CN117691572A - Adaptive transformation method for distributed photovoltaic grid-connected secondary equipment - Google Patents
Adaptive transformation method for distributed photovoltaic grid-connected secondary equipment Download PDFInfo
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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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- 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
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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
- H02H7/22—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 for distribution gear, e.g. bus-bar systems; for switching devices
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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
- H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
- H02J13/00002—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by monitoring
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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
- H02J3/007—Arrangements for selectively connecting the load or loads to one or several among a plurality of power lines or power sources
- H02J3/0075—Arrangements for selectively connecting the load or loads to one or several among a plurality of power lines or power sources for providing alternative feeding paths between load and source according to economic or energy efficiency considerations, e.g. economic dispatch
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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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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Abstract
The invention relates to a distributed photovoltaic grid-connected secondary equipment adaptability transformation method, which is used for acquiring a secondary equipment configuration principle of a power distribution network according to a secondary equipment configuration structure of the power distribution network; the acquired configuration principle of the secondary equipment of the power distribution network is modified; and constructing a configuration principle containing distributed photovoltaic according to the configuration principle of primary equipment of the modified power distribution network. The invention combines the energy development strategy and the distributed access mode with small installation scale, wherein the electric energy is consumed in situ and is close to the load. The method is mainly used for analyzing the influence of the distributed photovoltaic on the power distribution network by combining the current situation of the distributed photovoltaic and the power distribution network and providing a transformation strategy and a protection method of secondary equipment of the power distribution network suitable for the distributed photovoltaic access.
Description
Technical Field
The invention belongs to the technical field of operation of power distribution networks, and particularly relates to an adaptive transformation method of distributed photovoltaic grid-connected secondary equipment.
Background
As the permeability of distributed photovoltaic power sources increases in the distribution network, the distributed photovoltaic power sources increasingly affect the stability and power quality of the distribution network. The power flow unidirectional radial power supply mode of the traditional power distribution network is changed by the distributed photovoltaic access, and in the power distribution network with high photovoltaic permeability, especially in a weaker radial chained low-voltage power distribution network, if the system is lightly loaded, power flow countercurrent easily occurs, so that the power distribution network is over-voltage; the severe fluctuation of the photovoltaic output caused by cloud cover and the like can cause voltage dip, flicker and even system stability problems. Aiming at distributed photovoltaic grid connection, on the basis of a traditional protection strategy, a protection principle adapting to bidirectional tide is adjusted to prevent an unplanned island; meanwhile, in the aspects of dispatching automation, metering and the like, according to the safe and reliable operation and lean management requirements, a new configuration principle is required to be provided for distributed photovoltaic grid connection.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides an adaptive reconstruction method for distributed photovoltaic grid-connected secondary equipment, which can maintain stable operation of a power grid, rapidly and accurately give an optimal load transfer scheme, greatly improve the working efficiency of a dispatcher and ensure safe and stable operation of the power grid.
The invention solves the technical problems by adopting the following technical scheme:
a distributed photovoltaic grid-connected secondary equipment adaptive transformation method comprises the following steps:
step 1, acquiring a configuration principle of secondary equipment of a power distribution network according to a configuration structure of the secondary equipment of the power distribution network;
step 2, modifying the configuration principle of the secondary equipment of the power distribution network obtained in the step 1;
and 3, constructing a distribution network-containing photovoltaic configuration principle according to the primary equipment configuration principle of the transformation of the power distribution network in the step 2.
Moreover, the configuration principle of the secondary equipment of the power distribution network in the step 1 comprises the following steps: distribution network protection configuration principle, distribution network dispatching automation and metering equipment configuration principle, distribution network protection principle, dispatching automation principle and metering principle.
Moreover, the protection configuration principle of the power distribution network comprises the following steps: current quick break protection, time-limited current quick break protection and time-limited overcurrent protection.
Moreover, the distribution network dispatching automation and metering equipment configuration principle comprises a telecontrol system principle, a time setting device principle, an electric energy quality principle and a metering principle.
Moreover, the power distribution network protection comprises line protection, bus protection, reclosing configuration, island detection and safety automatic device
The modifying in the step 2 includes: the method comprises the following steps of 10kV special line access mode, 10kV public power grid access mode and 380V distributed photovoltaic special line access mode.
Moreover, the step 3 includes the steps of: the electric energy quality principle and the protection principle.
The invention has the advantages and positive effects that:
according to the configuration structure of the secondary equipment of the power distribution network, the configuration principle of the secondary equipment of the power distribution network is obtained; the acquired configuration principle of the secondary equipment of the power distribution network is modified; and constructing a configuration principle containing distributed photovoltaic according to the configuration principle of primary equipment of the modified power distribution network. The invention combines the energy development strategy and the distributed access mode with small installation scale, wherein the electric energy is consumed in situ and is close to the load. The method is mainly used for analyzing the influence of the distributed photovoltaic on the power distribution network by combining the current situation of the distributed photovoltaic and the power distribution network and providing a transformation strategy and a protection method of secondary equipment of the power distribution network suitable for the distributed photovoltaic access.
