IEEE International Conference on Smart Energy Grid Engineering (SEGE), 2015 17-19 Aug. 2015, Oshawa, ON, Canada DOI: 10.1109/SEGE.2015.7324601
Modeling and Simulation of ICT Network Architecture for Cyber-Physical Wind Energy System Mohamed A. Ahmed1, Yong Cheol Kang1,2, Young-Chon Kim1,3,* Dept. of Electrical Engineering2, Dept. of Computer Engineering3 WeGAT Research Center1, Smart Grid Research Center, Chonbuk National University Jeonju, Korea {mohamed, yckang}@jbnu.ac.kr, *Corresponding author:
[email protected] Abstract—There are many challenges and concerns about the impact of integrating more and more wind power farms (WPFs) into the power grid. A WPF can be considered as a cyberphysical energy system (CP-ES) due to the coupling between the physical power system and the cyber communication network. While the information and communication technology (ICT) infrastructure is the key concept to support a reliable operation, real-time monitoring and control of large-scale wind farms, it has been less addressed and rarely discussed. This work aims to design the ICT network architecture for a cyber-physical wind energy system (CP-WES) which consists of wind turbines, meteorological masts, substation, and a local control center. We consider different applications: operation data (analogue measurements & status information) from wind turbines, meteorological data from the meteorological towers, and protection & control data from intelligent electronic devices (IEDs). A real wind farm project (Zafarana-1, Egypt) has been considered as a case study. The proposed ICT network architecture is modeled and evaluated using OPNET Modeler. Network topology, link capacity, and end-to-end delay are three critical parameters investigated in this work. Our network model is validated by analyzing the simulation results. Keywords—wind power farm (WPF); Cyber-physical wind energy system (CP-WES); information and communication technology (ICT).
I. INTRODUCTION Nowadays, with the direction toward electricity generation from renewable energy resources, many projects of large-scale wind power farms (WPFs) are scheduled to be constructed in the near future. This expected growth in WPFs will significantly affect the monitoring, operation and control of today electric power grid. In this direction, information and communication technology (ICT) will play an important role to support the real-time monitoring and protection of both electric power system and wind turbines. Due to the coupling between the physical power system and the cyber communications network, WPFs are considered as a typical cyber-physical energy systems (CP-ESs) [1]. In view of wind farm electric power system, several research work and investigations have been carried out to study the wind farm sub-systems (wind turbine, collector system, substation, etc.) which have been addressed and discussed in many publications. However, the supervisory control and data acquisition (SCADA) systems and
the underlying communication network infrastructures are relatively less addressed and rarely discussed [2-4]. A typical WPF consists of wind turbines, meteorological system, local wind turbine grid, collecting point, transformers, and substation. Cables with different cross section areas are used to connect among wind turbines which are connected to the utility system through transformers and distribution lines [5]. From the communication network point of view, the communication network usually follows the electric topology configuration. However, different electric/communication topologies may be configured based on wind farm size. The main function of the ICT infrastructure is to transmit measured information and control signals between wind turbines and the control center [6-9]. This work aims to design the ICT network architecture for a cyber-physical wind energy system (CP-WES) where both the electric power system and the underlying communication network are interdependence and tightly connected. The physical power system consists of wind turbines, local wind turbine grid, transformers, and a substation, while the cyber communication network consists of network components (servers, switches, routers, network cables, etc.) and measurement devices (sensors, intelligent electronic devices, etc.). The communication network within WPF is regarded as a local area network (LAN). A Real wind farm project (Zafarana-1, Egypt) has been considered as a case study. Three critical parameters: network topology, link capacity and endto-end (ETE) delay have been investigated and discussed. This paper is organized as follows. Section 2 gives an overview of the cyber-physical wind energy system, wind farm electric topology, wind farm SCADA systems, and wind farm communication infrastructure. Section 3 shows the proposed ICT network architecture for a case study of a real project (Zafarana-1 wind farm, Egypt) and the simulation results. Finally, Section 4 concludes. II. CYBER-PHYSICAL WIND ENERGY SYSTEM A. Grid Integration of Wind Power Farms A typical electric power system consists of power generation, transmission, distribution and customers as shown in Fig. 1. The future smart grid aims to enable the two-way flow of electricity and information with the target to make the
