  In small/medium-sized isolated power networks with low rotational inertia and
high penetration of renewables, generation/load contingency events may cause
large frequency excursions, potentially leading to cascading failures and even
blackouts. Therefore, it is crucial for system operators to be able to monitor
the state of the network in real-time and predict the maximum possible
frequency deviations at all times.
  This paper presents a real-time frequency stability (RTFS) tool developed by
the Australian Energy Market Operator (AEMO) and operationalized in the control
room for the South West Interconnected System (SWIS) to ensure that the
available spinning reserve is sufficient and fast enough to arrest frequency
excursions under any conditions, and particularly low-inertia ones. To reduce
the computational burden and complexity of the different turbine-governor
models, a simple first-order lag function with two adjustable variables has
been used for each of the generator. These adjustable parameters, along with
other key model parameters such as load damping and inertia, have been
calibrated against actual frequency response using high-speed fault recorder
data from historical events. As demonstrated in several case studies, the
real-time tool has proven to be accurate at predicting the trajectory of system
frequency after credible contingencies, thus suggesting that similar
implementations could be carried out elsewhere while power systems worldwide
progress towards lower inertia.