Drawings
FIG. 1 is a flow chart of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
The invention is used for serving distributed photovoltaic popularization, improving the capacity of the power distribution network for absorbing the electric quantity of a distributed photovoltaic power supply, reasonably evaluating the current distributed photovoltaic absorbing capacity of the power distribution network, eliminating the link for restricting the grid connection of the distributed photovoltaic, pertinently formulating a secondary equipment transformation strategy, effectively controlling the operation safety risk of the distributed photovoltaic access power distribution network, achieving the purposes of 'having a basis for access, transforming, having measures and evaluating the principle', furthest improving the absorbing capacity of the distributed photovoltaic of the current power distribution network, adapting to the effective access of the distributed power supply, developing the research from evaluation and transformation, and supporting the transformation construction of the distributed photovoltaic access power distribution network. From the safety operation angle, for different distributed photovoltaic access modes, the influence of distributed photovoltaic grid connection on the power distribution network is analyzed from six aspects of the digestion capability, the tide distribution, the voltage distribution, the electric energy quality, the reliability and the system protection, and a secondary protection strategy adapting to the distributed photovoltaic is provided according to the current situation of the power distribution network.
The invention provides a distributed photovoltaic grid-connected coordination protection strategy by analyzing and aiming at the influence of the distributed photovoltaic grid-connected on protection.
(1) The configuration principle of the traditional three-section type current protection is mainly described. And analyzing typical power distribution network protection configuration, adopting one or a combination of current quick-break protection, time-limited current quick-break protection and time-limited overcurrent protection, and setting reclosing of the overhead line.
(2) Aiming at distributed power supply access, line protection, bus protection and reclosing setting under different access modes are provided, and the distributed power supply access is met with the requirements of protection directivity, sensitivity and selectivity.
(3) The configuration principle of the current distribution network dispatching automation and metering device is discussed, and a corresponding adaptive transformation strategy is provided for distributed photovoltaic grid connection.
(4) Three typical modes of 10kV special line access, 10kV T access and 380V access are selected, and a corresponding secondary equipment configuration principle is introduced.
A distributed photovoltaic grid-connected secondary equipment adaptive transformation method, as shown in figure 1, comprises the following steps:
and step 1, acquiring a configuration principle of secondary equipment of the power distribution network according to the configuration structure of the secondary equipment of the power distribution network.
The configuration principle of the secondary equipment of the power distribution network comprises the following steps: distribution network protection configuration principle, distribution network dispatching automation and metering equipment configuration principle, distribution network protection principle, dispatching automation principle and metering principle.
At present, the distribution network mainly adopts one protection or a combination of current quick-break protection, time-limited current quick-break protection and time-limited overcurrent protection.
(1) Current quick break protection
According to the requirement on relay protection mobility, the time for removing faults by the action of the protection device must meet the system stability and ensure the power supply reliability of important users. The faster and better the principle, the simpler, the more reliable and the selectivity is guaranteed. Therefore, the relay protection of the quick action is required to be installed on various electric elements by stress. The current protection that is reflected only in the transient operation of the current increase is called a current quick-break protection.
The quick break protection is set according to the maximum short-circuit current at the outlet of the next line. The setting formula of the quick break protection is as follows:
I dz2 ＝K k I d.B.max
I dz2 protecting a starting current for the quick-break protection;
K k the reliability coefficient is generally 1.2-1.3;
I d.B.max is the maximum short circuit current.
(2) Time-limited current quick-break protection
Because the current quick break cannot protect the whole length of the line, a new protection section is needed to be added for cutting off faults beyond the quick break range on the line, and the current quick break can be used as a backup for the quick break. The requirement for this new protection is, firstly, to protect the entire length of the line in any case and to have sufficient sensitivity, and secondly, to strive for a minimum time period of operation, provided that the above requirements are met. It is called limited time current quick break protection because it can quickly cut off faults in the whole line range with a small time limit.
And a time-limited current quick-break protection setting value formula:
I xdz2 ＝K k I dz
I xdz2 the starting current is protected for quick-break protection in a protection time limit;
K k the reliability coefficient is generally 1.1-1.2;
I dz setting values for the quick break protection of the lower section line.
(3) Timing over-current protection
Overcurrent protection generally refers to a protection device in which the starting current is set so as to avoid the maximum load current. The power grid protection circuit is not started in normal operation, can reflect the increase of current to act when the power grid fails, can protect the whole length of a circuit, can also protect the whole length of an adjacent circuit, and plays a role in backup protection.
Timing overcurrent protection setting formula:
K k for the reliability coefficient, 1.15-1.25 is generally adopted;
K zqd the self-starting coefficient is a numerical value which is larger than 1 and is determined by specific parameters and load properties of the network;
K j for the return coefficient of the current relay, 0.85 is generally used.
I max Is the maximum load current.
The protection configuration of each region is different, but mainly based on the three-section current protection principle. The level difference protection is realized by setting delay, three levels are recommended, the level difference protection is not recommended to be set for a main line, and the protection of a transformer substation outlet is considered to be matched with the protection of a transformer substation.
(1) Overhead line
And selecting all or part of the substation outlet circuit breaker, the branch line head-end switch and the user demarcation switch to be protected.
