The challenge for busbar disconnectors of gas insulated switchgear (GIS) in a 420kV mixed technology (Hybrid) substation (MTS)

Transcription

1 21, rue d Artois, F PARIS B3-107 CIGRE 2012 http : // The challenge for busbar disconnectors of gas insulated switchgear (GIS) in a 420kV mixed technology (Hybrid) substation (MTS) P. GLAUBITZ 1, C. WALLNER 1, W. FRÄBEL 2, H. PEIN 2 1 Siemens AG, Germany 2 TenneT TSO GmbH, Germany SUMMARY The demand for electrical energy in the southern part of Germany, with environmentally friendly power generation of increasing on-shore and especially off-shore wind farms in the northern part of Germany, puts high requirements on existing power transmission lines and substations in the 420kV range. The existing 420kV substations have to be modified for the higher energy transmission, from the northern to the southern part of Germany. Transmission lines will be operated on their current limits (transmission loads up to 3000 MVA) which cause feeder currents up to 4000A in the substations. This brings attention to the capability of the busbar disconnectors and their behaviour during busbar-transfer operations. In the product related international standard IEC (2001) [1] the related bus-transfer voltage (transfer voltage) for 420kV Air Insulated Substations (AIS) is given with 300V, while 20V is standard for Gas Insulated Substations (GIS). For the rated bus-transfer current, one common value for air-insulated and gas-insulated disconnectors is given with 1600A. This value considers a current distribution during commutation from one busbar to the other busbar of 80%/20% and therefore, a feeder current up to 2000A. The 1600A was chosen as being typically the highest current which can be switched, although the rated currents of the disconnectors may be substantially higher. These given values for the bus-transfer voltage are not sufficient for the case in which an AISsubstation is modified by using the existing AIS-busbars and installing GIS bays. These Mixed-Technology Substations (MTS) are used due to the higher number of bays which can be installed on an existing footprint. Additionally, a greater flexibility in the substation layouts can be achieved. Investigated substation configurations, which authorize the operator for bus-transfer operations, are double- or multi-busbar arrangements or substations using a transfer busbar for maintenance. The distance, respectively the impedance, of the AIS busbar configuration over the closed coupling bay is very important for commutation. In addition, the feeder current and the load situation on the busbar, define the transfer voltage on the disconnector before, during, and after the bus-transfer operation. christian.wallner@siemens.com

2 Although these voltages are very small compared to the system voltage of the substation, it has to be considered, because the switching capability of the disconnector is very limited to the design. Therefore, the transfer voltage can exceed the values related to the IEC standard. To find and define the maximum value of the transfer voltage for the specific investigated substations, studies were done on typical configurations for TenneT TSO GmbH. The evaluation has shown that the busbar transfer voltages for GIS-disconnectors used in hybrid substations are very well in the range of the values given for AIS configurations. In addition to the above mentioned reasons and from the specific high energy transmission, the required bus-transfer current has to increase up to 3200A. This is twice the recommended rating in the applicable standard. With these results, the technical performance of GIS busbar disconnectors have to be increased for the investigated hybrid substations. The contact system and the drive mechanism have to be modified to achieve the necessary technical requirements. The standard GIS disconnector designed according to the IEC fulfils the requirements for MTS solutions with limitation of transfer-currents and/or voltages. The new developed high-speed disconnector (HSDS) allows extending AIS substations with GIS technology, without recommendations for operation in any MTS configuration. KEYWORDS Air-Insulated-Substation (AIS), Gas-Insulated-Substation (GIS), Mixed-Technology- Substation (MTS), Disconnector, High-Speed Disconnector, Bus-Transfer Voltage, Bus- Transfer Current, IEC INTRODUCTION The task of the European transmission network has changed since the liberalisation of the energy market which started at the end of the 90ies in the last century. Energy-production, -transmission and -distribution play an important role in the European transmission network and is not related to local utilities. The challenge for the European System Operators to develop the European transmission network (so called European Supergrid) under technical, economical and ecologic aspects is the task of the European Network of Transmission System Operators for Electricity (ENTSO-E). The ten-year network development plan shows the three main pillars, security of supply, tackling climate changes and integration of renewable energy sources, and economic efficiency and realisation [2]. The target of the European transmission network can only be reached when the integration of the scheduled renewable energy generation functions properly. Therefore, investigations in the European energy market must be performed. The German Energy Agency (Deutsche Energie-Agentur - DENA) is working on these topics within the German transmission network. The first study, DENA Netzstudie I, was published in 2005 [3]. The second study - DENA Netzstudie II - shows the German transmission network with increased renewable power generation up to 2020 [4]. The conclusion of these studies is that the integration of the renewable energy production from wind and from solar radiation, results in additional requirements in the design- and operation-philosophies of the transmission systems. Therefore, one part beside the required transmission lines is to upgrade the performance of high voltage substations in specific areas. This is required to handle the massive wind power 2

