CN103928919A - Calculation curved surface method for determining short circuit current when distribution type generators are connected to power grid - Google Patents

Abstract

The invention discloses a calculation curved surface method for determining short circuit current when distribution type generators are connected to a power grid. When multiple common generators and the distribution type generators are connected to the power grid, transfer impedance between all power source nodes and fault points and transfer impedance between a common power source and distribution type generator connecting points are calculated. Mutual influence between the distribution type generators is not considered, the common power source nodes are combined, and transfer impedance between a three-node simplified network and different nodes in a triangular network is obtained. In order to reduce associated variables of short circuit current of the common power source and the distribution type generators, Thevenin equivalence is carried out on the system besides the distribution type generator connecting points, a calculation curved surface of the periodic component of the short circuit current of the distribution type generators, calculation impedance and open-circuit voltage is made, the calculation curved surface method for determining the short circuit current when the distribution type generators are connected to the power grid is formed, the calculation curved surface of the short circuit current is searched according to time, the calculation impedance and the open-circuit voltage, and the periodic component of the short circuit current injected into the fault points of the distribution type generators is obtained.

Description

A kind of computing Surface Method of definite distributed power generation access grid short circuit electric current

Technical field

The present invention relates to distributed generation system technical field, relate in particular to a kind of computing Surface Method of definite distributed power generation access grid short circuit electric current.

Background technology

Distributed power source (Distributed Generation, DG) access makes the structure of traditional power distribution network that change occur, the impact that DG brings traditional power distribution network has positive also has passively, and its access mainly concentrates on and to the improvement of the operational mode of system and to its connecting system, provides support to guarantee the aspects such as high efficient and reliable operation the positive impact bringing of power distribution network:

1) access of DG has increased the reserve capacity of electrical network, has the function of peak clipping, balanced load, and DG can improve energy utilization rate simultaneously.

2) DG is very low near load power supply power transmission and distribution loss, the loss of electric energy in transmitting procedure seldom, thereby can save cost of investment.

3) because DG can realize on-load islet operation, when meeting accident disaster, can be continuously sub-load power supply, in the raising that realizes power supply reliability, prevent the generation of great Voltage Instability accident.

When bringing benefit to the operation of power distribution network, the access of DG also brought a series of operation problems that can not be ignored:

1) impact on the electrical network quality of power supply, owing to thering is uncertain and intermittent feature, distributed power source generates electricity by way of merging two or more grid systems to exert oneself and will bring to the power distribution network of its access the problem of quality of power supply aspect, the access of DG is by the unidirectional mode by each load of the substation bus bar flow direction of the trend that changes power distribution network, when power distribution network normally moves, the size of trend and direction all will change, simultaneously the feeder line steady state voltage of power distribution network will be affected, and this makes the initial pressure regulation scheme of system not necessarily can meet the requirement to voltage of power distribution network after DG accesses; Have distributed power source greatly to adopt electric device grid-connected, this will bring such as power quality problems such as electric current and voltage harmonic waves system simultaneously.

2) access DG in power distribution network after, the original radial network structure of distribution spreads all over power supply and the interconnected network of user by becoming, and DG will be by providing short circuit current to produce significantly impact to the original relaying protection of distribution when the fault.The fault that the mode that power distribution network generally adopts reclosing preacceleration protection to move is excised instantaneity is fast to realize the raising of power supply reliability; when the power distribution network that contains DG breaks down; if the DG in system is not out of service; can continue provides electric current to fault point; cause unsuccessful reclosing, even can expand fault coverage.

As can be seen here; calculation of short-circuit current is the basis of Electric Power Network Planning and protection, utilizes distributed power generation short circuit calculation model and network equation interactive iteration, can obtain short circuit calculation result accurately; but both coupling variables are many and iterative computation amount is large, can not meet engineering calculation requirement.At present to the pertinent literature of studying containing the power distribution network calculation of short-circuit current of distributed power source few, the short-circuit current calculation method using both at home and abroad mainly comprises Practical algorithm, IEC standard and ansi standard, abroad to the research of short circuit calculation standard more be the difference of comparison IEC standard and ansi standard, domestic analysis mainly concentrates on the difference comparison to practical algorithm and IEC canonical algorithm.

