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ERACS Toolbars demonstration
This toolbar gives easy access to the calculations
ERACS can perform, such as, loadflow, transient stability, and IEC909.
Click on any of the buttons below to see an example of that calculation.
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Loadflow Study
The loadflow module calculates the steady state conditions of the
power system network. Under given constraints the module will determine
the network voltage profile, real and reactive power flows and transformer
automatic tap changer positions. On screen visual warnings are given
for overloaded system elements and busbars voltages outside user
specified limits. In the network below arrows indicate the direction
of power flow with tabular results available for inspection.
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Fault Calculation
(classical)
The fault module enables the user to calculate currents and voltages
around a network immediately following a fault condition. The module
provides facilities to simulate the following types of faults; phase
to earth, two phase to earth; phase to phase; and three phase to
earth. Faults may be applied at the terminals of any system elements
including busbars and at any point along the length of a cable or
line. The program also includes a survey option allowing user specified
faults to be calculated for each busbar in the system. In the example
below the location of the fault is highlighted by the 'results box'
and arrows indicate the direction of positive sequence power flow
with user selected results shown.
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Fault
Calculation (IEC909)
The ERACS IEC909 fault module is
a full implementation of the IEC standard. The module provides facilities
to simulate the following types of faults: phase to earth; two phase
to earth; phase to phase; and three phase to earth. The program also
includes a survey option allowing user specified faults to be calculated
for each busbar in the system. In the example below the location of
the fault is highlighted by the 'results box' with user specified
results shown. |
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Harmonic Injection
A polluting load, such as a rectifier or variable speed drive, has
the characteristics of drawing a non-sinusoidal current from a sinusoidal
voltage supply. Using Fourier analysis the current drawn from the
supply may be split into its fundamental and harmonic components.
This load may be represented as a harmonic current source 'injecting'
into the power system. The harmonic current will propagate into
the system and react with the network impedance to cause harmonic
voltage to appear. For any given study multiple injection points
may be specified at different voltages and locations across the
network. The harmonic characteristics are stored as user specified
library elements. The program calculates total harmonic voltage
and current distortion across the system as well as the individual
harmonic voltage and current values. In the example below percentage
total harmonic voltage distortion (TDv) and 7th harmonic voltage
(V) are shown.
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Harmonic
Impedance
A polluting load, such as a rectifier or variable speed drive has
the characteristic of drawing a non sinusoidal current from a sinusoidal
voltage supply. If the harmonic characteristic of the load is known
or can be approximated it can be injected into the system using the
harmonic injection program and its effect displayed. However if the
characteristic is not known the sensitivity of the network to harmonics
can be established by using the harmonic Impedance program. The harmonic
impedance calculation provides the facility to determine the impedance
at selected busbars over a range of definable harmonic frequencies.
This is achieved by injecting a one per unit current into selected
injection busbars. The resultant harmonic voltage is calculated for
the injected busbar and any other specified busbar known as the transfer
busbar. The voltage to current ratio gives the harmonic impedance.
The example output below shows the various resonance between busbars
in terms of harmonic number and impedance (Ohms). |
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Protection Co-ordination
The ERACS protection co-ordination program is three programs in
one. Protection devices (fuses, circuit breaker, relays and auto
re-closers) are added to the single line diagram and their co-ordination
and settings selected graphically on screen by moving between plug
and time settings etc.
Having selected the desired characteristics, the
protection program checks the suitability of the settings for the
current system connectivity under steady state loadflow conditions
(stability check).
The third facility allows a fault to be applied
to the network and the dynamic operation of the protection scheme
to be evaluated. This is particularly useful with interconnected
systems (many parallel fault paths). Typical graphical output is
shown below. During the dynamic stages results are also displayed
on the single line diagram.
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Transient
Stability Study
The ERACS transient stability program allows dynamic system behavior
to be studied (e.g. motor starting, fault application, load application
/ rejection and generator behavior). Multiple events are programmed
into ERACS with the result shown graphically (as below for a motor
start) and on the single line diagram. (The ERACS universal dynamic
modeller program (UDM) allows AVR and governor models to be built
and set-up for use within the transient stability program.) |
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