CN108336741B - Fault screening method and system for overall process voltage stability analysis - Google Patents
Fault screening method and system for overall process voltage stability analysis Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
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- H02J3/06—Controlling transfer of power between connected networks; Controlling sharing of load between connected networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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Abstract
The application provides a fault screening method and a system for overall process voltage stability analysis, wherein the fault screening method comprises the following steps: obtaining a static voltage stable serious fault set according to the obtained static power flow data of the power system; evaluating the static voltage stable severe fault set according to the acquired current operation mode to obtain a transient voltage stable severe fault set; and evaluating the transient voltage stability severe fault set to obtain a medium-long term voltage stability severe fault set. The application provides a voltage stability serious fault screening and sequencing method for three analysis stages of static, transient and medium and long periods, which enables the medium and long period dynamic simulation to play an important role in the fault scanning process, so that on one hand, the medium and long period analysis avoids scanning a large number of fault sets, ensures the calculation efficiency, and on the other hand, effectively screens out faults which cause medium and long period voltage instability.
Description
Technical Field
The application belongs to the field of power systems, and particularly relates to a fault screening method and system for overall process voltage stability analysis.
Background
In recent years, the power load of a receiving end power grid is rapidly increased, the construction of an internal main power plant is insufficient, meanwhile, the energy supply is far away from a load center, a large amount of electric energy needs to be conveyed in a long distance, and the problem of voltage stability is increasingly outstanding. Scanning faults and evaluating the severity are the basis for making auxiliary decisions and improving the stability of the power system. In a large-scale power system, the fault set to be scanned is large in scale, but serious faults possibly causing instability have small proportion, so that the fault set is required to be screened and ordered, and serious faults are selected from a large number of faults, so that a targeted auxiliary decision can be made.
The voltage stabilization analysis method mainly comprises static and dynamic analysis. The problem of voltage stabilization under large disturbances can be classified in time into transient (short-term) voltage stabilization and medium-long-term voltage stabilization. However, at present, the domestic and foreign literature utilizes static analysis or transient analysis means to screen and sort serious voltage stability faults, and medium-long term voltage instability possibly caused by faults cannot be fully considered under the condition of comprising medium-long term dynamic elements.
Disclosure of Invention
Aiming at the defect that the medium-long term analysis is difficult to cope with a large number of faults in the prior art, the application provides a fault screening method and a fault screening system for overall process voltage stability analysis, and serious faults are screened and sequenced through three analysis stages of static, transient and medium-long term. So that the medium-and-long-term voltage analysis means plays a role in voltage stability fault scanning and sequencing, and the capability of detecting medium-and-long-term voltage instability faults is improved.
A fault screening method for whole-process voltage stability analysis, comprising:
obtaining a static voltage stable serious fault set according to the obtained static power flow data of the power system;
evaluating the static voltage stable severe fault set according to the acquired current operation mode to obtain a transient voltage stable severe fault set;
and evaluating the transient voltage stability severe fault set to obtain a medium-long term voltage stability severe fault set.
Further, the obtaining a set of serious faults with stable static voltage according to the obtained static power flow data of the power system includes:
carrying out load flow calculation on the obtained static load flow data of the power system, and screening out overload faults;
calculating a power margin of the overload fault by using the continuous power flow;
and obtaining a static voltage stable serious fault set according to the power margin.
Further, the calculating the power margin of the overload fault by using the continuous power flow includes:
the power margin is calculated as follows:
wherein ,KP A power margin for overload faults; p is the initial operating point power value, P max Is the critical operating point power value.
Further, the obtaining the set of static voltage stable serious faults according to the power margin includes:
and taking the faults with the power margin smaller than the first threshold value or the power flow unconverged as elements in the static voltage stable serious fault set.
Further, the evaluating the set of static voltage stable serious faults according to the obtained current operation mode to obtain a set of transient voltage stable serious faults includes:
acquiring dynamic data used for transient voltage stability analysis according to a current operation mode;
performing transient analysis on the static voltage stable serious fault set according to the dynamic data to obtain stable faults;
performing voltage stability margin calculation on the stable fault to obtain a system voltage stability margin index;
and screening out a transient voltage stability serious fault set according to the system voltage stability margin index.
Further, the calculating the voltage stability margin for the stable fault to obtain a system voltage stability margin index includes:
the system voltage stability margin index is shown as follows:
VSM＝min{VSM t,i }
wherein VSM is a system voltage stability margin index; VSM (VSM) t,i Is the equivalent power margin of Thevenin; z is Z t , iThev ＝|Z t,iThev |∠β t,i The Thevenin equivalent impedance corresponding to the i node at the t moment is represented; z is Z t,Li ＝|Z t,Li |∠θ t,Li The load impedance of the i node at the t moment is represented; beta t,i and θt,Li Respectively, the impedance angle.
