NetPlan – Model for transmission expansion planning

NetPlan is an integrated computational environment for transmission network planning and analysis which includes:

• data management tools (data editing, external data importation)
• study management resources (data coherency checking and chronology)
• visualization resources for the network and study results (schematic diagrams, circuit flows, overflow indicators, expansion plan cost, load marginal cost, contour plots)
• graphical interface that allows interaction with different modules

The following modules are available in the NetPlan environment:

• OptNet, for optimization of expansion planning of high voltage transmission network
• PSRFlow, for AC and DC transmission network analysis
• OptFlow, for planning of reactive power resources (VAr)
• Tariff, for allocation of transmission costs among generators and loads

All models use optimization tools specially designed to solve large scale networks.

The OptNet module – Transmission expansion planning

Modeling Aspects

OptNet models the transmission expansion planning as a MIP problem with the following features:

• Representation of linearized power flow model for the transmission system
• Representation of generation dispatch scenarios produced by SDDP model in order to account for uncertainties in load and generation production (hydro plant inflows and renewable resources)
• Decisions on new transmission facilities: AC transmission lines, transformers, series capacitors and dc transmission system
• Representation of project constraints: sets of associated projects, sets of mutually exclusive projects and precedence constraints
• The expansion process can be applied considering all circuits in operation (base case) as well as to selected single circuit contingencies
• Outputs include the expansion plan decided by the model and detailed operating results that can be graphically displayed in the network diagram and\or visualized using Excel spreadsheet

Solution methodology

The objective function consists in minimizing the investment cost to install new facilities and the supply reliability cost, providing the best investment x supply reliability cost trade-off solution. The solution of the mixed integer optimization program is provided using advanced techniques of mixed integer programming.

The methodology combines a heuristic method, that guarantees a feasible solution, with a Benders decomposition method that provides an optimal solution when the convergency is reached. Dispatch scenarios and contingencies are dealt by an incremental expansion strategy which makes the algorithm suitable to be used in planning studies of large networks with high penetration of renewable generation.

The PSRFlow module AC and DC transmission network analysis

Modeling Aspects

• Applications designed for steady state analysis of transmission network
• Includes a conventional AC and DC power flow and contingency analysis
• Integration with generation dispatch scenarios produced by SDDP model
• Outputs include detailed operating results that can be graphically displayed in the network diagram and\or visualized using Excel spreadsheet

Solution methodology

The power flow application solves the load flow equations by use either a fast decoupled or a conventional Newton Raphson method, for AC and DC controls. Linearized power flow is also available.

The contingency analysis application processes a list of contingencies with the objective to detect and report network violations (circuit flow, bus voltage, etc.).

The OptFlow module – Planning of reactive power resources (VAr)

Modeling Aspects

The OptFlow module is the computational tool for reactive expansion planning with the following features:

• Representation of different generation and load scenarios produced by SDDP model to capture uncertainties in renewable sources (hydro inflow, wind, solar)
• Modeling of the non-linear active and reactive power balance of each node of the electric grid (Kirchhoff laws)
• Modeling of different network operation limits: voltage magnitude, active and reactive power flow transportation in the circuits, transformer taps, shunt, svc
• Outputs include the expansion plan decided by the model and detailed operating results that can be graphically displayed in the network diagram and\or visualized using Excel spreadsheet

Solution methodology

The objective function considers the minimization of the sum of shunt investment cost and the penalized deviation of the active power generation setpoint.

Decision variables include active and reactive power generation of the units, bus voltage angles, transformers taps, and capacitor/reactor susceptance.

The solution methodology consists in applying a robust primal-dual interior point algorithm for each represented scenario. The investment solution provided by the model guarantees the operation limits and constraints are obeyed for each generation and load scenario, where all available reactive controls are considered.

The Tariff module – Power transmission cost allocation (coming soon)

Modeling Aspects

The Tariff module is a computational tool designed to promote the allocation of costs related to the transmission system infrastructure among its users (producers and consumers). To perform such a task, the Tariff is able to:

• Identify how producers and consumers use the system to allocate costs accordingly
• Allocate costs considering an extensive range of operating scenarios, making tariff calculations adherent to the real electrical system operation and planning

The Tariff is a powerful tool for the power sector agents with relevant aspects for:

• System planners and regulators that can use it to reveal the transmission expansion actual costs and promote cost allocation and determination of tariffs; or it can be used as a planning tool to evaluate different cost allocation methodologies and select the more adherent to the electrical system
• Generator and consumers who seek to forecast future tariffs and costs

Solution methodology

The Tariff model can adopt three different transmission cost allocation methodologies:

1. The nodal: used by Brazil and UK to allocate transmission costs. It is based on the marginal impact generators' and consumer's injections have over the energy flow in transmission facilities

2. The Average Participation Factors: commonly used to allocate costs in problems involving transport infrastructure. It traces the path of generators' and consumers' injections over the grid

3. The Aumann-Shapley: based on the game theory concept, assures fair cost allocation, modeling the transmission business as a coalition in which each agent can optimize costs of energy transportation

Some recent applications

• Designing alternatives for the future development of the Chilean National Transmission System (horizon 2019-2040). NetPlan were used to optimize the expansion of the transmission network, considering the insertion of new energy resources (wind and solar) and batteries
• NetPlan were used to optimize the network expansion for the Brazilian system for the horizon 2035, taking in account a large degree of renewable energy sources (wind and solar)
• Analysis and regulatory proposals for the Ancillary Services for the Colombian systems, considering the insertion of variable energy renewable resources and new technologies in high and low voltage. NetPlan were used to study the expansion of the Colombian transmission system for the horizon 2019-2040
• Renewable integration of South America. NetPlan were used to optimize the transmission expansion (2017-2035) in nine South America countries, participants of the Andeans community (Chile, Colombia, Ecuador and Peru), Southern Cone (Argentina, Brazil, Paraguay and Uruguay) and Bolivia
• Expansion planning of the WECC transmission network for a 15-year horizon, peak yearly dispatch scenarios and 960 projects
• Analysis and regulatory proposals for transmission cost allocation mechanisms in Brazil. NetPlan was used to simulate the transmission tariff calculation using different methodologies in order to assess the impacts over tariffs of generators represented by the Brazilian Wind Power Association (ABEEólica).