CN110112732B - Method for calculating fault probability of nuclear power generating unit based on interval probability network source correlation - Google Patents

Method for calculating fault probability of nuclear power generating unit based on interval probability network source correlation Download PDF

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CN110112732B
CN110112732B CN201910421128.8A CN201910421128A CN110112732B CN 110112732 B CN110112732 B CN 110112732B CN 201910421128 A CN201910421128 A CN 201910421128A CN 110112732 B CN110112732 B CN 110112732B
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黄东山
王斌
林翔宇
王晓明
李明珀
彭博雅
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Electric Power Research Institute of Guangxi Power Grid Co Ltd
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Abstract

The invention belongs to the field of reliability evaluation of power equipment, and particularly relates to a method for calculating fault probability of a nuclear power unit based on interval probability network source correlation. The method adopts the interval probability form to express the fault probability of the nuclear power unit, fully deals with the restriction that the fault sample of the nuclear power unit is lack and difficult to obtain, makes up the limitation and deficiency of adopting accurate probability under the condition of small sample, and more reasonably provides the fault possibility interval of the nuclear power unit. Compared with the traditional independent fault probability model of the thermal power generating unit, the fault probability model not only considers the fault probability caused by self factors such as nuclear power generating unit aging, but also considers the influence of network source related characteristics, namely the change of the power grid operation parameters on the fault probability of the nuclear power generating unit, and the obtained fault probability parameters have higher reliability.

Description

Method for calculating fault probability of nuclear power generating unit based on interval probability network source correlation
Technical Field
The invention belongs to the field of reliability evaluation of power equipment, and particularly relates to a method for calculating fault probability of a nuclear power unit based on interval probability network source correlation.
Background
With the construction of extra-high voltage, alternating current-direct current hybrid connection, renewable energy access and the construction of global energy internet, the problem of safe and stable operation of an electric power system is increasingly prominent, and rapid and accurate reliability and risk assessment of the electric power system is urgent. The failure or outage of the power equipment is the root cause of failure of the power system, the safe operation of the power equipment is the basis of the safe operation of the system, the failure probability of the equipment depends on the factors such as the health condition, the external environmental condition, the system operation state and the like, and the establishment of a failure probability model of the power equipment is the basic problem for system reliability and risk assessment.
The research on the fault probability model of the power equipment is an important content in the field of equipment reliability evaluation, and the traditional equipment fault probability index is mainly applied to conventional reliability analysis such as power grid planning and equipment maintenance, so that the long-term stability of equipment operation is reflected, and the influence of short-time operation condition change on equipment fault is ignored. The failure probability of the equipment in the traditional reliability evaluation is usually replaced by the steady state probability obtained through statistics, the problems of low reliability, application lag and the like exist, and the problems are well solved through the occurrence of technologies such as a time-varying equipment failure probability model, a failure probability model considering the external environment, a failure probability model considering the operating condition and the like.
The generator is a key device in the power system, the health level and the operation condition of the generator are directly related to the safe and stable operation level of the whole system, and the research on the fault probability model of the generator is of great significance. In the traditional research, the measurement of the fault probability of the unit under the operation condition is directly expressed by using a Forced Outage Rate (FOR) in some cases, and is described by using an Outage Replacement Rate (ORR) in some cases. In addition, a student establishes a condition-dependent short-term generator reliability model, and factors such as aging failure and accidental failure are considered.
The single machine capacity of the nuclear power unit is large, and due to the particularity of nuclear energy, the failure or outage of the nuclear power unit easily has great influence on a power grid. At present, researches on the failure probability indexes of nuclear power generating units are rare, and the conventional method is to treat the nuclear power generating units by equivalently using the nuclear power generating units as traditional thermal power generating units. However, a strong interaction effect exists between the nuclear power unit and the power grid, the nuclear power unit is very sensitive to power grid disturbance or faults, an independent fault probability model is generally adopted in the conventional reliability analysis for the power unit, an average fault probability index is adopted, and the influence of the frequency of a nuclear power unit access point and voltage fluctuation on the unit fault probability is not considered, so that the conventional power unit fault probability model cannot reasonably represent the characteristics of the nuclear power unit, and a dependent fault probability model of the nuclear power unit needs to be established by considering the correlation of a grid source.
