JPH04347538A - Load characteristics measuring method for power system - Google Patents

Abstract

PURPOSE:To measure load characteristics based on natural fluctuation (micro fluctuation) occurring under steady state by calculating the load characteristics from a covariance for each combination of powers. CONSTITUTION:A voltage transformer 4 is connected with a bus 2 at a predetermined position thereof and the voltage of the bus 2 is measured at the input terminal of each load. An instrument transformer 5 is connected with each transmission line 3 in order to measure the current flowing through each transmission line 3. Voltage and the like are then measured through output terminal sections 8, 9. A covariance is then determined for each combination of thus measured voltages, currents and calculated powers and load characteristics are calculated using thus determined covariance. In other words, the load characteristics are measured based on an natural fluctuation(micro fluctuation) occurring under steady state. Consequently, voltage collapse phenomenon can be analyzed. Contrary to a conventional system, occurrence of disturbance is not the condition of measurement and many load characteristic data can be measured under desired conditions.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring load characteristics of an electric power system.

0002

[Prior art] From the substation to each customer (general household, company, etc.)
In order to supply stable power to factories, etc.), or to plan and operate a new power system, it is necessary to know the characteristics of the power system. In other words, equipment expansion and changes on the power supplier side and the consumer side, changes in the usage status on the consumer side (turning on/off switches of each equipment, etc.), and accidental accidents that may occur on the power system. The above-mentioned stable supply can be ensured by knowing in advance the effects and impacts of various changes on system stability.

On the other hand, the power system includes equipment on the power supply side, such as generators, transformers, and power transmission lines, and various equipment installed on the consumer side. The characteristics of the former can be analyzed by the power supplier measuring the characteristics of each individual piece of equipment, since it is their own equipment and the number of pieces is finite, but the It is virtually impossible to perform such measurements on individual equipment.

Conventionally, therefore, a method has been adopted in which the customer side is assumed to be a set of loads and the load characteristics thereof are measured. As for the load characteristics, for example, "Voltage stability analysis and operation index of large-scale power systems" (IEEJ Paper B
, Vol. 110, No. 11, 1990), P.
It is expressed as =P0・Vα・Fn (1). Here, P is active power, which is calculated from the measurement results of voltage and current at the input terminal of the load. P0, V, and F are a constant, a voltage at the input terminal, and a frequency, respectively. The larger each index α,n is, the greater the change in power with respect to voltage fluctuations and frequency fluctuations, and each index is usually in the range of 0 to 2. And considering that the frequency is constant, Fn
can also be considered a constant, so the above equation (1) becomes P
=Pc·Vα (2), and voltage fluctuation is the only parameter. Furthermore, reactive power is similarly defined.

[0005] This index α is determined by the following means. That is, when a disturbance such as a lightning strike occurs, the voltage drops significantly for a moment, and then recovers to the normal state in a relatively short period of time. The computer temporarily holds the transient phenomenon from this voltage drop to recovery,
It is applied to a model that has been created in advance, and the index is determined by the method of least squares. Since this calculation process takes a lot of time, it is usually performed off-line.

[0006]

[Problem to be Solved by the Invention] However, with the above-mentioned means, the determination can be made only after there is a disturbance such as a lightning strike, so it is necessary to constantly detect the presence or absence of a disturbance such as a lightning strike, such as detecting the presence or absence of a momentary power outage. In addition to having to check it, even if measurements are taken over such a long period of time, the number of samples that can be obtained is small because the index is actually obtained under the condition that a disturbance occurs. The above set of loads is actually not a single load, but an aggregation of many loads, and each individual load can be freely changed in output or turned on/off according to the convenience of each consumer. From the power supplier's perspective, the load on the aggregate has many uncertain factors. Therefore, in order to accurately measure load characteristics, a large number of samples are required for each of the many upper limits such as season and time of day, but if you rely on the occurrence of disturbances as described above, it is impossible to obtain the desired number of samples. Can not. In addition, offline output is required, and timely online measurement is not possible.