conventional electric grid more reliable, efficient and secure. In this direction, the ICT will play an essential role in order to bring the future smart grid into a reality [4]. In view of wind energy, as more and more wind turbines are integrated into the power grid, the monitoring scope has been expanded from monitoring individual wind turbines to cover the whole wind farm as well as the electric substation [6]. In such architectures, the communications network are considered the essential part that allow the exchange of measured information and control signals between the wind turbines and the control center. With the huge amount of monitoring data that need to be communicated with the control center, the network infrastructure will become a bottleneck. B. Wind Farm Physical Power System Generally, WPF is defined as a group of wind turbines connected together and tied to the utility through a system of transformers, transmission lines, and a substation. A wind turbine generator consists of the wind turbine itself, circuit breaker, and step-up transformer. The generation voltage of each wind turbine is stepped up using the step-up transformer. Wind turbines are divided into groups, and each group is connected to collector bus through a circuit breaker. Multiple collector feeders are connected to high voltage (HV) transformer which steps up the voltage to transmission level [10-11]. Figure 2 shows a single line diagram of a typical WPF. The WPF is divided into different zones: wind turbine zone, collector feeder zone, collector bus zone, high voltage transformer zone and transmission line zone. C. Wind Farm SCADA System The wind farm main components are wind turbines, meteorological system and electric system [12]. The SCADA systems are used for data acquisition, remote monitoring, realtime control, and data recording [13]. It remotely collects the process information from wind farm components and based on the collected information, the control center executes appropriate actions. Each WPF has a dedicated connection to a local control center for real-time monitoring and control. However, one control center can remotely manage and control one or more WPFs. There are multiple applications covered by the SCADA systems in a WPF. The three main applications are Turbine SCADA system, Wind Farm SCADA system and Security SCADA system [2], [7]. •
Turbine SCADA system provides the connectivity among wind turbines and enables the control center operator to remotely monitor and control each wind turbine and their associated sub-systems.
•
Wind Farm SCADA system provides the control center operator with the status of all devices in a WPF such as wind turbines, meteorological masts, electric substation system, protection and control devices (IEDs), etc. The main function is to connect all devices from all wind turbines, as well as the electric substation together.
•
Security SCADA system provides the IP telephony services and video surveillance system for the WPF.
Fig. 1. Grid integration of a wind power farm.
Fig. 2. Single line diagram of typical wind power farm.
D. Wind Farm Cyber Communication Infrastructure The SCADA communication network for WPF is based on Switch-based architecture, which consist of Ethernet Switches and communication links in every wind turbine [7]. The communication infrastructure provides the connection among wind farm elements, and is divided into two parts: turbine area network (within a turbine) and farm area network (between wind turbines and control center) [14-15]. Inside a wind turbine, there are a number of propriety communication protocols used such as field bus, industrial Ethernet protocols, and control area network (CAN) [16]. For a wind farm, pointto-point (P2P) communication and local area network (LAN) based on Ethernet-based architecture can be used for network configuration. In order to link the wind farm network with a remote control center, different wide area network (WAN) technologies wired/wireless could be configured such as optical fiber cables, microwave, and satellite. Figure 3 shows the wind farm SCADA communication infrastructure which consists of three hierarchical levels: process level, bay level, and station level.
one bus, and one transformer. The proposed ICT network architecture has been constructed using Switch-based architecture.
Fig. 3.
SCADA communication network architecture of a wind farm.
III. CASE STUDY: ZAFARANA WIND POWER FARM The Zafarana wind farm project is located in Egypt, approximately 190 Km Southeast of Cairo. The average annual wind speed is about 9.5 m/s. There are many projects have been constructed in different stages since 2001. The projects are named Zafarana-1 (30 MW- 50 WTs- 600 KW), Zafarana-2 (33 MW- 55 WTs- 600 KW), Zafarana-3 (30 MW- 46 WTs660 KW), Zafarana-4 (47 MW- 71 WTs- 660 KW), Zafarana-5 (85 MW- 100 WTs- 850 KW) and Zafarana-6 (80 MW94WTs- 850 KW) as shown in Fig. 4. In 2010, the wind farm total installed capacity was 545 MW, which includes 700 wind turbines from different models (Nordex, Vestas, and Gamesa) [11] [17-18]. The Zafarana-1 project has been considered as a case study in this work.