Typically set one: the outlet breaker of the transformer substation is provided with time-limited current quick-break protection and overcurrent protection, wherein the time-limited current quick-break protection setting time is 0.5s, the head-end switch of the branch line is provided with time-limited current quick-break protection and overcurrent protection, the time-limited current quick-break protection setting time is 0.2-0.3 s, and the user demarcation switch is provided with current quick-break protection and overcurrent protection, so that three-level differential protection is formed.
The outlet breaker of the transformer substation is provided with time-limited current quick-break protection and overcurrent protection, wherein the time-limited current quick-break protection is set for 0.2-0.3 s, and the head-end switch of the branch line is provided with current quick-break protection and overcurrent protection, so that two-stage level difference is formed.
Typical set two: the outlet breaker of the transformer substation is provided with current quick-break protection and overcurrent protection.
Three typical settings: the outlet circuit breaker of the transformer substation and the head end switch of the branch line are provided with current quick-break protection, the outlet circuit breaker of the transformer substation is provided with reclosing, and the protection action is matched with the reclosing operation, so that the fault influence range is reduced.
(2) Cable line
All or part of the inlet and outlet switches of the substation outlet breaker, the switching station or the ring main unit are selected to be protected.
And the protection time level difference is set according to the number of ring main units (breaker switches) or switching stations in cascade connection, so that the level difference protection of branches and main lines is formed.
Typically set one: the outlet circuit breaker of the transformer substation is provided with time-limited current quick-break protection and overcurrent protection, wherein the time-limited current quick-break protection setting time is 0.5s, the ring main unit outlet switch is provided with time-limited current quick-break protection and overcurrent protection, the time-limited current quick-break protection setting time is 0.2-0.3 s, and the user demarcation switch is provided with current quick-break protection and overcurrent protection, so that three-level differential protection is formed.
The outlet circuit breaker of the transformer substation is provided with time-limited current quick-break protection and overcurrent protection, wherein the setting time of the time-limited current quick-break protection is 0.2-0.3 s, and the outlet switch of the ring main unit is provided with current quick-break protection and overcurrent protection, so that two-stage level difference is formed.
Typical set two: the outlet breaker of the transformer substation is provided with current quick-break protection and overcurrent protection.
At present, no reclosing device is configured on the distribution network cable line, and the overhead line is configured to reclose.
The protection configuration described above is a network based on single power radiation, but when the network includes distributed photovoltaic power sources, the protection configuration should be changed accordingly to meet the requirements of rapidity, selectivity, sensitivity and reliability.
The distribution network dispatching automation and metering equipment configuration principle comprises a telemechanical system principle, a time setting device principle, an electric energy quality principle and a metering principle.
(1) Telemechanical system
At present, a main network dispatching system realizes a three-remote function of 10kV outgoing lines of a power distribution network, and a main line and branch lines (except for a part of power distribution automation implementation areas) are all configuration dispatching automation systems. The distribution automation is implemented in a partial area, so that a contact switch and a main section switch of an overhead line (including a mixed network) are realized, the functions of remote control, remote measurement and remote signaling are realized, and other section switches and branch switches can be configured with the functions of remote signaling and remote measurement; the connection open-loop point and the sectioning equipment of the cable line are generally configured according to remote control, remote measurement and remote signaling functions.
The distribution transformer area basically collects the distribution transformer active, reactive and electric quantity data through an electricity consumption information collecting system, and uploads the relevant distribution electricity consumption information system.
(2) Time setting device
And in an area for implementing power distribution automation, the power distribution terminal has a function of receiving the time service of the master station.
(3) Quality of electric energy
Various power quality monitoring points are dynamically adjusted along with the change of a power supply network.
Wherein:
class a 10 (6) kV busbar voltage for substations and power plants (direct genus) with regional power supply loads.
Class B35 (66) kV special line power supply and 110kV and above user terminal voltage.
Class C35 (66) kV non-private line powered and 10 (6) kV powered customer premises voltage. At least one voltage quality monitoring point should be set for every 10MW load.
Class D380/220V low voltage network and voltage at the customer premises. At least 2 voltage quality monitoring points are arranged on each hundred distribution transformers. Monitoring points should be set at the head and tail ends of a representative low-voltage distribution network and at part of important users.
(5) Metering device
The metering device is arranged at the title demarcation point. Public transformer users generally adopt a high-power low-power metering mode.
The power distribution network protection comprises line protection, bus protection, reclosing configuration, island detection and safety automatic devices.
Line protection:
(1) Accessing public power grid at 380/220V voltage level
When the distributed photovoltaic power generation is connected into a public power grid in 380/220V voltage class, the circuit breakers of the grid connection point and the public connection point have the functions of short circuit transient and long delay protection, shunt tripping, voltage-losing tripping, low-voltage locking closing and the like.
