JPH0757069B2 - System voltage stabilization relay - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a grid voltage stabilizing relay for monitoring voltage instability of a power system and stabilizing the system in advance.

(Prior Art) Recently, in the electric power system, there is a tendency for long-distance, large-capacity transmission to proceed as the electric power demand increases, and careful evaluation is performed during the system equipment planning and operation planning in order to maintain the voltage stability of the system. , Check and prepare for actual operation.

However, in actual operation, for example, large demand fluctuations, various accidents,
There is a possibility of all kinds of situations such as equipment malfunctions, and it is virtually impossible to check all these cases in advance.

Therefore, it is conceivable that the operating conditions may become unpredictable at the preliminary evaluation and check stages, and a voltage instability phenomenon may occur in some cases.

(Problems to be solved by the invention) By the way, the conventional voltage instability phenomenon is only evaluated and checked at the time of system equipment planning and operation planning. And the load current increases at the same time, causing the operation of the undervoltage relay, the distance relay, and the like. In this case, the distance relay operates by recognizing the situation of the voltage drop and the current increase as a distant short circuit, but this protection operation is not generally appropriate. Moreover, even if the distance relay does not operate, a wide area power failure may occur due to equipment overload or frequency fluctuation when a system instability phenomenon occurs.

An object of the present invention is to provide a system voltage stabilization relay capable of stabilizing the voltage of the system by detecting an unstable phenomenon of the system in real time and performing load control.

(Means for Solving the Problems) In order to achieve the above object, in the system voltage stabilizing relay according to the present invention, an input unit for taking in a bus voltage and a transmission line current at a power receiving end of a transmission system and an input unit for collecting the transmission line current are provided. First computing means for determining active power and reactive power based on the loaded voltage and current information, active power and reactive power determined by the first computing means, and voltage captured by the input means And second constant calculating means for obtaining the operating point from the system constant and equipment constant, stable region setting means for obtaining the voltage stable region of the system based on the voltage static characteristics of the load, and the second calculating means. Judgment means for judging whether the operating point is within the voltage stable area obtained by the stable area setting means or outside the voltage stable area, and this judging means judges that the operating point of the system is outside the voltage stable area. The operating point is And a load control means for limiting the pressure to enter the pressure stable region.

(Operation) In the system voltage stabilization relay having such a configuration, the operating point obtained from the active power, the reactive power and the voltage which changes in real time and the system constant, the equipment constant is the load voltage static characteristic. It is determined whether it is inside or outside the voltage stable region set based on, and if it is determined to be outside the voltage stable region, the load is limited so that the system voltage enters the voltage stable region. There is no inappropriate protection operation due to undervoltage relays, distance relays, etc. as in the past, and wide area power outages due to equipment overload or frequency fluctuation can be prevented.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of the configuration on the power receiving end side of a power system to which the present invention is applied. BG is a bus at the substation side, BL is a bus at the power receiving end, and a long-distance and large capacity between these two bus lines. It is interconnected by power lines. In addition, a plurality of load feeders (not shown) are connected to the bus BL on the power receiving end side so that they can be opened, and a plurality of capacitors C for compensating the reactive power are connected so that they can be opened. A current transformer CT is provided on the power transmission line L on the power receiving end side, and a transformer PT is connected to the busbar BL. A transmission line current I obtained from these current transformer CT and a busbar voltage obtained from the transformer PT. Input V to the system voltage stabilizing relay 1.

As shown in FIG. 2, the system voltage stabilizing relay 1 receives an input conversion unit 2 to which a transmission line current I and a bus voltage V are input, switch information of each load feeder, and switch information of a capacitor. Required for data processing by input converter 3, settling value memory 4, which stores settling value data such as transmission line impedance, capacitor capacity, load characteristic constant, load feeder order, bus voltage target value, and input converters 2 and 3. The current data, the voltage data, and the switch information, which have been converted into various signals, are respectively taken in, and a predetermined calculation, which will be described in detail later, is executed using the settling value information stored in the settling value memory 4. Calculation unit 5 for determining the presence / absence, a signal for amplifying the judgment result signal output from this calculation unit 5, and outputting this as a load cutoff signal or a capacitor cutoff signal In the signals necessary to display the arithmetic processing content and data at the amplification unit 6 and the arithmetic unit 5 and a display control unit 7 to be displayed on the outside of the display 8.