However, the statistical samples are few, the statistical period is long, the lack of historical fault data is a difficult problem which always puzzles the reliability data statistics of the power system, and the problem of the nuclear power unit on the aspect is particularly prominent. The nuclear power generation mode is different from the conventional power generation mode, and the confidentiality requirement is higher, so that the fault data of a nuclear power unit is usually difficult to obtain. In addition, the number of the nuclear power generating units is far less than that of the conventional thermal power generating units, and the scarcity of the nuclear power generating unit fault samples is further increased.
Disclosure of Invention
The invention provides a method for calculating the fault probability of a nuclear power generating unit based on interval probability network correlation, and aims to solve the problems that a traditional generating unit fault probability model cannot reasonably represent the characteristics of the nuclear power generating unit, the number of fault samples of the nuclear power generating unit is rare and difficult to obtain and the like in the field of reliability evaluation of power equipment.
The interval probability is also called as non-precise probability, which is a natural popularization of precise probability, and the core idea is to replace precise single-value probability with a probability interval of random event occurrence. The interval probability is an effective method for probability estimation under the condition of insufficient sample information, wherein an Inaccurate Dirichlet Model (IDM) is an effective interval probability statistical method.
The nuclear power unit has the characteristics of large single-machine capacity, high nuclear safety requirement, sensitivity of a nuclear island to power grid disturbance, long shutdown refueling time and the like, the nuclear power unit can have serious influence on each other after being connected into a power grid, and voltage and frequency are main parameters of the power grid influencing the nuclear power unit. When a power grid fails or is disturbed, the frequency and the voltage of an access point of the nuclear power unit fluctuate, so that the safe and stable operation of the nuclear power unit is influenced, and when the fluctuation degree exceeds an allowable range, the nuclear power unit can be shut down or stopped emergently, so that the power grid fault is further worsened.
Based on the characteristics of the mathematical tools and the nuclear power unit, the invention adopts the following technical scheme:
a method for calculating the fault probability of a nuclear power generating unit based on interval probability network source correlation comprises the following steps:
s1: determining the interval fault probability of various devices in the researched power grid containing the nuclear power generating unit; the equipment comprises a generator, a transformer and an overhead transmission line; according to historical operation statistical data of various devices in the power grid, a non-precise Dirichlet model is applied to estimate the interval fault probability of the three types of power devices;
s2: determining the voltage protection characteristic and the frequency protection characteristic of the nuclear power unit; giving partial frequency, voltage allowable range and tolerance time when the nuclear power unit is connected into a power grid to operate, and judging whether the nuclear power unit is in a normal operation state or a generator tripping operation quits according to the frequency and voltage level of the nuclear power unit access point;
s3: determining the average failure probability of the nuclear power unit caused by aging and defect factors;
s4: according to the characteristic that when the voltage and the frequency of an access point of the nuclear power unit are increased or decreased to a protection fixed value, a protection device of the nuclear power unit acts, and the action time limit of protection is reduced along with the deepening of the out-of-limit degree of the frequency and the voltage, and the probability that the nuclear power unit generator tripping operation is increased, the relation between the fault probability of the nuclear power unit and the change of the power grid frequency and the change of the voltage at the generator end of the nuclear power unit is respectively given, a sectional curve is obtained, and a corresponding calculation formula is given. Under given frequency and voltage levels, respectively obtaining the fault probability corresponding to the frequency and the fault probability corresponding to the voltage of the nuclear power unit, and taking the higher probability value of the two as the dependent fault probability related to the nuclear power unit network source;
s5: carrying out load flow calculation on the initial operation state of the power grid containing the nuclear power generating unit, and executing subsequent steps if the load flow is converged; if the power flow is not converged, the output of a generator of the power grid and parameters of balance nodes need to be adjusted, and power flow calculation is continued until the power flow is converged;
s6: sequentially carrying out N-1 fault simulation on three types of equipment in a power grid through a power system analysis software tool, checking the frequency and voltage level of an access point of a nuclear power unit after the fault occurs, and contrasting the frequency and voltage protection characteristics of the nuclear power unit to obtain the fault probability of the nuclear power unit under the fault;
s7: and integrating the interval fault probability of each device and the probability of the nuclear power unit failing when each device fails, and superposing the influences of aging and defect factors of the unit to obtain the nuclear power unit fault probability related to the network source based on the interval probability.
