Extending Asset Life

Preventive O&M strategies to ensure reliable supply

Substations and switchgear, the key elements in power systems, are critical components of an asset portfolio. Beyond the financial value, they play an even greater role in the overall business performance. Well-planned electrical substation and switchgear maintenance ensures reliable supply and reduction in failures. A major failure can result in significant time and cost overruns. Therefore, it is important to take optimised maintenance and replacement decisions by moving from reactive to proactive maintenance, reducing unplanned downtime and minimising costs to extend asset life. As the electrical grid grows in complexity, finding the right O&M strategy for substation assets is becoming ever more important.

O&M strategies

Over the years, a variety of maintenance strategies have been developed, based on utility preference, to maintain principal assets. In time-based maintenance (TBM), there is periodic maintenance according to the manufacturer’s generic maintenance schedule. This may include the provision of spare parts and consumables, and the replacement of worn-out components or systems during service life. In this type of strategy, preventive maintenance will be carried out at predefined intervals based on the experience of usage. Another strategy could be condition-based maintenance (CBM). In this, maintenance planning is designed according to the condition of the equipment. Condition-based monitoring of substation assets can be undertaken through a combination of intelligent electronic devices (IEDs), smart sensors, fully secure communications/open protocols and “intelligent” head end, which is a user-friendly software. A prerequisite is a detailed condition evaluation of the installed equipment. The real actual equipment condition is continuously assessed by the online detection of significant working device parameters and their automatic comparison with average values and performance. Maintenance is carried out when certain indicators give the signal that the equipment is deteriorating and the failure probability is increasing. This strategy, in the long term, helps in drastically reducing the costs associated with maintenance, thereby minimising the occurrence of serious faults and optimising the available economic resources management. Reliability-centred maintenance is another way that can be considered. Substation reliability modelling enables customers to understand the risk associated with each of its components. A reliability-centred maintenance is based on optimising maintenance investment by limiting the execution of unnecessary tasks while focusing on substation components representing a higher risk. This evaluation includes “failure mode and effect analysis” to determine the best maintenance strategy to maintain reliability. The life cycle cost-based evaluation of this strategy has to be derived from CBM analysis.

GIS Monitoring

The health of GIS equipment can be supervised in several ways and for different purposes or needs. Many of these techniques are not unique to GIS equipment and can also be found on other switchgear and breaker elements. The most frequent monitoring arrangement is typically gas monitoring. Gas monitoring is primarily used to make sure that sufficient quantity of sulphur hexafluoride (SF6) gas is provided to meet the equipment’s requirements. This typically involves some form of gas density monitoring. Nevertheless, gas density measurements have limitations. However, more accurate tracking of SF6 loss is only possible if SF6 quantified values of density are recorded at defined intervals with online intelligent gas monitoring systems, which are now being offered by technology providers. An online SF6 system typically comprises a gas density sensor, data capture and processing platform, as well as graphical user interface software. In recent times, partial discharge monitoring has earned interest as it promises to have the possibility to warn of developing insulation problems in GIS installations. Since GIS needs to be partial discharge-free, any detection of it above a minimum threshold is construed to be a developing problem. Online partial discharge monitor servers collect and analyse data from the sensor nodes. Expert system software automatically converts evidence of partial discharge activity into graphs and management reports, showing its location, type and severity. GIS installation that includes switchgear elements such as circuit breakers may also use some form of circuit breaker monitoring. A number of extra circuit breaker monitors are readily available but these are not specifically used for GIS breakers. These elements range from simple add-on devices to advanced systems completely integrated into SCADA with web-based user interfaces.

Conclusion

One of the dominant components of operating costs is maintenance and associated costs. The decisive parameters have to be identified along with their influence on the overall cost. Each device requires different strategies. Implementing the right action at the right time will define different electrical substation maintenance procedures, whether time, condition or reliability based. All of them must be supported using suitable testing tools. Ultimately, getting into an annual inspection routine can potentially avert expenditure on new equipment installation or repair. Simple maintenance measures can extend the equipment life by reducing the likelihood of malfunctioning.

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