Further, the screening the transient voltage stability serious fault set according to the system voltage stability margin index includes:
and taking the faults with the system voltage stability margin index smaller than the second threshold value, the faults with the bus voltage lower than the third threshold value after the stable faults reach the stable balance point and the faults with the generator overexcitation after the stable faults reach the stable balance point as elements in the transient voltage stability serious faults.
Further, the medium-long term voltage stability data obtained by the combination are used for evaluating the transient voltage stability serious fault set to obtain the medium-long term voltage stability serious fault set, and the method comprises the following steps:
performing medium-and-long-term voltage stability simulation on stable faults in the transient voltage stability severe fault set according to the data;
and screening out a medium-and-long-term voltage stability serious fault set according to the simulation result.
Further, the screening the medium-long term voltage stability serious fault set according to the simulation result includes:
the apparent power and current effective value of the receiving end system or the load node after fault is T C Meeting the constraint condition in time, at T C After time, the voltage is lower than a fourth threshold, and the fault is a voltage instability fault:
in the simulation process, the maximum power angle difference of the generator is larger than 270 degrees, and the fault is a power angle instability fault;
the voltage instability faults and the power angle instability faults are used as medium-long term voltage stability serious fault sets.
Further, the method further comprises the following steps: making an auxiliary decision on the voltage instability fault;
the making of the auxiliary decision on the voltage instability fault comprises:
performing transient/medium-and-long-term voltage stability evaluation on the fault, and judging whether the voltage is unstable or not;
if the voltage is not unstable, outputting a load shedding place and a sum of load shedding of each cycle;
if the voltage is unstable, calculating the Thevenin equivalent power margin, calculating the cut load quantity at a key node, performing transient/medium-long-term voltage stability evaluation on the fault, and judging whether the voltage is unstable or not;
the key nodes are load nodes meeting constraint conditions.
Further, the calculating the Thevenin equivalent power margin and calculating the cut load amount at the key node includes:
the Thevenin equivalent power margin is calculated as follows:
wherein ,VSMt,i Is the equivalent power margin of Thevenin; z is Z t,iThev ＝|Z t,iThev |∠β t,i The Thevenin equivalent impedance corresponding to the i node at the t moment is represented; z is Z t,Li ＝|Z t,Li |∠θ t,Li The load impedance of the i node at the t moment is represented; beta t,i and θt,Li Respectively representing impedance angles;
the cut load was calculated as follows:
wherein ,to cut the load; VSM (VSM) lim Is a set value; />And the maximum transmission apparent power of the Thevenin equivalent system corresponding to the inode at the t moment is obtained.
Further, the constraint condition is as follows:
I k+1 ＞I k
S k+1 ＜S k
wherein S is apparent power; i is the effective value of the current; k and k+1 represent adjacent simulation moments.
A fault screening system for whole process voltage stability analysis, comprising:
the static module is used for obtaining a static voltage stable serious fault set according to the obtained static power flow data of the power system;
the transient state module is used for evaluating the static voltage stable serious fault set according to the acquired current operation mode to obtain a transient voltage stable serious fault set;
and the medium-and-long-term module is used for evaluating the transient voltage stability severe fault set to obtain the medium-and-long-term voltage stability severe fault set.
Further, the static module includes:
the power flow calculation sub-module is used for carrying out power flow calculation on the obtained static power flow data of the power system and screening out overload faults;
the first power margin submodule is used for calculating the power margin of the overload fault by utilizing continuous power flow;
and the static voltage stable severe fault set submodule is used for obtaining a static voltage stable severe fault set according to the power margin.
Further, a static voltage stabilization severe fault collecting sub-module for,
and taking the faults with the power margin smaller than the first threshold value or the power flow unconverged as elements in the static voltage stable serious fault set.
Further, the transient module includes:
the first acquisition sub-module is used for acquiring dynamic data used for transient voltage stability analysis according to the current operation mode;
the transient analysis submodule is used for carrying out transient analysis on the static voltage stable serious fault set according to the dynamic data to obtain stable faults;
the second power margin submodule is used for calculating the voltage stability margin of the stable fault to obtain a system voltage stability margin index;
and the transient voltage stable severe fault set submodule is used for screening out a transient voltage stable severe fault set according to the system voltage stability margin index.
Further, the transient voltage stabilization severe fault collection sub-module is configured to,
and taking the faults with the system voltage stability margin index smaller than the second threshold value, the faults with the bus voltage lower than the third threshold value after the stable faults reach the stable balance point and the faults with the generator overexcitation after the stable faults reach the stable balance point as elements in the transient voltage stability serious faults.
Further, the medium-and-long-term module includes:
the simulation sub-module is used for performing medium-and-long-term voltage stability simulation on the stable faults in the transient voltage stability serious faults according to the data;
and the screening sub-module is used for screening the medium-and-long-term voltage stability serious fault set.