Preferably, in the step S1, M devices are set in the power grid under study except for the nuclear power generating unit to be solved, and the probability of failure of each device is Pim(Fi) I-1, …, M, wherein PimDenotes interval probability, FiIndicating that the ith equipment in the power grid is in failure; the interval probability is expressed in the form:
Figure GDA0002589409260000031
in the formula: pim(A) Representing the interval probability of occurrence of event A;P(A) is the lower bound of interval probability;
Figure GDA0002589409260000032
is the upper bound of the interval probability,P(A) and
Figure GDA0002589409260000033
satisfy the requirement of
Figure GDA0002589409260000034
And (4) restraining.
Preferably, the step S4 specifically includes the following steps:
s41: when the frequency of the nuclear power unit is in a normal range, the fault probability P (F) of the nuclear power unitNG) Taking its reference value
Figure GDA0002589409260000035
As shown in the following formula:
Figure GDA0002589409260000036
wherein,
Figure GDA0002589409260000037
representing the average failure probability of the nuclear power unit; fNGThe frequency of the nuclear power unit;
Figure GDA0002589409260000038
the lower limit of the normal frequency value of the nuclear power unit;
Figure GDA0002589409260000039
the upper limit of the normal frequency value of the nuclear power unit;
s42: when the frequency of the nuclear power unit exceeds the allowed limit value, the frequency protection action causes the nuclear power unit to be shut down, the fault probability is 1, and the following steps are performed:
Figure GDA00025894092600000310
wherein, FNG,maxThe upper limit value of the allowed frequency of the nuclear power unit; fNG,minThe lower limit value of the allowed frequency of the nuclear power unit;
s43: when the frequency of the nuclear power unit is between a normal value and a limit value, the action probability of the nuclear power unit protection device is increased along with the increase of the out-of-limit degree of the frequency, and the fault probability of the nuclear power unit is fit by adopting a straight line, and is as follows:
Figure GDA0002589409260000041
s44: when the voltage of the nuclear power unit is in a normal range, the fault probability P (U) of the nuclear power unitNG) Take their referencesValue of
Figure GDA0002589409260000042
As shown in the following formula:
Figure GDA0002589409260000043
wherein,
Figure GDA0002589409260000044
the lower limit of the normal voltage value of the nuclear power unit;
Figure GDA0002589409260000045
the upper limit of the normal voltage value of the nuclear power unit;
s45: when the voltage of the nuclear power unit exceeds the allowed limit value, the voltage protection action causes the nuclear power unit to be shut down, the fault probability is 1, and the following steps are performed:
Figure GDA0002589409260000046
wherein, UNG,minThe lower limit value of the voltage allowed by the nuclear power unit; u shapeNG,maxThe upper limit value of the voltage allowed by the nuclear power unit;
s46: when the voltage of the nuclear power unit is between a normal value and a limit value, the action probability of the nuclear power unit protection device is increased along with the increase of the frequency out-of-limit degree, and the fault probability of the nuclear power unit is linearly fitted, and is as follows:
Figure GDA0002589409260000047
s47: the fault probability of the nuclear power unit is affected by two factors of voltage and frequency, wherein the fault probability of any factor is 1 when the factor reaches a limit value, so that the fault probability of the nuclear power unit is defined as follows under the condition of known frequency and voltage of an access point of the nuclear power unit:
P(FNG,UNG)＝max{P(FNG),P(UNG)}； (7)。
preferably, in step S6, N-1 fault scene simulation is sequentially performed on the devices in the power grid through the power system analysis software tool PSD-BPA, and in the fault simulation process, a principle that the electrical distance between the simulated device and the nuclear power generating unit is from near to far is adopted, that is, an N-1 fault of a device adjacent to the nuclear power generating unit is simulated first, and the settable fault types include: (1) a nuclear power output line 'N-1' fault; (2) the 'N-1' fault of the power grid transmission line; (3) 1 large-capacity generator set is cut off; (4) and (5) the transformer fails and stops running.
