CN117406020B - Fault phase selection method for constructing generalized power ratio based on compensation abrupt quantity - Google Patents
Fault phase selection method for constructing generalized power ratio based on compensation abrupt quantity Download PDFInfo
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Abstract
The invention belongs to the field of relay protection of power systems, and discloses a fault phase selection method for constructing a generalized power ratio based on compensation mutation quantity. Aiming at the problem of false selection of phase selection based on abrupt change fault when a new energy source external line breaks down, the method demonstrates the cause of false selection of the current criterion, innovates a fault polarization factor to correct fault abrupt change current, innovates a new concept of generalized power ratio, and provides a new criterion of phase selection based on compensation abrupt change to construct the generalized power ratio. The criterion defines positive sequence and zero sequence fault polarization factors, unifies short-circuit current distribution coefficients through the polarization factors, realizes compensation calculation of current abrupt change, overcomes the influence of new energy side impedance and weak feedback on the current abrupt change, further defines generalized power ratio by using the compensation abrupt change, analyzes the difference of the generalized power ratio under different fault types, and constructs a new fault phase selection criterion based on the generalized power ratio. The criterion is novel, the fault phase selection principle is simple, the phase selection is reliable, and the circuit reclosing rate can be effectively improved by matching with the single-phase reclosing.
Description
Technical Field
The invention belongs to the field of relay protection of power systems, and discloses a fault phase selection method for constructing generalized power ratio based on compensation mutation quantity, aiming at meeting the requirements of fault phase selection of an external line of a new energy station and improving reclosing reliability by matching with single-phase reclosing of the line.
Background
The country advocates the development of renewable clean energy, new energy represented by photovoltaic power generation and wind power is developed rapidly, but as the power generation capacity of the new energy is larger and larger, the new energy has insufficient digestion capacity nearby and is far away from a load center, so that the new energy needs to be concentrated and delivered out in a large scale and long distance. In recent years, the installed capacity and the single-machine capacity of the new energy generator set are continuously increased and enlarged, the fault current characteristics of the new energy external line are complex and changeable, the operation modes are various, the relay protection function in the conventional power network is weakened, the problems of wrong phase selection and wrong operation of the new energy output line protection are serious, the quick and reliable operation of the relay protection device is seriously influenced, and a small challenge is formed for the safe and stable operation of the power grid.
Fault phase selection is a key technology for successful single-phase reclosing, and students at home and abroad have studied to generate a plurality of academic results, and are mainly divided into two types: phase selection principle based on steady state quantity and phase selection principle based on mathematical theory method. However, with the large-scale access of new energy, these traditional phase selection methods are obviously no longer applicable, and a phase selection scheme suitable for new energy needs to be found.
At present, the fault phase selection results of a new energy output line are less, and documents (Zhang Junfeng, highlight, shen Yifei, and the like) are used for fault voltage sequence component phase selection elements of a doubly fed machine set wind power plant, electric power system protection and control, 2018,46 (10): 136-143) are combined with the influence of crowbar protection on the phase of the fault voltage sequence component, a phase deviation angle is corrected, and a phase selection method based on the fault voltage sequence component is provided, but the method is not suitable for reclosing of an off-site line. Patent (Li Zhengtian, chen Yongxin, wu Tonghua, etc.), fault phase selection method, system, equipment and terminal of new energy concentrated sending line, application publication No. CN 115184735A) uses wavelet packet analysis to reconstruct high-frequency voltage signal and high-frequency current signal, and introduces voltage change coefficient to redefine the magnitude of the modulus of high-frequency composite phase current difference mutation to form phase selection criterion, and has high sampling rate requirement, and is difficult to match with the current protection device. The invention is based on the traditional sampling rate unchanged, improves on the basis of the original protection device, is convenient to realize, can be applied to fault phase selection of the external line of the new energy station, and has high preparation rate.