Further, the screening submodule is used for,
the apparent power and current effective value of the receiving end system or the load node after fault is T C Meeting the constraint condition in time, at T C After time, the voltage is lower than a fourth threshold, and the fault is a voltage instability fault:
in the simulation process, the maximum power angle difference of the generator is larger than 270 degrees, and the fault is a power angle instability fault;
the voltage instability faults and the power angle instability faults are used as medium-long term voltage stability serious fault sets.
Further, the method further comprises the following steps: and the auxiliary decision module is used for carrying out auxiliary decision on the voltage instability fault.
Further, the auxiliary decision module includes:
the judging sub-module is used for carrying out transient/medium-long-term voltage stability evaluation on the faults and judging whether the voltage is unstable or not;
the non-destabilization submodule is used for outputting a load shedding place and the sum of the load shedding of each cycle if the voltage is not destabilized;
the destabilizing sub-module is used for calculating the Thevenin equivalent power margin and the cut load quantity at the key node if the voltage is unstable, carrying out transient/medium-long-term voltage stability evaluation on the fault, and judging whether the voltage is unstable or not;
the key nodes are load nodes meeting constraint conditions.
Compared with the closest prior art, the technical scheme provided by the application has the following beneficial effects:
the application provides a voltage stability serious fault screening and sequencing method for three analysis stages of static, transient and medium and long periods, so that the medium and long period dynamic simulation plays an important role in the fault scanning process.
The technical scheme provided by the application only carries out medium-and-long-term voltage stability analysis on stable faults in transient voltage stability serious fault sets, so that the medium-and-long-term analysis avoids scanning a large number of fault sets, and the calculation efficiency is ensured; faults which cause medium-and-long-term voltage instability are effectively screened out, so that the voltage stability analysis and decision-making capability of power system dispatching operators is improved.
The technical scheme provided by the application only carries out continuous power flow calculation aiming at faults causing overload, so that the number of faults needing to be calculated in continuous power flow can be greatly reduced, and faults with lower power margin can be effectively detected.
Drawings
FIG. 1 is a flow chart of the present application;
FIG. 2 is a flowchart of a method for screening and sorting critical faults of voltage stabilization during the whole process according to an embodiment of the present application;
FIG. 3 is a static voltage stabilizing severe fault set screening and sorting flow according to an embodiment of the present application;
FIG. 4 is a Thevenin equivalent circuit diagram at node i in an embodiment of the present application;
FIG. 5 is a flow chart of an auxiliary decision for voltage instability fault according to an embodiment of the present application;
FIG. 6 is a graph comparing transient and mid-to-long term voltage response curves under cascading failure according to an embodiment of the present application;
fig. 7 is a graph showing the voltage response after implementation of the cascading failure-aid decision in accordance with an embodiment of the present application.
Detailed Description
The application is described in further detail below with reference to the accompanying drawings. For the purpose of making the objects, technical solutions and advantages of the embodiments of the present application more apparent, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments of the present application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
Embodiment 1, the present application provides a fault screening method for overall process voltage stability analysis, as shown in fig. 1, including:
obtaining a static voltage stable serious fault set according to the obtained static power flow data of the power system;
evaluating the static voltage stable severe fault set according to the acquired current operation mode to obtain a transient voltage stable severe fault set;
and evaluating the transient voltage stability severe fault set to obtain a medium-long term voltage stability severe fault set.
Embodiment 2, the present application provides a fault screening system for whole-process voltage stability analysis, including:
the static module is used for obtaining a static voltage stable serious fault set according to the obtained static power flow data of the power system;
the transient state module is used for evaluating the static voltage stable serious fault set according to the acquired current operation mode to obtain a transient voltage stable serious fault set;
and the medium-and-long-term module is used for evaluating the transient voltage stability severe fault set to obtain the medium-and-long-term voltage stability severe fault set.
Further, the static module includes:
the power flow calculation sub-module is used for carrying out power flow calculation on the obtained static power flow data of the power system and screening out overload faults;
the first power margin submodule is used for calculating the power margin of the overload fault by utilizing continuous power flow;
and the static voltage stable severe fault set submodule is used for obtaining a static voltage stable severe fault set according to the power margin.
Further, a static voltage stabilization severe fault collecting sub-module for,
and taking the faults with the power margin smaller than the first threshold value or the power flow unconverged as elements in the static voltage stable serious fault set.
Further, the transient module includes:
the first acquisition sub-module is used for acquiring dynamic data used for transient voltage stability analysis according to the current operation mode;
the transient analysis submodule is used for carrying out transient analysis on the static voltage stable serious fault set according to the dynamic data to obtain stable faults;
the second power margin submodule is used for calculating the voltage stability margin of the stable fault to obtain a system voltage stability margin index;
and the transient voltage stable severe fault set submodule is used for screening out a transient voltage stable severe fault set according to the system voltage stability margin index.
