JPH04101630A - Control of system voltage stabilizing relay - Google Patents

Abstract

PURPOSE:To prevent the decay of a system voltage by calculating in advance the product of a runaround current value and a transmission impedance of a route where the current runs around to determine a voltage drop which is caused by the fact that power runs around the remaining route of a loop system after the loop is cut off. CONSTITUTION:It is basically considered that a voltage drop is caused by a runaround current. In the case that a generator is located midway through a route where the current runs around, an increase in current of the generator is compensated in expectation of a voltage maintaining capability of the generator. When a section in which a pre-current is caused to flow in the opposite direction to the runaround current exists in the route where the current runs around, a voltage is compensated for that section, supposing that a voltage is maintained to such a current value as is same with that of the initial reverse current. Therefore, the voltage drop V is determined by the following formula: V=1 (IO-Ic)XZO- the corrected voltage value ¦. Nextly, a current pulled by the load after the route is cut off is reduced by load cutoff to raise the dropped voltage to a target value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling a system voltage stabilization relay used for emergency control after an accident in a power system.

[Conventional technology]

Conventionally, power flow calculation methods for power systems (Equations 1.1 to 1.
5), for example, "Power System Transient Analysis Theory," written by Taiji Sekine, published by Ohmsha, January 20, 1980, pages 276-287. The power system consists of generators, transmission lines,
It is a system that is a complex combination of transformers, switches, loads, etc. The generator supplies active power and reactive power, which is consumed by the load. A power transmission and distribution system connecting the generator and the load transmits the power supplied from the generator to the point of consumption. Therefore, it is important to know through which transmission lines and distribution lines the active power and reactive power generated by the generator flow to the load, and how the voltage and current are distributed at each point in the transmission system. It is necessary to know whether or not the system is installed when operating the power system or adding new equipment. However, in a power system, it is rare that the voltage or current (both vector quantities) are given to the bus to which the generator or load is connected, and what is usually known is the generator's active power P and the terminal terminals on the generator bus. The magnitude of the voltage is ■, and the active power P and reactive power Q consumed by the load on the load bus. Therefore, various amounts of electricity within the power system are determined based on these known amounts.

Next, a conventional method for determining the magnitude of each node voltage will be described. First, the active power P and the terminal voltage (hereinafter referred to as ■) of each node (hereinafter referred to as Q) or each node.

Pm and Qk flowing to each node are generally Pk +jQk
-9, ×i, ...... (1, 2) (
(Note: i indicates the complex conjugate of I) Therefore, equation (1, 1) is expressed as follows: When active power P and reactive power Q are specified, k is used as It is expressed as equation (1,1).

+ = YX</ or i, -Σ Y,, XQ,...
・(1, 1) where k: 1, 2 . in node number. ...
Among the variables of the N(1,1) equation, the values that can usually be known are the active power (hereinafter referred to as P) and the reactive power Vz-IQ of each node.
zl ・・・・・・・・・・・・ (
1, 5) However, 2 is pv specified.

Note that R and () in equations (1, 4) are functions that obtain the real part of a complex number.

Here, (1, 3), (1, 4L) It can be seen that equation (1, 5) is a nonlinear equation in which the left side is a known quantity and the right side is the node voltage as an unknown quantity.Power flow calculation is based on these nonlinear equations. The purpose is to solve equations, and various methods have been proposed (for example, "Power System Engineering" by Hiroshi Takahashi, published January 25, 1970, pages 69-80).

[Problem to be solved by the invention]

The conventional control method for grid voltage stabilization relays is performed as described above, so generator information, load information, and information on each part of the system are required, and nonlinear equations are repeatedly applied until the desired solution is obtained (until convergence). There were problems such as a large accumulation of errors and a long calculation time. Furthermore, when there are multiple solutions to a nonlinear equation, there is a problem that it does not necessarily converge to the target solution.

