01-05-2012, 10:23 AM
Capacitive Voltage substations Ferro resonance Prevention Using Power Electronic Devices
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Introduction
The development of sparsely populated areas
results in the extension of electrical transmission networks to
remote and rural communities as well as industries such as
mines, ore processing, forest products and secondary
industries such as tourism. The capacitive divider technique
has been known for quite a while but using this technology to
transform high voltage to medium voltage for delivering
power to remote areas is more recent. With this technique,
energy is drawn from the electric field of the high voltage
transmission line by use of discrete capacitors. This
technique leads to important cost reduction when compared
with more conventional electromagnetic coupling systems,
e.g. high voltage power transformers [1].
Model development
Using the data for a real capacitive substation, a
model is developed and simulated in this paper. EMTDC
andMATLAB software’s are used to develop the model.
Occurrence of Ferro resonance in different system conditions
such as short circuit, system energization and load rejection
are simulated and analyzed using this model. A capacitive
substation with the service capacity of 1650KVA three phase
and components data included in Table, as introduced in
reference [1] is used for this study. System load is assumed
to be pure ohmic and is modeled by a resistor. The
transformer saturation behavior is built from the voltagecurrent
curve given by reference [6].
Simulation of transient cases
Using the capacitive substation model, many
different simulation studies are performed and performance
of the model was evaluated. Obtained results are similar to
what is reported in the literature, so the model accuracy
issatisfactory.Through different simulations, it was observed
that in some transient cases, dangerous
ferroresonanceovervoltages occur. These critical cases are
outlined below.
Ferroresonance suppression method
Simulation results represented that in different
system conditions such as short circuit, system energization
atno-load and load on/off the Ferro resonance
overvoltagesoccur. This problem is the major obstacle in
using this optimal rural electrification technique. Hence, it is
necessary to find out a method to damp theferroresonance
overvoltages.A new technique to damp dangerous over
voltages is proposed and evaluated in this paper. In this
technique, by using power electronic devices a damper
resistor is switched to the secondary side of transformer,
when it isnecessary.For designing the desired FSC, the
following points should be considered:
Conclusion
The system of capacitive substation which is
intended to supply electricity to rural communities does not
require a costly power transformer and leads to major cost
reduction. In contrast, the problem of Ferro resonance is the
major obstacle of using this technique. In this paper a reliable
method to suppress the transient over voltages
offerroresonance is offered. The ability of this technique is
tested in transient cases in which the dangerous over voltage
can occur. Obtained simulation results prove the usefulness
of the proposed method.