Next, the function of the system voltage stabilizing relay thus configured will be described.

When the current I and the bus voltage V flowing through the power transmission line L are input to the system voltage stabilization relay 1, the input conversion unit 2 converts the current information and the voltage information into signals necessary for processing and adds the signals to the calculation unit 5. . Also, at this time, the switch information of the load feeder and the capacitor C for compensating the reactive power is input to the input conversion unit 3, and the switch information is also converted into a signal necessary for processing and added to the calculation unit 5. ing.

The computing unit 5 first obtains the active power P and reactive power Q at the operating point from the current information and the voltage information based on the following power equation.

P = VIcos ψ ... (1) Q = VIsin ψ ... (2) where V is the bus voltage, I is the transmission line current, and ψ is the phase difference between V and I.

Further, the calculation unit 5 uses the following equations based on the set values of the active power P, the reactive power Q and the bus voltage V obtained by the above equations, and the transmission line impedance and the capacitor capacitance stored in the settling value memory 4. The operating points P _V , Q _V defined by a special coordinate system standardized by

^{_{P V = P / (hV 2}} ) ... (3) Q V = Q / (hV 2) ... (4) Here, in h = 1 / X-C, X is the line reactance, CC capacitor in turned a total Indicates capacity.

Here, the conditions for stabilizing the voltage at the receiving end bus are derived as follows.

Now, a third view of the model system diagram in V voltage of the upper substation as shown _S, the transmission line reactance X, the capacitor of the power receiving end C, and bus voltage of the power receiving end V, the generatrix of the receiving end side Assuming that the phase angle of the voltage with respect to the voltage of the upper substation is given as Θ, P = V _S V / Xsin Θ (5) Q = (V _S Vcos Θ−V ² ) / X + CV ² as a power equation. (6) is established.

Furthermore, power _{P L} which flows to the load, when _{Q L,} are represented by ^{_{P L = P LC V kP ...}} (7) Q L = Q LC V kQ ... (8).

Therefore, if the above equations (5), (6), (7), and (8) are linearized around the operating point, ΔP = − (Q + hV ² ) · ΔΘ + (P / V) · ΔV (9) ΔQ = P ・ ΔΘ + (Q-hV ² ) / V ・ ΔV (10) ΔP _L = (Pk _P / V) ・ ΔV (11) ΔQ _L = (Qk _Q / V) ・ ΔV (12) Become.

Here, considering a small amount of balance on the bus bar on the receiving end side,
When ΔPd and ΔQd are defined as disturbances, they can be expressed as ΔP = ΔP _L + ΔPd (13) ΔQ = ΔQ _L + ΔQd (14) Therefore, substituting Eqs. (9) to (12) into Eqs. (13) and (14) and expressing in matrix form, Is obtained. In order to be stable against disturbance, it is sufficient if the value of the determinant of the coefficient matrix of [ΔΘ, ΔV] _{T on} the right-hand side of equation (15) is non-negative from various documents. Therefore, When the voltage stable region of the elliptic characteristic is obtained in this way, the operating point [P] obtained by the above equations (3) and (4) is obtained.
_V, or Q _V] is a voltage stable region, voltage stabilization area or outside of it is determined based on Equation (16), the determination result is outside of the display 8 through the display control unit 7 from the operation unit 5 Is output as display data, and the display 8 displays, for example, elliptic characteristics and operating points as shown in FIG.

