# Communication Architecture for Grid Integration of Cyber Physical Wind Energy Systems
## 3 CPWES Modeling and Assumption
### Traffic Model for an Offshore Substation Based on IEC 61850  
In this work, a WF is divided into different protection zones: the wind turbine zone, collector feeder zone, collector bus zone, and high-voltage transformer zone. Each zone has one or more protection devices associated with it, such as a wind turbine protection relay, step-up transformer protection relay, feeder protection relay, bus protection relay, and distance relay for the transmission line [22]. We considered three types of IEDs: a breaker IED, merging unit (MU) IED, and protection and control (P&C) IED [23; 24; 25; 26]. Based on IEC 61850, the function of a MU IED is to acquire the voltage and current signals from the field CT and PT. The function of a CB IED is to monitor the state and control the condition of the circuit breaker. Furthermore, it receives control signals from the P&C IEDs and updates the status change to the protection IEDs. The P&C IED is a universal device that integrates protection and control functionalities and operates at the bay level in the substation. All acquired signals from different zones were transmitted to the central protection and control (CPC) system on the offshore substation using point-to-point fiber communication. We considered one CPC system, which is responsible for all protection and control devices in the WF, as shown in Figure 5. In addition, each wind turbine generator (WTG) was configured with a merging unit to acquire current, voltage, and breaker signals for wind turbine protection. Data packets were transmitted over a communication network to a central relaying unit (CRU) for P&C functions of the whole WF. For MU-IEDs, we assumed that the sampling frequency of the voltage and current data was 6400 Hz for a 50 Hz power system, and each piece of sampling data was represented by 2 bytes [27]. Considering the 3-phase voltage and current measurement, the MU-IEDs send updated values of 76,800 bytes/s to the P&C server at the local control center [25]. Moreover, the CB-IED sends a status value of 16 bytes/s to the P&C server. The details of the process level, bay level, and station level are as follows:  
* Process Level: The primary equipment includes merging units (MUs), actuators, and I/O devices. * Bay Level: The secondary equipment includes different IEDs and protection relays. * Station Level: It is located on the offshore platform and includes a central protection and control unit, remote terminal units (RTU), and a human machine interface (HMI). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sensor Type** & **Sampling Frequency** & **Sample Size** & **Number of Channels** & **Data Rate** \\ \hline Temperature & 1 Hz & 16 bits & 1 & 2 bytes/s \\ Wind Speed & 1 Hz & 16 bits & 1 & 2 bytes/s \\ Displacement & 10 Hz & 16 bits & 2 & 40 bytes/s \\ Vibration & 200 Hz & 16 bits & 3 & 1200 bytes/s \\ Voltage & 2048 Hz & 16 bits & 3 & 12,288 bytes/s \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Measuring requirement for sensor nodes. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**LN** & **\# Sensors** & **Data Rate** & **LN** & **\# Sensors** & **Data Rate** \\ \hline _WROT_ & 14 & 642 bytes/s & _WNAC_ & 12 & 112 bytes/s \\ _WTRM_ & 18 & 2828 bytes/s & _WYAW_ & 7 & 220 bytes/s \\ _WTGEN_ & 14 & 73,764 bytes/s & _WTOW_ & 4 & 8 bytes/s \\ _WCNV_ & 14 & 74,060 bytes/s & _WFOU_ & 6 & 1434 bytes/s \\ _WTRF_ & 12 & 73,740 bytes/s & _WMET_ & 7 & 228 bytes/s \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Traffic configuration for a wind turbine. The communication network was constructed based on ethernet-based architecture. The offshore substation consisted of three feeders, one bus, and one transformer. Protection devices at wind turbines, feeders, and bus were modeled as a subnet consisting of one CB-IED, one MU-IED, one P&C-IED, and one ethernet switch. The step-up transformer was modeled as a subnet consisting of one CB-IED, one MU-IED, two P&C IED, and an ethernet switch. Table 4 shows the IEDs configuration.