JPS6011531B2 - Digital differential protection relay device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital differential protection relay system that collects electrical quantities from various parts of a power system as digital information at one electrical station, calculates this information, and outputs it as a relay output.

Conventionally, the amount of electricity in a system has been given to measurement, control, protection devices, etc. from CT, PD, (PT), etc. as a so-called analog amount. However, in recent years, as grids have become larger in capacity and more complex, the number of changes in protection methods, CT ratios, and settings of system protection devices has increased, making maintenance work difficult. Therefore, if the outputs of the CT and PD are digitized and all measurement, control, and protection are processed in digital quantities using a computer or the like, all of the above changes can be handled by changing the program. The present invention provides a method for protecting the power system in such a system by performing relay calculations using digitized electrical quantities.

BACKGROUND ART Hitherto, a protection relay layer using a so-called analog quantity and having the following operation has been proposed and implemented.

That is, to explain power transmission line protection as an example, Fig. 1 shows a general power transmission system, and the vector sum of the current 8 at the A end and the current 12 at the B end is the differential amount lo (actually, it is It is necessary for each phase, but only one phase will be described below), 1, and 1
1 when the maximum value of the absolute value of 2 is IM.

1k {IM-KR}+>K ...'11 However, k
・・・・・・Ratio KR・…”Limiter K ……Tap value {}10…If the value in parentheses is negative, the value in parentheses is zero. In the above formula {1}, lo and IM are rectified analogs. Needless to say, it's the quantity.

FIG. 2 is a ratio characteristic diagram of a differential operation relay system using the above formula '1' as an operating formula.

It is clear from equation {1} that the shaded area in the figure is the operating center. This formula '1} is not limited to power transmission line protection relays,
This is also common in rhombic relays such as busbar protection relays and equipment protection relays. In a relay system that receives digital quantities as input, in order to obtain the operating principle corresponding to equation '1) and the ratio characteristic corresponding to Figure 2, it is necessary to calculate rectified values such as effective values from each instantaneous value of the input waveform. need to ask. As an example, FIG. 3 shows a principle diagram of a method for determining the level of a sine wave from a digital quantity (hereinafter referred to as a digital input level determination method). This principle will be explained below. That is, in Fig. 3, 1(t) is the amount of electricity in the grid, and SP is the sampling pulse from the digital CT or PD (PT).The instantaneous value of the grid current or voltage at the point of generation of this pulse is sampled, and this magnitude is A/○
The data is converted, digitally encoded, and provided to a protection device, etc. This sampling pulse is 4n (n=1
, 2, ...) times the frequency, which is 12 in this figure.
The one with twice the frequency is shown. 1(t) indicates the instantaneous value of the electrical quantity at each sampling pulse generation point, but it is actually converted into a several-bit digital code corresponding to the polarity and height of this instantaneous value and processed. .

12(t) is 1(t) squared, P(t-3) is 1(t)
shows two plans for I(t) past 3 sampling pulses, and P(t)+12(t-3) is the result of these 12(t) and P
It shows the sum of (t-3).

12(t-3) is delayed by 3 sampling pulses, or 1/4 cycle, from 12(t), so P(t)+
12(t-3) becomes stable with a delay of 1'4 cycles after the occurrence of 1(t), and becomes stable with a delay of 1/4 cycle after the disappearance of 1(t).

After all, adding the two plans of data 1'4 cycles ago to the two plans of current data means that in the case of a 1(t) force sin curve, 1(t-3) corresponds to a cosine curve, and 12
(t) 10P(t-3) is calculating sin = 10cos = 1, and 12(t) 10P(t-3) is 1(
This is nothing but deriving two options for the maximum value of t).

If the above method is directly applied to a digital differential protection relay system, the squares of the maximum values of lo and IM in equation '1' can be obtained.

1.

2(t)={1,(t)+12(t)}20{1,(t
-3) 112(t-3)}2 ...■ IM2(t)=Nne×[1,2(t)11,2(t-3
), 122(t)+122(t-3)]...
...{3' Now, the system can be protected by substituting the currents ID and IM obtained from the above equations ① and '31 into the equation {1}.

