VGB POWERTECH 11 (2019)

A journey through 100 years VGB | VGB POWERTECH 4 (2006)
Pumped Storage Power Plants
minute reserve (MR). For this purpose, idle
plants are started manually as needed, in order
to compensate for unscheduled power
plant breakdown as well as other events.
These balancing modes enable PSP to make a
contribution to grid voltage control and reactive
power. Furthermore PSP re-establish the
supply of electricity in the case of grid breakdowns
by its black start feature.
Plant Characteristics and the
Power Plant Portfolio
PSP are used depending on their characteristics.
The key factors are plant size, roll-over
efficiency, mode-switching time and age.
High roll-over efficiency and large turbine
capacity predestine plants for classical peak
load covering. Primary control requires extremely
short mode-switching times, placing
high demands on dynamics. Therefore, very
old PSP, whose components no longer withstand
high stresses, are less suitable to this
task. In the context of grid control, these
plants tend to contribute to the MR instead.
However, the size and composition of a company's
or group's power plant portfolio also
affect the way in which their power plants are
operated. In small power plant portfolios, the
hydraulic short circuit can also be of interest,
as its effect on the grid can be controlled via
the turbine capacity when in simultaneous
pump and turbine operation mode. But this
mode of operation decreases efficiency due
to the pipe friction and pump losses incurred.
The composition of the available portfolio
of power plants has a major impact on the
number of mode switches required on a daily
basis.
Power Plant Operator Requirements
Analysis of Modified
Power Plant Operation
With the exception of the newest plants, PSP
are built for peak load covering. The grid
controlling tasks resulting from the change in
framework conditions have increased the importance
of by this type of power plant and
improved sales considerably. But the operational
demands placed on PSP have grown
substantially as well. A project group of the
Technical Committee “Hydro-power Plants”
of the VGB is addressing this problem and
has collected extensive amounts of data that
are currently being analysed.
However, the analysis is proving to be quite
difficult due to a very heterogeneous picture.
It is difficult to extrapolate clear trends. This
is due to the various ways in which different
PSP are operated, as described earlier (Figure
11). The chart shows the divergent
deployment paths taken by two of E.ON
Wasserkraft's pumped storage plants. Although
the plants both experienced a clear
rise in operating hours, this did not automatically
result in an increase in electricity production.
Electricity production in PSP Erzhausen
remained essentially unchanged, because
the plant is kept on standby at minimum
load, ready to increase turbine capacity
when needed. In fact, start-ups decrease over
the period under review, since the plant runs
at minimum load even outside peak periods.
Even individual units in one and the same
plant cannot be uniquely classified under a
major mode of operation since requirements
change over the course of the year. Therefore,
a more detailed analysis is underway,
which pays tribute to these circumstances.
Identifying Critical Components
PSP heightened status within the power plant
portfolio has led to a rise in their required
availability. Unscheduled breakdown would
result in significant follow-up costs. One of
the reasons for this is the fact that PSP differ
from each other, featuring specific technical
designs. Consequently, many spare parts are
built to order, causing prolonged downtime
in the event of a failure. To prevent such failures,
PSP operators are faced with the task of
identifying critical components, which can be
key components to plant failure under certain
conditions. This means they have to cooperate
closely with plant manufacturers, since
they are the only source of in-depth knowledge
of the plants' structural design. In turn,
plant manufacturers require the plant operators'
information and experience relating to
changes in the conditions under which the
plants are used. Once critical components are
identified, one must develop monitoring
measures for control during operation as well
as constructive suggestions for improvement
to ensure the reliability of plant operations.
Extrapolating Power Plant
Operation Standards
Growing sales are a strong incentive for using
PSP in the broadest possible capacity
spread. The minimum capacity in partial load
mode is very important in this context. Since
minimum capacity at partial load - an option
not originally envisaged – can last for extended
periods of time in certain plants, it has
to be taken in account that this does not damage
the plants. This requires one to conduct
technical assessments to determine the minimum
load possible without running into
problems.
Adapting the Maintenance
Philosophy
A plant's technical state largely depends on
its operating stress and hours of operation.
Dynamic work with frequent operating transitions
and load changes in many plants has
changed the mechanical stress to which they
are subjected. Maintenance carried out in all
PSP is definitely oriented towards the plant's
state, i.e. necessary maintenance tasks are derived
from the plant's technical state. In PSP,
however, many areas are very difficult to access
for inspection purposes. This holds true
especially for areas that come into contact
with water, making empirical expert estimates
indispensable. But they are yet to be
derived based on the change in usage requirements.
It is absolutely necessary to make an
accurate assessment, taking account of the
specific usage conditions.
Diagnostic systems including sophisticated
vibration monitoring devices and endoscopic
tools are increasingly used to improve the
monitoring of plant components that are difficult
to access.
Design Criteria for New Plants
It is to be expected that there will be a rise in
demand for peak-load plants, and thus for
PSP. Tradings on deregulated electricity markets
will rise, and additional wind capacity
will further be installed. What is crucial to
new PSP is that initial experience garnered
by plant operators be considered when plant
manufacturers work on their design. Both
parties should get together to cooperate constructively
in determining design criteria for
new plants aside from bid negotiations,
which are normally conducted under time
pressure and influenced by divergent interests.
The ensuing advantages would benefit
everyone involved.
Co-operating with Other
Plant Operators
It would be extremely beneficial if plant operators
shared experiences with each other,
especially since the impact of changes in
power plant deployment on PSP availability
and lifetime are so difficult to predict. Exchanging
information will accelerate the
learning curve, creating a broader basis for
deriving operational measures, e.g. as regards
monitoring, inspection, critical components,
minimum capacity and maintenance strategies.
It remains to be seen to which extent
further activities prove useful, e.g. real cooperation
in large-scale maintenance measures
with personnel support, in order to compensate
for bottlenecks in manpower. The VGB
has created a basis for this with its Pumped
Storage Plant Project Group.
Outlook
PSP must – and will be capable of – making
an important contribution to peak load covering
and grid controlling in the future as well.
The progressing deregulation of the EU electricity
market will lead to further growth in
cross-border trading. Furthermore, wind capacity
can be expected to expand. The only
unanswered question is the degree to which it
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