Franco Di Rosa, Claudio Celman, and Pablo Rifrani, Department of Testing and Engineering
Introduction – This article details the process carried out to achieve the commercial authorization of new generators to the wholesale electrical market (Mercado EléctricoMayorista, MEM). Before being connected to the Additional Provider of the Technical Transportation Function (PrestadorAdicional de la FunciónTécnica de Transporte, PAFTT) or to the Transporter, all Generators, Self-generators, and Co-generators must meet certain regulatory, information, and technical requirements for their entry into the MEM, commercial authorization, and dispatch.
- Energy sector in Argentina
On December 16th, 2015, Emergency of the National Electric Sector was declared until December 31st, 2017 and the Ministry of Energy and Mining (MEyM) was instructed to prepare a program of necessary actions required to power generation, transportation, and distribution segments, put it into effect, and implement it, to upgrade the quality and safety of the electrical supply, ensuring the provision of electricity to the public under adequate technical and economic conditions.
In this context, the Electrical Energy Department (Secretaría de EnergíaEléctrica, SEE) issued Resolution No. 21 on March 23rd, 2016, in which interested parties were invited to offer new thermoelectric generating capacity and associated electrical production, with a commitment to be available to the MEM to satisfy essential requirements of the demand, during the following Seasonal Periods: (i) Summer 2016/2017, (ii) Winter 2017, or (iii) Summer 2017/2018, in accordance with the guidelines of this resolution.
The most prominent bidders included companies such as AlbanesiEnergía, Genneia, Industrias Juan F. Secco SA, MSU Group, YPF Generación, and Pampa Energía, and project bids were received for a total of 6.6 GW of thermoelectric generation.
- The role of CAMMESA in the MEM
In Argentina, CAMMESA (CompañíaAdministradora del Mercado MayoristaEléctrico)is in charge of coordination of economic-technical deliveries from SADI(Sistema Argentino de Interconexión:Argentine Interconnection System), supervision of quality and safety of AISoperations, monitoring of the economic transactions in the spot and future markets, and management of billing, collection, and finance operations of the market funds.
To ensure a high-quality and safe electrical system, CAMMESA, as well as other electricity market regulators in other countries, use dedicated software for system simulations. In studies of electrical systems, the reliability of results that provide the calculations of power flows in steady state, and dynamic simulations, carried out with specific computer programs, depends mainly on adequate modeling and parameterization of the differentcomponents of the electrical system in question. The link between the real world and the simulation world is fundamental in the success of the operation and has an important impact on the economics of power systems.
CAMMESA manages a Database of SADImodels. In particular,this Database contains models of the generators and their associated control systems, which isused for stability studies in general, and in particular for dynamic or oscillatory stability studies, also called small signal stability.
- Technical Procedure No. 4
Technical Procedure No. 4 (PT4) contains the regulatory framework that must be complied with by any company that aspires to become a Generator, Co-generator, or Self-generator of the MEM. Regarding the technical requirements, we can separate those that deal with the automatic voltage regulator (AVR):
- To evaluate the full speed no load (FSNL)voltage regulator performance, the response to a small amplitude reference voltage change (generally 5%) should be fast, keeping the overshoot at values less than 15%; risingtime (from 10% to 90%) below 300 ms, and settling time (+/– 10% of the applied voltage increase) less than 1.5 seconds.
Figure 1: FSNLAVR performance
- For “Vfdmax” (generator excitation voltage), a minimum of 2 times the excitation voltage is established, at full load and nominal power factor.
- In orderto contribute to the damping of electromechanical oscillations (local, intra-plant, interplant, inter-area, etc.) of the grid, the AVR must be provided with a power system stabilizer (PSS), which will operate by modulating the voltage reference.
Andthose that apply to the automatic speed regulator (GOV):
- Dead band less than 0.1%.
- Permanent droop adjusted to between 4 and 7%.
- Settling time (necessary so that the mechanical power can enter the +/– 10% band of increased applied load), less than 30 seconds for thermal machines and less than 60 seconds for hydraulic machines.
Figure 2: GOV performance
- Mathematical modeling
The modeling process may be summarized comprehensivelyby the flow diagram in Figure 3. The final objective of this process is for the developed and parameterized mathematical model, during application of a certain perturbation, will respond identically to the actual physical system that it represents.
Figure 3: Basic flow diagram of the modeling process
Estudios Eléctricos has two principal departments, Simulation Studies and Field Testing. The latter is responsible for performing field tests and the later mathematical modeling of all types of generators and their associated controls.
Figure 4 shows the block diagram modeling of a turbogenerator unit, with AVR, limiters, and PSS, performed using Photon simulation software, property of Estudios Eléctricos.
Figure 4: Block diagram of generator, AVR, limiters, and PSS
- Success case
Since March 2016, Grupo Albanesi has carried out the following generation projects:
- Expansion of La Rioja Thermoelectric Plant, one Siemens SGT-800 gas turbine.
