CN108808639B - AC-DC hybrid power grid symmetrical short-circuit current calculation method and electric network protection method - Google Patents
AC-DC hybrid power grid symmetrical short-circuit current calculation method and electric network protection method Download PDFInfo
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- CN108808639B CN108808639B CN201810714663.8A CN201810714663A CN108808639B CN 108808639 B CN108808639 B CN 108808639B CN 201810714663 A CN201810714663 A CN 201810714663A CN 108808639 B CN108808639 B CN 108808639B
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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
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
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Abstract
The invention discloses a kind of AC-DC hybrid power grid symmetrical short-circuit current calculation methods, step 1: dividing AC-DC hybrid power grid node: step 2: establishing AC network nodal voltage equation and DC grid nodal voltage equation respectively；Step 3: AC network nodal voltage equation and AC network mixed connection node and DC grid mixed connection node in DC grid nodal voltage equation are eliminated, to obtain AC-DC hybrid power grid nodal voltage equation；Step 4: the symmetrical short-circuit electric current of AC-DC hybrid power grid is calculated using accident analysis principle of stacking and using AC-DC hybrid power grid nodal voltage equation.The present invention also provides a kind of electric network protection methods to calculate symmetrical short-circuit electric current using symmetrical short-circuit current calculation method of the invention, then formulates electric network protection scheme according to the calculated symmetrical short-circuit electric current of institute.The present invention can accurately and efficiently calculate AC-DC hybrid power grid symmetrical short-circuit electric current, be of great significance to the safe and stable operation for guaranteeing power grid.
Description
Technical field
The present invention relates to electric system O&M technical fields, and in particular to a kind of AC-DC hybrid power grid symmetrical short-circuit electric current
Calculation method and electric network protection method.
Background technique
D.C. high voltage transmission (High Voltage Direct Current, HVDC) is with it in long-distance and large-capacity power transmission
It is used widely with the significant advantage of asynchronous Power System Interconnection etc..In recent years, with the quick hair of HVDC Transmission Technology
Exhibition, large quantities of high voltage direct current transmission projects put into operation in China, and China's electric system has stepped into the AC-DC hybrid power grid epoch.
Currently, China is completed the AC-DC hybrid power grid that the whole world is largest, operating condition is most complicated, large-scale alterating and direct current is ensured
The safe and stable operation of net has become important and urgent Demand of Nation.
Short circuit calculation be implement AC-DC hybrid power grid protection basis, to AC-DC hybrid power grid carry out accident analysis with
Short circuit calculation can provide theoretical foundation for the formulation of AC-DC hybrid power grid protection scheme, to guarantee the safety and stability of power grid
Operation.When alterating and direct current Netcom multiple AC/DC inverters excessively interconnect, the short circuit current that power of alterating and direct current injects after failure passes through
It exchanges sequence net, DC grid and forms the constraint relationship in each node, and the mixed connection node failure that different short-circuit stage inverter determines
Electrical constraints present non-linear, this makes traditional AC network short-circuit current calculation method that can not be suitable for alternating current-direct current mixed connection
Power grid.
Therefore, it is necessary to the fault characteristic according to AC-DC hybrid power grid, research is suitable for the short circuit of AC-DC hybrid power grid
Current calculation method.
Summary of the invention
In view of the above shortcomings of the prior art, the present invention provides a kind of AC-DC hybrid power grid symmetrical short-circuit electric current calculating side
Method solves the technical issues of conventional AC grid short circuit calculation method can not be suitable for AC-DC hybrid power grid in the prior art,
The symmetrical short-circuit electric current that serial-parallel power grid can be calculated for the short trouble feature of AC-DC hybrid power grid, is protected for serial-parallel power grid
The braking of scheme provides theoretical foundation.
