When management at Newfoundland & Labrador Hydro’s Holyrood Thermal Generating Station learned that support for its legacy distributed control system (DCS) would end in 2005, they began planning a DCS upgrade almost immediately. The Holyrood plant powers about a third of the island’s grid and a reliable DCS is critical for safe, reliable and efficient operation.
“We were especially interested in the fault tolerance functionality of digital control systems. Our system cannot tolerate a single point of failure,” said Jeff Vincent, Holyrood’s project and maintenance manager. “A loss of one or more generating units could result in under-frequency load shedding on the power system, which would leave several customers without power.”
Plant management first evaluated the migration approach offered by their DCS original equipment manufacturer (OEM). While evaluating alternative solutions, they learned that Invensys’ Foxboro division could fit new I/O cards to the existing wiring and terminals and provide its I/A Series DCS with modern I/O cards for a price only slightly higher than their DCS OEM was proposing.
Blending Old and New
Newfoundland Hydro and Foxboro were also able to install the I/A Series distributed control operator interface equipment into existing consoles, with minor modification of existing systems, including upgrading monitors and keyboards.
With the control hardware infrastructure largely unspoiled, the plant’s engineers could focus on migrating existing control logic and data and developing new processes that would fully leverage the new digital control functionality.
To begin the migration, Newfoundland Hydro engineers provided the Invensys team with the software from the existing DCS, including the operator interface screen software files, database and control files, control logic drawings, piping and instrumentation diagrams (P&IDs) and verbal plant system descriptions.
Likewise, the historians, reports and performance monitoring logic all had to be mapped to the new logic. Although Foxboro provided tools that assisted in the process, this was an application and company specific processes
Operator Interface Transitioning
The operator interface, one of the most visible parts of the system and the spot where major informational exchange occurs between human users and applications, received much consideration. A senior member of the operations staff supervised migration of all screen graphics to the new DCS.
Making sure that new versions of existing displays presented themselves and interacted with the operator in the best way possible was a major area for attention and review. But, the existing operator consoles required minor modifications to accommodate the new Foxboro monitors and keyboards.
Testing and Training
With infrastructure, applications and interfaces in place, the system was ready for switchover. The physical switch, which amounted to unplugging the old cards and replacing them with the new, took place in a matter of days. This complied with a tight commissioning and startup schedule. Testing and training were also required to ensure a seamless switchover. In addition, to ensure that programmers had implemented the functionality of the OEM DCS correctly and completely, Newfoundland Hydro and Foxboro conducted a factory acceptance test.
Newfoundland & Labrador Hydro’s 490 MW oil-fired Holyrood thermal generating station provides electricity to one-third of the Canadian island. Photo courtesy of Newfoundland & Labrador Hydro.
To help Holyrood employees prepare for the installation and transition, Newfoundland Hydro and Foxboro developed customized training specific to the Holyrood installation which was delivered on-site and at the Foxboro training facility in Montreal.
Once the training was complete, Foxboro worked closely with the plant’s technicians and electricians to accomplish the following construction and commissioning procedures:
- Installing and testing control system software, including the DCS application itself and the operator Interface.
- Testing and debugging the installed DCS equipment.
- Confirming all motor start/stop and protection logic.
- Verifying control system circuitry and I/O (loop tests).
- Testing all interfaces to other control systems.
- Calibrating field devices as required.
- Testing other mechanical equipment as required.
- Running process and tune process controls.
When all installation, testing and training were complete, the switchover took approximately two weeks for each unit.
Generally, Newfoundland Hydro feels the migration of the DCS has resulted in greater reliability, improved operator efficiency, easier software maintenance and improved process documentation.
The new DCS screens, which incorporate all indication and control for a particular system on a single screen, improved operator efficiency by enabling the operator to make decisions and see the result of actions quickly. The screen looks like the P&ID, with which the operators are already familiar.
Because the new DCS runs on a Windows XP operating system, and the operators and technical staff are familiar with it, software maintenance and modifications are simpler. The programming environment makes it easier for developers to incorporate program functionality as techniques and languages advance.
Control logic, application data, hardware, and user interface are integrated yet independent, which means that advances in control processes, computing hardware and user interface can likely be implemented without ever facing a complete system upgrade again.