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As part of News24's reporting on The Eskom Files, an extensive data investigation into key performance metrics used by Eskom was undertaken. This glossary is intended to assist readers in understanding some of the terms.
Energy Availability Factor
The overall measure of Eskom generation performance. It is calculated by taking the total theoretically possible generation capacity over a given time period (100%) and deducting the "losses" incurred as a result of generation units being offline for PCLF, UCLF and OCLF (explained below). A more general description is that EAF represents the electricity that was available to be generated
Installed Capacity
This refers to the total, theoretical generation capacity (usually calculated in megawatt-hours - MWh) that an electricity generation unit has. This is calculated as follows:
There are 720 hours in a 30-day month. A 500MW generation unit therefore has an installed capacity of 360 000 MWh in that same month (500MW x 720 hours).
(A unit refers to the machinery associated with one turbine that generates power.)
Planned Capability Loss Factor – PCLF
This is the amount of time generation units were taken offline for planned outages – being planned repairs or maintenance – and is calculated as a percentage of the total installed capacity over the same time frame.
Unplanned Capability Loss Factor – UCLF
This is the amount of time generation units were taken offline for unplanned outages – being unplanned repairs or maintenance – and is calculated as a percentage of the total installed capacity over the same time frame. UCLF also includes Partial Load Losses, explained below.
Operational Capability Loss Factor - OCLF
This is the amount of time generation units were taken offline for outages caused by things that are outside of the unit’s manager’s control and is calculated as a percentage of the total installed capacity over the same time frame.
Outages
UCLF, PCLF and OCLF are also commonly referred to as outages simply meaning the unit was out of service.
Full Load Loss
This is when an entire unit is offline as a result of any factor that resulted in the unit being unable to run.
Partial Load Loss
This is when a unit is run at below optimal levels usually as a result of a fault that requires the unit to be run at lower speed, or load, either because the fault results in the unit being unable to run at higher load, or because running the unit at full load with the fault could result in the unit breaking down.
Generation Load Factor – GLF
This is an indication of how hard a unit is working. It is a percentage of the actual MWh produced compared to the total installed capacity over the same time frame. A 500MW unit that produced 234 000 MWh in a 30-day month, or over 720 hours, will have a generation load factor of 65%.
Energy Utilisation Factor – EUF
EUF is the most useful performance metric and is similar to GLF, but it also considers EAF. Simplistically, EUF is the generation load factor during the periods when the unit was available.
For example: A 500 MW unit can, theoretically, produce 360 000 MWh in a 30-day month. If planned maintenance is done for 5 days, this will result in PCLF of 16.67% because 60 000 MWh were ‘lost’. Then the unit breaks, leading to a repair that takes 48 hours, or two days. This will result in 6.67% of UCLF, because 24 000 MWh was ‘lost’. The unit produces 234 000 MWh in the same month. That means the unit had a generation load factor of 65%, and an EAF of 76.6% (100% - PCLF – UCLF -OCLF). The unit had no OCLF for this month.
The EUF for the month for the unit then is calculated as a percentage: GLF divided by EAF x 100. The unit then had an EUF of 84% for the month.
An EUF above 80% is not ideal for coal fired power stations and it shows the units at the power station were run harder than what is advisable.
Cold reserve
This is when a unit is not running because it is not needed. Eskom rules state however that if a unit is placed under cold reserve, the power station must be able to bring the unit back online within a stipulated time frame in case its needed, referred to as call up time. If a unit is placed under Avalailabe Cold Reserve, or AVCR, no work may be done on the unit.
Opportunity Maintenance during Operation - OMOR
This is when work is done on a unit while it is still running. The most common example of this is when a set of coal mills (which grind the coal into fine dust) is taken offline to be fixed while the remaining mills are used to keep up with the coal being supplied to the boiler.
Opportunity Maintenance during Cold Reserve - OMCR
This is when opportunity maintenance is undertaken on units while they are in cold reserve. The work is not allowed to be so significant that could affect its ability to come back online within the call up time may be done.