This invention was made in order to solve the above-mentioned problems, and it uses the existing microprocessor used in power system protection relays to perform advance processing with high precision, high speed, a small amount of information, and simple formulas. The purpose of this study is to obtain a control method for a system voltage stabilization relay that can calculate the amount of load cutoff.

[Means for Solving the Problems] A method for controlling a system voltage stabilizing relay according to the present invention is a method for controlling a system voltage stabilizing relay that is connected to a higher-level system and that controls a loop power transmission system after a loop disconnection occurs in a loop power system that has a load and a generator. The voltage drop in the route that occurs due to the bypass to the remaining route is estimated in advance from the bypass current value and the line impedance of the bypass route using a voltage drop estimation calculation formula, and the voltage drop increase calculated using the estimation formula is calculated. The target voltage of the voltage drop width is calculated from the estimated value using a control amount calculation formula, and when the calculation result of the control amount calculation formula is a voltage drop greater than or equal to the target voltage setting value of the voltage drop width, the load is cut off after detecting a loop break. This system is configured to perform system protection by implementing this system.

(Function) The method for controlling the grid voltage stabilizing relay in this invention is as follows:
The voltage drop caused by the power going around to the remaining route of the loop system after the loop is disconnected is calculated in advance by the product of the current value going around and the power transmission system impedance of the route going around, and L7, and the calculated result is higher than the set value. In the event of a significant voltage drop, the loop is disconnected and the load is cut off early to prevent system voltage collapse.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. First, before giving a concrete explanation, let us explain the theory underlying this invention (
The formula (principle) will be described with reference to flowchart 1 in FIG. First, the system voltage stabilization relay method according to the present invention calculates the voltage drop width and the load capacity as follows.

(1) Voltage drop estimation calculation (Step 5TI) Since the voltage drop is due to loop current due to route breakage, the voltage drop width is calculated using the wraparound current and the line impedance of the wraparound route as shown in the following formula. Estimate.

[Basic formula] Voltage drop increase - 1 surrounding current x line impedance of surrounding route Here, the surrounding current is calculated based on the following idea.

■ Basically, it is assumed that the preliminary current of the route disconnection is pulled by the constant current characteristic load, wraps around the healthy route, and is superimposed on the preliminary current. It is assumed that the voltage drop is caused by this wrap-around current (step 5T).
IA).

■ Next, if there is a generator on the wrap-around route (including the end), take into account the generator's AVR effect (voltage maintenance ability) and make a correction for the generator current increase (Step 5TI
B).

■ Furthermore, if there is a section in the wrap-around route where the preliminary current direction is opposite to (cancels) the wrap-around current direction, consider that the voltage will be maintained until the current value is the same as the original reverse current. Correct the voltage accordingly (step ST
IC).

Therefore, the voltage drop width (ΔV) calculation formula is as follows.

ΔV = l (1,-[G)XZo-V,, lil
-...-(2,1) The meaning of the capacitance in the formula (2,1) is as follows.

Io: Preliminary current hector of loop break route absolute (direct 1G = generator current increase correction value during wrap-around route Zo: wrap-around route impedance hector ■Supplementary:
Voltage correction value Note that 1 sentence [is the hector quantity sentence - x + absolute value of jy - Jx
2+y".

(2) Calculation of control amount (steps ST2, 5T3) Next, control is performed to eliminate the current drawn by the load when the route is interrupted by cutting off the load, and to raise the voltage from the voltage drop state to the target voltage. Therefore, the principle of the control amount calculation method is basically the same as the voltage drop escalation estimation method, and the control amount is determined so that the voltage drop width due to the sneak current of the load cutoff amount becomes the target voltage.

The basic formula is as follows.

IC=1(νt VO+ΔV) /Z, l ・
...(2,2) The meaning of the capacity in the formula (2,2) is as follows.

z,: Surrounding route impedance ■o: Prior voltage value Δ■: Voltage voltage drop peak calculation value: Control target voltage value IC = Absolute value of load cutoff current vector Note that generator current increase correction Nc) and voltage correction (V Supplementary)
The specific calculation of is as follows.

