CN104836214A - Distributed generation-based grid connection transition operation mode coordination comprehensive protection method - Google Patents

Abstract

The invention discloses a distributed generation-based grid connection transition operation mode coordination comprehensive protection method. When the DG capacity is continuously increased, the short-circuit current level is improved, the DG is changed from a "pure load" into a "small power supply", and a problem that conventional protection and switching breakpoints cannot meet the transition condition is solved. Based on the conventional protection and the switching breakpoints, the scheme provided by the invention performs continuous matching with a primary operation model and is continuously optimized, and the information and the state quantity are continuously exchanged to form a protection control interface adapted to a primary system, so that dual purposes of safe operation of a system and continuous power supplying are achieved. The fault isolation range is determined by collecting a new boundary which is determined by the switching breakpoints, and that whether the system sectionalizing and the island operation mode generated as a boundary point is determined is stable or not is comprehensively considered.

Description

A Coordinated Comprehensive Protection Method Based on Distributed Generation Grid-connected Transition Operation Mode

technical field

The invention relates to a coordinated comprehensive protection method based on distributed power generation grid-connected transition operation mode.

Background technique

In the early stage of distributed power network construction, due to its uncertain scale and small grid-connected capacity, the short-circuit current provided to the system is limited and has little impact on the protection of existing systems. At this time, it can be regarded as a "pure load" nature. However, when the capacity of distributed power sources continues to increase (>5MVA), DGs have the ability to provide relatively high fault current feeds. For example, DGs directly connected to 10-35kV buses can provide about 6 times the rated current, and the fault current of the DG unit connected to the inverter can also reach 4 times the rated current. At this time, it can no longer be treated as the nature of the load, but at this time the corresponding protection devices on the system side have not followed up, affecting the stable operation of the power grid.

Therefore, it is of positive significance to study how to obtain the most effective protection scheme with limited protection resources under the transition mode of DG. At the same time, in this transition mode, considering how to fully reflect the advantages of DG's continuous power supply to important loads when the system fails is also a goal that should be considered.

Contents of the invention

In order to solve the above problems, the present invention proposes a coordinated comprehensive protection method based on the distributed power generation grid-connected transition operation mode. This method solves the problem of DG changing from a simple "load" property to a "small load" through the optimization of the grounding mode and the secondary protection system. The complexity of the transition of the nature of "power supply", under the condition that the existing protection and automatic devices remain unchanged, through relevant technical means, the purpose of basically meeting the safe operation of the regional power grid after DG access is achieved.

In order to achieve the above object, the present invention adopts the following technical solutions:

A coordinated comprehensive protection method based on distributed power generation grid-connected transition operation mode, comprising the following steps:

(1) Define the fault isolation boundary of DG capacity, adjust its protection setting, determine the lower boundary point of island operation mode after fault isolation, and adjust the transformer grounding mode of grid-connected substation after the DG capacity increases to the set value;

(2) Under the existing protection configuration conditions, coordinate the local low-frequency and low-voltage devices with the distribution automation system, and complete the post-accident load transfer and island division;

(3) According to the island operation mode, formulate a protection configuration plan, conduct fault response analysis, realize continuous power supply during the fault period of the first-level important load, and corresponding micro-grid protection adjustment in the island.

In the above step (1), when the capacity of the local DG continues to increase and reaches the set capacity value, the DG cannot be considered as a simple load, but should be regarded as connected to the system and different in nature from the generator set. distributed power supply.

In the above step (1), it is first necessary to clarify at which point the DG capacity increases to cause the protection mismatch, so the protection setting needs to be adjusted; secondly, because the DG capacity is less than 50MW protection and the switch configuration is in the DG as a "small power source" It will be incomplete when considering it. If you want to effectively isolate the fault when the fault occurs, the fault disconnection point at this time needs to be adjusted as follows: jump the high-voltage side of the main transformer of the DG grid-connected substation and the bridge switch, and simultaneously cut off the parallel switch. .

