Alstom’s new modular plug-and-play transmission substation is claimed to be cheaper and quicker to install, and cheaper to run, than its competitors’ offerings, and to take up less ground space by a factor between 40 and 60% compared to conventional installations. It can be put together from off-the-shelf units with air insulated and gas insulated (SF6) components. The standard installation schedule has been cut down to six months reckoned from the contract signing, including a month for commissioning, and the finished ‘plug and play’ substation is designed for remote operation.

The speed of installation comes partly from the degree of pre-assembly that is possible. Standard components are prepared in the factory and shipped to the site in standard containers. The site itself needs minimal preparation and there is no need for a containment building, so civil works are reduced.

UniLox is based on a design that has been ‘optimised’ for use in any part of the world, and a flexible open architecture that is intended to facilitate adaptation to future system changes. A range of standard components centred on the PIX and Optigis products outlined below may be configured for transmission load transfer between grids or for installation at distributed generation sites. Overall limits for the HV GIS are 145 kV at 2500 A, 63 MVA for the power transformer, and for the medium voltage switchgear 12 to 36 kV at 2.5 kA.

The control section is open architecture with connections for GPS, SCADA and remote access, so it may be operated remotely, and is pre-configured for advanced software of the type associated with the deregulated market, such as e-terra.

HV function

The F35-2 Optigis HV switch is an encapsulated unit incorporating three phases with combined disconnector and circuit breaker together with the local controls. The air insulated module combines current transformer, circuit breaker, disconnector, local controls and earthing switch, and incorporates a rail system for quick removal of the contact breakers.

Ratings for GIS and AIM HV modules:

HV 72.5 – 145 kV, rated current 3150A

Short circuit 40 kA for up to 1s; impulse voltage limit 650 kV

Temperature range -25 to 40°C

MV function

For 12-24 kV, air insulated PIX units with a removable module accommodating SF6 or vacuum insulated circuit breakers are offered; for 12-36 kV the fully SF6 insulated WS unit is available. Both are metal enclosed and accommodate one or two busbars.

PIX/WS characteristics:

Impulse voltage limit 75 -125 kV; WS 170 kV

Impulse voltage limit at power frequency 50 kV; WS 70 kV

Rated current 3.15 – 2.5 kA (WS 2.5 kA)

Peak current limit 100 – 80 kA; WS 80 kA

Internal arc limit (PIX) 40-31.5 kA

First reference

GHF GmbH is one of the largest companies currently building and operating its own windfarms, mainly in Germany. Its subidiary Ventotec is currently bringing on-stream two new windfarms near Berlin – UW Lorf and UW Schwarzheide Ost. To meet constraints on the building of renewable energy projects in Germany, a simple and optimised connection to the 110 kV utility network was required, and in a short time frame. A conventional substation typically requires a design and installation period in the order of 12 months. Alstom was able to offer evaluation, design, engineering, erection, commissioning and siteworks in 5 months. Standardisation and prefabrication allowed immediate compliance with government and utility regulations, greatly speeding up the initial stages of the project.

Alstom gained this contract partly at least because of the existence of its ‘competence centres’ for the wind business located in Bremen and Kassel and partly for speed of installation. From the issuing of contracts in March 2003, the substations were fully operational six months later in September.

The substations were required to step-up the output power of the windfarms from 20 kV to the 110 kV required for the network. This was achieved using a standardised UniLox configuration based around a 40 MVA power transformer. The complete substation configuration, costing t1 million, included a UniLox WCAIS (wind compact air isolated switchgear), 40 MVA power transformer, 20 kV-gas isolated substation, MiCOM control and protection equipment, prefabricated foundations, steel work, earthing system, erection and commissioning.