1) Modeling the process level. The process level includes sensor nodes (SNs) and measurement devices (MDs) which are the basic data sources. Both the SNs and MDs are connected to different elements of WPF, where the main function is only to report the measurements such as temperature, speed, voltage, current and pressure [19]. The condition monitoring system (CMS) at wind turbine is continuously collecting a large volume of data signals in real time. Then, wind turbine controller (WTC) performs the control operation for the wind turbine based on data collected from CMS, sensors, and other devices. Also, the data of the weather condition such as wind speed, wind direction are collected using meteorological towers. Table 1 lists the types of wind farm traffic at the process level. For a wind turbine, the total number of sensor nodes and measurement devices are 102 based on IEC 61400-25, as shown in Table 2 [14].
Fig. 5. Zafarana-1 wind farm project. Note: The distance is extracted from Google Earth based on wind turbines location.
WIND FARM TRAFFIC AT THE PROCESS LEVEL.
TABLE I. Traffic
Type Analogue Measurements Status Information Meteorological data
Monitoring Protection
Protection Information
Control
Control Instructions
TABLE II.
Fig. 4.
Zafarana wind power farm [11].
A. Proposed ICT Network Architecture for Zafarana-1 The Zafarana-1 project consists of 50 wind turbines (Nordex N43). The wind turbines are arranged in two rows with a total capacity of 30 MW, as shown in Fig. 5. We assumed that the electric topology consists of three feeders,
Direction Uplink Continuous Uplink Continuous Downlink /On Demand
CONDITION MONITORING PARAMETERS FOR WIND TURBINE
Turbine Subsystem
Number of Sensors
Number of Analogue Measurement
Number of Status Information
Rotor Transmission Generator Converter Transformer Nacelle
14 18 14 14 12 12
9 10 12 12 9 8
5 8 2 2 3 4
Yaw
7
5
2
Tower Meteorological TOTAL
4 7 102
1 7 73
3 29
2) Modeling the bay level. The bay level includes the protection and control intelligent electronic devices (P&CIEDs). The IEDs are located at different portions of the WPF. Based on the IEDs function, there are five types of P&C devices: circuit breaker (CB) IED, merging unit (MU) IED, transformer (T) IED, feeder (F) IED, bus (B) IED and line (L) IED [20-24]. Given the CB-IED as an example, it control the breaker (open/close), monitors the status and condition of the CB, and receive command (trip/close) from P&C-IEDs or control center. If the breaker condition changed, it would send a state change event to P&C-IED. The IEDs configuration of Zafarana-1 project is given in Table 3. We assumed that each wind turbine generator (WTG) has a merging unit acquire current, voltage, and breaker signals for substation automation. Data packets are transmitted over a communication network to a central relaying unit (CRU) for P&C functions of the whole wind farm [10]. For MU-IEDs, we assumed that the sampling frequency of the voltage and current data are 6400 Hz for a 50 Hz power system, and each sampling data is represented by 2 bytes [25]. Considering 3phase voltage and current measurement, the MU-IEDs are sending updated values of 76,800 bytes/s to the P&C server at the local control center. Also, the CB-IED is sending a status value of 16 bytes/s to P&C server [23]. The wind turbines, feeders, and bus are modeled as a subnet consists of one CBIED, one MU-IED, one P&C-IED and one Ethernet Switch as shown in Table 3. The configuration of data flow for different IEDs are given in Table 4. TABLE III.
network architecture for Zafarana-1. In this work, only group 1 with 17 WTs (17 MU-WTG and 17 CB-WTG) was considered. The first task is to validate the network model by comparing the generated amount of traffic from different IEDs with the received traffic at the control center server. The CB-IEDs and MU-IEDs were configured to send their messages (given in Table 4) to the protection and control server at the local control center. The Server FTP traffic received traffic is about 368 bytes/s (23 CB-IEDs*16 bytes/s) and 1,689,600 bytes/s (22MU-IEDs*76,800 bytes/s) for CB-IEDs and MU-IEDs, respectively. The simulation results shown in Fig. 8 agree with our calculations discussed in the previous section.
IED CONFIGURATION FOR ZAFARANA-1 PROJECT Zone
MU IED
P&C IED
CB IED
Wind Generator (WTG) Collector Feeder (F1, F2, F3) Collector Buse (B1) Substation Transformer (T1)
1 1 1 1
1 1 1 1
1 1 1 2
TABLE IV.
Fig. 6.
Proposed ICT network architecture of CP-WES for Zafarana-1.
Fig. 7.
OPNET model of ICT network architecture for Zafarana-1.
