting failures of a plurality of monitoring target items of an internal circuit of the protection control device; and a monitoring failure detecting means for each monitoring target item. A failure occurrence duration calculating means for calculating a monitoring failure occurrence duration for a predetermined period periodically, and a monitoring failure occurrence duration for the predetermined period calculated by the failure occurrence duration calculation means which becomes longer sequentially. A failure occurrence determining means for determining that a failure has occurred, outputting a determination signal, and determining that no failure has occurred if the duration of the monitoring failure occurrence during the predetermined period is sequentially reduced, and returning the determination signal. Protection control device.