JPH01198213A - Digital protective relay - Google Patents

Abstract

PURPOSE:To remove offset values without and manual operation and without having no effect on relay characteristics by computing the offset value by arithmetically operating digital data and subtracting the offset value from each digital data. CONSTITUTION:The voltage or current value of a power system 10 is detected by current transformers 11-1n, and outputs from the current transformers are input to a CPU 6 through filter circuits 2, sample-and-hold circuits 3, a multiplexer 4 and an A/D converter 5. The CPU 6 integrates digital data output from the A/D converter 5 for a fixed time, and computes the mean value of each digital data as an offset voltage value from the result of the integration while subtracting the offset voltage value from each digital data and removoffsets.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital protective relay, and more particularly to a digital protective relay equipped with means for eliminating the effects of offset voltages in its analog input circuit. .

[Conventional technology]

Figure 3 is a block diagram showing an example of the general basic configuration of a digital protective relay.
(published in January 1986) under the title ``Digital Relay.''

In the figure, 1 is an input converter, which is connected to the power grid IO. This input converter 1 is connected to a power system 10 to be protected.
convert the voltage or current value into an appropriate voltage signal (analog signal)
It is composed of a plurality of current transformers 11, 12, .

2 is a filter circuit, and each current transformer 11 of the input converter 1
．． 12...1n, the fundamental frequency of the power system 10, for example 50 or 6011z, is extracted and output as analog data.

Reference numeral 3 denotes a sample and hold circuit, which holds the analog data output from the filter circuit 2 at the value at that time at a predetermined sampling timing.

A plurality of one-channel circuits each consisting of the current transformer 11 (or 12...In), filter circuit 2, and sample-and-hold circuit 3 are provided, and the output of each sample-and-hold circuit 3 is sent to a multiplexer 4. It is given.

The multiplexer 4 switches and outputs the output of each sample hold circuit 3 to the A/D converter 5. Specifically, since each sample and hold circuit 3 holds analog data at the same sampling timing, the multiplexer 4 sequentially switches and connects each sample and hold circuit 3 to the A/D converter 5. Sample hold circuit 3
sequentially outputs the analog data held by the A/D converter 5 to the A/D converter 5.

The A/Di converter 5 converts the analog data provided from the multiplexer 4 into, for example, 16-bit digital data and outputs it to the CPU 6, which is an arithmetic means.

The CPU 6 processes the digital data given from the A/D converter 5 using software according to a predetermined program.
As a result, if it is determined that a failure or the like has occurred within the power system, for example, an operation such as cutting off the system is performed.

[Problem to be solved by the invention]

Incidentally, in the digital protection relay as described above, the filter circuit 2 often has a circuit configuration using an operational amplifier. However, even when the input is zero, an operational amplifier generates a certain voltage (usually several mV) called an offset voltage. Further, since the sample hold circuit 3 also normally uses an operational amplifier like the filter circuit 2, an offset voltage is generated similarly.

Since such an offset voltage is output in a state where it is superimposed on an analog signal representing the voltage output from each circuit, a considerable amount is also included in the digital data after analog-to-digital conversion.

The value equivalent to the offset voltage included in this digital data becomes an error, but conventionally, this offset voltage has been removed as follows.

The first method is to adjust the offset voltage of the operational amplifier using a variable resistor so that the output voltage becomes zero when the input is zero.

In this case, the adjustment of the variable resistance must be done manually, and furthermore, it is necessary to individually adjust the variable resistance by the number of input channels, that is, the number of sets of current transformers, filter circuits, and sample-and-hold circuits.

In addition, there is a high possibility that the offset voltage of circuit components such as operational amplifiers will change due to temperature or deterioration over time (this makes the adjustment work more complicated).

The second method is to perform differential processing after A/D conversion. More specifically, the offset voltage is a DC component, and the voltage and current components of the power system are sine wave signals with a fundamental frequency. Therefore, in order to remove the DC component, data at a certain time and several sampling timings before that are used to remove the DC component. Offcents can be removed by performing a difference calculation with the data.

This difference processing also functions as a kind of digital filter, so if a process is adopted to subtract data from 30 degrees earlier, for example, in order to speed up the operation speed of the device, the frequency characteristic will have a pass peak that is 6 times the fundamental frequency. As a result, the gain at the fundamental frequency decreases significantly. For this reason, 1 which usually has a frequency characteristic with a peak gain at the fundamental frequency.
Difference processing is used to subtract data 80 degrees earlier. However, even in this case, if the system frequency is 5011z, 1
Since data between zero and zero is required, it is impractical for digital protective relays that require high-speed operation. Furthermore, since differential processing functions as a type of digital filter, it also affects the characteristics of the digital protective relay itself.