In the Practical algorithm of domestic employing, existing computing curved needle is formulated synchronous generator, calculating for asynchronous motor short circuit current initial value in practical algorithm adopts time mode of transient potential series connection subtranient reactance, does not all formulate special computing curve.

Summary of the invention

For above shortcomings in prior art, the invention provides a kind of computing Surface Method of definite distributed power generation access grid short circuit electric current, the method only needs to obtain DFIG access point calculating reactance and open circuit voltage in addition, Method And Principle is simple and amount of calculation is little, be applicable to short circuit current engineering calculation, for unsymmetrical short-circuit electric current, also can utilize positive sequence equivalent rule further to calculate.

In order to solve the problems of the technologies described above, the present invention has adopted following technical scheme:

A computing Surface Method for definite distributed power generation access grid short circuit electric current, comprises the steps:

Step 1: while having many conventional generators and distributed generator simultaneously to access electrical network, by the nodal impedance matrix of fault component network, can calculate the transfger impedance between all power supply nodes and fault point, normal power supplies and distributed generator access point;

Step 2: while not considering influencing each other between distributed generator, for ease of calculating separate unit distributed generator short circuit current, merge normal power supplies node, obtain different internodal transfger impedances in 3 node simplified networks and triangular net;

Step 3: the voltage support effect of analytic routines power supply to distributed generator, for reducing the short circuit current associated variable of normal power supplies and distributed generator, the system beyond distributed generator access point is carried out to Dai Weinan equivalence;

Step 4: utilize Dai Weinan equivalent circuit, formulate the computing curved surface of distributed generator periodic component of short-circuit current and computing impedance, open circuit voltage, form the short circuit current computing Surface Method of distributed generator access electrical network, by the moment, computing impedance and open circuit voltage, look into short circuit current computing curved surface again, can obtain the periodic component of short-circuit current that distributed generator injects fault point;

Step 5: provided distributed generator short circuit computing Surface Method calculation procedure.

As a preferred embodiment of the present invention, the concrete steps of described step 1 are:

If m ₁platform conventional generator and m ₂platform distributed generator is arranged on different nodes in electrical network, the grid nodes f fault that is short-circuited, and node 1 is to m ₁for conventional generator access point, node m ₁+ 1 to m ₁+ m ₂for distributed generator access point; By the nodal impedance matrix of fault component network, can calculate the transfger impedance z ' between all power supply nodes and fault point, normal power supplies and distributed generator access point _ijfor:

$z_{\mathrm{ij}}^{\′}=\frac{Z_{\mathrm{jj}}}{Z_{\mathrm{ij}}}{z}_i---\left(1\right)$

In formula: j is malfunctioning node or distributed generator access point, Z _jjand Z _ijfor self-impedance and the mutual impedance of fault component network nodal impedance matrix, z _ifor the equivalent impedance of power supply to access point i.

As another kind of preferred version of the present invention, the concrete steps of described step 2 are:

Do not consider influencing each other between distributed generator, can obtain the transfger impedance network of k platform distributed generator and fault point, normal power supplies point; For ease of calculating k platform distributed generator short circuit current, merge normal power supplies node 1 to m ₁, obtain 3 node simplified networks; Impedance Z _kf=z ' _kf, all the other impedances are:

$Z_{\mathrm{sf}}=\frac{1}{\underset{i=1}{\overset{m_1}{\mathrm{\Σ}}}1/z_{\mathrm{if}}^{\′}},Z_{\mathrm{sk}}=\frac{1}{\underset{i=1}{\overset{m_1}{\mathrm{\Σ}}}1/z_{\mathrm{ik}}^{\′}}---\left(2\right)$

Z wherein _sk, Z _sfand Z _kffor different internodal transfger impedances in triangular net.

As another preferred version of the present invention, the concrete steps of described step 3 are:

For distributed generator, not only via transfger impedance Z _kfbe connected with fault point, also pass through Z _skbe connected with normal power supplies, after fault, normal power supplies will play voltage support effect to distributed generator, and after fault, the variation of distributed power generation set end voltage will change the short circuit current of its injection; By the system beyond distributed generator access node k, carry out Dai Weinan equivalence, Z _jsand U _ocfor computing impedance and open circuit voltage.