In the step (1), when the DG capacity is increased to the set value, it is necessary to consider which switch breakpoint is disconnected to form an island operation mode. At the same time, after the island is formed, the protection of the micro-grid in the island should also be considered; For the load redistribution after fault isolation, it is also necessary to minimize the load loss through decoupling and low-frequency low-voltage load shedding devices under the premise of fully considering the importance of the load and the relationship with the local supply and distribution balance.

In the step (2), in the transition mode of operation, due to the distribution of switch disconnection points and the lack of available backup power supply, the corresponding protection and safety automatic device schemes need to be adaptively adjusted; when the scheme is determined, the first failure The determination of the isolation range needs to collect the new boundary determined by the disconnection point of the switch, and it is also necessary to comprehensively consider whether the system disconnection and the island operation mode that will occur once this boundary point is determined can operate stably.

In the step (2), in order to realize the reliable operation of important loads after accurate isolation of faults, it is necessary to comprehensively consider cost and energy information, management and environmental information, control and measurement information, critical state information and load user information; In the case of tight resources, it is necessary to comprehensively analyze and consider the network topology, power flow distribution, switch distribution, protection configuration, local DG load balancing capability and the nature of the local power supply load, in order to determine the reliable, Economic protection and safety automatic device scheme, the scheme determines the coordination relationship of each switch and protection configuration point, which is used to isolate faults with the minimum isolation range and obtain the optimal load transfer scheme at the minimum cost.

In the described step (3), because the DG property has changed, the high-voltage side of the grid-connected transformer is grounded, and the line protection of the opposite side system is stretched into the transformer from the original distance, and the zero-sequence I section is changed to 85% of the line protection, and by means of The zero-sequence protection on the high-voltage side of the transformer in this station is used as the main protection of the line, tripping the high-voltage side and the bridge switch, and simultaneously switching off the grid line switch.

In the step (3), the protection action is as follows: when the line is faulty, the circuit breakers at both ends are tripped and do not overlap, and the backup operation is performed, and the mode of cutting the DG grid-connected line is connected. At this time, the local area will enter the island operation mode; as the low-voltage side near The time-limited quick-break protection of the low-voltage side of the backup and low-voltage side bus main protection trips the switch on this side, cuts off the DG grid-connected line, and blocks the low-voltage side segmental backup switching; the main transformer differential and non-electrical protection action does not block the incoming line of the substation and the low-voltage side Segmentation preparation.

In the step (3), when one substation is running and the system side line fails, the switch on the high voltage side of the transformer of the backup switching device is activated to directly cut off the communication channel between the photovoltaic and the system, and the bus bar on the high voltage side loses voltage, and no It will affect the normal operation of standby automatic switching, but for the mode of simultaneous operation of two transformers, the switching action of the high-voltage side of the transformer cannot completely cut off the channel of distributed power supply, so it will affect the success rate of standby automatic switching, so the high backup protection action At the same time, it is necessary to cut the photovoltaic grid-connected line of the station, and after the parallel operation of the original two substations is changed to one substation operation, the low-frequency and low-voltage devices on the low-voltage side need to operate to balance the corresponding loads to ensure the quality of power supply The problem.

In the step (3), choose to install the bus differential protection on the high-voltage side of the distributed power grid-connected substation. When the bus fails, the bus differential protection action node outputs the blocking standby switching device; if the bus differential protection is not configured, pass Compare the magnitude of the fault current flowing through the switch on the incoming substation side and the switch on the high voltage side of the transformer to determine whether it is a bus fault.

In the step (3), when the current flowing through the switch on the incoming line substation side is greater than the fault current flowing through the high-voltage side blade of the transformer, it is explained as a bus fault; because only when the fault point is located between the two switches, will it appear The short-circuit current provided by the system felt by the switch on the incoming line substation side is much greater than the short-circuit current provided by the distributed power source on the high-voltage side switch of the transformer.

In the step (3), under the premise of not causing damage to DG-related equipment, both the frequency and voltage relays on the DG side are higher than the corresponding protection on the system side by a cooperation level difference, which also ensures that when the system side fails At this time, the DG will not act before the corresponding relay on the system side, resulting in failure to achieve effective support for the system.

