CN117458409A - Self-adaptive protection method for distribution network containing distributed power supply based on single-ended quantity - Google Patents
Self-adaptive protection method for distribution network containing distributed power supply based on single-ended quantity Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
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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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Abstract
The invention relates to the field of relay protection of power systems, in particular to a self-adaptive protection method for a distribution network containing a distributed power supply based on single-ended quantity, which comprises the steps of collecting bus voltage of the distribution network and outlet current of each feeder line; calculating output parameters of the distributed power supply on the feeder line under each fault type, and calculating the self-adaptive protection setting impedance under each fault; judging whether to start self-adaptive protection according to whether the instantaneous value of the line current power frequency variation is larger than a set threshold value, if so, starting the protection, judging the fault type and fault phase of the power distribution network, and calculating the measured impedance, the additional impedance angle and the fault impedance under each fault; judging whether absolute values of a real part and an imaginary part of fault impedance under the fault are smaller than or equal to a real part and an imaginary part of a setting value corresponding to the fault; if yes, tripping the circuit breaker; the invention is not affected by factors such as short-circuit transition resistance, fault position, system operation mode and the like, and has the advantages of high speed, good reliability, strong adaptability and no dependence on communication.
Description
Technical Field
The invention relates to the field of relay protection of power systems, in particular to a self-adaptive protection method for a distribution network containing distributed power sources based on single-ended quantity.
Background
Along with the further increase of the consumption and pollution of the traditional power generation mode to the environmental resources, the new energy power generation is gradually valued as a power generation mode with small pollution and strong reproducibility. The distributed power supply is widely connected into the power distribution network due to the advantages of simple structure, convenience in installation and the like. However, due to the influence of the inverter control strategy, the distributed power supply often has the characteristics of weak feedback, controlled current phase and the like, so that relay protection in the power distribution network such as adaptive current protection, current differential protection and the like has the risk of failure.
At present, technicians develop researches on relay protection of a power distribution network with a distributed power supply, and the research mainly comprises self-adaptive current protection based on a distributed power supply equivalent model and an iterative algorithm, power distribution network current differential protection based on multiple criteria and the like. However, these protection methods have drawbacks such as high protection delay and dependence on device communication. Compared with the existing protection method, the distance protection realizes the functions of fault location, protection of an outlet and the like by calculating the measured impedance and comparing the measured impedance with the protection setting impedance, and has the advantages of high response speed, no influence by the running mode of the system and the like. However, the distance protection of the distribution network accessed by the distributed power supply has the problems of poor transitional resistance, failure of branch coefficients and the like. Aiming at the problems, a learner improves a calculation formula of a distance protection branch coefficient based on a composite sequence network, and the method strengthens the reliability of distance protection, but needs to collect fault current output by a distributed power supply, has higher cost and limited practicability. The method can accurately calculate the position of the fault on the feed line, but cannot be suitable for the condition that a plurality of distributed power supplies are connected into a power distribution network, and lacks certain engineering practicability.
In summary, due to the weak feedback and phase control characteristics of the distributed power supply, the protection of the original power distribution network fails, and the protection is extremely easy to fail or malfunction. The existing protection of the distribution network with the distributed power supply has the problems of high cost, over ideal application scene, limited application range and the like, and an effective protection method of the distribution network with the distributed power supply is not available. Therefore, the method for protecting the distribution network with the distributed power supply, which has high sensitivity, reliable action and good economy, is an urgent problem to be solved by the person skilled in the art.
Disclosure of Invention
In view of the above, the invention provides a self-adaptive protection method for a distribution network containing distributed power sources based on single-ended quantity, which specifically comprises the following steps:
s1, collecting bus voltage of a power distribution network and outlet current of each feeder line;
s2, calculating output parameters of the distributed power supply on the feeder line under each fault type, and calculating the self-adaptive protection setting impedance under each fault;
s3, judging whether to start self-adaptive protection according to whether the instantaneous value of the line current power frequency variation is larger than a set threshold value, if so, starting the protection, otherwise, returning to the step S1;
s4, if the protection is started, judging the fault type and fault phase of the power distribution network, and calculating measured impedance, an additional impedance angle and fault impedance under each fault;
s5, judging whether absolute values of a real part and an imaginary part of fault impedance under the fault are smaller than or equal to the real part and the imaginary part of a setting value corresponding to the fault calculated in the step S2;
s6, if yes, tripping the circuit breaker, and cutting off a fault feeder line; otherwise, returning to the step S1.