(A) Generator current increase correction (Step 5TIB) Reactive power output limit Qc*ax and generator terminal voltage ■ obtained from the generator's preliminary output P6 and the output limit curve specific to the generator. It is calculated using the following formula, assuming that the power factor has been operated at a power factor of 1.0.

rc=Pressure Haru Takumi (QG,,,/VG)”-PG/VG
−・−・・−(2, 3) (B) Voltage correction for reverse current (Step 5TCI) If a current in the opposite direction to the wrap-around current due to route breakage is in the loop before the new route, the original It is assumed that the voltage will be maintained until the current value is the same as the reverse current, and the voltage drop in that line is corrected.

The voltage correction value (Vbi) is as follows.

(2, 4) K: correction coefficient -2 Next, an embodiment of the present invention will be described with reference to the drawings. First, Figure 2 (a) shows the impedance value of the power transmission system,
Figure 2(b) shows the current distribution before the new loop in the same system.

However, only the current value required by this device when assuming a loop break between node No. 2 and node floor 3 is shown in the diagram. Note that the portion indicated by an arrow on each bus line means that a load is present there. Also, Fig. 2(a),
(b) In both cases, the node Nα9 indicates the upper system to which the loop system shown in this embodiment is connected, and can be considered as an infinite bus with no voltage fluctuation. Furthermore, in particular, node floor 10
and node NCLII indicate generators Gl and G2.

Next, the operation will be explained. In Figure 2(b), if the loop between node Nα2 and node Nα3 is broken due to an accident or other reason, the current that was flowing through this transmission line and being supplied to the load before the loop was replaced will be transferred from node No. 8 to No. 7→
In the end, it will go around 6 → floor 5 → Nα4 → Nα3.

Therefore, the total impedance Z of the wrap-around route.

is as follows.

Z, = 0.343 +j 1.553 Also, in the wraparound route, there is a node N [1L11 G
There are two generators, and there are sections at node 5 and node 6 where the current before the loop is in the opposite direction to the wrap-around current, so if we correct each and calculate equation (2, 1), The following is true.

I o =0.314 1,: In formula (2,3), P c-0,356,Qc-□=0.267, V,=
1.0 All 1000MVA Heas p, u, (power factor)
The values and voltages are the rated base p, u, and values, and QGmaK is a value specific to the generator, and a preset input value is used.

Therefore, the formula (2,3) is Ic-(PG/VG)"+(QG, , /VG)2-
PG/VG = 0.089 Zo = 0.343 + j 1.291v complement; From Figure 2 (a), the impedance of the reverse route is 0.1
86+jo, 486, and the reverse current value is shown in Figure 2 (b)
As shown in 0.04, therefore, from formula (2,4), ■Supplementary −0・04X (0・IE16+30・486) X
Substituting 2 or more into equation (2,1), ΔV-(0,314-0,089)X(0,343+j
1.291) 0.04X (0,186+jO,486
) Figure) agrees well.

Next, the control amount is calculated using the formula (2, 2>) as follows. First, the preliminary voltage of the node Nα3 in FIG. 2(b) is rated 1.0 p, u, and the control target voltage is 0. .85p, u
, and substituting it into equation (2,2) yields the following.

IC= l (0,85-1,0+0.259)/(0
,343+j1.291! 0.0815 Regarding the obtained control quantity, FIG. 5 shows the results of a simulation in which approximately 20% of the load on node No. 3 is cut off, similar to the simulation in FIG. 4.

As shown in FIG. 5, it can be seen that the control target voltages o, ssp, and u were accurately controlled. The control conditions at this time are as follows. Loop breakage occurred due to accident-free opening at 0 seconds, and control was implemented after 10.8 seconds had elapsed.

The simulation conditions in Figure 4 are as follows.

Load characteristics: Constant current was 100%, effective component was 4%/Hz, and reactive component was 2%/Hz with respect to the deviation Δf (Hz) from the reference frequency.

Generator model: A model that takes into account the convex polarity of the synchronous machine and the transient phenomenon of the field winding, and adds an isometric damper effect was used.

