CN110994569A - Multi-level cooperative power distribution network protection strategy - Google Patents
Multi-level cooperative power distribution network protection strategy Download PDFInfo
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- CN110994569A CN110994569A CN201911297822.XA CN201911297822A CN110994569A CN 110994569 A CN110994569 A CN 110994569A CN 201911297822 A CN201911297822 A CN 201911297822A CN 110994569 A CN110994569 A CN 110994569A
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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
- H02H7/261—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 involving signal transmission between at least two stations
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Abstract
The invention discloses a multi-level cooperative protection strategy and provides a new optimization method for protecting a distribution network of a photovoltaic power station containing megawatts. The method is composed of analysis of influence on current protection after a megawatt photovoltaic power station is connected to a power distribution network, an integrated sum-difference phasor algorithm and a multi-level cooperative protection strategy. The invention aims to improve the reliability and the sensitivity of current differential protection, provides an integration and difference phasor algorithm aiming at a non-periodic attenuation component after a fault, divides a distribution network containing megawatt photovoltaic into a central layer, a regional layer and a system layer, provides an inverse time limit protection framework of multi-level protection, establishes a multi-level cooperative protection strategy and realizes intelligent and accurate removal of the fault.
Description
Technical Field
The invention relates to a multi-level cooperative power distribution network protection strategy used in the technical field of power distribution network relay protection.
Background
In the prior art, technicians analyze the influence of the access of a photovoltaic power station on fault current protection, setting scheme and protection configuration of a power distribution network from multiple angles, but the fault condition and the protection configuration of the power distribution network are not discussed after the megawatt photovoltaic power station is accessed, and the problem of gradual matching of protection is less researched.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides a multi-level cooperative power distribution network protection strategy, and provides a megawatt photovoltaic power station power distribution network protection optimization method based on the multi-level cooperative strategy.
One technical scheme for achieving the above purpose is as follows: a multi-level cooperative power distribution network protection strategy is used for a power distribution network containing megawatt photovoltaic power stations and is characterized by comprising analysis, integration and difference phasor algorithms and multi-level cooperative protection strategies of the influence on current protection after the megawatt photovoltaic power stations are connected to the power distribution network,
analyzing the influence of the megawatt photovoltaic power station on current protection after being accessed into a power distribution network, wherein the influence is divided into two dimensions, namely the influence of the photovoltaic power station on downstream current protection when being accessed into a downstream line and the influence of the photovoltaic power station on upstream line current protection when being accessed into an upstream line; for the influence on the downstream current protection, the maximum short-circuit current is increased, the selectivity of the current protection section I and the current protection section II is lost, the sensitivity of the current protection section III is improved, and the selectivity is not influenced; for the current protection influence on the upstream line, the current protection I section, the current protection II section and the current protection II section I section are protected to lose directionality, and the maximum reverse current needs to be avoided;
the integration and difference phasor algorithm has the function of reducing the influence of a direct attenuation component on phasor calculation after a megawatt photovoltaic power station is accessed through a 10kV feeder;
the multi-level cooperative protection strategy comprises a multi-level cooperative protection scheme, a fault point is taken as a center, protection is divided into a center layer, a regional layer and a system layer, different levels are overlapped and crossed in range, and sensitivity and isolation requirements are set.
According to the protection strategy of the multi-level cooperative power distribution network, the influence of the access of the megawatt photovoltaic power station on current protection is analyzed, and boost current generated by the megawatt photovoltaic power station is beneficial to performing reverse time limit overcurrent protection action, but misoperation of current quick-break protection can be possibly caused. The reverse false operation of inverse time-limit protection is caused because the power flow of the line can be reversed; according to the optimized current differential protection, the influence of the non-periodic attenuation component after the fault on phasor calculation is reduced by adopting the integral and differential phasor differential protection, and the reliability and the sensitivity of the differential protection are improved; according to the multi-level cooperative differential protection strategy provided by the invention, the distribution network is divided into a central layer, a regional layer and a system layer according to the structure of the distribution network, an inverse time limit protection framework of multi-level main protection is provided according to a step time limit principle among different levels of protection, and a multi-level protection algorithm can effectively cooperate with various types of protection to realize intelligent fault removal.
Drawings
Fig. 1 is a schematic diagram of differential protection of a multi-level cooperative power distribution network protection strategy according to the present invention;
FIG. 2 is a schematic diagram of differential protection based on an integration and difference phasor method for a multi-level cooperative power distribution network protection strategy according to the present invention;
fig. 3 is a schematic diagram of a multi-level cooperative protection strategy of a power distribution network according to a multi-level cooperative protection strategy of the present invention;
fig. 4 is a schematic diagram of a multi-level cooperative inverse time-lag protection architecture of a power distribution network of a photovoltaic power station related to a multi-level cooperative power distribution network protection strategy according to the present invention;
fig. 5 is a schematic flow diagram of a multi-level cooperative protection algorithm related to a multi-level cooperative protection strategy of a power distribution network according to the present invention.
