How to optimize availability through your power system architecture

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A power outage is defined as the loss of electrical supply within an end-user installation. Whether the electrical installation is in a factory, a hospital, an airport, a large industrial site, or a data center, the effects of power outages can be extremely damaging – ranging from financial consequences (loss of productivity, loss of data, equipment damage), to safety issues (equipment damage, pollution, personal injuries).

Here are some examples that illustrate the dramatic repercussions of a power system shutdown:

  • The average costs associated with a data center shutdown amount to about a million dollars (Ponemon Study) and can reach more than 100 million dollars (Upstack);
  • A hospital power outage of just a few hours can lead to a full building evacuation, putting patient safety at risk, not to mention the financial implications.
  • When an aluminum smelter is forced to shut down for just a few hours, the factory could be out of action for several months, due to damage to the electrolytic cells.

Power outage risk management

Given that power system outages can have a significant negative impact on end-user businesses, power system resilience must be taken into account throughout the power system lifecycle – from the design phase of the project, during its operational phase, right through to the modernization phase. The risks associated with power system failures should always be evaluated, and the robustness of the power system must be designed in accordance with the risk assessment.

Reliability Engineering During the Project Cycle

The reliability and availability levels of a typical power system are highly dependent on its overall architecture, which includes not just the power distribution equipment, but also the protection, control, and monitoring systems, in addition to the maintenance teams that oversee any planned or unplanned activities.

Integrate a reliability approach during the design phase

For mission-critical applications like data centers, healthcare, or nuclear power plants, the reliability requirements should be integrated during the early phase of the project.

Step 1: Identify critical loads and set reliability targets

The first step, and one of the most important ones, is to identify the critical events of the power system, by identifying the main system functions. For power systems, the main functions are the supply and control of the various electrical loads. Each critical event labeled “Undesirable Event” is defined by the loss of one or several critical loads during a given time. The acceptable occurrence probability of the “Undesirable Event” is set according to the severity of the outage and can be characterized by the impact on the end-users’ business.

Step 2: Design the power system according to reliability requirements

During the design phase, depending on the set reliability target, a consistent electrical architecture should be defined by setting the adequate redundancies, selecting the topology, and specifying maintenance requirements if necessary. The process can be repeated, to ensure that the system design is in accordance with the reliability requirements.

Power System Architecture

To ensure a consistent architecture, the redundant equipment can be categorized by the following stages:

  • 1st stage: electrical load redundancy
  • 2nd stage: 1st stage + source redundancy (back up in case of grid blackout)
  • 3rd stage: 2nd stage + power distribution redundancy (back up in case of failure to cable or switchboard)
  • When a very high-reliability level is required, the common-mode failure risks for redundant equipment should be identified and mitigated. Common mode failures can arise from various origins, such as the environment (e.g., fire, floods, extreme weather conditions, storms, earthquakes, etc.) the installation (e.g., common critical auxiliary supply, common cooling system, etc.), or as a result of human intervention (e.g., design error, installation error, maintenance error).

To operate the system most efficiently, adequate maintenance should be defined using the following criteria:

  • Monitoring of the state of the power system – to be able to react quickly when a failure occurs
  • Monitoring of critical devices – to detect any hidden failure, and to ensure that critical equipment functions are ready to operate when required
  • Planned maintenance operation is based on site conditions and the manufacturer’s recommendations
  • Respecting the manufacturer maintenance contracts for critical equipment, to optimize intervention time and availability of the equipment

Step 3: Analyze system reliability performance

By using equipment reliability statistics, probability theories, system functional analysis, and failure analysis, the resulting reliability analysis of a power system can set the reliability requirements, estimate the reliability and availability of the system, identify the system’s weak points and recommend improvements for the system design.

Power System Reliability Overview

System reliability analysis is, in essence, about studying the consequences of component failures on the system, based on the equipment failure information, and how the system behaves during failure.

To capture detailed analysis, the study shall take into account the following elements:

  • equipment specifications
  • system architecture
  • description of operating modes
  • description of automation and protection behaviors
  • layouts
  • equipment reliability data
  • planned and unplanned maintenance equipment data
  • onsite maintenance

By analyzing all possible failure sequences (single contingency and multiple contingencies if required), the reliability analysis can estimate the mean occurrence frequency (MTBF) and probability for each undesirable event, and identify the system’s weak points. Using these weak points, the designer can then upgrade the system to match the reliability targets.

Pre-engineered EcoStruxure Reference Designs

Schneider Electric has worked with more than 70,000 consulting companies and engineering firms that often require assistance relating to the prevention of downtime by design. Today, we make it easy and cost-effective to design, build, operate and maintain resilient, high-availability, and high-reliability power management systems. Furthermore, we help to ensure these systems are future-proof and optimized for maximum uptime, while also helping to keep CapEx and OpEx spending as low as possible. We offer high availability and high-reliability EcoStruxure Reference Designs for data centers, healthcare and hotels, and other applications. Log in to the mySchneider personalized digital Experience and download our useful EcoStruxure Power Reference Designs.

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