TRAFFIC GENERATION OF IEDS
Parameter
Type
From
MU-IED
Sampled value message 3-phase V, I
MU
CB-IED
Send Breaker Status
CB
To Station Server Station Server
Data Generation 76,800 bytes/s 16 bytes/s
3) Modeling the station level. The station level consists of three servers: SCADA server, protection, and control server, and meteorological mast server. Servers are used to store the data received from different wind farm applications. The control center executes appropriate actions based on the received data. B. Substation Automation Results The OPNET Modeler is used for network modeling and simulation of the proposed ICT network architecture. The Zafarana-1 WPF consists of 50 WTs divided into three groups: group 1 (17 WTs), group 2 (17 WTs) and group 3 (16 WTs) as shown in Fig. 6. Figure 7 shows the OPNET model of ICT
Fig. 9.
Fig. 8.
Traffic received at the protection and control server.
The second task focuses on the network performance by measuring the end-to-end delay for different WPF applications. It was observed that using 10Mbps for LAN speed is not sufficient, where the amount of network traffic is much higher than the channel capacity. The results obtained for the minimum and maximum end-to-end delay for the protection and control IEDs of the WTGs using LAN speed of 100Mbps and 1Gbps are shown in Table 5. The maximum E2E delay was about 12.99 ms for MU-IED and about 2.29 ms for CBIED. Table 6 shows the timing requirement for different applications based on IEEE 1646 standard of electric substation automation. Using 1Gbps for LAN speed satisfies the timing requirement for protection information of wind turbine generator as given in Table 5. The end-to-end delay of MU-IEDs for feeder protection (F1, F2, and F3) is shown in Fig.9. TABLE V.
ETE-DELAY OF WTG-IEDS
Wind Turbine Zone LAN Speed (Mbps)
End-to-end Delay (ms) Min
Max
100
CB-IEDs MU-IEDs
1.017 12.533
2.290 12.995
1000
CB-IEDs MU-IEDs
0.152 1.254
0.329 1.296
TABLE VI.
ETE delay of MU-IEDs for feeder protection (BW:100Mbps).
C. Real-Time Monitoring Data Results In this section, the design of the communication network infrastructure for Zafarana-1 is drawn from real large-scale projects such as the Horn Rev project in Denmark [8] and the Greater Gabbard project in United Kingdom [7]. This section shows the results obtained for the network modeling of SCADA system for group 1 of Zafaran-1 WPF (17 wind turbines and a meteorological tower). Table 7 shows the assumptions for different SCADA applications [14]. The traffic received at control center (SCADA server and MET Mast server) is shown in Fig. 10. The traffic received for analogue measurements, status information, and meteorological data are 3834248 bytes/s (225544*17), 986 bytes/s (58*17) and 1670 bytes/s, respectively. Figure 11 shows the ETE delay for realtime monitoring data. In case of 100Mbps channel capacity, the average ETE delay for SCADA and MET mast data was about 11ms and 1.4ms, respectively. In case of 1Gbps, the average ETE delay for SCADA and MET mast data was about 1.1ms and 0.46ms, respectively. TABLE VII.
WIND FARM MONITORING TRAFFIC
Type
From
To
Data Generation
Analogue Measurements Status Information
Wind Turbine MET Tower
SCADA Server Station Server
225,544 bytes/s 58 bytes/s
Meteorological data
1,670 bytes/s
TIMING REQUIREMENTS FOR DIFFERENT APPLICATIONS BASED ON IEEE 1646 STANDARD
Information Type
Internal
External
Monitoring and control
16 ms
1s
Protection
4 ms
8-12 ms
Operation and maintenance
1s
10 s Fig. 10.
Traffic received at the SCADA and MET Mast servers.
[5]
[6]
[7]
[8]
[9]
[10] Fig. 11.
Average ETE delay for SCADA and meteorological information. [11]
IV.
CONCLUSION
With the direction to maximize the penetration level of wind energy, reliable monitoring, operation and control are needed to ensure the grid stability. This work aims to design the ICT network architecture for a cyber-physical wind energy system. The WPF consists of wind turbines, meteorological towers, substation, and a local control center. For various wind farm applications, we defined and explained the data types, data volume and data interval on different WPF levels: process level, bay level, and station level. A real wind farm (Zafarana-1, Egypt) is considered as a case study to evaluate the proposed ICT network architecture. Simulation results showed that using a channel capacity of 1Gbps satisfies the requirements of IEEE 1646 Standard for the substation automation. Future work aims to design a co-simulation framework that integrates both the wind farm electric system and the communication network using the real-time digital simulator (RTDS) and the optimized network engineering tools (OPNET). ACKNOWLEDGMENT This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (2010-0028509).
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