Metrics for determining the frequency stability limits of a power system: A GB case study

Abstract

The changing power landscape introduces concerns about frequency management in a power system with significant amounts of non-synchronous sources of power. In islanded power systems like Great Britain and Ireland, electricity system operators are sometimes forced to undertake very expensive redispatch actions, including curtailing large amounts of renewable generation to meet statutory frequency stability constraints. Consequently, there is an imminent need to understand and quantify the limits that these constraints pose on the power system and develop metrics that can be easily integrated into current system planning and operational paradigm. This paper proposes three such metrics for quantifying the containment limits of a power system at a given operating point. The paper further argues that while the penetration of non-synchronous dispatch can indeed be used as the basis of a metric to define the containment limits of a power system, it does not account for variations in the contributions of other containment factors such as inertia. To address the aforementioned issue two alternatives are proposed: the first defines the containment limits of a power system without direct reference to penetration of non-synchronous power, instead it determines a relationship in terms of critical inertia. The second alternative improves upon the first and it considers the components of frequency stability constraints, offering an increased degree of flexibility in quantifying containment limits, and understanding the influence that certain key factors have on frequency containment.

Inertia and Frequency Support From Britain's AC Powered Trains

“…To investigate the effect that rail services could have had on the 9 th of August event a single bus model of the UK power network is utilised. The model was developed in DigSILENT PowerFactory [43] and has been validated in [44]. The model has been used previously by the UK ESO in a report assessing the system wide inertia and frequency response [45].…”

Study of the Inertia Support Potential From HVDC Cables in Power Systems With High Renewable Energy Source Penetration

“…The practical Rate of Change of Frequency (RoCoF) limit in future GB power system is estimated to be 0.5 Hz/s [33]. Therefore, 4 GW of power needs to be provided within 1 second to meet the requirement of system frequency balance.…”

An analysis of the August 9th 2019 GB transmission system frequency incident

“…Single Bus Frequency Model The single bus model developed in DigSILENT PowerFactory [19], described and validated in [20] and further applied in [17,21] is used to replicate and analyse the first 100s of the August 9th 2019 event. On moderately sized island systems such as that in Great Britain, a single bus model is typically sufficient in respect of modelling system frequency response in the event of disturbances and the performance of, or requirements for, frequency response services.…”

“…Demand sensitivity -the rate at which demand varies with system frequency -is included in the model and set at 2.5%/Hz [24]. -Demand (inertia): the contribution of demand to whole system inertia is modelled, in line with historical assumptions from the ESO as a motor load with an inertia constant of 1.83s applied to the transmission system demand [20]. It should be noted that this figure includes any contribution from synchronously connected DG.…”