Further, the transient voltage stabilization severe fault collection sub-module is configured to,
and taking the faults with the system voltage stability margin index smaller than the second threshold value, the faults with the bus voltage lower than the third threshold value after the stable faults reach the stable balance point and the faults with the generator overexcitation after the stable faults reach the stable balance point as elements in the transient voltage stability serious faults.
Further, the medium-and-long-term module includes:
the simulation sub-module is used for performing medium-and-long-term voltage stability simulation on the stable faults in the transient voltage stability serious faults according to the data;
and the screening sub-module is used for screening the medium-and-long-term voltage stability serious fault set.
Further, the screening submodule is used for,
post-failure receiver system orThe apparent power and current effective value of the load node is at T C Meeting the constraint condition in time, at T C After time, the voltage is lower than a fourth threshold, and the fault is a voltage instability fault:
in the simulation process, the maximum power angle difference of the generator is larger than 270 degrees, and the fault is a power angle instability fault;
the voltage instability faults and the power angle instability faults are used as medium-long term voltage stability serious fault sets.
Further, the method further comprises the following steps: and the auxiliary decision module is used for carrying out auxiliary decision on the voltage instability fault.
Further, the auxiliary decision module includes:
the judging sub-module is used for carrying out transient/medium-long-term voltage stability evaluation on the faults and judging whether the voltage is unstable or not;
the non-destabilization submodule is used for outputting a load shedding place and the sum of the load shedding of each cycle if the voltage is not destabilized;
the destabilizing sub-module is used for calculating the Thevenin equivalent power margin and the cut load quantity at the key node if the voltage is unstable, carrying out transient/medium-long-term voltage stability evaluation on the fault, and judging whether the voltage is unstable or not;
the key nodes are load nodes meeting constraint conditions.
Example 3, a flowchart of the overall process voltage stabilization fault screening and sequencing method is shown in fig. 2. The method comprises the following steps:
step 1: static voltage stability evaluation is carried out to obtain a static serious fault set;
step 2: the transient voltage stability is evaluated to obtain a transient serious fault set;
step 3: the medium-long term voltage stability is evaluated to obtain a medium-long term serious fault set;
step 4: voltage instability fault assist decision.
Step 1 comprises the following steps, as shown in fig. 3:
step 1-1: acquiring static power flow data of a current operation mode of the power system;
step 1-2: the N-1, N-2 break power flow is rapidly estimated by utilizing a method of modifying an admittance array, and faults which enable the line current to approach or exceed the rated value are screened out to be overload faults;
step 1-3: and (3) carrying out system power margin calculation on overload faults by adopting continuous power flow, wherein the power margin is less than 10% or the faults with non-converged power flow are used as a static voltage stable serious fault set. With a regional load active power margin K P For example, the power margin is
Wherein P is the initial operating point power value, P max Is the critical operating point power value.
In step 1-2, the line current may be far lower than the rated current in the actual system, so that the load value of each line after the fault is referred to when the fault is screened, and the load increasing proportion of other lines caused by the fault is not referred to, thereby having more practical value.
In the step 1-3, continuous power flow calculation is only carried out for faults causing overload, so that the number of faults required to be calculated for continuous power flow can be greatly reduced, and faults with lower power margin can be effectively detected.
Step 2 comprises the following steps:
step 2-1: dynamic data such as a generator, an induction motor load and the like used for transient voltage stability analysis are obtained according to a current operation mode, and data such as fault time and the like are provided according to a static voltage stability serious fault set;
step 2-2: transient analysis is performed towards the static voltage stable serious fault set and faults concerned by the dispatcher. And for stable faults, after the system reaches a new balance point, calculating the Thevenin equivalent system parameters of each load node seen from the system. And calculating the power margin in each equivalent system, and selecting the minimum margin from the power margin as a system voltage stability margin index.
Defining the power margin of the i-node Thevenin equivalent system at the t moment as
wherein ,St,i Andand the current transmission apparent power and the maximum transmission apparent power of the Thevenin equivalent system corresponding to the inode at the t moment are obtained. The Thevenin equivalent power margin can be expressed as
wherein ,Zt,iThev ＝|Z t,iThev |∠β t,i Represents Thevenin equivalent impedance corresponding to i node at t moment, Z t,Li ＝|Z t,Li |∠θ t,Li The load impedance of the inode at time t is shown.
For stable faults, firstly, calculating the power margin VSM of the Thevenin equivalent system of each node at the end time EndT of the simulation after reaching a new balance point EndT,i Taking the minimum value as the voltage stability margin index VSM of the system under the fault, namely
VSM:＝min{VSM EndT,i }
Step 2-3: the low system voltage stability margin index (VSM lower than 0.80) after the fault indicates that the power generation change and the bus load power change are easier to cause voltage instability under the new disturbance; reaching a stable equilibrium point bus voltage below 0.9pu after a fault indicates that the fault is more likely to cause medium-to-long term voltage instability; the stable fault may cause the system to reach an equilibrium point and then over-excite the generator, and the over-excitation limit may be triggered and cause voltage instability in the middle-long period dynamic process. The three faults are serious faults of transient voltage stability, and are required to be checked in a medium-long-term voltage stability evaluation stage.
