CN110601176A - Method and system for improving static stability limit of power grid tie line and early warning - Google Patents

Abstract

The invention provides a method and a system for improving and early warning the static stability limit of a power grid tie line. According to the method and the system, a calculation formula of equivalent reactance of a tie line and equivalent impedance of three coils of transformers on two sides of the tie line is determined through equivalent circuit models of the three coils of transformers on two sides of the tie line and the power grid, and then a large amount of real-time electric quantity of the power grid measured by a WAMS system is taken into the calculation formula to calculate and determine the value of the real-time electric quantity, so that the accuracy of determining the equivalent reactance of the tie line and the equivalent impedance of the three coils of transformers on two sides of the tie line is improved.

Description

Method and system for improving static stability limit of power grid tie line and early warning

Technical Field

The invention relates to the field of power simulation, in particular to a method and a system for improving and early warning a static stability limit of a power grid tie line.

Background

In the prior art, the development of extra-high voltage alternating current and direct current is greatly promoted, large-scale and large-scale resource optimization configuration is realized, and the advantages of extra-high voltage alternating current and direct current large-capacity and long-distance power transmission are exerted. For a large power supply outgoing line, a cross-line between large-area power grids, weak sections in a network and the like need to be subjected to static stability analysis. The transmission section static stability limit plays an important role in the operation personnel of the power system to master the transmission capacity of the transmission section.

With the rapid development of electric power systems, the power of the transmission section of the existing power grid line channel is higher and higher, and is closer to the thermal stability limit, so that the safety of energy transmission is seriously influenced. The complex power system of large-area networking has too many influence factors, thousands, to the static stability limit of single contact channel, and the change rule of the static stability limit of contact channel has been difficult to explain to traditional power system classical formula. The increase of the quiescent power limit of the communication channel falls into a bottleneck.

Disclosure of Invention

In order to solve the technical problems that the law of static stability limit change of a power grid tie line is difficult to explain by a traditional power system classical formula and the limit of static stability limit power of the tie line is difficult to promote and early warn, the invention provides a method for promoting and early warning the static stability limit of the power grid tie line, which comprises the following steps:

step 1, determining equivalent reactance of a power grid tie line and equivalent impedance from a high-voltage side and a medium-voltage side to a central point in equivalent circuit models of three-coil transformers on two sides of the tie line according to electric quantity measured by a power grid wide area measurement system WAMS, wherein the power grid tie line refers to a tie line higher than the voltage levels of power grids on two sides, the high-voltage sides of the three-coil transformers on two sides of the tie line are connected to the tie line, the medium-voltage sides of the three-coil transformers are connected to a power grid of the tie line, the low-voltage sides of the three-coil transformers are in-situ installation positions of a reactive compensation device, the equivalent circuit models of the three-coil transformers on two sides of the tie line are classic three-coil three-side gamma-shaped equivalent circuit models, and the central point is a virtual central node of the equivalent impedance of the high-voltage side;

step 2, according to the determined equivalent reactance of the tie line and the equivalent impedance of the three coils of transformers on the two sides of the tie line, determining the configuration number and the capacity of the medium-voltage side dynamic reactive power sources of the three coils of transformers on the two sides of the tie line by adopting a power system simulation calculation program under the preset operation mode and constraint conditions, wherein the constraint conditions comprise the upper limit value and the lower limit value of the medium-voltage side capacity of the three coils of transformers on the two sides of the tie line;

step 3, determining the static stability limit of the tie line according to the configuration and the preset operation mode of the medium-voltage side dynamic reactive power sources of the three coils of transformers on two sides of the tie line and the historical electric quantity measured by the WAMS;

and 4, determining the static stability margin of the tie line and carrying out early warning according to the calculation result of the static stability limit of the tie line and the control limit of the tie line in a preset operation mode.

Further, the determining the equivalent reactance of the grid tie line according to the electrical quantity measured by the power grid wide area measurement system WAMS and the equivalent impedances from the high-voltage side and the medium-voltage side to the central point in the equivalent circuit model of the three-coil transformer on the two sides of the tie line include:

the WAMS measures the electric quantity for N times in one day;

according to the ith measured electrical quantity, calculating the equivalent reactance of the power grid tie line and the equivalent impedance from the high-voltage side and the medium-voltage side to the central point in the equivalent circuit model of the three-coil transformer on the two sides of the tie line, wherein the calculation formula is as follows:

in the formula, the side a is a connecting line power transmitting end, the side b is a connecting line power receiving end, in the electrical quantity measured by the WAMS system at the ith time,the port node voltages of the high-voltage side of the three-coil transformer on the side a and the side b are respectively,the voltage of the port node at the middle voltage side of the three-coil transformer at the side a and the side b respectively,the voltages of the port nodes at the low-voltage side of the three-coil transformer at the side a and the side b are respectively;respectively the currents from the virtual center node of the equivalent circuit model of the three-coil transformer at the side a and the side b to the voltage node of the high-voltage side port,the positive direction is defined as the virtual center node of the three-coil transformer at the a side to the voltage node of the high-voltage side port,the positive direction is defined as the voltage node from the high-voltage side port of the three-coil transformer on the b side to the virtual center node,is the input current of the voltage node of the voltage side port in the a-side three-coil transformer,the positive direction is defined as the voltage node of the medium-voltage side port of the a-side three-coil transformer to the virtual center node,is the input current of the voltage node of the voltage side port in the b-side three-coil transformer,the positive direction is defined as the virtual center node of the three-volume transformer on the b side to the voltage node of the medium-voltage side port,currents from a virtual center node of the three-coil transformer on the side a and the side b to a voltage node of a low-voltage side port are respectively defined as the current from the voltage node of the low-voltage side port to the virtual center node in the positive direction; x_L(i) For the network to communicate equivalent impedance, delta_a(i)、δ_b(i) Three-coil transformer high-voltage side port voltage on the side a and the side b of the connecting line respectivelyAngle of (d), angle difference delta between both sides of the tie line_a,b(i)＝δ_a(i)-δ_b(i)，P_L(i) Active power for a power grid tie line; z_Ta,2、Z_Tb,2The impedance from the virtual center node of the equivalent circuit model of the three-coil transformer on the a side and the b side to the voltage node of the high-voltage side port, Z_Ta,1、Z_Tb,1The impedance of the virtual center node on the a side and the b side to the voltage node of the medium-voltage side port, Z_Ta,3、Z_Tb,3The impedance of the virtual center node to the low-voltage side port voltage node, Z, of side a and side b, respectively_Ta、Z_TbGround impedance transformed to the medium voltage side for side a and side b, respectively; z_Ta、Z_Tb、Z_Ta,3、Z_Tb,3Is a known quantity obtained by a short circuit test;

according to the determined equivalent reactance X of the power grid tie line_L(i) Z of equivalent impedance from high-voltage side and medium-voltage side to central point in equivalent circuit model of three-coil transformer on two sides of connecting line_Ta,1(i)、Z_Ta,2(i)Z_Ta,2(i)、Z_Tb,1(i)、Z_Tb,2(i) Counting the N X_L(i)、Z_Ta,1(i)、Z_Ta,2(i)、Z_Tb,1(i)、Z_Tb,2(i) The calculation results with the largest occurrence number in the values of (A) are respectively used as the equivalent reactance X of the power grid tie line_LEquivalent impedance Z from high-voltage side and medium-voltage side to central point in equivalent circuit model of three-coil transformer on two sides of connecting line_Ta,1、Z_Ta,2、Z_Tb,1、Z_Tb,2。

Further, the determining, according to the determined equivalent reactance of the tie line and the equivalent impedance of the three-winding transformer on the two sides of the tie line, the configuration capacity of the dynamic reactive power sources on the two sides of the tie line by using a power system simulation calculation program under a preset operation mode and constraint conditions includes:

step 1, implanting the determined equivalent reactance of the tie line and the equivalent impedance of three coils of transformers at two sides of the tie line into a power system simulation calculation program;

step 2, calculating the first power of the tie line when the high power of the power grid system is in a fault state under the preset operation mode and constraint conditions, and when the system generates tie line asynchronous oscillation or the system does not generate tie line asynchronous oscillation and the active power of the tie line does not reach the required transmission value according to the first power calculation result of the tie line, turning to step 3, wherein the calculation formula for calculating the first power of the tie line is as follows:

in the formula, P_LThe power of the power grid tie line in the set operation mode; x_LFor a determined equivalent impedance of the grid connection, Z_Ta,2、Z_Tb,2Respectively calculating and determining the impedance from a virtual center node of the equivalent circuit model of the a-side and b-side three-coil transformer to a voltage node of a high-voltage side port, Z_Ta,3、Z_Tb,3For a known quantity obtained by a short circuit test,an electrical quantity measured for a set mode of operation;

step 3, determining three coils of transformer medium-voltage sides needing to be additionally provided with the dynamic reactive power sources in two sides of the tie line according to a criterion of additionally arranging the priority side of the dynamic reactive power sources, additionally arranging a dynamic reactive power source with a fixed capacity value, and calculating the second power of the tie line after the dynamic reactive power sources are additionally arranged on the medium-voltage side when the capacity value of the additionally arranged dynamic reactive power source does not reach the upper limit value of the capacity of the medium-voltage side, wherein a calculation formula of the criterion of additionally arranging the priority side of the dynamic reactive power source is as follows:

when H is larger than or equal to 0, a dynamic reactive power source is additionally arranged on the medium-voltage side of the three-coil transformer on the side a of the connecting line; when H is present<When 0, a dynamic reactive power source is additionally arranged on the medium-voltage side of the three-winding transformer on the side of the connecting line b, and the t is P_LmaxThe method for calculating the second power of the tie line is the same as the method for calculating the first power of the tie line when the first power of the tie line of the power grid reaches the maximum value;

step 4, returning to the step 3 when the asynchronous oscillation of the tie line occurs in the system according to the second power calculation result of the tie line; when the asynchronous oscillation of the tie line does not occur in the system and the calculation result meets the conveying requirement of the tie line, the configuration of the dynamic reactive power sources at the two sides of the tie line is finished; when the system does not generate the asynchronous oscillation of the tie line and the calculation result does not reach the transmission requirement of the tie line, the third power of the tie line is calculated after the transmission power of the tie line is increased to the transmission requirement value, wherein the formula for calculating the third power of the tie line is the same as the method for calculating the power of the first tie line;

step 5, when the asynchronous oscillation of the tie line does not occur and the tie line is stable in the power grid system according to the calculation result of the third power of the tie line, the configuration of the dynamic reactive power sources on the two sides of the tie line is finished; and (3) returning to the step 3 when the asynchronous oscillation of the tie line occurs in the power grid system.

Further, the determining the static stability limit of the tie line according to the configuration and the preset operation mode of the voltage-side dynamic reactive power sources in the three-winding transformers on two sides of the tie line and the historical electrical quantity measured by the WAMS includes:

according to the configuration and the preset operation mode of the voltage side dynamic reactive power sources in the three coils of transformers on two sides of the connecting line, in a quasi-real-time early warning environment, a first curve of the static stability limit of the active power of the connecting line after a given high-power locking fault changes along with time is determined, and the expression is as follows:

in the formula, Pmax _ pre (t)₁) A first curve of active power of the tie line over time after a given high power blocking fault;

where Pmax _ pre _ vertex is a first curve Pmax _ pre (t)₁) A peak value of (1);

according to the historical electrical quantity measured by the WAMS, determining a second curve of the change of the static stability limit of the active power of the tie line after the given high-power locking fault along with the time on the same historical day, wherein the expression is as follows:

in the formula, Pmax _ sm (t)₂) For the active power of the tie-line over time t after a given high-power blocking fault₂A second curve of variation, wherein t₂Is t of the same day in history₁Time of day;

where Pmax _ sm _ vertex is a second curve Pmax _ sm (t)₂) A peak value of (1);

determining a static stability limit of the connecting line according to the peak values of the first curve and the second curve, wherein the calculation formula is as follows:

Pmax_pre＝Min(Pmax_pre_vertex,Pmax_sm_vertex)。

further, determining a static stability margin of the tie line and performing early warning according to a calculation result of the static stability limit of the tie line and a control limit of the tie line in a preset operation mode comprises:

according to the calculation result of the static stability limit of the tie line and the control limit of the tie line in a preset operation mode, a calculation formula for determining the static stability margin of the tie line is as follows:

Mg＝((Pmax_pre-Pcontrol)/Pmax)*100％

in the formula, Mg is the static stability margin of the tie line, Pcontrol is the control limit of the tie line in a preset operation mode, and Pmax _ pre is the determined static stability limit of the tie line;

and when the calculation result of the static stability margin of the connecting line is smaller than a preset safety threshold value, carrying out safe operation alarm of the power grid.

According to another aspect of the present invention, the present invention provides a system for improving and early warning the static stability limit of a tie line, which comprises:

the impedance calculation unit is used for determining the equivalent reactance of a grid tie line and the equivalent impedance from a high-voltage side and a medium-voltage side to a central point in an equivalent circuit model of three-coil transformers on two sides of the tie line according to the electrical quantity measured by a wide area measurement system WAMS (wide area measurement system), wherein the grid tie line refers to a connecting line with a voltage level higher than that of the grids on two sides, the high-voltage sides of the three-coil transformers on two sides of the tie line are both connected to the tie line, the medium-voltage sides are both connected to the grid, the low-voltage sides are the local installation positions of a reactive compensation device, the equivalent circuit model of the three-coil transformers on two sides of the tie line is a three-coil classic inverted-L-shaped equivalent circuit model, and the central point is a virtual central node of the equivalent impedance on the high-voltage side, the medium-voltage side and the low;

the first simulation unit is used for determining the configuration quantity and capacity of the medium-voltage side dynamic reactive power sources of the three coils of transformers on two sides of the tie line by adopting a power system simulation calculation program under the preset operation mode and constraint conditions according to the determined equivalent reactance of the tie line and the equivalent impedance of the three coils of transformers on two sides of the tie line, wherein the constraint conditions comprise the upper limit value and the lower limit value of the medium-voltage side capacity of the three coils of transformers on two sides of the tie line;

the second simulation unit is used for determining the static stability limit of the tie line according to the configuration and the preset running mode of the medium-voltage side dynamic reactive power sources of the three coils of transformers on two sides of the tie line and the historical electric quantity measured by the WAMS;

and the alarm unit is used for determining the static stability margin of the tie line and carrying out early warning according to the calculation result of the static stability limit of the tie line and the control limit of the tie line in a preset operation mode.

Further, the impedance calculation unit determines the equivalent reactance of the grid tie line according to the electrical quantity measured by the grid wide area measurement system WAMS, and the equivalent impedances from the high-voltage side and the medium-voltage side to the central point in the equivalent circuit model of the three-coil transformer on two sides of the tie line include:

the WAMS measures the electric quantity for N times in one day;

according to the ith measured electrical quantity, calculating the equivalent reactance of the power grid tie line and the equivalent impedance from the high-voltage side and the medium-voltage side to the central point in the equivalent circuit model of the three-coil transformer on the two sides of the tie line, wherein the calculation formula is as follows:

in the formula, the side a is a connecting line power transmitting end, the side b is a connecting line power receiving end, in the electrical quantity measured by the WAMS system at the ith time,the port node voltages of the high-voltage side of the three-coil transformer on the side a and the side b are respectively,the voltage of the port node at the middle voltage side of the three-coil transformer at the side a and the side b respectively,the voltages of the port nodes at the low-voltage side of the three-coil transformer at the side a and the side b are respectively;virtual center node of equivalent circuit model of three-coil transformer on side a and side b respectivelyTo the high side port voltage node current,the positive direction is defined as the virtual center node of the three-coil transformer at the a side to the voltage node of the high-voltage side port,the positive direction is defined as the voltage node from the high-voltage side port of the three-coil transformer on the b side to the virtual center node,is the input current of the voltage node of the voltage side port in the a-side three-coil transformer,the positive direction is defined as the voltage node of the medium-voltage side port of the a-side three-coil transformer to the virtual center node,is the input current of the voltage node of the voltage side port in the b-side three-coil transformer,the positive direction is defined as the virtual center node of the three-volume transformer on the b side to the voltage node of the medium-voltage side port,currents from a virtual center node of the three-coil transformer on the side a and the side b to a voltage node of a low-voltage side port are respectively defined as the current from the voltage node of the low-voltage side port to the virtual center node in the positive direction; x_L(i) For the network to communicate equivalent impedance, delta_a(i)、δ_b(i) The phase angles of the voltage of the high-voltage side ports of the three coils of transformers on the a side and the b side of the connecting line respectively, and the angle difference delta between the two sides of the connecting line_a,b(i)＝δ_a(i)-δ_b(i)，P_L(i) Active power for a power grid tie line; z_Ta,2、Z_Tb,2Impedance from virtual center node of equivalent circuit model of a-side and b-side three-coil transformer to voltage node of high-voltage side port，Z_Ta,1、Z_Tb,1The impedance of the virtual center node on the a side and the b side to the voltage node of the medium-voltage side port, Z_Ta,3、Z_Tb,3The impedance of the virtual center node to the low-voltage side port voltage node, Z, of side a and side b, respectively_Ta、Z_TbGround impedance transformed to the medium voltage side for side a and side b, respectively; z_Ta、Z_Tb、Z_Ta,3、Z_Tb,3Is a known quantity obtained by a short circuit test;

according to the determined equivalent reactance X of the power grid tie line_L(i) Z of equivalent impedance from high-voltage side and medium-voltage side to central point in equivalent circuit model of three-coil transformer on two sides of connecting line_Ta,1(i)、Z_Ta,2(i)

Z_Ta,2(i)、Z_Tb,1(i)、Z_Tb,2(i) Counting the N X_L(i)、Z_Ta,1(i)、Z_Ta,2(i)、Z_Tb,1(i)、Z_Tb,2(i) The calculation results with the largest occurrence number in the values of (A) are respectively used as the equivalent reactance X of the power grid tie line_LEquivalent impedance Z from high-voltage side and medium-voltage side to central point in equivalent circuit model of three-coil transformer on two sides of connecting line_Ta,1、Z_Ta,2、Z_Tb,1、Z_Tb,2。