On the other hand, in addition to the sudden characteristics caused by the above-mentioned disturbances, these characteristics include natural fluctuations that occur in a steady state, that is, switches are turned on and off without permission in the equipment on the customer side. As a result, the load changes, and in addition, the generator rotor fluctuates, and when demand is high, the voltage adjustment tap of the transformer also fluctuates, so P, V, etc. constantly fluctuate slightly. There are characteristics in the state.

[0008] When measuring the characteristics in such a steady state, if the above-mentioned means is applied, the following problems arise. In a steady state, changes such as load fluctuations are slow, so holding all of them once and analyzing them is not only impractical in terms of memory capacity, but also making it complicated to create a model in advance.

[0009] In addition, normally each piece of equipment lowers its own impedance and increases the current in order to keep the power supplied to itself (each piece of equipment) constant once the power is reduced when the voltage drops due to a disturbance or the like. However, if the impedance is lowered for some reason and the current is increased, the power (voltage) will also decrease accordingly, meaning that once the voltage begins to drop, it will return to its original state. A voltage collapse phenomenon may occur in which the voltage continues to drop without returning, and eventually reaches zero (power cannot be supplied). In order to analyze such phenomena, it is necessary to investigate the load characteristics of steady load fluctuations in response to minute disturbances, but for the reasons mentioned above, it was not possible to perform such analysis because measurements could only be made in conjunction with large disturbances. .

The present invention has been made in view of the above-mentioned background, and its purpose is to be able to measure load characteristics based on natural fluctuations (minor fluctuations) occurring in a steady state. An object of the present invention is to provide a method for measuring load characteristics of a power system that can obtain a desired number of samples without waiting for the occurrence of a disturbance.

[0011]

[Means for Solving the Problems] In order to achieve the above-mentioned object, a power system load characteristic measuring method according to the present invention measures the voltage and current at the load end in the power system,
In a load characteristic measurement method that calculates the power based on the measured value and calculates the load characteristics that represent the influence on the fluctuation of the power when the voltage fluctuates, when determining the load characteristics, the voltage, current, and power This is done by using covariance for various combinations of.

0012

[Operation] Measures the voltage and current at the input terminal of the load to be measured. Then, based on the voltage and current,
Desired power, ie, active power or reactive power, is calculated. Next, the covariance for each combination of the above-mentioned actually measured voltage, current, and calculated power is determined, and the results are used to calculate the load characteristics. That is, the load characteristics are measured based on natural fluctuations (minor fluctuations) occurring in a steady state. Furthermore, when calculating the load characteristics described above, there is no need to select and use one of a plurality of models created in advance, which was conventionally essential, so high-speed calculation processing is possible.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the power system load characteristic measuring system according to the present invention will be described in detail below with reference to the accompanying drawings. Figure 1 shows an example of the main circuit in a substation on the power supply side. As shown in the figure, the upper power transmission line 1 connected to the power generation side
is connected to the bus 2, and power is supplied to each consumer side (load) via multiple (only two are shown in this example) power transmission lines 3 connected in parallel to the bus 2. It has become. A potential transformer 4 is connected to a predetermined position of the bus 2, so that the voltage at the input end of the bus 2, that is, each load can be measured. Further, an instrument current transformer 5 is connected to each power transmission line 3.
The current flowing through can be measured. and,
These voltage values (effective values), current values (effective values), various kinds of power calculated based on them, and the like are displayed on the display 6. Note that the reference numeral 7 in the figure is a protection circuit, which disconnects the power system where an accident has occurred and protects it. Further, reference numerals 8 and 9 in the figure are output terminal sections attached to the front surface of the device, respectively, and the above voltage and current can be taken out through the output terminal sections, and in the present invention, the output Load characteristics are measured by measuring voltage and the like via the terminals 8 and 9. Specifically, the details are as follows.

FIG. 2 shows a model of a power system to which the first embodiment of the present invention is applied. As shown in the figure,
A plurality of (two in this example) load feeders 12 and 13 (corresponding to the transmission line 3 in FIG. 1) are connected in parallel from the power generation side upper system 10 (corresponding to the upper power line 1 in FIG. 1) via the bus bar 11. has been done. Then, the voltages V1, V2 and currents I1, I2 at the input terminals of each load feeder 12, 13
However, since the voltage at the input terminal of each load feeder 12, 13 is the same (V1 = V2), it is hereinafter referred to as V. In addition, when three or more load feeders are connected, two load feeders arbitrarily selected from them are used.

