UTILIZACIÓN DE SISTEMAS DE BATERÍAS EN LA REGULACIÓN DE FRECUENCIA EN EL SISTEMA INTERCONECTADO DEL NORTE GRANDE

Abstract

One of the main difficulties in the Electrical Power System (EPS) and operators theadobe, is to maintain the security and continuity of electricity supply to contingencies thatmay occur in the system, such as fault lines, odd outputs power plants, sudden increasesand declines in demand, among others. As the main objective of the electricity system isto meet the demand, which is impossible to predict exactly as the customer consumptionis random, during the actual operation constant monitoring frequency is performed, suchthat by control schemes adjust the states of operation of generators to achieve a balanceof power in the system. Sometimes the system is also facing major imbalances betweengeneration and demand due to the untimely departure of generation blocks or suddenchanges in demand, which is why the system must have certain characteristics that enableit to respond appropriately naturally, giving time control systems to act on the generatorsand the balance of power is restored to the system. If the imbalance is such that it can‘t stopthe fall of the frequency, low frequency relays give a signal to the switches to disconnectload blocks previously defined, to prevent the frequency reaches dangerous values. Thissituation is undesirable, but it is necessary to maintain system security. Subsequently,manually, a slower frequency to return to its nominal value control is performed.In the Northern Interconnected System of Chile (SING) all generators participatingin the primary frequency control, for it leaves 7% of its nominal capacity and spinningreserve for this purpose. It was found that new energy storage technologies can adequatelyprovide the service, being more efficient and economical for the system. This was whatmade the company AES Gener, which installed two Batteries Energy Storage Systems(BESS´s); a system of 12 MW/4 MWh in the Andes Substation in 2009 and another20 MW/5 MWh in the Angamos Substation, which can operate for 20 to 15 minutes atnominal power respectively. Thus the BESSs replace a 4% reservation based power plantsNorgener and Angamos.The BESS´s must absorb/release energy once the frequency exceeds the deadband 0,3Hz determined by the Technical Standard of Safety and Quality of Service. In previousstudies it has been determined that BESSs can release their energy, at nominal power,in a time of hundreds milliseconds. However, in actual operation, according to reports offailures given by the CDEC-SING it shows that on average BESS´s release their energyat a rate of generation of the order of seconds, however, the total time is relatively lessthan some conventional plants need to raise its power to participate in primary frequencycontrol.What if the BESS´s could enter service just after a contingency occurs, and not expectthat exceeds the dead band frequency?, the maximum frequency deviation (Nadir)?, therate will be reduced drop the frequency (ROCOF)?, or what would happen to the frequency deviations if the rated power of the BESS´s be greater than the current? Concern overthese questions led to a study to determine what would be the frequency deviations in theSING if BESS´s they were controlled an alternative and safe way (avoiding the intermittentoperation) so they could release their energy as soon as possible, and not wait on averagebetween about 2.5 and 3.5 seconds (according to information obtained in the reportsof failure of the CDEC-SING). This would be possible without causing any additionalrequirement to BESS´s as they have the ability to release energy for several minutes,taking care for less than seven minutes observed in actual operation, so that only itsoperation is brought forward.The cases analyzed show that with appropriate control that allows BESS´s enter servicejust after a contingency (untimely departure of a generation block) will cause a benefitto the system since the frequency deviations will be reduced his Nadir and ROCOF,depending on the analyzed contingency, that is, the generation block is disconnected, theywill be more or less noticeable, preventing operation of some step of EDAC underfrequencyunder normal conditions (without BESS) operate, which results in the continuity of supplyof blocks of heavy loads. These benefits will become more apparent the higher the rate ofgeneration of BESS´s. On the other hand, in a hypothetical situation in which the ratedpower of the BESS´s were higher, considerable benefits to medium-scale contingencies areobtained, even avoiding full operation of EDAC underfrequency as the existing excursiondoes not reach the minimum threshold activation, that is, 49 Hz.