Further, the first simulation unit determines the configuration capacity of the dynamic reactive power sources on the two sides of the tie line according to the determined equivalent reactance of the tie line and the equivalent impedance of the three-coil transformer on the two sides of the tie line by adopting a power system simulation calculation program under a preset operation mode and constraint conditions, and the configuration capacity includes:

step 1, implanting the determined equivalent reactance of the tie line and the equivalent impedance of three coils of transformers at two sides of the tie line into a power system simulation calculation program;

step 2, calculating the first power of the tie line when the high power of the power grid system is in a fault state under the preset operation mode and constraint conditions, and when the system generates tie line asynchronous oscillation or the system does not generate tie line asynchronous oscillation and the active power of the tie line does not reach the required transmission value according to the first power calculation result of the tie line, turning to step 3, wherein the calculation formula for calculating the first power of the tie line is as follows:

in the formula, P_LThe power of the power grid tie line in the set operation mode; x_LFor a determined equivalent impedance of the grid connection, Z_Ta,2、Z_Tb,2Respectively calculating and determining the impedance from a virtual center node of the equivalent circuit model of the a-side and b-side three-coil transformer to a voltage node of a high-voltage side port, Z_Ta,3、Z_Tb,3For a known quantity obtained by a short circuit test,an electrical quantity measured for a set mode of operation;

step 3, determining three coils of transformer medium-voltage sides needing to be additionally provided with the dynamic reactive power sources in two sides of the tie line according to a criterion of additionally arranging the priority side of the dynamic reactive power sources, additionally arranging a dynamic reactive power source with a fixed capacity value, and calculating the second power of the tie line after the dynamic reactive power sources are additionally arranged on the medium-voltage side when the capacity value of the additionally arranged dynamic reactive power source does not reach the upper limit value of the capacity of the medium-voltage side, wherein a calculation formula of the criterion of additionally arranging the priority side of the dynamic reactive power source is as follows:

when H is larger than or equal to 0, a dynamic reactive power source is additionally arranged on the medium-voltage side of the three-coil transformer on the side a of the connecting line; when H is present<When 0, a dynamic reactive power source is additionally arranged on the medium-voltage side of the three-winding transformer on the side of the connecting line b, and the t is P_LmaxThe method for calculating the second power of the tie line is the same as the method for calculating the first power of the tie line when the first power of the tie line of the power grid reaches the maximum value;

step 4, returning to the step 3 when the asynchronous oscillation of the tie line occurs in the system according to the second power calculation result of the tie line; when the asynchronous oscillation of the tie line does not occur in the system and the calculation result meets the conveying requirement of the tie line, the configuration of the dynamic reactive power sources at the two sides of the tie line is finished; when the system does not generate the asynchronous oscillation of the tie line and the calculation result does not reach the transmission requirement of the tie line, the third power of the tie line is calculated after the transmission power of the tie line is increased to the transmission requirement value, wherein the formula for calculating the third power of the tie line is the same as the method for calculating the power of the first tie line;

step 5, when the asynchronous oscillation of the tie line does not occur and the tie line is stable in the power grid system according to the calculation result of the third power of the tie line, the configuration of the dynamic reactive power sources on the two sides of the tie line is finished; and (3) returning to the step 3 when the asynchronous oscillation of the tie line occurs in the power grid system.

Further, the second simulation unit determines the static stability limit of the tie line according to the configuration and the preset operation mode of the voltage-side dynamic reactive power sources in the three coils of transformers on two sides of the tie line and the historical electrical quantity measured by the WAMS, and includes:

according to the configuration and the preset operation mode of the voltage side dynamic reactive power sources in the three coils of transformers on two sides of the connecting line, in a quasi-real-time early warning environment, a first curve of the static stability limit of the active power of the connecting line after a given high-power locking fault changes along with time is determined, and the expression is as follows:

in the formula, Pmax _ pre (t)₁) A first curve of active power of the tie line over time after a given high power blocking fault;

where Pmax _ pre _ vertex is a first curve Pmax _ pre (t)₁) A peak value of (1);

according to the historical electrical quantity measured by the WAMS, determining a second curve of the change of the static stability limit of the active power of the tie line after the given high-power locking fault along with the time on the same historical day, wherein the expression is as follows:

in the formula, Pmax _ sm (t)₂) For the active power of the tie-line over time t after a given high-power blocking fault₂A second curve of variation, wherein t₂Is t of the same day in history₁Time of day;

where Pmax _ sm _ vertex is a second curve Pmax _ sm (t)₂) A peak value of (1);

determining a static stability limit of the connecting line according to the peak values of the first curve and the second curve, wherein the calculation formula is as follows:

Pmax_pre＝Min(Pmax_pre_vertex,Pmax_sm_vertex)。

further, the step of determining a static stability margin of the tie line and performing early warning by the alarm unit according to a calculation result of the static stability limit of the tie line and the control limit of the tie line in a preset operation mode comprises:

according to the calculation result of the static stability limit of the tie line and the control limit of the tie line in a preset operation mode, a calculation formula for determining the static stability margin of the tie line is as follows:

Mg＝((Pmax_pre-Pcontrol)/Pmax)*100％

in the formula, Mg is the static stability margin of the tie line, Pcontrol is the control limit of the tie line in a preset operation mode, and Pmax _ pre is the determined static stability limit of the tie line;

and when the calculation result of the static stability margin of the connecting line is smaller than a preset safety threshold value, carrying out safe operation alarm of the power grid.

The method and the system for improving and early warning the static stability limit of the power grid tie line provided by the technical scheme of the invention determine the equivalent reactance of the power grid tie line and the equivalent impedance from a high-voltage side and a medium-voltage side to a central point in an equivalent circuit model of three transformers on two sides of the tie line according to the electric quantity measured by a wide area measurement system WAMS of the power grid, and then carry out dynamic reactive power configuration on the medium-voltage measurement of the three transformers on two sides of the tie line according to the determined equivalent reactance of the tie line and the equivalent impedance of the three transformers on two sides of the tie line in a simulation program according to the requirement of the power transmission of the tie line of a future power grid in a preset operation mode so as to improve the static stability limit power of the tie line; and then determining the active power peak value of the tie line in a quasi-real-time environment when the future power grid carries out power transmission according to a preset operation mode, comparing the active power peak value with the active power peak value of the tie line on the same historical day, determining the static stability limit power of the preset operation mode when the future power transmission is carried out, and determining the static stability margin of the tie line and carrying out power grid safe operation early warning according to the calculation result of the static stability limit power and the preset control limit of the tie line. The method and the system of the invention determine the calculation formula of the equivalent reactance of the tie line and the equivalent impedance of the three-coil transformers at two sides of the tie line by the equivalent circuit model of the three-coil transformers at two sides of the tie line, and then bring a large amount of real-time electric quantity of the power grid measured by the WAMS system into calculation and determine the value of the electric quantity, thereby improving the accuracy of determining the equivalent reactance of the tie line and the equivalent impedance of the three-coil transformers at two sides, and through the determined value and the active power calculation formula of the tie line, according to the load change of the tie line near area, the static stability limit of the tie line of the complex power system is obviously improved by dynamically adjusting the configuration information of the three coils of transformer dynamic reactive power sources at the two sides of the tie line in a preset operation mode, and when the power system carries out power transmission according to a preset power operation mode, early warning is carried out, and the safety of power grid operation is improved.

Drawings

A more complete understanding of exemplary embodiments of the present invention may be had by reference to the following drawings in which:

fig. 1 is a flow chart of a method for grid tie line static stability limit lifting and early warning according to a preferred embodiment of the present invention;

fig. 2 is a schematic diagram of a grid tie and an equivalent circuit model of three-coil transformers on both sides of the tie, according to a preferred embodiment of the invention;

fig. 3 is a schematic structural diagram of a system for static stability limit lifting and early warning of a power grid tie line according to a preferred embodiment of the present invention.

Detailed Description

The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, the same units/elements are denoted by the same reference numerals.

Unless otherwise defined, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.

Fig. 1 is a flowchart of a method for raising and warning the grid tie static stability limit according to a preferred embodiment of the present invention. As shown in fig. 1, the method 100 for grid tie static stability limit increase and early warning according to the preferred embodiment starts from step 101.

In step 101, according to the electrical quantity measured by the power grid wide area measurement system WAMS, an equivalent reactance of a power grid tie line and equivalent impedances from a high-voltage side and a medium-voltage side to a central point in equivalent circuit models of three-coil transformers on two sides of the tie line are determined, wherein the power grid tie line refers to a connection line higher than the voltage levels of power grids on two sides, the high-voltage sides of the three-coil transformers on two sides of the tie line are both connected to the tie line, the medium-voltage sides are both connected to the power grid, the low-voltage sides are in-situ installation places of reactive compensation devices, the equivalent circuit models of the three-coil transformers on two sides of the tie line are classic three-coil three-side Γ -shaped equivalent circuit models, and the central point is a virtual central node of the equivalent impedances on the high-voltage side, the medium-voltage side and the low-voltage.

The traditional three-roll variable tau-shaped three-side equivalent impedance and the impedance of a ground branch (4 impedances in total) are obtained by offline circuit test, and then are converted; the innovation of the invention is that: under the condition that the impedance of the ground branch and the impedance of the low-voltage side obtained off-line are known, the equivalent impedances from the high-voltage side and the medium-voltage side to the central point can be calculated in real time through online PMU data. Compared with the traditional method for solving the impedance of the transformer, the method can find the change of the impedance of the transformer in time when the physical characteristics of the transformer change; the impedance data obtained by online real-time refreshing calculation is equivalent to real-time electrical sampling calculation, and after the obtained result is analyzed and processed, the possibility of accuracy degree is more accurate than that obtained by an offline test.

