JP2504405B2 - Power system stabilization method - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a power system stabilization method, and in particular, a heavy overload system receiving a large amount of power from another system is considered to be a single system due to a transmission line failure or the like. In this case, the present invention relates to a power system stabilization method capable of preventing a frequency drop in the power system by cutting off part of the load to balance the supply and demand of the single power system.

[Technical background of the invention and its problems] Generally, when a heavy overload system receiving a large amount of electric power from another system is disconnected from the other system due to a transmission line failure or the like and becomes a single system, it is greatly affected. Overload condition and system voltage
The frequency drops sharply. If this frequency is drastically reduced, the generator in its own system will be disconnected by the protection relay, making stable operation of the independent system impossible. Therefore, conventionally, as a stabilization method at the time of such a system failure, the frequency of the bus voltage or the frequency change rate is detected, and a part of the load is cut off according to a preset value to maintain the supply-demand balance of the single system. There is a load cutoff method that prevents the system frequency from decreasing.

FIGS. 1 (a) and 1 (b) show that when a general heavy overload system becomes a single system, a load blocking system cuts off a part of the load to stabilize the voltage and frequency of the system, respectively. FIG. On the other hand, a cable system in which most of the power transmission lines are underground cable lines,
The system has an excessive capacitance to ground, and Fig. 2 shows an example of this cable system heavy overload system. As shown in Fig. 2, the cable system heavy overload system is composed of a cable system 10, a generator 11 in its own system, a step-up transformer 12, cable lines 13a to 13d, an interconnection line 14, a load 15, and a phase adjusting facility 16. It is configured.

Therefore, when such a cable system heavy overload system becomes isolated system (t ₁ point), to cut off some of the load in order to maintain the supply-demand balance by conventional load cutoff manner as (t ₂ time), Due to the excessive ground capacitance of the system, the voltage sharply rises as shown in FIGS. 3 (a) and 3 (b). If this voltage rises sharply, the power consumption of the remaining load sharply increases due to the voltage characteristics of the load, and it is not possible to maintain a balance between supply and demand. Therefore, the frequency of the system decreases more and more, and stable operation of the independent system becomes impossible.

The problem described above is because the system has an excessive phase-advancing reactive power load, which is the electrostatic capacitance to the ground of the cable line, and it is not sufficient to simply balance the supply and demand of active power as a frequency drop prevention measure. It is necessary to try to balance some reactive power at the same time.

[Object of the Invention] The present invention has been made to solve the above problems, and its object is to reduce the voltage and frequency of a heavy overload system when it becomes an independent system due to a failure of a transmission line or the like. The purpose of the present invention is to provide a power system stabilization method capable of stabilizing the system by preventing a decrease in power consumption.

[Summary of the Invention] In order to achieve the above object, according to the present invention, a heavy overload system which has an excessively large electrostatic capacitance to the ground and receives electric power from another system is isolated by a system failure due to a transmission line failure or the like. In the power system stabilization method that cuts off part of the load to stabilize the system frequency when it becomes a system, select the load corresponding to the active power of the received power based on the received power before the failure. In addition, the reactive power component of the selected load is calculated, and the active power component and the reactive power component are combined to determine the load blocking amount, while the remaining active / reactive power after the load blocking,
Calculate the amount of phase-modulating equipment input to control the load terminal voltage to a preset target value from a predetermined calculation formula that includes the terminal voltage value before the grid separation of the generator in the grid and the reactance value of the step-up transformer. It is characterized in that the load is selectively cut off and the phase-modulating equipment is selectively inserted so that the load and the phase-modulating equipment input amount match when the system is formed.

[Embodiment of the Invention] First, a basic idea of the present invention, that is, a method of calculating a load cutoff amount and a phase adjusting equipment input amount will be described.

As described above, the cable system heavy overload system is almost entirely composed of cable lines with a small line impedance, and the system itself is local, so the line impedance in the system can be almost ignored. Therefore, load the same system with the output on the high voltage side of the boost transformer of the generator in the system.
Using P _G + jQ _G , the received power P _T + jQ _T from another system, and the system voltage V _LO in the steady state, the admittance of the load can be expressed by equations (1) and (2). The system can be reduced to the system shown in FIG.

G _L ≈ (P _G + P _T ) / V _LO ² …… (1) B _L ≈− (Q _G + Q _T ) / V _LO ² …… (2) That is, the system shown in FIG. Generator 11, step-up transformer 12 of generator in the system and load admittance (G _L + j
B _L ).

Next, a method of calculating the load cutoff amount and the phase-adjustment equipment input amount will be described with reference to FIG.

