Energy Reliability - Downtime Metrics

Metrics To Measure The Downtime Of Electricity Generation Methods

Contents

1. Introduction

2. Measuring Downtime

3. Concluding Remarks

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Bitesize Edition

• Electricity generation systems can’t be operating 100% of the time. Of course, some methods achieve closer to 100% than others such as nuclear which has a consistent fuel supply and little downtime for maintenance. If we compare this to wind and solar which can experience more downtime due to intermittency, and its clear that nuclear is more reliable.

• While a few weeks ago we found it useful to assess the availability factor, we can also learn valuable lessons in assessing the downtime of an electricity generation system, whether this is planned or unplanned downtime. There are many other aspects we can explore here such as mean time between maintenance, forced outage rate, and duration of interruptions that we’ll also explore below through a collection of metrics.

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Introduction

A few weeks ago, we explored two reliability metrics: Availability factor and reserve margin. I’d recommend checking out that piece first, especially because today I’ll explore how we can measure downtime in electrical systems, and downtime is a vital piece of the calculation for availability factor. Of course, without reading last week’s piece, this one will still make sense individually, so let’s dive in!

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Measuring Downtime

1. Planned Maintenance Downtime - This refers to a power plant intentionally taking time out of operation for scheduled maintenance, repairs, or upgrades.

Calculation:

\(\text{Planned Maintenance Downtime} = \frac{\text{Total Planned Downtime}}{\text{Total Time Period}} * 100\)

Example:

• Planned Downtime = 200 Hours

• Total Time Period = 8760 Hours (1 Year)

\(\text{Planned Maintenance Downtime} = \frac{200}{8760} * 100 = 2.28\%\)

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2. Unplanned Maintenance Downtime - This, of course, refers to the power plant unintentionally taking time out of operation for any given reason. Interestingly, adding this and the planned maintenance downtime should give the exact opposite metric to availability factor, which calculates the percentage of time for which a power system is operating.

Calculation:

\(\text{Unplanned Maintenance Downtime} = \frac{\text{Total Unplanned Downtime}}{\text{Total Time Period}} * 100\)

Example:

• Unplanned Downtime = 100 Hours

• Total Time Period =8760 Hours (1 Year)

\(\text{Unplanned Maintenance Downtime} = \frac{100}{8760} * 100 = 1.14\%\)

Photo by Paul Pastourmatzis on Unsplash

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3. Mean Time Between Maintenance - Measures the average operating time of any system before the system is stopped for planned or unplanned maintenance. This is hence a key indicator of system reliability.