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This paper presents an auxiliary planning method for intelligent substation access system based on security region. Firstly, the method of resolving the static voltage security region is proposed. Secondly, the method of constructing the optimal index of substation accession is given, which is used to describe the priority of the node into the substation. Finally, a complete set of intelligent substation access system auxiliary planning strategy is given, which takes into account the constraints of the normal operation of the grid on the voltage amplitude.

Intelligent substation as the physical basis of smart grid, will go through the smart grid construction process [

In paper [

In this paper, we use the security region method, which can give the relative position of the current operating point in the domain to characterize the security and stability margin of the whole system [

The mathematical description of the static security region is as follows: For a given network topology, the static security region is a set of all system operating points in the decision space that satisfy the power flow equation

Assuming that the system has n − 1 nodes and nb branches, where node 0 is the equilibrium node, there are g + 1 generator nodes; G is used to denote the set of generator nodes except the equilibrium node; L is the load node A set of all branches.

According to the node power injection equation:

Using the method in paper [

In the formula,

The decision space of the static voltage safety domain defined in this paper includes the active power injection of the node and the reactive power injection of the load node, and increases the voltage amplitude of the generator node.

In general, the power system operates in a small neighborhood of the point (V = 1, θ = 0), and the mapping from the V − θ space to the P − Q space is mapped one by one. Therefore, in the V − θ space, the inverse mapping of the Equation (2) exists in a neighborhood of the run point (V = 1, θ = 0).

Assume that the system has

In the formula, Where the PV node and the PQ node are separated. A, B, C, D, E, F, G, H and I are the block matrix, the order is

According to the Equation (4):

From the Equation (5), Equation (6) can be obtained:

The above equation can be organized as:

Thus, the static security region of the upper limit of the load node voltage can be defined as:

Similarly, the static safety region of the lower limit of the load node voltage can be defined as:

The static voltage safety region of the whole system is the intersection of the static voltage safety region where the upper and lower limits of the voltage of all nodes are satisfied.

This paper uses the stability margin of the security region to quantify the system security level, to find the node that is closest to the security region boundary under the current operating conditions. This paper presents the optimized index of substation access (OISA), and describes the auxiliary planning strategy of substation access system in detail.

The calculation equation for the stability margin of the load node j is as follows:

The equation of the stability margin of the system (SRM):

According to the optimized index of substation access (OISA), forming appropriate planning.

The specific method is as follows:

1) The stability margin analysis of the system is carried out to find the node with the smallest stability margin, meanwhile, obtaining the corresponding domain boundary coefficient information of the node;

2) Sorting the optimized index of substation access(OISA), the larger the index value of the node, give priority to the node into the substation;

3) Replace the PQ node with the PV node in the position obtained in step 2);

4) Recalculate the security region of different schemes and the corresponding system stability margin. By comparison, the optimal access scheme is obtained.

Auxiliary planning strategy of substation access’s flow chart, as shown in

The following is an example of the IEEE 118 node system. The system has a total

of 55 PV nodes, 63 PQ nodes, and node 69 is the balance node. The voltage constraint is

According to the current power system network topology data, and the corresponding constraints, in the decision space of the system, obtain the corresponding static voltage security region in the current situation. Select the two- dimensional cross-section of the security region boundary corresponding to load node 9 on P11 and Q11.As shown in

In this paper, different load levels were selected for stability margin analysis. The results are shown in

From the analysis of Table, the system load increases, the system's stability margin decreases. As the installed capacity of the system is sufficient, the increase of load has little effect on the system stability margin. The current operating point is closest to the security region boundary of BUS 9.

According to the information on the security region boundary of BUS 9, Sorting the optimized index of substation access (OISA). Part of the data shown in

For analysis of OISA, in the

In the case of input substation parameters consistent, the stability margin analysis for Option 1and Option 2 is shown in

From the table can conclude that, access substation in the BUS 11 and BUS 13 can improve system stability margin. However, BUS 11 access substation’s effect of Stability margin improvement is more obvious.

Total system load (MW) | Stable margin value | The margin value corresponds to the load node number |
---|---|---|

4242.0 | 0.047 | BUS 9 |

4666.2 | 0.0466 | BUS 9 |

variable | Boundary coefficient | Variable value (Pu) | variable | Boundary coefficient | Variable value (Pu) | OISA value |
---|---|---|---|---|---|---|

Q11 | 0.05017 | −0.253 | P11 | −0.0147 | −0.77 | 0.023990201 |

Q13 | 0.04302 | −0.176 | P13 | −0.0141 | −0.374 | 0.01284962 |

Q16 | 0.04106 | −0.11 | P16 | −0.0163 | −0.275 | 0.009007075 |

Q7 | 0.04241 | −0.022 | P7 | −0.016 | −0.209 | 0.004270041 |

Q20 | 0.04425 | −0.033 | P20 | −0.014 | −0.198 | 0.004230664 |

Q17 | 0.0434 | −0.033 | P17 | −0.0167 | −0.121 | 0.003456626 |

Q2 | −0.0009 | −0.099 | P2 | −0.0145 | −0.22 | 0.003085325 |

Q14 | 0.04026 | −0.011 | P14 | −0.0152 | −0.154 | 0.002787811 |

In this paper, the direct construction method of static voltage safety domain is proposed. For the first time, the idea of “domain” is applied to the auxiliary planning of intelligent substation. This paper presents a set of complete intelligent substation access system program auxiliary planning method.

This work is supported by the National Science Foundation of China (No.51507108) and the project of State Grid Tianjin Electric Power Company (KJ15-1-08).

Yi, G., Zhang, S.T., Qin, C., Zeng, Y., Yang, Y., Liu, Y.Y. and Li, S.W. (2017) A Method of Auxiliary Planning for Intelligent Substation Access System Based on Security Region. Energy and Power Engineering, 9, 675-682. https://doi.org/10.4236/epe.2017.94B073