However, this has the following problems. The first method that can be considered is to compute the square roots of both sides of equations ■ and {3} to obtain lo and IM, and then substitute them into equation (1) for determination, but this would significantly increase the calculation time using normal digital calculation methods. Therefore, system protection cannot be performed at high speed.In order to avoid this drawback, using two values for the current value and constant in equation [1}', 102-k2{IM2
-Fox R2} 10>Fox 2...[4] is sufficient.

Here, k. The reason why KR and K are squared is because the multipliers were combined to correspond to formula m, and the reason why R2, is set to 2 is because each digital quantity is equal to the peak value (twice the effective value) of the sine wave. This is because it is considered as a standard.

The ratio characteristic of equation (4} is as shown in FIG. 4.

Figure 4 shows a linear characteristic, but lo2 is plotted on the y-axis, and IN
A linear characteristic is obtained with 2 as the x-axis, and l
It cannot be said that linear characteristics have been obtained for o and IM. That is, the ratio characteristic according to formula {4) is 1 when k, KR, and K have an arbitrary relationship. is the y-axis, I
If M is expressed as an x-axis, it becomes a hyperbolic function and a linear ratio characteristic cannot be obtained. This causes the inconvenience that the ratio changes depending on the magnitude of the current IM, and if the system conditions fluctuate and the magnitude of the fault current changes, the relay may operate each time. It is necessary to reset the ratio of This invention uses the square of the current sampling value and the square of the sampling value 1/4 cycle (n is an integer) previous
The purpose of this invention is to solve the above-mentioned problems and to perform system protection at high speed and with a linear ratio characteristic in a system that performs power protection by determining the current by the sum of the current and the current.

In this invention, on the equation side, k・KR=K ”“”'5'
As a result, in the region where the current IM is larger than the limiter KR, a linear ratio characteristic passing through the origin determined only by the ratio k is obtained, and the shaded area shown in Fig. 5 is the operating limit. becomes.

At the same time, calculation time can also be reduced. Also l
Since the ratio characteristic between o and IM is linear, once the ratio is set, the ratio of the differential amount that the relay can operate to the amount of suppression will not change depending on the magnitude of the fault current, and the Even if system conditions such as size change, the characteristics remain uniform, and there is no need to reset the ratio. The above explanation is
Although we have shown a method to obtain lo2 and la based on the principle of Fig. 3, other methods can be used to obtain 1.

2. Even if 1 is sought, there is no change in the gist of this invention.

In addition, although the above description is based on the case where the sampling frequency is 12 times the fundamental wave, it is only necessary to obtain data from 1/4 cycle before, so 4n of the fundamental wave (n=1, 2, . . .
...) It goes without saying that a sampling frequency that is twice that is sufficient.

In addition, although a power transmission line protection relay is taken as an example, it is clear that the present invention is also effective for differential protection relays such as busbar protection relays as long as the following relationship is satisfied: be.

[Brief explanation of the drawing]

Figure 1 is a general power transmission system diagram, Figure 2 is a ratio characteristic diagram of the differential protection relay layer that has been proposed and implemented in the past, and Figure 3 is the level of digital input cited in the explanation of this invention. FIG. 4 is a diagram showing the principle of the determination method, FIG. 4 is a ratio characteristic diagram of the differential protective relay layer considered before reaching this invention, and FIG. 5 is a ratio characteristic diagram of the differential protective relay layer according to the present invention. Middle S
P is the sampling pulse, 1(t) is the amount of grid electricity, and 12(t) is its square, 12(t-3) is the square of 1(t) three sampling minutes earlier than 1(t). . Note that the same reference numerals in each figure indicate the same or corresponding parts. Figure 1 Figure 2 Figure 4 Figure 3 Figure 5

Claims (1)

[Claims] 1. Sampling at a frequency 4n (n = 1, 2, ...) times the fundamental frequency and using digitally encoded electrical quantity to calculate the square of the current sampling value, In something that responds to the sum of the square of the sampling value n samplings earlier than this sampling value, I_D^2-k
＾2＾＾＾2−2K_R＾2＝＾+＞2K＾2However, k・K_R=K where I_D＾2...Differential amount I_M^2...Suppression amount k...Ratio K_R...Limiter K... ...Tap value {}^+...The ratio characteristics for I_D and I_M are configured to be linear by satisfying a meaningful operation formula in which the inside of the tap is zero when the inside of the tap is negative. Digital differential protection relay device.