Now, if the cable system heavy overload system is separated into a single system due to a transmission line failure, etc., the unbalanced amount of active power supply and demand becomes the active power P _T that was flowing to the interconnection line before the system separation. . Therefore, the load corresponding to this active power P _T is selected and cut off to balance the supply and demand of active power. In addition,
When the load for the active power P _T is cut off, not only the active power but also the reactive power of the load is cut off. Therefore, the actual load cutoff amount is as shown in equation (3).

Load cutoff amount = _PT + _{j [} Sigma] _q (3) Here, [Sigma] _q is the reactive power of the loads to be cut off at the same time.

Next, a method of calculating the input amount of the phase adjusting equipment will be described. Now, in the reduced system of Fig. 4, after the system becomes an independent system due to a transmission line failure, etc., the load cutoff calculated by equation (3) is executed, and further the phase-adjustment equipment is installed to suppress the overvoltage after the load cutoff. The equivalent circuit after turning on is as shown in FIG. In the figure, G _L ^* and B _L ^* are the conductance component and the susceptance component, respectively, of the residual load after the load is cut off, and are represented by the equations (4) and (5), respectively.

G _L ^* = P _G / V _LO ² (4) B _L ^* =-(Q _G + Q _T -Σ _q ) / V _LO ² (5) On the other hand, the generator terminal voltage V _t is After that, in the steady state, the value before the grid separation is restored by the operation of the automatic voltage regulator (AVR), so that V _t = V _to can be set. Therefore, the steady-state value _VL of the load terminal voltage of the load after becoming the independent system is Becomes On the contrary, if the target value _L of the load terminal voltage is settled, the optimum input capacity B _R of the phase adjusting equipment can be obtained by the following equation.

According to the present invention, the load cutoff amount is determined by the above-mentioned method, and the input amount of the phase-modulating equipment is calculated from the received power before the failure so that the system voltage becomes the steady state value before the system separation. After (t ₁ time), the load and the phase-modulating equipment are selectively cut off so as to coincide with this calculation result (at t ₂ time), thereby stabilizing the voltage and frequency of the independent system. An example is shown in FIGS. 6 (a) and 6 (b).

An embodiment of the present invention based on the above concept will be described below with reference to FIG. FIG. 7 shows a system configuration example of the power system stabilizing method according to the present invention. As shown in the figure, the central processing unit 1, the generator terminal unit 2, the load terminal unit.
It is composed of 3, phase adjusting equipment terminal 4, and interconnection line terminal 5.
In the present embodiment, for simplification of description, the load and the phase adjusting equipment are provided in one place.

In FIG. 8, first, before the system separation, the generator terminal unit 2 outputs the high-voltage side output P _G + jQ _G of the step-up transformer 12 of the internal generator 11 and the terminal voltage V _to The load terminal unit 3 supplies the power P _Li + jQ _Li (i
= 1, n) and the terminal voltage V _LO of the load 15, and the phase-modulating equipment terminal unit 4 uses each phase-modifying device (static capacitor, static capacitor,
Shunt reactor) parallel connection, the interconnection line terminal unit 5 measures the tidal current of the interconnection line 14, that is, the received power P _T + jQ _T ,
It is transmitted to the central processing unit 1 via a transmission system (not shown). The central processing unit 1, as shown the input _{V LO, P G + jQ G} , the power P _Li + jQ _Li of each feeder line of the load 15 with P _T + jQ _T in Table 1, phase modifying equipment 16 The parallel solution sequences of the respective phase adjusting devices are stored respectively as shown in [Table 2]. [Table 2] also shows the pre-stored capacities in addition to the parallel solution sequence of each phase adjusting device.

The central processing unit 1 selects the feeder line of the load 15 to be cut off after the system separation and the phase-adjusting device of the phase-adjusting equipment 16 to be parallelized according to the flow chart shown in FIG. To do.

That is, the central processing unit 1 first, in step S1,
The feeder line of the load 15 to be cut off is selected so as to be commensurate with the received active power P _T , and the reactive power component Σ _q to be cut off at the same time is calculated as shown in equation (3). For example, if it is decided to cut off the feeder lines 1, 2, and 3 shown in [Table 1] after grid separation, the reactive power component Σ _q is as in the following equation.

Σ _q = Q _L1 + Q _L2 + Q _L3 (MVar) (8) Next, in step S2, the high-voltage side output P _G + jQ _G of the step-up transformer 12 of the internal generator 11 and the load 15 Terminal voltage
From V _LO , received reactive power Q _T , and Σ _q (4), (5)
The conductance component G _L ^* and susceptance component B _L ^* of the residual load are calculated from the equations.

Next, in step S3, the reactance value X _t of the step-up transformer 12 of the internal generator 11 and the voltage V on the low voltage side
_{From to} , G _L ^* , B _L ^* , and the preset target value _L of the load terminal voltage, the optimum injection amount B _R of the phase adjusting equipment is calculated.

