Working under tension

from Wikipedia, the free encyclopedia

Working on live electrical equipment with operating voltages above 120 V DC and 50 V AC is referred to as live work (AuS)  . Working under voltage requires specially trained employees (in Germany trained electricians , in Switzerland specially trained electricians ), special work equipment and special organizational measures.

Overview

One advantage of working under voltage is that it avoids business interruptions and the effort involved in activation .

There are 3 categories or cases of live work:

  1. Working in the vicinity of live equipment. The distances that could lead to a current flow are not fallen below, but these are areas that for safety reasons cannot normally be entered or where nobody is allowed to be. The person performing the work must ensure that he never gets too close to live equipment.
  2. Working on live equipment by working directly on it. The person carrying out the work is not electrically connected to the equipment and must always ensure that this is avoided through insulation.
  3. Working with voltage on the same potential. The person carrying out the work is at the same electrical potential as the equipment, i.e. it is live with respect to earth and other conductors. He must avoid having earth contact or contact with conductive parts of other potential.

Live work in the high and extra high voltage range can only be carried out at the same potential, i.e. H. be done with insulating platforms or helicopters with previous potential equalization. For this purpose, the performers wear conductive suits and are always connected to the high-voltage parts. The cause is the capacitive currents as well as the sparks of the charge equalization upon first approach.

Cleaning work on live parts can also be carried out with special insulating cleaning devices such as brushes on insulating rods or industrial vacuum cleaners with plastic hoses .

Safety precautions

Work on low voltage (up to 1 kV) can be carried out with insulating tools without the person carrying out the work having a defined potential. Arc faults due to unintentional or intentional switching operations can lead to severe skin and facial injuries.

Depending on the work, special protective equipment, consisting of insulating clothing (gloves, shoes) or face protection (visor), is necessary. Work on contact lines, for example, is often done from insulating platforms. This ensures that there is no flow through the body to earth when live parts are touched. However, earthed structural parts (masts, booms, guy ropes) that are within easy reach can still pose a hazard. They are therefore covered where applicable.

Working with isolating tools is not possible at high and extra high voltage. Working on potential at maximum voltage is only possible if field control takes place so that the body is protected from pre-discharges , corona discharges and charge equalization events. This is done using special conductive full-body suits with incorporated metallic fibers. These conduct currents according to the capacitive discharge towards the environment or according to the. Before the conductor cables of helicopters or from the insulating platform come into contact, potential equalization is necessary despite the insulation in order to achieve a charge equalization.

Examples

Assembly work on a mast (low voltage)

In the case of low voltage, the following work under voltage is common:

  • Replacing NH fuses
  • Installation of house connections
  • Installation of branch sleeves in underground cables

For example, the following work is carried out on low and medium voltage networks:

  • Preparation of cleaning and conversion work in the vicinity of live system parts (covering, barriers)
  • Maintenance and cleaning of transformer stations , air-insulated medium-voltage switchgear
  • Refilling of wet cable terminations
  • Checking the disconnection of HV HRC fuses and Buchholz relays using a mobile bridging unit (MÜE)

In the area of ​​maximum voltage, live work is only carried out in exceptional cases and is mostly limited to countries such as the USA, where the system cannot be switched off for maintenance due to the lack of reserve lines:

  • Replacement of spacers for bundle conductors in overhead lines , with fitters being lowered by helicopters or being lifted onto the conductor cables by means of insulating cables and devices on the mast.
  • Installation of line branches in overhead lines from isolated platforms

Rules in Switzerland

Only electricians with a federal certificate of competence or persons with equivalent training are allowed to work on live installations. They must be specially trained and equipped for such work in accordance with the latest findings. Two people are always to be appointed, one of whom is to be determined as responsible. (SR 734.27 Art. 22, paras. 2–3)

literature

  • Lathan, Daniel : Save time and money when cleaning under tension. In: Reinigungs Markt 10th year (2007) issue 7, pp. 42–45. [1]
  • oV : fuse switch disconnector bridged by means of a mobile unit. In: np (Netzpraxis) Volume 46 (2007) Issue 4, p. 64.
  • Muschong, Michael : Working at the switch without interrupting the energy supply. In: de (Der Elektro- und Gebäudetechniker) Volume 46 (2007) Heft 4, p. 64.Download (broken link)

Web links