PON: Delivering Reliable Communications for Wind Farms
| By Jiang Nan, Energy Industry Marketing Manager, Huawei Enterprise Business Group
Wind is a clean, renewable energy source widely used for generating electricity. Because wind resources fluctuate greatly, it is crucial that power companies stabilize the feed to the transmission grid. Apart from electrical monitoring and control, modern wind farms are adding services such as IP phones and video surveillance for equipment and environment monitoring.
Challenges Facing Traditional Wind Farm Infrastructure Networks
The standard configuration for turbine monitoring networks has been industrial Ethernet switches in a ring topology. The problem is that when a turbine fails or is stopped for inspection and maintenance, the Ethernet switch connected to that turbine are also powered off. When two or more Ethernet switches in the ring are down, the entire ring fails. Restoring the turbine-monitoring network to full power is extremely difficult even at land-based wind farms, to say nothing of the challenge of restoring an installation 12 kilometers offshore. Wind farm managers can solve this problem by using Ethernet switches that incorporate "optical bypass," though, only a handful of manufacturers make this type of Ethernet switch and are considered cost prohibitive.
Ethernet-based wind farm turbine monitor networks serve critical tasks, and face multiple challenges. The primary task for the monitoring infrastructure is to collect operating status and production data in real time, and in turn, use this data to remotely control the turbines, generators, and transformers. The control system is crucial to the security and reliability of power generation. Other real-time data feeds include wind speed and direction, power output, blade rotation speed, and generator rotation speed. Each Ethernet switch in the ring transmits the data of the turbine to which it is connected, and also the data in transit throughout the ring. The challenge when adding new services, especially voice and video, is maintaining Quality of Service (QoS) for the legacy services and applications. Additional points of failure are introduced when new interfaces are deployed to connect low-speed devices with high-speed optical networks. Increasing construction costs are a further complication.
PON Becomes Mainstream Broadband Access Technology
Standardized in mid-1990s, Passive Optical Network (PON) technology is widely used by telecom carriers for Fiber-To-The-Home (FTTH) rollouts. PON consists of Optical Line Terminals (OLTs) located at the carrier central office, Optical Network Units (ONUs), or Optical Network Terminals (ONTs), deployed near end-user locations, and an Optical Distribution Network (ODN) consisting of a passive optical interconnect for these various elements. The OLT central office downlink broadcasts IP, voice, and video data streams over 1:N passive optical splitters on the ODN to different ONUs. The uplink data streams from different ONUs are aggregated on the 1:N passive optical combiners on the ODN and then transmitted to the OLT over a single strand of fiber. This scheme ensures zero interference between data streams. EPON and GPON (collectively: xPON) are the two dominant PON technologies. With flexible bandwidth allocation and ease of maintenance, xPON is now routinely deployed to eliminate the "last-mile" bandwidth bottleneck.
The State Grid Corporation of China (SGCC) started using PON technologies to build communications networks for power distribution automation in 2009, including remote measurement, monitoring, control, and adjustment. PON technologies have since been widely applied throughout the power industry.
Delivering Improved Communications Reliability for Wind Farms
The xPON family of transmission technologies is replacing traditional Ethernet rings for advanced services on electric turbine wind farms. The benefits of PON include improved reliability, enhanced efficiency, reduced maintenance requirements, support for various communications interfaces, higher bandwidth availability for multiple services, and flexible networking.
Passive optical splitter reduces the possible points of failure in a deployed network. Each ONU communicates directly with the OLT, where, unlike Ethernet rings, if a turbine fails or is stopped for maintenance, only the directly connected ONU is affected. This feature greatly improves communications network uptime. The superior scalability of xPON allows each turbine to be put into production immediately following construction and installation, accelerating the ramp up to full power generation.
- Enhanced Efficiency, Low Maintenance and Management
In an xPON-based communications network, congestion is eliminated by assigning each ONU to a single turbine. Further, xPON guarantees QoS and provides network management access for many service level parameters, including latency, jitter, and minimum-maximum bandwidths. xPON also allows signal prioritization, collection in the uplink direction and control in the downlink, to ensure the highest-priority data is transmitted smoothly regardless of concurrent demand.
xPON supports a remote, visualized network management approach, which delivers higher O&M efficiency when compared to traditional Ethernet ring topologies.
- Support for Various Communications Interfaces
xPON uses RS232/RS485 serial interfaces customized for electric industry deployment scenarios. Industrial Ethernet switches use optical interfaces to connect upstream equipment, and metallic interfaces to connect to downstream equipment. The xPON eliminates the complexity of the traditional requirement for each turbine to have a server with serial interfaces or an interface converter for communicating with the Ethernet switches. The benefit is that fewer interface converters are required. Maintenance costs and possible points of failure are all reduced.
- Higher Bandwidth Availability for Multiple Services
Given a download bandwidth of 2.5 Gbit/s and an upload bandwidth of 1.25 Gbit/s, xPON is in a superior position to support video surveillance and other bandwidth intensive services. A traditional Ethernet ring network typically provides a shared bandwidth of only 100 Mbit/s.
An xPON can be deployed in a ring, chain, or tree configuration, offering greater scalability and flexibility. Capacity expansions at PON-equipped wind farms do not interrupt the operation of existing services.
As a result of these multiple benefits, xPON technology is ideal for communications network build-outs for wind farms. xPON offers higher reliability than traditional Ethernet rings and provide ample bandwidth for multiple, advanced services.