At a glanceSiemens Power Technologies Interna-tional (Siemens PTI) has decades ofexperience in planning public distribu-tion grids. From the low voltage levelup to the 110 kV distribution grid level,we cover the entire spectrum of chal-lenges. From conceptual questions,such as the development of optimumgrid structures and planning criteria, tostrategic considerations, such as targetgrid planning, and operational tasks,such as protection setting calculationsand the optimum placement of smartgrid technologies on the grid.

The challengeIn the context of regulations and theenergy transition, operators of publicdistribution grids face a wide range ofchallenges, some of which mutuallyinfluence each other.

Initially, the optimum annual budgetsfor grid investments are determinedwithin the regulatory framework. Overthe years, these investments mustthen be implemented on the grid atthe correct location and at the correctpoint in time, such that the grid devel-ops into the most efficient and reliabletarget grid. Furthermore, the most ro-bust possible planning criteria must bedefined so that the target grid conceptcan be retained even if load and gen-eration prognoses are off the mark -

e.g. due to increasing penetration ofelectric vehicles or distributed powergeneration systems. If necessary, thesenew boundary conditions must be metwith the new technologies of smartgrid generation. This in turn requires areasonable implementation process forthese technologies, so that they canalso be implemented from the correctperspective, at the right place and atthe right time. Finally, the implement-ed protection concept must also be asrobust as possible, so that the settingsdo not have to be continually adjustedfor changing grid and feed-in condi-tions.

Our solutionsAsset simulationThe long-term annual budgets for gridinvestments and operating costs(CAPEX, OPEX) are determined fromthe equipment available and the agestructure of the current grid.

Figure 1: Asset simulation for cables in themedium voltage grid

A forecast of the aging behavior of thegrid and the future supply reliability itprovides can also be derived by varyingthe budget limitations for the differentgroups of resources.

Target grid planningA target grid that ensures high effi-ciency with regard to grid costs andreliability provided over the long-termis developed in close cooperation withgrid operators. Target grid planning isbased on previously agreed upon gen-erally applicable planning criteria.Compliance with these planning crite-ria is checked through load flow, short-circuit and reliability calculations.Planning efficiency is verified by com-parison of the costs and the providedsupply reliability of the actual and tar-get grids. All of the necessarymeasures for implementation of thetarget grid are documented in detail.

Distribution gridplanningSolutions in the context of the energytransition and regulation

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Figure2: Target grid planning in an MV gridwith the necessary measures for implementa-tion

Reinvestment and implementationplanningUnder consideration of the annualbudget and knowledge of the targetgrid to be achieved, the sequence ofreinvestments and of the measures forimplementation of the target grid arederived from the condition and signifi-cance of the resources that are stillpresent or are no longer present in thetarget grid.

Figure 3: Condition/significance diagram forcables in the MV grid

Grid protectionThe current protection concept ischecked for selectivity and practicabil-ity (general applicability). Improve-ments are suggested based on this,and individual protection settings aredetermined for distance and definitetime overcurrent protection.

Figure 4: Grid protection concept for a MV grid

Smart planningIf the assumed boundary conditions fortarget grid planning change – for ex-ample due to an increasing penetra-tion of the grid by electric vehicles ordistributed power generation systems– impending violations of restrictionsmust be counteracted at an early stagethrough targeted implementation ofinnovative resources from the smartgrid generation in the existing gridstructure. This could mean measuressuch as an implementation process forcontrollable local grid transformers(rONT) and/or medium voltage in-phase regulators or an implementationprocess for intelligent transformer sub-stations (iONS) for remote signaling inthe event of a fault and remote controlof disconnector switches.

Figure 5: Smart Planning: Intelligent place-ment of resources from the smart grid genera-tion

Low-voltage grid investigationsBecause low-voltage grids are directlyaffected by changes in load behavior,

this – long-neglected – grid level willmerit increasing attention in the fu-ture.

Figure 6: Low-voltage networked grids withsingle-phase input

Typical tasks on the low-voltage sideare as follows:

· Determination of the optimum low-voltage grid form

· Determination of generally applica-ble planning criteria

· Resolution of low-voltage net-worked grids

· Evaluation of effects on the gridfrom distributed power generationsystems

· Investigations regarding compliancewith the shutdown condition

· Dimensioning of charging infra-structures for electric vehicles

· "What-if" investigations:Quantification of the critical growthof PV systems, electric vehicles, heatpumps etc

Published bySiemens AG 2017

Energy Management DivisionFreyeslebenstrasse 191058 Erlangen, Germany

For more information, please contact:power-technologies.energy@siemens.com

AL=N, ECCN=EAR99Subject to changes and errors. The infor-mation given in this document only con-tains general descriptions and/or perfor-mance features which may not alwaysspecifically reflect those described, orwhich may undergo modification in thecourse of further development of theproducts. The requested performance fea-tures are binding only when they are ex-pressly agreed upon in the concluded con-tract.