JPH0691702B2 - Overexcitation detection relay - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an overexcitation detection relay device, and more particularly to an overexcitation detection relay device used for protection of a generator, a transformer and the like.

[Technical background of the invention]

Continuous operation of electric power equipment such as a generator and a transformer in an overexcited state causes overheating of the equipment and thus damage to the equipment. Further, the limit of the allowable operation time due to the continuous over-excitation operation depends on the degree of over-excitation to the electric power equipment. A quantity proportional to the voltage V and inversely proportional to the frequency, that is, a quantity V / has been used as a measure for measuring the degree of over-excitation, and the operation of the electric power equipment is restricted by the magnitude of this V /. Is being done.

[Problems of background technology]

On the other hand, as digital technology has advanced in recent years, various attempts have been made to digitally protect and control electric power equipment. It has not been established until now.

[Object of the Invention]

The present invention has been made to solve the above-mentioned problems, and a method of digitally calculating the amount V / which is a measure for detecting an overexcitation operating state of a power device such as a generator and a transformer. It is an object of the present invention to provide an overexcitation detection relay device that can be derived with high accuracy.

[Outline of Invention]

In the present invention, by using the sample value of the AC voltage sampled at a constant time interval and converted into a digital amount, by adding the absolute value of the sample value of a half wave of the AC voltage or a period of an integral multiple of the half wave, It is intended to obtain the amount corresponding to the above V / and limit the continuous operation time of the protected equipment according to this amount.

[Basic concept of the present invention]

Prior to the description of the embodiments of the present invention, the basic concept of the present invention will be described. FIG. 2 is a diagram for explaining the V / calculation method which is the main point of the present invention, and shows, as an example, the case where the frequency of the input AC voltage V is 50 Hz and the sampling frequency is 1,200 Hz. As shown in Fig. 2, the input AC voltage is sampled at a fixed cycle (1/1200 seconds), and the analog / digital exchanged voltage sample value is v _-1 , v
It is represented as ₀ , v ₂₅ . In the present invention, the area of the hatched portion shown in FIG. 2, that is, the area of one half wave of either the positive wave or the negative wave is approximately proportional to the magnitude of the voltage V, and
It was made by knowing that it is approximately inversely proportional to the frequency of. In short, the area of the hatched part shown in FIG.
It is proportional to the sum of each sample value v ₁ , v ₂ , ... v ₁₁ . Therefore, by calculating equation (1), the amount P proportional to V /
An approximate expression of is obtained.

V / ∝P≈v ₁ + v ₂ + ... v ₁₁ (1) The above equation (1) can be expressed more generally as equation (2).

However, i is the sampling number at the beginning of the positive or negative wave, j is the number of sample values included in the positive or negative wave, and the values at rated voltage and rated frequency are calculated in this way.
Fig. 3 shows the error of P (∝V /) when the frequency is changed to 1P.U. That is, when V / is calculated based on the equation (2), the range shown as the hatched portion in FIG. 3 becomes the error range. In short, the calculation result of V / according to the present invention shows that the result can be obtained with high accuracy of ± 0.75% or less as shown in FIG. 3 in the practical frequency range of 70 Hz or less.

Example of Invention

Embodiments will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of an overexcitation detection relay device according to the present invention.

In FIG. 1, G is a generator and TR is a transformer, which supplies power to the grid through a circuit breaker CB. PT is a voltage transformer for introducing the voltage of the bus bar B to the overexcitation detection relay 1. Here, the overexcitation detection relay device is composed of a conventionally known digital relay, and the introduced AC voltage V is sampled at a constant cycle through an analog / digital converter (A / D) 2 and converted into a digital amount. It The central processing unit (CPU) 3 performs the overexcitation detection calculation described below using the above-described digital amount and the data memory (RAM) 5 according to the program stored in the program memory (ROM) 4 in advance, and as a result, When the excitation state is detected, the output (OUT) 6 indicates the degree of overexcitation, that is, V /
The trip command 7 is issued to the generator G after a time limit determined according to the magnitude of the.

FIG. 4 is a flowchart for explaining overexcitation detection calculation processing executed in the central processing unit. In FIG. 4, in step 41, the analog / digital converter (A /
D) The sample value (v ₁ , v ₂ ...) Of the voltage converted into the digital value in ₂ is taken in, and the process proceeds to step 42. In step 42, an approximate value of the quantity P proportional to V / is calculated based on the equation (2). In step 43, the calculation result of the equation (2) is compared with a constant K that has been set in advance, and it is determined whether or not it is in the overexcitation operating state. When it is determined that the overexcitation operation state is not established, the process ends. If it is determined in step 43 that it is in the over-excitation operating state, the process proceeds to step 44, it is determined whether or not the over-excitation operation time has continued for a predetermined time, and if it is determined that it has not continued for the predetermined time, the process ends. To do. If it is determined in step 44 that it has continued for the predetermined time,
Moving to step 45, the trip command 7 is issued to the generator G.

