CN112803376A - Power distribution network protection coordination method after grid connection of photovoltaic power supply - Google Patents

Power distribution network protection coordination method after grid connection of photovoltaic power supply Download PDF

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Publication number
CN112803376A
CN112803376A CN201911106559.1A CN201911106559A CN112803376A CN 112803376 A CN112803376 A CN 112803376A CN 201911106559 A CN201911106559 A CN 201911106559A CN 112803376 A CN112803376 A CN 112803376A
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protection
power supply
photovoltaic
grid
photovoltaic power
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Inventor
丁晓兵
华秀娟
陈宏山
宋兵
李正红
魏阳
史泽兵
陆明
桂海涛
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China Southern Power Grid Co Ltd
NR Engineering Co Ltd
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China Southern Power Grid Co Ltd
NR Engineering Co Ltd
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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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/006—Calibration or setting of parameters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/02—Details
    • H02H3/06—Details with automatic reconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/24—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to undervoltage or no-voltage
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B10/00—Integration of renewable energy sources in buildings
    • Y02B10/10—Photovoltaic [PV]

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Abstract

The invention relates to a power distribution network protection coordination method after grid connection of a photovoltaic power supply, which adopts a maximum power tracking control strategy to carry out model construction on a photovoltaic power supply grid-connected system, simulates the internal characteristics of the photovoltaic power supply, checks whether the connected photovoltaic capacity can influence the normal judgment of protection, adopts a method combining photovoltaic low-voltage ride-through and island protection with automatic reclosing, and simultaneously adopts a control strategy of 'synchronous detection' and 'no voltage detection', thereby avoiding the impact current generated during closing from influencing the power grid protection, fully utilizing the island protection and ensuring the safety of the power grid when a fault occurs.

Description

Power distribution network protection coordination method after grid connection of photovoltaic power supply
Technical Field
The invention relates to a power distribution network protection coordination method after grid connection of a photovoltaic power supply, and belongs to the technical field of power distribution protection.
Background
With the development of science and technology and economy, the power consumption and the power load tend to increase rapidly at present and in the future for a long time, and the traditional centralized power supply mode needs to be changed based on the consideration of factors such as environment, environmental protection and the like. The solar energy storage capacity is rich, Photovoltaic (PV) power generation is realized by collecting and utilizing light energy, and the power generation mode not only has the characteristics of cleanness and no pollution, but also meets the requirements of sustainable development, so that the popularization of the Photovoltaic (PV) power generation mode in the world is possible.
The incorporation of photovoltaic systems changes the topology of the distribution grid so that the protective action cannot be as rapid, sensitive and selective as before. After the photovoltaic power supply is accessed, the power distribution network is converted from a single-end power supply network into a multi-end power supply network, so that the tidal current distribution is fundamentally changed, the solar PV power generation system injects power into the power distribution network, the relay protection range of the power distribution network is changed, and the power transmission line of the power distribution network cannot be effectively protected.
Meanwhile, the distributed power supply is reasonably utilized in combination with research of the distributed power supply, and construction and development of a power distribution network are facilitated. However, the output of the power distribution network has randomness, and the power flow change of the power distribution network is greatly influenced, so that the relay protection measures customized for the traditional single-ended radiation network power distribution network can be influenced, for example, if a short-circuit fault occurs in an adjacent feeder, the power distribution protection of the line which should not act at this time can have a false operation. In conclusion, the intensive research on the power distribution protection problem of the solar photovoltaic power supply can ensure that the power system can accurately and timely find out faults and remove the faults, so that the system can recover to a normal state in as short a time as possible, and the system has obvious theoretical and practical values in more reasonable operation of power grid dispatching and improvement of system operation safety and reliability.
Disclosure of Invention
The invention provides a power distribution network protection coordination method after grid connection of a photovoltaic power supply, which adopts a method combining photovoltaic low-voltage ride through and island protection with automatic reclosing and simultaneously adopts control strategies of 'synchronous detection' and 'no voltage detection', avoids the impact current generated during closing from influencing the power grid protection, fully utilizes the island protection and ensures the safety of the power grid when a fault occurs.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the embodiment of the invention provides a power distribution network protection coordination method after grid connection of a photovoltaic power supply, which comprises the following steps:
when the power distribution network has a fault, judging whether the over-current protection of the photovoltaic power supply acts or not;
if the protection action is started, determining the protection action time;
starting the automatic reclosing after the protection action time is reached;
and after the automatic reclosing action is finished, the photovoltaic power supply is connected to the grid again.