Disclosure of Invention
In order to solve the problem of reliable identification of fault phase selection of an external line of a new energy station, and matching with single-phase reclosing of a line, improving the reclosing rate and reducing the off-grid of a new energy power generation system, the invention provides a fault phase selection method for constructing a generalized power ratio based on compensation mutation. The criterion redefines positive sequence and zero sequence fault polarization factors, corrects current and voltage abrupt change calculation modes, enables abrupt change not to be influenced by sequence impedance change caused by new energy access, further provides a generalized power ratio based on compensation abrupt change, and constructs a novel fault line selection method based on differences under different fault types.
The technical scheme adopted by the invention is as follows:
A fault phase selection method based on compensation abrupt quantity construction generalized power ratio comprises the steps of fault polarization factor construction, adaptability demonstration of a new energy side fault line selection model, novel abrupt quantity calculation under the fault polarization factor, generalized power ratio definition and calculation, novel fault phase selection criterion and the like. The method comprises the following specific steps:
Step 1: defining positive sequence fault polarization factor p=c 2/C1 based on positive, negative and zero sequence current distribution coefficients C 1、C2、C0; zero sequence fault polarization factor q=c 2/C0 is defined.
Step 2: substituting positive sequence fault polarization factor p into a phase current difference mutation calculation new energy side fault line selection model, wherein the value range of p is r < p < 1, and p is a fluctuation value, so that the false selection demonstration of the conventional fault phase selection method is realized.
Step 3: and substituting the positive sequence fault polarization factor and the zero sequence fault polarization factor into the calculation of the phase current abrupt change quantity, so that the correction of the phase current abrupt change quantity is realized, the current distribution coefficients of the current calculation are unified, and the abrupt change quantity phase selection is not influenced by the positive, negative and zero sequence calculation impedance characteristics of the wind power plant.
Step 4: cross-polarizing voltage abrupt change and current abrupt change to form a generalized power ratio of abrupt change compensated by current and voltage
Step 5: based on the comparison of the generalized power ratio, fault phase selection criteria of single-phase grounding short circuit, two-phase grounding short circuit and three-phase short circuit are respectively constructed.
The invention has the beneficial effects that:
(1) The fault phase selection based on the abrupt change is applicable to the fault phase selection of the new energy station outgoing line without changing the traditional protection device constitution, and is beneficial to engineering realization;
(2) The fault polarization factor is applied to compensate the abrupt quantity, the influence of the sequence impedance is avoided, and the fault phase selection accuracy is effectively improved;
(3) The innovative generalized power comparison principle is simple in criterion and easy to implement, and different fault types can be effectively identified.
Drawings
FIG. 1 is a diagram of an equivalent network before a doubly fed wind turbine access system fails.
FIG. 2 is an equivalent network diagram after a doubly fed wind turbine access system failure.
FIG. 3 is a diagram of a positive sequence equivalent fault network for a doubly fed wind turbine access system.
FIG. 4 is a negative sequence equivalent network diagram of a doubly fed wind turbine access system.
Fig. 5 is a zero sequence equivalent network diagram of a doubly fed wind turbine access system.
FIG. 6 is a flow chart of a fault-selective flow based on generalized power ratio of compensation bursts.
FIG. 7 is a diagram of a doubly-fed wind farm delivery system.
FIG. 8 is a graph of phase jump power values for a graph of the result of a generalized power ratio simulation of a phase A fault.
FIG. 9 is a graph of phase-to-phase jump power values for a compensated generalized power ratio simulation result graph at phase A failure.
FIG. 10 is a generalized power ratio diagram of compensation mutations of a generalized power ratio simulation result diagram for phase A faults.
FIG. 11 is a graph of phase jump power values for a graph of the result of a generalized power ratio simulation of the BC phase-to-phase short circuit.
FIG. 12 is a graph of phase jump power values for a compensated generalized power ratio simulation result for BC phase-to-phase shorting.
