Basic Design Aspects of Ballia-Bhiwadi 2500MW HVDC Power Transmission System
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1 Basic Design Aspects of Ballia-Bhiwadi 2500MW HVDC Power Transmission System R.K. Chauhan, M. Kuhn, D. Kumar, A. Kölz, P. Riedel shown in Fig.2. Abstract— The ±500kV, 2500MW Ballia-Bhiwadi HVDC shall transmit energy from Ballia to Bhiwadi stations in India over about 780km. Ballia Converter Station is located in the state of Uttar Pradesh approximately 75km from Ballia District Head Quarter. The Bhiwadi Converter Station is located in the state of Rajasthan approximately 60km from Delhi City. Pole 1 of the ±500kV DC Transmission scheme is planned to be put in operation beginning of June 2009 whereas pole 2 is supposed to follow beginning December 2009. The project is owned and operated by Powergrid Corporation of India Ltd., a Govt. of India Enterprise. The paper deals with the required performance criteria and design studies of the Ballia-Bhiwadi HVDC transmission system. Furthermore it highlights major technical features and main components of the project including state of the art light triggered thyristors, control and protection systems, converter transformers, smoothing reactors, AC/DC filters and DC switches. Index Terms—HVDC system, Power Transmission, Design Aspects, Performance Requirements Converter transformer, AC/DC filters, Thyristor valves I. INTRODUCTION ECTION I of this paper gives an overview of the Ballia- S Bhiwadi HVDC power transmission system. Section II 1 Ballia- Bhiwadi and III deal with the design criteria and studies. In section IV 2 Talcher –Kolar (ESI Interconnector) the main equipment and the major technical features are 3 Rihand-Dadri described. Fig. 1. Long Distance HVDC Transmission Systems in India belonging to The ±500kV, 2500MW Ballia-Bhiwadi HVDC project Powergrid Coorporation of India Ltd. shall transmit energy from Ballia to Bhiwadi stations in India over about 780km. Ballia Converter Station is located in the state of Uttar Pradesh approximately 75km from Ballia District Head Quarter. The Bhiwadi Converter Station is located in the state of Rajasthan approximately 60km from Delhi City. Pole 1 of the ±500kV DC Transmission scheme is planned to be put in operation beginning of June 2009 whereas pole 2 is supposed to follow beginning December 2009. The project is owned and operated by Powergrid Corporation of India Ltd., a Govt. of India Enterprise. The Ballia-Bhiwadi system will then be one of three long distance HVDC schemes in operation or construction in India belonging to Powergrid Corporation of India Ltd. (Fig. 1). A single line diagram of the bipolar Ballia-Bhiwadi scheme is Rajeev Kumar Chauhan is with Powergrid Corporation of India Ltd, Gurgaon (Haryana), India. Matthias Kuhn, Devinder Kumar, Andreas Kölz and Peter Riedel are with Siemens AG, PTD H1, Erlangen, Germany. 2 Ballia Converter Station DC Overhead Line Bhiwadi Converter Station outages, is 97%. 400 kV, 50 Hz Smoothing Reactor Smoothing Reactor 400 kV, 50 Hz AC System AC System In order to ensure the highest level of component and Thyristor Thyristor system reliability and availability with minimal downtimes, Valves Valves 2 DC Filters: 2 DC Filters: fast fault detection, effective repair and maintenance strategies (DT12/24, (DT12/24, DT12/36) DT12/36) as well as fault-tolerant control systems, redundancy, spare Converter Converter components and quality assurance are required. To provide Transformer Transformer the highest quality of the HVDC control and protection system intensive off-side tests (e.g. functional performance 2 DC Filters: 2 DC Filters: test) will be performed. (DT12/24, (DT12/24, DT12/36) DT12/36) The performance requirements for dynamic response, reactive power exchange with ac system, overvoltage control, ac voltage distortion, equivalent disturbing current on the dc 3 Filter Banks: 3 Filter Banks: side, radio interference and audible noise have been considered in the system design as per the limits stated in the Owner's Technical specification. Noise filter equipment is provided for the ac switchyards and the dc lines in order to 4 AC Filters: 4 AC Filters: 3 AC Filters: 4 AC Filters: 4 AC Filters: 3 AC Filters: (DT12/24, (DT12/24, meet the specified power line carrier interference limits. (DT12/24, (DT12/24, (DT12/24, (DT12/24, DT12/36, DT12/36, ST12, ST24) DT12/36, DT12/36, ST12, ST24) ST12, ST24) ST12, ST24) 1 C-Shunt ST12, ST24) ST12, ST24) 2 C-Shunts Low loss design was of central importance for technical 1 C-Shunt 1 C-Shunt 1 Shunt Reactor 1 C-Shunt 1 C-Shunt 1 Shunt Reactor 1 Shunt React. and economical optimisations. This resulted in converter Fig. 2. Single Line Diagram of Ballia-Bhiwadi HVDC System station designs with total losses of approximately of 1.3% for both stations at 2500 MW of transmission power. At rated II. DESIGN CRITERIA transmission capacity the main loss sources within the converter station are the converter valves and the converter A. Power Transmission Capacity transformers. The bipolar dc system is rated