FIG. 3 shows a block diagram of a measuring device for carrying out this embodiment. That is, an A/D converter 15 for converting the voltage V and currents I1 and I2 measured via the instrument transformer 4 and the instrument current transformer 5 into digital signals, and the A/D converter 15 and its A/D It consists of an arithmetic device 16 connected to the output of the converter 15 to calculate load characteristics, and a display/record device 17 connected to the output of the arithmetic device 16 to display the calculation results of the arithmetic device 16. For example, a computer is used as the arithmetic device 16,
As the display/recording device 17, a display such as a CRT, a printer, or the like is used. Note that the computer may also serve as the storage means. Note that since the V actually measured in this example is an instantaneous value, the value converted to an effective value is used in various calculations.

The processing performed by the arithmetic unit 16 will now be explained. First, each load feeder 12, 13 is
Active powers P1, P2 and reactive powers Q1, Q2 are calculated, respectively. Here, focusing on the active powers P1 and P2, each load feeder 12 and 13 is considered to have the same load characteristic constant (index) α since they are in the same area, so from the above formula (2), Its load characteristic is P1
=Pc1・Vα (3)P2=Pc2・
It can be written as Vα (4). In addition, Pc1,
Pc2 is a specific constant.

[0017] In the present invention, the index α indicating this load characteristic is calculated without using a model prepared in advance as in the conventional method.
It is characterized by being calculated by arithmetic processing, and the specific calculation means and the principle of derivation thereof are as shown below. When each side of the above equations (3) and (4) is transformed logarithmically, p1=pc1+α・v (5) p2=pc2
+α·v (6). Here, v=lo
g[V], p1=log[P1], pc1=log[P
c1], p2=log[P2], pc2=log[Pc
2].

[0018] As mentioned above, Pc1 and Pc2
Since they are constants that do not depend on voltage fluctuations, they can be regarded as independent probability variables, and therefore, pc1 and pc2 are also independent from each other. Therefore, these covariances are zero, and <pc1,pc2>=0 (7
). Here, by substituting equations (5) and (6) into equation (7), <p1-α・v, p2 −α・v>=0 (
8) holds, and if we further organize this, < p1, p
2>-α<v, (p1+p2)>+α2 <v, v>=
0(9).

Therefore, if each covariance CPP=<p1, p2>CVP=<v,(p1+p2)>CVV=<v,v> is obtained, then from the formula for the solution of the quadratic equation to equation (9), An index α indicating the characteristics of the load is determined by the following equation (10). α=[CVP+(CVP2 -4・CVV・CPP)1
/2 ]/(2·CVV) (10) Note that the load characteristic constant β for reactive power can also be calculated in the same manner. β=[CVQ+(CVQ2 -4・CVV・CQQ)1
/2]/(2・CVV) (11) In other words, in this example, after logarithmically transforming each power (load characteristic equation with power as the left side), various covariances are calculated,
The load characteristic constants α and β are determined based on the covariance.

By the way, α determined by the above equation (10) is a value at a certain moment, so it cannot be said that the value directly represents the load characteristics of the measured load. It was quantified using the measuring device shown in 4. Note that FIG. 4 is a block configuration diagram showing a more specific configuration of the arithmetic device 16 described above.

That is, in this device, at regular intervals (sampling time), the voltage V(i) and current I1 (i), I
2 (i), sample M pieces of each data, and calculate the above index α based on the sampling data.
is now being sought. By adjusting the length of this sampling time, it becomes possible to measure fluctuations (characteristics) over a relatively short period of time or, conversely, fluctuations (characteristics) over a relatively long period of time. The specific configuration and means are as follows.

First, each of the voltages and currents mentioned above is input to the power calculation means 20, and each active power P1(i), P2(i) and reactive power Q1(i), Q2(i) are calculated, and the input voltage is Together with V(i), the calculation result is input to the logarithmic conversion means 21 at the next stage.