Preferably, the calculation method of the nuclear power generating unit fault probability related to the interval probability network source in the step S7 is as follows:
Figure GDA0002589409260000051
wherein M is the number of equipment except the nuclear power generator set in the researched power grid, Pim(Fi) Expressed as the interval probability, P, of each device failingi(FNG,UNG) In order to obtain the fault probability of the nuclear power unit by carrying out fault simulation on the ith device in the power grid,
Figure GDA0002589409260000052
the mean failure probability of the nuclear power unit.
The invention has the beneficial effects that:
(1) the method adopts the interval probability form to express the fault probability of the nuclear power unit, fully deals with the restriction that the fault sample of the nuclear power unit is lack and difficult to obtain, makes up the limitation and deficiency of adopting accurate probability under the condition of small sample, and more reasonably provides the fault possibility interval of the nuclear power unit.
(2) Compared with the traditional independent fault probability model of the thermal power generating unit, the fault probability model not only considers the fault probability caused by self factors such as nuclear power generating unit aging, but also considers the influence of network source related characteristics, namely the change of the power grid operation parameters on the fault probability of the nuclear power generating unit, and the obtained fault probability parameters have higher reliability.
(3) The method aims to calculate the fault probability of the nuclear power generating unit related to the interval probability network source, can effectively deal with uncertainty in the system, lays a foundation for realizing reliability and risk assessment of the nuclear power grid interval form, and has wide application potential.
Drawings
FIG. 1 is a schematic flow diagram of the present invention;
FIG. 2 is a variation curve of nuclear power unit fault probability and frequency correlation;
FIG. 3 is a variation curve of nuclear power generating unit fault probability and terminal voltage correlation.
Detailed Description
For a better understanding of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings in which:
the interval probability is expressed in the form:
Figure GDA0002589409260000053
in the formula: pim(A) Representing the interval probability of occurrence of event A;P(A) is the lower bound of interval probability;
Figure GDA0002589409260000054
is the upper bound of the interval probability,P(A) and
Figure GDA0002589409260000055
satisfy the requirement of
Figure GDA0002589409260000056
And (4) restraining.
The non-exact dirichlet model (IDM) is an extension of the deterministic dirichlet model, which uses a series of dirichlet prior distributions, with the corresponding prior probability density function set as:
Figure GDA0002589409260000061
Figure GDA0002589409260000062
in the formula: theta ═ theta1,θ2,…,θN) A vector composed of probability of occurrence of each state of random variable satisfying thetanNot less than 0, N is 1,2, …, N and
Figure GDA0002589409260000063
the constraint of (2); r isnN is 1,2, …, N represents the a priori weighting factor for each state of the random variable, which represents θnThe mean value of (a); s is a setting parameter, usually in [1,2 ]]Taking values in the interval; s rnIs the prior weight of the nth state of the random variable.
Under the condition of obtaining sample observation data M, according to the updating process in the Bayesian principle, the posterior probability density function set of the IDM is as follows:
Figure GDA0002589409260000064
Figure GDA0002589409260000065
in the formula: m isnN is 1,2, …, N represents the number of times each state of the random variable occurs;
Figure GDA0002589409260000066
representing the total number of samples, M may be substituted.
Thus, the interval probability of occurrence of each state of the random variable in the IDM, i.e., the parameter
Figure GDA0002589409260000067
Can be obtained by calculating the mathematical expectation of the set of IDM posterior probability density functions, as shown below
Figure GDA0002589409260000068
A method for calculating the fault probability of a nuclear power generating unit based on interval probability network source correlation comprises the following steps:
s1: determining the interval fault probability of various devices in the researched power grid containing the nuclear power generating unit; the equipment comprises a generator, a transformer and an overhead transmission line; the method comprises the steps of setting M devices except a nuclear power unit to be solved in a researched power grid, wherein the interval probability of each device having a fault (namely a simple N-1 fault) is Pim(Fi) I-1, …, M, wherein PimDenotes interval probability, FiIndicating that the ith device in the grid is faulty. Pim(Fi) And the interval probability of the fault of the ith equipment in the power grid is represented. And according to historical operation statistical data of various types of equipment in the power grid, estimating the interval fault probability of the three types of power equipment by applying a non-precise Dirichlet model.