- Expansion of Modesto Maranzana Thermoelectric Plant, two Siemens SGT-800 gas turbines.
- Expansion of Independencia Plant, one Siemens SGT-800 gas turbine.
- New installation in Alejandro Petión, Province of Buenos Aires, two Siemens SGT-800 gas turbines.
- Expansion of Roca Thermoelectric Plant, steam cycle closure, GET-10R turbine.
La Riojana Thermoelectric Generating Plant, located in the town of La Rioja, Province of La Rioja, is an open-cycle thermal power plant with two Fiat TG16 machines, 16 MW each, and a John Brown turbine, 16 MW, installed and operating, for a total of 48 MW of nominal power.
In January of this year, Estudios Eléctricos carried out the tests for commercial authorization of the new Siemens SGT-800 TG24 turbogenerator unit, which was part of the expansion projects mentioned above.
Figure 5 shows the unloaded response of the terminal voltage (blue curve) using the mathematical model presented in Figure 4, contrasted with the unit response recorded in field (green curve), after a change in the voltage reference of the automatic voltage regulator.
Figure 5: FSNLresponse of the dynamic model (blue) and the tested generator (green) after a reference change of 5%
Figure 6shows similar results, but for the generator synchronized with the System; that is, operating under load. This shows the temporal evolution of the terminal and reactive voltage generated by the unit, for both the mathematical model (blue curve) and the field test (green curve), after a change in the voltage reference of the automatic voltage regulator.
Figure 6: Loaded response of the dynamic model (blue) and the tested generator (green) after a reference change of 2%
The generator limiters, power system stabilizer, and automatic speed regulator were also tested, in order to obtain an appropriate model for representation of the unit in question.
- Future projection
As mentioned in this article, the country is in a process of restructuring of the energy sector due to the incessant change in the demand by the users. To face this situation the National State assigned the corresponding authority to the MEyM so that it could take action in the matter. As result, the first bidding tender for thermoelectric generation projects was launched in March 2016.
Decree 531/2016 was elaboratedon the same date, whose purpose wasthe national promotion of the use of renewable energy sources intended for electric power production. This brings about favorable consequences for the country, since it implies expansion of the installed power in the short term, the reduction of energy generating costs, price predictability in the medium and long term, greater diversification of the national energy matrix, the objective was to achieve a contribution from renewable energy sources of up to eight percent (8%) of national electricity consumption as of December 31st, 2017, and the contribution to mitigation of climate change, generating secure conditions for the electrical supply for the Republic of Argentina.
Article 12 of the aforementioned decree states that the Enforcement Authority must provide the actionsthat are conducive to incorporation into the MEM of new offers of electricity from renewable sources, through public and competitive procedures. Therefore, using Resolution No. 136 on June 25th, 2016, the MEyM instructed CAMMESA to issue the National and International Tender “RenovAr Program (Round 1)” for the qualification and eventual adjudication of offers for the conclusion of contracts for the supply of electric power generated from renewable sources.
Table 1: Summary of the offers received in Round 1
Table 2: Offers awarded Round 1
As can be seen in Table 1, the power offered would sextuple the power to be contracted within the framework of Round 1. As consequence of the large number of offers received and the quality of the projects involved, in particular for Wind and Solar Photovoltaic Technologies, the MEyM considered it convenient to adopt the actionsnecessary to offer the possibility of improving the bids submitted and not awarded in the aforementioned Round 1, with a significant reduction in the prices offered, taking as a reference certain market prices from the bids awarded in the aforementioned round.
Therefore, by way of Resolution No. 252 on October 28th, 2016, the presentation of new offers related to Wind and Solar Photovoltaic Technologies projects presented and not awarded in Round 1 was officially announced, within the framework of the RenovAr Program, maintaining the fundamental guidelines established in Resolutions No. 71 and No. 136, for contracting by the MEM of electrical energy from renewable sources of generation, denominated “RenovAr Program (Round 1.5)”.
Table 3: Summary of the offers received in Round 1.5
Table 4: Offers awarded Round 1.5
Due to the results obtained and the expectations generated, it was deemed convenient to provide continuity to the RenovAr Program through a new tender, in order to award new generating capacity for electricity from renewable sources, and at the same time continue to improve the prices offered in the previous rounds, contributing to the reduction of energy cost in SADI.
In this context, the MEyM declaration of Resolution No. 275 on August 17th, 2017, once again invited interested parties to bid in the National and International Open Tender Process for contracting in the MEM, called “RenovAr Program (Round 2)”.
The Simulation Studies department is currently performing Stage 1 and 2 works on several plants resulting from projects awarded in the RenovAr Program. Some of these are named below.
- La Puna Solar Park, 100 MW, Fieldfare / Isolux, Salta.
- Villalonga Wind Farm, 50 MW, GENNEIA, Buenos Aires
- Nonogasta Solar Park, 35 MW, Fides Group SA, La Rioja.
- Saujil Solar Park, 23 MW, Energías Sustentables SA, Catamarca.