## 4 The Architecture of the ASI (Figure 1)
#### The Input Module  
The Input Module monitors the state of the system at the ASI location. The values measured are the current and voltage and from these values, the real and reactive power, frequency and apparent impedance are calculated. Breaker status and certain impedance relay quantities are also monitored.  
These calculated values are transformed into system parameters by the internal algorithms of the Input Module.  
Some of these system parameters include the rate of change of:  
The apparent resistance  
The bus voltage  
The frequency  
Voltage with real power  
Voltage with reactive power  
The internal algorithms that produce these system parameters mark the beginning of the ASI process since no progress can be made without these parameters. The patterns that they form and the functions that they fulfill are all the work of these algorithms as discussed in the Methodology.  
_The Predictive Module_  
The Predictive Module stores the system parameters supplied by the Input Module as well as the system parameters that it calculates from the simulation of system disturbances carried out off-line at the ASI location. The Predictive Module then compares these two sets of system parameters to determine if a system disturbance is occurring and its degree of severity in terms of a Performance Level which it will transfer to the Output Module.  
The Predictive Module is a processing model based on data- mining technology. It predicts the system Performance Level at a specific location by processing and analyzing historical and real-time parameters. This model is constructed from five basic performance characteristics that are sensitive to system stress. As illustrated in Figure 1, these characteristics comprise transient power swing, transient voltage, transient frequency, voltage instability and steady-state limits. These characteristics generate the ASI Predictors and are discussed in detail in the Methodology dealing with the associated algorithms.  
_The Output Module_  
The Output Module stores the Performance Levels supplied by the Predictive Module and will initiate an alert to the System Operator if the Performance Level indicates a stressful condition in the system.  
Thus the output of this module is a stress-level indicator corresponding to the severity of a disturbance at a given location. The stress-level indicator ranges from having no appreciably adverse effects to having a substantial effect. As indicated in Figure 1, four levels describe the states Normal, Alert, Emergency and Extreme (NAEX). These levels correspond to the North American Electric Reliability Council/Western Electricity Coordinating Council (NERC/WECC) Planning Standards [10].  
The methodology for the operation of an ASI is now discussed in terms of the functions associated with these three modules and their embedded algorithms.  
The Output Module could be considered as the stress-alert device since its function is to alert the System Operator of the degree of severity of the system disturbance.  
The real question is whether there is time to identify the severity of a system disturbance and predict its consequences.  
Perhaps the first application of ASI should be limited to the A (Alert) state.