The commissioning of a SCADA system has recently been completed at an open-sea test facility in the UK’s Orkney Islands that will enable the gathering and analysis of wave and tidal marine energy information 24/7, and will play an important role in Scottish Power’s new Pelamis wave power project.

By Iain Mitchell, Real Time Engineering Limited, UK

In the coming decades renewable energy’s share of power generation in the UK will rise rapidly, increasing the need for a greater portfolio of renewable energy technologies. The UK has the best wave and tidal resource in Europe, which means that the future for marine renewables is looking bright. Although marine energy is currently at the same stage wind power was 10-15 years ago, interest in this area is growing rapidly. One organization that is supporting the commercial development of tidal and wave technologies is the European Marine Energy Centre (EMEC). Based at Stromness in the Orkney Islands, the EMEC operates two multi-berth, purpose-built, open sea test facilities for wave and tidal marine energy converters.


Source: Ocean Power Delivery
Click here to enlarge image

An exciting development at EMEC’s site is the recently completed commissioning of a SCADA (supervisory control and data acquisition) system, which will monitor the operation and performance of both wave and tidal energy converters. The EMEC Data Collection and Supervision System (EDCSS) was developed by Real Time Engineering Limited.

Wave and tidal sites

The Wave Site consists of four open water berths for wave energy converters, sited off the western edge of mainland Orkney and connected by a subsea cable to an electrical substation at Billia Croo. EMEC’s offices are linked to the Billia Croo substation using single mode fibre optic cables.

The Tidal Site consists of five berths for tidal energy converters, located off the southwest tip of the island of Eday, in an area known as the Fall of Warness. Each berth is connected by a subsea cable to an electrical substation at Caldale, on the island of Eday. EMEC’s offices are linked to the Caldale substation via two ADSL (asymmetric digital subscriber lines), commonly known as Broadband.

These facilities provide developers with the opportunity to test their prototype devices in unrivalled wave and tidal conditions. Wave and tidal energy converters are connected to the National Grid via seabed cables running from the open-water test berths. Testing takes place in a wide range of sea and weather conditions, with comprehensive round-the-clock monitoring provided by the EDCSS.

EDCSS system in detail

The EDCSS employs state-of-the-art technologies to overcome the limitations of the communications network in the Orkney Islands and the remoteness of the substation locations, to deliver high quality performance data for the devices under test.

The EDCSS was developed in two phases, with the Wave System (Figure 1) developed and commissioned in 2004. The EDCSS was extended recently with the construction of the tidal energy site at Caldale. The Tidal System (Figure 2) has only recently been commissioned.


Figure 1: Schematic of the Wave System
Click here to enlarge image

 


Figure 2: Schematic of the Tidal System
Click here to enlarge image

The EDCSS consists of two powerful SCADA Servers (one for the Wave Site and one for the Tidal Site) and seven client workstations, each capable of monitoring any wave or tidal test berth. An additional supervisory workstation has also been provided to allow EMEC to monitor all test berths and the main electrical supply to the substations at Billia Croo and Caldale. These machines communicate over a dedicated Local Area Network (LAN), which extends to the substation at Billia Croo over single mode fibre optic cables. The Tidal Site Server and two workstations located at the Caldale substation are linked to the LAN over twin Broadband lines using specialized firewalls that combine the bandwidth of the individual lines using a technique called “Tunnel Bonding”.

The SCADA system is responsible for monitoring the electrical performance of the wave and tidal energy devices, via electrical protection and monitoring systems located in the substations at Billia Croo and Caldale. The SCADA system also allows the devices to be connected or disconnected from the National Grid remotely from workstations located at EMEC’s offices in Stromness.

A separate dedicated Historian Server provides the all important historical data collection function that allows developers to analyze the electrical performance of their device under test. Weather and wave state data are also collected to allow the developers to analyze the electrical performance of their device in the varying conditions experienced throughout the year.

sCADA SERVERS

Each SCADA Server is a Dell Poweredge 2850, which has GE Fanuc’s Proficy iFix HMI/SCADA application (v4.0) installed and configured to provide monitoring of data received from the following equipment:

  • Power Measurement Centres
  • Switchgear Protection Relays
  • Remote I/O modules (Wave Site only)
  • Weather data collection PCs
  • Wave State data collection PC
  • Supervisory PLC (Tidal Site only)

Each SCADA Server also has an alarm notification application (TopView) installed that transmits alarms via SMS text messages. This allows developers to operate their devices round-the-clock with EMEC staff on call ready to respond to any alarms generated outside office hours.