The current quick-break protection, the time-limited current quick-break protection and the overcurrent protection are all protection modes reflecting actions with current rising. The main difference between them is that the starting current is selected according to different tuning principles. The starting current is the minimum current value required for the protection action, that is to say, as soon as the current through the protection device reaches this value, the protection device is activated so as to cut off the fault current. The current quick-break protection is set according to a method of avoiding the maximum three-phase short-circuit current generated when the tail end of the line is broken, and the full length of the line cannot be protected; the time-limited current quick-break protection is set according to the principle of avoiding the current quick-break protection starting current of the adjacent line, so that the full length of the line can be protected; the time-limiting overcurrent protection is set according to the current which avoids the maximum load, can be used as the near backup protection of the current 1 and 2 sections of the current of the line and as the far backup protection of the adjacent lines 1 and 2, and can protect the whole lengths of the current line and the adjacent lines.
(2) When the public power grid is accessed at the voltage level of 10kV
1) Access system using special outgoing line
The distributed photovoltaic power generation adopts a special outgoing line to be connected into a transformer substation or a 10kV bus of a switch, and the direction overcurrent protection or the distance protection can be configured on one side of the transformer substation or the switch station in general; when special requirements exist, the longitudinal current differential protection can be configured.
2) Access system using T-line
When the distributed photovoltaic power generation adopts a T-junction access system, over-current protection is generally required to be configured at the photovoltaic power station side.
And (3) bus protection:
when the distributed photovoltaic power generation system is provided with a bus, special bus protection can be omitted, and faults can be removed by backup protection of bus active connecting elements when faults occur. When special requirements exist, if the backup protection time limit cannot meet the requirements, a protection device can be correspondingly configured to quickly cut off bus faults. And the bus protection of the transformer substation or the switch station side needs to be checked, and if the requirements cannot be met, the transformer substation or the switch station side needs to be provided with a protection device, so that bus faults are rapidly removed.
Reclosing configuration:
as shown in table 1, when the 10kV public power grid line is put into automatic reclosing, the reclosing time should be adjusted or the voltage-free reclosing function should be added, and the automatic reclosing can be stopped to prevent asynchronous closing.
TABLE 1 comparison of reclosing configurations before and after distributed photovoltaic access
Island detection and safety automatic device:
the distributed photovoltaic power generation inverter must have the capability of rapidly detecting an island and immediately disconnecting from the power grid after the island is detected, and the island prevention scheme of the distributed photovoltaic power generation inverter should be matched with relay protection configuration, frequency voltage abnormality emergency control device configuration, low voltage ride through and the like, and are matched with each other in time limit.
The distributed photovoltaic power generation access system is characterized in that an automatic device is required to be arranged at a grid-connected point, so that the emergency control function of abnormal frequency and voltage is realized, and a grid-connected point breaker is tripped; if the 10kV line protection has the functions of voltage-losing tripping and low-voltage locking and closing, disconnection according to Un can be realized, and an independent safety automatic device can be omitted.
The 380V voltage level can be provided with no anti-islanding detection and safety automatic device, and an inverter with anti-islanding capability is adopted. The distributed photovoltaic power generation system with the planned island requirement is provided with a frequency and voltage control device, and when the voltage and frequency in the island are abnormal, the power generation system can be controlled. And the grid connection is not connected with the Internet, and reliable anti-countercurrent protection measures are needed.
Scheduling automation:
the 10kV accessed distributed photovoltaic power generation project is brought into the dispatching operation management of a regulation center of a city or county company, and the uploaded information comprises the state of grid-connected equipment, grid-connected point voltage, current, active power, reactive power and power generation capacity, and the regulation center is required to monitor the operation condition in real time; and the 380V accessed distributed photovoltaic power generation project only needs to upload the generated energy information temporarily.
(1) Telemechanical system
The 380/220V voltage class connected distributed photovoltaic power generation only considers the metering information of the collecting gateway charging electric energy meter.
The function of the remote system of the distributed photovoltaic power generation body accessed by the voltage class of 10kV is preferably integrated by a body monitoring system, and the body monitoring system has the information remote transmission function; when the body does not have the condition, the remote terminal needs to be independently configured to acquire related information.
When 10kV/380V multipoint and multi-voltage-class access is performed, 380V part information is collected and transmitted in a unified mode through the functions of a distributed photovoltaic power generation body remote control system accessed by the 10kV voltage class.
(2) Time setting system
When the distributed photovoltaic power generation 10kV voltage level is accessed, the measurement and control device and the telemechanical system can realize the time setting function, and the Beidou or GPS time setting mode and the network time setting mode can be adopted.
(3) Quality of electric energy
The distributed photovoltaic power generation access system is provided with an on-line power quality monitoring device at a public connection point, and related data are sent to a superior operation management department.
When the 10kV voltage class is accessed, an electric energy quality online monitoring device is required to be configured at a grid-connected point; if necessary, an on-line monitoring device for the electric energy quality is also required to be configured at the public connection point. The power quality parameters including voltage, frequency, harmonics, power factor, etc. are monitored.
When the 380/220V voltage level is accessed, the electric energy meter has an electric energy quality on-line monitoring function, and can monitor three-phase unbalanced current.