Further, the determining whether the photovoltaic power supply overcurrent protection is activated or not includes:
determining an adaptive current interruption protection range:
Figure BDA0002271496690000021
wherein beta is the self-adaptive current interruption protection range, KkFor a reliability factor, ZsThe equivalent impedance of the power grid side, Z and L are the impedance value of the power transmission line in unit length and the total length of the protected power transmission line respectively,
and if the size of the impact current exceeds the self-adaptive current flowing breaking protection range, starting an over-current protection action.
Further, the reliability coefficient KkTaking 1.2-1.3.
Furthermore, current protection based on current limiting and overcurrent, overvoltage and undervoltage protection, voltage unbalance, island protection and inverse power protection are arranged on the photovoltaic power supply.
Further, the photovoltaic power supply is protected, and the method comprises the following steps:
the maximum power tracking of the photovoltaic power supply is realized by adopting a conductance incremental method, and a photovoltaic grid-connected model is constructed;
simulating by adopting the photovoltaic grid-connected model, and checking whether the accessed photovoltaic capacity influences the normal judgment of protection;
if the influence is caused, calculating and adjusting a protection setting value based on the self-adaptive current outage protection principle:
Figure BDA0002271496690000022
wherein, IsetTo protect the setting value, KdAs a fault type parameter, 1 is selected if the fault type parameter is a three-phase short-circuit fault, and 1 is selected if the fault type parameter is a two-phase short-circuit fault
Figure BDA0002271496690000023
KkFor a reliability factor, UEFor grid equivalent potential, ZsThe equivalent impedance of the power grid side is shown, alpha is the ratio of the distance length from a fault occurrence point to protection to the total length of the line, and Z and L are the impedance value of the power transmission line in unit length and the total length of the protected power transmission line respectively.
Further, the determining the protection action time includes:
when three-way transient faults occur in a circuit and the voltage drops to 30% of rated voltage, the reclosing device is controlled to act;
when three phases in a circuit have permanent faults and the voltage drops to 30% of rated voltage, the reclosing action is controlled after the time delay duration is required to be increased;
the delay time is determined by the following method, including:
setting fault occurrence time and circuit breaker tripping time;
setting different delay time lengths and then starting reclosing;
and respectively measuring the three-phase voltage and the low-voltage ride through value, and obtaining the optimal delay time length through comparison.
Further, after reaching the protection action time, starting automatic reclosing means that reclosing is performed by adopting a mode of matching 'checking synchronization' and 'checking no voltage', and the method comprises the following steps:
on the system power supply side, the system power supply side works only when the automatic reclosing relay and the voltage detection relay are closed simultaneously;
at least one of the synchronous verification relay and the voltage-free detection relay is switched on at the photovoltaic power supply side, and the automatic reclosing relay is closed, so that the switch at the photovoltaic power supply side can be opened, and the photovoltaic power supply enters a working state.
Further, after the automatic reclosing action is completed, the photovoltaic power supply is connected to the grid again, and the method includes the following steps:
if the reclosing action is successfully executed, connecting the split photovoltaic power supplies to the grid;
and if the execution is not successful, the permanent fault is cleared, the power supply is recovered, and meanwhile, the split photovoltaic power supply is connected to the grid.
The invention achieves the following beneficial effects:
according to the self-adaptive protection setting method, aiming at different situations of a photovoltaic access place when a fault occurs, the protection action is changed along with the operation and fault state in real time through on-line setting, so that the protection action is more timely and accurate.
In the embodiment of the invention, when reclosing is carried out, time and a mode of executing the reclosing action are respectively considered, the execution time is determined by the trip time of a fault point and the low voltage ride through capacity to the longest time limit, the execution mode considers the effect of photovoltaic after grid disconnection, if the planned island operation is carried out, the 'synchronous detection period' and the 'voltage detection free' are coincided and combined, so that impact can be greatly reduced, and the defect of the traditional current protection is overcome.