As a modification of the present invention scheme, the concrete steps of described step 3 are:

After node f breaks down:

$\left\{\begin{array}{c}{Z}_{\mathrm{js}}==\frac{Z_{\mathrm{sk}}{Z}_{\mathrm{kf}}}{Z_{\mathrm{sk}}+Z_{\mathrm{kf}}}\\ {\stackrel{\·}{U}}_{\mathrm{oc}}=\frac{Z_{\mathrm{kf}}}{Z_{\mathrm{sk}}+Z_{\mathrm{kf}}}{E}_s\end{array}\right.---\left(3\right)$

By the Z in formula (2) _sk, Z _sfand Z _kfsubstitution formula (3), can obtain the computing impedance Z of distributed generator access point k after node f fault _jswith open circuit voltage U _oc; Again by the moment t, Z _jsand U _oc, look into short circuit current computing curved surface, can obtain the periodic component of short-circuit current that distributed generator injects fault point.

As another kind of preferred version of the present invention, the concrete steps of described step 3 are:

The step of application short circuit current computing curved surface Computation distribution formula generator short circuit electric current is as follows:

1) form primitive network nodal impedance matrix, append m ₁platform conventional generator is to the impedance z of access point _i, obtain n * n rank nodal impedance matrix Z of fault component network, wherein node 1 is to m ₁for normal power supplies point, node m ₁+ 1 to m ₁+ m ₂for distributed generator access point;

2) according to formula (1), calculate m ₁individual normal power supplies is put to the transfger impedance z ' of short circuit node f _if, make k=1, enter 3);

3) by Z, z _iand formula (1) is calculated m ₁individual normal power supplies o'clock is to the transfger impedance z ' of k platform distributed generator access point _ik, and k platform distributed generator is to the transfger impedance z ' of fault point _kf;

4) by m ₁individual normal power supplies point merges, and is obtained the three-terminal network transfger impedance Z of k platform distributed generator by formula (2) _sk, Z _sfand Z _kf, then substitution formula (3) can obtain the computing impedance Z of k platform distributed generator access point _jswith open circuit voltage U _oc;

5) press fault moment t, Z _jsand U _oclook into k platform distributed generator short circuit current computing curved surface, obtain the periodic component of short-circuit current perunit value that k platform distributed generator injects fault point, and calculate the famous value of short circuit current by basic parameter;

6) if k<m ₂, after k=k+1, forward step 3 to); Otherwise short circuit calculation finishes, output m ₂the short circuit calculation result of platform distributed generator.

Advantage of the present invention: the present invention utilizes Dai Weinan equivalent circuit, formulates distributed generator periodic component of short-circuit current and computing impedance Z _js, open circuit voltage U _occomputing curved surface, then by constantly t, Z _jsand U _oclook into short circuit current computing curved surface, can obtain the periodic component of short-circuit current that distributed generator injects fault point, the method principle is simple and amount of calculation is little, be applicable to short circuit current engineering calculation, for unsymmetrical short-circuit electric current, also can utilize positive sequence equivalent rule further to calculate.

Accompanying drawing explanation

Fig. 1 is the primitive network schematic diagram of distributed generator short circuit current computing Surface Method;

Fig. 2 is the transfger impedance network diagram of distributed generator short circuit current computing Surface Method;

Fig. 3 is the triangle simplified network schematic diagram of distributed generator short circuit current computing Surface Method;

Fig. 4 is the Dai Weinan equivalent circuit schematic diagram of distributed generator short circuit current computing Surface Method.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in further detail.

A kind of computing Surface Method of definite distributed power generation access grid short circuit electric current, in complicated electric power system, retain conventional generator, distributed generator point and fault point, through network abbreviation, can be able to the duplicate supply network centered by short dot, star network is further simplified to triangular net, also can obtain the Radiation network of Fig. 3, wherein Z _sk, Z _sfand Z _kffor different internodal transfger impedances in triangular net.For conventional generator, utilize the not computing curve of power supply short circuit electric current and transfger impedance in the same time pre-establish, then system simplification become to Radiation network, just can by not in the same time with the transfger impedance Z of power supply to fault point _sf, look into the short circuit current that computing curve obtains normal power supplies.