Detailed Description
In order to better understand the technical solution of the present invention, the following detailed description is made by specific examples:
referring to fig. 1, a differential protection scheme according to the present invention is shown.
The distribution network of photovoltaic power station containing megawatt level is composed of resistance and inductive elements, because the current quantity in the inductance can not be changed suddenly, in order to maintain the current in the inductance unchanged at the initial moment of short circuit, a direct current component is generated, and the direct current component is attenuated according to the time constant of the direct current component flowing through the loop. Formula 1 is an expression of the aperiodic component:
i″(t)＝Ae-t/τ＝A(1+(-t/τ)+o(t2)) (1)
in the formula, A represents a direct current amplitude and is determined by the starting condition of short circuit; τ is the decay time constant of the dc component, determined by the line parameters. Wherein the constant DC component and the first component of time t are the main components of the attenuated DC component, and o (t) is ignored2) Only the first two terms are considered.
Phasor in the power system is calculated by utilizing a Discrete Fourier Transform (DFT) at sampling points, and the DFT is calculated as the formula 2:
The imaginary part of the DFT is then processed by integration and difference, as shown in equation 4:
similar to the real part processing method, the cosine is shifted by half lattice as in equation 5:
in summary, the influence of the straight attenuation component on the phasor calculation can be greatly reduced by using equations 8 and 9; especially for the direct current component with slow error, the improved calculation algorithm can obtain the phasor result with high accuracy after one cycle.
Fig. 3 is a schematic diagram of a multi-level cooperative protection strategy for a power distribution network according to the present invention.
The protection is divided into a center layer, a regional layer and a system layer by taking a fault point as a center, different levels are overlapped and crossed in range, and sensitivity and isolation need to be set, so that a flexible and changeable operation mode of a power distribution network containing a photovoltaic power station is effectively dealt with, and multi-level cooperative protection of the power distribution network containing the photovoltaic power station is formed.
(1) The Core Layer Protection (CLP) uses a single line as a basic unit for protection, and is a main protection for the line including the photovoltaic power station. The central layer protection adopts a distributed structure, namely, protection units are arranged on all lines containing the photovoltaic power station,
(2) the Regional Layer Protection (RLP) faces to a region formed by connecting multiple lines, and the protection range can be divided according to feeder branches of a power distribution network containing a photovoltaic power station.
(3) The System Level Protection (SLP) is directed to a Bus (Bus 1 in fig. 2) and a Point of Common Connection (PCC) of a distribution network including a photovoltaic power station, monitors a grid-connected or isolated island operation mode of the distribution network including the photovoltaic power station, and adaptively adjusts configuration parameters of a protection system.
Fig. 4 is a schematic diagram of a multi-level cooperative inverse time-lag protection architecture of a power distribution network including a photovoltaic power station according to the present invention.
The protection system consists of 'central layer main protection-regional layer multi-level backup protection-system layer grid-connected protection', a fault region is identified by utilizing multi-layer differential current, the protection action time is related to the fault severity, the protection of different levels is cooperatively matched by a step time limit principle, and the overall protection system presents a step inverse time limit differential protection characteristic. For the faults of the power distribution network, the inverse time-limited low-voltage protection is designed at a system layer, and the fault isolation and low-voltage ride-through capability of the power distribution network containing a photovoltaic power station are considered.
Please refer to fig. 5, which is a flowchart illustrating a multi-level cooperative protection algorithm according to the present invention.
In order to realize a multi-level cooperative protection scheme of a power distribution network containing a photovoltaic power station, a multi-level cooperative protection algorithm is designed based on the principle of integrated and differential phasor differential protection according to a cooperative strategy shown in FIG. 4
1) Protection of the central layer:
(1) the protection criterion can be directly applied to an integral and differential phasor differential protection equation of action.
(2) And if the fault is not removed after the protection action is executed, monitoring the state of the corresponding breaker and sending the state to the regional layer protection unit.
2) Protection of a regional layer:
(1) according to the topological structure in the region, dividing all the integration and difference phasor differential protection rings and determining the protection level, as shown in FIG. 4.
(2) And configuring regional backup protection criteria for the integration and difference phasor differential protection rings.
(3) Adjacent phasor differential protection rings may overlap, and in order to reduce the influence range of a fault as much as possible, the same-level phasor differential protection ring is specified, and the protection priority on the weak feed side of the photovoltaic power station is higher, for example, in fig. 4, the priority of the differential protection 5 is higher than that of the differential protection 4.
(4) When a line has a fault, the differential protection of the pre-action is determined by combining the breaker state returned by the superior protection and the priority of the differential protection ring.