In step 2-2, for a stable fault, calculating the Thevenin equivalent system parameters of each node at the end time EndT of the simulation after reaching a new balance point, then calculating the power margin of each equivalent system, and taking the minimum value as the voltage stability margin index of the system under the fault. The lower the system voltage stability margin index after the fault is, the more easily the voltage instability is caused by the power generation change and the bus load power change under the new disturbance.
In the step 2-3, from the voltage stability margin index, the bus voltage after reaching the stable balance point after the fault, whether the generator overexcitation exists or not and the like are evaluated, and whether the generator overexcitation exists or not is determined, and the generator is checked at a medium-long-term voltage stability evaluation node.
Step 3 comprises the following steps:
step 3-1: the method comprises the steps of preparing medium-long term dynamic data such as over-excitation limit of an excitation system and a boiler for medium-long term voltage stability analysis according to a current operation mode;
step 3-2: performing medium-long term voltage stability simulation calculation for stable faults in a transient voltage stability severe fault set, screening the medium-long term severe fault set, including: medium-long term voltage instability faults and faults with lower voltage stability margin indexes.
And judging the voltage instability by using a power current reverse criterion. If the receiving end system or the load voltage is unstable, the receiving end system or the load voltage is in a voltage unstable area in the whole voltage dropping process, namely: when the load tries to get more power by increasing the current, the load power decreases instead. Thus, if the apparent power S (or active power) and the current Iavailable value of the receiving end system or the load node after the fault are within a certain time (set as T C ) Satisfy the following requirements
I k+1 ＞I k &S k+1 ＜S k
And T is C After that, the voltage is lower than 0.8pu (for transient voltage stability evaluation) or 0.9pu (for medium-long term voltage stability evaluation), the voltage is unstable. Where k and k+1 represent adjacent simulation moments. In order to get rid of the situation where the voltage recovers quickly after the fault, it is prescribed that the power current reversal relationship needs to last for a while, and the voltage should be below a certain limit. The criterion can play an important role in distinguishing whether the instability of the power system is dominant in power angle instability or dominant in voltage instability. If the maximum power angle difference of the generator is more than 270 degrees in the simulation process, andthe simulation time sequence is prior to the voltage instability criterion, and the power system instability which is the dominant power angle instability is considered.
In the step 3-2, the medium-long term voltage stability analysis is performed only for stable faults in the transient voltage stability serious fault set, so that on one hand, the medium-long term analysis avoids scanning a large number of fault sets, the calculation efficiency is ensured, and on the other hand, the faults which cause the medium-long term voltage instability are effectively screened out. And combining the voltage instability criterion with the maximum power angle difference to distinguish the voltage instability fault and the power angle instability fault.
Step 4 includes the following steps, as shown in fig. 5:
step 4-1: performing transient/medium-long-term voltage stability evaluation on the fault, if the voltage is stable, turning to step 4-2, otherwise turning to step 4-3;
step 4-2: outputting the sum of load shedding places and the load shedding of each cycle;
step 4-3: calculating the Thevenin equivalent power margin at the balance point or EndT after the fault;
step 4-4: the cut load is calculated at the critical node. The load nodes meeting the criteria are regarded as voltage instability key nodes; to make the Thevenin equivalent power margin of the load node i at the moment t higher than a set value VSM lim The apparent power of the load to be cut is
Step 4-5: at key nodes in proportion toAnd (4) compiling an active and reactive load-shedding card, and returning to the step 4-1.
Example 4, failure screening was performed on the Liaoning grid. The Liaoning grid is located in the south of the northeast grid and is a typical receiving grid. The northeast power grid has more than 2000 nodes, and the Liaoning power grid has more than 500 nodes. Test data in three modes are formed on the basis of the winter mode of the northeast power grid in a certain year, and mode 1: a base mode; mode 2: the load of the near-end area of the direct current receiving end of the Huliao (including Anshan, benxi, liaoyang, yingkou and Fushun five areas) is increased by 20 percent; mode 3: the load of the near-end area of the direct current receiving end of the Huliao is increased by 40 percent.
Static severe fault set screening and ordering are performed in these three ways using the method of fig. 3, respectively. This example uses an excess current rating as an overload, and for a default line current rating, 500kV line current rating 2000A and 220kV line rating 1000A are adopted. When the tide calculation is carried out, the constant power factor of all the subareas loads in the Liaoning power grid is increased, the balanced active load of the local generator is increased, and after all the generators reach the upper limit of the active output, the balancing machine bears the active increase. The number of overload faults and the number of static severe faults in the three modes are shown in table 1. In mode 1, static severe faults are concentrated in the sunk partition because the partition is more heavily loaded than other partitions. The five partitions under mode 3 are loaded, static catastrophic failures within the partitions are increased, and the set of severe failures ordered earlier, the (part of the) set of severe failures under mode 3 is shown in table 2.