Drawings
FIG. 1 is a diagram of a typical power distribution network architecture;
FIG. 2 is a schematic diagram of the photovoltaic low voltage ride through and reclosing lock cooperation simulation of the present invention;
FIG. 3 is a schematic diagram of the photovoltaic island operation and reclosing lock cooperation of the present invention;
fig. 4 is a waveform diagram of an impact current of a synchronous reclosing switch in the coordination of the photovoltaic island operation and the reclosing switch shown in fig. 3;
fig. 5 is a waveform diagram of an impulse current of a non-synchronous reclosing switch in the coordination of the photovoltaic island operation and the reclosing switch shown in fig. 3;
FIG. 6 is a circuit diagram of a reclosing lock according to the invention, with "check period" and "check voltage free";
fig. 7 is a flow chart of the power distribution network protection coordination action after the photovoltaic power supply is connected to the grid.
Detailed Description
The invention is further described below. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
The influence of the photovoltaic power supply on the current protection of the access power grid is considered, the influence of the photovoltaic power supplies with different capacities and permeabilities on the power grid shows great difference, the influence of the photovoltaic power supply with small capacity and low permeability on the power grid can be ignored, the situation that the original protection of a system is impacted and even damaged due to the fact that short-circuit current generated when the photovoltaic power supply with large capacity and high permeability is in fault is large is considered, and the influence on the power grid needs to be considered at the moment.
The over/under voltage protection object is a small-scale photovoltaic grid-connected system, the voltage of a photovoltaic grid-connected joint is higher than a specified value, and the photovoltaic does not generate electricity. When abnormal voltage occurs in operation, the system is required to be able to detect the abnormality and give an action within an allowable time.
1. Aiming at the protection of a photovoltaic power supply body, a control strategy of maximum power tracking is completed by adopting a conductance incremental method, so that the internal and external characteristics of the photovoltaic power supply are simulated, and the research on the connection of the photovoltaic power supply to a power grid is greatly facilitated. And simulating the photovoltaic grid-connected model to check whether the accessed photovoltaic capacity influences the normal judgment of protection.
If the influence is caused, the protection setting value is properly adjusted by utilizing the simulation result to avoid the regions of false action and refusal action, or the maximum capacity of photovoltaic access is directly limited to meet the protection requirement.
In the embodiment of the invention, the self-adaptive current outage protection principle is utilized to realize calculation and adjust the protection setting value, so that the false action and refusal action areas are avoided, and the protection function under different running and fault states is realized.
The self-adaptive current interruption protection setting value is calculated as follows:
Figure BDA0002271496690000051
wherein, KdAs a fault type parameter, 1 is selected if the fault type parameter is a three-phase short-circuit fault, and 1 is selected if the fault type parameter is a two-phase short-circuit fault
Figure BDA0002271496690000053
KkThe reliability coefficient is generally 1.2-1.3; u shapeEIs the equivalent potential of the power grid; zsIs the equivalent impedance of the grid side; alpha is the ratio of the distance length from the fault occurrence point to the protection to the total length of the line, and Z and L are the impedance value of the transmission line in unit length and the total length of the protected transmission line respectively.
The protection range is as shown in formula (2), the protection range is the limit of the fault position range of the power transmission line during photovoltaic grid connection, if the fault occurs in the protection range, reclosing action is carried out, the further influence and damage of the whole line and even the power distribution system caused by the fault are avoided, and if the fault occurs outside the protection range, the system cannot be protected:
Figure BDA0002271496690000052
in the formula, beta is a protection range in the self-adaptive current interruption protection, and the protection range is changed in real time according to the change of the operation mode of the power grid.
