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FIELD OF INVENTION
This invention relates to a method for testing thyristor controlled series capacitor (TCSC) including its control devices for Flexible AC transmission system (FACTS). More particularly, the invention relates to a method for integrated testing, monitoring, and control of a thyristor controlled series capacitor (TCSC) in a flexible AC transmission system.
BACKGROUND OF THE INVENTION
The electricity supply industry of the world is developing fast, providing the users high voltage transmission systems with new opportunities and challenges. These opportunities arise mainly from the increase in inter regional and/or international power transfer, the effect of deregulation, and political, economical, and ecological considerations on the building of new transmission facilities.
Technically, limitations on power transmission capability in a grid can always be eliminated by adding new transmission and/or generation capacity. This, however may not be practicable or desirable in the real situation for a variety of reasons. Adding new lines and/or extending existing substations may be too costly and time consuming. Concessions for new right-of-way may be hard or impossible to come. The environmental impact aspects today are much more important than they used to be and need to be addressed in a serious way in conjunction with transmission development procedures. Therefore, it is imperative to develop methods for determining location of the Flexible AC

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Transmission System (FACTS) device, controller type and capacity through device analysis, and to analyze and evaluate FACTS application, to decide methods for structuring the FACTS system and basic specification.
TCSC is an important FACTS device that helps in balancing load flows, power swing oscillation damping, and mitigation of SSR.
To transmit large amount of power over distances, for example, in conjunction with establishing of power links between countries or different regions of countries, Thyristor-Controlled Series Compensation (TCSC) based on state of the art high power electronics helps to alleviate such constraints. TCSC thereby offers a superior option, from technical and environmental points of view.
FACTS has now developed into sophisticated system technology that combines conventional power system technologies with power electronics, micro-processor control, and information technology. Its objectives are achieving the enhancement of power system flexibility and minimum utilization of power transfer capability through improvements in system reliability, controllability, and efficiency. The choice of location, type, capacity and control algorithm of the FACTS device used has to be decided by analyzing requirements of the power systems and economics. Compared to conventional power system control devices, FACTS devices are expected to enhance the competence of the power system industry. It results in meeting the increasing demands of the system and provides methods for network congestion management and power system flexibility enhancement.

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The conventional method of testing the TCSC (Thyristor Controlled Series Capacitor) comprises testing of the individual components like the controller, the Base electronics, triggering system, the thyristor valves and reactor separately. The interfaces are then checked and the system is charged, which lacks proper synchronization and adjustment of network impedance resulting disruption in stability of the power system, balancing of loads, damping of power swing oscillation etc.
The integrated testing of all the components in the system can not be done as high voltage and current is required to carry out the test which is not feasible during installation of high voltage power transmission system.
The firing instant of the thyristor valves in TCSC being very critical as any change in the firing angle can cause huge changes in the resultant impedance of the "TCSC" which warrants proper synchronization of all the components. Any error in the synchronization process can cause considerable over voltage and stress damaging the expensive power equipment.
Further, a thyristor valve comprises multiple thyristor levels which would require large voltage for triggering. Another disadvantage is that the synchronizing current being low, synchronizing voltage will be very low which results in erroneous triggering due to noise amplification.
A still another disadvantage of the art is that the valve voltage and the TCSC voltage measurement becomes quite difficult due to small magnitudes of the measured voltage.

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OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a method for carrying out integrated testing of all the components of thyristor controlled series capacitor.
Another object of the present invention is to propose a method for carrying out integrated testing of all the components of thyristor controlled series capacitor which is provided with multiple thyristor levels and monitoring system for proper triggering to ensure sequencing of firing of thyristor valves.
A still another object of the present invention is to propose a method for carrying out integrated testing of all the components of thyristor controlled series capacitor which is capable of achieving amplification of synchronized signal without noise amplification.
A further object of the present invention is to propose a method for carrying out integrated testing of all components of thyristor controlled series capacitor which enables direct voltage measurement across the thyristor valve and the TCSC.