The present invention was made with the aim of solving the above-mentioned problems in removing offset voltage in conventional digital protective relays. The purpose is to provide a digital protective relay that can eliminate the effects of voltage.

[Means to solve the problem]

When removing offset voltage, the digital protection relay of the present invention focuses on the fact that the input data is a sine wave that oscillates with a certain voltage level as a reference, and uses a very large number of data, for example, 65536 (2") pieces of data. When sequentially added, the sine wave component becomes zero for each cycle of the fundamental frequency, and in the end, only the DC component remains. Taking advantage of this fact, divide the remaining DC component by the number of additions, that is, the average value. The structure is designed to seek the following.

[Effect]

In the digital protection relay of the present invention, since the offset value is calculated by calculating the digital data, the offset value can be removed simply by subtracting the offset from each digital data.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to the drawings showing embodiments thereof.

The hardware configuration of the digital protective relay of the present invention is basically the same as that of the conventional one. That is, the third
As shown in the figure, there are a plurality of current transformers 11, 12, 11, 12, 12, 12, 12, 12, 12, 12, 22, 22, 22, 32, 32, 22, 22, 32, 32, 32, 42, 32, 32, 43, 43, 43, 43, 43, 43, 43, 44, 44, 44, 44, 34 34 44 4 4 3 4 3 4 3 3 3 3 3 4 4 current transformer current transformers were connected to the power grid 10 and convert the voltage or current value of the power grid 10 to be protected into an appropriate voltage signal (analog signal).
. . 1n, an input converter 1. The fundamental frequency of the power system 10, for example 50 or 60 Hz, is extracted by removing harmonic components etc. contained in the analog voltage signals output from the current transformers 11, 12...1n of the input converter 1. Filter circuit 2 outputting as analog data
．． A sample hold circuit 3 that holds the analog data output from the filter circuit 2 at a value at that time at a predetermined sampling timing. Multiplexer 4. A
It is composed of a /D converter 5, a CPU 6, etc.

Current transformer 11 (or 12...In) and filter circuit 2
A plurality of one-channel circuits each consisting of a sample and hold circuit 3 are provided, and each sample and hold circuit 3
The output of is given to multiplexer 4.

The multiplexer 4 switches and outputs the output of each sample hold circuit 3 to the A/D converter 5. Specifically, since each sample and hold circuit 3 holds analog data at the same sampling timing, the multiplexer 4 sequentially switches and connects each sample and hold circuit 3 to the A/D converter 5. Sample hold circuit 3
sequentially outputs the analog data held by the A/D converter 5 to the A/D converter 5.

The A/D converter 5 converts the analog data provided from the multiplexer 4 into, for example, 16-bit digital data and outputs it to the CPU 6, which is an arithmetic means.

The CPU 6 processes the digital data given from the A/D converter 5 using software according to a predetermined program.
As a result, if it is determined that a failure or the like has occurred within the power system, for example, an operation such as shutting off the system is performed.

By the way, the digital protection relay of the present invention is
It is characterized by the content of the arithmetic processing according to No. 6.

Hereinafter, the content of the arithmetic processing by the CPU 6 will be explained in detail.

FIG. 1 is a flowchart showing a procedure for removing offset voltage of a digital protection relay according to the present invention, which is actually executed by CP[I6 as a calculation means.

First, when the digital protection relay of the present invention is powered on, the initial value OSI of the offset value O5 is set to 0 (step Sl).

Next, the data number n is set to 1 and the data integrated value tUM is set to O (step S2), after which actual data reading is performed. That is, data V (t) is read at each sampling timing (step S3), and at each subsequent sampling timing, the data number n is incremented by 1, and the data V (t) obtained at each sampling timing is read. The data integrated value SUN is integrated (step S4).

In this step S4, after the data V (t) is added to the data integrated value St1M, an offset value O5 (0 immediately after power-on) is subtracted from the data V (t), and the remainder is the data V at that sampling timing. (1
).

Then, the processing of steps 83 to S5 is repeated a predetermined number of times, in this embodiment, 65536 (2'') times for reasons to be described later (step S6).

