Title of Invention

"AN APPARATUS FOR PROVIDING REACTIVE POWER SUPPORT REQUIRED BY POWER SYSTEMS"

Abstract

1. An apparatus for providing reactive power support required by power systems, comprising: - a controlled shunt reactor (1) coupled to thyristor (4); and - a controller for generating firing pulses based on the input signals; characterized in that a circuit breaker (CB1) in series with an inductive coil (L)being connected in parallel to the thyristor (4) across the controlled shunt reactor (1); said controller (16) capable of closing or opening the circuit breaker (CB1) based on the availability of the line voltage, thereby providing full reactive power support right from the first cycle of energisation.

Full Text

FIELD OF THE INVENTION The present invention generally relates to an apparatus for providing reactive power support required by power systems. More specifically the invention relates to a controlled shunt reactor with a bypass arrangement for providing synchronization with respect to the line voltage and availability of full reactive capacity right from the first cycle of energization. BACKGROUND OF THE INVENTION Application of controlled shunt reactor for the control of dynamic over voltages duringthe energization of transmission lines has been discussed in the patents Application Nos.l092/Del/98 filed on 27.4.1998 and 1481/De1/98 filed on 1.6.1999.The controlled shunt reactor (CSR) while possessing great technical advantages over the fixed shunt reactors (FSR), pose some technical challenges and special requirements. The purpose of the controlled shunt reactor is to provide inductive reactive power support whenever required by the power system. Controlled shunt reactor limits the dynamic over voltages an the line during line energization and sudden load throw off conditions by providing rated reactive power. On the other hand, under different line load conditions it provides variable reactive power support and thereby maintains improved voltage profile of the line. This fast variation of reactive power is achieved by controlled shunt reactor with the use of thyristor valves which can provide the necessary speed of switching and control by means of firing angle control. Controlled shunt reactor is a high impedance transformer controlled by anti parallel connected thyristors( valve) on the secondary side at a suitable voltage level. The impedance of controlled shunt reactor can be controlled by varying the firing angle of the pair through a controller. The controller is a logical and programmable device which generates firing pulses based on the input signals. For desired operation of controlled shunt reactor perfect synchronization with respect to the primary voltage is essential. As in the case of a fixed reactor, the controlled shunt reactor is expected to be available with full reactive capacity right from the first cycle of energization to control the switching dynamic over voltages. As the line is not energized there will not be any voltage reference available for correct synchronization. Thus availability of full reactive capacity cannot be ensured. This is one of the major challenge in the application of controlled shunt reactor in place of a fixed shunt reactor. Another aspect the utilities need to consider is the availability of reactive power under various operating conditions. The conventional fixed shunt reactor is a simple equipment with no control system. One end of fixed shunt reactor is connected to the line and with the other end connected to the ground, the equipment is permanently connected to the system.On the other hand controlled shunt reactor is controlled through thyristor valves. As these valves are meant to operate for high voltages and high power, they require continuous monitoring and protection. The eventualities of device failure in spite of redundancies built in, will lead to outages of the equipment. This situation is not desirable with an equipment which is expected to provide reactive power—support under all operating conditions. Thus, the advantages derived by retracting the reactive power under line loaded conditions will be offset by the damage that can occur due to non availability of reactor during line energization and sudden load throw off. SUMMARY OF THE INVENTION Thus the main object of the present invention is to provide an apparatus with a controlled shunt reactor that will ensure its full reactive capacity right from the first cycle of line energisation. Another object of the present invention is to provide an apparatus with a controlled shunt reactor that will ensure perfect synchronization of thyristor firing pulses. Yet another object of the present invention is to provide an apparatus with a controlled shunt reactor which ensures availability of full reactive capacity in the event of any failure or maintenance requirement on the part of thyristor valves and associated sub systems. These and other objects of the present invention are achieved by providing a bypass arrangement in the controlled shunt reactor configuration. The provision of this bypass arrangement with the control system will ensure the synchronization and availability requirements of the controlled shunt reactor. Thus the present invention provides an apparatus for providing reactive power support required by power systems,comprising a controlled shunt reactor coupled to thyristors and a controller for generating firing pulses based on the input signals characterized in that a circuit breaker in series with an inductive coil being connected in parallel to the thyristor across the controlled shunt reactor; said controller capable of closing or opening the circuit breaker based on the availability of the line voltage, thereby providing full reactive power support right from the first cycle of energization. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The invention can now be describned with reference to the figures of the accompanying drawing where Fig. 1 shows the general arrangementof a controlled shunt reactor on which the present inventionis applied Fig 2 shows the apparatus of the present invention with a controlled shunt reactor having a bypass arrangement . DETAILED DESCRIPTION The general arrangement of the controlled shunt reactor is shown in Fig. 1. The controlled shunt reactor 1 is connected to the lines 2 of the power system through an isolator 3. The controlled shunt reactor 1 is a high impedance transformer controlled by anti parallel connected pairs of thyristors (valve) 4 on the secondary side at a suitable voltage level. The impedance of the controlled shunt reactor 1 is controllable by varying the firing angle of the pair with the help of a controller 6. The controlled shunt reactorof the present invention with a bypass arrangement will now be describedwith the help of a circuit diagram depicted in Fig. 2. A circuit breaker CB1 is connected in parallel to the thyristor valve 4 in series with an inductive coil L across the secondary ( control) winding of the reactor transformer 1. As the secondary is star connected the other end of the choke L is grounded like the other end of thyristor valve 4. The value of L is chosen in such a way that when the current is flowing through the by pass path 4 the voltage drop across L will provide sufficient forward voltage to the thyristor valve 4 to conduct. A controller 16 which is a programmable device monitors the line voltage and regulates the operation of the circuit breaker CB1 and thyristor valve 4. The controller 16 is a programmable logic controlled capable of firing pulses based on the input signals. When the line 2 is not energized or when the voltage of the line 2 is not available the controller 16 keeps the circuit breaker CB1 closed. This condition takes care of the line energization condition with no voltage available. As the circuit breaker CB1 is closed the secondary of the reactor transformer 1 gets short circuited and on energization full capacity of reactive power is provided. After the line 2 gets energized controller 16 senses the line voltage and synchronized firing o pulses are released at 90 . With this the secondary current of the reactor transformer! gets diverted through the thyristor valve path. The circuit breaker CB1 is then opened by the controller 16. Thus, during the line energization controlled shunt reactor will be able to provide full reactive power support right from the first cycle of energisation. After the energizatgion the controller 16 can regulate the reactive power by providing firing pulses at the required firing angle with o respect to voltage signal. With pulses at 180 the reactive power becomes zero. Thus the controller 16 with voltage dependent control loop can bring the full reactive capacity within a maximum of 10 milliseconds during a sudden over voltage and bring down the capacity from full to zero under low voltage condition. The controller 16 also will be monitoring the health of the thyristor valves 4 and its sub systems. In case of any failure of any of these systems the controller 16 closes the circuit breaker CB1 and blocks the pulses to the thyristor 4. The controller shunt reactor continues to supply full reactive power under this condition also. By opening an isolator 5, required maintenance work can be undertaken on the thyristor valve side. After restoring normalcy the controlled shunt reactor can be brought back to thyristor control on line by closing the isolator 5. Sensing the healthiness of the thyristor valves 4 the o controller 16 issues firing pulses at 90 and subsequently opens the circuit breaker CB1. Thus the controlled shunt reactor of the present invention ensures availability of full reactive capacity right from the first cycle of energization. The provision of the proposed bypass arrangement fulfils the synchronization and availability requirement of the controlled shunt reactor of the present invention. Further, the arrangement of the present invention has provision for carrying out required maintenance work on the thyristor valve side. This together with the provision of monitoring the health of the thyristor valves ensure that the outages of the equipment is minimized and reactive power support is provided under all operating conditions. Although the present invention has been described with some degree of particularity, it is to be understood that the description is by way of illustration only. Various changes in form and detail can be made by one skilled in the art without departing from the spirit and scope of the invention as claimed hereinafter. WE CLAIM; 1. An apparatus for providing reactive power support required by power systems, comprising: - a controlled shunt reactor (1) coupled to thyristor (4); and - a controller for generating firing pulses based on the input signals; characterized in that a circuit breaker (CB1) in series with an inductive coil (L)being connected in parallel to the thyristor said controller (16) capable of closing or opening the circuit breaker (CB1) based on the availability of the line voltage, thereby providing full reactive power support right from the first cycle of energization. 2. The apparatus as claimed in claim 1 wherein said controlled shunt reactor (1) is a high impedance transformer. 3. The apparatus as claimed in claims 1 or 2 wherein said thyristars (4) are connected in an anti parallel combination of two thyristors. 4. The apparatus as claimed in proceeding claims, wherein said controller (16) is a programmable logic controller for generating firing pulses based on input signals. 5. The apparatus as claimed in proceeding claims, wherein between said thyristor 4 and said controlled shunt, reactor (1), an isolator (5) is provided for undertaking maintenance work. 6. An apparatus for providing reactive power support required by power systems, substantially as herein described and illustrated in the accompanying drawings.

Documents:

920-del-2003-abstract.pdf

920-del-2003-claims.pdf

920-del-2003-correspondence-others.pdf

920-del-2003-correspondence-po.pdf

920-del-2003-description (complete).pdf

920-del-2003-drawings.pdf

920-del-2003-form-1.pdf

920-del-2003-form-19.pdf

920-del-2003-form-2.pdf

920-del-2003-form-3.pdf

920-del-2003-gpa.pdf

920-del-2003-petition-138.pdf