Ansaldo_EDISON_MEMORIA_Crippa

Ancillary Services supplied to the grid: the case of Thisvi CCGT power plant (Greece) Claudio Cavandoli, Alessandro Crippa 27/06/2012 – pag. 1 Ancillary Services supplied to the grid: the case of Thisvi CCGT power plant (Greece) Claudio Cavandoli, Alessandro Crippa Edison S.p.A. Engeneering Department Ancillary Services supplied to the grid: the case of Thisvi CCGT power plant (Greece) Claudio Cavandoli, Alessandro Crippa 27/06/2012 – pag. 2 1. Introduction Elpedison Power (a Joint Venture Company owned/controlled jointly by Edison S.p.A. and Hellenic Petroleum) owns and operates since December 2010 a 421.6 MW Combined Cycle Power Plant located in Thisvi (Beotia prefecture, Greece). The realization of the plant has been carried out by THISVI JV, a Joint Venture between Edison (65%) and Aktor (35%) under an EPCM contract. The power plant erection (earthworks) has started in June 2008; commissioning and testing activities (including tests requested by the Greek grid operator HTSO in order to achieve the “commercial operation”) have been concluded in November 2010, while handover to the final Customer (Elpedison Power) has been completed in December 2010. Edison Engineering department and Aktor have managed the Engineering, Procurement, Construction and Commissioning/Testing of the plant on a “shopping around” basis. The main equipment were purchased to Ansaldo Energia (GT and ST), Nooter Eriksen (HRSG) and GEA (ACC). The combined cycle has been designed in order to be a fully flexible plant (daily start and stop) and in full compliance with European and Greek regulations. In particular it is highlighted that the Greek Grid Code requirement in terms of primary frequency regulation contribution is 3% of Gross Registered Capacity to be delivered to the grid within 30 seconds from the disturbance occurrence [1]. Given the high contribution requested and the GT allowable loading gradient (characteristic of the machine) it is not possible to fulfil the requirement with the GT contribution only. For this reason, a specific frequency regulation procedure (which foresees, in addition to the GT load increase, a ST contribution through the HP control valve) has been developed, dynamically simulated, implemented and tested. The article describes the modifications with respect to the “combined cycles standard operating procedures” that has been necessary to implement in order to fulfil the Greek Grid Code requirements in terms of primary frequency regulation response and the results obtained during the relevant tests. Ancillary Services supplied to the grid: the case of Thisvi CCGT power plant (Greece) Claudio Cavandoli, Alessandro Crippa 27/06/2012 – pag. 3 2. Plant description THISVI C.C.P.P. is based on a “multi-shaft” arrangement (GT & ST with dedicated generator and step-up transformer), air cooled condenser, with an air insulated electrical substation. The Gas Turbine can be operated both on natural gas (normal operation) and on diesel oil (only for 10 days/year, in emergency conditions as requested by the authorization documents). The Power Island is composed by the following main equipment: • GAS TUBINE: Ansaldo Energia AE94.3A.4 (275 MW ISO) • STEAM TURBINE: Ansaldo Energia MT (146 MW ISO) • STEAM GENERATOR: Nooter Eriksen (3 pressure levels + RH with post-firing) • AIR CONDENSER: GEA Energietechnik (21 fans) The Heat Recovery Steam Generator is equipped with a supplementary firing system (approx. 33 MWth duty) necessary to meet the gross capacity specified in the authorization process (421.6 MW, ISO conditions). All the auxiliary systems, necessary for correct and safe operation of the plant, have been designed and installed (water treatment, gas compression/reduction station, compressed air, diesel oil unloading and storage, auxiliaries cooling system, fire-fighting systems, HVAC etc.). In the following figure, a picture of the completed power plant is presented. Figure 2.1 – Plant Front View 3. Greek grid code primary frequency regulation requirements According to the Greek Grid Code, The Unit must be able to fulfil the requirements in terms of Primary Control Reserve (indicated in articles 125 and 275) [1]. Ancillary Services supplied to the grid: the case of Thisvi CCGT power plant (Greece) Claudio Cavandoli, Alessandro Crippa 27/06/2012 – pag. 4 The Grid Code (Article 275) defines, for thermal Power Plants with a Registered Capacity of at least 100 MWe, the following requirements [1]: 1. Each Generation Unit must have primary frequency control capability; 2. The operating reserve shall be not less than 3% of the registered capacity in the range between 50% and 97% of the registered capacity; 3. The operating reserve in the range between 97% and 100% shall be not less than that indicated by a straight line with fixed slope from 3% of registered capacity at 97% output and 0% at full load; 4. The production license holder must be capable of activating, within 30 seconds, the total primary operating reserve and of maintaining supply for at least 15 minutes; 5. The primary operating reserve must be available again 15 minutes after activation. Considering a Registered Capacity of 421.6 MWe in post-firing mode, the operating reserve required between 50% and 97% CCPP load corresponds to 12.6 MWe/30sec. Between 97% and 100% power plant load, the contribution required by the Code is represented by the curve showed in Figure 3.1: Load variation Vs plant load0246810121495%96%97%98%99%100%Power Plant LoadGrid required load variation MW/30s Figure 3.1 – Contribution required by the Greek Grid Code 4. Requirements impacts on control strategy Most of the Combined Cycle Power Plants normally fulfil the primary frequency regulation grid requirements with the gas turbine contribution only. In such cases, the requested contribution is provided by the Gas Turbine (either operating it slightly below the relevant Base Load, or over-firing it when possible), with the Steam turbine following in “sliding pressure”. In Thisvi case, given the high contribution required and the load ramp-rates allowed by the GT (see below details) such operating mode is not enough to meet the requirements. In particular, the main issue is that the GT power output ramp-rate is reduced at high