Long distance diagnostics

A major driver for the increasing involvement of Siemens, and, for that matter, other original equipment manufacturers (OEMs), in centralised remote monitoring of distant power plants is the rise of the long-term service agreement.

Very often these long-term contracts between the OEM and plant owner cover a sizeable proportion of a power plant's expected life. They require the OEMs to take on a share of the risks associated with plant operation that they did not have to shoulder a few years ago. To properly manage this risk, it is in the interests of the OEM to know as much as possible about how the plants with whom it has a long-term relationship are actually operating and to make technological support as effective as possible.

As an extension of the long-term service idea, there are also a growing number of cases where the OEM is actually taking over complete responsibility for plant operation and maintenance. In the case of this kind of long-term O&M contract, the OEM is not just looking to achieve a certain level of availability, but it is also in his interests to improve power plant performance as much as possible, especially if a bonus/penalty system is incorporated in the contract.

The essential requirement in making these long-term arrangements work is that the OEM must receive reliable operational data from the plants. In addition, analytical and diagnostic tools must be applied to obtain more precise and detailed knowledge about the power plant's major components and their actual condition.

At present, Siemens uses its Power Diagnostics Centers in Orlando, USA, and Erlangen, Germany, and the associated technology support, exclusively for the long-term service and O&M projects - primarily to facilitate the internal management of these contracts. There are about 150 combustion turbines with such contracts, which Siemens calls long-term programmes (LTPs), and the remote expert centre support is offered to LTP customers as an added benefit. In the future, the centres might be opened up to other plants needing technical expertise, but the business decision was taken to concentrate in the initial phase on these special contracts.

Working from the centre

The two remote diagnostics centres established by Siemens use the same diagnostics technology and work closely together. The six-hour time difference between them can be used to advantage, allowing the Orlando centre to take over a shift seamlessly from the Erlangen team, for example. Recently, 24/7 surveillance has been introduced.

The main objectives of the centres can be summarised as follows:

• data acquisition, data handling, and controlled distribution within Siemens;

• analysis of the operational state of power plant equipment;

• diagnostics and prognosis, with the aim of avoiding unplanned outages;

• damage prevention;

• support to reduce the duration of unplanned outages and to speed up commissioning;

• providing the interface between the power plants and the experts within Siemens;

• performance optimisation;

• assistance in maintenance planning.

But the benefits are not just restricted to already-operating plants. The data and analytical resources of the remote diagnostics centres can also prove beneficial in the design phase of a plant and during commissioning. The centres are well geared up to provide in-depth comparisons between individual machines across the fleet. So, for example, during the introduction phase of a new piece of gas turbine technology, design enhancements can be carried out and reductions in commissioning times can be achieved. This has proved important in the current "gas boom", which has stretched expert commissioning resources to the limit.

By transferring raw data and providing evaluation results without delay to the design specialists in the back offices of the company, fact-finding and root cause analysis are speeded up dramatically. This is a very important advantage as the shortening of the commissioning phase has a direct impact on a plant's overall construction costs, while one day of outage, particularly for a peaking plant, is a very expensive business.

The interaction between the plants, the Power Diagnostics Centres and the existing "back offices" demonstrates a feature of the Siemens remote monitoring strategy that the company believes is unique. The centres are not operating in isolation from the rest of the company, only contacting other departments where they cannot handle the situation themselves. Rather, the aim is to keep the whole company in the loop because the Power Diagnostics Centres are constantly providing regular fleet data and routine evaluations to specialists in the design and service departments and the existing "competence centres", eg Mülheim in the case of gas and steam turbines.

To take one example, during the recent commissioning of the ISAB IGCC plant in Sicily, gas turbine burner specialists were able to monitor the testing from Mülheim, without needing to visit the plant.

In setting up the Power Diagnostics Centres, Siemens has been at pains to plug into existing centres of competence within the company rather than moving people into a new organisation. The approach was to use existing people at their own desks, still integrated into their own product development work and remaining connected to their own departments.

Diagnostic tools

At the heart of the remote monitoring and diagnostics system operated by Siemens are high speed data loggers, so-called "flight recorders", which are installed at many plants in the fleet.

These flight recorders are linked closely to the WIN_TS data acquisition platform. The flight recorders store data in CMOS memory, which can then be transferred to the WIN_TS computer system. Some 50-70 high speed signals are surveyed, with analog values recorded at 100 ms intervals and digital values sampled at 10 ms intervals.

In the case of unforeseen events, data stored in these flight recorders can be transferred immediately via the Power Diagnostics Centres to the relevant specialists to analyse the situation and to minimise outage time.

These flight recorders have proven their value many times, for example in addressing the issue of humming/combustion-instability encountered during the introduction of the 3A machines or as a data collecting platform used for special measurements during the commissioning of the new W501Gs.

Another illustrative example is a plant which lost a tooth in a gearbox. The I&C systems simply registered the trip, while the flight recorder captured 11 data points reflecting the incident and enabling it to be analysed before opening the gearbox casing.

The WIN_TS data acquisition platform was developed several years ago precisely because it was recognised that existing I&C systems on power plants were not really geared up to analysis and diagnostics, which need much larger data storage capacity. The kind of tasks that WIN_TS does, not catered for in conventional I&C, include: flexible data acquisition; high resolution data storage for fault analysis in connection with flight recorders (tens of milliseconds, compared with around 1 s for a typical I&C system); early fault detection using trending; thermal performance monitoring; and providing a channel for sharing large amounts data with experts outside the plant, eg for rapid analysis of faults encountered during commissioning.

Siemens' Michael Scheidel, manager, WIN_TS, points out that "WIN_TS is designed to decrease the computer farm around the gas and steam turbines. It provides a single platform for all kinds of advanced diagnostics modules, including those of third parties." Analysis modules at site integrated in WIN_TS are able to send out warnings much earlier than the I&C system. As the remote monitoring systems are not part of the I&C's plant protection system - which actually initialises the plant trips - the thresholds for sending out first alerts can be adjusted to be significantly lower, to obtain the highest possible sensitivity and to register any deviation from normal as early as possible.

Additionally, a comprehensive expert system used in the Power Diagnostics Centers continuously analyses and evaluates all incoming data sets from the plants.

Called GTAID (gas turbine artificial intelligence diagnostics) this gives additional security in parallel with the local analysis modules at the power plants. GTAID "never sleeps" and provides an additional margin against human error and the potential to miss early signs of trouble. In addition the expert system is a useful tool to evaluate long term trending and to perform statistical analysis for the entire fleet.

On request, a thermal performance evaluation module can also be made available, using identical software to the standard Siemens heat cycle design program. This provides particularly high accuracy, especially at part load, as OEM expertise is incorporated in the software.

But Siemens' Hans-Gerd Brummel, Manager for Advanced Research and Development in Power Diagnostics™ Services, believes the current diagnostic tools are "only the beginning". In the future we will see "much more intelligent diagnostics" with integrated economic models and using new measurement techniques (eg sophisticated optical sensors) "now in the embryonic phase" which could help increase availability. These could also be used to analyse trade-offs such as stressing the plant vs maximising revenue from selling peak electricity.