Further, the process of calculating the output parameters of the distributed power supply on the feeder line under each fault type includes:
s21, connecting the ith distributed power supply in normal running state to positive sequence voltageAnd positive sequence current->Let k=1 as an iteration initial value;
s22, in the kth iteration process, aiming at the ith distributed power supply, if the equivalent of the power supply is that the output current isRespectively establishing a power distribution network composite sequence network when single-phase grounding, two-phase short circuit, two-phase grounding and three-phase short circuit occur at the tail end of a power supply feeder line, and solving positive sequence voltage of a (k+1) generation distributed power supply grid connection point when single-phase grounding, two-phase short circuit, two-phase grounding and three-phase short circuit occur through the composite sequence network>
S23, calculating the positive sequence current output by the k+1th generation distributed power supply by utilizing the positive sequence voltage of the k+1th generation distributed power supply grid-connected point;
s24, judging whether the iteration converges or not according to the positive sequence voltage amplitude values of the distributed power supply grid connection point of the kth iteration and the (k+1) th iteration, and outputting the grid connection point voltage of the distributed power supply of the (k+1) th iteration if the iteration convergesAnd the output current of the distributed power supply +.>
S25, if not converging, let k=k+1 and return to step S22.
Further, calculating the tuning impedance of the adaptive protection under each fault includes:
wherein Z is zd Setting impedance; z is Z L Line impedance for the feed line; n is the number of distributed power sources on the feeder;the current output for the ith distributed power supply; />Current output by the mth distributed power supply; />A feeder outlet current measured for the protection device; z is Z setDGi Representing the impedance at location i, representing the line impedance between the protection installation and the 1 st distributed power supply point when i=0, representing the line impedance between the i-th distributed power supply and the i+1-th distributed power supply point when i=1, 2..n-1, and representing the line impedance between the i=n>
Further, the process of judging the fault type and the fault phase of the power distribution network comprises the following steps:
if it isAnd->Judging that the ground fault occurs;
when the fault type is a ground fault, if it isJudging that a ground fault occurs at the o-phase, and taking the ground fault as a first fault type;
when the fault type is a ground fault, if it isJudging that a ground fault occurs between the o-phase and the p-phase, and taking the ground fault as a second fault type;
if it isAnd->Judging that a non-grounding fault occurs;
when the fault type is a non-earth fault and the conditions among the three phases of o, p and q are satisfiedThen there is a short between the o-phase and the p-phase, which is taken as a third fault type;
when the fault type is a non-grounding fault and the two-phase short-circuit fault condition is not satisfied, judging that a three-phase short-circuit fault occurs, and taking the three-phase short-circuit fault as a fourth fault type;
wherein,phase current amplitudes of the outlets of the feed lines of the o phase, the p phase and the q phase are respectively +.>For negative sequence current amplitude, ε, at the feeder outlet 2 Is a negative sequence threshold value; />For the zero sequence current amplitude of the feeder outlet epsilon 0 Is a zero sequence threshold value;for the o-phase current fault component of the feeder outlet, is>For the p-phase current fault component of the feeder outlet, is->K' is a reliability factor for the q-phase current fault component of the feeder outlet.
Further, when the first fault type occurs, i.e. if a ground fault occurs at the q-phase, the measured impedance is expressed as:
when the first fault type occurs, the additional impedance angle is expressed as:
wherein,representing the voltage phasors protecting the q-phase of the measured bus; />As the q-phase current phasor of the feeder outlet,for zero sequence current phasors, k, at the feeder outlets 0 Is a zero sequence compensation coefficient.
Further, when the second fault type occurs, i.e., a ground fault occurs between the p-phase and the q-phase, the measured impedance is expressed as:
when the second fault type occurs, the additional impedance angle is expressed as:
wherein,representing the voltage phasor of the p-phase of the busbar to be protected, for example +.>P-phase current phasors for feeder outlets;representing the voltage phasor of the q-phase of the busbar to be protected, +.>Q-phase current phasors for feeder outlets; />For the zero sequence current phasors of the feeder outlets, +.>Is the negative sequence current phasor of the feeder outlet.
Further, if a third fault type occurs, i.e. a short circuit occurs between the p-phase and the q-phase, the measured impedance is expressed as:
if a third fault type occurs, the additional impedance angle is expressed as:
further, if the fourth fault type occurs, that is, a three-phase short occurs, the measured impedance is expressed as:
if a fourth fault type occurs, the additional impedance angle is expressed as:
further, calculating the fault impedance according to the measured impedance and the value of the additional impedance angle under each fault type comprises:
wherein Z is f Z is the fault impedance m In order to measure the impedance of the electrical conductor,for setting the phase angle of the impedance +.>For additional impedance angle->To measure the phase angle of the impedance.
Further, when the circuit breaker is judged to be tripped in the step S5, the following conditions are satisfied:
|ReZ f |≤|ReZ zd |and | ImZ f |≤|ImZ zd |
Where Re represents the real part of the complex number and Im represents the imaginary part of the complex number.
