|Electrical Installation - Basic Vocational Knowledge|
|4. Low-voltage switchgear and distribution systems|
Low-voltage switchgear and distribution systems are being operated in centres of power consumption with consumers voltages up to 1 kV ac voltage and 1.5 kV dc voltage.
Low-voltage switchgear and distribution systems serve to distribute electrical power. They may be installed outdoors and within buildings. Their design determines the place of installation.
A distinction is made between:
- open-type switchgear systems
- enclosed (factory-finished) switchgear systems
- encapsulated switchgear systems and
- installation distributions.
Cables are connected to the switchgear in the wiring space of the switchgear and distribution systems.
Bus bars serve as main current conductors within switchgear and distribution systems.
Bus bars are solid, non-insulated conductors. They are made in different shapes and with standardized cross sections.
For processing bus bars special attention will have to be paid to:
- Prior to further processing, bus bars are to be cleaned.
- Distortions at bus bars are to be eliminated.
- Bus bars are not to be marked by scriber.
- The bending angle of bus bars is 90°. The minimum bending radius has to be maintained at that.
- Holes are to be drilled or punched into bus bars.
- The contact surfaces of bus bars are to be plane and metallic-bright.
In order to allow bus bars to extend in case of temperature variations they are to be mounted in sliding position.
Installation of bus bars in switching panels or cubicles is to be performed according to a fixed sequence of conductors:
- from left to right
- from above to below
- from front to rear.
Joining bus bars to each other may take place by:
- bars outgoing
- unilaterally offset overlap
- strap connection.
Prior to commencing assembly work at live switchgear, the parts to be worked on are to be disconnected. For that purpose the following steps will have to be taken:
- disconnecting the working site,
- safeguarding against reclosing
- ascertaining dead condition.
The sequence of the above individual actions has to be observed. After completion of assembly work
- the working sites are to be inspected
- workmen, not required any more, are to be withdrawn
- the protective measures undertaken are to be cancelled
- the system is to be put under voltage again.