The beneficial effects of the present invention are:

(1) When the capacity of DG continues to increase, its short-circuit current level increases, and the nature of DG is also converted from the original "pure load" to "small power supply". The existing protection and switch breakpoints can no longer meet the needs of the transitional situation , under the existing protection and switch breakpoint conditions, the present invention forms a protection control interface adapted to the primary system through continuous matching with the primary operation mode, continuous optimization of the scheme, and continuous exchange of information and state quantities to achieve system The dual purpose of safe operation and continuous power supply;

(2) By changing the grounding method of the transformer, it is ensured that the fault can be effectively found when the system fails;

(3) At the same time, the effective isolation of system faults is realized by means of zero-sequence overcurrent and switches on the high-voltage side of the transformer;

(4) Through the coordination of the protection and the fixed value of the automatic device, it is ensured that the load is effectively transferred after the fault is isolated; through the operation of the DG isolated island, the continuous power supply of the DG to the local load is maintained, and its protection also realizes the protection function of the micro-grid , which provides an effective solution to the situation that a large number of DGs are continuously connected to the local area.

Description of drawings

Fig. 1 is a flow chart of related scheme selection based on DG property transition of the present invention;

Fig. 2 is a schematic diagram of the principle of the protection and safety automatic device scheme based on the high degree of information fusion of the present invention;

Fig. 3 is the wiring diagram of distributed power supply access 110kV substation of the present invention;

Figure 4 is the initial protection and de-listing scheme determined by the DG property transition and switch disconnection point;

Figure 5 is a schematic diagram of the specific implementation of the protection scheme;

Figure 6 is a schematic diagram of fault response analysis;

Figure 7(a) is a schematic diagram of the microgrid protection cooperation relationship applicable to the island operation mode;

Figure 7(b) is a schematic diagram of the microgrid protection cooperation relationship applicable to the island operation mode;

Fig. 7(c) is a schematic diagram of the microgrid protection coordination relationship applicable to the island operation mode.

Detailed ways:

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

The present invention introduces an advanced fault management system solution during the transition period of DG. This solution is based on the existing protection configuration and distribution network automation system equipment (including equipment automation and remote controllable switches), which can provide the required energy for DG grid connection. Protection, while reducing the fault duration, reducing the unsupplied DG electric energy and the DG shaft torque caused by the imbalance between electric energy and mechanical energy. It includes the following contents:

1) When the DG capacity increases to a certain extent, adjust the grounding method of the transformer in the grid-connected substation;

2) Under the existing protection configuration conditions, coordinate the local low-frequency and low-voltage devices with the distribution automation system, and complete the load transfer and island division after the accident;

3) Through the operation of the "island" operation mode, the continuous power supply to the first-level important load during the failure period and the corresponding micro-grid protection adjustment in the island are realized.

The purpose of the present invention is to solve the complex problem of DG transitioning from a simple "load" property to a "small power source" property through the optimization of the grounding method and the secondary protection system. Under the condition that the existing protection and automatic devices remain unchanged , through relevant technical means, to basically meet the purpose of safe operation of the regional power grid after DG access.

This scheme minimizes the fault duration and prevents DG damage by changing the grounding mode of the transformer in the substation, the configuration of the protection device, the setting scheme of the fixed value, and the mode of standby self-switching, low-frequency and low-voltage decoupling. 1) When the DG capacity increases to a certain extent, adjust the grounding method of the transformer in the grid-connected substation;

2) Under the existing protection configuration conditions, coordinate the local low-frequency and low-voltage devices with the distribution automation system, and complete the load transfer and island division after the accident;

3) Through the operation of the "island" operation mode, the continuous power supply to the first-level important load during the failure period and the corresponding micro-grid protection adjustment in the island are realized.