Metering:
in the construction of a traditional power grid, a power distribution network line is radial, and electric energy flows singly. The metering modes of the power distribution network to the electric energy are all unidirectional metering, and the distributed photovoltaic power generation equipment is introduced, so that the flow of the electric energy can be multidirectional, and the original unidirectional metering mode is not suitable for the power distribution network at the present stage for the convenience of electric energy statistics. The current-stage power distribution network is changed from unidirectional metering to bidirectional metering.
(1) Electric energy meters are classified into two categories according to metering purposes: the gateway metering electric energy meter is used for metering the power on/off the network between a user and the power grid; the grid-connected electric energy meter can be used for generating capacity statistics and electricity price compensation.
1) Before the distributed photovoltaic power generation is connected to the power distribution network, the gateway metering points of the on-line electric quantity and the off-line electric quantity are arranged at the title demarcation point in principle. And a special gateway metering electric energy meter is required to be configured, and charging information is uploaded to an operation management department.
2) The grid-connected electric energy meter is arranged on the grid-connected point of the distributed photovoltaic power generation and is used for photovoltaic power generation quantity statistics and electricity price compensation. For the purchase and sale operation mode, the special gateway meter can be used for metering the electric energy meter to simultaneously complete the functions of electricity price compensation metering and gateway electricity fee metering.
(2) The voltage class of 10kV and below is connected into the power distribution network, and the gateway metering device is generally not lower than the class II electric energy metering device. The 380/220V voltage class is connected to the distribution network, and the gateway metering device is generally not lower than the class III electric energy metering device.
(3) And a distributed photovoltaic power generation system accessed through a voltage class of 10kV is provided, and the gateway metering points are provided with one set of main and auxiliary electric energy meters with the same model, the same specification and the same accuracy. And (3) configuring a power meter sleeve of the distributed photovoltaic power generation system with 380V/220V voltage class access.
(4) When the 10kV voltage level is accessed, the electric energy gateway point is preferably provided with a special electric energy information acquisition terminal, and the acquired information can support access to a plurality of electric energy information acquisition systems. When the 380V voltage level is accessed, a wireless collection mode can be adopted. The combination scheme of multi-point and multi-voltage grade access is that metering information of each meter should be collected uniformly.
(5) Accuracy requirement of metering current transformer and voltage transformer
The 10kV electric energy metering device adopts a special metering voltage transformer (accuracy 0.2) and a special metering current transformer (accuracy 0.2S). The 380/220V electric energy metering device adopts a special voltage transformer (accuracy is 0.5) and a special current transformer (accuracy is 0.5S).
(6) The electric energy metering device of the distributed photovoltaic power generation system connected with the power generation system at the voltage level of 380/220V has the functions of current, voltage, electric quantity and other information acquisition and three-phase current unbalance monitoring, and is provided with an uploading interface.
Typical secondary equipment transformation scheme adapting to distributed photovoltaic grid connection:
(1) Special line access mode for 10 kilovolts
The basic situation is the same as the typical access mode one of the fourth chapter.
1) Line protection configuration principle
When the circuit of the photovoltaic power station has a short-circuit fault, the circuit protection can act quickly, and the circuit breaker is instantaneously tripped, so that the requirement of quickly and reliably cutting off the fault when the whole line fault occurs is met.
The 10kV line is provided with 1 set of line direction overcurrent protection or distance protection at the system side, the photovoltaic power station side can not be protected by the line, and line faults are removed by the system side.
For a boosting transformer station or a collecting station of 2 or more boosting transformers, a 10kV line can be provided with 1 set of longitudinal current differential protection, and the reverse overcurrent protection is adopted as backup protection.
2) Bus protection configuration principle
As shown in table 2, if the photovoltaic power station side is a line transformer group, the voltage is directly output after being boosted, and no bus protection is configured. For a photovoltaic power station provided with a 10kV bus, the 10kV bus protection configuration should be comprehensively considered with 10kV line protection. When the system side is configured with line overcurrent or distance protection, the photovoltaic power station side can be not configured with bus protection, and faults are removed only by the side line protection of the transformer substation; when the line longitudinal current differential protection is configured on the two sides of the line, a protection device is correspondingly configured on the photovoltaic power station side, so that bus faults are rapidly removed; when the photovoltaic power station time limit allows, faults can be removed only by the backup protection of each incoming line.
Table 2 comparison of protection configurations before and after access to a distributed photovoltaic private line
Note that: the marking device is configured according to actual needs
3) Scheduling automation
The photovoltaic power station body configuration monitoring system has a telemechanical function, the acquisition and the processing of information about the photovoltaic power station body are completed by adopting the monitoring system, and a single configuration sleeve of the monitoring system is used for a telemechanical communication server for information telemechanical transmission. Or the RTU (single set of remote host configuration) with advanced individual configuration technology and easy flexible configuration is required to have the functions of remote measurement, remote signaling, remote control, remote regulation, network communication and the like, and the grid-connected operation information is acquired in real time.
And a measurement and control device is required to be correspondingly configured, the related information of the photovoltaic power station line is collected, and the current monitoring system of the transformer substation is accessed.
A set of A-type power quality online monitoring devices meeting the standard requirements of GB/T19862 general requirements for power quality monitoring equipment are arranged at grid connection points.