As described above, 65536 (2”) pieces of data V
When the integrated value SUN of (t) is obtained, this is divided by the number of samples, that is, 65536 (2"), and the data V (t
) is calculated, and this is the new offset value O3.
1 and stored (step S7).

Then, from this point (sampling timing), when 65536 (2") pieces of data are integrated again in the same manner as described above, the average value of the data V (t) is calculated and this is used as the new offset value OS2. Ru.

Here, we will explain the reason why the number of samples to obtain the new offset value O8 was set to 65536 (2"). Normally, the CPU of a digital protective relay has 16
The bit specification is used because division by 216 is a very simple process in a 16-bit microprocessor. In other words, the addition of 216 1-word data results in 2-word data, but dividing this by 216 means that the upper 1 word of the 2-word data directly represents the division result, so processing by the microprocessor is required. It has the advantage that it is extremely simplified.

Of course, even if 215 is used, for example, it can be easily processed by shifting the focus of the data.

Now, when considering the above-described embodiment of the present invention in more detail, for example, if the fundamental frequency of the power system is 50Hz,
If the sampling frequency is 30 degrees electrical angle of the fundamental frequency, the 216 sampling period is approximately 109 seconds (=1
150x360/30x 2”).

That is, for about 109 seconds after power is applied to the digital protection relay, the digital protection relay operates with the offset value O3 kept at 0, and thereafter, the offset value O8 is updated every time about 190 seconds have elapsed. In this case, if some kind of failure occurs in the power system, a DC component or a high frequency component will be superimposed on the input temporarily, but the failure usually lasts for several tens of meters to several seconds. By taking an average value of about 109 seconds, the influence of failures and the like is diffused to such an extent that it can be practically ignored.

In the above embodiment, the number of sampling data for periodically calculating the offset value is kept constant (216) from the time the power is turned on to the digital protective relay, but the number of sampling data is kept constant (216) from the time the power is turned on. By making the length shorter than that, it is possible to eliminate concerns about the operation of the digital protective relay or inconvenience during testing. A flowchart showing the procedure of such an embodiment is shown in FIG.

In this flowchart, steps S1 to S
5 and step S7 are exactly the same processes as in the flowchart of FIG. 1 described above, and when the data number n becomes 211 in step SIO corresponding to step S6 of FIG. 1, a new offset value of 051 is calculated. I try to do that. As a result, the offset value O8 is set to 0 for only about 8.5 seconds after the digital protection relay is powered on.

After that, steps 512 to S17 are performed in the first
Exactly the same processing as steps 82 to S7 in the figure is performed,
The offset value O3 is updated every time the number of data samples is 216, that is, at an interval of about 109 seconds.

In this second embodiment as well, the arithmetic processing is performed using C.
Needless to say, this is executed by the PU6.

〔Effect of the invention〕

As detailed above, according to the digital protection relay of the present invention, it is possible to automatically and completely eliminate the influence of offset voltage of operational amplifiers used in filter circuits, sample-and-hold circuits, etc. It can also respond to changes in temperature or changes over time. Furthermore, unlike offset removal using differential processing, data from 180 electrical degrees earlier is not used, so digital preservation is j4N! Guarantees high-speed operation of electrical appliances.

[Brief explanation of the drawing]

Fig. 1 is a flowchart showing one embodiment of the arithmetic processing procedure for removing offset voltage of a digital protective relay according to the present invention, Fig. 2 is a flowchart showing another embodiment, and Fig. 3 is a general flowchart of a digital protective relay. FIG. 2 is a block diagram showing a typical configuration. 2... Filter circuit 3... Sample hold circuit 5... A/D converter 6... CPU 1
0...Electric power system Note that the same reference numerals in each figure indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A filter circuit that extracts a fundamental frequency component from an electrical signal representing a voltage or current value of a power system, and a sample hold circuit that samples and holds the output of the filter circuit in time series; An A/D converter that converts the analog data held in the sample and hold circuit from analog to digital.
A digital protective relay comprising a D converter and a calculation means for performing predetermined calculation processing on digital data output from the A/D converter, and operates according to the calculation processing result of the calculation means, wherein the calculation means is , a timer for measuring a predetermined time that is sufficiently long compared to the frequency of the power system; and an integrating means for integrating digital data output by the A/D converter during the timer's measurement of the predetermined time. A digital protective relay comprising: an average value calculation means for calculating an average value of each digital data as an offset voltage value from the integration result by the integration means.