Fig. 2 is a schematic diagram of a grid tie and an equivalent circuit model of three-coil transformers on both sides of the tie, according to a preferred embodiment of the invention. As shown in fig. 2, in the equivalent circuit model of the three-winding transformer on both sides of the tie line and the tie line, the a side is the power transmitting end of the tie line, the b side is the power receiving end of the tie line,the port node voltages of the high-voltage side of the three-coil transformer on the side a and the side b are respectively,the voltage of the port node at the middle voltage side of the three-coil transformer at the side a and the side b respectively,the voltages of the port nodes at the low-voltage side of the three-coil transformer at the side a and the side b are respectively; z_Ta,2、Z_Tb,2The impedance from the virtual center node of the equivalent circuit model of the three-coil transformer on the a side and the b side to the voltage node of the high-voltage side port, Z_Ta,1、Z_Tb,1The impedance of the virtual center node on the a side and the b side to the voltage node of the medium-voltage side port, Z_Ta,3、Z_Tb,3The impedance of the virtual center node to the low-voltage side port voltage node, Z, of side a and side b, respectively_Ta、Z_TbA-side and b-side conversion, respectivelyImpedance to ground to the medium voltage side;respectively the currents from the virtual center node of the equivalent circuit model of the three-coil transformer at the side a and the side b to the voltage node of the high-voltage side port,the positive direction is defined as the virtual center node of the three-coil transformer at the a side to the voltage node of the high-voltage side port,the positive direction is defined as the voltage node from the high-voltage side port of the three-coil transformer on the b side to the virtual center node,is the input current of the voltage node of the voltage side port in the a-side three-coil transformer,the positive direction is defined as the voltage node of the medium-voltage side port of the a-side three-coil transformer to the virtual center node,is the input current of the voltage node of the voltage side port in the b-side three-coil transformer,the positive direction is defined as the virtual center node of the three-volume transformer on the b side to the voltage node of the medium-voltage side port,currents from a virtual center node of the three-coil transformer on the side a and the side b to a voltage node of a low-voltage side port are respectively defined as the current from the voltage node of the low-voltage side port to the virtual center node in the positive direction; x_LFor the network to communicate equivalent impedance, delta_a(i)、δ_b(i) The phase angles of the voltage of the high-voltage side ports of the three coils of transformers on the a side and the b side of the connecting line respectively, and the angle difference delta between the two sides of the connecting line_a,b＝δ_a-δ_b，P_LActive power for a power grid tie line; z_Ta、Z_Tb、Z_Ta,3、Z_Tb,3As a known quantity obtained by a short circuit test.

In step 102, according to the determined equivalent reactance of the tie line and the equivalent impedance of the three coils of transformers on two sides of the tie line, determining the configuration number and capacity of the medium-voltage side dynamic reactive power sources of the three coils of transformers on two sides of the tie line by adopting a power system simulation calculation program under the preset operation mode and constraint conditions, wherein the constraint conditions comprise the upper limit value and the lower limit value of the medium-voltage side capacity of the three coils of transformers on two sides of the tie line.

Preferably, the determining the equivalent reactance of the grid tie line according to the electrical quantity measured by the grid wide area measurement system WAMS and the equivalent impedances from the high-voltage side and the medium-voltage side to the central point in the equivalent circuit model of the three-coil transformer on two sides of the tie line include:

the WAMS measures the electric quantity for N times in one day;

according to the ith measured electrical quantity, calculating the equivalent reactance of the power grid tie line and the equivalent impedance from the high-voltage side and the medium-voltage side to the central point in the equivalent circuit model of the three-coil transformer on the two sides of the tie line, wherein the calculation formula is as follows:

in the formula, in the electrical quantity measured by the WAMS system at the ith time,the port node voltages of the high-voltage side of the three-coil transformer on the side a and the side b are respectively,the voltage of the port node at the middle voltage side of the three-coil transformer at the side a and the side b respectively,the voltages of the port nodes at the low-voltage side of the three-coil transformer at the side a and the side b are respectively;respectively the currents from the virtual center node of the equivalent circuit model of the three-coil transformer at the side a and the side b to the voltage node of the high-voltage side port,the positive direction is defined as the virtual center node of the three-coil transformer at the a side to the voltage node of the high-voltage side port,the positive direction is defined as the voltage node from the high-voltage side port of the three-coil transformer on the b side to the virtual center node,is the input current of the voltage node of the voltage side port in the a-side three-coil transformer,the positive direction is defined as the voltage node of the medium-voltage side port of the a-side three-coil transformer to the virtual center node,is the input current of the voltage node of the voltage side port in the b-side three-coil transformer,the positive direction is defined as the virtual center node of the three-volume transformer on the b side to the voltage node of the medium-voltage side port,currents from a virtual center node of the three-coil transformer on the side a and the side b to a voltage node of a low-voltage side port are respectively defined as the current from the voltage node of the low-voltage side port to the virtual center node in the positive direction; x_L(i) For the network to communicate equivalent impedance, delta_a(i)、δ_b(i) The phase angles of the voltage of the high-voltage side ports of the three coils of transformers on the a side and the b side of the connecting line respectively, and the angle difference delta between the two sides of the connecting line_a,b(i)＝δ_a(i)-δ_b(i)，P_L(i) Active power for a power grid tie line; z_Ta,2、Z_Tb,2The impedance from the virtual center node of the equivalent circuit model of the three-coil transformer on the a side and the b side to the voltage node of the high-voltage side port, Z_Ta,1、Z_Tb,1The impedance of the virtual center node on the a side and the b side to the voltage node of the medium-voltage side port, Z_Ta,3、Z_Tb,3The impedance of the virtual center node to the low-voltage side port voltage node, Z, of side a and side b, respectively_Ta、Z_TbGround impedance transformed to the medium voltage side for side a and side b, respectively; z_Ta、Z_Tb、Z_Ta,3、Z_Tb,3Is a known quantity obtained by a short circuit test;

according to the determined equivalent reactance X of the power grid tie line_L(i) Z of equivalent impedance from high-voltage side and medium-voltage side to central point in equivalent circuit model of three-coil transformer on two sides of connecting line_Ta,1(i)、Z_Ta,2(i)Z_Ta,2(i)、Z_Tb,1(i)、Z_Tb,2(i) Counting the N X_L(i)、Z_Ta,1(i)、Z_Ta,2(i)、Z_Tb,1(i)、Z_Tb,2(i) The calculation results with the largest occurrence number in the values of (A) are respectively used as the equivalent reactance X of the power grid tie line_LEquivalent impedance Z from high-voltage side and medium-voltage side to central point in equivalent circuit model of three-coil transformer on two sides of connecting line_Ta,1、Z_Ta,2、Z_Tb,1、Z_Tb,2。

In step 103, a static stability limit of the tie line is determined according to the configuration and the preset operation mode of the voltage-side dynamic reactive power source in the three-winding transformer on the two sides of the tie line and the historical electric quantity measured by the WAMS.

Preferably, the determining, according to the determined equivalent reactance of the tie line and the equivalent impedance of the three-winding transformer on the two sides of the tie line, the configuration capacity of the dynamic reactive power sources on the two sides of the tie line under the preset operation mode and constraint conditions by using a power system simulation calculation program includes:

step 1, implanting the determined equivalent reactance of the tie line and the equivalent impedance of three coils of transformers at two sides of the tie line into a power system simulation calculation program;

step 2, calculating the first power of the tie line when the high power of the power grid system is in a fault state under the preset operation mode and constraint conditions, and when the system generates tie line asynchronous oscillation or the system does not generate tie line asynchronous oscillation and the active power of the tie line does not reach the required transmission value according to the first power calculation result of the tie line, turning to step 3, wherein the calculation formula for calculating the first power of the tie line is as follows:

in the formula, P_LThe power of the power grid tie line in the set operation mode; x_LFor a determined equivalent impedance of the grid connection, Z_Ta,2、Z_Tb,2Respectively calculating and determining the impedance from a virtual center node of the equivalent circuit model of the a-side and b-side three-coil transformer to a voltage node of a high-voltage side port, Z_Ta,3、Z_Tb,3For a known quantity obtained by a short circuit test,an electrical quantity measured for a set mode of operation;

step 3, determining three transformer medium-voltage sides needing to be additionally provided with the dynamic reactive power sources in two sides of the tie line according to a criterion of additionally arranging the priority side of the dynamic reactive power sources, additionally arranging a dynamic reactive power source with a fixed capacity value, and calculating the second power of the tie line after the dynamic reactive power sources are additionally arranged on the medium-voltage side when the capacity value of the additionally arranged dynamic reactive power source does not reach the upper limit value of the capacity of the medium-voltage side, wherein a calculation formula of the criterion of additionally arranging the priority side of the dynamic reactive power source is as follows:

when H is larger than or equal to 0, a dynamic reactive power source is additionally arranged on the medium-voltage side of the three-coil transformer on the side a of the connecting line; when H is present<When 0, a dynamic reactive power source is additionally arranged on the medium-voltage side of the three-winding transformer on the side of the connecting line b, and the t is P_LmaxThe method for calculating the second power of the tie line is the same as the method for calculating the first power of the tie line when the first power of the tie line of the power grid reaches the maximum value;

step 4, returning to the step 3 when the asynchronous oscillation of the tie line occurs in the system according to the second power calculation result of the tie line; when the asynchronous oscillation of the tie line does not occur in the system and the calculation result meets the conveying requirement of the tie line, the configuration of the dynamic reactive power sources at the two sides of the tie line is finished; when the system does not generate the asynchronous oscillation of the tie line and the calculation result does not reach the transmission requirement of the tie line, the third power of the tie line is calculated after the transmission power of the tie line is increased to the transmission requirement value, wherein the formula for calculating the third power of the tie line is the same as the method for calculating the power of the first tie line;

step 5, when the asynchronous oscillation of the tie line does not occur and the tie line is stable in the power grid system according to the calculation result of the third power of the tie line, the configuration of the dynamic reactive power sources on the two sides of the tie line is finished; and (3) returning to the step 3 when the asynchronous oscillation of the tie line occurs in the power grid system.