4) Metering device
And setting a gateway metering electric energy meter at the title demarcation point, and setting each block of main and standby charging meters.
(2) T-connection access 10kV public power grid
The basic situation is the same as the typical access mode II of the fourth chapter.
1) Line protection configuration principle
When the circuit of the photovoltaic power station has a short-circuit fault, the circuit protection can act quickly, and the circuit breaker is instantaneously tripped, so that the requirement of quickly and reliably cutting off the fault when the whole line fault occurs is met. In order to ensure the power supply reliability and reduce the power failure range, 1 set of overcurrent protection is arranged on the photovoltaic power station side and is used for 10kV T connection.
2) Bus protection configuration principle
As shown in table 3, if the photovoltaic power station side is a line transformer group, the voltage is directly output after being boosted, and no bus protection is configured. For a photovoltaic power station provided with a 10kV bus, the 10kV bus is preferably provided with 1 set of overcurrent protection for bus protection; and when the time limit allows, the faults can be cut off only by the backup protection of each incoming line.
TABLE 3 comparison of front-to-rear protection configurations for distributed photovoltaic T-junctions
3) Scheduling automation
The photovoltaic power station body configuration monitoring system has a telemechanical function, the acquisition and the processing of information about the photovoltaic power station body are completed by adopting the monitoring system, and a single configuration sleeve of the monitoring system is used for a telemechanical communication server for information telemechanical transmission. Or the RTU (single set of remote host configuration) with advanced individual configuration technology and easy flexible configuration is required to have the functions of remote measurement, remote signaling, remote control, remote regulation, network communication and the like, and the grid-connected operation information is acquired in real time.
A set of A-type power quality online monitoring devices meeting the standard requirements of GB/T19862 general requirements for power quality monitoring equipment are arranged at grid connection points.
4) Metering device
And setting a gateway metering electric energy meter at the title demarcation point, and setting each block of main and standby charging meters.
(3) Distributed photovoltaic special line is connected into 380V
The basic situation is the same as the typical access mode three of the fourth chapter.
1) 380V/220V line protection
The circuit breaker of the parallel point and the public connection point has the functions of short circuit instantaneous and long delay protection and shunt tripping and under-voltage tripping, and when a circuit has a short circuit fault, the circuit protection can rapidly act to instantly trip the circuit breaker, thereby meeting the requirement of rapidly and reliably cutting off the fault when the circuit has a full line fault. The circuit breaker should also be provided with auxiliary contacts reflecting the fault and the operating conditions.
2) Bus bar protection
As shown in Table 4, the present scheme does not provide bus bar protection at 380V/220V.
Table 4 distributed photovoltaic Access 220/380V front-to-rear protection configuration contrast
3) Scheduling automation
Only the generated energy information is uploaded and sent to the main management mechanism, and an independent telemechanical system is not configured.
4) Metering device
When the operation mode is spontaneous, a grid-connected electric energy meter is arranged in a single set, so that charging compensation is facilitated. When the operation mode is the allowance surfing, a gateway metering electric energy meter is arranged besides a single set of grid-connected electric energy meter. The electric energy metering gateway point is arranged at the title demarcation point.
And 2, modifying the configuration principle of the secondary equipment of the power distribution network obtained in the step 1.
The transformation comprises transformation of a protection configuration principle of the power distribution network and transformation based on an electric energy amount measurement principle.
The transformation of the protection configuration principle of the power distribution network comprises a 10kV special line access mode, a T-connection 10kV public power grid access mode and a distributed photovoltaic special line 380V access mode.
(1) 10kV line protection
When the special line is connected to the 10kV bus of the user, the 10kV line is provided with 1 set of line direction overcurrent protection or distance protection at the user side, the photovoltaic power station side can be free from line protection, and line faults are cut off by the user side; there are 2 or more boost transformer stations or collecting stations, the 10kV line can be configured with 1 set of longitudinal current differential protection, the directional overcurrent protection is adopted as the backup protection, and the protection fixed value is measured and calculated according to the distributed photovoltaic capacity.
(2) 380V/220V line protection
The circuit breaker of the 380V/220V parallel network point has the functions of short circuit instantaneous and long delay protection and shunt tripping and under-voltage tripping, when a circuit has a short circuit fault, the circuit protection can act rapidly, the circuit breaker is tripped instantaneously, and the requirement of rapidly and reliably cutting off the fault when the whole line fault occurs is met. The circuit breaker should also have auxiliary contacts reflecting faults and operating conditions, and protection values should be calculated according to the distributed photovoltaic capacity.
Reforming based on an electric energy metering principle:
the electric energy measurement needs to be provided with two types of gateway measurement electric energy meters and grid-connected electric energy meters: and the grid-connected electric energy meter is used for charging compensation of photovoltaic power generation. The gateway metering electric energy meter is used for metering the power of the user and the power grid in the on-line and off-line modes, namely, a bidirectional metering mode is adopted.
The electric energy meter adopts a static multifunctional electric energy meter, at least has bidirectional active and four-quadrant reactive power metering function and event recording function, is provided with a standard communication interface, and has the functions of local communication and remote communication through an electric energy information acquisition terminal.