The logarithmic conversion means 21 performs logarithmic conversion on the above five data and inputs it to the statistical processing means 22 at the next stage. In this example, (M-1) delay circuit means 23 are provided between the logarithmic conversion means 21 and the statistical processing means 22, and the data output from the logarithmic conversion means 21 is directly statisticized as described above. The data input to the processing means 22 and the first delay circuit means 23a are inputted to the first delay circuit means 23a with a delay of one step, and at the same time, the data is input to the delay circuit means 23b. By doing so, the statistical processing means 22 receives M pieces of past data.

The statistical processing means 22 calculates the average value of each voltage and power based on M pieces of data. That is, the following calculations are performed. v=Σi[v(i)]/M
(12) p1=Σi[p1(i)]/M
(13) p2=Σi[p2(i)]/M
(14) q1=Σi[q1(i)]/M
(15) q2=Σi[q2(i)
]/M (16) Here, v(i)
=log[V(i)], p1(i)=log[P1(i
)], p2(i)=log[P2(i)], q1(i)
=log[Q1(i)], q2(i)=log[Q2(
i)]. Moreover, "i" in each formula indicates the step number (1 to M) of the sampling data.

[0025] Then, in the load characteristic constant calculation means 24,
By substituting the average value of each data calculated by the above equations (12) to (16) to each variable of the above equations (10) and (11), the load characteristic constant α of the active power P and the reactive power Q The load characteristic constant β is determined. The load characteristic constants α and β thus obtained are displayed in the display/storage device 17.
It is displayed and stored, and used for various analyses.

FIG. 5 shows a second embodiment of the invention. In this embodiment, unlike the first embodiment described above, one load feeder 30 is used to calculate the load characteristic constants α and β. In this example, from upper system 31 to 2
two busbars (upper busbar 32 and load busbar 33 one stage lower than the upper busbar 32)
) is connected to one load feeder 30,
This load feeder 30 is any one system of the power transmission lines 3 in FIG. Further, the load bus bar 33 corresponds to the bus bar 2 in FIG. 1, and the upper electric wire 1 in FIG. 1 is a line connecting both bus bars 32 and 33 in this figure. Then, an impedance element such as a transformer or a power transmission line located between both bus bars 32 and 33 is set as "r+jX".

Next, to explain the specific process, the general configuration of the measuring device used is the same as that of the first embodiment shown in FIG. 3, and the basic flow is the same as that of the first embodiment described above. is the same as that of the first embodiment, except that in addition to the voltage V and current I at the input terminal of the load, the voltage Vs at the upper bus bar 31 is used as parameters for calculation, and the logarithmic transformation as in the first embodiment is not performed. Because of the difference, the specific configuration of the arithmetic device is different as shown in FIG.

That is, as shown in FIG.
Voltage Vs at each D-converted sampling time
(i), V(i) and current I(i) are input to the power value calculation means 35, where active power P(i) and reactive power Q(i) are calculated, voltage Vs(i), V(i)
Output with.

A statistical processing means 36 and a delay circuit means 37 are connected to the output side of the power value calculation means 35, and as in the first embodiment, each M piece of data is sent to the statistical processing means. 36, where the average value of the various data shown below and the covariance based thereon are determined.

(Calculation of average value) Vs=Σi[Vs(i)]/M (17
)V=Σi[V(i)]/M
(18) P=Σi[P(i)]/M
(19) Q=Σi[Q(i)]/M
(20) Here, i is the number of sampling steps (1 to M).

(Calculation of covariance) DVV=Σi[{V(i)-V}{Vs(i)
−Vs]/M (21) DVP=Σ
i[{P(i)-P}{Vs(i)-Vs]/M
(22) DVQ=Σi[{Q(i)−Q
}{Vs(i)-Vs]/M (23)

0
[032] The covariance thus obtained is input to the load characteristic constant calculating means 28, and each value is substituted into the following equation to obtain the constants α' and β'. α′={DVP・V}/{DVV・P}
(24) β′={DVQ・V}/{DVV・
Q} (25)

The derivation principle for determining the load characteristic constant using the above equations (24) and (25) in this embodiment is as follows. The load characteristic for the active power P at the input end of the load is P=Pc・Vα′ from the above equation (2).
It can be expressed as (26). And considering the relationship of minute quantities from the above equation, ΔP=ΔPc・Vα′+ΔV・α′・P
/V (27) holds true. And upper busbar 3
Taking the covariance of the voltage Vs of 1 and the various quantities in equation (27) above, <ΔP, ΔVs>=<ΔPc, ΔVs>Vα+<ΔV,
ΔVs>α′·P/V (28).