3 generation in northern Germany and transmit the energy to the load centres in southern Germany. 2. SUBSTATION CONCEPTS During the concept phase, the main focus is given to handle the high energy demand. The challenge to the substations in the European Supergrid network is to transmit and distribute the high transmitted energy. As a result, the capability of the required lines is defined by 4000A for the substation. Irrespective of these feeder currents, the currents on the busbar could be higher (e.g. 5000A or 6300A). This corresponds to the general trend for higher rated values [5]. Substation concepts from TenneT TSO GmbH are based on long term experience. Typical configurations are double or in rare cases triple busbar arrangements. Using this kind of substation configurations, the busbar disconnectors has a special function. This function is bus-transfer current switching. From the standpoint of bus-transfer switching capability, the basic concept is always the same. The concept does not differ between AIS, GIS or MTS solutions. The value of the bus-transfer current depends on the ratio between the impedances before and after the bus-transfer operation. The bus-transfer voltage depends on the feeder current and load flow on the busbar. In principle, AIS, GIS and MTS substation were examined. Beside the technical parameters, the life-cycle costs, e.g. available space, maintenance concepts, reliability and availability are very important, but not considered in this technical study. Of course these important parameters must be evaluated differently at each substation. For pure AIS or GIS installations, the existing technology is already capable of theses higher requirements. MTS applications show recommendation for operation, e.g. limitation of the bus-transfer currents and/or voltages. Therefore, the requirements and the development will be done. 3. REQUIREMETNS FOR THE SUBSTATION EQUIPMENT To transfer current from one busbar to another busbar is called bus-transfer current switching (as examples see Figure 1a, 1b). Reasons therefore can be to separate the load flow, limited short-circuit currents or for periodic maintenance. The bus-transfer operation starts with closing the disconnector and the circuit-breaker in the bus-coupler bay. After that, the designated first feeder closes the busbar disconnector to the second busbar. At this moment, the feeder current flows over the original busbar and additionally over the second busbar and the couple bay. The distribution of the currents depends on the impedances of both current paths [6]. A common ratio between the current supplying busbar I and the current supplying busbar II is related to 80%/20%. 3

4 Figure 1: Principle explanation of the bus-transfer current switching case Investigations were done for substations up to 10 feeders. Impedances for AIS busbar are in the range of 0.25mΩ/m and 0.30mΩ/m. For the GIS part, the values are in the range of 0.10mΩ/m and 0.15mΩ/m. The bay width for one feeder is in the range of 20m. For the calculation simulation programs like PSS SINCAL are used. Load flows on the busbar, which can reduce or increase the commutation voltages, can be simulated in a proper way. Beside these detailed calculations, a worst case scenario can be estimate by the following formula: U btv 2 x Z bb x d x I btc (1) U btv Z bb d I btc bus-transfer voltage (V) busbar impedance (Ω/m) distance between the commutating feeder and couple bay (m) bus-transfer current (A) A worst case scenario for bus-transfer switching is a bus-transfer over the maximum length of the busbar. Therefore, the incoming feeder is defined as feeder 1, the first possible outgoing feeder is feeder 3 and the couple bay is places as feeder 10. The feeder current is related to 4000A result in a bus-transfer current of 3200A. The calculated voltage is in the limit between 256V and 307V, which is very well in the range for AIS requirements concerning the bustransfer voltage. 4. DEVELOPMENT OF A HIGH-SPEED DISCONNECTOR The basis for the development is the existing GIS disconnector. Due to MTS applications, the bus-transfer voltage is already designed and tested for 100V, which is 5 times higher than the required 20V according to the IEC standard for GIS equipment. The target for the 4