TABLE 1 number of overload faults and number of static severe faults in three modes
| Mode 1 | Mode 2 | Mode 3 | |
| Number of overload faults | 20 | 38 | 56 |
| Static severe failureNumber of | 11 | 29 | 54 |
| Severe fault concentration area | Shenyang | Near the receiving end | Near the receiving end |
TABLE 2 Severe Fault set ordering (partial) under mode 3
| Ordering of | Failure of | K P | Belonging to a partition |
| 6 | Liaoping-Liaoning Shen Dong kV double circuit line N-2 | Non-convergence | Smooth and smooth |
| 7 | Liaoyang-Liaoshaling 500kV double circuit line N-2 | Non-convergence | Liaoyang |
| 8 | LiaopuHe-Liao Sha Ling 500kV double-circuit line N-2 | Non-convergence | Shenyang |
| 9 | Liaoqijia-Liao Shen Dong 220kV double-circuit line N-2 | Non-convergence | Shenyang |
| 10 | Liao Li Danzhai-Liao Xujia 220kV line N-1 | 5.57％ | Smooth and smooth |
| 11 | Liaocheng-Liaonan Feng 220kV double circuit line N-2 | 5.66％ | Benxi (Chinese character) |
B. All the subareas loads in the Liaoning power grid are set to be 50% of asynchronous motor loads and 50% of constant impedance loads. In the medium-long term voltage stability evaluation stage, liaoning network dynamic data comprise a boiler model, a boiler turbine coordination control model and an overexcitation limiting model which takes a heat value which is kept for 10 seconds under the condition of 2 times of rated excitation current as an action basis.
The duration Tc used with the voltage instability criterion is selected through a plurality of tests on the voltage instability faults, and when the Liaoning network is tested for a plurality of times and the Tc is selected to be 0.5 seconds, the voltage instability criterion can effectively judge the voltage instability faults.
Setting static serious faults as three-phase short circuits and then exiting operation in transient state and medium-long term evaluation stages, wherein the fault removal time of a 500kV line is 0.1 second; the 220kV line fault removal time was 0.12 seconds. Besides the static serious faults screened out in the static voltage stability evaluation stage, the faults focused by operators are added to serve as fault sets for transient state and medium-long-term voltage stability evaluation stage. These faults include the complete stop of the 500kV Liaoshan transformer substation, the Huliao direct current bipolar lockout, the cascading faults in Shen Dong-Pu He areas, etc.
The partial results of the transient and medium-to-long term voltage stability severe fault screening and sequencing in the three modes are shown in table 3. The static voltage stable severe fault in mode 3 failed to cause instability in transient analysis, but some faults were over-excited or have a low stability margin indicator (VSM below 0.8), and these faults are listed in the table. And the excitation current is gradually recovered to the rated value in the late simulation stage after checking the excitation current in the medium-long-term stability evaluation stage, the over-excitation limit is not triggered, and the system keeps stable voltage.
TABLE 3 partial results of transient and medium-to-long term voltage stability severe fault screening and sequencing in three modes
In three ways, during the transient analysis phase, a part of operators pay attention to the faults, so that the power angle is unstable, and the other part of faults are stable, but cause the over-excitation of the generator. The over-excitation fault is checked in the middle-long period analysis stage, and partial faults finally lead to voltage instability.
And Shen Dong-Pu He region cascading failure simulates that a 220kV wind power-containing receiving end region power grid in a railway region generates cascading failure. The area is powered by Pu He and Shen Dong kV substations, and after cascading failure, a receiving area which is only connected with a main network by the Pu He and 500kV substations through a single-circuit 220kV line is formed, and the receiving area contains Liaoqing river thermal power generating unit.
Under the condition of mode 1, in the transient voltage stability evaluation stage, the transient voltage of the system is stable under the cascading failure of Shen Dong-Pu He region, but the exciting current of the Liaoqing river G7 of the generator is 1.4 times of the rated value, so that the generator is identified as the failure checked by medium-long term voltage stability evaluation. In the medium-long voltage stability evaluation stage, the generator Liaoqing river G7 is subjected to over-excitation limitation in 32.3 seconds, then is cut off, and the reactive power of the receiving end area is suddenly short, so that the voltage is unstable. The transient and medium-to-long term voltage response curve pairs for cascading failures in regions Shen Dong-Pu He are shown in fig. 6.
The load buses such as Liaohushi table meet the voltage instability criteria at about 32.9 seconds, and the key nodes of the voltage instability and the time for meeting the criteria are shown in table 4.
