JPH0658388B2 - Inspection and monitoring method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an inspection / monitoring method for inspecting an analog AC input section of a protection / control device that responds to an AC input abnormality such as a digital relay.

(Prior Art) A protective relay using a microcomputer, a so-called digital relay, is usually constructed as shown in FIG.

In the figure, 30 is an analog AC input unit for inputting the current and voltage of the power system, 40 is a computing unit consisting of a microcomputer, 50 is a display / setting for inputting and displaying set values, and displaying the operation of each relay element. The unit 60 is an output unit for obtaining a trip command and the like.

In the analog AC input section 30, first, the current and the voltage taken from the power system through the transformer for the meter are respectively transformed by the current transformer CT.
And input to the auxiliary transformer consisting of the instrument transformer PT to perform insulation and level conversion. Then, these AC inputs are connected to the fundamental wave (typically commercial frequency, that is, 50 Hz or
After being input to the analog filter AF for extracting only (60 Hz), the sample and hold circuit SH samples and holds it at a constant cycle.

The sampled and held analog input value is switched by the multiplexer 31 and input to the A / D (analog / digital) converter 32, which is sequentially converted into a digital signal and stored in the buffer memory BM. In addition, OSC
Is an oscillator that generates sampling pulses and clock pulses.

The arithmetic unit 40 performs various arithmetic operations using the contents of the buffer memory BM and realizes various protection and control functions such as obtaining a trip command to the circuit breaker via the output unit 60 by comparison with a set value or the like. is doing.

The digital relay configured in this manner is generally equipped with a self-diagnosis function for constantly monitoring hardware defects by using the arithmetic / judgment function of a microcomputer in order to eliminate maintenance. Since this function alone is insufficient for detecting defects in the input / output circuits, an automatic inspection function is provided to detect defects in these circuits. Here, the automatic check function is a function that temporarily locks the function of the device and checks whether it responds normally when an input that should be operated is applied, and it is used for analog input check or digital input / output check. Although the details are different depending on the case, these functions are generic names.

Therefore, even in the analog AC input section of the digital relay as shown in FIG. 3, there has been proposed a method of detecting the defect by the automatic inspection circuit as shown in FIG.

That is, in FIG. 4, after the output of the digital relay is locked, the inspection relay 73 is excited through the digital output section 72 which receives the inspection power supply application command, and its contact 73
When a to 73c are closed, an inspection signal is applied from the inspection power source 71 to the primary side of each auxiliary transformer CT, PT. This value is a predetermined value, and the arithmetic unit in the subsequent stage determines whether or not a normal conversion value via the auxiliary transformers CT and PT can be obtained, and monitors whether or not there is an abnormality in the analog AC input unit. To do.

(Problems to be Solved by the Invention) However, this automatic inspection and monitoring method has the following problems.

A dedicated circuit is required to perform automatic inspection, and the entire apparatus tends to be expensive and its outer shape also becomes large.

Since the contacts 73a to 73c of the inspection relay 73 enter the main circuit,
There is a problem in terms of life and reliability, and maintenance is required.

Since the original protection / control function of the digital relay is locked for inspection, the system is not protected during this period.

Because the inspection power supply with high voltage accuracy is generally expensive and large, the inspection power supply 71 uses the AC power supply in the substation or the like as it is, so the voltage fluctuation is about ± 15%. Further, in consideration of the error of the auxiliary transformer, the filter, etc., the detection calculation accuracy, etc., it is impossible to detect the secular change such as the deterioration of the electric / electronic parts constituting the analog AC input section.

The present invention has been proposed in order to solve these problems, and its object is to check the analog AC input section with a circuit structure that is inexpensive and can be downsized, and protects the original device. It is an object of the present invention to provide an inspection and monitoring method that realizes a control function without temporarily losing it, has high reliability, and can detect secular changes of electric and electronic parts.

(Means for Solving Problems) In order to achieve the above object, the present invention provides a protection / control device which responds to an abnormality of an AC input detected via an analog AC input section, in which the basic frequency of the AC input is changed. A check signal having a frequency of 3 times or 4 times is combined with the AC input in the preceding stage of the analog AC input unit, and a combined value of the AC input and the check signal at each sampling point is obtained in the latter stage of the analog AC input unit. The value of the inspection signal is detected by using the added value of these combined values, and the function of the analog AC input section is inspected by comparing the detected value of the inspection signal with its design value.

(Operation) According to the present invention, the AC input and the inspection signal are combined in the preceding stage of the analog AC input unit, and thereafter, the arithmetic unit including a microcomputer or the like combines the AC input and the inspection signal at each sampling time point. The value of the inspection signal is detected using the value and the added value of these combined values, and is discriminated from the AC input. Of these, the AC input is for protection of digital relays, etc.
It is used as an input for abnormality detection of the control device. In parallel with this, the inspection signal is used for comparison with a value known in advance as a design value via the analog AC input section, and by determining whether the measured value of the inspection signal matches the design value, the analog The function of the AC input section is inspected and monitored.