In the preferred embodiment, the preset operation mode is a future power grid operation mode.

In step 104, according to the calculation result of the static stability limit of the tie line and the control limit of the tie line in a preset operation mode, the static stability margin of the tie line is determined and early warning is performed.

Preferably, the determining the static stability limit of the tie line according to the configuration and the preset operation mode of the voltage-side dynamic reactive power sources in the three-winding transformers on two sides of the tie line and the historical electrical quantity measured by the WAMS includes:

according to the configuration and the preset operation mode of the voltage side dynamic reactive power sources in the three coils of transformers on two sides of the connecting line, in a quasi-real-time early warning environment, a first curve of the static stability limit of the active power of the connecting line after a given high-power locking fault changes along with time is determined, and the expression is as follows:

in the formula, Pmax _ pre (t)₁) A first curve of active power of the tie line over time after a given high power blocking fault;

where Pmax _ pre _ vertex is a first curve Pmax _ pre (t)₁) A peak value of (1);

according to the historical electrical quantity measured by the WAMS, determining a second curve of the change of the static stability limit of the active power of the tie line after the given high-power locking fault along with the time on the same historical day, wherein the expression is as follows:

in the formula, Pmax _ sm (t)₂) For the active power of the tie-line over time t after a given high-power blocking fault₂A second curve of variation, wherein t₂Is t of the same day in history₁Time of day;

where Pmax _ sm _ vertex is a second curve Pmax _ sm (t)₂) A peak value of (1);

determining a static stability limit of the connecting line according to the peak values of the first curve and the second curve, wherein the calculation formula is as follows:

Pmax_pre＝Min(Pmax_pre_vertex,Pmax_sm_vertex)。

preferably, determining the static stability margin of the tie line and performing early warning according to the calculation result of the static stability limit of the tie line and the control limit of the tie line in a preset operation mode comprises:

according to the calculation result of the static stability limit of the tie line and the control limit of the tie line in a preset operation mode, a calculation formula for determining the static stability margin of the tie line is as follows:

Mg＝((Pmax_pre-Pcontrol)/Pmax)*100％

in the formula, Mg is the static stability margin of the tie line, Pcontrol is the control limit of the tie line in a preset operation mode, and Pmax _ pre is the determined static stability limit of the tie line;

and when the calculation result of the static stability margin of the connecting line is smaller than a preset safety threshold value, carrying out safe operation alarm of the power grid.

Fig. 3 is a schematic structural diagram of a system for static stability limit lifting and early warning of a power grid tie line according to a preferred embodiment of the present invention. As shown in fig. 3, the system 300 for grid tie static stability limit lifting and early warning according to the preferred embodiment includes:

the impedance calculation unit 301 is configured to determine an equivalent reactance of a grid tie line and equivalent impedances from a high-voltage side and a medium-voltage side to a central point in an equivalent circuit model of three-winding transformers on two sides of the tie line according to the electrical quantity measured by the grid wide area measurement system WAMS, where the grid tie line refers to a connection line higher than the voltage levels of the grids on two sides, the high-voltage sides of the three-winding transformers on two sides of the tie line are both connected to the tie line, the medium-voltage sides are both connected to the grid itself, the low-voltage side is a local installation place of a reactive compensation device, the equivalent circuit model of the three-winding transformers on two sides of the tie line is a classic three-winding three-side inverted-L-shaped equivalent circuit model, and the central point is a virtual central node of the equivalent impedances on the high-voltage side, the medium-voltage side and the low-voltage side;

a first simulation unit 302, configured to determine, according to the determined equivalent reactance of the tie line and the equivalent impedance of the three coils of transformers on two sides of the tie line, the configuration number and capacity of the medium-voltage side dynamic reactive power sources of the three coils of transformers on two sides of the tie line by using a power system simulation calculation program under a preset operation mode and constraint conditions, where the constraint conditions include upper limit values and lower limit values of medium-voltage side capacities of the three coils of transformers on two sides of the tie line;

a second simulation unit 303, configured to determine a static stability limit of the tie line according to the configuration and preset operation mode of the voltage-side dynamic reactive power sources in the three coils of transformers on both sides of the tie line and historical electrical quantities measured by the WAMS;

and an alarm unit 304, configured to determine a static stability margin of the tie line according to a calculation result of the static stability limit of the tie line and a tie line control limit in a preset operation mode, and perform early warning.

Preferably, the impedance calculating unit 301 determines the equivalent reactance of the grid tie line according to the electrical quantity measured by the grid wide area measurement system WAMS, and the equivalent impedances from the high-voltage side and the medium-voltage side to the central point in the equivalent circuit model of the three-coil transformer on two sides of the tie line include:

the WAMS measures the electric quantity for N times in one day;

according to the ith measured electrical quantity, calculating the equivalent reactance of the power grid tie line and the equivalent impedance from the high-voltage side and the medium-voltage side to the central point in the equivalent circuit model of the three-coil transformer on the two sides of the tie line, wherein the calculation formula is as follows:

in the formula, in the electrical quantity measured by the WAMS system at the ith time,the port node voltages of the high-voltage side of the three-coil transformer on the side a and the side b are respectively,the voltage of the port node at the middle voltage side of the three-coil transformer at the side a and the side b respectively,the voltages of the port nodes at the low-voltage side of the three-coil transformer at the side a and the side b are respectively;respectively the currents from the virtual center node of the equivalent circuit model of the three-coil transformer at the side a and the side b to the voltage node of the high-voltage side port,the positive direction is defined as the virtual center node of the three-coil transformer at the a side to the voltage node of the high-voltage side port,the positive direction is defined as the voltage node from the high-voltage side port of the three-coil transformer on the b side to the virtual center node,is the input current of the voltage node of the voltage side port in the a-side three-coil transformer,positive direction defined as a side three-winding transformerA voltage node of the pressure side port to a virtual center node,is the input current of the voltage node of the voltage side port in the b-side three-coil transformer,the positive direction is defined as the virtual center node of the three-volume transformer on the b side to the voltage node of the medium-voltage side port,currents from a virtual center node of the three-coil transformer on the side a and the side b to a voltage node of a low-voltage side port are respectively defined as the current from the voltage node of the low-voltage side port to the virtual center node in the positive direction; x_L(i) For the network to communicate equivalent impedance, delta_a(i)、δ_b(i) The phase angles of the voltage of the high-voltage side ports of the three coils of transformers on the a side and the b side of the connecting line respectively, and the angle difference delta between the two sides of the connecting line_a,b(i)＝δ_a(i)-δ_b(i)，P_L(i) Active power for a power grid tie line; z_Ta,2、Z_Tb,2The impedance from the virtual center node of the equivalent circuit model of the three-coil transformer on the a side and the b side to the voltage node of the high-voltage side port, Z_Ta,1、Z_Tb,1The impedance of the virtual center node on the a side and the b side to the voltage node of the medium-voltage side port, Z_Ta,3、Z_Tb,3The impedance of the virtual center node to the low-voltage side port voltage node, Z, of side a and side b, respectively_Ta、Z_TbGround impedance transformed to the medium voltage side for side a and side b, respectively; z_Ta、Z_Tb、Z_Ta,3、Z_Tb,3Is a known quantity obtained by a short circuit test;

according to the determined equivalent reactance X of the power grid tie line_L(i) Z of equivalent impedance from high-voltage side and medium-voltage side to central point in equivalent circuit model of three-coil transformer on two sides of connecting line_Ta,1(i)、Z_Ta,2(i)Z_Ta,2(i)、Z_Tb,1(i)、Z_Tb,2(i) Counting the N X_L(i)、Z_Ta,1(i)、Z_Ta,2(i)、Z_Tb,1(i)、Z_Tb,2(i) The calculation results with the largest occurrence number in the values of (A) are respectively used as the equivalent reactance X of the power grid tie line_LEquivalent impedance Z from high-voltage side and medium-voltage side to central point in equivalent circuit model of three-coil transformer on two sides of connecting line_Ta,1、Z_Ta,2、Z_Tb,1、Z_Tb,2。