If it is determined that the operating point is at the point B, which gradually moves from the point A in the voltage stable region shown as an elliptic characteristic in FIG. 4, the operation unit 5 should be disconnected to the load. A cutoff command is output. In this case, when the load is to be cut off, the calculation unit 5 determines the load to be cut off by the following judgment and calculation. That is, the load to be cut off is performed by selecting a feeder to be cut off based on the load cutoff order stored in the set value memory 4 and outputting a cutoff command to the feeder of the corresponding load, and at the same time, the load remaining after the cutoff. the amount _{P R,} determine the _{Q R.}

Further, in order to keep the residual load after cutoff (P _R, Q _R) of the bus voltage to the proper value, the capacitor must also be cut off at the same time as the load cutoff. Therefore, when the capacitor is cut off, the calculation unit 5 determines the capacitor to be cut off by obtaining the capacitor capacity for making the voltage corresponding to P _R , Q _R by the capacitor capacity calculation formula described below. That is, the capacitor capacity to cut off is
This is the difference between the current value and the appropriate value after interruption, and since the actual capacitor capacity cannot take a continuous amount, the one closest to the calculated value will be interrupted.

Now, if the bus voltage at the power transmission end (upper substation) is V _S , the power transmission characteristic of the system is expressed as P ² + (Q + hV ² ) ² = V ² V _S ² / X ² , so this P, Q, V to P _R, Q _R, is solved for h by substituting V _{R (bus} voltage target value), Therefore, as the proper value C _R of the capacitor after the cutoff, To get

In this way, when the load and the capacitor determined by the judgment and the calculation are disconnected in the arithmetic unit 5, the operating point moves from the point B to the point C in FIG. 4 and enters the voltage stable region.

Here, the basic operation of the arithmetic unit 5 described above is shown in a flowchart of FIG.

As described above, in the present embodiment, the active power is calculated by the calculation unit 5,
The operating point is calculated from the reactive power and voltage and the system constants and equipment constants stored in the settling value memory 4, and the voltage stability region is set as an elliptic characteristic based on the voltage static characteristic of the load stored in the setting value memory 4. If it is determined that the operating point is outside the voltage stable region, the load and reactive power compensation capacitors are set so that the system voltage falls within the voltage stable region and corresponding to the target voltage value of the system at that time. Even if an unstable phenomenon occurs in the system voltage, it is possible to stabilize the system voltage before the distance relays etc. operate, and wide area blackouts due to equipment overload and frequency fluctuations. It will never happen.

In addition, in this embodiment, the voltage stable region is displayed as an elliptic characteristic together with the current system operating point on the display 8. Therefore, the system voltage that changes in real time with respect to the voltage stable region can be operated at any point. It is possible to visually grasp whether or not there is any, and it is possible to know in advance the trends in the operation of the power system.

In addition, in the above-mentioned embodiment, in addition to displaying the voltage stable region and the operating point of the system on the display 8, it is provided with a printout function of various data at the time of relay operation such as judgment data in the calculation unit 5 and calculation data. Good.

[Effects of the Invention] As described above, according to the present invention, since the voltage instability phenomenon of the system in real time is detected and the load control is performed in correspondence with the target value of the system voltage, another protection is provided. It is possible to stabilize the voltage of the system before the relay operates, and thus it is possible to provide a system voltage stabilizing relay that enables highly reliable system operation.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a power system to which the present invention is applied, FIG. 2 is a block diagram showing an example of a system voltage stabilizing relay according to the present invention, and FIG. 3 is an explanation of the operation of the same example. FIG. 4 is a system model diagram necessary for the above, FIG. 4 is an explanatory diagram of the relationship between the voltage stable region displayed on the display and the operating point in the embodiment, and FIG. 2,3 ... Input converter, 4 ... Set value memory, 5 ... Calculator, 6 ... Signal amplifier, 7 ... Display controller, 8 ... Display.

Claims (1)

[Claims] 1. An input means for taking in a bus voltage and a transmission line current at a power receiving end of a power transmission system, and a first power for obtaining active power and reactive power based on voltage and current information fetched by this input means. The voltage of the load, the calculation means, the second calculation means for obtaining the operating point from the active power, the reactive power obtained by the first calculation means, the voltage and the system constant and the equipment constant taken in by the input means. Stable region setting means for obtaining the voltage stable region of the system from the static characteristics, and whether the operating point obtained by the second computing means is within the voltage stable region obtained by the stable region setting means or outside the voltage stable region. And a load control means for restricting the load so that the operating point falls within the voltage stable region when the operating point of the system is outside the voltage stable region. System voltage stabilization featuring Leh.