Planning for a rainy day

In unplanned power plant outages, with commercial implications and financial costs mounting, the pressure to provide a quick and effective solution is high. Alstom’s Emergency Response Planning offers one such solution.

Wynand Pienaar and Paul Stokes, Alstom, UK

In today’s increasingly commercial and efficiency-driven environment in the power industry, forced outages have a significant effect on revenues. Thus, the reliability and availability of any plant are key drivers. When a forced outage situation occurs, significant time is lost in the early stages – evaluating the incident, identifying the cause and determining the type of remedial action to be taken. With lost generation and commercial implications and financial costs mounting, it is essential to be able to provide a quick and effective solution.

Alstom’s Emergency Response Planning (ERP) can offer one such solution. It complements asset management by identifying areas of high risk within a plant component and providing detailed recovery plans for pre-agreed failure scenarios. In addition, online condition monitoring can be incorporated, monitoring the high-risk areas in order to understand the maintenance requirements of the machines.

What is ERP?

ERP offers a bespoke and modular service aimed to address various potential fault scenarios and developed to minimize lost generation through forced outages. ERP is built on Alstom’s knowledge and fleet history, combined with experience of well planned and executed maintenance strategies.

This experience, when applied to a forced outage situation, enables a road map to be drawn up, whereby Alstom works with the customer and concentrates on getting the plant back into commercial service in a timely and efficient manner.

Schemtic of the ERP process
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Every potential failure mode identified is analyzed in-depth, then each ERP module created provides the correct information to crucial questions such as: “What ifࢀ¦?”, “How long?” and “How much?”.

Implementing ERP

The starting point for a successful ERP project is dialogue between Alstom and the customer’s engineers and operators. One of the main objectives of this dialogue is to produce an appreciation of the various types of fault that can arise in practice from a wide range of causes.

An understanding of the risks that are most important for the customer’s plant is also crucial, as is a plant assessment and criticality review, which will help establish key areas of concern and identify the ERP modules required.

The identification of all fault scenarios that are to be analyzed and planned for are implemented. When these objectives are met Alstom and the plant operator will jointly put together the agreed ERP modules, based on the machine design, age, operating philosophy, service history, available monitoring information and future operational demands.

ERP deliverables

The deliverables for ERP can be customized to suit any particular requirement. In its standard form, ERP documentation (electronic or hard copy) is presented in two parts.

Part one covers issues that are common across almost all fault scenarios. These simple steps, when prepared in advance, can save valuable time (hours or even days) in commencing repair activities. These deliverable are:

  • Master flow diagram for management overview
  • The first actions required to mobilize personnel and materials
  • A joint project team led by Alstom for successfully dealing with an unplanned outage
  • Defined emergency response team, i.e. the numbers and skills of Alstom personnel who would be required on site, including senior engineering and project staff when necessary
  • Predetermined communication channels

In part two – for every separate fault scenario, each ERP module created is made up of ten specific sections that contain all the relevant information to enable efficient execution in a cost effective and timely manner. These are:

Section 1: Verifying the identification of requirements
Section 2: ERP process – detailed implementation procedure
Section 3: ERP process map – workflow and decision-making charts
Section 4: ERP programmes – PERT & Gantt project planning charts
Section 5: Comprehensive quality documentation – QA plans, method statements, risk assessments, identification of drawings and process specifications
Section 6: Maintenance parts – schedule of requirements, identifying logistical spare parts for outage
Section 7: Identification of required consumables
Section 8: Tooling – identification of all tooling required
Section 9: Resource schedule with key interface personnel
Section 10: Recommendations – engineering to proactively provide information that enhances future requirements, and site activities to complete the outage quickly and efficiently

ERP to the rescue

An example of ERP in action is the programme that was developed in 2003 to cover a steam generating unit at a nuclear power plant in the USA. Alstom applied the ERP philosophy to the 1200 MW Southern California Edison’s SanOnofre nuclear generating station (SONGS) unit.

The ERP allowed SONGS to operate without a forced outage and conduct the repair within the planned outage duration. Edison was also able to put in place all preparations to repair the generator in the shortest possible time should it fail in service, and continue to run the unit until the planned outage through condition monitoring, as well as identify the required spares and obtain them upfront.

The unit had operated reliably without fault for a number of years. However, in April 2003, and again in October 2003, the unit 3 generator exhibited a step increase in shaft vibrations. The machine was therefore in an unacceptable condition for long-term service. On both occasions, the step changes in vibration were associated with severe grid disturbances, and large negative sequence currents that initiated the switchyard data recorder.

The generator rotor at SONGS during its planned outage
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A thermal sensitivity test was carried out to establish whether the problem was mechanical or thermally induced. This was combined with the flux probe data, which revealed that several interturn short circuits were present within the winding. The sensitivity test showed that the vibrations were sensitive to excitation current, and therefore thermally induced. In this case caused by the interturn short circuits.

The customer, in conjunction with Alstom, implemented ERP. This was combined with real time monitoring of the rotor flux waveform. The real time monitoring established the condition of the rotor winding as the interturn faults spread throughout the rotor. The rotor was then monitored and trended to identify any deteriation of the insulation over time.

The ERP was developed and used as an outage optimization tool to meet the customer’s aspirations of completing the rotor work in a 14-day window, excluding disassembly and reassembly of the machine. The total outage duration was 28 days, breaker-to-breaker.

Comprehensive documentation was created, with key decision points identified. The ERP module included a dedicated plan, which identified all key resources, specialist tooling and equipment to be able to execute a partial rewind of the rotor on-site.

With the ERP module in place, the customer could continue operating the unit with the knowledge that the repair plans could be implemented if or when required.

Maintenance strategy

Although the ERP package had identified all the potential failure scenarios, it had also highlighted some significant gaps in strategic spares holdings. The rotor was operating at high risk, and therefore the customer decided to procure a set of spare parts for the eventuality of the machine failing in service.

This demonstrates the benefit of implementing an ERP in this type of situation. Had the machine failed in service, the plans would have been in place, but the critical spares would not. This would have significantly delayed the repair time.

In addition to the ERP package, the customer decided to repair the unit at the next planned outage. The benefit to the customer was that all the pre-outage planning was complete, together with resource levels, tools, spares and consumables – all of which were on-site pre-prepared.

The generator rotor being re-threaded after the planned outage
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This meant that the planned maintenance activities would run smoothly, with detailed hour-by-hour programmes, saving the customer both time and money in pre-outage preparation, and minimizing the planned repair time for the rotor.

By monitoring the machine the customer was able to run the machine until the planned outage. The machine was taken off-line on the planned date. All of the interturn faults were found and repaired within the planned 14 days. The machine was returned to service in the planned 28-day period with the vibrations back to normal.

Why have ERP?

In order to demonstrate the benefits of the ERP model, it is useful to compare the above case study with a similar situation, requiring a similar scope of work, where the operator had not adopted ERP.

The operator suffered an earth fault of the generator rotor because of three interturn short circuits. In this case, because the rotor did not have continuous condition monitoring the rotor failed in service, and had to be removed for rectification and repair. The customer had already procured a strategic spare rotor, but had not identified all the necessary components required to fit the rotor into the unit.

Consequently, procurement of the necessary spares and decisions made to repair some damaged components meant that the outage duration approached 50 days in length. If an ERP module had been in place, the time duration could have been effectively reduced to 28 days.

In conclusion, the implementation of the ERP process can offer a number of benefits that include: optimizing planned outages and identifying and evaluating total cost and timescales prior to the onset of any work. Thus, it serves as an invaluable tool to support both maintenance and asset management strategies.

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