Combined Cycle Power Plants
Control systems for combined cycle power plants
A combined cycle power plant is three machines that have to behave as one: a gas turbine, a heat recovery steam generator and a steam turbine, each with its own dynamics, tied together by a control system that has to hold the unit on load while any one of them is changing state.
ISYSTEMS AUTOMATION has worked on CCPP automatic control systems as the investor's representative — the engineer who checks that what the design organisation and the DCS supplier deliver is what the plant will actually be able to operate.
CCPP project experience
Combined cycle power plant, Pančevo, Serbia, 2019–2021. Two gas turbines and one steam turbine. Automatic process control system on Emerson Ovation and ABB Symphony Plus, with safety instrumented systems on Foxboro Triconex and ABB AC800 at SIL 3.
Our scope covered the ACS from design review through to trained operators: HMI architecture for both gas turbines and the steam turbine, fuel gas systems, unit load control, and the DCS grounding scheme. Contracted work over the final year alone ran to 1,980 engineering hours.
Owner's engineer scope for a CCPP control system
This is the full scope we contracted for and delivered. It is also, in practice, the checklist an investor needs when someone else is building their control system.
Design documentation
- Verification of compliance of the design for execution documentation
- Review of the completeness and quality of the developed control algorithms, representing the interests of the client within the design organisation
- Review of the completeness and quality of the signal database
- Participation in the review and approval of video frames and mnemonic schemes
Schedule
- Participation in the development of time schedules for the execution of works on instrumentation and control equipment, ACS and DCS
- Monitoring of execution against those schedules
- Where deviations occur, informing the client of the causes and of the ways to eliminate them
Equipment
- Participation in the inspection of instrumentation and control equipment, ACS and DCS at the manufacturers, in accordance with the quality control programmes
- Participation in taking over instrumentation and control equipment, ACS and DCS at site, including entrance control
Erection and commissioning
- Quality control of erection works and commissioning execution on instrumentation and control equipment, ACS and DCS
- Review of test and commissioning programmes, with recommendations
- Participation in commissioning, including the performance test
Operators
- Development of training programmes and training of CCPP operating personnel
Throughout
- Participation in technical meetings representing the interests of the investor
Why the investor needs their own engineer
On a CCPP the design organisation, the DCS supplier and the erection contractor each have a defensible reading of the specification, and the readings do not agree. Every disagreement that is not resolved on paper is resolved during commissioning, at the point where it costs the most and where the investor has the least leverage.
The work is unglamorous: reading algorithm sheets against the functional specification, checking that the signal database matches the P&IDs, sitting through a factory inspection and asking what was not demonstrated. It is also where the money is, because a control system accepted with defects becomes a plant that runs below specification for twenty years.
We do this because we have also been on the other side of it. The same engineers have designed, commissioned and maintained DCS on operating plant for two decades — four turbines and four boilers of an industrial CHP plant, continuously from 2007. Reviewing someone else's algorithms is a different job from writing your own, and it is much easier if you have written your own.
HMI architecture for CCPP
An operator on a combined cycle unit has to see three machines and one unit at the same time. We developed the HMI architecture for a CCPP covering:
- Unit overview: gas turbines, HRSG, steam turbine and the electrical connection on one picture
- Per-machine displays for gas turbine 1 and gas turbine 2, including fuel gas systems
- Steam system displays across the pressure levels
- Unit load control
- SIL 3 safety system status integrated into the operator picture rather than left on a separate panel
- The DCS grounding scheme, to the supplier's requirements
Platforms
Emerson Ovation · ABB Symphony Plus · ABB Industrial IT 800xA · Foxboro Triconex · ABB AC800 · Siemens PCS7 · Yokogawa Centum VP · HIMA HIQuad
Related
Gas and steam turbine control, island mode operation and plant coordinated control are covered under Power Generation. Factory and site acceptance testing is covered under Acceptance Testing.