In order to solve the above-mentioned technical problem, present invention employs the following technical solutions: a kind of AC-DC hybrid power grid pair
Claim short-circuit current calculation method, the AC-DC hybrid power grid utilizes AC/DC inverter progress AC network and DC grid
Mixed connection, comprising the following steps:
Step 1: it divides AC-DC hybrid power grid node: whether being mixed connection node according to AC-DC hybrid power grid node, it will
The node division of AC network is AC network mixed connection node collection AD and other nodes of AC network collection AC, by the section of DC grid
Point is divided into DC grid mixed connection node collection DA and other node collection of DC grid DC；
Step 2: according to the equivalent network for calculation of short-circuit current of AC-DC hybrid power grid, establishing AC network respectively
Nodal voltage equation and DC grid nodal voltage equation；
Step 3: utilizing the port transient state of reflection exchange side and the AC/DC inverter of DC side transient state electrical quantity mapping relations
Equation of transfer is measured, the AC network mixed connection node in AC network nodal voltage equation and DC grid nodal voltage equation is eliminated
And DC grid mixed connection node, to obtain AC-DC hybrid power grid nodal voltage equation；
Step 4: calculating alternating current-direct current using accident analysis principle of stacking and using AC-DC hybrid power grid nodal voltage equation
The symmetrical short-circuit electric current of serial-parallel power grid, the symmetrical short-circuit electric current of the AC-DC hybrid power grid include pair of AC network short dot
Claim the symmetrical short-circuit electric current of short circuit current and DC grid short dot.
Preferably, AC network nodal voltage equation is indicated using nodal impedance matrix:
Wherein, UADFor the node voltage of AC network mixed connection node, UACFor the node voltage of other nodes of AC network；
IADInjection Current from AC/DC inverter to AC network mixed connection node, I forACFor AC/DC inverter, to AC network, other are saved
The Injection Current of point；ZAD、ZACThe respectively nodal impedance matrix of AC network mixed connection node, AC network other nodes；ZAm1、
ZAm2The respectively mutual resistance matrix of AC network mixed connection node and other nodes of AC network, and the two transposed matrix each other.
Preferably, DC grid nodal voltage equation is indicated using node-resistance matrix:
Wherein, UDAFor the node voltage of DC grid mixed connection node, UDCFor the node voltage of other nodes of DC grid；
IDAIt is AC/DC inverter to the Injection Current of DC grid mixed connection node, IDCFor AC/DC inverter, to DC grid, other are saved
The Injection Current of point；RDA、RDCThe respectively node-resistance matrix of DC grid mixed connection node, DC grid other nodes；RDm1、
RDm2The respectively mutual resistance matrix of DC grid mixed connection node and other nodes of DC grid, and the two transposed matrix each other.
Preferably, the port transient equation of transfer of AC/DC inverter are as follows:
Wherein, TDAFor the port transient transfer matrix of AC/DC inverter,
T11For the transfer matrix between the voltage of AC/DC inverter alternating current-direct current side, T22For AC/DC inverter alternating current-direct current side electricity
Transfer matrix between stream, T12For the transfer matrix between AC/DC inverter alternating current and DC voltage, T21Respectively AC/
Transfer matrix between DC inverter alternating voltage and DC current.
Preferably, the AC-DC hybrid power grid nodal voltage equation after mixed connection node is eliminated are as follows:
Wherein, ZAC+ΔZACFor the nodal impedance matrix of AC network after cancellation mixed connection node, RDC+ΔZDCTo eliminate mixed connection
The nodal impedance matrix of DC grid after node；ΔZADTo eliminate the alternating current-direct current mixed connection mutual resistance matrix after mixed connection node, indicate
Influence of the DC grid short circuit current to AC network；ΔZDATo eliminate the alternating current-direct current mixed connection mutual resistance matrix after mixed connection node,
Indicate influence of the AC network short circuit current to DC grid.
The present invention also provides a kind of electric network protection methods, and the power grid is AC-DC hybrid power grid, using friendship of the invention
Direct current serial-parallel power grid symmetrical short-circuit current calculation method, calculates the symmetrical short-circuit electric current of AC-DC hybrid power grid, then according to institute
Calculated symmetrical short-circuit electric current formulates electric network protection scheme.
Compared with prior art, the invention has the following advantages:
1, symmetrical short-circuit current calculation method of the invention, for AC network in AC-DC hybrid power grid and DC grid
Between interactional characteristic, design the calculation method of AC-DC hybrid power grid symmetrical short-circuit electric current, solve the prior art
Middle conventional AC grid short circuit calculation method can not be suitable for the technical issues of AC-DC hybrid power grid, can be accurately and efficiently
Realize AC-DC hybrid power grid symmetrical short-circuit electric current calculate, for AC-DC hybrid power grid protection scheme formulation provide theory according to
According to, to guarantee power grid safe and stable operation be of great significance.