Further, in Sutetappu S4, as appropriate to the optimum dosages B _R of the phase modifying equipment, to select the compensator device parallel disconnection to phase modifying equipment 16. For example, the phase adjusting device shown in [Table 2] The sum of the capacities of R ₁ + R ₂ + R ₃ is approximately equal to the optimum input capacity B _R Decide to input.

From this state, the interconnection line is now
When 14 is cut off and system separation occurs (at time t ₁ ), the central processing unit 1 causes the load terminal unit 3 to select the load selected above.
Cut off the 15 feeder lines, and the phase adjustment equipment terminal 4
Similarly, the parallel parallel command of the phase-adjusting device of the phase-adjusting equipment 16 selected above is sent out via a transmission system (not shown). As a result, the load terminal unit 3 and the phase adjusting equipment terminal unit 4
In, performing selective introduction of feeder lines of cut-off and phase modifying equipment 16 compensator device of the load 15 in accordance with the command (t ₂ time)
Then, the voltage and frequency of the independent system are stabilized.

In the above embodiment, the input capacity B _R of the phase-modulating equipment is calculated from the equivalent circuit of the contracted system shown in FIG. 5, but it can also be calculated by performing the power flow calculation in the non-contracted system.
Here, the power flow calculation has two specified values of the magnitude V of the voltage of each bus, the phase angle θ, the active power P, and the reactive power Q,
This is a calculation method for obtaining the other two quantities. Therefore, assume the system state after load cutoff before system isolation and after connecting the busbar to which the phase-adjustment equipment is connected to P,
By performing the power flow calculation as V specified bus, phase modifiers bus of voltage connected equipment can be obtained reactive energy for maintaining the target value, phase modifying equipment dosages B _R easy by the following formula Required to.

B _R = − / ² (9) [Advantages of the Invention] As described above, according to the present invention, the load cutoff amount as the frequency countermeasure is determined based on the supply and demand state before the failure, and the load cutoff amount after the load cutoff is determined. As a measure to suppress voltage rise, the amount of phase-modulating equipment input is calculated so that the system voltage takes a steady-state value before system separation, and after system separation due to a transmission line failure, etc. Since the phase-in equipment is selectively turned on, when the heavy overload system becomes a single system due to a transmission line failure, etc., the voltage and frequency of the system are prevented from decreasing and the system voltage is separated. A power system stabilization method capable of stabilizing the system by controlling to the previous steady state value can be provided.

[Brief description of drawings]

1 (a) and 1 (b) are diagrams showing an example of the case where a general heavy overload system is a single system and is stabilized by a conventional load cutoff method, and FIG. 2 is a cable system heavy load system. The figure which shows an example of a load system, FIG.3 (a) (b) shows the phenomenon when a part of load is cut off by the conventional load cutoff system, when a cable system heavy overload system becomes an independent system. Fig. 4 is a diagram showing a reduction system of the cable system heavy overload system, Fig. 5 is a diagram showing the equalization circuit of Fig. 4, and Figs. 6 (a) and (b).
FIG. 7 is a diagram showing an example in which the load is cut off and stabilization is performed by inputting phase adjusting equipment when the cable heavy overload system becomes a single system, and FIG. 7 is a configuration diagram showing an embodiment of the present invention, FIG. The figure is a flow chart for explaining the operation in FIG. 1 ... Central processing unit, 2 ... Generator terminal unit, 3 ... Load terminal unit, 4 ... Phase adjusting terminal device, 5 ... Collective line terminal unit, 10
...... Cable system, 11 …… Internal power generator, 12 …… Step-up transformer, 13a to 13d… Cable line, 14 …… Linking line, 15 ……
Load, 16 ... Phase adjusting equipment.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hitoshi Otsuka 1-3-3 Uchisaiwaicho, Chiyoda-ku, Tokyo TEPCO (72) Inventor Kazuya Omata 1 Toshiba-cho, Fuchu-shi, Tokyo TOSHIBA CORPORATION Fuchu Factory (72) Inventor Masahiro Sato 1 Toshiba Town, Fuchu City, Tokyo TOSHIBA Corporation Fuchu Factory

Claims (1)

(57) [Claims] 1. A part of a load when a heavy overload system having an excessive capacitance to ground and receiving electric power from another system is separated into a single system due to a transmission line failure or the like. In the power system stabilization method that shuts off the power to stabilize the system frequency, selects the load corresponding to the active power of the received power based on the received power before the failure and determines the reactive power of the selected load. While calculating the active power component and the reactive power component to determine the load cutoff amount, the remaining active / reactive power after the load cutoff, the terminal voltage value before the grid separation of the generator in the single grid and the step-up transformer Calculate the amount of phase-modulating equipment input to control the load terminal voltage to a preset target value from the predetermined calculation formula that includes the reactance value. Negative to match A power system stabilization method characterized in that the load is selectively cut off and the phase-modulating equipment is selectively input.