For the distributed generator in Fig. 3, not only via transfger impedance Z _kfbe connected with fault point, also pass through Z _skbe connected with normal power supplies, after fault, normal power supplies will play voltage support effect to distributed generator, and after fault, the variation of distributed power generation set end voltage will change the short circuit current of its injection.By the system beyond distributed generator access node k, carry out Dai Weinan equivalence, as shown in Figure 4, Z wherein _jsand U _ocfor computing impedance and open circuit voltage.After node f breaks down, by Fig. 1 to Fig. 4, can be obtained:

$\left\{\begin{array}{c}{Z}_{\mathrm{js}}==\frac{Z_{\mathrm{sk}}{Z}_{\mathrm{kf}}}{Z_{\mathrm{sk}}+Z_{\mathrm{kf}}}\\ {\stackrel{\&CenterDot;}{U}}_{\mathrm{oc}}=\frac{Z_{\mathrm{kf}}}{Z_{\mathrm{sk}}+Z_{\mathrm{kf}}}{E}_s\end{array}\right.---\left(1\right)$

Transfger impedance Z between power supply _skwhen very large, corresponding to the open circuit voltage U of Fig. 4 equivalent circuit _occlose to 0, now can ignore the coupled relation of distributed generator and normal power supplies, only utilize distributed generator short circuit current and it is to fault point transfger impedance Z _kfcomputing curve, can calculate not the short circuit current of unit in the same time.But the coupling of normal power supplies and distributed generator strong (Z often in actual electric network _skless), the open circuit voltage U of Dai Weinan equivalence after fault _ocbe not 0, and along with Z _skreduce to move closer to E _s.Therefore,, when distributed generator short circuit current is carried out to engineering calculation, can, by the expansion of short circuit current calculation curve method, obtain in advance shifting impedance Z in its short circuit current and Fig. 3 _kf, Z _skwith normal power supplies electromotive force E _srelation.For reducing the associated variable of distributed generator short circuit current, adopt Fig. 4 Dai Weinan equivalent circuit, formulate distributed generator periodic component of short-circuit current and computing impedance Z _js, open circuit voltage U _occomputing curved surface, form the short circuit current computing Surface Method of distributed generator access electrical network.

If m ₁platform conventional generator and m ₂platform distributed generator is arranged on different nodes in electrical network, the grid nodes f fault that is short-circuited, as shown in Figure 1.Node 1 is to m ₁for conventional generator access point, node m ₁+ 1 to m ₁+ m ₂for distributed generator access point, in Fig. 2, only give egress k access distributed generator.By the nodal impedance matrix of fault component network, can calculate the transfger impedance z ' between all power supply nodes and fault point, normal power supplies and distributed generator access point _ijfor:

$z_{\mathrm{ij}}^{\&prime;}=\frac{Z_{\mathrm{jj}}}{Z_{\mathrm{ij}}}{z}_i---\left(2\right)$

In formula: j is malfunctioning node or distributed generator access point, Z _jjand Z _ijfor self-impedance and the mutual impedance of the corresponding fault component network of Fig. 1 nodal impedance matrix, z _ifor the equivalent impedance of power supply to access point i.

When not considering influencing each other between distributed generator, can obtain the transfger impedance network of the k platform distributed generator shown in Fig. 2 and fault point, normal power supplies point.For ease of calculating k platform distributed generator short circuit current, merge normal power supplies node 1 to m ₁, obtain the 3 node simplified networks of Fig. 3.The impedance Z in Fig. 3 _kf=z ' _kf, all the other impedances are:

$Z_{\mathrm{sf}}=\frac{1}{\underset{i=1}{\overset{m_1}{\mathrm{\&Sigma;}}}1/z_{\mathrm{if}}^{\&prime;}},Z_{\mathrm{sk}}=\frac{1}{\underset{i=1}{\overset{m_1}{\mathrm{\&Sigma;}}}1/z_{\mathrm{ik}}^{\&prime;}}---\left(3\right)$

By Z _sk, Z _sfand Z _kfsubstitution formula (1), can obtain the computing impedance Z of distributed generator access point k after node f fault _jswith open circuit voltage U _oc.Again by the moment t, Z _jsand U _oc, look into short circuit current computing curved surface, obtain injecting the periodic component of short-circuit current of fault point.