When the photovoltaic power supply is connected to the grid, most of the photovoltaic power supply is connected to the grid through buses below 110kV and 220kV, in order to solve the problem that the photovoltaic grid connection affects a photovoltaic power supply body, firstly, protection for the photovoltaic power supply body is set, and the safety and independent operation of the photovoltaic power supply body are guaranteed. The damage degree of a power grid is directly determined in a positive correlation mode according to the scale of the photovoltaic power supply, corresponding protective measures are taken for protecting the photovoltaic power supply body, wherein the protective measures comprise current protection based on current limiting and overcurrent, overvoltage and undervoltage protection, voltage unbalance, island protection and reverse power supply protection, and the normal operation of the photovoltaic power supply body can be guaranteed by arranging the protective device.
2. On the basis of the step 1, the influence of photovoltaic power supply access on the current of the power grid needs to be reduced, firstly, the influence of different photovoltaic access points and fault points on the power grid is determined, and the specific positions are set as follows: fig. 1 shows a typical distribution network structure diagram, wherein F1-F5 are set fault points, and A, B, C, D, E, F, G, H are grid current monitoring points.
And setting a fault point at the upstream of the photovoltaic, and detecting the current magnitude of the point B by adopting current detection equipment. And fault points are respectively arranged at positions F1, F2 and F3, and when the fault points are positioned at F1, photovoltaic increased current does not act on current protection of a point B. When the failure point is at F2, there is only a weak link between point B and the power source. When the fault point is at F3, the current at point B is detected, and the power generation scale is large, and protection misoperation can exist.
And setting a fault point at the downstream of the photovoltaic, and detecting the current magnitude of the point C by adopting current detection equipment. The failure points are set at F4, F5, respectively. When the fault point is located at F4, observing the C point, the C point is connected with the power supply, the C point has the effect of increasing the current, when the fault point is located at F5, observing the C point, C, D point has the photovoltaic increased current flowing through, the current of both points is increased, the C point can be mistakenly moved, the sensitivity of the D point is increased, and the selectivity can be lost.
3. On the basis of step 2, in order to reduce the experiment cost, a simplified 35kV power distribution system is adopted for modeling analysis, and an equivalent circuit diagram is also shown in FIG. 1. Equivalent impedance ZsJ0.4248 Ω, unit impedance (0.27+ j0.35) Ω/km, constant impedance loads at E, G points of 3MVA and 1MVA, respectively, and power factors of 0.95. Starting from two aspects of the photovoltaic power supply access and the photovoltaic power supply full-power access, it can be known that when the capacity of the incorporated photovoltaic power supply is gradually increased, the current flowing through the upstream of the protection power grid is also increased, so that the selectivity of the upstream is possibly lost, and the misoperation condition occurs; the photovoltaic power supply has a shunting function, the magnitude of fault current at the downstream of a protection power grid can be reduced, the reduction degree of the fault current is in negative correlation with the capacity of the photovoltaic power supply, and therefore the fault current does not touch the setting value of the current at the downstream of the power grid, namely far backup protection does not act. At 70% of the current-grid upstream observation point and the current of the current-grid downstream observation point, it can be known that the fault current gradually increases with the increasing access scale at the power-grid upstream observation point, and the sensitivity needs to be enhanced in order to make the protection action operate correctly.
4. On the basis of the step 3, under the condition that the photovoltaic power supply is connected with full power, in the graph 1, according to the protection setting values calculated at the protection 1 and the protection 4 in the table 1, the photovoltaic is connected to the point C, the fault is at the point D, and the current flowing through the protection 1 and the protection 4 is measured, so that the fault current of the protection 4 is reduced along with the reduction of the photovoltaic output, the protection sensitivity is further enhanced, and the protection can be enabled to act correctly. The fault current at the protection 1 is extremely large when the light is extremely small, so that the setting value of the section II of the protection 1 is invalid and cannot work normally. Photovoltaic is connected to point C, and the CD interval has 70% fault section, and the current that flows through protection 1 and protection 4 is measured. Protection 4 fault current variation is the same as above, except that when the fault current is extremely small, the sensitivity of the protection is unchanged, and normal operation is affected. Along with the reduction of the output, the fault current flowing through the protection 1 is larger than the setting value of the section II of the fault current, at the moment, the section I of the protection 4 fails, and the section II of the protection 1 normally acts.