for a continuous power of 2500 MW (±500 kV, 2500 A) at the dc terminals of the III. DESIGN STUDIES rectifier converter station. The HVDC scheme can be operated in bipolar mode and monopolar mode with ground return or A. Overview of Design Studies metallic return. For maximum ambient dry bulb temperature The design studies for Ballia-Bhiwadi HVDC project can of 50°C the converter stations are designed to transmit be classified in three groups. continuously full rated power without redundant cooling To the first group belong all studies, which results are system in service and for 2 hours an overload of 1.1 p.u. rated required as per the technical specification of the project, like power with redundant cooling in operation. For maximum main circuit parameter study, overvoltage, reactive power, ambient dry bulb temperature of 25°C the converter stations insulation co-ordination, ac/dc filter performance and rating are designed to transmit continuously 1.1 pu of rated power studies, ac breaker, dc switches and interference studies as an without redundant cooling system in service and 1.15 pu of example. These studies have been mainly finalised in July rated power with redundant cooling in service. For half-an- 2007. hour an overload of even up to 1.15pu (bipolar) or 1.2pu The second group of system studies, like the load flow and (monopolar) is possible up to maximum ambient dry bulb stability study, the sub-synchronous resonance and ac temperature. equivalent study, as well as the interaction study for existing The HVDC interconnection scheme is capable of nearby converter stations, affect the stability control continuous operation at any reduced dc voltage level from requirements of the interconnected ac/dc system and have 500 kV down to 350 kV (70%). At 80% dc voltage the been mainly finalized before start of functional and dynamic maximum dc current is 2250 A and at 70% dc voltage the performance tests. maximum dc current is 2145 A without redundant cooling The functional and dynamic performance tests as the third equipment in service. group are studies for control, protection and communication Although the normal power flow direction is from Ballia to which shall commence in mid 2008. Bhiwadi, the HVDC system is designed to transmit power in B. Reactive Power Management the reverse direction. The reactive power compensation elements have been B. Performance Requirements designed to comply with the specified absorption and supply The maximum specified equivalent outage frequency requirements as well as with the specified maximum voltage (EOF= number of one pole outages x 1+ number of other pole change after switching i.e. 3.5% and the maximum size of outages x 1+ number of bipole outages x 2) is 10. subbanks of 150 MVAr. The guarantied energy availability per year of the complete In order to satisfy the maximum reactive power demand of bipole averaged during the three years availability guarantee the converters up to the 2hour-overload and for minimum ac period, considering both forced and scheduled maintenance voltages and frequencies with one subbank out of service, in 3 total 1904 MVAr and 2054 MVAr (at 400kV) are necessary in - deionized water cooling of thyristors, direct water cooled Ballia and Bhiwadi respectively (Fig. 2, Table 1). snubber resistors and valve reactors A special control mode with increased firing/extinction - wire-in-water technology for snubber resistors angles the reactive power consumption of the dc converter can - exclusive use of fire retardant insulating material and wide be increased in order to limit the reactive power flow into the spacing for thermal separation of components ac systems. Available shunt reactors at respective converter - 5 inch LTTs station may also be used to limit reactive power exchanges The same valve design is adopted for the rectifier and with the grid under certain AC / DC system conditions. inverter station. The thyristor valves of Ballia-Bhiwadi project are arranged in three twin towers for one pole same as for C. Overvoltage (OV) Control Tian-Guang and Gui-Guang I and II projects (Fig. 3). One The overvoltage condition of the AC system may faced twin tower represents one quadrivalve comprising the four during recovery periods. The impact of overvoltages are valves connected to the same ac phase. Each of the four valves minimised by the strategy of restarting the dc system and in one quadrivalve structure consists of two and a half restoring the power transfer to the predisturbance level as modular units. Thus one tower comprises 10 modular units. soon as possible. Furthermore an overvoltage control has been Each valve modular unit in turn includes two valve sections established which prevents the ac bus voltages to exceed the connected in series and each valve section comprises 15 specified limits in order to protect the equipment and at the thyristor levels. Therefore a thyristor valve for Ballia-Bhiwadi same time avoids unnecessary filter and shunt capacitor project with two and a half modular units comprises five valve switching.