## 4 Classifications in Cyber Attacks
### Detection and Identification Methods
Phasor measurement units (PMUs) are used to account for monitoring time and control measures in the electrical grid. The principle of working is based on the equations shown below:  
\[x(t)=X_{m}\cos(\omega t+\varphi) \tag{1}\]  
Equation (1) can be represented as  
\[X=\frac{X_{m}}{\sqrt{2}}e^{j\varphi}=\frac{X_{m}}{\sqrt{2}}(\cos\varphi+j\sin \varphi)=X_{r}+jX_{i} \tag{2}\]  
where \(X_{m}\) isthe peak value of the waveform and \(\varphi\) is the phase angle depending on the timescale at \(t=0\). A functional block diagram of a PMU is shown in Figure 7.  
For the three phase AC current or voltage waveforms, PMU (electronic device) provides synchrophasors and frequency measurements. PMU uses hybrid processors to capture signal phase and three phase voltages and currents. The captured signal is passed through the front end anti-aliasing filter and for the elimination of signals of high frequency and digitalized using A/D converter. A synchronized GPS clock provides a fixed sampling rate. The digitized signals and the carrier signal are multiplied to obtain the real and imaginary parts of the phasor. The resultant signal is passed through the backend performance class filter for proving the required accuracy during transient conditions. The final values are used to estimate the voltage, current, phase, frequency and rate of change of frequency (ROCF). In earlier days, SCADA was used to effectively monitor a power system based on steady-state power flow analysis. However, with the help of ST, dynamic measurements can also be made. Table 4 shows the differences between SCADA and PMU. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Features** & **Supervisory Control Aspects** & **PMU** \\ \hline Least Count & One sample every Two-Four/s & Ten-Sixty samples/s \\ \hline Observability & Settled Condition & Transient \\ \hline Measurement & Voltage and Current & Voltage, Current, Frequency and ROCOF \\ \hline Synchronization & Not considered & Considered \\ \hline Phase Angle & Not considered & Considered \\ \hline Focus & Local monitoring and control & Large area monitoring and control \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Differences between SCADA and PMU. Figure 7: PMU block diagram. The architecture of ST is shown in Figure 8 and consists of measurement layer, data collection layer and energy management layer. Many critical measurements are used to communicate with the data of PMU and with the rest of the grid. The measurement layer consists of PMUs, current and potential transformers and analog units. GPS are installed in PMU in order to record the location of the transformers and store data. The Phasor data concentrators (PDC) receive the data from the PMU. PMU collates all data available from different measurements. Functions of PDC include data monitoring, synchronization, processing, and storage in the data collection layer. During normal operations, the major substation connected through PMU and the data transmission is performed using fiber optics. A locally available PDC collects the data and stores it in a database. It is through this channel that the PDC sends the data to a control room. Major applications of ST in a power system are large area recognition and observation of frequency, voltage stability and identification. Several IEEE standards of synchrophasors are shown in Table 5.