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  November, 2007
Winds of Change - Using OPC in Guaranteed Data Delivery for Wind Farms
by Eric Murphy

High oil prices and global warming concerns have more people looking at renewable energy sources such as wind power. Wind power installations have unique challenges of diverse locations of multiple generating stations. OPC can provide continuous access to real-time information needed for equipment monitoring and making production decisions.

Harness the Wind
People have harnessed the wind for energy for thousands of years, and technology has been steadily reinvented and improved. The cost of energy production is continually decreasing as strides are made in material usage, rotor design and turbine technology. This gives wind power more competitive footing with conventional fossil fuel based energy sources. Successful integration of renewable energy into utility portfolios is increasing, yet owners and operators still face many business challenges. Optimizing operations, effective maintenance and increasing the accuracy and timeliness of decisions all affect the bottom line. Not to mention issues like utility integration, accurate data analysis and forecasting and scheduling energy output. All these business aspects require reliable real time data for making effective decisions.

Wind power is converted to electricity by a wind turbine. A wind farm consists of multiple wind turbines in the same location, although the may not all come from the same vendor. In addition to data from multiple generating turbines, information is needed about the substations and utilities, as well as key meteorological data. Wind farm systems may contain up to hundreds of windmills, covering long distances and harsh environments. Users need a reliable communication network capable of providing standardized information monitoring and centralized control and data storage.

The Answer is Blowing in the Wind
OPC can provide real time data access for remote supervision, control, and data acquisition required for operation and maintenance. It also is a means of standardized communication among energy management centers and regulatory bodies. High resolution data is essential for optimizing wind farm assets and realizing incremental gains critical to improving the bottom line. OPC not only overcomes the challenges of gathering data from various sources into a centralized repository, but also ensuring guaranteed deliver of the data, even if it spans different manufacturers, technological generations or geographical locations.

OPC enables interoperability between disparate control systems, condition monitoring and production management systems. OPC DA provides plug-and-play connectivity between the various wind farm data sources. The OPC specification ensures that regardless of the underlying system and the product vendor, the interfaces will connect and exchange data in the same way. MatrikonOPC has OPC DA enabled products available for common turbines protocols such as Modbus. OPC servers are also available for common wind farm SCADA platforms such as Rockwell Allen-Bradley, Siemens and GE Fanuc. For connectivity with common electrical utility protocols like DNP 3.0 and IEC 60870-5, MatrikonOPC offers full telemetry grade OPC servers that include redundant communication channel support.

Changing Winds and Constant Data
Historized data from the wind farms is used for many functions including efficiency improvements, statistical process control, quality assurance and reporting. Storing the real time process data allows wind companies to create genealogical records of processes, track equipment conditions and better forecast and schedule energy production.
Reliance on this critical data means it is becoming increasingly important to guarantee that all data from an OPC server is accurately recorded in history. Some method is needed to ensure data is not lost or corrupted during times of communication loss between the historian and the OPC server.

Most ‘home grown’ or ad-hoc systems involves a proprietary data collection format that begins buffering data to a custom binary file in the event communication is lost with the historian.

Although these systems do the job, they have several disadvantages over a standard OPC HDA architecture;
1. The solutions are proprietary to the historian manufacturer. This makes it difficult to standardize on a single architecture for multiple wind farms.
2. The interim stored data is usually in a proprietary, inaccessible format. Applications must wait for communications to the historian to be restored and the buffer emptied before the critical data can be accessed.
3. The solutions have not been designed for redundant systems.

The OPC HDA (Historical Data Access) specification standardizes on how historical data is transferred. A guaranteed data delivery architecture using the OPC HDA capabilities of an OPC historian as the storage mechanism at the source offers several advantages;
1. Configuration options on the size of the historical data buffer.
2. Standard, at the source, access to historical data, even during times of communication loss to the central historian.
3. Increased flexibility on how and when the data is backfilled to the historian.

Since OPC is a client/server model, users have several options of which architecture best suits their needs for retrieving the buffered data. One method has an OPC HDA client read the history from an OPC based data buffer and ‘push’ or write the data into a central historian. This approach offers several benefits.

Any compliant product that follows the OPC HDA standard provides an architecture that can easily be duplicated to create a redundant solution. OPC HDA clients may also make use of the standard OPC HDA Insert Replace functionality to ensure no data is missed yet no duplication occurs in the historian repository.

In addition, when deployed in a redundant mode, a well written OPC transfer client could continually synchronize transaction records to ensure no data is lost. The MatrikonOPC History Link is an example of an OPC HDA client that employs such guaranteed data delivery functions (see Figure 2). Reaping the Wind OPC provides the means to manage wind farms in a standardized fashion by providing applications with real-time data and critical information on each point in the system. Most of the wind industry is using the proprietary or homegrown types of applications.

Standardizing access with OPC supplies a better way to manage wind performance and control assets. OPC products that gather high-resolution, real-time data gives the end user far more capability to analyze and affect the operation of the wind farm, than the currently used technology. Using OPC HDA technology guarantees the data is always available, regardless of how hard the wind is blowing. The way the blows may continually change, but the need for real time data to manage energy production systems, and the ability of OPC to provide it is constant.

Eric Murphy is Advanced Architecture System Design Engineer, MatrikonOPC. Eric Murphy,BSc, PEng (Alberta), Eric is a Chemical Engineer with a Process Control specialization and an OPC expert. Eric has been a part of the OPC community since its early beginnings in the mid-1990s. Eric is heavily involved with the OPC Foundation and currently acts as the chair for the OPC Historical Data Access (HDA) working group. Eric is also a member of the OPC Technical Steering Committee (TSC) and an active member of the OPC Unified Architecture (UA) working group. Eric's Contact Information

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