At present, research on relay protection development of a power distribution network with a distributed power supply mainly comprises self-adaptive current protection based on a distributed power supply equivalent model and an iterative algorithm, power distribution network current differential protection based on multiple criteria and the like. However, these protection methods have drawbacks such as high protection delay and dependence on device communication. Compared with the existing protection method, the distance protection realizes the functions of fault location, protection of an outlet and the like by calculating the measured impedance and comparing the measured impedance with the protection setting impedance, and has the advantages of high response speed, no influence by the running mode of the system and the like. However, the distance protection of the distribution network accessed by the distributed power supply has the problems of poor transitional resistance, failure of branch coefficients and the like. Aiming at the problems, a learner improves a calculation formula of a distance protection branch coefficient based on a composite sequence network, and the method strengthens the reliability of distance protection, but needs to collect fault current output by a distributed power supply, has higher cost and limited practicability. The method can accurately calculate the position of the fault on the feed line, but cannot be suitable for the condition that a plurality of distributed power supplies are connected into a power distribution network, and lacks certain engineering practicability. Compared with the prior art, the invention has the following beneficial effects:
1. the invention uses the output parameters of the distributed power supply during normal operation as iteration initial values, calculates the grid-connected point voltage and the output current of the distributed power supply under various fault types by using an iteration algorithm, and avoids the condition of obtaining the fault parameters of the distributed power supply depending on a communication system while conforming to the actual operation condition of the power distribution network, thereby reducing the configuration cost and the complexity of protection.
2. On the basis of the traditional protection setting impedance of the power distribution network, the feeder line impedance influenced by the output current of the distributed power supply is counted into the protection setting impedance, so that the additional impedance only comprises the transition impedance and the branch coefficient thereof, the additional impedance which is caused by uncertain fault positions is prevented from being computationally infeasible, and the accuracy of the self-adaptive protection setting impedance is improved.
3. The invention is based on the negative sequence and zero sequence passage of the multi-feeder distribution network under the fault condition, and the negative sequence and zero sequence current at the feeder outlet equivalently flow through the negative sequence and zero sequence current of the transition resistor, so that the problem that the current flowing through the transition resistor cannot be measured is solved on the premise of ensuring the calculation accuracy, and the calculation complexity of the additional impedance angle is greatly simplified.
4. The invention utilizes the impedance triangle formed by the measured impedance, the additional impedance and the fault impedance to provide the fault impedance calculation method based on the triangle sine theorem, eliminates the influence of the additional impedance on the measured impedance under the condition of only utilizing single-end quantity and fixed value, obtains the fault impedance reflecting the actual fault condition, compares the fault impedance with the set impedance to realize action judgment, and greatly improves the reliability of self-adaptive protection.
5. The method is clear in implementation mode, only bus voltage and feeder outlet current of the power distribution network are required to be collected, self-adaptive protection setting impedance under single-phase grounding, two-phase short circuit, two-phase grounding and three-phase short circuit is calculated through an iterative algorithm, influence of additional impedance on measured impedance is eliminated based on sine theorem, fault impedance is obtained, and protection action judgment is completed. The whole scheme is easy to realize, and has stronger economy and practicability.
Drawings
FIG. 1 is a flow chart of the self-adaptive protection method of the distribution network containing the distributed power source based on single-ended quantity, which is disclosed by the invention;
FIG. 2 is a diagram of a topology of a power distribution network in an embodiment of the invention;
FIG. 3 is a comparison of fault impedance and tuning impedance for a single-phase earth fault in an embodiment of the present invention;
FIG. 4 is a comparison of the fault impedance and the tuning impedance for a two-phase ground fault in accordance with an embodiment of the present invention;
FIG. 5 is a comparison of fault impedance and tuning impedance for a two-phase short circuit fault in accordance with an embodiment of the present invention;
fig. 6 is a comparison of fault impedance and tuning impedance for a three-phase short circuit fault in an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention provides a self-adaptive protection method for a distribution network containing distributed power sources based on single-ended quantity, which specifically comprises the following steps:
s1, collecting bus voltage of a power distribution network and outlet current of each feeder line;
s2, calculating output parameters of the distributed power supply on the feeder line under each fault type, and calculating the self-adaptive protection setting impedance under each fault;
s3, judging whether to start self-adaptive protection according to whether the instantaneous value of the line current power frequency variation is larger than a set threshold value, if so, starting the protection, otherwise, returning to the step S1;
s4, if the protection is started, judging the fault type and fault phase of the power distribution network, and calculating measured impedance, an additional impedance angle and fault impedance under each fault;
s5, judging whether absolute values of a real part and an imaginary part of fault impedance under the fault are smaller than or equal to the real part and the imaginary part of a setting value corresponding to the fault calculated in the step S2;
s6, if yes, tripping the circuit breaker, and cutting off a fault feeder line; otherwise, returning to the step S1.