FIG. 13 is a generalized power ratio diagram of compensation mutations in a BC phase-to-phase short circuit compensated generalized power ratio simulation result diagram.
Detailed Description
The invention provides a fault phase selection method for constructing generalized power ratio based on compensation mutation quantity, which comprises the following steps:
step 1: fault polarization factor definition.
(1) Object-oriented network description
For a new energy station, taking a doubly-fed fan as an example, due to a complicated power electronic device in the doubly-fed fan, the voltage and current expression of the fan is difficult to determine, and the electrical quantity of the fan outlet is equivalent to a time-varying voltage source and a virtual impedance series connection form by utilizing a black box theory to carry out theoretical analysis. The network before the fault under the access of the doubly-fed wind machine is shown in figure 1, the network after the fault is shown in figure 2, the network of the positive sequence equivalent fault of the system is shown in figure 3, the network of the negative sequence equivalent fault of the system is shown in figure 4, and the network of the zero sequence equivalent fault of the system is shown in figure 5. In the figure, m is the position of the fault point from the fan side, M, N is the fan side and the system side respectively, Z S1、Zk1 is the positive sequence impedance of the system side and the sending-out line respectively, Z T1 is the total positive sequence impedance from the main transformer and the collecting line of the fan to the box transformer,Is a system side power supply, is basically unchanged before and after the fault,/>Is positive sequence fault voltage, current at fault point of tie line,/>Equivalent internal electromotive force and internal impedance of fan before failure,/>, respectivelyZ W1 is equivalent internal electromotive force and internal resistance of the fan after the fault respectively, and as the positive sequence impedance of the main transformer of the fan is unchanged before and after the fault, the fault component can be obtained by utilizing the extraction algorithm of the fault component, namely subtracting the electric quantity measured by protection after the fault from the electric quantity measured by protection before the fault, and the positive sequence fault voltage/>, namely M point, of the protection installation part is obtainedAnd positive sequence fault current/>Positive sequence fault impedance/>, at the fan sideThe reactance is a virtual positive sequence equivalent reactance and has no specific physical significance. From the analysis, the magnitude of the delta Z W1 is influenced by the equivalent internal potential and the equivalent internal impedance before and after the wind farm faults. Z S2、Zk2 is the negative sequence impedance of the system side and the sending-out line, and Z T2 is the total negative sequence impedance from the main transformer of the fan to the box transformer of the collecting line; /(I)Respectively sending out negative sequence current and voltage of a fault point on the line; /(I)The negative sequence fault current and the negative sequence fault voltage at the protection installation position are respectively; z W2 is the negative-sequence equivalent impedance of the wind farm in the fault network. Because the wiring mode of the main transformer of the wind power plant is YNd and the wiring mode of the box-type transformer is Yd, no equivalent zero sequence internal impedance exists in the wind power plant, wherein Z S0、Zk0 and Z T0 are respectively negative sequence impedance of the system side, the outgoing line and the main transformer of the fan,/>Zero sequence current and voltage of fault points on the sending line respectively; /(I)The zero sequence fault current and the zero sequence fault voltage of the protection installation place are respectively.
(2) Positive sequence, zero sequence fault polarization factor definition
And respectively obtaining positive, negative and zero sequence fault current distribution coefficients C 1、C2、C0 at the protection installation position according to the positive, negative and zero sequence fault networks.
Defining positive sequence fault polarization factor as p, p=C 2/C1, substituting formulas (1) and (2) into p to obtain assuming that positive sequence impedance and negative sequence impedance of system side and connecting line are equal
Similarly, the zero sequence fault polarization factor is defined as q=c 2/C0.
Where Z Σ＝ZS1+Zk1≈ZS2+Zk2, the magnitude of p and q can be obtained independently of the location of the fault point.
