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General Task of a Grid Study
In general, the purpose of a grid study is the analysis
of a mains with regard to load flow, short-circuit resistance and
selectivity. Resulting from this analysis it is possible to
ascertain the general state of the operating conditions and verify
the correct dimensioning of grid elements and protective device
settings.
Analysis
The analysis comprises the following operation steps in
order
- Compilation of the necessary grid data.
- Load flow calculation of different grid configurations and
load conditions with check of the branches’ capacity and nodes
voltage level.
- Calculation of the minimum and maximum fault currents during
short circuit and earth fault for different grid
configurations.
- Control of the grid and grid components’ dimensioning and
modification, in need of improvement .
- Verification of the protective devices’ selectivity.
- Determination/improvement of the protection concept.
Evaluation
With each grid study, the following load flow data are
calculated:
- Inadmissible deviations of calculated node voltages from the
nominal voltages.
- Inadmissible deviations of calculated branch currents from
the nominal currents.
- Maximal operating currents, total losses, reactive power
balance.
Furthermore, the load flow study may as well give evidence of
the grids effectiveness.
Short circuit currents are calculated in compliance with the IEC
standard 909 or with DIN VDE 0102. The following short circuit
types are part of our calculations:
- three-pole short circuit as max. short circuit 3 Pmax
- two-pole short circuit as min. short circuit 2 Pmin
- one-pole short circuit as max. earth fault 1 Pmax
- one-pole short circuit as min. earth fault 1 Pmin
Selection and dimensioning of the electrical equipment and
installations with regard to their mechanical and thermal
resistance is determined by the maximal short circuit current. The
minimal short circuit current is responsible for the selection and
setting of a protective system.
Optimisation
Analysis is only one thing – what counts more is, how
results are being handled!
As a responsible system provider, we do not leave you alone with
the results of this study. Together with you, we will look for
shortcomings and find possibilities for improvement in order to
then work out a tailor- made solution that will comply with your
wishes and requirements. Your advantage: You can get everything
from one single source: development of protective devices, LV –
switchboards or a complete mechanical construction. Whatever you
need: Our specialists will be glad to engineer, coordinate and
immediately implement all these things for you. Thanks to our
long-year experience in the range of power generation, transmission
and distribution, we can assist and accompany you step by step
right from the start of a problem up to its’ solution.
Grid Studies with SEG – Some interesting facts
The computer-aided calculations are made with the program
NEPS-W, that was developed by DigSILENT GmbH (a German limited
liability corporation) and has been established in the market for
more than 10 years now. For almost the same period, this program is
being successfully applied by SEG. The enormous capacity of the
program allows grid calculations comprising a maximum of 10,000
operational devices. On principle, it is possible to calculate
three-phase systems for voltage ranges from 110V to 400 kV with
frequencies of 50 Hz and 60 Hz. For all calculations, different
operating- and load conditions as well as switch positions can be
simulated. All results are available in form of lists and can be
supplied as printouts. The most important information is directly
shown in the grid graphic where any overstepping of the
pre-selected electrical equipment limits is clearly marked.