The protocol includes the following specific steps:

1 Proposal of coordinated comprehensive protection scheme strategy based on DG grid-connected transition operation mode

The International Committee on Large Power Systems (CIGRE) pointed out that distributed generation is defined as "unplanned or centrally dispatched power production, usually connected to the distribution network, and the general power generation scale is between 50 and 100MW. Therefore, when local The capacity of DG keeps increasing, and when it reaches the set capacity value (50MVA), DG should not be considered as a simple "load", but should be regarded as a "distributed power supply" connected to the system and different in nature from the generator set. ". The problems to be solved by its protection and automatic devices are two-level problems: 1. Effective isolation of faults; 2. Guaranteeing effective power supply in the largest range. In order to solve the first problem, it is first necessary to clarify at which point the DG capacity is increasing. Therefore, it is necessary to adjust the protection setting; secondly, the protection and switch configuration when the DG capacity is small will be incomplete when DG is considered as a "small power supply". If you want to be effective when a fault occurs The isolated fault of the fault, at this time, the fault disconnection point needs to be adjusted accordingly. In order to solve the second problem, that is, the ability to support the local load when the DG capacity increases to a certain extent, it is necessary to consider which switch disconnection point to disconnect , forming an isolated island operation mode. At the same time, after the island is formed, the realization of micro-grid protection in the island also needs to be considered. Similarly, for load redistribution after fault isolation, it is also necessary to fully consider the importance of the load and the relationship with the local Under the premise of supply-distribution balance relationship, the load loss is minimized by decoupling and low-frequency low-voltage load shedding devices. Figure 1 shows the logic flow chart of this strategy adjustment. It can be seen from the figure that the protection scheme should consider both One is how to determine the fault isolation boundary when DG as a "small power supply" continuously provides short-circuit current to the fault point, and the other is the determination of the boundary point under the island operation mode after fault isolation. Therefore, the disconnection point should not only act as a fault isolation break The function of the DG point is also the boundary point for dynamically dividing the island operation mode; in the same way, the DG also has a "dual role". Finally, it will also act as a local power supply to maintain the island operation mode.

In the transitional operation mode, due to the distribution of switch disconnection points and the lack of backup power supply, it is necessary to make adaptive adjustments to the corresponding protection and safety automatic device scheme. When determining the scheme, firstly, the determination of the fault isolation range needs to collect the new boundary determined by the disconnection point of the switch, and it is also necessary to comprehensively consider whether the system disconnection and the island operation mode that will follow once this boundary point is determined are feasible. Stable operation. Therefore, in order to achieve reliable operation of important loads after accurate isolation of faults, multiple factors need to be considered comprehensively, so the interaction of information flow will involve the following five aspects:

·Cost and energy information

·Management and environmental information

· Control and measurement information

·Critical state information

· Load user information

In the case of relatively tight power resources, it is necessary to comprehensively analyze and consider factors such as network topology, power flow distribution, switch distribution, protection configuration, local DG load balancing capability, and the nature of local power supply loads, and properly consider some variables The possible parameter errors can be used to determine the reliable, economical protection and safety automatic device scheme suitable for the current operation mode. The scheme determines the coordination relationship between each switch and protection configuration points, which is used to isolate faults with the minimum isolation range and the following The minimum cost to obtain the optimal load transfer scheme. The information flow and fusion method are shown in Figure 2. Determine the load transfer scheme according to the load importance level and local load balancing capability. It can be seen from Figure 2 that the proposal and solution of the scheme are essentially based on the analysis, processing and synthesis of five different types of information sources. In short, the formation of the first-level protection scheme is mainly based on the results of the switch (fault disconnection point) and fault state analysis; and in order to successfully transfer the load after the accident, the system unloading method must not only consider the current There is an island division method formed after the switch is disconnected, and several aspects such as power flow analysis, economic analysis, and load nature must be considered comprehensively. Therefore, in the entire data source, it is necessary to first extract the relevant information needed to solve the problem, and then design according to the existing rules and weights, and finally form an efficient solution for the safe and stable operation of the power grid and the reliable and economical operation of users.