Taking an overhead transmission line as an example, in a researched power grid containing nuclear power access, based on historical statistical data of the power grid, the average operation time of an overhead line in the power grid is t1Mean time to failure of line since year-on-stream is t2In hours, the interval probability of the line fault is determined by applying the interval probability estimation method based on IDM
Figure GDA0002589409260000071
Similarly, the interval probability of the generator failure is
Figure GDA0002589409260000072
The interval probability of the transformer fault is
Figure GDA0002589409260000073
S2: determining the voltage protection characteristic and the frequency protection characteristic of the nuclear power unit; and giving partial frequency, voltage allowable range and tolerance time when the nuclear power unit is connected into the power grid to operate, and judging whether the nuclear power unit is in a normal operation state or a generator tripping operation quits according to the frequency and voltage level of the nuclear power unit access point.
The nuclear power unit must operate in a certain voltage and frequency range, and if the fluctuation degree exceeds the range, the protection measures in the nuclear power plant can be automatically started, so that a power grid is disconnected with the nuclear power unit, and the power grid loses an important power supply and suffers from large impact.
In combination with relevant references and actual operation experience of a nuclear power plant, standard requirements of partial frequency, voltage allowable range and duration when a nuclear power unit is connected to a power grid to operate are shown in table 1.
TABLE 1 allowable frequency, voltage range and duration of the part of nuclear power generating unit connected to the power grid
frequency/Hz Duration/s Terminal voltage/p.u. Duration/s
Higher than 53.5 0.1 Higher than 1.25 0.5
51.0～52.0 5 0.8～1.05 Normal operation
49.5～50.5 Normal operation 0.7～0.75 0.8
47.0～47.5 6 Less than 0.7 0.3
Less than 47.0 0.5
Therefore, when the frequency range of the access point of the nuclear power unit is 49.5-50.5 Hz and the voltage range is 0.8-1.05 p.u., the nuclear power unit can normally operate. When the frequency of the access point is higher than 53.5Hz or lower than 47.0Hz, the terminal voltage is higher than 1.25p.u. or lower than 0.7p.u., the frequency or voltage protection of the nuclear power unit can act rapidly, so that the unit is disconnected from the power grid.
S3: and determining the average failure probability of the nuclear power unit caused by aging and defect factors. The mean failure probability of a nuclear power unit is set as
Figure GDA0002589409260000074
The method can be given by long-term operation experience and statistical data of manufacturers of nuclear power units or domestic and foreign nuclear power plants.
S4: according to the characteristic that when the voltage and the frequency of an access point of the nuclear power unit are increased or decreased to a protection fixed value, a protection device of the nuclear power unit acts, and the action time limit of protection is reduced along with the deepening of the out-of-limit degree of the frequency and the voltage, and the probability that the nuclear power unit generator tripping operation is increased, the relation between the fault probability of the nuclear power unit and the change of the power grid frequency and the change of the voltage at the generator end of the nuclear power unit is respectively given, a sectional curve is obtained, and a corresponding calculation formula is given. Under the given frequency and voltage level, the fault probability corresponding to the frequency and the fault probability corresponding to the voltage of the nuclear power unit are respectively obtained, and the higher probability value of the two is taken as the dependent fault probability related to the nuclear power unit network source. The method comprises the following specific steps:
s41: as shown in FIG. 2, when the frequency of the nuclear power generating unit is within the normal range, the failure probability P (F) of the nuclear power generating unitNG) Taking its reference value
Figure GDA0002589409260000081
As shown in the following formula:
Figure GDA0002589409260000082
wherein,
Figure GDA0002589409260000083
representing the average failure probability of the nuclear power unit; fNGThe frequency of the nuclear power unit;
Figure GDA0002589409260000084
the lower limit of the normal frequency value of the nuclear power unit;
Figure GDA0002589409260000085
the upper limit of the normal frequency value of the nuclear power unit;