TABLE 1 photovoltaic off-grid protection setting value
Figure BDA0002271496690000071
According to the analysis of the process, if the access photovoltaic capacity is not considered in the protection setting timing, the protection 4 can be mistakenly operated, and the in-zone fault protection 1 can be refused to be operated; if the set maximum capacity is considered, the protection 1 may malfunction when the outside fails, and the protection 4 may refuse to operate when the inside fails. In practical application, simulation can be performed according to the situation to avoid regions of false operation and refusal operation, or to limit the maximum capacity of access, so that the requirement of safe operation of a power grid is met.
5. In order to solve the problem that the reclosing function of most photovoltaic grid-connected power transmission and distribution line relay protection is in a locking state, a control strategy of automatic closing cooperation of a photovoltaic power supply and a power grid is provided, and the control strategy specifically comprises the following steps:
firstly, the cooperation between photovoltaic low-voltage ride through and automatic reclosing is considered, when three paths of transient faults occur in a circuit and the voltage drops to 30% of rated voltage, the reclosing device is controlled to act, the voltage fluctuation energy is reduced to about 91.5% at the lowest, and low-voltage ride through can be well completed;
when three phases in a circuit have permanent faults and the voltage drops to 30% of the rated voltage, the reclosing action is controlled after the delay time is required to be prolonged, and the photovoltaic can be guaranteed to complete low-voltage ride through. For the control of the delay time, as shown in fig. 5, which is a schematic diagram of the cooperation of photovoltaic low voltage ride through and reclosing, all the faults are set to occur within 0.5s, the breaker is tripped off in 0.1s, and different delay times T are tried to be setdelayThen restarting the reclosing switch, respectively measuring the three-phase voltage and the low-voltage ride through value, and directly obtaining the proper TdelayThe value is obtained. T acquired by different photovoltaic grid-connected systemsdelayIn contrast, in the present invention, T occurs when three phases in the line have a permanent faultdelayAnd is less than 1.02s, low voltage ride through can be completed.
The farther the fault point is from the distributed photovoltaic power supply in the actual operation execution, TdelayThe larger the maximum allowable value of (a), the more sufficient the time margin for controlling reclosing is. The more serious the fault is, TdelayThe smaller the maximum allowable value of (A), the smaller the time allowance for controlling reclosing, the serious influence of the existence of transition resistance, the larger the transition resistance, the larger TdelayThe larger. By utilizing the control strategy, the cooperation of low-voltage ride-through and automatic reclosing can be well completed.
6. After a photovoltaic power supply is connected to the grid, reclosing is carried out in a mode of matching 'synchronous detection' with 'non-voltage detection', and an island state is utilized, so that the island of photovoltaic power generation operates in a control mode, namely, a planned island state is realized, and the problems of failures of automatic reclosing, non-synchronous closing and the like caused by inconsistent coordination of action time of island protection and automatic reclosing are solved.
Fig. 2 is a schematic diagram of photovoltaic low voltage ride through and reclosing cooperation simulation, where F1, F2, F4, and F5 are set fault lines, and A, B, C, D are grid current monitoring points, respectively. The photovoltaic power supply is connected through the C position, the fault time is set to be 0.5s, the breaker operates to trip after 0.1s, and the photovoltaic power supply passes through the TdelayThe reclosing is started.
Analyzing the condition that the fault is positioned at the downstream of the photovoltaic power supply: a three-phase permanent fault and a three-phase transient fault are set at the midpoint of line F1, and a three-phase permanent fault is set at the head end of line F1, respectively. When a three-phase transient fault occurs at the midpoint of a line F1, the voltage drops to about three-fold of rated voltage, reclosing action is carried out, the voltage drops to about 91.5%, and low-voltage ride-through is successful. The three-phase permanent fault is at the midpoint of a line F1, the rated voltage is used as a reference, the voltage drops to about three times, the reclosing device works after the time passes, the voltage drops continuously, the degree is more serious, and the ride-through fails. When the reclosing time needs to be less than about 1.035, the photovoltaic low-voltage ride-through can be completed satisfactorily. When a three-phase permanent fault occurs at the head end of a line F1, the voltage drops to be near two or five times by taking the rated voltage as reference, then reclosing is carried out, the voltage continuously drops, the dropping degree is more serious than that of the middle point, and the ride-through failure is caused at a high probability. The condition for completing the photovoltaic low voltage ride through is that the reclosing time does not exceed 0.87 s.