3 Implementation of protection scheme based on DG properties and cut-off points

3.1 The initial protection and de-loading scheme based on the primary transport and switch protection

In this scheme, due to the change in the nature of DG, the high-voltage side of the grid-connected transformer is grounded, and the line protection of the opposite side system is extended from the original distance, zero-sequence section I into the transformer, and changed to protect 85% of the line. The zero-sequence protection on the side is used as the main protection of the line, tripping the high-voltage side and the bridge switch, and simultaneously disconnecting the grid line switch. The break point of the switch determined by its new operation mode and the non-complete protection configuration are shown in Fig. 4 .

3.2 Switch breakpoint determined by transitional operation mode and insufficient protection configuration scheme

Fig. 3 Wiring diagram of distributed power supply connected to 110kV substation. Among them, the MV/LV substation adopts the inner bridge connection, and the 01 and 02 are knife switches, and the function of tripping and cutting the parallel network line L1 is realized by the tripping and cutting function of the 03 switch. Due to the small scale of its initial design, the substation whose distributed power supply is connected to the grid is regarded as a terminal station without small power supply connected to the grid. Therefore, the switches (03, 04) on the substation side are not equipped with protection devices. Therefore, with the help of #1, #2 Transformer high backup protection is preferred. Generally, as long as the protection sensitivity requirements are met, the high backup of the transformer will not be equipped with distance protection. At the same time, considering that the photovoltaic power supply has poor short-circuit current capability when the system fails, and there is no algorithm that can be applied to engineering practice so far, it is necessary to find a Reliably and accurately reflect the fault source of the system fault. Combining the above two factors, the most direct solution is to regard the distributed power supply as a "small power supply" and ground the 110kV side of the substation. At the same time, the zero-sequence overcurrent protection in the high backup protection is regarded as the line protection of the load side 03 and 04, and its setting principle also follows the principle of line protection configuration on the local side; section I hides the end-of-line fault of the main line; section II maintains the full length of the main line And ensure the sensitivity, and cooperate with all outgoing lines of the opposite side substation (220kV station). In this way, when a fault occurs in the system, the grounding point of the high-voltage side of the transformer provides enough zero-sequence fault current to the fault point, so that the high backup protection of the transformer operates, and the switch 03 (or 04) trips. It can be seen from the analysis that the determination of the grounding point of the transformer is which transformer the distributed power supply is connected to the grid, and the high-voltage side of the transformer of this one is grounded. Ground operation is only to provide a zero-sequence current source for system faults, and this zero-sequence system has nothing to do with distributed power. Nevertheless, since the distributed power is connected to the grid at this main transformer, the distributed power is effectively isolated from the grid after the high-voltage side switch of the local transformer is tripped.

3.3 Failure response analysis

According to the current protection configuration, the protection action is as follows: when the line is faulty, the circuit breakers at both ends trip and do not overlap, and the backup operation is performed, and the mode of cutting the DG grid-connected line is connected. At this time, the local area will enter the island operation mode; The low-voltage side time-limited quick-break protection of the main protection of the low-voltage side busbar trips the switch on this side, cuts off the DG grid-connected line, and blocks the low-voltage side segmental backup; the main transformer differential and non-electrical protection action does not block the incoming line of the substation and the low-voltage side segment Prepare to vote.

When one substation is running, if the line on the system side fails, the 03 switch will act to directly cut off the communication channel between the photovoltaic system and the system, and the busbar on the high-voltage side will lose pressure, which will not affect the normal operation of the standby automatic switch. However, for the mode of simultaneous operation of two transformers, the action of switch 03 on the high voltage side of the transformer cannot completely cut off the channel of the distributed power supply, so it will affect the success rate of backup and automatic switching. According to the current protection configuration, this line can be satisfied. And after the parallel operation of the original two substations is changed to the operation of one substation, the low-frequency and low-voltage devices on the low-voltage side need to operate to balance the corresponding loads to ensure the quality of power supply. And the load that jumps out after balancing can be solved by means of the hand in hand of the distribution network.