Aiming at the defects of the prior art, the invention actually solves the problems that: determining grid-connected point voltage and output current of a distributed power supply under various fault types under the condition of not depending on a device communication function; how to carry out self-adaptive transformation on the protection setting impedance of the power distribution network, and eliminate the interference of uncertainty of a fault position on the protection setting; how to calculate additional impedance angles under various fault conditions using bus voltage and feeder current; how to use the collected and calculated parameters to eliminate the additional impedance caused by the weak feedback and the phase controlled characteristic and the influence on the measured impedance, and obtain the fault impedance reflecting the actual fault position; how to design proper protection action criteria and realize the reliable action of self-adaptive protection.
As shown in fig. 1, in this embodiment, a self-adaptive protection method for a distribution network including a distributed power source based on single-ended quantity includes the following steps:
s101: collecting bus voltage and feeder line outlet current of a power distribution network;
s102: according to the feeder line outlet current and the bus voltage, respectively calculating the grid-connected point voltage and the output current of a distributed power supply on a feeder line under single-phase grounding, two-phase short circuit, two-phase grounding and three-phase short circuit;
s103: the self-adaptive protection setting impedance under single-phase grounding, two-phase short circuit, two-phase grounding and three-phase short circuit of the power distribution network is calculated respectively;
s104: judging whether the self-adaptive protection is started, if so, executing a step S105, otherwise, executing a step S101;
s105: judging the type and the fault phase of the power distribution network fault;
s106: calculating and measuring impedance by using bus voltage and feeder current;
s107: calculating an additional impedance angle by using the bus voltage, the feeder current and the measured impedance;
s108: calculating fault impedance by using the tuning impedance, the measured impedance and the additional impedance angle;
s109: judging whether the action criterion is met according to the fault impedance and the setting impedance, if yes, judging that the protected feeder fails, and sending out tripping or alarming signals, otherwise, judging that the fault is located outside the protected feeder, and returning to S101.
In the embodiment of the invention, based on collecting the busbar voltage and feeder line outlet current of the power distribution network, the self-adaptive protection setting impedance under single-phase grounding, two-phase short circuit, two-phase grounding and three-phase short circuit is calculated through an iterative algorithm, the influence of additional impedance on the measured impedance is eliminated based on a sine theorem, the fault impedance is obtained, and the action judgment of protection is completed. The invention can accurately judge whether the short circuit fault occurs on the protected feeder line, and perform corresponding protection action, thereby ensuring the safe and stable operation of the power distribution network.
In implementation, the topology of the power distribution network is shown in fig. 2. The voltage of the upper power grid is 110kV, the equivalent impedance is 0.05+0.0044jΩ, the bus voltage of the power distribution network is 10kV, and the transformer is grounded by adopting an arc suppression coil and resistance mode. Feeder line L 1 、L 2 、L 3 The lengths of the impedance unit are respectively 20km, 40km and 10km, and the impedance unit length is 0.58-6.58j omega/km; load LD 1 Capacity is 2MVA, power factor is 0.672; load LD 2 Capacity 5MVA, power factor 0.826; load LD 3 Capacity is 3MVA, power factor is 0.741; load LD 4 Capacity is 2MVA, power factor is 0.729; load LD 5 Capacity is 2MVA, power factor is 0.815; access feeder L 2 The active and reactive power reference values for normal operation of all distributed power supplies are 0.866MW, 0.5Mvar. At the feed line L 2 Single-phase earth fault, two-phase short circuit fault and three-phase short circuit fault occur when the two-phase short circuit fault is respectively set for 0.1 secondPhase short circuit failure, each lasting 0.1 seconds.
In the specific implementation, in step S102, the voltage and the output current of the grid-connected point of the distributed power supply under various fault types are calculated through an iterative algorithm, and the method specifically includes the following steps:
step S201, taking the positive sequence voltage and the positive sequence current of the distributed power grid connection point in the normal running state as iteration initial valuesAnd->i denotes the ith distributed power supply.
Step S202, equivalent the distributed power supply as output currentRespectively establishing a power distribution network composite sequence network when single-phase grounding, two-phase short circuit, two-phase grounding and three-phase short circuit occur at the tail end of a feeder line, and solving positive sequence voltage of the (k+1) generation distributed power supply grid connection point when single-phase grounding, two-phase short circuit, two-phase grounding and three-phase short circuit occur through the composite sequence network>Where k is the iteration number, and k=0, 1,2 …, where k=0 represents the value of the initial iteration, i.e. in this embodiment, the positive sequence voltage and the positive sequence current of the distributed power grid connection point in the normal operation state are taken as the initial iteration value ∈ ->And->Iteration is performed on this basis.
Step S203, the positive sequence voltage of the k+1st generation distributed power supply grid-connected point is utilized, and the positive sequence current of the k+1st generation distributed power supply output is calculated according to the following formula:
wherein,a complex power command value for the ith distributed power supply,/->Positive sequence current is output for the k+1st generation distributed power supply.