Step 2: inapplicable demonstration of new energy access to abrupt change phase selection, when a system fails, three-phase current abrupt change quantity is calculated as shown in formula (5)
Wherein: three-phase current abrupt change amounts at the protection installation position respectively; /(I) Positive, negative and zero sequence fault currents of the A phase at the fault point are respectively; c 1、C2、C0 is the positive, negative, zero sequence fault current distribution coefficient at the protection installation, and α=e j120° is the twiddle factor. The phase current difference mutation amount refers to the mutation amount of the phase difference current of two phases, and the definition of the phase current difference mutation amount at the protection installation part is that
In the method, in the process of the invention,Is the phase current difference mutation.
Substituting p into (5) and (6) to obtain
Wherein: By taking the amplitude value, can be obtained:
In this case, let the doubly-fed wind turbine side Z 'W1/ZW2 =r, because of the weak feed characteristic of the wind farm under the fault condition, Z' W1＞＞ZT1+Z∑,ZW2＞＞ZT2+Z∑ is Z 'W1＞＞ZT1+Z∑,ZW2＞＞ZT2+Z∑, where p=r, if Z' W1＜＜ZT1+Z∑ exists, p=1, so that the obtained p has a value range of r < p <1, and is a fluctuation value, the amplitude of the phase current difference mutation quantity is greatly affected by p, when p approaches 0, the amplitudes of the three phase current difference mutation quantities are approximately equal, the easy error option is a three-phase fault, when p approaches 1, The root cause of the phase error is the uncertainty of the Z' W1、ZW2 parameter of the wind power plant, the amplitude change degree of the positive and negative sequence equivalent impedance is related to the slip ratio, the input crowbar resistance and the transient characteristic of the fan, the positive and negative sequence fault current distribution coefficients are difficult to be equal, and the phase error is difficult to be selected according to the traditional phase current difference mutation quantity.
Step 3: novel mutation calculation under fault polarization factor
The positive sequence fault polarization factor p reflects the difference of positive and negative sequence current distribution coefficients, the difference of the distribution coefficients is compensated by utilizing the fault polarization factor on the basis of the original current abrupt change, so that the current distribution coefficients are unified, and as can be known from the formula (4), the positive and negative sequence impedance of the system side and the interconnecting line is assumed to be approximately equal, the positive sequence fault polarization factor is mainly obtained by obtaining Z T1+Z′W1、ZT2+ZW2, and the fault component principle is utilized to obtain the positive sequence fault polarization factor by combining the figures 4 and 5
The negative sign of the formula (9) merely indicates that the direction is opposite to the actual reference direction (the direction of the fault point at the protected installation site), and it is not practical to substitute the formula (9) into the formula (4)
The current abrupt change under the positive sequence fault polarization factor can be obtained by combining the formulas (5), (1), (2) and (10), and the positive sequence fault current component is compensated by introducing the positive sequence fault polarization factor as shown in the formula (11):
in the method, in the process of the invention, For M-terminal phase current abrupt change quantity compensated by positive sequence fault current,/>For the positive sequence current fault component of the wind power plant side protection installation place, the positive sequence fault current coefficient of the fault point on the right of the equation is compensated to be C 2 by comparison with the equation (4), so that the inadaptability of the positive sequence transient equivalent impedance to fault phase selection in the wind power system is avoided.
The zero sequence current distribution coefficient is less influenced by the slip ratio, the running state and the transient faults of the wind farm, but by introducing the zero sequence fault polarization factor q to compensate the zero sequence fault current distribution coefficient at the wind farm side, the current fault characteristics caused by large capacity difference between the system side and the wind farm side can be reduced, and the current abrupt change quantity at the time of the grounding fault can be highlighted. By using the principle of fault components and combining the graphs of fig. 4 and 5, it can be obtained that
And on the basis of the formula (11), continuously compensating zero sequence fault current, and combining the formulas (4), (2), (3) and (5) to obtain the current abrupt change under the zero sequence fault polarization factor as shown in the formula (13).
