vincenzo.iuliani@terna.it

Compact Substations for Quick Installation SCRI (Stazioni Compatte a Rapida Installazione)

FALORNI Daris, IULIANI Vincenzo, REBOLINI Massimo, SEMBIANTE Falco

Terna SpA CAMERONI Roberto, GATTI Pierernesto, GRANATA Carlo, PIAZZA Costante

ABB SpA ITALY

SUMMARY

Terna has successfully developed, in less than a year, a mobile substation 145 – 170 kV Compact Substation for Quick Installation called SCRI. This application responds simultaneously to two challenges: the fast increasing number of renewable power plants (wind & solar) in the last two years and the not so fast construction process of traditional substations due to the necessary installation time and the authorization procedures to connect the substations to the RTN (Italian National high voltage grid).

SCRI High Voltage section is composed of three line bays (single bus bar type) equipped with cable plug-in terminations; it is assembled on a 40 ft-long standard trailer that can be freely moved on road (no special permits for oversize load required). Also the Low Voltage section (protection & control equipment, HV bay cabinet and station auxiliaries) is assembled in a transportable container on the same standard trailer.

The SCRI distinguishes itself by the innovative solutions in order to obtain the smallest possible dimension and a solid mechanical construction, essential prerequisites for the easy transportability.

The innovative solution consists in the utilization of line bays MTS (Mixed Technology Switchgear) modules, characterized by wide use of multifunctional equipment and High Voltage dry-type terminations, in combination with SF6 insulated bus bar.

This allows to guarantee the same full functionality of conventional substations having a compact and transportable application.

To make the transportability possible even on rough roads and in site areas the equipment is properly fixed on trailer platform by means of steel support structure and shock absorbers.

In order to minimize the installation time, the High Voltage connections are realized by means of XLPE cables and plug-in terminations. Likewise the Low Voltage connections (among High Voltage components, Protection & Control and auxiliary) are made by “poka-yoke” connectors.

21, rue d’Artois, F-75008 PARIS B3 – 102 CIGRE 2012 http : //www.cigre.org

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Furthermore, the above mentioned features allow the fully assembling and testing of the entire mobile substation (High Voltage, Low Voltage and Protection &Control components) in the factory with elimination of the majority of the on-site activities during the first installation and re-installation in other sites as well.

The two main AC power supplies are designed in order to be connected directly to the high voltage network without any need of Medium Voltage and Low Voltage feeders arising from local electric distributors. Those sources are two Service Station Voltage Transformers (TIP – Trasformatore Induttivo di Potenza) insulated by means of SF6 able to provide a power of 25 kVA each at 230 Vac.

The SCRI is also equipped with a back-up generator set of 25 kVA, which is a useful power supply during the installation stage.

A space of 20x50 m with compacted and leveled ground (with earthing grid) nearby an overhead line is enough for the installation of the SCRI.

The first SCRI has been codesigned by Terna and ABB Italy Unità Operativa Adda-HV and manufactured by ABB Italy Unità Operativa Adda-HV in 4 months, using the PASS M0 Module.

It is in operation since 21st December 2010, one year earlier than the inlet of renewable power, connecting in infeed-outfeed mode (entra-esci) a Solar power plant in Aprilia (Rome).

The easy installation together with the numerous requests for grid connections, led Terna to acquire further units.

The SCRI for its features of transportability and quick installation “plug and switch“ is also suitable to reduce the outage of the Substations in case of refurbishment or of major faults.

KEYWORDS RTN: Italian National Transmission High Voltage Grid; IPPs: Independent Power Producers; MTS: Mixed Technology Switchgear; TIP: Service Station Voltage Transformer for auxiliary supply; XLPE: Cross-Linked Polyethylene.

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1 Compact Substation for Quick Installations (SCRI)

The increasing number of requests of renewable energy connections in the recent years and the need for quick installation have intensified both need and urgency to identify innovative solutions suitable for connecting the new plants to the national transmission grid and to compensate for the long bureaucratic time for local authorizations and permits.