(Example) An example of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration of a main part of a digital relay to which this embodiment is applied. In FIG. 1, reference numeral 1 is an instrument to which a voltage input of a system is applied via an instrument transformer (not shown). Auxiliary transformer such as a transformer, 2 is an analog type synthesizing circuit composed of resistors for synthesizing this system input and an inspection signal to be described later, 4 is an analog filter for extracting a fundamental wave, 5 is a sample and hold circuit, 6 Is a sample hold command circuit for outputting a command of sampling and hold operation at a predetermined timing, 7 is a multiplexer for switching and inputting the output of the sample hold circuit 5, and 8 is A
An A / D converter, 9 is a memory, and 10 is an arithmetic unit including a microcomputer.

Therefore, the above-mentioned inspection signal is, for example, 2 to 5 times (preferably 3 or 4 times) the fundamental frequency of the system input.
It is supplied from the inspection power supply 3 which outputs a rectangular wave alternating current of the frequency of. This inspection power supply 3 is preferably made by a constant voltage power supply common to the arithmetic unit 10, and its frequency is also generated by appropriately dividing the accurate clock signal of the arithmetic unit 10 obtained from the crystal oscillator. Also, the basic frequency of the system input is 50Hz
In this case, a 600 Hz pulse is usually generated as a pulse for sampling by the sample-hold circuit 5 and already exists, so the inspection power supply 3 divides the sampling pulse into 1/4. A highly stable and highly accurate power supply can be easily realized by way of a buffer amplifier or the like.

Now, the inspection and monitoring operation when a rectangular wave inspection signal having a frequency three times the fundamental frequency is used will be described with reference to FIG. The rectangular wave inspection signal is approximated by a sinusoidal alternating current as shown by the broken line in FIG.

As described above, the digital relay generally employs a sampling frequency that is 12 times the commercial frequency (600 Hz for 50 Hz, 720 Hz for 60 Hz), and its timing is controlled by the sample hold command circuit 6. Therefore, when the system input (shown by the solid line in the figure) and the inspection signal as shown in FIG. 2 are combined by the combining circuit 2,
Times t _n , t _{n + 1} , t separated by each sampling period t _s
Combined value of system input and check signal at _{n + 2} , tn _{+ 3} , ... (A _n , A _{n + 1} , A _{n + 2} , A _{n + 3} , ...)
Is finally stored in the memory 9.

Then, the arithmetic unit 10, t n when _~t adding each composite value A _n ~A _n + ₃ in the n + _3, the total value of the apparent inspect the signal from the second figure system input is zero Only the total value of remains. This action is realized by a so-called digital filter. Therefore, after properly correcting the phase and magnitude of this total value, this is used to perform calculations for the original protection and control of the digital relay. That is, according to this embodiment, even if the inspection signals are combined, the original protection / control function of the apparatus is not impaired.

Further, calculation is performed using the combined values A _{n to} A _{n + 3} stored in the memory 9 at each sampling time point and the added value of these (the total value of only the system input after the inspection signal is removed). Department
By 10, only the inspection signal can be extracted and its value can be detected. Therefore, since the voltage value of the inspection signal 3 via the analog filter 4, the sample hold circuit 5, the multiplexer 7, the A / D converter 8 and the memory 9 is known as a design value, this design value and the above-mentioned extracted value are extracted. By comparing the measured value of the inspection signal with the arithmetic unit 10 and determining the coincidence or non-coincidence, the functions of the components after the analog filter 4 can be inspected and monitored with high accuracy.

Next, change the frequency of the inspection signal to the basic frequency of 2, 3, 4, 5
The effect of the double setting will be considered below.

(1) When the second harmonic is used In this case, the data between the half C / S of the fundamental wave is necessary for the process of removing the inspection input by the digital filter. The obtained filter cannot completely remove the third harmonic generated at the time of a system fault, which leads to a reduction in response speed during protection / control and a complicated processing by a digital filter.

Therefore, it can be said that the use of the second harmonic is unsuitable for a protection device that requires a high response speed.

Also, in a device such as a transformer protection relay that locks the relay output when the content rate of the second harmonic component contained in the exciting inrush current or the like is a certain value or more, it is included in the inspection signal and the exciting inrush current. It is difficult to discriminate the second harmonic, and it is difficult to apply because of the inconvenience that the relay output is locked by the inspection input.