It can be seen from the protection range of the high-backup zero-sequence protection that the protection range of the 03 switch is extended to the high-voltage side bus. It can be seen from the analysis that when the high-voltage side bus fails, if there is no effective identification and blocking measures, it will cause the backup switch to fail again, causing another impact on the system. The best solution is to install bus differential protection on the high-voltage side of the distributed power grid-connected substation. When the bus fails, the bus differential protection action node will output the blocking backup switching device; if the bus differential protection is not configured, you can compare The magnitude of the fault current flowing through the 03 and 01 switches can be used to judge whether it is a bus fault. When I03>I01, it means bus failure. Because, only when the fault point is located between the two switches, the short-circuit current provided by the system felt by the 03 switch is much greater than the short-circuit current provided by the distributed power supply of the 01 switch. Note that the zero-sequence current is no longer the basis for judging here, but directly compares the short-circuit current provided by the power supplies on both sides.

4 Implementation of load transfer and island operation scheme based on DG properties and shutdown points

As shown in Figure 3, the DG grid-connected line on the low-voltage side of the transformer and each DG power generation unit constitute a complete protection coordination system. It can be seen that with the grid-connected line as the demarcation point, the system side should take the short-circuit current provided by the system side as the setting reference, and the protection system under the island operation mode after the grid-connected switch trips should start from PD2, so in order to ensure its performance Applicable to micro-grid operation mode, this system should be based on the much smaller short-circuit current provided by DG. As a result of this treatment, although the short-circuit current level provided by DG will be very sensitive to the system side protection, and it will also cause its action to enter the island operation mode when the system fails, but this problem can be solved through time cooperation, and at the same time it can be protected. It can also be applied to the selectivity of grid-connected and "isolated island" protection.

Considering that the DG needs to be used as a power supply to effectively support the local load when the system fails, we do not want the DG to shut down during the system failure, during the fault removal process and when the system load balance is not completed. Therefore, the voltage related to the power supply quality , frequency protection and low frequency, low voltage load shedding device and the corresponding cooperation relationship with the system side as shown in Figure 7 (a), (b), (c).

From the coordination relationship in Figure 7(a), (b), and (c), it can be seen that under the premise that it will not cause damage to DG-related equipment, both the frequency and voltage relays on the DG side are higher than the corresponding protection on the system side by one coordination This also ensures that when a fault occurs on the system side, the DG will not act before the corresponding relay on the system side, resulting in failure to achieve effective support for the system. At the same time, it can also be seen that based on the consideration of the DG island operation mode, the fixed value of the DG side protection is based on the DG rated capacity, that is, PD _3a = 2.5I _n-DG ; while the system side protection is based on the local side The rated current is based on PD _3a =2.5I _n-LV . Although the fixed value of the DG side is relatively low, due to the coordination of the time difference, the protection will not malfunction after a fault occurs on the system side. Eliminate malfunctions that occur on the island.

This paper introduces a coordinated comprehensive protection scheme strategy based on the DG grid-connected transition operation mode. When the DG capacity continues to increase, its short-circuit current level increases, and the DG nature is also converted from the original "pure load" to "small power supply". Existing protection and switch breakpoints can no longer meet the needs of transitional situations. Under the existing protection and switch breakpoint conditions, this scheme forms a protection control interface suitable for the primary system through continuous matching with the primary operation mode, continuous optimization of the scheme, and continuous exchange of information and state quantities to achieve system security. The dual purpose of operation and power supply continuity. First of all, the determination of the fault isolation range needs to collect the new boundary determined by the disconnection point of the switch, and also comprehensively consider whether the system disconnection and island operation mode that will occur once this boundary point is determined can operate stably. By changing the grounding mode of the transformer, it is ensured that the fault can be effectively detected when the system fails; at the same time, the effective isolation of the system fault is realized by means of the zero-sequence overcurrent and the switch on the high voltage side of the transformer; After isolation, the load is effectively transferred; through the operation of the DG island, the continuous power supply of the DG to the local load is maintained, and its protection also realizes the micro-grid protection function. This solution provides an effective solution to the situation where a large number of DGs are continuously connected to the local area.