In the method, in the process of the invention,For new phase current abrupt change compensated by zero sequence fault current,/>For the positive sequence current fault component and the zero sequence current fault component measured at the wind farm side protection installation place, the comparison formula (4) can show that the coefficient before the zero sequence fault current of the fault point on the right side of the equation is already compensated as C 2, the current distribution coefficient is unified, so that the abrupt change phase selection is not influenced by the positive sequence, negative sequence and zero sequence calculation impedance characteristics of the wind farm any more, and the voltage abrupt change based on the positive sequence and zero sequence fault polarization factor compensation can be constructed according to the formula (13);
in the method, in the process of the invention, For the new phase voltage abrupt change quantity compensated by the positive sequence and zero sequence fault voltage, Positive sequence voltage fault component, zero sequence voltage fault component,/>, measured for an M-terminal protection devicePositive sequence, negative sequence and zero sequence voltages for phase a of k where the fault occurs.
Step 4: generalized power ratio calculation of current and voltage compensated abrupt quantities
The current difference abrupt change phase selection has good action characteristics on the strong power supply side, but the sensitivity on the weak power supply side is insufficient, the effect of the voltage difference abrupt change phase selection is just opposite, the action characteristics on the weak feed side are better, the abrupt change characteristic is more obvious, and the problem of insufficient sensitivity on the weak feed side can be effectively solved by using the voltage difference abrupt change phase selection on the weak feed side. Therefore, the method for selecting the phase of the voltage and current comprehensive abrupt change, which can not be influenced by the system parameter change at two sides and can meet the weak feed characteristic of the wind power plant and the transient state uncertainty change after the fault, is constructed by carrying out cross polarization on the voltage abrupt change and the current abrupt change according to the fault characteristic principle. Because the strong and weak feed state of wind field side is affected by the parameters of system side, a current and voltage compensated abrupt change generalized power ratio is constructed as shown in formula (15)
Subscript ofIs any phase of A, B, C three phases,/>For the differentiated representation of three phases,/>For/>Generalized power ratio of compensation abrupt quantity of phase,/>, andFor/>Abrupt power of phase,/>The power is the abrupt difference of the other two phases.
In order to determine different fault types more intuitively and clearly, the application writes the generalized power ratio of each abrupt change power value, the abrupt change difference power value and the compensation abrupt change value compensated by current and voltage under different fault conditions as shown in table 1. It should be noted that table 1 is only schematic in the power of the compensation mutation, and cannot represent a true value, because the calculated power of the compensation mutation will be different from one failure type to another in 11 failures, and so H m does not represent an actual mathematical meaning.
TABLE 1 Power values and generalized Power ratios for Compensation mutations for different fault types
As shown in table 1, the general power ratio of the compensation abrupt change amount is basically the phase line with larger power loss abrupt change amount is the failed phase, and the power loss abrupt change amount of the non-failed phase is small and is not comparable to the failed phase. Selecting generalized power ratio of compensation mutation quantityThe single-phase faults and the three-phase faults can be identified, but the electric quantity of each abrupt change under the conditions of the two-phase short-circuit grounding faults and the two-phase short-circuit faults shows consistency in form, so that the two types of faults become difficult to distinguish, and whether the faults are grounded or not can be determined by judging whether zero sequence voltage and zero sequence current exist at the protection installation position.
Step 5: generalized power ratio fault phase selection criterion based on compensation abrupt quantity
Taking the generalized power ratio H A、HB、HC of the compensation abrupt amount can most prominently identify the characteristics under different faults, because even though the fault current and the fault voltage amplitude can change under different fault types, the power ratio is calculated, and the result is not affected. Therefore, the generalized power ratio of the compensation abrupt quantity is adopted as the criterion of fault phase selection to be most suitable. The generalized power ratio H A、HB、HC of the compensation mutation quantity of A, B, C three phases is ordered according to the order from big to small, namely, the generalized power ratio H A、HB、HC is arranged into H max≥Hmid≥Hmin, and different types of fault types are specifically analyzed to form different phase selection criteria.
