08-09-2014, 10:49 AM
FLEXIBLE AC TRANSMISSION SYSTEM – THRISTOR CONTROLLED SERIES CAPACITOR PROJECT REPORT
TRANSMISSION SYSTEM.pdf (Size: 982.88 KB / Downloads: 35)
ABSTRACT
As our topic is Flexible AC transmission System, till yet we have covered the literature
survey of the topic including the scenario of current power system and need of FACTS
devices to improve the situation. We have discussed various types of FACTS devices as
series and shunt. We also have discussed the working of various of such devices. We
also took help of MATLAB simulation help to analyze the performance of such devices
in closed loop system. Further onwards we will be doing the analysis of one of the FACT
device “Thyristor Controlled Series Capacitor (TCSC)”. Here we will be doing circuit
analysis of TCSC with respect to power system, including steady state and transient
state stability. Here all study is done by the help of dynamic phasor model of TCSC. The
dynamic phasor model is derived based on previous work done by Mattavelli et al. The
concept of generalized averaging method, also referred to as dynamic phasors
approach, was proposed into model power electronics based equipment. The main idea
behind this method is to represent the periodical or nearly periodical system quantities
not by their instantaneous values but by their time varying Fourier coefficients
(dynamic phasors). The variations of the time varying Fourier coefficients are much
slower than the original instantaneous values.
INTRODUCTION
Thyristor-controlled Series Capacitor (TCSC) is capacitive reactance compensator which
consists of a series capacitor bank in parallel with a thyristor-controlled reactor (TCR) in
order to provide a smoothly variable series capacitive reactanceThe main control unit of the TCSC is the TCR, which is a static var controller providing
fast control over the reactive power using power electronics. By means of the firing
angle of the thyristors the effective inductive reactance can be controlled and causes
rapid reactive power exchange between the TCR and the system. By controlling the
TCSC reactance one can compensate the line impedance and thus allow increased
power flow through the line. This fast control of line impedance can be used for
damping power system oscillations,
CHARACTERISTIC AND CIRCUIT ANALYSIS OF TCSC
the TCSC has a hybrid characteristic due to the thyristors T1 and T2. The thyristor can
be modelled as an ideal switch that closes if the voltage between anode and cathode is
positive and a non-zero gate signal is applied. It opens again if the current through the
thyristor re-crosses zero. The switchings of the thyristors are alternated at the system
frequency. Hence the time domain model equations of the per-phase TCSC can be
given as
where q is a switching function that shows the thyristor status: q = 1 if one thyristor is
conducting and q = 0 if both thyristors are blocking. The time argument t has been
omitted for clarity. Now by seeing the behavior of two thyristors the whole operation
can be divided into 5 parts.
STEADY STATE ANALYSIS OF TCSC
The steady state harmonic contents of the capacitor voltage v and TCR current i can be
calculated with the steady state analytical expressions independence of the reference
conduction angle σr
. For example, the k
th steady state harmonic content Vk of the
capacitor voltage v yields,
where the steady state capacitor voltage depends on the reference conduction angle
σr
. To calculate the analytical expression for Vk in dependence of σr
, the analytical
expressions for the v and i in intervals (1-5) must be calculated. Starting with interval
(2) where the TCR branch is conducting, the TCSC model is given by the equations (6.5)
and (6.6). There are two boundary conditions in this interval, namely the TCR branch
current must be zero at the beginning and at the end of the conducting interval.
CONCLUSION
In this project report we have tried to calculate and analyse the harmonics introduced
by both current and voltage waveforms when TCSC is employed in transmission line.we
have also tried to analyse the steady state stability of the system after employing facts
device.
In our further research we will try to simulate various fault conditions and see how
employing facts devices effects the faulty conditions.