The client workstations provide a user-friendly graphical display system that allows the developers to monitor the performance of their device during testing. The relevant weather information is made available to all developers, but they are restricted to seeing electrical performance data for their device only. Only wave developers can view wave state data. This is achieved through the user security features available in iFix.

EMEC has access to all graphical displays, which allows them to independently monitor all test activities and respond to any problems that arise, for example, an unplanned trip of the electrical supply to the device.

The Historian Server is the same specification as the SCADA Server and runs GE Fanuc’s Proficy Historian application. A historical data collector resides on each SCADA Server, which captures the data being monitored by the iFix application and transmits it to the Historian Server. Data compression is applied at the collector to reduce the amount of data being transferred across the LAN (or the Broadband lines) to the Historian Server. The compressed data are then stored in a database, which is accessible for reporting and analysis.

EMEC can provide various standard reports for electrical performance from the information held in the database using a powerful add-in tool. It is also possible to provide data extracts in Excel, which can be further processed by the developers themselves.

Each test berth has a dedicated switchgear section in the substation with a Power Measurement Centre to monitor all aspects of electrical performance of the device, such as real power, reactive power, power factor, phase voltages and currents. The Power Measurement Centre has a Modbus serial interface, which is used to communicate with each SCADA Server.

Also within each switchgear section, there is a Switchgear Protection Relay, which is programmed to detect any problems with the electrical supply to the device. This will trip the circuit breaker should the supply go beyond acceptable operating parameters. This is to protect the substation switchgear, the developer’s device and to maintain the electrical supply to the other test berths. A number of alarms generated by the Protection Relay are transmitted to the SCADA Servers so that EMEC and the developer are made aware of the cause of any trip.

There are a number of digital status signals and alarms generated by various items of equipment at the Billia Croo substation as well as some status signals from the switchgear, which do not originate from the Protection Relays. In order to monitor these signals at the SCADA Server, some remote I/O modules have been installed at the Billia Croo substation, including a digital output module to drive relays that allow the circuit breakers to be opened and closed remotely from the client workstations. The Remote I/O Modules have a Modbus serial interface, which is used to communicate with the SCADA Server.

The Supervisory Programmable Logic Controller (PLC) is a GE Fanuc 90-30 series device, which provides the equivalent function for the Tidal Site that the Remote I/O modules provide on the Wave Site (i.e., other status and alarm signals and the ability to operate circuit breakers remotely). The Supervisory PLC has an Ethernet interface, which is used to communicate with the SCADA Server over the LAN.

data collection

There are two weather data collection PCs (one for the Wave Site and one for the Tidal Site), which are programmed to download meteorological data from the weather stations periodically for onward transmission to the SCADA Servers. This data can be viewed on a client workstation and is also captured by the Historian Server for later analysis.

The Wave State Data Collection PC is programmed to download data periodically from two wave rider buoys located north and south of the test berths. The data forwarded to the SCADA Server can be viewed on a client workstation and is also captured by the Historian Server for later analysis.

technology behind edcss

The EDCSS has been developed using several technologies, without which EMEC’s performance and functionality requirements could not have been met. Those worth mentioning in detail are as follows:

  • LAN extension over fibre optic cables;
  • Device Servers for Modbus Communications;
  • Tunnel Bonding for increased ADSL bandwidth;
  • Alarm Notification by SMS.

The LAN is the foundation that the whole system is built on. Communications between SCADA Servers, client workstations, data collection PCs, the Supervisory PLC and the various devices with Modbus serial interfaces all rely on the network switches, copper cables and fibre optic cables that comprise the LAN.

The original Wave Site design was visionary in that it was realized at an early stage that high bandwidth communications between Stromness and Billia Croo would be essential to effectively monitor the wave devices under test and collect electrical performance data remotely. Any other solution would have meant installing more equipment and personnel at Billia Croo, which would have increased the environmental impact of the substation and possibly increased EMEC’s annual operating costs.