At this time, assuming that the impedance element r+jX between both bus bars 32 and 33 is sufficiently large, ΔVs and Δ
Since Pc varies independently, <ΔP between the two
c, ΔVs>=0 (29) holds true. Therefore, the load characteristic constant α can be obtained by substituting equation (29) into equation (28), α′={<ΔP, ΔVs>V}/{<ΔV, ΔVs>P
} (30) is obtained, and this equation (30) is nothing but the above equation (24). The same applies to the load characteristic constant β for the reactive power Q. In this embodiment, the calculation process is simpler than that of the first embodiment described above, so that higher-speed processing is possible.

By the way, as shown in FIG. 1, normally there is an upper bus bar and a load bus bar, and a plurality of load feeders are connected to the load bus bar, so no matter which of the above two methods is adopted, the load characteristics The constants can be measured, and according to the simulation results, α and α' and β and β' determined by either of the two equations are almost the same, so it does not matter which one is used.

However, due to the structure of the system, for example, if there is no upper load bus, only the first embodiment can be applied, and if there is only one load feeder, only the second embodiment can be applied. Furthermore, even if there is no configuration restriction as described above, there may be cases where only one of them can be applied to obtain accurate data due to the characteristics restrictions described below.

In other words, in the case of the first embodiment, since the measurement is performed on the assumption that the load characteristics of the two load feeders are approximately equal, even if there are a plurality of load feeders, if the load characteristics of each of them are significantly different, is not suitable. For example, one load feeder may supply power to a general residential area, and the other load feeder may supply power to an industrial area.

Further, in the case of the second embodiment, since it is assumed that the impedance element between the upper bus and the load bus is large, it cannot be applied when the impedance element is small.

[0039]

[Effects of the Invention] As described above, in the power system load characteristic measurement method according to the present invention, the covariance for each combination of the measured voltage and current and the power calculated based on it is determined, and the results are calculated. Since the load characteristics are calculated using this method, the load characteristics can be measured based on natural fluctuations (minor fluctuations) occurring in a steady state. the result,
It also becomes possible to analyze voltage collapse phenomena. moreover,
Since the generation of disturbance is not required as in the conventional method, it is possible to measure a large amount of load characteristic data under desired conditions. Furthermore, there is no need to create various models in advance, and high-speed arithmetic processing is possible, allowing timely online measurements.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a main circuit in a substation.

FIG. 2 is a schematic diagram of a power system to which a first embodiment of the power system load characteristic measurement method according to the present invention is applied.

FIG. 3 is a block configuration diagram showing a measuring device for implementing this embodiment.

FIG. 4 is a block diagram showing in more detail the arithmetic processing unit that is a main part of the measuring device shown in FIG. 3;

FIG. 5 is a schematic diagram of a power system to which a second embodiment of the present invention is applied.

FIG. 6 is a block configuration diagram showing an arithmetic processing device used in a measuring device for carrying out this embodiment.

[Explanation of symbols]

11 Bus bars 12, 13, 20 Load feeder 16 Arithmetic device means 20, 35 Power value calculation means 21 Logarithmic conversion means 22, 36 Statistical processing means (covariance calculation) 23, 37
Delay circuit means 24, 38 Load characteristic constant calculation means 32 Upper bus line 33 Load bus line

Claims (1)

[Claims] Claim 1: A load that measures voltage and current at a load end in a power system, calculates power based on the measured values, and calculates load characteristics that represent the influence on fluctuations in power when the voltage fluctuates. A method for measuring load characteristics of an electric power system, characterized in that the load characteristics are determined by utilizing covariance for various combinations of the voltage, current, and power.