When the self-power-supply is performed, a grid-connected electric energy meter is arranged in each grid-connected point in a single set; the title demarcation point meter is configured according to conventional 10kV user requirements. When the allowance is on the internet, a grid-connected electric energy meter is arranged in each grid-connected point single sleeve, so that charging compensation is facilitated; and setting a gateway metering electric energy meter at the title demarcation point, wherein 10kV is configured according to the main meter and the auxiliary meter, and 380V is configured according to the single meter.
The secondary transformation scheme is as follows:
and carrying out simulation distributed photovoltaic access analysis on a typical line to obtain secondary transformation suggestions of the power distribution network on island detection, current protection fixed value, special protection, reclosing, metering and the like.
1. Anti-islanding protection configuration
When the power distribution network fails or overhauls, if the distributed photovoltaic is unable to be cut off and continues to supply power to the power distribution network, the safety of an electric power system operation and overhauling personnel is possibly threatened, and therefore the anti-islanding protection condition of the distributed photovoltaic is detected before the distributed photovoltaic is connected. If the requirements cannot be met, an operator is influenced to provide island detection and protection devices, and meanwhile, visible breakpoints are additionally arranged near the island prevention devices.
2. Current protection constant value adjustment
Due to the access of the distributed photovoltaic, the short-circuit current of the power distribution network short-circuit point is increased. The original protection fixed value of the power distribution network is changed, so that the protection fixed value of the photovoltaic access line is required to be recalculated and set aiming at the distributed photovoltaic access project.
3. With additional special protections
The distributed photovoltaic access can cause reverse flow of current to a certain extent, so that misoperation of original protection is caused, and the addition of some protection such as over-current protection, line longitudinal difference protection and the like in a power distribution network of the distributed photovoltaic access is suggested.
4. Line reclosing
In the power distribution network, only the overhead line adopts reclosing configuration, so that the reclosing of the line is adjusted when the distributed photovoltaic is connected into the power grid. The low-frequency low-voltage disconnection device can be configured at the distributed photovoltaic grid-connected position, so that the distributed photovoltaic is cut off before automatic reclosing and spare power automatic switching actions, a power grid side reclosing detection line is pressureless, the distributed photovoltaic side reclosing detection period is shortened, and the voltage fixed value of the pressureless verification is reduced relatively. The problem of unsuccessful reclosing caused by the problem of asynchronous reclosing caused by the belt photovoltaic is prevented, so that the power failure range is enlarged.
5. Upgrading and reforming of metering equipment
The traditional distribution network lines are in a radial shape, and electric energy flows singly. The distribution network meters the electric energy in a unidirectional manner, and because the distributed photovoltaic power generation equipment is introduced, the electric energy flows in a multidirectional manner, so that the distribution network containing the distributed photovoltaic power is recommended to be transformed into the bidirectional metering capability for the convenience of electric energy statistics.
And 3, constructing a distribution network-containing photovoltaic configuration principle according to the primary equipment configuration principle of the transformation of the power distribution network in the step 2.
Including distributed photovoltaic configuration principles include: the electric energy quality principle and the protection principle.
The electric energy quality principle:
(1) The operation scheduling can monitor the power quality and the output condition of each distributed photovoltaic, and the distributed photovoltaic is provided with a communication interface.
(2) Meets the basic requirement on the quality of electric energy.
(3) Frequency deviation: the frequency of the power grid accords with the specification of GB/T15945-1995, the rated frequency is 50Hz, and the normal frequency deviation is not more than +/-0.2 Hz.
(4) Voltage deviation: the network voltage level should be calculated during the planning and design of the power grid. The allowable deviation range of the 10kV bus of the system is 0 to +7%; the allowable deviation of the voltage of the receiving end of the user meets the specification of GB 12325, and the allowable deviation of the voltage of the 10kV and 380V user power supply is +/-7% of the nominal voltage of the system; the 220V user supply voltage allows deviation of-10% to +7% of the nominal voltage of the system.
(5) Synchronization requirements
When the distributed photovoltaic grid-connected operation is performed, the output voltage of the distributed photovoltaic grid-connected operation is required to track the voltage of a power grid. The distributed photovoltaic grid-tie synchronization requirements are as follows.
ΔU＝±10％，Δf＝±0.3Hz，Δδ＝±15°。
(6) Harmonic limitation: the harmonic voltage of the public power grid and the harmonic current injected into the power grid by a harmonic source user are in accordance with the specification of GB/T14549-2008.
When the consumer electric equipment comprises a converter device (such as an aluminum profile factory), an electric arc furnace (such as a steel mill), an iron core device and nonlinear electric equipment, a filter device is additionally arranged, and field test is carried out before the consumer electric equipment is put into use, so that harmonic current is ensured to meet the specification of GB/T14549-2008. For the centralized large harmonic source, the principle of 'who pollutes and who administers' should be implemented, and the centralized large harmonic source is urged to take control measures. When the power grid is expanded and transformed, harmonic wave design and verification are carried out on the capacitor bank, and the capacity of the series reactor is reasonably configured so as to prevent harmonic wave resonance or serious amplification.