Embodiment 1: As shown in Figure 3, the DG grid-connected line at the low-voltage side of the transformer and each DG power generation unit constitute a complete protection coordination system. It can be seen that with the grid-connected line as the demarcation point, the system side should take the short-circuit current provided by the system side as the setting reference, and the protection system under the island operation mode after the grid-connected switch trips should start from PD2, so in order to ensure its performance Applicable to micro-grid operation mode, this system should be based on the much smaller short-circuit current provided by DG. As a result of this treatment, although the short-circuit current level provided by DG will be very sensitive to the system side protection, and it will also cause its action to enter the island operation mode when the system fails, but this problem can be solved through time cooperation, and at the same time it can be protected. It can also be applied to the selectivity of grid-connected and "isolated island" protection.

Considering that the DG needs to be used as a power supply to effectively support the local load when the system fails, we do not want the DG to shut down during the system failure, during the fault removal process and when the system load balance is not completed. Therefore, the voltage related to the power supply quality , frequency protection, low frequency, low voltage load shedding device and the corresponding cooperation relationship on the system side are shown in Fig. 7(a), Fig. 7(b) and Fig. 7(c).

From the coordination relationship in Figure 7(a), Figure 7(b), and Figure 7(c), it can be seen that, on the premise that it will not cause damage to DG-related equipment, the DG side, whether it is frequency or voltage relay, is better than the system side. It is higher than a coordination level difference, which also ensures that when a fault occurs on the system side, the DG will not act before the corresponding relay on the system side, resulting in failure to achieve effective support for the system. At the same time, it can also be seen that based on the consideration of the DG island operation mode, the fixed value of the DG side protection is based on the DG rated capacity, that is, PD _3a = 2.5I _n-DG ; while the system side protection is based on the local side The rated current is based on PD _3a =2.5I _n-LV . Although the fixed value of the DG side is relatively low, due to the coordination of the time difference, the protection will not malfunction after a fault occurs on the system side. Eliminate malfunctions that occur on the island.

Although the specific implementation of the present invention has been described above in conjunction with the accompanying drawings, it does not limit the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, those skilled in the art do not need to pay creative work Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims (10)

1. coordinate a comprehensive method of protection based on the grid-connected transition operational mode of distributed power generation, it is characterized in that: comprise the following steps:

(1) the Fault Isolation border of clear and definite DG capacity, adjusts its protection definite value, determines decoupled mode lower boundary point after Fault Isolation, after DG capacity increases to set point, the transformer grounding mode of grid-connected transformer station adjusted;

(2) under existing relaying configuration condition, local low-frequency and low-voltage device is coordinated mutually with electrical power distribution automatization system, complete the transfer of accident afterload and isolated island division;

(3) according to decoupled mode, formulate relaying configuration scheme, carry out failure response analysis, the continued power between realizing one-level important load age at failure, and the protection of corresponding microgrid adjusts on the island in.

2. as claimed in claim 1 a kind of based on distributed power generation grid-connected transition operational mode coordination comprehensive method of protection; it is characterized in that: in described step (1); when local DG capacity constantly increases; when reaching the capability value of setting; DG is not just used as simple load and considers, and should be regarded as be connected with system, with the distributed power source of generating set different in kind.

3. coordinate a comprehensive method of protection based on the grid-connected transition operational mode of distributed power generation, it is characterized in that: in described step (1), first want clear and definite DG capacity to cause mismatching of protection when which rising to and putting, thus need adjustment protection definite value; Next is less than 50MW protection and switchgear distribution carries out following adjustment at fault cut-off point when DG capacity: jump DG and to surf the Net transforming plant main transformer high-pressure side and bridge switch, grid-connected wiretap cut by connection simultaneously.

4. as claimed in claim 1 a kind of based on distributed power generation grid-connected transition operational mode coordination comprehensive method of protection, it is characterized in that: in described step (1), when DG capacity increases to set point degree, which need to consider at switch breakpoint to disconnect, form decoupled mode, meanwhile, after formation isolated island, take into account and consider for microgrid protection in island; Redistributing for the load after Fault Isolation, is equally also to take into full account load importance and under supplying the prerequisite of balancing relation with locality, load loss to be down to minimum by off-the-line and low-frequency low-voltage load shedding device.