However, in a protection control device such as a transmission line that does not have the above-mentioned properties, there is almost no second harmonic distortion in the system input during normal times, and the inspection signal is less likely to be attenuated by the analog filter. Therefore, if the standardization of the inspection and monitoring device is excluded, it is meaningful to use the second harmonic as the inspection signal. However, even in this case, there is a risk that the second harmonic will be superimposed on the system input due to phenomena such as inrush current and saturation of the current transformer. In order to detect it, the inspection signal is configured to be able to be confirmed for a predetermined time by a confirmation timer of, for example, 10 to 30 seconds, in consideration of the time when the exciting inrush current disappears and the time when the current transformer is saturated. There is a need to.

(2) When the third harmonic is used The digital filter that removes the inspection signal is also effective in removing the third harmonic that occurs when a system fault occurs, and the digital filter has a simple configuration and a fast response speed. Here, the third harmonic component generated at the time of a system fault disappears within a relatively short time (maximum about 10 seconds) due to the disappearance of the system fault or removal of the system fault by a circuit breaker, etc. As with the case of harmonics, the effect can be avoided by using a confirmation timer of about 10 to 30 seconds.

However, the system input at all times contains distortion of the third harmonic (mainly odd harmonics) in many cases, and it is generally difficult to discriminate the third harmonic component from the inspection signal. For the third harmonic, which is always present in, another measure is needed.

Here, for example, the 3rd harmonic that is always present in the system is averaged based on the results of the harmonics survey shown in “Electrical Cooperation Research Vol. 37, No. 3,“ Countermeasures for Harmonic Disorders in Distribution Systems ””. Is less than 1% and at most about 3%. And
The intermittent time in which the third harmonic causes great distortion is about 3 hours, and it is the third by the electric power company and the region.
For harmonics only, there are hours when the distortion rate is extremely low for some hours of the day.

Therefore, in order to remove the influence of the 3rd harmonic that always exists in the system, a timer for confirmation of, for example, about 24 hours is provided to enable the application to all regions, and the 3rd harmonic is intermittent for 24 hours. If so, a configuration may be adopted in which this is discriminated as an inspection signal. The purpose of accuracy monitoring using this inspection signal is to detect the secular change of power components, and even if it takes 24 hours for this purpose, there is almost no problem.

(3) When the 4th harmonic is used In this case, in addition to the digital filter that removes the 4th harmonic, which is the inspection signal, a digital filter that removes the 3rd harmonic that is always present in the system fault or in the system Since it is necessary to use a filter as well, the time to collect the required number of data required to remove the inspection signal, that is, the response time becomes relatively long (about 90 ° min: 5 ms in 50 Hz system), but the inspection signal Therefore, it can be said that this response time is considerably faster than the case where the second harmonic is used.

On the other hand, in the analog filter, the higher order (sixth to thirteenth) harmonics are removed in order to reduce the folding error of the sampling theorem, and the fourth harmonic is also −2.
Attenuation of 2.8 dB (attenuation rate of 7.2%) may occur, which may cause detection errors in the calculation unit, but the speed of response speed described above and the distortion of the 4th harmonic in the regular system input are extremely small. Considering the above, it can be said that it is effective to use the fourth harmonic as the inspection signal.

Also, in this case, a timer for confirmation of, for example, about 10 to 30 seconds is provided in consideration of the time when the inrush current of the excitation disappears and the time when the saturation of the current transformer is resolved, as in the case of the second harmonic. Is preferred.

(4) When the 5th harmonic is used When sampling is performed at a frequency 12 times the fundamental frequency, the digital filter that completely removes the 5th harmonic, which is the inspection signal, becomes complicated. In addition, the 5th harmonic is the most frequent harmonic in the system, which makes it difficult to distinguish from the inspection signal, and the analog filter causes a lot of attenuation, resulting in a large detection error. It cannot be said that.

From the above background, the frequency of the inspection signal is the third
Or the fourth harmonic is appropriate. Hereinafter, the detection accuracy when the third and fourth harmonics are used as inspection signals will be considered.

The error factors in such inspection and monitoring methods are roughly as follows. First, the inspection signal accuracy (almost equal to the power supply voltage accuracy) is ± 1%, the adjustment error of the inspection power supply buffer amplifier is ± 0.5%, The error of the analog type synthesis circuit 2 shown in FIG. 1 is ± 1%, and the initial adjustment error of the analog filter 4 is ± 0.5%. The influence of the distortion factor of the system input is ± 1% for the 3rd harmonic, almost 0% for the 4th harmonic, and the detection error consisting of quantization error and calculation error is ± 2% for the 3rd harmonic and the 4th harmonic. ± 3% per wave.

Of these, the final detection error will be examined below.