Harmonic monitoring points are arranged on a 10kV bus, a public transformer low-voltage side and a private transformer user power supply (receiving) side of the transformer substation.
(7) Voltage flicker: voltage flicker may be due to rapid changes in the output power of the generator, such as a wind turbine, rapid changes in load current or significant changes in spur voltage as is the case with current arc furnaces and induction motor starts. International electrotechnical Commission standard IEC 61400-21 specifies wind turbinesGrid-connected power quality, suggesting limiting single wind generator flicker to P lt =0.25, the index is the average flicker measure weighted for 2h, it is also recommended to limit the total flicker of the wind generator at any node of the medium voltage network to P lt ＝0.5。
(8) Reactive power control: when the output active power of the small photovoltaic power station is generally required to be more than 50% of the rated power, the power factor is not less than 0.98; when the output active power is 20% -50%, the power factor is not less than 0.95, and when special requirements exist, the power factor is required to be determined by negotiation with a power grid enterprise; the power factor of large and medium-sized photovoltaic power stations should be continuously adjustable between 0.98 to-0.98.
Protection principle:
the technical standard of the current protection basically requires that the distributed photovoltaic should not damage the automatic reclosing, the coordination of the original power system protection is not changed, and the requirement of anti-islanding protection must be met. However, as the capacity of the distributed photovoltaic increases more and more than the capacity of the system and the distributed photovoltaic island is allowed to operate, the working principle and logic of protection become complex. The protection regulations in the current standards need to be further refined.
(1) Island protection
The private generator operated in a grid-connected mode must meet the anti-islanding protection requirements, including the following measures: reverse power, neutral voltage offset, directional overcurrent, frequency change rate, power factor conversion, voltage vector change, voltage control overcurrent protection, all switching values must be equipped with synchronous devices or interlocking devices. When the voltage of the power grid incorporated by the photovoltaic system is lost, the photovoltaic system is disconnected from the power grid within 2 seconds, so that the island effect is prevented.
(2) Reclosing valve
GB 19939-2005 also specifies for over/under frequency and over/under voltage tripping and recovery grid-connection of photovoltaic systems, requiring that protection should be active within 0.2 seconds when the frequency at the grid interface is outside of the specified range.
Secondary modification of typical lines:
the following analysis will be made from the retrofitting of the main secondary equipment of the cable network and the overhead network for a typical distribution line of 10 kV.
1. Cable line
The required modification is shown in table 5 for the case of distributed photovoltaic capacity and location in the cabling.
Table 5 distributed photovoltaic access cable network retrofit measures
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2. Overhead line
The required retrofit solutions for the distributed photovoltaic capacity and location in overhead lines are shown in table 6.
Table 6 distributed photovoltaic access overhead network modification measure
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It should be emphasized that the examples described herein are illustrative rather than limiting, and therefore the invention includes, but is not limited to, the examples described in the detailed description, as other embodiments derived from the technical solutions of the invention by a person skilled in the art are equally within the scope of the invention.
Claims (7)
1. A distributed photovoltaic grid-connected secondary equipment adaptability modification method is characterized by comprising the following steps of: the method comprises the following steps:
step 1, acquiring a configuration principle of secondary equipment of a power distribution network according to a configuration structure of the secondary equipment of the power distribution network;
step 2, modifying the configuration principle of the secondary equipment of the power distribution network obtained in the step 1;
and 3, constructing a distribution network-containing photovoltaic configuration principle according to the primary equipment configuration principle of the transformation of the power distribution network in the step 2.
2. The distributed photovoltaic grid-connected secondary equipment adaptation method according to claim 1, wherein the method comprises the following steps of: the configuration principle of the secondary equipment of the power distribution network in the step 1 comprises the following steps: distribution network protection configuration principle, distribution network dispatching automation and metering equipment configuration principle, distribution network protection principle, dispatching automation principle and metering principle.
3. The distributed photovoltaic grid-connected secondary equipment adaptation method according to claim 2, wherein the method comprises the following steps of: the protection configuration principle of the power distribution network comprises the following steps: current quick break protection, time-limited current quick break protection and time-limited overcurrent protection.
4. The distributed photovoltaic grid-connected secondary equipment adaptation method according to claim 2, wherein the method comprises the following steps of: the distribution network dispatching automation and metering equipment configuration principle comprises a telecontrol system principle, a time setting device principle, an electric energy quality principle and a metering principle.
5. The distributed photovoltaic grid-connected secondary equipment adaptation method according to claim 2, wherein the method comprises the following steps of: the power distribution network protection comprises line protection, bus protection, reclosing configuration, island detection and a safety automatic device.
6. The distributed photovoltaic grid-connected secondary equipment adaptation method according to claim 2, wherein the method comprises the following steps of: the modification in the step 2 comprises the following steps: the method comprises the following steps of 10kV special line access mode, 10kV public power grid access mode and 380V distributed photovoltaic special line access mode.
7. The distributed photovoltaic grid-connected secondary equipment adaptation method according to claim 2, wherein the method comprises the following steps of: the step 3 includes the following steps: the electric energy quality principle and the protection principle.
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