Distribution analysis in a GIS environment
Since the PSS/Engines are function libraries, the interface to the PSS/Engines is accomplished at
the programming level with function calls. There are no intermediate files to maintain. Each engine
has a well-defined and stable application program interface (API). Interface with the user of the
GIS is entirely under control of the programmers doing the integration and should retain the look
and feel of the GIS environment. The PSS/Engines are written in C++ to take maximum advantage
of object-oriented software technology but the functions in API of the PSS/Engines follow C
programming conventions. This permits the PSS/Engines to be used with programs written in C,
C++, or even Visual Basic on Windows computers. The individual engines within the PSS/Engines
are described below.
Base Engine
The base engine provides a number of support services used to build and maintain an electric
network and the components that make up the electric network. An electric network (also called a
power system) is a collection of producers of electric power (sources and generators), consumers
of electric power (loads, motors, etc.), devices to transfer electric power from producers to
consumers (lines, transformers, switches, etc.) and miscellaneous other items (shunt capacitors,
controllers, etc.). The base engine's support services consist of functions to manipulate these
items; that is add, delete, and modify. The base engine also provides functions that perform loadflow,
short-circuit, and motor-starting calculations.
Capacitor Placement
The capacitor placement engine is used to find the best sites in a network to place capacitors.
Here "best" refers to the locations with the highest financial return considering the initial cost of the
capacitor, annual maintenance cost of the capacitor, and cost of real and reactive power losses.
Several load levels can be considered at the same time. Result of the optimization is the set of
locations where capacitors should be placed; which capacitor(s) should be placed at each site; and
whether or not a switched capacitor is needed at the site because of voltage constraints. Where
switched capacitors are required, a switching schedule is produced. Loss, cost of loss, and
information that quantifies financial return is also calculated.
Predictive Reliability
The distribution reliability analysis engine implements predictive reliability calculation methods for a
radial network. It uses equipment outage-frequency and repair-time statistics to calculate
customer-specific and/or system-wide loss of service statistics. The calculations in the predictive
reliability engine can be used to evaluate the performance of a protection scheme or compare the
reliability of alternate protection schemes.
Fault Decrement
The fault decrement engine is used to estimate currents in a network during the first few cycles
following a fault. Both time-decaying DC offset and machine contribution to fault currents are
considered. The fault decrement engine calculates make and break duty as well as symmetrical
and asymmetrical rms currents and can be used for breaker sizing as well as relay coordination.
Harmonics Engine
The harmonics engine is used to put harmonic analysis into an application. Harmonic analysis
investigates the behavior of an electric network at frequencies higher than the fundamental
frequency. Most electric networks operate at 50 or 60 Hz, called the fundamental frequency. Some
devices on these networks cause significant noise at higher frequencies. This noise, or harmonic
pollution, corrupts the normal voltage waveform and can cause unwanted heating in transformers,
misoperation of protective devices, and excitation of resonance. The harmonics engine provides
tools to investigate these phenomena including functions to calculate standard measures of
harmonic distortion such as total harmonic distortion (THD), telephone influence factor (TIF) in
addition to functions that determine harmonic spectra and find resonance frequencies.
Load Estimation
The load estimation engine is used to scale or estimate loads in a portion of an electric network.
Often, because of insufficient instrumentation, only the location and rough characteristic of loads
are known. The exact magnitude of the load is unmeasured and therefore unknown. When an
"upstream" measurement of power or current is available, it can be used to estimate the magnitude
of "downstream" loads. The load estimation engine adjusts the magnitude of selected loads so
that power or current in a selected line or transformer matches a specified value. In this way, an
estimate of load magnitudes is obtained.