The invention provides an island operation strategy, impact current generated at the moment of reclosing is reduced by adopting synchronous closing to influence a photovoltaic grid-connected system, a photovoltaic island operation and reclosing matching mode is shown in a figure 3, in the figure, F1, F2, F4 and F5 are set fault lines respectively, and A, B, C, D are power grid current monitoring points respectively. Photovoltaic access D department, when upper circuit mid point F2 department trouble, by circuit 2 head end and terminal protection circuit with circuit 2 excision, the operation of photovoltaic area local load isolated island this moment, if the power that the photovoltaic sent out can match local load, photovoltaic can the isolated island operation, otherwise will be amputated it by self isolated island protection, maintain F50 Hz, 1s time trouble takes place, the circuit breaker is through 0.1 trip-out, control delay time, calculate the impact current size of closing a floodgate with in the same term and not closing a floodgate in the same term respectively. At this time, if the reclosing is unsuccessful, the downstream part of the protection 2 at the position C is cut off by the section II, so that the damage caused by the unsuccessful reclosing is avoided. Under the control strategy of synchronous closing, the impact current of closing is very low, so that the damage of the impact current to the protection is avoided.
The photovoltaic is in an island operation state, when reclosing in the same period, the reclosing time of the photovoltaic side is 1.6029, and the impact current of the reclosing is shown in figure 4. The maximum values of the load current, the fault current and the impact current obtained by measurement are respectively 19.3kA, 22.5kA and 20.0kA, and compared with the load current, the impact current at the reclosing moment and the instantaneous short-circuit current at the fault moment are respectively about 1.029 times and 1.198 times, so that the reclosing impact current at the same period can be judged to be small, and the impact current has no influence on equipment and work.
Compared with system voltage, when the photovoltaic network in an island operation state is not in phase with the system voltage, when the photovoltaic side reclosing time is 1.6789s, the load current and the fault current are the same as those of synchronous reclosing, the maximum value of the impact current is smaller than the value at the synchronous reclosing moment, the maximum value is 20kA, and the figure 5 shows that the maximum value of the impact current is larger than the maximum value of the impact current at the synchronous reclosing moment. With the load current as a reference, the impact current and the instantaneous short-circuit current at the reclosing moment are about 1.878 times and 1.152 times, and the result can be obtained that the asynchronous reclosing impact current is larger.
The reclosing circuit diagram of "check period" and "check no voltage" is shown in fig. 6: the KU1 is a synchronous verification relay, the KU2 and the KU3 are voltage detection relays, and the KRC is an automatic reclosing relay. On the system power supply side, the system power supply side works only when the automatic reclosing relay and the voltage detection relay are closed simultaneously. At least one of the synchronous verification relay and the voltage-free detection relay is switched on at the photovoltaic power supply side, and the automatic reclosing relay is closed, so that the switch at the photovoltaic power supply side can be opened, and the photovoltaic power supply enters a working state.
7. Based on the steps and the power grid relay protection principle of the photovoltaic power supply, a power distribution network protection coordination action flow chart after photovoltaic grid connection is provided and shown in fig. 7. When a power distribution network fault occurs, judging whether the over-current protection action of the photovoltaic power supply is performed or not in the first step, wherein the judgment is based on the magnitude of the impact current; secondly, considering the conditions of low-voltage ride through and island protection, and executing the island protection action of the photovoltaic power supply by adopting a 'synchronous detection' and 'no voltage detection' mode; and thirdly, completing the execution of the automatic reclosing action, namely completing the island protection action of the photovoltaic power supply, if the reclosing action is successfully executed, connecting the disconnected photovoltaic power supply to the grid, and if the reclosing action is not successfully executed, removing the permanent fault, recovering power supply and connecting the disconnected photovoltaic power supply to the grid.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.

Claims (8)

1. A power distribution network protection coordination method after grid connection of a photovoltaic power supply is characterized by comprising the following steps:
when the power distribution network has a fault, judging whether the over-current protection of the photovoltaic power supply acts or not;
if the protection action is started, determining the protection action time;
starting the automatic reclosing after the protection action time is reached;
and after the automatic reclosing action is finished, the photovoltaic power supply is connected to the grid again.