Step S204, judging whether the (k+1) th generation iteration converges according to the following formula:
in the method, in the process of the invention,positive sequence voltage amplitude values of the grid-connected points of the distributed power supplies of the k generation and the k+1th generation are respectively epsilon which is a threshold value for iteration convergence.
Step S205, if the (k+1) th generation converges, stopping the iteration, and calculating the grid-connected point voltage of the distributed power supply asThe output current of the distributed power supply is +.>If the (k+1) th generation is not converged, let k=k+1, and return to step S202.
In the specific implementation, in step S103, the power distribution network generates self-adaptive protection setting impedance under single-phase grounding, two-phase short circuit, two-phase grounding and three-phase short circuit; the method comprises the following steps:
wherein n isZ is the number of distributed power sources on the feeder line zd To adjust the impedance, Z L Is the line impedance of the feed line,feed line outlet current measured for protection device, < >>Z is the current output by the ith and mth distributed power supplies setDGi For the impedance at location i, expressed as:
when the distribution network feeder L shown in figure 2 2 When single-phase grounding, two-phase short circuit and three-phase short circuit faults occur, the setting impedance calculated in the step S103 is shown in table 1.
TABLE 1 tuning impedances for various fault types
In the specific implementation, in step S104, the protection starting adopts a line current abrupt quantity starting criterion, and the specific form is as follows:
wherein DeltaI zd Starting a fixed value for the line current abrupt quantity; ΔI T A floating threshold is automatically adjusted step by step along with the change of the variable quantity output;for the instantaneous value of the line current power frequency variation, the following formula can be used for solving:
wherein,instantaneous values of line current between any two phases (including between A phase and B phase, between C phase and A phase, between B phase and C phase in a three-phase power system) at time T, time T-T and time T-2T respectively;the effective value of the line current between any two phases at the time T-T and the time T-2T, T-3T respectively; t is a period, 20ms is taken in this embodiment, and T is the time when the fault occurs.
In the specific implementation, in step S105, the fault type is determined according to the magnitude of the negative sequence and the zero sequence current of the feeder outlet. Wherein, the ground fault criterion is:
and->
In the method, in the process of the invention,the zero sequence current amplitude of the feeder outlet is the zero sequence current amplitude of the feeder outlet; epsilon 0 Is threshold value corresponding to zero sequence current, +.>A negative sequence current amplitude value for a feeder outlet; epsilon 2 Threshold corresponding to negative sequence currentValues.
The non-ground fault criteria are:
and->
In particular, in step S105, a faulty phase is determined according to the magnitude of the phase current at the feeder outlet.
When a ground fault occurs, it is required to determine whether a single-phase ground fault or a two-phase ground fault occurs, where in this embodiment, if a ground fault occurs at the o-phase, a phase selection criterion of the single-phase ground fault in the three-phase power system is:
wherein,the phase current amplitudes of the outlets of the o-phase feeder line, the p-phase feeder line and the q-phase feeder line are respectively determined.
Specifically, when an a-phase ground fault occurs:
in the method, in the process of the invention,phase a current amplitude for feeder outlet, +.>Phase B current amplitude for feeder outlet, +.>C-phase current amplitude at feeder outlet; k (k) sg Is a single-phase jointThe phase coefficient of ground fault is 3, k' sg Taking 0.2 for the single-phase grounded non-fault phase coefficient.
When a B-phase earth fault occurs:
when a C-phase earth fault occurs:
in a three-phase power system, a ground fault occurs between any two phases, and the ground fault between an o phase and a p phase is assumed to be satisfied:
specifically, if a two-phase ground fault occurs between the phase a and the phase B in the three-phase power system, the following conditions are satisfied:
wherein k is dg Taking 3 as a two-phase ground fault phase coefficient; k' dg The value of the phase-to-phase grounding non-fault phase coefficient is 0.2.
When the B phase and the C phase indirectly fail, the following conditions are satisfied:
when the C phase and the A phase indirectly fail, the following conditions are satisfied:
when a non-ground fault occurs, it is required to determine whether a two-phase short-circuit fault or a three-phase short-circuit fault occurs, where in this embodiment, if a short-circuit fault occurs between any two phases in the three-phase power system, the following is satisfied:
wherein,for the o-phase current fault component of the feeder outlet, is>For the p-phase current fault component of the feeder outlet, is->Is the q-phase current fault component of the feeder outlet.