Preferably, the determining, by the first simulation unit 302, the configuration capacity of the dynamic reactive power sources on both sides of the tie line according to the determined equivalent reactance of the tie line and the equivalent impedance of the three-winding transformer on both sides of the tie line under the preset operation mode and constraint conditions by using a power system simulation calculation program includes:

step 1, implanting the determined equivalent reactance of the tie line and the equivalent impedance of three coils of transformers at two sides of the tie line into a power system simulation calculation program;

step 2, calculating the first power of the tie line when the high power of the power grid system is in a fault state under the preset operation mode and constraint conditions, and when the system generates tie line asynchronous oscillation or the system does not generate tie line asynchronous oscillation and the active power of the tie line does not reach the required transmission value according to the first power calculation result of the tie line, turning to step 3, wherein the calculation formula for calculating the first power of the tie line is as follows:

in the formula, P_LThe power of the power grid tie line in the set operation mode; x_LFor a determined equivalent impedance of the grid connection, Z_Ta,2、Z_Tb,2Respectively calculating and determining the impedance from a virtual center node of the equivalent circuit model of the a-side and b-side three-coil transformer to a voltage node of a high-voltage side port, Z_Ta,3、Z_Tb,3For a known quantity obtained by a short circuit test,an electrical quantity measured for a set mode of operation;

step 3, determining three coils of transformer medium-voltage sides needing to be additionally provided with the dynamic reactive power sources in two sides of the tie line according to a criterion of additionally arranging the priority side of the dynamic reactive power sources, additionally arranging a dynamic reactive power source with a fixed capacity value, and calculating the second power of the tie line after the dynamic reactive power sources are additionally arranged on the medium-voltage side when the capacity value of the additionally arranged dynamic reactive power source does not reach the upper limit value of the capacity of the medium-voltage side, wherein a calculation formula of the criterion of additionally arranging the priority side of the dynamic reactive power source is as follows:

when H is larger than or equal to 0, a dynamic reactive power source is additionally arranged on the medium-voltage side of the three-coil transformer on the side a of the connecting line; when H is present<When 0, a dynamic reactive power source is additionally arranged on the medium-voltage side of the three-winding transformer on the side of the connecting line b, and the t is P_LmaxThe method for calculating the second power of the tie line is the same as the method for calculating the first power of the tie line when the first power of the tie line of the power grid reaches the maximum value;

step 4, returning to the step 3 when the asynchronous oscillation of the tie line occurs in the system according to the second power calculation result of the tie line; when the asynchronous oscillation of the tie line does not occur in the system and the calculation result meets the conveying requirement of the tie line, the configuration of the dynamic reactive power sources at the two sides of the tie line is finished; when the system does not generate the asynchronous oscillation of the tie line and the calculation result does not reach the transmission requirement of the tie line, the third power of the tie line is calculated after the transmission power of the tie line is increased to the transmission requirement value, wherein the formula for calculating the third power of the tie line is the same as the method for calculating the power of the first tie line;

step 5, when the asynchronous oscillation of the tie line does not occur and the tie line is stable in the power grid system according to the calculation result of the third power of the tie line, the configuration of the dynamic reactive power sources on the two sides of the tie line is finished; and (3) returning to the step 3 when the asynchronous oscillation of the tie line occurs in the power grid system.

Preferably, the determining, by the second simulation unit 303, the static stability limit of the tie line according to the configuration and the preset operation mode of the voltage-side dynamic reactive power sources in the three coils of transformers on both sides of the tie line and the historical electrical quantity measured by the WAMS includes:

according to the configuration and the preset operation mode of the voltage side dynamic reactive power sources in the three coils of transformers on two sides of the connecting line, in a quasi-real-time early warning environment, a first curve of the static stability limit of the active power of the connecting line after a given high-power locking fault changes along with time is determined, and the expression is as follows:

in the formula, Pmax _ pre (t)₁) A first curve of active power of the tie line over time after a given high power blocking fault;

where Pmax _ pre _ vertex is a first curve Pmax _ pre (t)₁) A peak value of (1);

according to the historical electrical quantity measured by the WAMS, determining a second curve of the change of the static stability limit of the active power of the tie line after the given high-power locking fault along with the time on the same historical day, wherein the expression is as follows:

in the formula, Pmax _ sm (t)₂) For the active power of the tie-line over time t after a given high-power blocking fault₂A second curve of variation, wherein t₂Is t of the same day in history₁Time of day;

where Pmax _ sm _ vertex is a second curve Pmax _ sm (t)₂) A peak value of (1);

determining a static stability limit of the connecting line according to the peak values of the first curve and the second curve, wherein the calculation formula is as follows:

Pmax_pre＝Min(Pmax_pre_vertex,Pmax_sm_vertex)。

preferably, the determining the static stability margin of the tie line and performing the early warning by the alarm unit 304 according to the calculation result of the static stability limit of the tie line and the control limit of the tie line in the preset operation mode includes:

according to the calculation result of the static stability limit of the tie line and the control limit of the tie line in a preset operation mode, a calculation formula for determining the static stability margin of the tie line is as follows:

Mg＝((Pmax_pre-Pcontrol)/Pmax)*100％

in the formula, Mg is the static stability margin of the tie line, Pcontrol is the control limit of the tie line in a preset operation mode, and Pmax _ pre is the determined static stability limit of the tie line;

and when the calculation result of the static stability margin of the connecting line is smaller than a preset safety threshold value, carrying out safe operation alarm of the power grid.

The steps of the system for improving and early warning the static stability limit of the power grid tie line are the same as the steps of the method for improving and early warning the static stability limit of the power grid tie line, the technical effects are the same, and the description is omitted.

The invention has been described with reference to a few embodiments. However, other embodiments of the invention than the one disclosed above are equally possible within the scope of the invention, as would be apparent to a person skilled in the art from the appended patent claims.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [ device, component, etc ]" are to be interpreted openly as referring to at least one instance of said device, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

Claims (10)

1. A method for improving and early warning the static stability limit of a power grid tie line is characterized by comprising the following steps:

step 1, determining equivalent reactance of a power grid tie line and equivalent impedance from a high-voltage side and a medium-voltage side to a central point in equivalent circuit models of three-coil transformers on two sides of the tie line according to electric quantity measured by a power grid wide area measurement system WAMS, wherein the power grid tie line refers to a tie line higher than the voltage levels of power grids on two sides, the high-voltage sides of the three-coil transformers on two sides of the tie line are connected to the tie line, the medium-voltage sides of the three-coil transformers are connected to a power grid of the tie line, the low-voltage sides of the three-coil transformers are in-situ installation positions of a reactive compensation device, the equivalent circuit models of the three-coil transformers on two sides of the tie line are classic three-coil three-side gamma-shaped equivalent circuit models, and the central point is a virtual central node of the equivalent impedance of the high-voltage side;

step 2, according to the determined equivalent reactance of the tie line and the equivalent impedance of the three coils of transformers on the two sides of the tie line, determining the configuration number and the capacity of the medium-voltage side dynamic reactive power sources of the three coils of transformers on the two sides of the tie line by adopting a power system simulation calculation program under the preset operation mode and constraint conditions, wherein the constraint conditions comprise the upper limit value and the lower limit value of the medium-voltage side capacity of the three coils of transformers on the two sides of the tie line;

step 3, determining the static stability limit of the tie line according to the configuration and the preset operation mode of the medium-voltage side dynamic reactive power sources of the three coils of transformers on two sides of the tie line and the historical electric quantity measured by the WAMS;

and 4, determining the static stability margin of the tie line and carrying out early warning according to the calculation result of the static stability limit of the tie line and the control limit of the tie line in a preset operation mode.

2. The method of claim 1, wherein determining the equivalent reactance of the grid tie line according to the electrical quantity measured by the grid wide area measurement system WAMS, and the equivalent impedance from the high-voltage side and the medium-voltage side to the central point in the equivalent circuit model of the three-coil transformer on two sides of the tie line comprises:

the WAMS measures the electric quantity for N times in one day;

according to the ith measured electrical quantity, calculating the equivalent reactance of the power grid tie line and the equivalent impedance from the high-voltage side and the medium-voltage side to the central point in the equivalent circuit model of the three-coil transformer on the two sides of the tie line, wherein the calculation formula is as follows:

in the formula, the side a is a connecting line power transmitting end, the side b is a connecting line power receiving end, in the electrical quantity measured by the WAMS system at the ith time,the port node voltages of the high-voltage side of the three-coil transformer on the side a and the side b are respectively,the voltage of the port node at the middle voltage side of the three-coil transformer at the side a and the side b respectively,the voltages of the port nodes at the low-voltage side of the three-coil transformer at the side a and the side b are respectively;respectively the currents from the virtual center node of the equivalent circuit model of the three-coil transformer at the side a and the side b to the voltage node of the high-voltage side port,the positive direction is defined as the virtual center node of the three-coil transformer at the a side to the voltage node of the high-voltage side port,the positive direction is defined as the voltage node from the high-voltage side port of the three-coil transformer on the b side to the virtual center node,is the input current of the voltage node of the voltage side port in the a-side three-coil transformer,the positive direction is defined as the voltage node of the medium-voltage side port of the a-side three-coil transformer to the virtual center node,is the input current of the voltage node of the voltage side port in the b-side three-coil transformer,the positive direction is defined as the virtual center node of the three-volume transformer on the b side to the voltage node of the medium-voltage side port,currents from a virtual center node of the three-coil transformer on the side a and the side b to a voltage node of a low-voltage side port are respectively defined as the current from the voltage node of the low-voltage side port to the virtual center node in the positive direction; x_L(i) For the network to communicate equivalent impedance, delta_a(i)、δ_b(i) The phase angles of the voltage of the high-voltage side ports of the three coils of transformers on the a side and the b side of the connecting line respectively, and the angle difference delta between the two sides of the connecting line_a,b(i)＝δ_a(i)-δ_b(i)，P_L(i) Active power for a power grid tie line; z_Ta,2、Z_Tb,2The impedance from the virtual center node of the equivalent circuit model of the three-coil transformer on the a side and the b side to the voltage node of the high-voltage side port, Z_Ta,1、Z_Tb,1The impedance of the virtual center node on the a side and the b side to the voltage node of the medium-voltage side port, Z_Ta,3、Z_Tb,3The impedance of the virtual center node to the low-voltage side port voltage node, Z, of side a and side b, respectively_Ta、Z_TbGround impedance transformed to the medium voltage side for side a and side b, respectively; z_Ta、Z_Tb、Z_Ta,3、Z_Tb,3Is a known quantity obtained by a short circuit test;

according to the determined equivalent reactance X of the power grid tie line_L(i) Z of equivalent impedance from high-voltage side and medium-voltage side to central point in equivalent circuit model of three-coil transformer on two sides of connecting line_Ta,1(i)、Z_Ta,2(i)Z_Ta,2(i)、Z_Tb,1(i)、Z_Tb,2(i) Counting the N X_L(i)、Z_Ta,1(i)、Z_Ta,2(i)、Z_Tb,1(i)、Z_Tb,2(i) The calculation results with the largest occurrence number in the values of (A) are respectively used as the equivalent reactance X of the power grid tie line_LEquivalent impedance Z from high-voltage side and medium-voltage side to central point in equivalent circuit model of three-coil transformer on two sides of connecting line_Ta,1、Z_Ta,2、Z_Tb,1、Z_Tb,2。

3. The method of claim 2, wherein determining the configured capacity of the dynamic reactive power sources on both sides of the tie line under the preset operation mode and constraint conditions by adopting a power system simulation calculation program according to the determined equivalent reactance of the tie line and the equivalent impedance of the three-coil transformer on both sides of the tie line comprises:

step 1, implanting the determined equivalent reactance of the tie line and the equivalent impedance of three coils of transformers at two sides of the tie line into a power system simulation calculation program;

step 2, calculating the first power of the tie line when the high power of the power grid system is in a fault state under the preset operation mode and constraint conditions, and when the system generates tie line asynchronous oscillation or the system does not generate tie line asynchronous oscillation and the active power of the tie line does not reach the required transmission value according to the first power calculation result of the tie line, turning to step 3, wherein the calculation formula for calculating the first power of the tie line is as follows:

in the formula, P_LThe power of the power grid tie line in the set operation mode; x_LFor a determined equivalent impedance of the grid connection, Z_Ta,2、Z_Tb,2Respectively calculating and determining the impedance from a virtual center node of the equivalent circuit model of the a-side and b-side three-coil transformer to a voltage node of a high-voltage side port, Z_Ta，3、Z_Tb，3For a known quantity obtained by a short circuit test,an electrical quantity measured for a set mode of operation;

step 3, determining three coils of transformer medium-voltage sides needing to be additionally provided with the dynamic reactive power sources in two sides of the tie line according to a criterion of additionally arranging the priority side of the dynamic reactive power sources, additionally arranging a dynamic reactive power source with a fixed capacity value, and calculating the second power of the tie line after the dynamic reactive power sources are additionally arranged on the medium-voltage side when the capacity value of the additionally arranged dynamic reactive power source does not reach the upper limit value of the capacity of the medium-voltage side, wherein a calculation formula of the criterion of additionally arranging the priority side of the dynamic reactive power source is as follows:

when H is larger than or equal to 0, a dynamic reactive power source is additionally arranged on the medium-voltage side of the three-coil transformer on the side a of the connecting line; when H is present<When 0, a dynamic reactive power source is additionally arranged on the medium-voltage side of the three-winding transformer on the side of the connecting line b, and the t is P_LmaxThe method for calculating the second power of the tie line is the same as the method for calculating the first power of the tie line when the first power of the tie line of the power grid reaches the maximum value;

step 4, returning to the step 3 when the asynchronous oscillation of the tie line occurs in the system according to the second power calculation result of the tie line; when the asynchronous oscillation of the tie line does not occur in the system and the calculation result meets the conveying requirement of the tie line, the configuration of the dynamic reactive power sources at the two sides of the tie line is finished; when the system does not generate the asynchronous oscillation of the tie line and the calculation result does not reach the transmission requirement of the tie line, the third power of the tie line is calculated after the transmission power of the tie line is increased to the transmission requirement value, wherein the formula for calculating the third power of the tie line is the same as the method for calculating the power of the first tie line;

step 5, when the asynchronous oscillation of the tie line does not occur and the tie line is stable in the power grid system according to the calculation result of the third power of the tie line, the configuration of the dynamic reactive power sources on the two sides of the tie line is finished; and (3) returning to the step 3 when the asynchronous oscillation of the tie line occurs in the power grid system.

4. The method of claim 2, wherein determining the static stability limit of the tie line according to the configuration and preset operation mode of the voltage side dynamic reactive power source in the three-winding transformer on two sides of the tie line and the historical electric quantity measured by the WAMS comprises:

according to the configuration and the preset operation mode of the voltage side dynamic reactive power sources in the three coils of transformers on two sides of the connecting line, in a quasi-real-time early warning environment, a first curve of the static stability limit of the active power of the connecting line after a given high-power locking fault changes along with time is determined, and the expression is as follows:

in the formula, Pmax _ pre (t)₁) A first curve of active power of the tie line over time after a given high power blocking fault;

wherein Pmax _ pre _ vertex is the firstA curve Pmax _ pre (t)₁) A peak value of (1);

according to the historical electrical quantity measured by the WAMS, determining a second curve of the change of the static stability limit of the active power of the tie line after the given high-power locking fault along with the time on the same historical day, wherein the expression is as follows:

in the formula, Pmax _ sm (t)₂) For the active power of the tie-line over time t after a given high-power blocking fault₂A second curve of variation, wherein t₂Is t of the same day in history₁Time of day;

where Pmax _ sm _ vertex is a second curve Pmax _ sm (t)₂) A peak value of (1);

determining a static stability limit of the connecting line according to the peak values of the first curve and the second curve, wherein the calculation formula is as follows:

Pmax_pre＝Min(Pmax_pre_vertex,Pmax_sm_vertex)。

5. the method of claim 4, wherein determining the quiet margin of the tie and making an early warning based on the calculated result of the tie quiet margin and the tie control limit in the preset operation mode comprises:

according to the calculation result of the static stability limit of the tie line and the control limit of the tie line in a preset operation mode, a calculation formula for determining the static stability margin of the tie line is as follows:

Mg＝((Pmax_pre-Pcontrol)/Pmax)*100％

in the formula, Mg is the static stability margin of the tie line, Pcontrol is the control limit of the tie line in a preset operation mode, and Pmax _ pre is the determined static stability limit of the tie line;

and when the calculation result of the static stability margin of the connecting line is smaller than a preset safety threshold value, carrying out safe operation alarm of the power grid.

6. The utility model provides a system of static stability limit promotion of electric wire netting tie and early warning which characterized in that, affiliated system includes:

the impedance calculation unit is used for determining the equivalent reactance of a grid tie line and the equivalent impedance from a high-voltage side and a medium-voltage side to a central point in an equivalent circuit model of three-coil transformers on two sides of the tie line according to the electrical quantity measured by a wide area measurement system WAMS (wide area measurement system), wherein the grid tie line refers to a connecting line with a voltage level higher than that of the grids on two sides, the high-voltage sides of the three-coil transformers on two sides of the tie line are both connected to the tie line, the medium-voltage sides are both connected to the grid, the low-voltage sides are the local installation positions of a reactive compensation device, the equivalent circuit model of the three-coil transformers on two sides of the tie line is a three-coil classic inverted-L-shaped equivalent circuit model, and the central point is a virtual central node of the equivalent impedance on the high-voltage side, the medium-voltage side and the low;

the first simulation unit is used for determining the configuration quantity and capacity of the medium-voltage side dynamic reactive power sources of the three coils of transformers on two sides of the tie line by adopting a power system simulation calculation program under the preset operation mode and constraint conditions according to the determined equivalent reactance of the tie line and the equivalent impedance of the three coils of transformers on two sides of the tie line, wherein the constraint conditions comprise the upper limit value and the lower limit value of the medium-voltage side capacity of the three coils of transformers on two sides of the tie line;

the second simulation unit is used for determining the static stability limit of the tie line according to the configuration and the preset running mode of the medium-voltage side dynamic reactive power sources of the three coils of transformers on two sides of the tie line and the historical electric quantity measured by the WAMS;

and the alarm unit is used for determining the static stability margin of the tie line and carrying out early warning according to the calculation result of the static stability limit of the tie line and the control limit of the tie line in a preset operation mode.