Generator control system, AVR is a general exciter model, and the governor is a single shaft governor. Calculation conditions: Accident-free opening between node Nl12 and No. 3 at 0 seconds, calculation in 0.01 second increments until 0.3 seconds, and 0.0 seconds thereafter.
Calculated in 0.05 second increments. In the above embodiment, only -. route impedances for loop breakage determined by the system configuration were given; however, according to the method of the present invention, all can be calculated in advance. Alternatively, by simply inputting system configuration information, the impedances of each power transmission line and transformer n set in advance may be combined in series and parallel and automatically calculated.

In addition, formulas (2, 3) used in calculating the generator current increase correction amount assume that the generator was operating at a power factor of 1.0 before the new loop, but this is based on the generator information. As,
If active power P and reactive power output Q can be obtained at the same time, it can be determined with even higher precision using the following equation (2, 5). In any case, the calculation is based on the assumption that the output current increases from the previous output current to the generator output limit, and is based on the same principle as (2, 4) 2.

I c −(Pc/Vc) ”+ (QGIIIIX/
VG) ” (Pc/Vc) ”+ (Qt, /V
c) ”・・・・・・・・・ (2,5) In addition, although the loop breakage between the node Nα2 and the node Nt13 has been explained in the embodiment, the loop breakage is not limited to this.
Needless to say, even if the loop is broken in the loop section, the control amount can be calculated as if the power generation is decreasing using the same principle.

〔Effect of the invention〕

As described above, according to the present invention, the voltage drop due to a loop disconnection in a loop power system is calculated by using the prior current value at the loop disconnection point and the impedance of the route through which the current that has detoured to the remaining route of the loop power transmission system passes. The calculation formula is used to estimate the drop peak, and the target voltage for the voltage drop width is calculated from the voltage drop estimation value using the control amount calculation formula.The calculation formula is simplified, and the microprocessor used in the existing protection relay can be used to calculate the target voltage. This has the effect of easily realizing calculation control. Furthermore, since the voltage during the wrap-around route and the increase in generator current are corrected, it is possible to obtain a voltage stabilizing relay control method using a highly accurate pre-calculated formula.

[Brief explanation of the drawing]

FIG. 1(a) is an explanatory diagram showing the current direction of the system before loop breakage for explaining one embodiment of the present invention, FIG. 1(b) is an explanatory diagram showing the current direction of the loop disconnection, and FIG. Figure (a) is an impedance diagram of a power system to which an embodiment of the present invention is applied, and Figure (b) is a current distribution diagram showing the positive-sequence current distribution, generator output, and load before loop renewal in the same power system. , FIG. 3 is a flowchart for explaining the present invention in detail, and FIG. 4 is a voltage fluctuation waveform of a simulation result from a stability calculation performed to confirm the accuracy of the voltage drop range calculated in the embodiment of the present invention. 5A and 5B are voltage fluctuation waveform diagrams of simulation results obtained by stability calculation for confirming the control effect of the control amount calculated according to the present invention. In the figure, STI is voltage drop escalation estimation calculation, ST2 is control amount calculation, and ST3 is load breaker determination. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Figure 1 (a) (b) (outward) Figure (a) [Φ position = 1000MVA, straight] Figure Figure 1 (b) 0) Direction of the IJ droplet figure

Claims (1)

[Claims] After a loop break occurs in a loop power transmission system that is connected to the upper system and has a load and a generator, the current value that flows around to the remaining route of the loop power transmission system and the voltage drop that occurs in the route, and the line impedance of the roundabout route. The voltage drop width is estimated and determined in advance using the voltage drop width estimation formula, and the target voltage of the voltage drop width is calculated using the control amount calculation formula from the voltage drop width estimated value obtained using the above estimation calculation formula. A control method for a system voltage stabilization relay that performs load shedding after detecting a loop break to protect the system when the calculation result of the voltage drop exceeds a target voltage setting value of the voltage drop width.