2. The method according to claim 1, wherein the determining whether the photovoltaic power supply overcurrent protection is performed or not comprises:
determining an adaptive current interruption protection range:
Figure FDA0002271496680000011
wherein beta is the self-adaptive current interruption protection range, KkFor a reliability factor, ZsThe equivalent impedance of the power grid side, Z and L are the impedance value of the power transmission line in unit length and the total length of the protected power transmission line respectively,
and if the size of the impact current exceeds the self-adaptive current flowing breaking protection range, starting an over-current protection action.
3. The method according to claim 2, wherein the reliability coefficient K is the reliability coefficient K of the method for protecting and coordinating the power distribution network after the photovoltaic power supply is connected to the gridkTaking 1.2-1.3.
4. The method for protecting and coordinating the power distribution network after the grid connection of the photovoltaic power supply as claimed in claim 1, wherein current protection based on current limiting and overcurrent, overvoltage and undervoltage protection, voltage unbalance, island protection and inverse power protection are provided for the photovoltaic power supply.
5. The method for protecting and coordinating the power distribution network after the grid connection of the photovoltaic power supply according to claim 4, wherein the protecting the photovoltaic power supply comprises:
the maximum power tracking of the photovoltaic power supply is realized by adopting a conductance incremental method, and a photovoltaic grid-connected model is constructed;
simulating by adopting the photovoltaic grid-connected model, and checking whether the accessed photovoltaic capacity influences the normal judgment of protection;
if the influence is caused, calculating and adjusting a protection setting value based on the self-adaptive current outage protection principle:
Figure FDA0002271496680000012
wherein, IsetTo protect the setting value, KdAs a fault type parameter, 1 is selected if the fault type parameter is a three-phase short-circuit fault, and 1 is selected if the fault type parameter is a two-phase short-circuit fault
Figure FDA0002271496680000021
KkFor a reliability factor, UEFor grid equivalent potential, ZsThe equivalent impedance of the power grid side is shown, alpha is the ratio of the distance length from a fault occurrence point to protection to the total length of the line, and Z and L are the impedance value of the power transmission line in unit length and the total length of the protected power transmission line respectively.
6. The method according to claim 1, wherein the determining the protection action time comprises:
when three-way transient faults occur in a circuit and the voltage drops to 30% of rated voltage, the reclosing device is controlled to act;
when three phases in a circuit have permanent faults and the voltage drops to 30% of rated voltage, the reclosing action is controlled after the time delay duration is required to be increased;
the delay time is determined by the following method, including:
setting fault occurrence time and circuit breaker tripping time;
setting different delay time lengths and then starting reclosing;
and respectively measuring the three-phase voltage and the low-voltage ride through value, and obtaining the optimal delay time length through comparison.
7. The method for protecting and coordinating the power distribution network after the photovoltaic power supply is connected to the grid according to claim 1, wherein starting automatic reclosing when the protection action time is reached is to perform reclosing in a mode of matching 'synchronization detection' with 'no voltage detection', and comprises the following steps:
on the system power supply side, the system power supply side works only when the automatic reclosing relay and the voltage detection relay are closed simultaneously;
at least one of the synchronous verification relay and the voltage-free detection relay is switched on at the photovoltaic power supply side, and the automatic reclosing relay is closed, so that the switch at the photovoltaic power supply side can be opened, and the photovoltaic power supply enters a working state.
8. The method for protecting and coordinating the power distribution network after the grid connection of the photovoltaic power supply, according to claim 1, wherein after the automatic reclosing action is completed, the grid connection of the photovoltaic power supply is resumed, and the method comprises the following steps:
if the reclosing action is successfully executed, connecting the split photovoltaic power supplies to the grid;
and if the execution is not successful, the permanent fault is cleared, the power supply is recovered, and meanwhile, the split photovoltaic power supply is connected to the grid.
CN201911106559.1A 2019-11-13 2019-11-13 Power distribution network protection coordination method after grid connection of photovoltaic power supply Pending CN112803376A (en)

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