As described above, according to the present embodiment, by using the data sampled at a constant cycle and converted into the digital amount, the extremely simple calculation as shown in the equation (2),
It has become possible to detect the degree of over-excitation operation of electric power equipment with high accuracy. Therefore, the problem of V / calculation, which had been an obstacle to the digitization of generator protection, was solved, and it became possible to digitize the generator protection relay device.

Other Embodiment 1 In the above embodiment, an example of obtaining the amount corresponding to the area of the positive wave or the negative wave of the input AC amount has been described, but the present invention is not limited to this, and one wave portion or 1.5 wave portions, etc. An area that is an integral multiple of a half wave of the input AC amount may be obtained.
For example, if the area of one wave is calculated,
Using the figure, the quantity q proportional to V /
An approximate value of is obtained.

V / ∝q ≒ v ₁ ＋ v ₂ ＋… v ₁₁ ＋ | v ₁₂ ｜ ＋ | v ₁₃ ＋＋＋＋ v ₂₃
| (3) Equation (3) is generally expressed as Equation (4).

However, i is the sampling number at the beginning of the positive wave or the negative wave, and k is the number of sample values included in one cycle of the alternating current. Therefore, even if the calculation is performed in step 42 of FIG. The effect is obtained. In this case, the constant k previously set in step 43 of FIG. 4 is set.
Should, of course, be 2k.

Other Embodiment 2 In the above embodiment, an example of calculating in units of positive wave or negative wave has been described, but the present invention is not limited to this and the calculation is performed by shifting the positive wave and the negative wave respectively as shown below. You may.
That is, to explain with reference to FIG. 2, the above equation (1) can be transformed into equation (5).

_{V / αP ≒ v 3 + v} 4 + ... v 11 + | v 12 | + | v 13 | + | v 14 | ...
(5) If this expression (5) is generally expressed, it becomes the expression (6).

However, l is an arbitrary sampling number j is the number of sampled values included in the half-wave Note that equation (6) is equivalent to equation (2) above, and therefore (2) in steps 42 and 43 in FIG. Even if the formula is replaced by the formula (6), the same effect can be obtained.

In each of the above-mentioned embodiments, the voltage is sampled at 1200 Hz because of the relationship shown in FIG. However, the sampling frequency is not limited to 1200 Hz as a matter of course, and can be arbitrarily changed according to the accuracy required for calculating V /. For example, if a high accuracy of ± 0.7% at a frequency of 70 Hz or less is not required, the sampling frequency may be 1200 Hz or less. If higher accuracy is required, it is necessary to set the sampling frequency to 1200 Hz or higher.

〔The invention's effect〕

As described above, according to the present invention, by using each sampled value of the AC voltage sampled at a constant time interval and converted into a digital value, the sampled value within the period of a half wave of the input AC voltage or an integral multiple of the half wave is used. Since the absolute value is added to obtain an amount corresponding to V /, it is possible to calculate V /, which is a measure of overexcitation that causes overheat damage of power equipment, with high accuracy. This solved the problem of V / calculation, which had been an obstacle to the digitization of generator protection, and made it possible to digitize generator protection using digital technology, which has made remarkable progress in recent years.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of an overexcitation detection relay device according to the present invention, FIG. 2 is a waveform diagram for explaining a basic concept of an overexcitation detection relay device according to the present invention, and FIG. Is a diagram showing to what extent V / calculated by the embodiment of FIG. 1 has an error within a practical frequency range, and FIG. 4 shows the overexcitation detection calculation processing executed in the central processing unit. It is a flowchart explaining. 1 ... Overexcitation detection relay device, 2 ... Analog / digital conversion unit 3 ... Central processing unit, 4 ... Program memory 5 ... Data memory, 6 ... Output unit 7 ... Trip command

Continuation of the front page (56) Reference JP-A-49-88058 (JP, A) JP-A-51-82676 (JP, A) JP-A-56-56126 (JP, A) JP-A-61-258622 (JP , A) Actual development Sho 59-149434 (JP, U) Japanese patent Sho 49-15721 (JP, B1) Japanese public Sho 51-35698 (JP, B1)

Claims (1)

[Claims] 1. An analog / digital converter for sampling an AC voltage waveform at a constant time interval independent of a central processing unit and converting the sampled value into a digital quantity, and a data memory for storing the converted digital quantity. , The absolute value | v _m | of the digital quantity of the number j of sample values included in each period of the half-wave of the AC voltage or an integral multiple of the half-wave, using the absolute value Pv corresponding to the area of the AC voltage waveform. Is calculated in a predetermined cycle using the following formula, and a central processing unit that obtains a protection command that limits the operating time of the protected power equipment according to the magnitude of the calculated value, and from the result of this central processing unit An overexcitation detection relay device, comprising: an output unit that gives a protection command to a protected power device. However, 1 is the sampling number at the beginning of the calculation period that is determined by the predetermined cycle of area calculation.