Specifically, if a two-phase short circuit fault occurs between the phase A and the phase B, the following conditions are satisfied:
in the method, in the process of the invention,is the A, B, C phase current fault component of the feeder outlet. k' is a reliable coefficient and is generally 2;
if a two-phase short circuit fault occurs between the B phase and the C phase, the following conditions are satisfied:
if a two-phase short circuit fault occurs between the C phase and the A phase, the following conditions are satisfied:
/>
and when the current at the outlet of the feeder meets the non-ground fault criterion but does not meet the three two-phase short circuit phase selection criterion, judging that a three-phase short circuit fault occurs on the feeder.
In the specific implementation, in step S106, when calculating the measured impedance of the single-phase earth fault, it is assumed that the earth fault occurs at the q-phase, and the measured impedance is expressed as:
wherein,representing the voltage phasors protecting the q-phase of the measured bus; />Q-phase current phasors, k, for feeder outlets 0 Is a zero sequence compensation coefficient; the q phase is any one of the A phase, the B phase and the C phase in the three-phase power system.
Specifically, if the a phase fails in the three-phase power system, the measured impedance is expressed as:
wherein Z is m In order to measure the impedance of the electrical conductor,for protecting the measured phase A voltage phasor of the bus, < >>Phase a current phasors for feeder outlets, +.>For zero sequence current phasors, k, at the feeder outlets 0 For the zero sequence compensation coefficient, the calculation formula is as follows:
wherein Z is 1 、Z 0 Positive sequence impedance and zero sequence impedance of a feeder line unit length.
Similarly, the measured impedance when a single-phase ground fault occurs in the B phase is:
in the method, in the process of the invention,for protecting the measured bus B-phase voltage phasor, +.>Is the B-phase current phasor at the feeder outlet.
Similarly, the measured impedance when the single-phase ground fault occurs in the C phase is:
in the method, in the process of the invention,for protecting the measured bus C-phase voltage phasor,/->Is the C-phase current phasor at the feeder outlet.
In this embodiment, if a ground fault occurs between the p-phase and q-phase, the measured impedance is expressed as:
wherein,representing the voltage phasors of the p-phase of the bus that is measured for protection; />P-phase current phasors for feeder outlets; the q phase and the p phase are any one of the A phase, the B phase and the C phase in the three-phase power system, and the q phase and the p phase are not the same phase.
Specifically, if the measured impedance when the a phase and the B phase are short-circuited to ground in the three-phase power system is:
similarly, the measured impedance when the B phase and C phase are in short circuit grounding is as follows:
similarly, the measured impedance when the C phase and the A phase are in short circuit grounding is as follows:
in calculating the measured impedance for a two-phase short circuit fault, assuming a short circuit between the p-phase and q-phase, the measured impedance is expressed as:
the q phase and the p phase are any one of an A phase, a B phase and a C phase in a three-phase power system, and the q phase and the p phase are not the same phase.
Specifically, if a two-phase short circuit occurs between the a phase and the B phase in the three-phase power system, the measured impedance is:
similarly, the measured impedance when the B phase and the C phase are in short circuit is as follows:
similarly, the measured impedance at the time of short circuit between the C phase and the A phase is:
if three-phase short circuit occurs in the three-phase power system, only the measured resistance between any two phases is needed to be calculated when the measured impedance is calculated, and the measured impedance is calculated according to the following method:
specifically, in this embodiment, taking calculating a phase and a C phase in a three-phase power system as an example, the measured impedance is expressed as:
in the specific implementation, in step S107, if a single-phase ground fault occurs, that is, if a q-phase ground fault occurs, the additional impedance angle is expressed as:
specifically, if the additional impedance angle at the time of the a-phase ground in the three-phase power system is expressed as:
/>
in the middle of，For additional impedance angle->Phase a current for feeder outlet, +.>For zero sequence current at feeder outlet, k 0 Is a zero sequence compensation coefficient.
Similarly, the additional impedance angle at the B-phase grounding is expressed as:
in the method, in the process of the invention,phase B current at the feeder outlet.
Similarly, the additional impedance angle at which C meets is expressed as:
in the method, in the process of the invention,and C-phase current at the outlet of the feeder.
If a ground fault occurs between the p-phase and q-phase, the measured impedance is expressed as:
specifically, if the additional impedance angle at the time of a-phase and B-phase short circuit grounding in the three-phase power system is expressed as:
in the method, in the process of the invention,is the negative sequence current at the feeder outlet.
Similarly, the additional impedance angle at the time of B-phase and C-phase short circuit to ground is expressed as:
similarly, the additional impedance angle at the time of the C-phase and A-phase short circuit grounding is expressed as:
if a short circuit occurs between the p-phase and q-phase, the additional impedance angle is expressed as:
specifically, when a short circuit occurs between the a-phase and the B-phase in the three-phase power system, the additional impedance angle is expressed as:
similarly, the additional impedance angle at the time of B-phase and C-phase short circuit is expressed as:
/>
similarly, the additional impedance angle at the time of a short circuit between the C-phase and the a-phase is expressed as:
if a three-phase short circuit fault occurs in the three-phase power system, the additional impedance angle is calculated according to the following method:
in specific implementation, in step S108, the fault impedance is calculated according to the following method:
wherein Z is f Z is the fault impedance m In order to measure the impedance of the electrical conductor,for the phase angle of the tuning impedance, j represents an imaginary unit;the calculation method of (1) is as follows:
in the method, in the process of the invention,for additional impedance angle->The calculation method of (1) is as follows:
in the method, in the process of the invention,to measure the phase angle of the impedance.
