A secure and reliable power system that meets Singapore’s current and future electricity needs is the result of detailed system planning that involves the large-concentrated and small-distributed generating plants design, electricity transmission development and so on. The role that the Power System Operation Division (PSOD) plays in the different aspects of system planning is briefly enumerated below.

Review of Development Plan for Transmission Network

Power System Operator reviews Singapore’s long-term electricity transmission system development plan submitted by the Transmission Licensee to ensure that the transmission network meets the planning criteria stipulated in the Transmission Code.

Access Design & Impact of Proposed Generating Plants

Power System Operator reviews the design of generating plants that plans to connect to the power system. It also assesses their impact on the stability and security of the power system. This includes reviewing of test plans and witnessing of site test to ensure the generating plants’ compliance with requirements stipulated in the Transmission Code.

Intermittent: Renewable energy sources like wind & solar are considered Intermittent Distributed Generators. Due to the intermittency in their generation output, assessing their impact on power system operation poses a major challenge to the Power System Operator. As more renewable sources are expected to be installed in the near future, assessments of their performance would provide a better gauge of how these intermittency could be   better managed and mitigated.

Co-generation: The need for electricity, steam and cooling from industries like petrochemicals and pharmaceuticals drives the requirements for combined-heat power (CHP) plants. The capacity of these CHP plants varies from 1MW to 110MW. These CHP plants are connected to the power system at the both the transmission and distribution network and are typically non-frequency responsive operating at base-load. Proliferation of such plants could displace the conventional frequency responsive generating plants that provide spinning reserve essential for secure operation of the power system. Hence, allowable capacity of the non-frequency responsive plants has to be assessed with rigorous engineering studies.

Inter-dependency of Gas & Electricity System

About 80% of Singapore's electricity is generated from combined cycle plants using natural gas. Natural gas disruption has significant impact on the secure operation of the power system and vice versa. The PSOD conducts studies on the inter-dependency of the electricity and gas systems to assess these effects and possible mitigation measures.

Demand Response (IL) Facility

PSOD initiated the Interruptible Load (IL) scheme for the National Electricity Market of Singapore (NEMS) on 1 Jan 2004. This is an important development in Singapore’s liberalisation of its electricity industry, where the consumer (‘load’) can also participates in the spinning reserve market.  This scheme enables the  consumers to voluntarily choose to have their electricity supply interrupted in exchange  for reserve payment, thereby competing with the generating plants directly in the reserve market. Depending on the types of reserves the consumers intend to participate in, these ILs should either be disconnect  automatically once the system frequency reaches a preset threshold setting or are manually disconnected by the IL provider when instructed. To ensure inadvertent non performance of ILs does not compromise power system security, PSOD estimate the safe quantum of ILs that can be scheduled as reserve. This quantum is review annually.

Operating Reserve Policy

The reserve margin is defined as the amount by which the total generation capacity exceeds the annual electricity peak demand. In Singapore, the minimum reserve margin to maintain system security is currently 30%, based on a loss of load probability ('LOLP) of 3 days per year. The 30% required reserve margin is to cater to scheduled maintenance as well as forced outages of generating units in the power system.

Spinning Reserve (SR) is called upon to arrest decay in the power system frequency in the event of sudden outage of any generating unit and to return the power system frequency close to the nominal value of 50Hz as soon as possible. Insufficient SR could lead to load lost under such contingency. Under normal operating condition, SR must be sufficient to cater for tripping of the largest on-line generating unit.

The power system must match aggregate generation and load instantaneously and continuously. Regulation Reserve (RR) is employed to achieve this generation/load balance in order to maintain the system frequency close to 50Hz with an allowable deviation of ±0.2Hz. The RR requirement can vary from one dispatch period to another and is reviewed annually based on historical records of actual RR used.

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