2, it is mixed for the ease of eliminating AC network mixed connection node and DC grid for dividing AC-DC hybrid power grid node
Interlink point, the port transient equation of transfer reflection exchange side of AC/DC inverter and DC side transient state electrical quantity mapping relations, from
And AC-DC hybrid power grid can be decomposed using accident analysis principle of stacking: when symmetrical short-circuit failure occurs for AC network
When, AC-DC hybrid power grid is resolved into the AC network of normal DC grid and failure, thus allows for AC network
The calculating of fault point symmetrical short-circuit electric current；When symmetrical short-circuit failure occurs for DC grid, AC-DC hybrid power grid is resolved into
The DC grid of normal AC network and failure, thus allows for the calculating of DC grid fault point symmetrical short-circuit electric current.
Detailed description of the invention
Fig. 1 is the structural schematic diagram of the equivalent network for calculation of short-circuit current of AC-DC hybrid power grid.
Specific embodiment
The present invention is described in further detail with preferred embodiment with reference to the accompanying drawing.It now proposes a kind of based on end
The AC-DC hybrid power grid symmetrical short-circuit current calculation method of mouth transient transfer matrix, for the protection of AC-DC hybrid power grid from now on
The formulation of scheme provides theoretical foundation, has important academic significance and engineering value.
A kind of AC-DC hybrid power grid symmetrical short-circuit current calculation method, the AC-DC hybrid power grid are changed using AC/DC
Flow the mixed connection that device carries out AC network and DC grid, comprising the following steps:
Step 1: it divides AC-DC hybrid power grid node: whether being mixed connection node according to AC-DC hybrid power grid node, it will
The node division of AC network is AC network mixed connection node collection AD and other nodes of AC network collection AC, by the section of DC grid
Point is divided into DC grid mixed connection node collection DA and other node collection of DC grid DC；
Step 2: according to the equivalent network for calculation of short-circuit current of AC-DC hybrid power grid, the structure of equivalent network is such as
Shown in Fig. 1, AC network nodal voltage equation and DC grid nodal voltage equation are established respectively；
Step 3: utilizing the port transient state of reflection exchange side and the AC/DC inverter of DC side transient state electrical quantity mapping relations
Equation of transfer is measured, the AC network mixed connection node in AC network nodal voltage equation and DC grid nodal voltage equation is eliminated
And DC grid mixed connection node, to obtain AC-DC hybrid power grid nodal voltage equation；
Step 4: calculating alternating current-direct current using accident analysis principle of stacking and using AC-DC hybrid power grid nodal voltage equation
The symmetrical short-circuit electric current of serial-parallel power grid, the symmetrical short-circuit electric current of the AC-DC hybrid power grid include pair of AC network short dot
Claim the symmetrical short-circuit electric current of short circuit current and DC grid short dot.
Symmetrical short-circuit current calculation method of the invention, for AC network in AC-DC hybrid power grid and DC grid it
Between interactional characteristic, design the calculation method of AC-DC hybrid power grid symmetrical short-circuit electric current, solve in the prior art
Conventional AC grid short circuit calculation method can not be suitable for the technical issues of AC-DC hybrid power grid, can be accurately and efficiently real
Existing AC-DC hybrid power grid symmetrical short-circuit electric current calculates, for AC-DC hybrid power grid protection scheme formulation provide theory according to
According to, to guarantee power grid safe and stable operation be of great significance.
Dividing AC-DC hybrid power grid node is for the ease of eliminating AC network mixed connection node and DC grid mixed connection
Node, the port transient equation of transfer reflection exchange side of AC/DC inverter and DC side transient state electrical quantity mapping relations, thus
AC-DC hybrid power grid can be decomposed using accident analysis principle of stacking: when symmetrical short-circuit failure occurs for AC network
When, AC-DC hybrid power grid is resolved into the AC network of normal DC grid and failure, thus allows for AC network
The calculating of fault point symmetrical short-circuit electric current；When symmetrical short-circuit failure occurs for DC grid, AC-DC hybrid power grid is resolved into
The DC grid of normal AC network and failure, thus allows for the calculating of DC grid fault point symmetrical short-circuit electric current.
In present embodiment, it is contemplated that in Power System Shortcuts electric current engineering calculation, AC network is most important
Be calculate short circuit current fundamental component initial value size utilize section for this purpose, can indicate node voltage and electric current with its modulus value
Point impedance matrix indicates AC network nodal voltage equation:
Wherein, UADFor the node voltage of AC network mixed connection node, UACFor the node voltage of other nodes of AC network；
IADInjection Current from AC/DC inverter to AC network mixed connection node, I forACFor AC/DC inverter, to AC network, other are saved
The Injection Current of point；ZAD、ZACThe respectively nodal impedance matrix of AC network mixed connection node, AC network other nodes；ZAm1、
ZAm2The respectively mutual resistance matrix of AC network mixed connection node and other nodes of AC network, and the two transposed matrix each other.