To meet this need, Terna has developed, in less than one year, a movable 170 kV substation, called “SCRI” (from the Italian Stazioni Compatte a Rapida Installazione) which means Compact Substations for Quick Installation.

This innovative solution can be also used with a different scope during refurbishment and revamping of existing substations or in case of major faults in a part of the transmission system: the SCRI, requiring a limited and slim footprint, can be easily installed both inside and in proximity of the existing substation, reducing the need for overhead lines outages in both situations. A fast restoration of the service is extremely important, considering also the new rules of the Italian power system market which foresees penalties in case of service unavailability.

The first two SCRIs have been applied to the connection of a solar power plant and a wind farm to the Italian National Grid (RTN) in infeed-outfeed mode (incoming / outgoing), one year earlier than the inlet of their relevant renewable power. As in 2011 the requests for connection confirmed the trend and the effectiveness of the solution was proved by first installations, Terna acquired six further units.

Once the necessity to connect IPPs (Independent Power Producers) is concluded, the SCRI, thanks to its features of transportability and “plug and switch” installation, will be used to reduce the outage of the substations in case of refurbishment or of major faults.

2 SCRI description

The SCRI (figure 1) is mainly composed of three High Voltage modules (Single Bus Bar type) which are fully remote controlled by the three Italian Dispatching Centers, like all the standard RTN substations.

Keywords:

“Sb” SF6 Busbar

“TV” SF6 Inductive Voltage Transformer

“89 T” Earthing switch

“89 A” Busbar disconnector

“52 CB” Circuit breaker

“89 T-L” Line disconnector and earthing switch

“CT” Current Transfomer

“T” High Voltage Plug-in terminal

“TIP” Service Station Voltage Transformer

“ZnO” Surge Arrester

Figure 1: SCRI Single Line Diagram.

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The High Voltage section is composed of three Single Bus Bar modules with plug-in cable terminals assembled on a pad permitting an easy transportation by means of a 40 ft standard trailer.

The bus bar system is SF6 gas encapsulated like line modules. Each line bays uses devices arising from MTS (Mixed Technology Switchgear), obtaining the smallest possible dimension and a solid mechanical construction, essential prerequisites for easy and safe transportability.

SCRI active parts in the High Voltage section are segregated and hence not accessible. This allows the access to the substation core even when it is in operation.

The SCRI High Voltage connections are made of XLPE cables and plug-in terminations dry type. The nine one-phase cables are wound around three metallic reels and transported by a standard container (see figures 2 and 3).

The protection and control system and the AC/DC auxiliary panels are assembled inside a container which is fastened on a pad like the High Voltage modules and transportable in the same way (see figure 4).

Figure 3: XLPE cables and plug-in terminations dry type. Figure 2: High Voltage plug-in connection.

Figure 4: Protection and Control Panels inside the container.

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The Low Voltage connections (among High Voltage components, Protection & Control and auxiliary) are made by “poka-yoke” connectors (see figure 5). The two main alternative power supplies for auxiliary systems are designed in order to be connected directly to the RTN high voltage network with no need for Medium Voltage and Low Voltage feeders. These sources are two Service Station Voltage Transformers (TIP) insulated by means of SF6, each one able to transform a power of 25 kVA directly from 150 kV to 230 V (see figure 6). The SCRI is also equipped with one back-up generator set of 25 kVA which is a useful power supply during the installation stage.

3 Peculiarities

The SCRI distinguishes itself for the complex of innovative solutions adopted which have brought to a substation pre-assemblable and pre-testable in factory.

The layout of the three units (High Voltage trailer - Protection & Control trailer - the metallic cable reels with accessories trailer) and their fixing system to the metallic pad allow Terna to use standard trailers for transportation (Length 12 m, Width 2,45 m and total Height to ground 4m) easy to be retrieved and suitable in case of tortuous and spoiled roads. Therefore, there is no need for special permits.

The reduced footprint of 20 m x 50 m compacted and leveled soil, complete with grounding system and temporary fences, makes the SCRI a solution with very low environmental impact. The site installation of the electrical components requires a really short time, less than two weeks, as well as it is easily dismountable for the re-utilization in other sites.