When the picture is2, a distribution network feeder line L 2 When single-phase grounding, two-phase short circuit and three-phase short circuit faults occur, the fault impedance calculated in the step S108 is shown in table 2.
TABLE 2 Fault resistance under various fault types
In the specific implementation, in step S109, the protection action criteria are:
|ReZ f |≤|ReZ zd |and | ImZ f |≤|ImZ zd |
Wherein Re represents the real part of the complex number and Im represents the imaginary part of the complex number; z is Z f Z is the fault impedance zd To set the impedance.
When the distribution network feeder L shown in figure 2 2 When a single-phase grounding, two-phase short circuit or three-phase short circuit fault occurs, the comparison result of the fault impedance and the setting impedance in the step S109 is as follows:
the comparison result of the single-phase earth fault is shown in fig. 3; the comparison result of the two-phase ground faults is shown in fig. 4; the comparison result of the two-phase short circuit fault is shown in fig. 5; the comparison result of the three-phase short-circuit fault is shown in fig. 6.
Figures 3, 4, 5 and 6 show that when the feed line L 2 When single-phase grounding, two-phase short circuit and three-phase short circuit faults occur on the circuit breaker, the self-adaptive protection method provided by the invention can accurately judge whether the short circuit faults occur on the protected feeder line, further acts on the circuit breaker to trip, and timely cuts off the faulty feeder line, thereby ensuring the safe and stable operation of the power distribution network.
Those of ordinary skill in the art will appreciate that all or part of the steps in the various methods of the above embodiments may be implemented by a program to instruct related hardware, the program may be stored in a computer readable storage medium, and the storage medium may include: ROM, RAM, magnetic or optical disks, etc.
Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (10)
1. A self-adaptive protection method for a distribution network containing distributed power supplies based on single-ended quantity is characterized by comprising the following steps:
s1, collecting bus voltage of a power distribution network and outlet current of each feeder line;
s2, calculating output parameters of the distributed power supply on the feeder line under each fault type, and calculating the self-adaptive protection setting impedance under each fault;
s3, judging whether to start self-adaptive protection according to whether the instantaneous value of the line current power frequency variation is larger than a set threshold value, if so, starting the protection, otherwise, returning to the step S1;
s4, if the protection is started, judging the fault type and fault phase of the power distribution network, and calculating measured impedance, an additional impedance angle and fault impedance under each fault;
s5, judging whether absolute values of a real part and an imaginary part of fault impedance under the fault are smaller than or equal to the real part and the imaginary part of a setting value corresponding to the fault calculated in the step S2;
s6, if yes, tripping the circuit breaker, and cutting off a fault feeder line; otherwise, returning to the step S1.
2. The adaptive protection method for a distribution network including distributed power sources based on single-ended quantity according to claim 1, wherein the process of calculating the output parameters of the distributed power sources on the feeder lines under each fault type comprises:
s21, connecting the ith distributed power supply in normal running state to positive sequence voltageAnd positive sequence current->Let k=1 as an iteration initial value;
s22, in the kth iteration process, aiming at the ith distributed power supply, if the equivalent of the power supply is that the output current isRespectively establishing a power distribution network composite sequence network when single-phase grounding, two-phase short circuit, two-phase grounding and three-phase short circuit occur at the tail end of a power supply feeder line, and solving positive sequence voltage of a (k+1) generation distributed power supply grid connection point when single-phase grounding, two-phase short circuit, two-phase grounding and three-phase short circuit occur through the composite sequence network>
S23, calculating the positive sequence current output by the k+1th generation distributed power supply by utilizing the positive sequence voltage of the k+1th generation distributed power supply grid-connected point;
s24, judging whether the iteration converges or not according to the positive sequence voltage amplitude values of the distributed power supply grid connection point of the kth iteration and the (k+1) th iteration, and outputting the grid connection point voltage of the distributed power supply of the (k+1) th iteration if the iteration convergesAnd the output current of the distributed power supply +.>
S25, if not converging, let k=k+1 and return to step S22.