In present embodiment, DC grid nodal voltage equation is indicated using node-resistance matrix:
Wherein, UDAFor the node voltage of DC grid mixed connection node, UDCFor the node voltage of other nodes of DC grid；
IDAIt is AC/DC inverter to the Injection Current of DC grid mixed connection node, IDCFor AC/DC inverter, to DC grid, other are saved
The Injection Current of point；RDA、RDCThe respectively node-resistance matrix of DC grid mixed connection node, DC grid other nodes；RDm1、
RDm2The respectively mutual resistance matrix of DC grid mixed connection node and other nodes of DC grid, and the two transposed matrix each other.
In present embodiment, the port transient equation of transfer of AC/DC inverter are as follows:
Wherein, TDAFor the port transient transfer matrix of AC/DC inverter,
T11For the transfer matrix between the voltage of AC/DC inverter alternating current-direct current side, T22For AC/DC inverter alternating current-direct current side electricity
Transfer matrix between stream, T12For the transfer matrix between AC/DC inverter alternating current and DC voltage, T21Respectively AC/
Transfer matrix between DC inverter alternating voltage and DC current.
In present embodiment, AC-DC hybrid power grid nodal voltage equation is to be derived as follows:
By the transient equation of transfer of formula (3) mixed connection node, the AC network and DC grid section of formula (1) and (2) are substituted into
Point voltage equation.The voltage and current vector of DC side mixed connection node is eliminated, then the combination of AC and DC voltage vector can be obtained formula
(4):
The voltage for exchanging side mixed connection node, current vector combination can be obtained into formula (5):
It is by the voltage and current that formula (5) calculate exchange side mixed connection node,
Wherein, CADFor with AC network nodal impedance matrix Z, DC grid node-resistance matrix R and the alternating current-direct current change of current
Device port transient transfer matrix TDARelated constant；
Formula (6) are substituted into formula (4), can must eliminate the alternating current-direct current power grid nodal voltage equation of alternating current-direct current mixed connection node are as follows:
It is obtained by formula (7), the AC-DC hybrid power grid node voltage side in present embodiment, after eliminating mixed connection node
Journey are as follows:
Wherein, ZAC+ΔZACFor the nodal impedance matrix of AC network after cancellation mixed connection node, RDC+ΔZDCTo eliminate mixed connection
The nodal impedance matrix of DC grid after node；ΔZADTo eliminate the alternating current-direct current mixed connection mutual resistance matrix after mixed connection node, indicate
Influence of the DC grid short circuit current to AC network；ΔZDATo eliminate the alternating current-direct current mixed connection mutual resistance matrix after mixed connection node,
Indicate influence of the AC network short circuit current to DC grid.
In present embodiment, when symmetrical short-circuit failure occurs in AC network, if short dot is fA, then alternating current
There was only short dot f in netAThere is Injection Current-IfA, short dot f is calculated as followsAShort circuit current IfA:
Step 101: AC-DC hybrid power grid being resolved into normal operation and fault component using accident analysis principle of stacking
Network, to form the nodal voltage equation of AC-DC hybrid power grid fault component network:
Step 102: the event of short dot voltage is obtained according to the nodal voltage equation of AC-DC hybrid power grid fault component network
Hinder component Δ UfAAre as follows: Δ UfA=-IfAZfAfA；Wherein, ZfAfAFor short dot self-impedance；
Step 103: by the Δ U in step 102fA=-IfAZfAfAIt rewrites are as follows:
ΔUfA=-UfA|0|+IfAzfA；
Wherein, UfA|0|For short dot open-circuit voltage, zfAFor short dot impedance ground；
Step 104: it is obtained according to formula revised in step 103:
Step 105: enabling UfA|0|=1, zfA=0, to obtain AC network short dot fAShort circuit current IfAAre as follows:
In present embodiment, when symmetrical short-circuit failure occurs in DC grid, if short dot is fD, then direct current
There was only short dot f in netDThere is Injection Current-IfD, short dot f is calculated as followsDShort circuit current IfD:
Step 201: AC-DC hybrid power grid being resolved into normal operation and fault component using accident analysis principle of stacking
Network, to form the nodal voltage equation of AC-DC hybrid power grid fault component network:
Step 202: the event of short dot voltage is obtained according to the nodal voltage equation of AC-DC hybrid power grid fault component network
Hinder component Δ UfDAre as follows: Δ UfD=-IfDZfDfD；Wherein, ZfDfDFor short dot self-impedance；
Step 203: by the Δ U in step 202fD=-IfDZfDfDIt rewrites are as follows:
ΔUfD=-UfD|0|+IfDrfD；
Wherein, UfD|0|For short dot open-circuit voltage, rfDFor short dot ground resistance；
Step 204: it is obtained according to formula revised in step 203:
Step 205: enabling UfD|0|=1, rfD=0, to obtain DC grid short dot fDShort circuit current IfDAre as follows:
A kind of electric network protection method, the power grid is AC-DC hybrid power grid, using AC-DC hybrid power grid of the invention
Symmetrical short-circuit current calculation method calculates the symmetrical short-circuit electric current of AC-DC hybrid power grid, then calculated symmetrical according to institute
Short circuit current formulates electric network protection scheme.