(1) Single phase earth fault
When a single-phase earth fault occurs in the new energy sending line at the fault point k, current and voltage abrupt changes compensated by the positive sequence fault polarization factor and the zero sequence fault polarization factor are obtained, the generalized power ratio H A、HB、HC of the compensated abrupt changes is calculated, and by taking the single-phase fault occurring in the phase A as an example, the ratio H A＞＞HB≈HC of the two is obtained by the table 1, namely H max＞＞Hmid≈Hmin, the condition can be met only when the single-phase fault occurs, so that the phase selection criterion 1 of the single-phase earth fault can be obtained as follows:
Hmax＞σHmid (16)
In the formula, sigma is a setting coefficient, and in engineering practice, the phase corresponding to 10 and H max can be taken as a fault phase when the single-phase fault occurs in the line, and the method also meets the requirement when the single-phase earth fault occurs in the B, C phase.
(2) Two-phase short circuit fault
When a new energy source sending line has a two-phase short circuit fault, current and voltage abrupt changes compensated by a positive sequence fault polarization factor and a zero sequence fault polarization factor are obtained, generalized power ratio H A、HB、HC of the compensated abrupt changes is calculated, and by taking the two-phase short circuit fault of a BC phase as an example, P B≈PC＞PA,PBC＞PCA≈PAB is obtained from table 1, the ratio H B≈HC＞＞HA of the two is obtained, namely H max≈Hmid＞＞Hmin, the condition can be met only when the two-phase fault occurs, so that phase selection criterion 2 of the two-phase short circuit fault can be obtained as follows:
in the formula, eta is a setting coefficient, and in engineering practice, two phases corresponding to 0.5, H max and H mid can be taken as fault phases when two-phase faults occur to the circuit, and the method also satisfies the conditions when two-phase short circuit faults occur to the AB and CA phases.
(3) Two-phase short circuit ground fault
When judging the two-phase short circuit, using the formula (17) to judge, if the fault is grounded, judging whether the zero sequence current or voltage component exceeds the threshold value, so that the criterion 3 is added on the basis of the formula (17)
In the formula, mu is a setting coefficient, 0.15 can be taken in engineering practice, and the method also meets the requirement when the AB and CA phases have two-phase short circuit ground faults.
(4) Three-phase short circuit
As can be seen from table 1, regardless of whether the three-phase short-circuit fault or the three-phase short-circuit ground fault P A≈PB≈PC,PBC≈PCA≈PAB occurs, the generalized power ratio H A≈HB≈HC of the compensation mutation, i.e., H max≈Hmid≈Hmin, is satisfied only when the three-phase fault occurs, so that the phase selection criterion 4 of the three-phase short-circuit fault can be obtained as follows:
In the formula, epsilon is a setting coefficient, 3 can be taken in engineering practice, and if whether three phases of ground are needed to be judged, judgment can be carried out according to whether zero sequence current exceeds a fixed value.
Fig. 6 shows a fault phase selection flow based on the generalized power ratio of the compensation abrupt change, from the viewpoint of the composition of the generalized power of the compensation abrupt change, firstly, the abrupt change of the voltage and the current under compensation is calculated, secondly, the phase selection criterion is constructed by utilizing the principle that the power of the fault phase before and after the fault is much higher than that of the non-fault phase.
And (3) carrying out calculation analysis: in order to more explain the accuracy of simulation data, based on the wind farm outgoing system diagram shown in fig. 7, PSCAD is used for simulation verification, the capacity of each wind driven generator in the wind power generation system is 5MW, 20 fans are adopted, a box-type transformer is 0.69/10kV, the field boosting is changed to 10/220kV, the wiring group is YNd11, the rated capacity is 200MVA, the length of a connecting line is 60km, and the parameters of the doubly-fed wind generator set are shown in table 2.
