Power Engineering Guide Transmission and Distribution (3)

Design of Air-Insulated Outdoor Substations

outdoor substations

Air-insulated outdoor substations of open design must not be touched. Therefore, air-insulated switchgear (AIS) is always set up in the form of a fenced-in electrical operating area, to which only authorized persons have access. Relevant IEC 60060 specifications apply to outdoor switchgear equipment. Insulation coordination, including minimum phase -to-phase and phase-to-ground clearances, is effected in accordance with IEC 60071.

Outdoor switchgear is directly exposed to the effects of the environment such as the weather. Therefore it has to be designed based on not only electrical but also environmental specifications.

Currently there is no international standard covering the setup of air-insulated outdoor substations of open design. Siemens designs AIS in accordance with DIN/VDE standards, in line with national standards or customer specifications. The German standard DIN VDE 0101 (erection of power installations with rated voltages above 1 kV) demonstrates typically the protective measures and stresses that have to be taken into consideration for air insulated switchgear.

Circuit-Breakers for 72 kV up to 800 kV

Circuit-breakers are the main module of both AIS and GIS switchgear. They have to meet high requirements in terms of:

_ Reliable opening and closing

_ Consistent quenching performance with rated and short-circuit currents even after many switching operations

_ High-performance, reliable maintenance-free operating mechanisms.

Technology reflecting the latest state of the art and years of operating experience are put to use in constant further development and optimization of Siemens circuitbreakers. This makes Siemens circuitbreakers able to meet all the demands placed on high-voltage switchgear. The comprehensive quality system,

ISO 9001 certified, covers development, manufacture, sales, installation and aftersales service. Test laboratories are accredited to EN 45001 and PEHLA/STL.

Main construction elements

Each circuit-breaker bay for gas-insulated switchgear includes the full complement of isolator switches, grounding switches (regular or proven), instrument transformers, control and protection equipment, interlocking and monitoring facilities commonly used for this type of installation

(See chapter GIS, page 2/30 and following).

Circuit-breakers for air-insulated switchgear are individual components and are assembled together with all individual electrical and mechanical components of an AIS installation on site.

All Siemens circuit-breaker types, whether air or gas-insulated, are made up of the same range of components, i.e.:

_ Interrupter unit

_ Operating mechanism

_ Sealing system

_ Operating rod

_ Control elements.