Protective separation
The protective separation is a protective measure based on the safe galvanic separation of the circuits , for example by means of an isolating transformer .
It is a possible measure against electrical accidents in low-voltage networks if, due to certain situations, such as when working in confined spaces, there is a risk of people inadvertently touching live parts.
motivation
Usual public power supply networks in the low-voltage range, such as the TN system or TT system , have an earthed star point . The protective separation removes the earthing of the supply network, so that on the protected side (secondary side) there is no voltage difference between the outer conductors and earth. In the event of a short to body , i.e. a conductive connection between the active conductor and the housing, no contact voltage to earth can occur. The housing can be touched without danger, as shown in the figure on the right. Even with direct, single-pole contact with a secondary-side conductor, there is no voltage to earth, which means that there is no danger for the person concerned in this case either. Without protective separation, on the other hand, if there is a physical shock or contact, a current flow through the person, shown in red dotted line, which can be fatal under certain circumstances (left situation).
The protective separation, on the other hand, does not offer any protection if, in the event of a short to body, another fault such as an additional earth fault occurs. This earth fault can lead to the protective separation being canceled and a current to flow through the earth.
Structure and regulations
The protective measure is complex because an isolating transformer is used for galvanic isolation , which is subject to special requirements. Breakdown of the insulation between the windings must be particularly difficult. The insulation must withstand a voltage of at least 3000 volts and the connections must be designed in such a way that they cannot accidentally touch.
Only one electrical consumer may be connected to the isolating transformer with the prescribed protective separation . If several devices are connected to an isolating transformer, an earth-free local equipotential bonding must be established between the individual devices . To do this, the devices are connected to one another via a potential equalization line. The equipotential bonding cable prevents contact voltage from developing if several devices are shorted to the body. Since the publication of the new VDE 0100 Part 410 on June 1, 2007, systems of this type may only be used by qualified electricians or persons who have been trained in electrical engineering.
Protective separation is mandatory for safety extra-low voltage transformers, when working in confined spaces and in container construction.
The cable length with protective separation must not exceed 500 m. The voltage must not exceed 500 V; In addition, the product output voltage (secondary voltage) • Cable length must be less than 100,000 Vm.
If protection against a short-term power failure is also required, a converter can be used instead of an isolating transformer , which bridges the failure by means of an energy storage device (flywheel).
Laws and norms
- DIN VDE 0100-410 (VDE 0100-410): 2007-06 Construction of low-voltage systems - Part 4-41: Protective measures - Protection against electric shock (IEC 60364-4-41: 2005, modified); German takeover HD 60364-4-41: 2007. VDE-Verlag, Berlin.
See also
literature
- Gerhard Kiefer: VDE 0100 and practice. 1st edition, VDE-Verlag GmbH, Berlin and Offenbach, 1984, ISBN 3-8007-1359-4
- Günter Springer: Expertise in electrical engineering. 18th edition, Verlag - Europa - Lehrmittel, Wuppertal, 1989, ISBN 3-8085-3018-9
- Werner Hörmann, Bernd Schröder: Protection against electric shock in low-voltage systems - Comment from DIN VDE 0100-410 (VDE 0100-410): 2007-06. VDE series of publications Volume 140, VDE-Verlag, Berlin, ISBN 978-3-8007-3190-9 .
Individual evidence
- ↑ "Protection against electric shock when setting up low-voltage systems (2)" ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (PDF; 279 kB), on page 28 of "de 15-16 / 2007" (accessed on October 22, 2013 at 8:04 p.m.)