Grid nodes f breaks down, and the step of application short circuit current computing curved surface Computation distribution formula generator short circuit electric current is as follows:

1) form primitive network nodal impedance matrix, append m ₁platform conventional generator is to the impedance z of access point _i, obtain n * n rank nodal impedance matrix Z of fault component network, wherein node 1 is to m ₁for normal power supplies point, node m ₁+ 1 to m ₁+ m ₂for distributed generator access point.

2) according to formula (2), calculate m ₁individual normal power supplies is put to the transfger impedance z ' of short circuit node f _if, make k=1, enter 3).

3) by Z, z _iand formula (2) is calculated m ₁individual normal power supplies o'clock is to the transfger impedance z ' of k platform distributed generator access point _ik, and k platform distributed generator is to the transfger impedance z ' of fault point _kf.

4) by m ₁individual normal power supplies point merges, and is obtained the three-terminal network transfger impedance Z of k platform distributed generator by formula (3) _sk, Z _sfand Z _kf, then substitution formula (1) can obtain the computing impedance Z of k platform distributed generator access point _jswith open circuit voltage U _oc.

5) press fault moment t, Z _jsand U _oclook into k platform distributed generator short circuit current computing curved surface, obtain the periodic component of short-circuit current perunit value that k platform distributed generator injects fault point, and calculate the famous value of short circuit current by basic parameter.

6) if k<m ₂, after k=k+1, forward step 3 to); Otherwise short circuit calculation finishes, output m ₂the short circuit calculation result of platform distributed generator.

Finally explanation is, above embodiment is only unrestricted in order to technical scheme of the present invention to be described, although the present invention is had been described in detail with reference to preferred embodiment, those of ordinary skill in the art is to be understood that, can modify or be equal to replacement technical scheme of the present invention, and not departing from aim and the scope of technical solution of the present invention, it all should be encompassed in the middle of claim scope of the present invention.

Claims (6)

1. a computing Surface Method for definite distributed power generation access grid short circuit electric current, is characterized in that, comprises the steps:

Step 1: while having many conventional generators and distributed generator simultaneously to access electrical network, by the nodal impedance matrix of fault component network, can calculate the transfger impedance between all power supply nodes and fault point, normal power supplies and distributed generator access point;

Step 2: while not considering influencing each other between distributed generator, for ease of calculating separate unit distributed generator short circuit current, merge normal power supplies node, obtain different internodal transfger impedances in 3 node simplified networks and triangular net;

Step 3: the voltage support effect of analytic routines power supply to distributed generator, for reducing the short circuit current associated variable of normal power supplies and distributed generator, the system beyond distributed generator access point is carried out to Dai Weinan equivalence;

Step 4: utilize Dai Weinan equivalent circuit, formulate the computing curved surface of distributed generator periodic component of short-circuit current and computing impedance, open circuit voltage, form the short circuit current computing Surface Method of distributed generator access electrical network, by the moment, computing impedance and open circuit voltage, look into short circuit current computing curved surface again, can obtain the periodic component of short-circuit current that distributed generator injects fault point;

Step 5: provided distributed generator short circuit computing Surface Method calculation procedure.

2. the computing Surface Method of a kind of definite distributed power generation access grid short circuit electric current according to claim 1, is characterized in that, the concrete steps of described step 1 are:

If m ₁platform conventional generator and m ₂platform distributed generator is arranged on different nodes in electrical network, the grid nodes f fault that is short-circuited, and node 1 is to m ₁for conventional generator access point, node m ₁+ 1 to m ₁+ m ₂for distributed generator access point; By the nodal impedance matrix of fault component network, can calculate the transfger impedance z ' between all power supply nodes and fault point, normal power supplies and distributed generator access point _ijfor:

$z_{\mathrm{ij}}^{\&prime;}=\frac{Z_{\mathrm{jj}}}{Z_{\mathrm{ij}}}{z}_i---\left(1\right)$

In formula: j is malfunctioning node or distributed generator access point, Z _jjand Z _ijfor self-impedance and the mutual impedance of fault component network nodal impedance matrix, z _ifor the equivalent impedance of power supply to access point i.

