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Distributed Generation Control Methodologies and Network Reconfiguration: Effects on Voltage Profile A. AGUSTONI, M. BRENNA, R. FARANDA, E. TIRONI Dipartimento di Elettrotecnica Politecnico di Milano, Milan, Italy Politecnico di Milano Dipartimento di Elettrotecnica G. SIMIOLI CESI Milan, Italy Clemson, March 13, 2002 Distribution test network B L01 L12 L23 1 HV Network 2 3 HV/MV Transformer A Load 1 Load 2 G ~ Load 3 G ~ DG1 G ~ DG2 DG3 0 C L04 L45 L56 4 Load 4 Politecnico di Milano Dipartimento di Elettrotecnica 5 Load 5 6 Load 6 Clemson, March 13, 2002 Voltage Profile in MV Distribution Network These figures show the voltage diagrams along a 20 kV line in the absence and in the presence of a regulation system. The use of ULTC (Under-Load-TapChangers) at the primary substation greatly improves the trend along the time axis, but the voltage drop along the line remains almost the same. Politecnico di Milano Dipartimento di Elettrotecnica Clemson, March 13, 2002 Costant Power Factor Control of Distributed Generation We have limited to ±4% the, voltage drop: Load Generator VLk n n k r Li Pj x Li Q j j i j i i 1 V2 Results Vk VLk VGkh k kh Politecnico di Milano Dipartimento di Elettrotecnica k VGkh min h , k r Li PG x Li QG i 1 V2 kh Objective function min h max k k kh Clemson, March 13, 2002 Costant Power Factor Control of Distributed Generation Table shows the maximum voltage drop at any node k in the course of one day as a function of a 5 MW generator's position. The space-time diagram of the voltage along the line shows how the generator and the UTLC at the primary sub-station can improve the voltage profiles (surface more flat). Politecnico di Milano Dipartimento di Elettrotecnica Pos Node 1 1 0.0055 2 3 0.0055 0,0055 2 0.0196 –0.0084 –0.0084 3 0.0266 0.0110 –0.0195 Clemson, March 13, 2002 Constant Voltage Control of Distributed Generation Condition h hh h Generator Reactive Power n n 2 r L P P x L Q V h i j G i j i 1 j i j i h x Li h QGhT i 1 Politecnico di Milano Dipartimento di Elettrotecnica Clemson, March 13, 2002 Constant Voltage Control of Distributed Generation To keep the rated voltage at the node where a 5 MW DG is inserted h = 0 corresponds. By carrying out the procedure described we obtain the results in table. The graph shows that constant voltage control further improves the voltage profiles along the line, but that, especially with changes in the load, it maintains the voltage most stable at the node where the generator is inserted. Politecnico di Milano Dipartimento di Elettrotecnica Pos 1 2 3 1 0 0.0035 0.0035 2 0.0141 0.0071 0.0071 3 0.0212 0 0 QG [Mvar] 4.4049 3.1803 1.9557 Node Clemson, March 13, 2002 Network reconfiguration B L01 L12 L23 1 HV Network 2 3 HV/MV Transformer A Load 1 Load 2 G ~ Load 3 G ~ DG1 G ~ DG2 DG3 0 L36 C L04 L45 4 Load 4 Politecnico di Milano Dipartimento di Elettrotecnica L56 5 Load 5 6 Load 6 Clemson, March 13, 2002 Network reconfiguration B L01 L12 L23 1 HV Network 2 3 HV/MV Transformer A Load 1 Load 2 G ~ G ~ DG1 Load 3 G ~ DG2 DG3 0 L36 C L04 L45 4 Load 4 Politecnico di Milano Dipartimento di Elettrotecnica 5 Load 5 6 Load 6 Clemson, March 13, 2002 Network reconfiguration B L01 L12 L23 1 HV Network 2 3 HV/MV Transformer A Load 1 G ~ Load 2 Load 3 G ~ DG1 G ~ DG2 DG3 0 L36 C L04 L56 4 Load 4 Politecnico di Milano Dipartimento di Elettrotecnica 5 Load 5 6 Load 6 Clemson, March 13, 2002 Network reconfiguration B L01 L12 L23 1 HV Network 2 3 HV/MV Transformer A Load 1 Load 2 G ~ Load 3 G ~ DG1 G ~ DG2 DG3 0 L36 L45 L56 4 Load 4 Politecnico di Milano Dipartimento di Elettrotecnica 5 Load 5 6 Load 6 Clemson, March 13, 2002 Network reconfiguration We want to insert in 3 two 5 MW groups with a power factor of 0.9; that is, with total power exceeding the line's total load, but such as not to overload the line. The power flow has now been inverted, and the voltage at the end of L1 is consequently greater than at the beginning that are unacceptable for the proper operation of the electric power system. By operating a network reconfiguration the optimal network configuration, that is the one that minimizes voltage variations at the nodes, is the one that involves shifting loads 5 and 6 from line L2 to line L1. Politecnico di Milano Dipartimento di Elettrotecnica Clemson, March 13, 2002 Conclusion • The introduction of generators into distribution networks, built and operated in such a way that they are passive, alters the power flows and consequently the voltage profiles. • It has been pointed out that the correct positioning of the generators may lead to an improvement in the voltage profiles, both in terms of space (along the line) and in terms of time (with variations in absorption). In the second case, a decisive factor is the type of generator control: indeed, as we have seen, constant voltage control greatly reduces the voltage variations during the day, but is generally speaking more expensive to operate than constant power factor control. How economical it is will therefore depend on the sensitivity of the loads to voltage variations. Politecnico di Milano Dipartimento di Elettrotecnica Clemson, March 13, 2002 Conclusion • Should it not be possible to select the position in which to insert the generator, overvoltages may occur at the point of insertion of the generator. In such an event, the problem can be solved by suitable reconfiguration of the network and more uniform redistribution of the power flows. • If adequate reconfiguration of the network were not possible, it would be necessary to reduce the maximum injectable power of the generator, or else to adapt line L1 to the new requirements. Politecnico di Milano Dipartimento di Elettrotecnica Clemson, March 13, 2002