Table 2 parameters of doubly-fed wind turbine
Calculation example 1: and A phase fault phase selection judgment. It is necessary to combine the abrupt current and abrupt voltage compensated under the fault, select phases by using the generalized power values, obtain the generalized power values of each phase and each phase under the a-phase fault as shown in fig. 8 and 9, and calculate the generalized power ratio again, so that the effect is more obvious, and the generalized power ratio of the compensated abrupt is used as the simulation result of fault phase selection as shown in fig. 10.
As can be seen from fig. 10, in the case of a phase failure, the generalized power ratio of the compensation mutation amount of the a phase is the largest, the B phase is the next smallest, but the value thereof is also small, the generalized power ratio of the compensation mutation amount of the C phase is almost 0, and H max＝61.784Hmid can be satisfied even at the lowest point, and when criterion 1 is satisfied, it can be determined that a single-phase ground failure is generated, and when H max corresponds to the a phase, conforms to the actual failure type, and phase selection is successful.
Calculation example 2: and BC interphase short circuit phase selection judgment. The generalized power values of each phase and each phase under the BC phase short-circuit fault after compensation are shown in fig. 11 and 12, and the generalized power ratio is calculated again, so that the effect is more obvious, and the generalized power ratio of the compensation abrupt quantity is adopted as a simulation result of fault phase selection and is shown in fig. 13.
As can be seen from fig. 11-13, when BC two-phase short circuit occurs, the generalized power ratio of the compensation mutation quantity of B, C phases is higher than that of the a phase, P B≈PC＞PA,PBC＞PCA≈PAB is satisfied, and the ratio H B≈HC＞＞HA of the two phases, i.e. H max≈Hmid＞＞Hmin, is obtained, criterion 2 is satisfied, and phase selection is successful.
Calculation example 3: and judging the fault phase selection under different fault types. The method has the advantages that the fault phase selection results of the generalized power ratio of the compensated mutation quantity under different fault types are verified, the results fully show the correctness of the method applied to fault phase selection, a large number of simulations verify that the method is high in sensitivity, the fault type can be identified at the moment of faults, the influence of transient impedance characteristics of a wind farm is avoided, large-scale data setting is not needed, the workload of a phase selection device in engineering practice is reduced, and sufficient time is vacated for the actions of relay protection devices, particularly automatic reclosing devices.
TABLE 3 generalized Power ratio results for compensated mutation amounts for different fault types
Calculation example 4: and judging fault phase selection under different fault positions and different transition resistances. The values of H max/Hmid are shown in Table 4, when single-phase earth faults occur at the positions of 25%,50%,75% of the line length from the wind field outlet protection, respectively, and the transition resistances are 25 omega, 50 omega, 75 omega and 100 omega, respectively.
TABLE 4 generalized Power ratio results for compensated abrupt changes at different fault locations and transition resistances
The phase selection result shows that H max/Hmid gradually decreases with the increase of the transition resistance, but sufficient margin is left, and the phase selection result is not affected. The phase selection method has strong capability of resisting transition resistance, can correctly select phases for different fault positions, has high sensitivity, and meets the requirements of new phase selection criteria.