3. The method for adaptively protecting a distribution network including a distributed power source based on single-ended quantity according to claim 1, wherein calculating the tuning impedance of the adaptive protection under each fault comprises:
wherein Z is zd Setting impedance; z is Z L Line impedance for the feed line; n is the number of distributed power sources on the feeder;the current output for the ith distributed power supply; />Current output by the mth distributed power supply; />A feeder outlet current measured for the protection device; z is Z setDGi Representing the impedance at location i, representing the line impedance between the protection installation and the 1 st distributed power supply point when i=0, representing the line impedance between the i-th distributed power supply and the i+1-th distributed power supply point when i=1, 2..n-1, and representing the line impedance between the i=n>
4. The self-adaptive protection method for a distribution network with distributed power sources based on single-ended quantity according to claim 1, wherein the process of judging the fault type and fault phase of the distribution network comprises the following steps:
if it isAnd->Judging that the ground fault occurs;
when the fault type is a ground fault, if it isJudging that a ground fault occurs at the o-phase, and taking the ground fault as a first fault type;
when a fault is likeIs a ground fault if it meetsJudging that a ground fault occurs between the o-phase and the p-phase, and taking the ground fault as a second fault type;
if it isAnd->Judging that a non-grounding fault occurs;
when the fault type is a non-earth fault and the conditions among the three phases of o, p and q are satisfiedThen there is a short between the o-phase and the p-phase, which is taken as a third fault type;
when the fault type is a non-grounding fault and the two-phase short-circuit fault condition is not satisfied, judging that a three-phase short-circuit fault occurs, and taking the three-phase short-circuit fault as a fourth fault type;
wherein,phase current amplitudes of the outlets of the feed lines of the o phase, the p phase and the q phase are respectively +.>For negative sequence current amplitude, ε, at the feeder outlet 2 Is a negative sequence threshold value; />For the zero sequence current amplitude of the feeder outlet epsilon 0 Is a zero sequence threshold value; />For the o-phase current fault component of the feeder outlet, is>For outlet of feeder linesP-phase current fault component of>K' is a reliability factor for the q-phase current fault component of the feeder outlet.
5. The adaptive protection method for a distribution network including distributed power sources based on single-ended quantities according to claim 4, wherein when a first fault type occurs, i.e. if a ground fault occurs at q-phase, the measured impedance is expressed as:
when the first fault type occurs, the additional impedance angle is expressed as:
wherein,representing the voltage phasors protecting the q-phase of the measured bus; />Q-phase current phasors for feeder outlets, < >>For zero sequence current phasors, k, at the feeder outlets 0 Is a zero sequence compensation coefficient.
6. The method of claim 4, wherein when the second fault type occurs, i.e., a ground fault occurs between the p-phase and the q-phase, the measured impedance is expressed as:
when the second fault type occurs, the additional impedance angle is expressed as:
wherein,representing the voltage phasors of the p-phase of the bus that is measured for protection; />Representing the voltage phasors protecting the q-phase of the measured bus; />P-phase current phasors for feeder outlets; />Q-phase current phasors for feeder outlets, < >>For the zero sequence current phasors of the feeder outlets, +.>Is the negative sequence current phasor of the feeder outlet.
7. The method of claim 4, wherein if a third fault type occurs, i.e., a short circuit occurs between the p-phase and the q-phase, the measured impedance is expressed as:
if a third fault type occurs, the additional impedance angle is expressed as:
wherein,representing the voltage phasors of the p-phase of the bus that is measured for protection; />Representing the voltage phasors protecting the q-phase of the measured bus; />P-phase current phasors for feeder outlets; />Q-phase current phasors for feeder outlets, < >>Is the negative sequence current phasor of the feeder outlet.
8. The adaptive protection method for a distribution network including distributed power sources based on single-ended quantities according to claim 1, wherein if a fourth fault type occurs, a three-phase short circuit occurs, the measured impedance is expressed as:
if a fourth fault type occurs, the additional impedance angle is expressed as:
wherein,representation ofProtecting the measured voltage phasors of the p-phase of the bus; />Representing the voltage phasors protecting the q-phase of the measured bus; />P-phase current phasors for feeder outlets; />Is the q-phase current phasor of the feeder outlet.
9. The adaptive protection method for a distribution network including distributed power sources based on single-ended quantity according to claim 1, wherein calculating fault impedance according to the measured impedance and the value of the additional impedance angle for each fault type comprises:
wherein Z is f Z is the fault impedance m In order to measure the impedance of the electrical conductor,for setting the phase angle of the impedance +.>For additional impedance angle->To measure the phase angle of the impedance.
10. The self-adaptive protection method for the distribution network with the distributed power supply based on the single-ended quantity according to claim 1, wherein when the circuit breaker is judged to be tripped in the step S5, the following conditions are satisfied:
|ReZ f |≤|ReZ zd |and | ImZ f |≤|ImZ zd |
Wherein Re represents the real part of the complex number and Im represents the imaginary part of the complex number; z is Z f Z is the fault impedance zd To set the impedance.
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