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SUMMARY OF THE INVENTION
Accordingly there is provided a method for integrating testing, monitoring, and control of a thyristor controlled series capacitor (TCSC) in a flexible A.C. transmission system (FACTS). The TCSC comprise, at least one thyristor valve having a plurality of anti-parallely connected thyristor in series, a voltage divider connected across the TCSC to measure voltage, a reactor disposed in series with the thyristor valve, a series compensating capacitor shunted by the reactor being connected to the thyristor valve in series, a controller and regulator for generating, control pulses representing data on system conditions, a triggering and monitoring device for converting the control pulses to firing and monitoring pulses and transmitting the converted pulses to the thyristor valve. A cathode ray oscilloscope is provided for directly measuring the voltage across the thyristor valve. A 415 - V. AC power supply source is arranged for power supply. The method comprise the steps of energizing the TCSC via the power supply source, amplifying the synchronized signals without noise amplification via the current transformer disposed in the power transmission line, impedance matching of the system by connecting the reactor in parallel with the compensating capacitor; and controlling the resultant impedance in measuring the voltage of the thyristor valve via the CRO; synchronizing the line current via the first CT, TCSC voltage through the voltage divider, and the reactor current through a second CT; generating control signals via the controller and regulator based on synchronized signals and receiving the control signals and converting the received signals to a plurality of firing and monitoring signals to fire and monitor the thyristor valve.

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BRIEF DESCRIPTION OF THE ACCOMPANYING DRWAINGS
Fig. 1 shows the TCSC main circuit.
Fig. 2 shows the Generic waveforms for the TCS. From top to bottom: line current, valve current, capacitor voltage and apparent reactance.
Fig. 3 shows the Typical Impedance characteristics of TCSC. Fig. 4 shows the TCSC and its components. Fig. 5 shows a Detail of the Thyristor Valve and its Triggering. Fig. 6 shows all the Equipment to be integrated for testing. Fig. 7 shows a Scheme for Integrated testing.
Fig. 8 shows how the Bypassing the levels in the thyristor valve is carried out for the integrated testing.
Fig. 9 shows a plot of the Thyristor voltage during integrated test at maximum conduction.

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DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION
According to the present invention a modified thyristor valve, modified line current measurement devices and direct measurement interfaces to the thyristor valve have been provided.
The method of the invention comprises connecting a series compensating capacitor (1) shunted by thyristor-controlled-reactor (2) with a thyristor valve (3) in series as illustrated in fig (1).
The inventive feature constitutes in a step of configurating an add-on thyristor controlled reactor branch in parallel with the series capacitor bank.
When a forward biased thyristor is fired a circulating current pulse flows through the LC circuit constituted by the thyristor controlled inductive branch and the capacitor bank. The circulating current pulse passes through the capacitor in phase with the line current. It creates an additional voltage across the capacitor in excess of the voltage, which is caused by the line current. The increased voltage at a given line current amplitude is perceived by the transmission system as if the inserted capacitive reactance had been increased or boosted by the action of the thyristor valves. The generic wave form of the TCSC is shown in Fig. (2). According to the invention a continuously variable capacitor is provided. Since the TCR at the fundamental system frequency is continuously variable reactive impedance, controllable by delay angle V, the steady state impedance

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of the TCSC constitutes that of a parallel LC circuit, consisting of a fixed capacitive impedance, XC, and a variable inductive impedance XL (a),

The resultant impedance characteristics of impedance versus firing angle is given in fig (3).
According to the present invention, the operation of the integrated system can be illustrated as per Fig. (7), which depicts the complete assembly of components comprising compensating capacitor (1), a thyristor valve (3), a reactor (2), a voltage divider (4). A line current transformer (8) current transformer for reactor current (16), CRO (9) triggerings monitoring device (11), controller and regulator (12) and a 415 V, A.C source (7). The thyristor valve (3) comprises a plurality of anti-parallel connected thyristors (14) in series as shown in fig (5).
The thyristors (14) have a thyristor electronics (15) controlled device which can trigger and monitor the health of the thyristors. The thyristor electronics modules (15) are optically interface to a Base Electronics and thyristor monitoring (BETM) panel (Triggering and monitoring device).