5. as claimed in claim 1 a kind of based on distributed power generation grid-connected transition operational mode coordination comprehensive method of protection, it is characterized in that: in described step (2), under transition operational mode, due to switch cut-off point distribution and can the deficiency of stand-by power supply need corresponding protection and automatic safety device scheme to make accommodation; When carrying out scheme and determining, first the determination of Fault Isolation scope needs to collect the determined new border of switch cut-off point, and this boundary point will be considered once the system splitting determining and produce thereupon and decoupled mode whether Absorbable organic halogens runs.

6. as claimed in claim 1 a kind of based on distributed power generation grid-connected transition operational mode coordination comprehensive method of protection, it is characterized in that: in described step (2), in order to realize the reliability service of the important load after accurate isolated fault, needing considering cost and energy information, manage and environmental information, to control and metrical information, critical condition information and load user profile; When power resources anxiety; need comprehensively to analyze consideration to network topology structure, trend distribution, switch distribution, relaying configuration and the load balancing ability of local DG and the character factor of local supply load; could determine to be applicable to reliable, the economic protection under current operational mode and automatic safety device scheme; scheme determines the matching relationship of each switch and relaying configuration point, is used for realizing originally obtaining optimum load transfer plan scheme with minimum isolation range isolated fault and with minimum one-tenth.

7. as claimed in claim 1 a kind of based on distributed power generation grid-connected transition operational mode coordination comprehensive method of protection; it is characterized in that: in described step (3); because DG character there occurs change; by grid-connected high voltage side of transformer ground connection; the protection of offside system line stretches into transformer by original distance, zero sequence I section, changes into and protects circuit 85%, and by means of the zero-sequenceprotection of our station high voltage side of transformer as power line main protection; jump high-pressure side and bridge switch, grid-connected wiretap cut by connection simultaneously.

8. as claimed in claim 1 a kind of based on distributed power generation grid-connected transition operational mode coordination comprehensive method of protection, it is characterized in that: in described step (3), protection act is as follows: during line fault, two ends circuit breaker tripping does not overlap, standby throwing action, connection cuts DG and the pattern of netting twine, and now regional area will enter decoupled mode; As this side switch of low-pressure side time-limit quick break protection tripping of the nearly standby of low-pressure side and low-pressure side bus main protection, connection cuts DG and netting twine, and the segmentation of locking low-pressure side is standby throws; Main transformer differential and non-ionizing energy loss action, not locking transforming plant lead-in and the standby throwing of low-pressure side segmentation.

9. as claimed in claim 1 a kind of based on distributed power generation grid-connected transition operational mode coordination comprehensive method of protection, it is characterized in that: in described step (3), when becoming operation for one, system side line failure, by standby high voltage side of transformer switch motion of throwing Union Switch Device, the service channel of direct cut-out photovoltaic and system, high-voltage side bus decompression, the regular event of prepared auto restart can not be affected, but become for two the mode simultaneously run, high voltage side of transformer switch motion can not cut off the passage of distributed power source completely, therefore the success rate of prepared auto restart can be affected, need connection to cut the also netting twine of our station photovoltaic while high backup protection action for this reason, and becoming paired running by original two changes by after a change operation, need the low frequency of low-pressure side, low-voltage device action, equilibrium is carried out to corresponding load, to reach the problem ensureing power supply quality.

10. as claimed in claim 1 a kind of based on distributed power generation grid-connected transition operational mode coordination comprehensive method of protection, it is characterized in that: in described step (3), select at distributed power source grid-connected transformer station high-pressure side installing bus differential protection, when bus breaks down, export locking spare power by bus bar differential prptection operation node; If do not configure bus differential protection; busbar fault is determined whether by comparing the fault current size flowing through inlet wire transformer substation side switch and high voltage side of transformer disconnecting link; when the electric current that inlet wire transformer substation side switch flows through is greater than the fault current that transformer high-voltage side tool flows through, be illustrated as busbar fault.