How to define a PSS™MUST
subsystem file to compute TDF factors:
NERC TDF (Transfer Distribution
Factors) factors show the impact of the Control area to Control
area transfers on the flowgates. To compute these factors using
PSS™MUST you need to create a subsystem file defining one
subsystem for each control area.
You may want to limit this file
to control areas of interest only. TDF factors report some average
distribution factors for proportional scaling of generators within
control areas. There are several different methods to define participation
factors (see PSS™MUST manual, section 3.2 for more details)
including:
Scaling load
Scaling generation
Scaling based on the machine's MBASE
In the past, NERC interim IDC has
been using "scaling by MBASE" with custom modification
for some (mostly nuclear) generators. If you try to create TDF
factors for your load flow case, it is likely that you would not
want to modify MBASE, as this would force you to use another adjustment
method such as scaling load or generation.
For most flowgates, different adjustment
methods yield similar factors. Unfortunately, for flowgates within
or close to the control areas of interest, results can be very
sensitive to the modeling assumptions. PSS™MUST has several
functions to study the sensitivity of the results to various adjustment
methods.
To create subsystems for load scaling,
use a subsystem file with just one line:
Add all areas scale load suffix " "
Subsystem names will be formed based
on area names as defined in your load flow case.
To create subsystems for scaling
generation, use a subsystem file with just one line:
Add all areas scale generation suffix "
"
An example of the subsystem file
for NERC seasonal IDC, to scale based on MBASE, can be downloaded
here.
How to define a PSS™MUST
subsystem file to compute GSF factors:
NERC GSF (Generator Shift Factors)
factors show the impact of generation redispatch between generator
pairs on the flowgates. To compute these factors using PSS™MUST
you have two options:
Define a subsystem for every generator
of interest using the command shown below:
/ The "Busnumbers" command forces bus
numbers to precede bus
/ names within automatically built subsystem
names
/ a 100 MW cutoff has been selected for illustrative
purpose only
Busnumbers
Add systems by generator with pmax greater 100
MW
Areas 1 9999
End
This will allow you to study the
impact of generation redispatch between any pair of generators
in the Eastern Interconnection. For the defined flowgates or for
the selected flowgate(s), you can obtain factors for selected
generator pairs. The only problem is that automatically created
names will not reveal control area ids within the subsystem name.
For internal studies, to reduce the total number of generators,
you may want to limit selected areas to the areas or regions of
interest.
If you want to perform a mass factors
calculation, you may want to create a large Excel table with the
‘reference’ bus factors on many or even all flowgates.
In this case it may be more convenient to create one subsystem
which includes all generators of the interest and then create
a sensitivity report for subsystem participating points. Subsystem
sensitivity reports display the control area number for each participating
generator which is helpful when dealing with NERC huge load flow
cases with over a hundred control areas and thousands of generators.
The following definition will help you to define these types of
subsystems:
Subsystem all_gens
Areas 1 999
Add all generators
End
Note that Excel is limited to
256 columns which limits the PSS™MUST sensitivity analysis
to 200 monitored elements. If you need to examine more than 200
elements, run the sensitivity analysis with 200 elements, save
the report and then run another sensitivity analysis with a different
set of 200 elements. The results are not co-dependent so you are
free to choose any set of 200 elements per report.
Do I need to define a contingency
file for TDF and GSF calculations?
Flowgate contingencies are defined
within the NERC flowgate monitored file. You do not need to define
contingencies, simply create an empty contingency file with only
the "end" statement.