3. the computing Surface Method of a kind of definite distributed power generation access grid short circuit electric current according to claim 2, is characterized in that, the concrete steps of described step 2 are:

Do not consider influencing each other between distributed generator, can obtain the transfger impedance network of k platform distributed generator and fault point, normal power supplies point; For ease of calculating k platform distributed generator short circuit current, merge normal power supplies node 1 to m ₁, obtain 3 node simplified networks; Impedance Z _kf=z ' _kf, all the other impedances are:

$Z_{\mathrm{sf}}=\frac{1}{\underset{i=1}{\overset{m_1}{\mathrm{\&Sigma;}}}1/z_{\mathrm{if}}^{\&prime;}},Z_{\mathrm{sk}}=\frac{1}{\underset{i=1}{\overset{m_1}{\mathrm{\&Sigma;}}}1/z_{\mathrm{ik}}^{\&prime;}}---\left(2\right)$

Z wherein _sk, Z _sfand Z _kffor different internodal transfger impedances in triangular net.

4. the computing Surface Method of a kind of definite distributed power generation access grid short circuit electric current according to claim 3, is characterized in that, the concrete steps of described step 3 are:

For distributed generator, not only via transfger impedance Z _kfbe connected with fault point, also pass through Z _skbe connected with normal power supplies, after fault, normal power supplies will play voltage support effect to distributed generator, and after fault, the variation of distributed power generation set end voltage will change the short circuit current of its injection; By the system beyond distributed generator access node k, carry out Dai Weinan equivalence, Z _jsand U _ocfor computing impedance and open circuit voltage.

5. the computing Surface Method of a kind of definite distributed power generation access grid short circuit electric current according to claim 4, is characterized in that, the concrete steps of described step 3 are:

After node f breaks down:

$\left\{\begin{array}{c}{Z}_{\mathrm{js}}==\frac{Z_{\mathrm{sk}}{Z}_{\mathrm{kf}}}{Z_{\mathrm{sk}}+Z_{\mathrm{kf}}}\\ {\stackrel{\&CenterDot;}{U}}_{\mathrm{oc}}=\frac{Z_{\mathrm{kf}}}{Z_{\mathrm{sk}}+Z_{\mathrm{kf}}}{E}_s\end{array}\right.---\left(3\right)$

By the Z in formula (2) _sk, Z _sfand Z _kfsubstitution formula (3), can obtain the computing impedance Z of distributed generator access point k after node f fault _jswith open circuit voltage U _oc; Again by the moment t, Z _jsand U _oc, look into short circuit current computing curved surface, can obtain the periodic component of short-circuit current that distributed generator injects fault point.

6. the computing Surface Method of a kind of definite distributed power generation access grid short circuit electric current according to claim 5, is characterized in that, the concrete steps of described step 3 are:

The step of application short circuit current computing curved surface Computation distribution formula generator short circuit electric current is as follows:

1) form primitive network nodal impedance matrix, append m ₁platform conventional generator is to the impedance z of access point _i, obtain n * n rank nodal impedance matrix Z of fault component network, wherein node 1 is to m ₁for normal power supplies point, node m ₁+ 1 to m ₁+ m ₂for distributed generator access point;

2) according to formula (1), calculate m ₁individual normal power supplies is put to the transfger impedance z ' of short circuit node f _if, make k=1, enter 3);

3) by Z, z _iand formula (1) is calculated m ₁individual normal power supplies o'clock is to the transfger impedance z ' of k platform distributed generator access point _ik, and k platform distributed generator is to the transfger impedance z ' of fault point _kf;

4) by m ₁individual normal power supplies point merges, and is obtained the three-terminal network transfger impedance Z of k platform distributed generator by formula (2) _sk, Z _sfand Z _kf, then substitution formula (3) can obtain the computing impedance Z of k platform distributed generator access point _jswith open circuit voltage U _oc;

5) press fault moment t, Z _jsand U _oclook into k platform distributed generator short circuit current computing curved surface, obtain the periodic component of short-circuit current perunit value that k platform distributed generator injects fault point, and calculate the famous value of short circuit current by basic parameter;

6) if k<m ₂, after k=k+1, forward step 3 to); Otherwise short circuit calculation finishes, output m ₂the short circuit calculation result of platform distributed generator.