The design called for fibre optic cables to be installed between Stromness and Billia Croo, and the HP Procurve network switches used to extend the LAN have an in-built Gigabit fibre optic link capability straight out of the box. Thus, any item of equipment connected to the LAN at Billia Croo is instantly accessible to the SCADA Server, Historian Server and the client workstations at Stromness. The Power Measurement Centres, Protection Relays and Remote I/O Modules all communicate to the SCADA Servers using Modbus serial communications over the LAN. To achieve this required the LAN extension as discussed above and the deployment of Serial to Ethernet Device Servers to allow the SCADA Servers and the various Modbus devices to communicate and exchange data over the LAN.

A Device Server is a piece of hardware that converts serial communications into TCP/IP communications capable of being transmitted over an Ethernet IP-based LAN. The SCADA Servers of the EDCSS are configured with a device driver that configures each Device Server as a virtual serial port. Application software, such as iFix, is simply configured to communicate via the virtual serial port and the driver ensures successful communication with the device server and hence the Modbus serial device.

The Caldale substation is too far away from the Stromness office to allow the two sites to be connected by fibre optic cables. Therefore, another solution had to be found to try and ensure robust high bandwidth communications for monitoring devices via workstations and to allow vital performance data to be collected and stored on the Historian Server. The advent of ADSL and its proliferation to remote islands such as Eday provided an opportunity of establishing communications via the Internet.

With the recognition that the potential amount of data to be transmitted could be significant, it was decided that multiple Broadband lines would be required. Initially, each link was going to be dedicated to a particular function – one link for data transmission between the historical data collector and the Historian Server and another for data transmission between iFix clients and servers. However, a firewall device that had the ability to utilize the bandwidth of multiple Broadband lines was discovered, thereby negating the need to dedicate lines to specific functions. This feature is called “Tunnel Bonding”. These firewalls have been successfully deployed to combine two Broadband lines, which is sufficient for EMEC’s immediate bandwidth requirements. The firewalls do have the ability to combine up to four Broadband lines, which provides some headroom for the future. Of course, it is anticipated that Broadband speeds will increase at some stage as well, allowing further increases in data transmission.

24/7 EMEC Support

EMEC has to be able to provide 24/7 support coverage to afford developers the maximum amount of time to conduct their tests. EMEC chose to set up a support rota for outside office hours, with engineers on standby, ready to respond to any alarms or incidents at the facility, rather than have engineers permanently on site. Therefore, there was the requirement to notify on-call support engineers of any significant alarms and advice on how to tackle them. A number of options were explored, including email notification, SMS text message notification, voice notification and pager message notification. An application called TopView by American company Exele Systems Inc was eventually chosen. This application is able to provide all of the options looked at above. However, as the LAN used for the EDCSS is completely isolated from EMEC’s email server, only voice or SMS text messaging was feasible.

EMEC had been using a similar package for the Wave Site since going operational in 2004, which was now obsolete. With the Tidal Site expansion it was decided to replace the obsolete package with TopView.

TopView provides comprehensive features to ensure that notifications reach their intended destination, with configurable retries and alternative contact telephone numbers. All notifications and errors are logged, providing complete visibility of all actions. TopView automatically splits long messages so that advice on tackling a particular problem is not restricted to the maximum character length of a single SMS text message. The flexible configuration, the messaging options and the methods for dealing with errors make TopView an essential part of the quality service offered by EMEC.

Edcss role in NEW pelamis project

The future is looking positive for marine energy as a viable supplement to more conventional power generation technologies, and EMEC is currently at the forefront to establish cost-effective methods of harnessing UK’s wave and tidal energy resources.

In 2008, CRE Energy Limited, a wholly owned subsidiary of Scottish Power, plans to install the world’s biggest wave energy farm at EMEC, consisting of four Pelamis devices. The project is reported to be worth in the region of £10 million ($20 million).

The word Pelamis means ‘sea snake’ in Greek. This floating generator, designed and manufactured by Ocean Power Delivery (OPD), comprises four 24-m canisters (tubular segments) aligned perpendicular to the waves. Electricity is generated from the relative motion at the flexible joints between each of the canisters.

Each Pelamis machine has three power conversion modules that together generate a maximum output of 750 kW. This could produce enough energy to power 600 homes. Two Pelamis machines will be connected in series to each of two test berths and the energy generated will be exported to the National Grid.

A number of infrastructural changes will be required at Billia Croo to accommodate the wave farm design and this may require further modifications to the EDCSS. However, the founding blocks upon which the EDCSS has been designed mean that the system can be adapted easily to meet any additional requirements as a result of this exciting new development.