TABLE 4 Voltage instability Key node and timetable meeting criteria
| Bus name | Voltage (kV) | Time(s) |
| Liaoniu sentry 22 | 220.0 | 32.9 |
| Liaofeoling change | 220.0 | 32.9 |
| Liaoxifeng 22 | 220.0 | 32.9 |
| Liaohu stone table | 220.0 | 32.9 |
| Liaochang figure 22 | 220.0 | 33.7 |
| Liaokaiyuan 22 | 220.0 | 33.7 |
| Liaoning citizen 22 | 220.0 | 32.9 |
C. Power margin lower limit VSM used for auxiliary decision-making calculation formula lim The voltage is selected to be 0.8, and multiple simulation tests on the Liaoning power grid show that the VSM is maintained above 0.8, so that the voltage stability can be effectively ensured.
Under the condition of mode 1, aiming at the cascading failure of the Shen Dong-Pu He region, load shedding is carried out on the voltage instability key node according to the method of fig. 5, and the auxiliary decision is shown in table 5. The auxiliary decision is implemented after the cascading failure, and after the load is cut, the generator Liaoqinghe G7 is free from over-excitation, so that the generator is prevented from being cut off, the voltage is kept at a higher level, and the power system can keep the voltage stable. The voltage response curves after implementation of the cascading failure aid decisions in regions Shen Dong-Pu He are shown in fig. 7.
Table 5 auxiliary decision table
D. The embodiment shows that the faults with lower power margin can be effectively identified by utilizing the open-close power flow and the continuous power flow in the static analysis stage, and the static voltage stable serious fault set can be reasonably adjusted according to the regional load change. In the transient analysis stage, a static voltage stability serious fault set and faults concerned by operators are checked, and faults with lower over-excitation and voltage stability margin can be screened out by utilizing voltage stability margin indexes based on Thevenin equivalent tracking, and the faults are partially screened outThe fault is a fault that may cause medium-to-long voltage instability. FIG. 4 is a Thevenin equivalent circuit at node i, where E t,iThev Representing the equivalent potential of Thevenin, Z t,iThev Representing the equivalent impedance of the thevenin,represents node voltage, +_>Indicating load current, Z t,Li Representing the load impedance. In the medium-long term analysis stage, under the condition of considering the medium-long term dynamic models such as over-excitation limit, boiler steam turbine and the like, the medium-long term voltage instability fault can be screened out and the voltage instability key node can be found by utilizing the power current reverse voltage instability criterion. Aiming at the voltage instability fault, an auxiliary decision is made at a key node, and the system can keep voltage stable after implementation.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical aspects of the present application and not for limiting the same, and although the present application has been described in detail with reference to the above embodiments, it should be understood by those of ordinary skill in the art that: modifications and equivalents may be made to the specific embodiments of the application without departing from the spirit and scope of the application, which is intended to be covered by the scope of the claims.
Claims (10)
1. The fault screening method for the overall process voltage stability analysis is characterized by comprising the following steps of:
obtaining a static voltage stable serious fault set according to the obtained static power flow data of the power system;
evaluating the static voltage stable severe fault set according to the acquired current operation mode to obtain a transient voltage stable severe fault set;
evaluating the transient voltage stability severe fault set to obtain a medium-long term voltage stability severe fault set;
the obtaining a set of serious faults with stable static voltage according to the obtained static power flow data of the power system comprises the following steps:
carrying out load flow calculation on the obtained static load flow data of the power system, and screening out overload faults;
calculating a power margin of the overload fault by using the continuous power flow;
obtaining a static voltage stable serious fault set according to the power margin;
the step of evaluating the static voltage stable serious fault set according to the acquired current operation mode to obtain a transient voltage stable serious fault set, comprising the following steps:
acquiring dynamic data used for transient voltage stability analysis according to a current operation mode;
performing transient analysis on the static voltage stable serious fault set according to the dynamic data to obtain stable faults;
performing voltage stability margin calculation on the stable fault to obtain a system voltage stability margin index;
screening out a transient voltage stability serious fault set according to the system voltage stability margin index;
the step of evaluating the transient voltage stability severe fault set to obtain a medium-long term voltage stability severe fault set comprises the following steps:
performing medium-and-long-term voltage stability simulation on stable faults in the transient voltage stability severe fault set according to the data;
and screening out a medium-and-long-term voltage stability serious fault set according to the simulation result.
2. A fault screening method for whole process voltage stability analysis according to claim 1, wherein said calculating a power margin for said overload fault using continuous power flow comprises:
the power margin is calculated as follows:
wherein ,KP A power margin for overload faults; p is the initial operating point power value, P max Is the critical operating point power value.
3. The fault screening method for whole-process voltage stability analysis according to claim 1, wherein said obtaining a set of static voltage stability severe faults based on said power margin comprises:
and taking the faults with the power margin smaller than the first threshold value or the power flow unconverged as elements in the static voltage stable serious fault set.