s42: when the frequency of the nuclear power unit exceeds the allowed limit value, the frequency protection action causes the nuclear power unit to be shut down, the fault probability is 1, and the following steps are performed:
Figure GDA0002589409260000086
wherein, FNG,maxThe upper limit value of the allowed frequency of the nuclear power unit; fNG,minThe lower limit value of the allowed frequency of the nuclear power unit;
s43: when the frequency of the nuclear power unit is between a normal value and a limit value, the action probability of the nuclear power unit protection device is increased along with the increase of the out-of-limit degree of the frequency, and the fault probability of the nuclear power unit is fit by adopting a straight line, and is as follows:
Figure GDA0002589409260000087
s44: as shown in FIG. 3, when the voltage of the nuclear power generating unit is within the normal range, the fault probability P (U) of the nuclear power generating unitNG) Taking its reference value
Figure GDA0002589409260000088
As shown in the following formula:
Figure GDA0002589409260000089
wherein,
Figure GDA00025894092600000810
the lower limit of the normal voltage value of the nuclear power unit;
Figure GDA00025894092600000811
the upper limit of the normal voltage value of the nuclear power unit;
s45: when the voltage of the nuclear power unit exceeds the allowed limit value, the voltage protection action causes the nuclear power unit to be shut down, the fault probability is 1, and the following steps are performed:
Figure GDA00025894092600000812
wherein, UNG,minThe lower limit value of the voltage allowed by the nuclear power unit; u shapeNG,maxThe upper limit value of the voltage allowed by the nuclear power unit;
s46: when the voltage of the nuclear power unit is between a normal value and a limit value, the action probability of the nuclear power unit protection device is increased along with the increase of the frequency out-of-limit degree, and the fault probability of the nuclear power unit is linearly fitted, and is as follows:
Figure GDA0002589409260000091
s47: the fault probability of the nuclear power unit is affected by two factors of voltage and frequency, wherein the fault probability of any factor is 1 when the factor reaches a limit value, so that the fault probability of the nuclear power unit is defined as follows under the condition of known frequency and voltage of an access point of the nuclear power unit:
P(FNG,UNG)＝max{P(FNG),P(UNG)}； (7)。
s5: carrying out load flow calculation on the initial operation state of the power grid containing the nuclear power generating unit, and executing subsequent steps if the load flow is converged; if the power flow is not converged, the output of a generator of the power grid and parameters of the balance nodes need to be adjusted, and the power flow calculation is continued until the power flow is converged. And after the load flow calculation is converged, checking the frequency and voltage level of the access point of the nuclear power unit, and judging whether the nuclear power unit is in a normal operation state or not according to the frequency and voltage protection characteristics of the nuclear power unit.
S6: n-1 fault simulation is sequentially carried out on three types of equipment in a power grid through a power system analysis software tool, the frequency and the voltage level of a nuclear power unit access point after the fault occurs are checked, and the fault probability of the nuclear power unit under the fault is obtained by contrasting the frequency and the voltage protection characteristics of the nuclear power unit.
Sequentially carrying out N-1 fault scene simulation on equipment in a power grid through a power system analysis software tool PSD-BPA, and in the fault simulation process, adopting the principle that the electrical distance between the simulated equipment and a nuclear power unit is from near to far, namely firstly simulating the N-1 fault of equipment close to the nuclear power unit, wherein the settable fault types comprise: (1) a nuclear power output line 'N-1' fault; (2) the 'N-1' fault of the power grid transmission line; (3) 1 large-capacity generator set is cut off; (4) and (5) the transformer fails and stops running.
Performing fault simulation on ith equipment in a power grid, checking the voltage and frequency level of a nuclear power unit access point after a fault, and combining table 1 and formulas (7) - (13) to obtain the fault probability P of the nuclear power unit under the fault scenei(FNG,UNG)。
S7: and integrating the interval fault probability of each device and the probability of the nuclear power unit failing when each device fails, and superposing the influences of aging and defect factors of the unit to obtain the nuclear power unit fault probability related to the network source based on the interval probability.