The SCRI pad units are provided with four hydraulic supports suitable to lift up and down and therefore unload them from the trailer with no need for an expensive crane.

To minimize the installation time, the High Voltage connections are made of XLPE cables and plug-in terminations dry type. The cable, thanks to its nature and to the technology chosen, ensures flexibility and versatility for the connection to the High Voltage transmission lines.

Figure 5: LV connections among HV components, P&C and auxiliary.

Figure 6: 25 kVA Service Station Voltage Transformers (TIP).

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Consequently, it is definitely easier to locate the above mentioned apparatus inside the substation area, making the overhead lines dead-end towers (where the conductors are bare) independent from the positioning of the High Voltage trailer. This allows a higher possibility of adaptation to different available unutilized spaces. Finally, XLPE insulation avoids the necessity of clearance distances and further safety protections for the personnel.

4 Challenging situations

To demonstrate the usefulness of this technical solution, below are described three real cases where the SCRI has been installed in critical and challenging situations as for connection time, service availability during refurbishment activities and quick service recovery in case of disaster.

4.1 Quick connection time.

A good example is the connection of a Wind Farm in Sicily to Italian High Voltage transmission network (RTN) which has enabled an Independent Power Producer to start the operation in advance of the initial planning. It is plain that this has facilitated the producer’s return on investment. A further advantage has been represented by the reduced environmental impact of the civil works, such as limited excavations and few concrete structures (see figure 7).

Even in an impervious and hardly achievable environmental context as the above mentioned substation, the SCRI design has allowed to reach the site easily (see figure 8).

The easiness of connection and the possibility to lay the apparatuses in limited space which can be effortlessly developed in length, allow the positioning underneath and inside the “right of way” of the existing overhead power lines.

Figure 8: arriving at the SCRI substation.

Figure 7: SCRI applied in a wind farm (Sicily).

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4.2 Service availability during refurbishment.

A SCRI substation has been also installed as auxiliary connection during the refurbishment of an existing 132kV station in Piedmont. SCRI installation on the outline of the existing substation enables to temporarily connect the different incoming lines keeping them live during the reconstruction of their bays (see figure 9).

As XLPE pretested cabling systems do not have any clearance distance limitations, they allow to identify the most economical and flexible layout in terms of footprint. Moreover, they do not require any invasive modifications of the existing structures.

4.3 Disaster Recovery

The SCRI for its features of transportability and quick installation (plug and switch) can be utilized to reduce the outage of the substations not only in case of refurbishment but also in case of major faults due to catastrophic events. SCRI flexibility enables an easy installation on the existing substation exploiting the internal roads to accommodate it with no need for any considerable works.

Figure 9: single line diagram of Piedmont substation.

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A example of SCRI installation to connect two lines to the bus bar in case of bays fault is shown in figure 10.

Moreover recent natural disasters, which are unpredictable, have made electrical authorities more sensitive to provide themselves with more and more agile and adaptable substation solutions.

With reference to the above mentioned technical demands, SCRI represents Terna’s solution which is certainly on the cutting edge, but only a stepping stone towards the possibility to expand the present approach even to 220 and 380 kV voltage levels. Bibliography [1] C. Twomey - Substation design in a challenging regulatory environment - CIGRE SC B3 Berlin

2007 [2] M. Blundell, D. Roby, C. Piazza - Compact integrated bay modules for new 145 kV substations;

CIGRE SC A3 & B3 Colloquium, Paper 121, Tokyo, Japan 2005 [3] M. Cameroni, C. Granata and L. Calamari – Assembly of high voltage devices; CIGRE SC A3

& B3 Colloquium, Paper 116, Tokyo, Japan 2005 [4] M. Bues, E. Mikes - Compact optimised GIS, Modular Hybrid Substation bays, Mobile GIS

substations; CIGRE SC A3 & B3 Colloquium, Paper 120, Tokyo, Japan 2005

Figure 10: top view of standard Terna’s substation.