VGB POWERTECH 11 (2019)

VGB PowerTech 11 l 2019
VGB-Book
Failures and Forced Unavailability of Power Plants
Henk C. Wels
VGB-B 035 | 2019
DIN B5, 276 pages, price: 48.– €, + VAT and postage
Failures and
Forced Unavailability
of Power Plants
Henk C. Wels
VGB-B 035
Power plants are not functioning to the fullest 100 % of the time. Maintenance and inspection of some components
require them to be off-line in time, however, this can be planned such that customers continue receiving power from
the electrical grid, steam or district heating from other plants. Unplanned outages due to failures or external conditions
may cause surprises and can lead to situations in which the demand is not satisfied at short term at large costs.
When plants are similar in size or when feasible given the number of plants, the N-1 principle can be followed. The
electrical grid operator has contracted a plant in hot standby or makes the plants in operation to set their power by
an amount of spare sufficient to remedy loss of a plant and that can be controlled up or down to keep the frequency
constant and the total demand being met. When a large number of plants are meeting the demand, a reserve factor
>1 can be applied depending on economical boundary conditions and/or grid connections with abroad.
When demand is not met, the grid operator has to lower this demand by curtailing load to make sure that generators
protection systems do not switch off so many generators that due to a domino effect a blackout occurs with
large parts of the grid without power. Therefore, forced unavailability results in additional installed power that takes
time to realize and it is costly. Unavailability, planned or forced, results for the owner of the plant in fixed costs
(capital, maintenance, personnel) that are not compensated by income from MWhrs produced if no margin would
be added to income.
Given this relevance, unavailability must be minimized, however, not at all costs. For reserve units that operate only
a few hours per year it does not pay to repair around the clock resulting in minimum forced unavailability.
The overall costs must be minimized at maximum production income within market and regulatory constraints.
In this book unavailability is modeled both qualitatively and quantitatively. Without modeling, (describing how
power plants seem to react on the factors that define unavailability) one cannot optimize. With modeling comes the
ability to forecast unavailability as a factor of influence factors such as operation hours, starts, plant layout. Models
for human decision making are not discussed, only the effects of this decision making are studied.
The book is derived from earlier papers presented at ESREDA, PGMON, VGB Working Groups and other committees
while working with KEMA and its legacy companies and departments NRG, DNV-GL and DEKRA. The consent of
representatives of these organizations and firms for copying and further publishing has been granted. The names of
power plants still operating have been omitted or made anonymous. A description of the work of ESREDA is given.
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