7. The system of claim 6, wherein the impedance calculating unit determines the equivalent reactance of the grid tie line according to the electrical quantity measured by the grid wide area measurement system WAMS, and the equivalent impedance from the high voltage side and the medium voltage side to the central point in the equivalent circuit model of the three-coil transformer on two sides of the tie line comprises:

the WAMS measures the electric quantity for N times in one day;

according to the ith measured electrical quantity, calculating the equivalent reactance of the power grid tie line and the equivalent impedance from the high-voltage side and the medium-voltage side to the central point in the equivalent circuit model of the three-coil transformer on the two sides of the tie line, wherein the calculation formula is as follows:

in the formula, the side a is a connecting line power transmitting end, the side b is a connecting line power receiving end, in the electrical quantity measured by the WAMS system at the ith time,the port node voltages of the high-voltage side of the three-coil transformer on the side a and the side b are respectively,the voltage of the port node at the middle voltage side of the three-coil transformer at the side a and the side b respectively,the voltages of the port nodes at the low-voltage side of the three-coil transformer at the side a and the side b are respectively;respectively the currents from the virtual center node of the equivalent circuit model of the three-coil transformer at the side a and the side b to the voltage node of the high-voltage side port,the positive direction is defined as the virtual center node of the three-coil transformer at the a side to the voltage node of the high-voltage side port,the positive direction is defined as the voltage node from the high-voltage side port of the three-coil transformer on the b side to the virtual center node,is the input current of the voltage node of the voltage side port in the a-side three-coil transformer,the positive direction is defined as the voltage node of the medium-voltage side port of the a-side three-coil transformer to the virtual center node,is the input current of the voltage node of the voltage side port in the b-side three-coil transformer,the positive direction is defined as the virtual center node of the three-volume transformer on the b side to the voltage node of the medium-voltage side port,three-coil transformer virtual center node on a side and b side to low-voltage side port voltage node current, squareTo a voltage node defined as a low voltage side port to a virtual center node; x_L(i) For the network to communicate equivalent impedance, delta_a(i)、δ_b(i) The phase angles of the voltage of the high-voltage side ports of the three coils of transformers on the a side and the b side of the connecting line respectively, and the angle difference delta between the two sides of the connecting line_a,b(i)＝δ_a(i)-δ_b(i)，P_L(i) Active power for a power grid tie line; z_Ta,2、Z_Tb,2The impedance from the virtual center node of the equivalent circuit model of the three-coil transformer on the a side and the b side to the voltage node of the high-voltage side port, Z_Ta,1、Z_Tb,1The impedance of the virtual center node on the a side and the b side to the voltage node of the medium-voltage side port, Z_Ta,3、Z_Tb,3The impedance of the virtual center node to the low-voltage side port voltage node, Z, of side a and side b, respectively_Ta、Z_TbGround impedance transformed to the medium voltage side for side a and side b, respectively; z_Ta、Z_Tb、Z_Ta,3、Z_Tb,3Is a known quantity obtained by a short circuit test;

according to the determined equivalent reactance X of the power grid tie line_L(i) Z of equivalent impedance from high-voltage side and medium-voltage side to central point in equivalent circuit model of three-coil transformer on two sides of connecting line_Ta,1(i)、Z_Ta,2(i)Z_Ta,2(i)、Z_Tb,1(i)、Z_Tb,2(i) Counting the N X_L(i)、Z_Ta,1(i)、Z_Ta,2(i)、Z_Tb,1(i)、Z_Tb,2(i) The calculation results with the largest occurrence number in the values of (A) are respectively used as the equivalent reactance X of the power grid tie line_LEquivalent impedance Z from high-voltage side and medium-voltage side to central point in equivalent circuit model of three-coil transformer on two sides of connecting line_Ta,1、Z_Ta,2、Z_Tb,1、Z_Tb,2。

8. The system of claim 7, wherein the first simulation unit determines the configuration capacity of the dynamic reactive power sources on both sides of the tie line according to the determined equivalent reactance of the tie line and the equivalent impedance of the three-coil transformers on both sides of the tie line by using a power system simulation calculation program under the preset operation mode and constraint conditions, and comprises the following steps:

step 1, implanting the determined equivalent reactance of the tie line and the equivalent impedance of three coils of transformers at two sides of the tie line into a power system simulation calculation program;

step 2, calculating the first power of the tie line when the high power of the power grid system is in a fault state under the preset operation mode and constraint conditions, and when the system generates tie line asynchronous oscillation or the system does not generate tie line asynchronous oscillation and the active power of the tie line does not reach the required transmission value according to the first power calculation result of the tie line, turning to step 3, wherein the calculation formula for calculating the first power of the tie line is as follows:

in the formula, P_LThe power of the power grid tie line in the set operation mode; x_LFor a determined equivalent impedance of the grid connection, Z_Ta,2、Z_Tb,2Respectively calculating and determining the impedance from a virtual center node of the equivalent circuit model of the a-side and b-side three-coil transformer to a voltage node of a high-voltage side port, Z_Ta,3、Z_Tb,3For a known quantity obtained by a short circuit test,an electrical quantity measured for a set mode of operation;

step 3, determining three coils of transformer medium-voltage sides needing to be additionally provided with the dynamic reactive power sources in two sides of the tie line according to a criterion of additionally arranging the priority side of the dynamic reactive power sources, additionally arranging a dynamic reactive power source with a fixed capacity value, and calculating the second power of the tie line after the dynamic reactive power sources are additionally arranged on the medium-voltage side when the capacity value of the additionally arranged dynamic reactive power source does not reach the upper limit value of the capacity of the medium-voltage side, wherein a calculation formula of the criterion of additionally arranging the priority side of the dynamic reactive power source is as follows:

when H is greater than or equal to 0A dynamic reactive power source is additionally arranged on the medium-voltage side of the three-coil transformer on the side a of the connecting line; when H is present<When 0, a dynamic reactive power source is additionally arranged on the medium-voltage side of the three-winding transformer on the side of the connecting line b, and the t is P_LmaxThe method for calculating the second power of the tie line is the same as the method for calculating the first power of the tie line when the first power of the tie line of the power grid reaches the maximum value;

step 4, returning to the step 3 when the asynchronous oscillation of the tie line occurs in the system according to the second power calculation result of the tie line; when the asynchronous oscillation of the tie line does not occur in the system and the calculation result meets the conveying requirement of the tie line, the configuration of the dynamic reactive power sources at the two sides of the tie line is finished; when the system does not generate the asynchronous oscillation of the tie line and the calculation result does not reach the transmission requirement of the tie line, the third power of the tie line is calculated after the transmission power of the tie line is increased to the transmission requirement value, wherein the formula for calculating the third power of the tie line is the same as the method for calculating the power of the first tie line;

step 5, when the asynchronous oscillation of the tie line does not occur and the tie line is stable in the power grid system according to the calculation result of the third power of the tie line, the configuration of the dynamic reactive power sources on the two sides of the tie line is finished; and (3) returning to the step 3 when the asynchronous oscillation of the tie line occurs in the power grid system.

9. The system of claim 7, wherein the second simulation unit determines the static stability limit of the tie line according to the determined configuration and preset operation mode of the voltage-side dynamic reactive power sources in the three-winding transformers on two sides of the tie line and the historical electrical quantity measured by the WAMS, and comprises the following steps:

according to the configuration and the preset operation mode of the voltage side dynamic reactive power sources in the three coils of transformers on two sides of the connecting line, in a quasi-real-time early warning environment, a first curve of the static stability limit of the active power of the connecting line after a given high-power locking fault changes along with time is determined, and the expression is as follows:

in the formula，Pmax_pre(t₁) A first curve of active power of the tie line over time after a given high power blocking fault;

where Pmax _ pre _ vertex is a first curve Pmax _ pre (t)₁) A peak value of (1);

according to the historical electrical quantity measured by the WAMS, determining a second curve of the change of the static stability limit of the active power of the tie line after the given high-power locking fault along with the time on the same historical day, wherein the expression is as follows:

in the formula, Pmax _ sm (t)₂) For the active power of the tie-line over time t after a given high-power blocking fault₂A second curve of variation, wherein t₂Is t of the same day in history₁Time of day;

where Pmax _ sm _ vertex is a second curve Pmax _ sm (t)₂) A peak value of (1);

determining a static stability limit of the connecting line according to the peak values of the first curve and the second curve, wherein the calculation formula is as follows:

Pmax_pre＝Min(Pmax_pre_vertex,Pmax_sm_vertex)。

10. the system of claim 9, wherein the determining and warning the quiet margin of the tie line according to the calculation result of the quiet stability limit of the tie line and the control limit of the tie line in the preset operation mode comprises:

according to the calculation result of the static stability limit of the tie line and the control limit of the tie line in a preset operation mode, a calculation formula for determining the static stability margin of the tie line is as follows:

Mg＝((Pmax_pre-Pcontrol)/Pmax)*100％

in the formula, Mg is the static stability margin of the tie line, Pcontrol is the control limit of the tie line in a preset operation mode, and Pmax _ pre is the determined static stability limit of the tie line;

and when the calculation result of the static stability margin of the connecting line is smaller than a preset safety threshold value, carrying out safe operation alarm of the power grid.