4. The fault screening method for whole-process voltage stability analysis according to claim 1, wherein the step of calculating a voltage stability margin for the stable fault to obtain a system voltage stability margin index comprises:
the system voltage stability margin index is shown as follows:
VSM＝min{VSM t,i }
wherein VSM is a system voltage stability margin index; VSM (VSM) t,i Is the equivalent power margin of Thevenin; z is Z t,iThev ＝|Z t,iThev |∠β t,i The Thevenin equivalent impedance corresponding to the i node at the t moment is represented; z is Z t,Li ＝|Z t,Li |∠θ t,Li The load impedance of the i node at the t moment is represented; beta t,i and θt,Li Respectively, the impedance angle.
5. The fault screening method for whole-process voltage stability analysis according to claim 1, wherein the screening the transient voltage stability serious fault set according to the system voltage stability margin index comprises:
and taking the faults with the system voltage stability margin index smaller than the second threshold value, the faults with the bus voltage lower than the third threshold value after the stable faults reach the stable balance point and the faults with the generator overexcitation after the stable faults reach the stable balance point as elements in the transient voltage stability serious faults.
6. The fault screening method for whole-process voltage stability analysis according to claim 1, wherein the screening of the medium-long term voltage stability serious fault set according to the simulation result comprises:
the apparent power and current effective value of the receiving end system or the load node after fault is T C Meeting the constraint condition in time, at T C After time, the voltage is lower than a fourth threshold, and the fault is a voltage instability fault:
in the simulation process, the maximum power angle difference of the generator is larger than 270 degrees, and the fault is a power angle instability fault;
the voltage instability faults and the power angle instability faults are used as medium-long term voltage stability serious fault sets.
7. A fault screening method for whole process voltage stability analysis as claimed in claim 1, further comprising: making an auxiliary decision on the voltage instability fault;
the making of the auxiliary decision on the voltage instability fault comprises:
performing transient/medium-and-long-term voltage stability evaluation on the fault, and judging whether the voltage is unstable or not;
if the voltage is not unstable, outputting a load shedding place and a sum of load shedding of each cycle;
if the voltage is unstable, calculating the Thevenin equivalent power margin, calculating the cut load quantity at a key node, performing transient/medium-long-term voltage stability evaluation on the fault, and judging whether the voltage is unstable or not;
the key nodes are load nodes meeting constraint conditions.
8. The fault screening method of a full process voltage stability analysis of claim 7 wherein said calculating a davin equivalent power margin and calculating a cut load at key nodes comprises:
the Thevenin equivalent power margin is calculated as follows:
wherein ,VSMt,i Is the equivalent power margin of Thevenin; z is Z t,iThev ＝|Z t,iThev |∠β t,i The Thevenin equivalent impedance corresponding to the i node at the t moment is represented; z is Z t,Li ＝|Z t,Li |∠θ t,Li The load impedance of the i node at the t moment is represented; beta t,i and θt,Li Respectively representing impedance angles;
the cut load was calculated as follows:
wherein ,to cut the load; VSM (VSM) lim Is a set value; />And the maximum transmission apparent power of the Thevenin equivalent system corresponding to the inode at the t moment is obtained.
9. A fault screening method for whole process voltage stability analysis according to claim 6 or 7, wherein the constraint is as follows:
I k+1 ＞I k
S k+1 ＜S k
wherein S is apparent power; i is the effective value of the current; k and k+1 represent adjacent simulation moments.
10. A fault screening system for whole process voltage stability analysis, comprising:
the static module is used for obtaining a static voltage stable serious fault set according to the obtained static power flow data of the power system;
the transient state module is used for evaluating the static voltage stable serious fault set according to the acquired current operation mode to obtain a transient voltage stable serious fault set;
the medium-long term module is used for evaluating the transient voltage stability severe fault set to obtain a medium-long term voltage stability severe fault set;
the static module includes:
the power flow calculation sub-module is used for carrying out power flow calculation on the obtained static power flow data of the power system and screening out overload faults;
the first power margin submodule is used for calculating the power margin of the overload fault by utilizing continuous power flow;
the static voltage stable severe fault set submodule is used for obtaining a static voltage stable severe fault set according to the power margin;
the transient module includes:
the first acquisition sub-module is used for acquiring dynamic data used for transient voltage stability analysis according to the current operation mode;
the transient analysis submodule is used for carrying out transient analysis on the static voltage stable serious fault set according to the dynamic data to obtain stable faults;
the second power margin submodule is used for calculating the voltage stability margin of the stable fault to obtain a system voltage stability margin index;
the transient voltage stable severe fault collection sub-module is used for screening out a transient voltage stable severe fault collection according to the system voltage stability margin index;
the medium-and-long-term module comprises:
the simulation sub-module is used for performing medium-and-long-term voltage stability simulation on the stable faults in the transient voltage stability serious faults according to the data;
and the screening sub-module is used for screening the medium-and-long-term voltage stability serious fault set.
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