Claims (1)
1. A fault phase selection method for constructing generalized power ratio based on compensation abrupt quantity is characterized in that: the phase selection method comprises the steps of fault polarization factor construction, adaptability demonstration of a new energy side fault line selection model, novel abrupt change calculation under the fault polarization factor, generalized power ratio definition and calculation and novel fault phase selection criterion process;
The fault polarization factor construction process is as follows: calculating positive sequence fault current distribution coefficient of protection installation position according to positive, negative and zero sequence fault network during system fault Negative sequence fault current distribution coefficient/>Zero sequence fault current distribution coefficient/>Wherein/>Respectively positive, negative and zero sequence fault currents at fault points,/> Positive sequence fault current abrupt change, negative sequence fault current and zero sequence fault current of the protection installation position respectively; defining p as positive sequence fault polarization factor, p=c 2/C1;q＝C2C0, and q as zero sequence fault polarization factor;
The adaptability demonstration process of the new energy side fault line selection model is as follows: according to the conventional phase current difference mutation amount calculation,
Wherein alpha is a twiddle factor, substituting positive sequence fault polarization factor p into a phase current difference mutation quantity calculation new energy side fault line selection model, as shown in formula (1), wherein,Three-phase current abrupt change of protection installation place,/>, respectivelyIs the abrupt change of the line current difference,/>Respectively short-circuit current at fault points;
The ratio Z' W1ZW2 = r of the virtual positive sequence impedance and the virtual negative sequence impedance of the new energy station, the value range of p is r < p < 1, p is a fluctuation value, the amplitude of the current difference mutation quantity is greatly influenced by p, when the p approaches 0 in single-phase grounding fault, the amplitudes of three phase current difference mutation quantities are approximately equal, the fault is easy to select as a three-phase fault, and when the p approaches 1, the phase is easy to select as a two-phase-to-phase short circuit;
the novel mutation amount calculation process under the fault polarization factor is as follows:
Step 1: assuming that the positive and negative sequence impedances of the system side and the interconnecting line are approximately equal, the positive sequence fault polarization factor is mainly calculated by calculating Z T1+Z′W1、ZT2+ZW2,ZT1、ZT2 as the total positive sequence impedance and the negative sequence impedance from the main transformer, the collector line to the box transformer of the fan and using the fault component principle Calculation of substituted positive sequence fault polarization factor based on current distribution coefficientAnd further from the public representation (1) the availability (2)
Wherein the method comprises the steps ofThe M-terminal phase current abrupt change quantity is compensated by positive sequence fault current; the coefficient before the positive sequence fault current of the fault point on the right side of the equation is compensated to be C 2, so that the inadaptability of the positive sequence transient equivalent impedance to fault phase selection in the wind power system is avoided;
Step 2: the current abrupt change under the zero sequence fault polarization factor can be obtained based on the formula (2) as shown in the formula (3)
In the method, in the process of the invention,A new phase current abrupt quantity compensated by zero sequence fault current; the coefficient before the zero sequence fault current of the fault point on the right side of the equation is compensated as C 2, and the current distribution coefficient is unified so that the abrupt change phase selection is not influenced by the positive and negative zero sequence calculation impedance characteristics of the wind power plant any more;
The generalized power ratio is defined and calculated as follows: cross-polarizing the voltage abrupt change and the current abrupt change to construct a current-voltage compensated abrupt change generalized power ratio as shown in formula (4)
Subscript ofIs any phase of A, B, C three phases,/>For the differentiated representation of three phases,/>To/>To calculate the generalized power ratio of the compensating abrupt quantity of the phase,/>To/>To calculate the phase break power,/>The power is the abrupt difference of the other two phases;
the novel fault phase selection criterion process is as follows: calculating three-phase generalized power ratios and constructing fault phase selection criteria of different fault types based on comparison of the three-phase generalized power ratios:
(1) The single-phase earth fault phase selection criterion is H max＞σHmid, wherein sigma is a setting coefficient, sigma is 10, and the phase corresponding to H max is the fault phase when the single-phase fault occurs to the circuit;
(2) The two-phase short circuit fault phase selection criterion is (H mid-Hmin)Hmax & gteta, wherein eta is a setting coefficient, eta is 0.5, and two phases corresponding to H max and H mid are fault phases when two-phase faults occur to a line;
(3) The two-phase grounding short circuit phase selection criterion is satisfied when the two-phase short circuit fault phase selection criterion is satisfied Wherein μ is a tuning coefficient, μ is 0.15;
(4) The three-phase short circuit fault phase selection criterion is (H max-Hmin)/Hmin < epsilon, wherein epsilon is a setting coefficient, and epsilon is 3.
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