3) And (4) system layer protection:
(1) and monitoring the state of a grid-connected point of the photovoltaic power station, judging the operation mode of the photovoltaic power station, and setting a parameter setting value of the protection system according to the operation mode. In order to avoid the transient influence of the switching process of the operation mode of the power distribution network comprising the photovoltaic power station, a certain time delay can be set for the switching of the protection setting value.
(2) And the bus protection is combined with a grid-connected protection algorithm of a grid-connected point of the photovoltaic power station.
The influence of the access of the megawatt photovoltaic power station on the current protection is analyzed. 1) When a downstream line of the photovoltaic power station has a fault, the photovoltaic power station provides an auxiliary current for a fault point, and the auxiliary current is beneficial to the reverse time-limit overcurrent protection action, but can cause the false action of the current quick-break protection. 2) When an upstream line of a photovoltaic power station breaks down, the line between a system and the photovoltaic power station is powered by an original single-end power supply and is changed into a double-end power supply, the power flow of the line can be reversed, the directivity can be lost, and reverse misoperation can be caused.
Because the embodiment adopts the integration and difference phasor algorithm, the traditional DFT algorithm is influenced by the attenuated direct current component, and after the delay of one cycle, the result is still in the process of attenuated oscillation, so that the error is large. The improved integration and difference phasor algorithm tends to be stable after passing through the point, a calculation result with high accuracy can be obtained, and the method can be better suitable for a protection scheme.
Because this embodiment adopts novel phasor differential protection, according to the regional understanding of trouble electric current action, the protection sensitivity is high, and can effectively discern the district's interior trouble through transition resistance, has certain anti transition resistance ability.
Because the present embodiment adopts a multi-level cooperative protection scheme, the differential current of the line after the fault is rapidly increased and is far greater than the protection starting current, and the ratio of the differential current to the braking current trips, so that the protection acts correctly. The main protection of the line is the corresponding central layer protection, the regional layer protection provides II-level and III-level backup protection, and if the fault is not cut off, the upstream line protection can be used as the far backup protection of the line. The multi-level main protection can be matched with each other correctly.
It should be understood by those skilled in the art that the above embodiments are only for illustrating the present invention and are not to be used as a limitation of the present invention, and that changes and modifications to the above described embodiments are within the scope of the claims of the present invention as long as they are within the spirit and scope of the present invention.
Claims (1)
1. A multi-level cooperative power distribution network protection strategy is used for a power distribution network containing megawatt photovoltaic power stations and is characterized by comprising analysis, integration and difference phasor algorithms and multi-level cooperative protection strategies of the influence on current protection after the megawatt photovoltaic power stations are connected to the power distribution network,
analyzing the influence of the megawatt photovoltaic power station on current protection after being accessed into a power distribution network, wherein the influence is divided into two dimensions, namely the influence of the photovoltaic power station on downstream current protection when being accessed into a downstream line and the influence of the photovoltaic power station on upstream line current protection when being accessed into an upstream line; for the influence on the downstream current protection, the maximum short-circuit current is increased, the selectivity of the current protection section I and the current protection section II is lost, the sensitivity of the current protection section III is improved, and the selectivity is not influenced; for the current protection influence on the upstream line, the current protection I section, the current protection II section and the current protection III section lose directionality, and the maximum reverse current needs to be avoided;
the integration and difference phasor algorithm has the function of reducing the influence of a direct attenuation component on phasor calculation after a megawatt photovoltaic power station is accessed through a 10kV feeder;
the multi-level cooperative protection strategy comprises a multi-level cooperative protection scheme, a fault point is taken as a center, protection is divided into a center layer, a regional layer and a system layer, different levels are overlapped and crossed in range, and sensitivity and isolation requirements are set.
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| CN111509683A (en) * | 2020-05-21 | 2020-08-07 | 南方电网科学研究院有限责任公司 | Current protection configuration and setting method after T-connection photovoltaic access of power distribution network |
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| CN107645155A (en) * | 2017-09-05 | 2018-01-30 | 广东电网有限责任公司电力科学研究院 | Distribution network line distance protecting method after large-scale distributed photo-voltaic power supply access |
| CN107706893A (en) * | 2017-10-31 | 2018-02-16 | 广东电网有限责任公司惠州供电局 | A kind of computational methods of DG accesses distribution optimum capacity |
| CN109361198A (en) * | 2018-10-10 | 2019-02-19 | 上海交通大学 | Micro-capacitance sensor multi-layer cooperates with inverse time lag line protection method and device |
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| CN107645155A (en) * | 2017-09-05 | 2018-01-30 | 广东电网有限责任公司电力科学研究院 | Distribution network line distance protecting method after large-scale distributed photo-voltaic power supply access |
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| CN111509683A (en) * | 2020-05-21 | 2020-08-07 | 南方电网科学研究院有限责任公司 | Current protection configuration and setting method after T-connection photovoltaic access of power distribution network |
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