The present invention, which solves conventional AC grid short circuit calculation method in the prior art, can not be suitable for alternating current-direct current mixed connection electricity
The technical issues of net, can calculate the symmetrical short-circuit electric current of serial-parallel power grid for the short trouble feature of AC-DC hybrid power grid,
It can accurately and efficiently realize that AC-DC hybrid power grid symmetrical short-circuit electric current calculates, be AC-DC hybrid power grid protection scheme
Formulation provides theoretical foundation, is of great significance to the safe and stable operation for guaranteeing power grid.
Claims (8)
1. a kind of AC-DC hybrid power grid symmetrical short-circuit current calculation method, the AC-DC hybrid power grid utilizes the AC/DC change of current
The mixed connection of device progress AC network and DC grid, which comprises the following steps:
Step 1: dividing AC-DC hybrid power grid node: whether being mixed connection node according to AC-DC hybrid power grid node, will exchange
The node division of power grid is AC network mixed connection node collection AD and other nodes of AC network collection AC, and the node of DC grid is drawn
It is divided into DC grid mixed connection node collection DA and other node collection of DC grid DC；
Step 2: according to the equivalent network for calculation of short-circuit current of AC-DC hybrid power grid, establishing AC network node respectively
Voltage equation and DC grid nodal voltage equation；
Step 3: the port transient using reflection exchange side and the AC/DC inverter of DC side transient state electrical quantity mapping relations turns
Move equation, eliminate AC network nodal voltage equation and AC network mixed connection node in DC grid nodal voltage equation and
DC grid mixed connection node, to obtain AC-DC hybrid power grid nodal voltage equation；
Step 4: calculating alternating current-direct current mixed connection using accident analysis principle of stacking and using AC-DC hybrid power grid nodal voltage equation
The symmetrical short-circuit electric current of power grid, the symmetrical short-circuit electric current of the AC-DC hybrid power grid include the symmetrical short of AC network short dot
The symmetrical short-circuit electric current of road electric current and DC grid short dot.
2. AC-DC hybrid power grid symmetrical short-circuit current calculation method according to claim 1, it is characterised in that: utilize section
Point impedance matrix indicates AC network nodal voltage equation:
Wherein, UADFor the node voltage of AC network mixed connection node, UACFor the node voltage of other nodes of AC network；IADFor
Injection Current, I of the AC/DC inverter to AC network mixed connection nodeACIt is AC/DC inverter to the note of other nodes of AC network
Enter electric current；ZAD、ZACThe respectively nodal impedance matrix of AC network mixed connection node, AC network other nodes；ZAm1、ZAm2Point
Not Wei AC network mixed connection node and other nodes of AC network mutual resistance matrix, and the two transposed matrix each other.
3. AC-DC hybrid power grid symmetrical short-circuit current calculation method according to claim 2, it is characterised in that: utilize section
Resistor matrix is put to indicate DC grid nodal voltage equation:
Wherein, UDAFor the node voltage of DC grid mixed connection node, UDCFor the node voltage of other nodes of DC grid；IDAFor
Injection Current of the AC/DC inverter to DC grid mixed connection node, IDCIt is AC/DC inverter to the note of other nodes of DC grid
Enter electric current；RDA、RDCThe respectively node-resistance matrix of DC grid mixed connection node, DC grid other nodes；RDm1、RDm2Point
Not Wei DC grid mixed connection node and other nodes of DC grid mutual resistance matrix, and the two transposed matrix each other.