Now, assuming that the inspection signal is a 5 V (zero-peak value) rectangular wave alternating current, the Fourier series of this waveform is Becomes According to the characteristics of the analog filter described above, the second term of this equation, (1/3) sin3χ, becomes the ninth harmonic when the inspection signal is the third harmonic, and is attenuated to a negligible extent. Therefore, the output of the analog filter is almost (20 / π) sin χ due to the first term of the above equation.

Now, assume that the A / D converter 8 (see FIG. 1) converts ± 10 V into ± 2048 by 12 bits including the sign bit,
Sampling data of two points at an electrical angle of 90 ° to the above inspection signal is squared, these are added, and the square root of this added value is calculated to obtain the effective value of the inspection signal from the peak value of the alternating current. Then, assuming that the sampling data A ₁ and A ₂ at the above two points is 4.50 V, the attenuation rate of the third harmonic is 17.2.
% Is 4.50 × 0.172 = 0.774V, which is 15
Equivalent to 8.6 bits.

Therefore, the quantization error is 0.63%. Also, at this time,
The calculation error of A ₁ ² + A ₂ ² is about 1.5%, and the total detection error of both is about ± 2% as described above.

On the other hand, in the case where the inspection signal is the fourth harmonic, assuming that the attenuation rate is 7.2%, it becomes 4.50 × 0.072 = 0.324V, which corresponds to 66.4 bits. Therefore, the quantization error is about 1.5.
%, The calculation error of A ₁ ² + A ₂ ² becomes about 1.5%,
The combined detection error is about ± 3% as described above.

Therefore, the accumulated errors of the third and fourth harmonics are both around ± 6%. Therefore, in order to detect the secular change of 5% with respect to the rated value such as the resistance value of the components forming the analog AC input section, the detection level may be set to 11%. However, in this case, in the case where the accumulation of each error and the secular change cancel out in the positive and negative opposite directions, this can be detected when there is a 17 (= 11 + 6)% secular change.

Therefore, in this embodiment, when the third or fourth harmonic is used as the inspection signal, it is possible to detect the secular change of 5 to 17% of the parts, and conventionally, for example, to detect the secular change of 5%. Compared with the detection level of about 25% required and the secular change of 5 to 45% of parts that can be detected, the detection accuracy can be greatly improved.

In the above embodiments, the case where the AC voltage as the check signal is combined with the voltage input of the system has been described, but the present invention can also be realized with a method of combining the AC current as the check signal with the current input of the system. is there. Further, the present invention can be applied not only to the analog AC input section of the digital relay but also to the inspection and monitoring of various analog AC input sections other than the above in principle.

(Effect of the Invention) As described above, according to the present invention, the inspection signal is synthesized from the preceding stage of the analog AC input section to the AC input, and then the measured value of the inspection signal discriminated from the AC input is compared with the design value. Since it is to inspect and monitor the analog AC input section,
The inspection signal may be always superimposed on the AC input, and the digital output section for switching between the AC input (system input) and the inspection power supply during inspection, the relay for inspection, and its contacts inserted in the main circuit as in the past. And the like are not necessary, and there is no concern about their life, reliability, maintenance, or the like.

In addition, the inspection power supply can be easily made small and highly accurate as an electronic circuit by utilizing existing sampling pulses, etc., so that the inspection monitoring device can be made compact, low cost and highly accurate. It is possible. Furthermore, the third harmonic or the fourth
Since it is possible to greatly improve the inspection accuracy regardless of which of the harmonics is used, it is possible to reliably detect the secular change of the electric / electronic parts constituting the analog AC input section.

In addition, since the original protection / control function is not impaired at the time of inspection / monitoring, there is no risk of the system being unprotected, and the reliability of the protection / control device can be improved.

[Brief description of drawings]

1 is a configuration diagram of a main part of a digital relay to which an embodiment of the present invention is applied, FIG. 2 is an explanatory diagram of a system input and a check signal, and FIG. 3 is a configuration diagram of a main part of a digital relay,
FIG. 4 is an explanatory diagram of a conventional automatic inspection circuit. DESCRIPTION OF SYMBOLS 1 ... Auxiliary transformer, 2 ... Synthesis circuit 3 ... Power supply for inspection, 4 ... Analog filter 5 ... Sample hold circuit 6 ... Sample hold command circuit 7 ... Multiplexer, 8 ... A / D converter 9 ... Memory, 10 ... Arithmetic unit

Claims (1)

[Claims] 1. A protection / control device which responds to an abnormality of an AC input detected through an analog AC input unit, wherein a check signal having a frequency three times or four times the fundamental frequency of the AC input is used as the analog AC input unit. Of the check signal by combining the AC input in the preceding stage and the combined value of the check signal and the AC input at each sampling point in the subsequent stage of the analog AC input section. Is detected and the detected value of the inspection signal is compared with the design value of the inspection signal.