10 TRIGGERING AND MONITORING DEVICE
The Triggering and monitoring device converts the control pulses to firing and monitoring pulses and sends these optical pulses to the thyristor valve.
A controller (12) is housed in the main control room which generates the control pulses depending on the system conditions and these pulses are interfaced to the triggering and monitoring device. The line current measured by the line is used for synchronization and the voltage divider (4) connected across the TCSC (1) is used to measure the voltage.
But integrated testing at the module circuit is not feasible at site during installation and a separate supply source required the present invention has further resolved the problems by providing an integrated testing device of the components as shown in fig (6) & (7), wherein a 415V, 3ph supply (7) has been provided to energize the circuit of system parameters, a voltage divider (4) connected across the TCSC (1) to measure the voltage, a first CT (8) of lower ratio instead of higher ratio CT provided, so that adequate amplification of the synchronizing signal is achieved without noise amplification.
A CRO (9) has been provided to directly measure voltage across the thyristor valve (3). A reactor (2) is provided in series with the system for impedance matching. A triggering and monitoring device (11) has been provided which receive control signals from the controller and regulator (12) wherein triggering and monitoring device (11) converts control pulses to firing and monitoring pulses and send these optical pulses to the thyristor valve (3).

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The line current through the first CT (8), TCSC voltage through the voltage divider (4) and reactor current through second CT (16) are used for synchronization and generating control signals for firing and monitoring of the thyristor. The integrated testing is carried out with the above set up and thyristor voltage form is plotted as per fig (9) and fig (10) at maximum and minimum conduction interval which has been found in order.

12 WE CLAIM
1. A method for integrating testing, monitoring, and control of a thyristor controlled series capacitor (TCSC) in a flexible A.C. transmission system (FACTS), the TCSC comprising:
at least one thyristor valve (3) having a plurality of anti-parallely connected thyristor in series (14),
a voltage divider (4) connected across the TCSC (1) to measure voltage;
a reactor (2) disposed in series with the thyristor valve (3);
a series compensating capacitor (1) shunted by the reactor (2) being connected to the thyristor valve (3) in series;
a controller and regulator (12) for generating, control pulses representing data on system conditions;
a triggering and monitoring device (11) for converting the control pulses to firing and monitoring pulses and transmitting the converted pulses to the thyristor valve (3);

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a cathode ray oscilloscope (9) for directly measuring the voltage across the thyristor valve;
a 415 - V. AC power supply source (7), the method comprising the steps of :
energizing the TCSC via the power supply source (7),
compensating the line impedance via connecting the capacitor (1) in series with the transmission line
impedance matching of the system via connecting the reactor (2) in parallel with the compensating capacitor and controlling the resultant impedance
measuring the voltage of the thyristor valve (3) via the CRO (9);
sensing the line current via the first CT (8), TCSC voltage through the voltage divider (4), and the reactor current through a second CT (16);
generating control signals via the controller and regulator (12) based on synchronized signals; and

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receiving the control signals and converting the received signals to a plurality of firing and monitoring signals to fire and monitor the thyristor valve (3), leading to generating controlled current to flow through the capacitor/reactor circuit.
2. The method as claimed in claim 1, wherein the first current transformer
(8) senses the line current for the controller and regulator (12).
3. The method as claimed in claim 1, wherein the voltage divider (2) senses
the voltage of the compensating capacitor (1).
4. The method as claimed in any of the preceding claims, wherein the
second current transformer (16) senses the reactor current.
5. A method for integrating testing, monitoring, and control of a thyristor
controlled series capacitor (TCSC) in a flexible A.C. transmission system
(FACTS), as substantially described and illustrated in the accompanying
drawings.
Dated this 4th day of JANUARY 2007.