Synthesizing interval probability P of each fault sceneim(Fi) And probability P of nuclear power unit failure caused by the failurei(FNG,UNG) The product is calculated. Summing probability products under all N-1 fault scenes, and simultaneously superposing influences of self factors such as aging and defects of the nuclear power generating units on fault occurrence probability to obtain fault probability of the nuclear power generating units related to the interval probability network source, namely the fault probability of the nuclear power generating units related to the interval probability network source
Figure GDA0002589409260000101
Wherein M is the number of equipment except the nuclear power generator set in the researched power grid, Pim(Fi) Expressed as the interval probability, P, of each device failingi(FNG,UNG) In order to obtain the fault probability of the nuclear power unit by carrying out fault simulation on the ith device in the power grid,
Figure GDA0002589409260000102
the mean failure probability of the nuclear power unit.
After the simulation of all the N-1 fault scenes is completed, the relation between the nuclear power unit fault probability and the power grid equipment fault is analyzed, and a set of external equipment faults which can cause the nuclear power unit to stop running or to have faults is searched. Due to the high requirement on safe and stable operation of the nuclear power unit, corresponding measures need to be taken to deal with the adverse effect on the nuclear power unit caused by the occurrence of the external faults.
The present invention is not limited to the above-described embodiments, which are merely preferred embodiments of the present invention, and the present invention is not limited thereto, and any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (5)

1. A method for calculating the fault probability of a nuclear power generating unit based on interval probability network source correlation is characterized by comprising the following steps: the method comprises the following steps:
s1: determining the interval fault probability of various devices in the researched power grid containing the nuclear power generating unit; the equipment comprises a generator, a transformer and an overhead transmission line; according to historical operation statistical data of various devices in the power grid, a non-precise Dirichlet model is applied to estimate the interval fault probability of the three types of power devices;
s2: determining the voltage protection characteristic and the frequency protection characteristic of the nuclear power unit; giving partial frequency, voltage allowable range and tolerance time when the nuclear power unit is connected into a power grid to operate, and judging whether the nuclear power unit is in a normal operation state or a generator tripping operation quits according to the frequency and voltage level of the nuclear power unit access point;
s3: determining the average failure probability of the nuclear power unit caused by aging and defect factors;
s4: under given frequency and voltage levels, respectively obtaining the fault probability corresponding to the frequency and the fault probability corresponding to the voltage of the nuclear power unit, and taking the higher probability value of the two as the dependent fault probability related to the nuclear power unit network source;
s5: carrying out load flow calculation on the initial operation state of the power grid containing the nuclear power generating unit, and executing subsequent steps if the load flow is converged; if the power flow is not converged, the output of a generator of the power grid and parameters of balance nodes need to be adjusted, and power flow calculation is continued until the power flow is converged;
s6: sequentially carrying out N-1 fault simulation on three types of equipment in a power grid through a power system analysis software tool, checking the frequency and voltage level of an access point of a nuclear power unit after the fault occurs, and contrasting the frequency and voltage protection characteristics of the nuclear power unit to obtain the fault probability of the nuclear power unit under the fault;
s7: and integrating the interval fault probability of each device and the probability of the nuclear power unit failing when each device fails, and superposing the influences of aging and defect factors of the unit to obtain the nuclear power unit fault probability related to the network source based on the interval probability.
2. The method for calculating the fault probability of the nuclear power generating unit based on the interval probability network source correlation is characterized in that: in step S1, M devices are set in the power grid under study, except for the nuclear power generating unit to be solved, and the probability of each device failing is Pim(Fi) I-1, …, M, wherein PimDenotes interval probability, FiIndicating that the ith equipment in the power grid is in failure; the interval probability is expressed in the form:
Figure FDA0002589409250000011
in the formula: pim(A) Representing the interval probability of occurrence of event A;P(A) is the lower bound of interval probability;
Figure FDA0002589409250000012
is the upper bound of the interval probability,P(A) and
Figure FDA0002589409250000013
satisfy the requirement of
Figure FDA0002589409250000014
And (4) restraining.
