Challenges of Real-Time Operation of the

Brazilian Electricity System with the Insertion

of Wind Generation

Flávio Guimarães LinsFábio Henrique de Andrade LimaRicardo VieiraGustavo Leonardo Pinheiro de OliveiraYlani FreitasRodrigo Gama Tenório

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Brasil Wind Power Generation - General Overview

• Brasil have one of the best mean capacity factor of the world;• However, high variability and low predictability;

Challenges of Real-Time Operation of the Brazilian Electricity System with the Insertion of Wind Generation | Lins F. G. et al 2 /

• The big challenge is todeal with this variabilityand dispatcheconomically othersgeneration powersources, like termal andhydro plants.

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• Major restraints to deal with:• Thermal power generation start-up delays and on-line minimum operation time;• Critical reservoir levels in hidropower cascaded systems;• Reserve margin to account windpower variability;• Equipment overload operation prevention;• Optimal voltage control;

Challenges of Real-Time Operation of the Brazilian Electricity System with the Insertion of Wind Generation | Lins F. G. et al

Brasil Wind Power Generation - General Overview

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• Large amount of wind generation has been incorporated into the Brazilian Electrical System (SEB)

• Practically, all wind farms are in the northeast (80%) and in the South (20%) regions.• This altered the operation way in last years, making it dependent on the performance of the

wind farms.• According to the 2017 report of the Global Wind Energy Council, Brazil came to occupy the

eighth place in accumulated installed capacity, surpassing, in this last year, Canada. Considering only the wind generation incorporated in the year 2017, Brazil was in sixth place.

Challenges of Real-Time Operation of the Brazilian Electricity System with the Insertion of Wind Generation | Lins F. G. et al

Brasil Wind Power Generation - General Overview

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% Eólica na demanda NE e Fator de Capacidade (%)

% Demanda = Gera.Verif. / Carga verif. (1min) Fator Cap (%) = Gera.Verif.(1 min.) / Cap.instalada

• Example of19/08/2018

• Windpowergeneration record8247 MW

• 82% FC & 98% ofdemand.

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• The ONS made an revision proposal of de Grid Operation Statements to account the windpower generation variability in the operation reserve margin (RPO).

• The RPO have 3 parts:• R1 – Primary Reserve: Accounts reserve on own control area;• R2 – Secondary Reserve: Accounts the reserve on generation units operated by the

automatic generation control (AGC) of the area;• R3 – Tertiary Reserve: May be account on every generation units on own area,

including in the AGC, and this reserve are utilized to deal with load variability andgeneration units outages.

• The proposal is to include in R2 an parcel to account the wind power variability, as shown in the following equation:

Where the subscripts means the reserve on area(i) to increase (e) or reduce (r).C is the load on control area i, and Reol is the wind power reserve.

Challenges of Real-Time Operation of the Brazilian Electricity System with the Insertion of Wind Generation | Lins F. G. et al

Operation Reserve Margin

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• However, in adverse hydrological periods, its difficult do allocate this reserve in unitgenerators on the AGC, because its off most of the time. In this cenário, the priority is tomaximize the energy delivery for particular region, and this situation becomes a challenge tothe system operators that needs to compensate the windpower variability on the otherpower sources.

• This difficulty is increased by the energy interchange maximization, because in most of thetime, these transmission lines operates in their maximum operative capacity (stability limits)

Challenges of Real-Time Operation of the Brazilian Electricity System with the Insertion of Wind Generation | Lins F. G. et al

Operation Reserve Margin

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Equipment Scheduled Maintenances

• These activities are ruled by the grid operation statements, and all requests must beevaluated by ONS to ensure reliability to the electrical system in the case of equipmentoutages (contingency) during the scheduled maintenance.

• The major concerns are due to influence of the level of windpower generation during thesesmaintenances.

• It may be necessary to control the value of the active power generated in each wind power plant, before or after the contingency.

• This control may be done by limiting the windpower generation of each group of wind farms proportionally to the observed generation in real time.

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Equipment Loading Control

• During real-time operation, control actions in active and reactive power in wind power plantsmust be done to avoid equipment overload.

• To achieve this goal, its necessary that the windfarms can execute this type of control by thePower Plant Control and its very important that these systems stays fully operational.

• One of the most critical problems is related to failure in communications links of the supervisioning systems, whichprevents the sending of signals to the wind turbines.

• To explain the need to control, is shown the case in the substationof Irecê, in the southwest of Bahia state, where the goal is avoidoverload in the transmission line Irecê / Morro do Chapéu. The ONS do active power controls that shown in figure:

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9 / Challenges of Real-Time Operation of the Brazilian Electricity System with the Insertion of Wind Generation | Lins F. G. et al

Voltage Control

• According the grid operation statements, thewindfarms must comply in their connection nodes, resources to operate with reactive power fator between 0,95 inductive to 0,95 capacitive fator.

• To wind conditions below the cut-in point, thewindfarms must comply with the same specificationsof reactive power in their nodes.

• In the figure below are shown the use of thesesresources to control the reactive power and thevoltage in the electrical system main grid. Thesesresources are Essentials to keep the voltages under theoperational limits for each load threshold, improve theresources optimization and performance in case ofequipment outages

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Energy Transfer Between Regions

• The northeast region of Brazil have about 80% of total installed capacity of wind power generation andthe critical energy situation in this regions directly influences the exchange of energy between regions.

• Today, the largest hydroelectric basin in the northeast, the São Francisco River, is in a very delicate situation, passing through the greatest water crisis in its history.

• The generation of hydraulic power plants in the river has been reduced due to the reduction of defluence, in an attempt to give a survival to the river, considering the multiple use of water. The low number of synchronized hydro units causes an reduced system inertia.

• Before the advent of wind power, it was necessary a high dispatch of thermal plants and, in addition, to receive large blocks of energy from others regions.

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Energy Transfer Between Regions

• There are risks of shutdown of the North / Northeast, North / Southeast and Southeast / Northeast interconnections, mainly during fires, which occur historically between August and November.

• Additionally, there is a coincidence between the period that occurs the fires under the interchange lines, with the period of high wind generation due to the high incidence of winds in the region, which occurs in the months of August to November.

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Real Time Wind Power Forecast

• The wind power generation forecast is a important requirement to the sucessfull integration ofrenewable sources of energy, that have as mainly feature the variability.

• The world trends, points to the use of several wind power predictions models, taking advantage of the best characteristics of each one.

• In real time operation, the forecast is important to the decision making process as described up to now.

• In a simplified way, the solution adopted in Brazil and other European countries. There is a combination module that process all input forecast models and chose one that has the best performance in the last hours. From this, the module trends the wind power forecast for the next hours based in that choosen model. The forecast curve is adjusted to the observed wind power generation using an persistence forecast model in the firsts time steps and, inverse exponentially, decay to the choosen model, softening the resulting forecast curve and avoiding discontinuities.

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Real Time Wind Power Forecast

• This methodology allow to increase the operation reliability and efficiency in the use of thermal and hydro generation resources, exploring the energy exchange between regions. This optimization results in a low cost operation too.

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Real Time Wind Power Forecast

• The figure below shows the combination module output graph. It can be shown up to six wind power prediction curves (models) plus the yesterday and today wind power observed curves. The dashed line shows the output curve from the combination module.

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