5 development was to achieve the AIS values at an increased transfer current of 3200A. The main focus during the development was given to the transfer voltage level. The higher current has an impact, but the higher current was neglected during the development phase due to the well known material characteristic of the arcing contacts used. The used graphite nozzles are in similar behaviour used in high-voltage circuit breakers for more than 40 years for short-circuit interruption up to 100kA. In this content, the main focus was given to the transfer voltage, in respect to the commutation time (see Figure 1c). The arc can be spread between the opening contacts as a function of contact stroke during this time. In comparison to AIS disconnectors, there is a limited space for the arc due to the enclosure. The decision was to increase the opening speed to achieve similar conditions (commutation times) between the different bus-transfer voltage levels. Other possible solution, e.g. a contact system with active arc quenching system, is not essential. The assumption was to increase the velocity of the contact between 3 and 4 times. Based on platform concept philosophies, the spring charge mechanism of the high-speed earthing switch was adapted. The weight of a few parts were reduced and several levers were modified to withstand the extended mechanical endurance of 2,000 operatings. Figure 2: 8DQ1-550kV-63kA-5000A with High-Speed Disconnector (HSDS) The time from starting the development, the type testing as far as to the delivery of the first bays, was less than one year (Figure 2). This short development-, purchasing- and manufacturing time could only be achieved by using existing and well known components. The supply chain management was optimized due to involving the purchasing and manufacturing stakeholders at an early stage of development process. TenneT TSO as a potential customer for this solution was witnessing the successful development test. 5. CONCLUSIONS The integration of the renewable energy production in the European Supergrid is a challenge for the TSOs and results in additional requirements in the design- and operation-philosophies 5

6 of the transmission system. In the case of TenneT TSO GmbH, high-voltage substations have to be extended expanded or up-rated. Therefore AIS, GIS and MTS solution have been investigated researched. The transmission capacity is up to 3000 MVA, which corresponds to 4000A for the line respectively for the incoming feeders of the substations. Investigated configurations with double or multi busbar configurations bring attention to the capability of the busbar disconnectors and their behaviour during busbar-transfer operations. In the product related standards, bus-transfer voltages are defined for AIS and GIS equipments. MTS are not specifically mentioned. This study shows that in investigated cases (e.g. AIS extension with MTS, high energy transmission) the MTS values are similar to the AIS guidelines. For AIS and GIS installations, the existing technologies are capable for these high requirements. MTS solutions are not mentioned in the standard. Therefore investigations for MTS substations were made. The results of these investigations show, that the requirements for bus-transfer switching are in the range as for AIS equipment. Recommendations e.g. limitations of transfer-current and voltage would be required. For new installation couple bays could be shifted close to the middle, but not in the case of extension. To bring the MTS technology in a competitive situation, the capability regarding bus-transfer switching of the GIS disconnectors has been improved. The main modification was the spring charge mechanism, required for a higher contact speed. Optimization of a few components of the contact system completed the design modification on the new high-speed disconnector. Finishing the development of the high-speed disconnector, the MTS solutions can be used for extension of AIS substations. AIS, GIS and MTS solutions are now available for TenneT TSO to be implemented in the European Supergird. BIBLIOGRAPHY [1] International Standard IEC ; High-voltage switchgear and controlgear - Part 102: Alternating current disconnectors and earthing switches (First edition. 2001) [2] ENTSOE ENTSO-E s Pilot Ten-Year Network Development Plan. Executive Summary ( 2010) [3] Deutsche Energie-Agentur Energiewirtschaftliche Planung für die Netzintegration von Windenergie in Deutschland an Land und Offshore bis zum Jahr 2020 ( 2005) [4] Deutsche Energie-Agentur DENA-Netzstudie II. Integration erneuerbarer Energien in die deutsche Stromversorgung im Zeitraum mit Ausblick 2025 ( 2010) [5] P. Rudenko, C. Wallner, M. Behne State of the Art GIS Technology and Trends (IEEE PES Transmission & Distribution Conference & Exposition May. Orlando. FL. USA. 2012) [6] H. Lipken, C. Neumann Der Sammelschienenwechsel als Schaltaufgabe für Trennschalter (Elektrizitätswirtschaft. Jg. 83 (1984). Heft 20. Seite ) 6