KPI Calculation Service – KPI Definitions¶
This section introduces common Key Performance Indicators (KPIs), which are based on the following standards:
- Gas turbines - Procurement - Part 9: Reliability, availability, maintainability and safety. BS ISO 3977-9:1999. British Standards.
- IEEE Standard Definitions for Use in Reporting Electric Generating Unit Reliability, Availability, and Productivity. IEEE Std 762™-2006. IEEE Power Engineering Society.
These standards were mainly designed for gas turbines and compressors. However, the specified KPI values are mandatory in any analysis of an industrial system whose reliability, availability and maintainability should be quantified based on historical data, such as sensor and control unit signals or a maintenance calendar.
An asset spends time in various KPI states, which are referred to as State KPIs. The KPI Calculation Service uses the following State KPIs:
- No Data Hours (
NoData) - Time, in hours, where required data from the unit is unavailable. This KPI is introduced to deal with possible data gaps.
- Period Hours (
PH) – Time, in hours, inside the period under consideration.
- Available Hours (
AH) – Time, in hours, during which the unit was capable of providing service, regardless of the capacity level that it provides.
- Service Hours (
SH) – Time, in hours, during which the unit was in-service.
- Reserve Shutdown Hours (
RSH) – Time, in hours, during which the unit was available, but not in service.
- Unavailable Hours (
UH) – Time, in hours, during which the unit was not capable of operation because of operational or equipment failures, external restrictions, testing, work being performed, or an adverse condition. The unavailable state persists until the unit is made available for operation.
- Planned Outage Hours (
POH) – Time, in hours, during which the unit (or a major item of equipment) was originally scheduled for a planned outage including the estimated duration plus the extension of planned work beyond this. The extension due to either a condition discovered during the planned outage or a startup failure would result as forced (unplanned) outage.
- Forced Outage Hours (
FOH) – Time, in hours, during which the unit was unavailable due to a component failure or another condition that requires the unit to be removed from service immediately or before the next planned outage.
The following equations always hold true:
1 2 3
PH = NoData + AH + UH AH = RSH + SH UH = FOH + POH
Availability Factor (
AF) - Probability that the unit will be usable at a point in time, based on the experience:
AF = [AH/ (PH – NoData)] x 100%
Unavailability Factor (
UF) - Probability that the unit will be unusable at a point in time, based on the experience:
UF = [UH/ (PH – NoData)] x 100%
Reliability Factor (
RF) - Probability that the unit will not be in a forced outage condition, based on the experience:
RF = [(PH – FOH – NoData) / (PH – NoData)] x 100%
Service Factor (
SF) - Probability that the unit will not be in an operating condition, based on the experience:
SF = [SH/ (PH – NoData)] x 100%
Forced Outage Factor (
FOF) - Probability that the unit will be in a forced outage condition, based on the experience:
FOF = [FOH/(PH – NoData)] x 100%
Mean Time Between Failures (
MTBF) - Average time between failures which initiate a forced outage, based on the experience:
MTBF = SH / FO
FOis the number of forced outages.
For simplicity, N/A is used for indicating when the KPI value cannot be correctly computed, e.g., when PH = 0, PH = NoData or FO = 0.
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