3. The method for calculating the fault probability of the nuclear power generating unit based on the interval probability network source correlation is characterized in that: the step S4 specifically includes the following steps:
s41: when the frequency of the nuclear power unit is in a normal range, the fault probability P (F) of the nuclear power unitNG) Taking its reference value
Figure FDA0002589409250000015
As shown in the following formula:
Figure FDA0002589409250000021
wherein,
Figure FDA0002589409250000022
representing the average failure probability of the nuclear power unit; fNGThe frequency of the nuclear power unit;
Figure FDA0002589409250000023
the lower limit of the normal frequency value of the nuclear power unit;
Figure FDA0002589409250000024
the upper limit of the normal frequency value of the nuclear power unit;
s42: when the frequency of the nuclear power unit exceeds the allowed limit value, the frequency protection action causes the nuclear power unit to be shut down, the fault probability is 1, and the following steps are performed:
Figure FDA0002589409250000025
wherein, FNG,maxThe upper limit value of the allowed frequency of the nuclear power unit; fNG,minThe lower limit value of the allowed frequency of the nuclear power unit;
s43: when the frequency of the nuclear power unit is between a normal value and a limit value, the action probability of the nuclear power unit protection device is increased along with the increase of the out-of-limit degree of the frequency, and the fault probability of the nuclear power unit is fit by adopting a straight line, and is as follows:
Figure FDA0002589409250000026
s44: when the voltage of the nuclear power unit is in a normal range, the fault probability P (U) of the nuclear power unitNG) Taking its reference value
Figure FDA0002589409250000027
As shown in the following formula:
Figure FDA0002589409250000028
wherein,
Figure FDA0002589409250000029
the lower limit of the normal voltage value of the nuclear power unit;
Figure FDA00025894092500000210
the upper limit of the normal voltage value of the nuclear power unit;
s45: when the voltage of the nuclear power unit exceeds the allowed limit value, the voltage protection action causes the nuclear power unit to be shut down, the fault probability is 1, and the following steps are performed:
Figure FDA00025894092500000211
wherein, UNG,minThe lower limit value of the voltage allowed by the nuclear power unit; u shapeNG,maxThe upper limit value of the voltage allowed by the nuclear power unit;
s46: when the voltage of the nuclear power unit is between a normal value and a limit value, the action probability of the nuclear power unit protection device is increased along with the increase of the frequency out-of-limit degree, and the fault probability of the nuclear power unit is linearly fitted, and is as follows:
Figure FDA0002589409250000031
s47: the fault probability of the nuclear power unit is affected by two factors of voltage and frequency, wherein the fault probability of any factor is 1 when the factor reaches a limit value, so that the fault probability of the nuclear power unit is defined as follows under the condition of known frequency and voltage of an access point of the nuclear power unit:
P(FNG,UNG)＝max{P(FNG),P(UNG)}； (7)。
4. the method for calculating the fault probability of the nuclear power generating unit based on the interval probability network source correlation is characterized in that: in the step S6, N-1 fault scene simulation is sequentially performed on the devices in the power grid through the power system analysis software tool PSD-BPA, and in the fault simulation process, a principle that the electrical distance between the simulated device and the nuclear power generating unit is from near to far is adopted, that is, an N-1 fault of a device adjacent to the nuclear power generating unit is simulated first, and the settable fault types include: (1) a nuclear power output line 'N-1' fault; (2) the 'N-1' fault of the power grid transmission line; (3) 1 large-capacity generator set is cut off; (4) and (5) the transformer fails and stops running.
5. The method for calculating the fault probability of the nuclear power generating unit based on the interval probability network source correlation is characterized in that: the calculation method of the nuclear power generating unit fault probability related to the interval probability network source in the step S7 is as follows:
Figure FDA0002589409250000032
wherein M is the number of equipment except the nuclear power generator set in the researched power grid, Pim(Fi) Expressed as the interval probability, P, of each device failingi(FNG,UNG) In order to obtain the fault probability of the nuclear power unit by carrying out fault simulation on the ith device in the power grid,
Figure FDA0002589409250000033
the mean failure probability of the nuclear power unit.
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