4. AC-DC hybrid power grid symmetrical short-circuit current calculation method according to claim 3, it is characterised in that: AC/DC
The port transient equation of transfer of inverter are as follows:
Wherein, TDAFor the port transient transfer matrix of AC/DC inverter,
T11For the transfer matrix between the voltage of AC/DC inverter alternating current-direct current side, T22Between the electric current of AC/DC inverter alternating current-direct current side
Transfer matrix, T12For the transfer matrix between AC/DC inverter alternating current and DC voltage, T21The respectively AC/DC change of current
Transfer matrix between device alternating voltage and DC current.
5. AC-DC hybrid power grid symmetrical short-circuit current calculation method according to claim 4, it is characterised in that: eliminate mixed
AC-DC hybrid power grid nodal voltage equation after interlink point are as follows:
Wherein, ZAC+ΔZACFor the nodal impedance matrix of AC network after cancellation mixed connection node, RDC+ΔZDCTo eliminate mixed connection node
The nodal impedance matrix of DC grid afterwards；ΔZADTo eliminate the alternating current-direct current mixed connection mutual resistance matrix after mixed connection node, direct current is indicated
Influence of the grid short circuit electric current to AC network；ΔZDATo eliminate the alternating current-direct current mixed connection mutual resistance matrix after mixed connection node, indicate
Influence of the AC network short circuit current to DC grid.
6. AC-DC hybrid power grid symmetrical short-circuit current calculation method according to claim 4, it is characterised in that: work as exchange
When symmetrical short-circuit failure occurring in power grid, if short dot is fA, then there was only short dot f in AC networkAThere is Injection Current-IfA,
Short dot f is calculated as followsAShort circuit current IfA:
Step 101: AC-DC hybrid power grid is resolved into normal operation and fault component network using accident analysis principle of stacking,
To form the nodal voltage equation of AC-DC hybrid power grid fault component network:
Step 102: short dot voltage failure point is obtained according to the nodal voltage equation of AC-DC hybrid power grid fault component network
Measure Δ UfAAre as follows: Δ UfA=-IfAZfAfA；Wherein, ZfAfAFor short dot self-impedance；
Step 103: by the Δ U in step 102fA=-IfAZfAfAIt rewrites are as follows:
ΔUfA=-UfA|0|+IfAzfA；
Wherein, UfA|0|For short dot open-circuit voltage, zfAFor short dot impedance ground；
Step 104: it is obtained according to formula revised in step 103:
Step 105: enabling UfA|0|=1, zfA=0, to obtain AC network short dot fAShort circuit current IfAAre as follows:
7. AC-DC hybrid power grid symmetrical short-circuit current calculation method according to claim 4, it is characterised in that: work as direct current
When symmetrical short-circuit failure occurring in power grid, if short dot is fD, then there was only short dot f in DC gridDThere is Injection Current-IfD,
Short dot f is calculated as followsDShort circuit current IfD:
Step 201: AC-DC hybrid power grid is resolved into normal operation and fault component network using accident analysis principle of stacking,
To form the nodal voltage equation of AC-DC hybrid power grid fault component network:
Step 202: short dot voltage failure point is obtained according to the nodal voltage equation of AC-DC hybrid power grid fault component network
Measure Δ UfDAre as follows: Δ UfD=-IfDZfDfD；Wherein, ZfDfDFor short dot self-impedance；
Step 203: by the Δ U in step 202fD=-IfDZfDfDIt rewrites are as follows:
ΔUfD=-UfD|0|+IfDrfD；
Wherein, UfD|0|For short dot open-circuit voltage, rfDFor short dot ground resistance；
Step 204: it is obtained according to formula revised in step 203:
Step 205: enabling UfD|0|=1, rfD=0, to obtain DC grid short dot fDShort circuit current IfDAre as follows:
8. a kind of electric network protection method, the power grid is AC-DC hybrid power grid, it is characterised in that: using in claim 1 to 7
Any AC-DC hybrid power grid symmetrical short-circuit current calculation method calculates the symmetrical short-circuit electricity of AC-DC hybrid power grid
Then stream formulates electric network protection scheme according to the calculated symmetrical short-circuit electric current of institute.
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