Protective line system

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Protective line system was the earlier name for a protective measure that is still used today as insulation monitoring in IT networks . Since it may not be used in the public power grid, it is also less known than other protective measures.

Basics

In the isolated network, a simple earth fault does not trigger the protective devices. As a result, an insulation fault on an active conductor can go unnoticed for a long time. If a double fault then occurs, this can lead to a dangerously high fault voltage . For this reason it is necessary that the insulation resistance in the IT network is constantly monitored. Insulation monitoring is only permitted as a protective measure in the IT network. In TN networks and TT networks , this measure alone would not guarantee sufficient protection. With this protective measure, protection is provided in the event of a fault by means of a message. Too high a contact voltage is avoided by equipotential bonding of all system parts.

Layout and function

IT system with insulation monitoring

The basic requirement for the function of this protective measure is that the system in which this protective measure is used has a separate power supply and is operated isolated from the rest of the network . In addition to the earthing of all housing parts and equipotential bonding, additional local equipotential bonding is required for protection by insulation monitoring devices. This additional equipotential bonding is intended to achieve absolute equipotentiality in a locally limited area. The inclusion of external conductive parts in the earthing measure is, however, a matter of discretion for the installer of the system. In the event of a simple error, a message about the error status of the system is issued. The message can be made optically or acoustically. In order to ensure that the error message is recognized, the messages are sensibly given both visually and acoustically. Since the contact voltage to earth is not too high in the event of a simple error , the system can continue to be operated safely and work processes that have been initiated can still be completed, although the first error must be eliminated immediately.

Different systems

Basically, the insulation status of the system against earth is continuously determined with the insulation monitoring device, the monitoring device recognizing the low-resistance connection of an external conductor to earth potential as a fault. A low-resistance connection exists when the insulation resistance of the system falls below a certain limit value. This error case is reported. One method of an insulation monitoring device is the insulation monitor . It can also be used to detect insulation faults during operation. However, it is not possible with these devices to localize the fault. However, since an initial fault must be eliminated as quickly as possible, but the manual search for the cause of the fault can sometimes take a long time, insulation fault search systems are advantageous here. If insulation monitoring systems are used to monitor circuits with superimposed external DC voltage, special devices with a suitable measuring voltage must be used that cannot be disabled by the external DC voltage.

In underground mining and in potentially explosive areas, earth-fault barriers are used for ongoing monitoring of insulation faults. These also enable insulation monitoring of switched-off stub lines. Earth fault relays are used to monitor the insulation of control circuits up to 42 volts AC voltage . These earth fault relays also serve as a restart lock in disconnected spur lines up to 1000 volts alternating voltage.

Possible areas of application

According to the standard, this protective measure is only permitted in limited systems. Possible areas of application for this protective measure are summarized below.

In hospitals, for example, this protective measure is used in rooms used for medical purposes, in which treatment must be continued even in the event of a fault. In the event of an error, the supply can be maintained and the error elimination or the transfer of the patient initiated.

This protective measure is also used in mines. Insulation monitoring can also be used on ships so that important electrical equipment or navigation and control equipment does not immediately fail in the event of an insulation fault. Here, too, priority is given to reporting the error while maintaining the operational function.

Norms

  • IEC 60364-4-1 / VDE 0100 part 410 protective device and switch-off conditions
  • IEC 60364-7-710 / VDE 0100 Part 710 Electrical safety in medical areas

literature

  • Wolfgang Hofheinz: Protection technology with insulation monitoring . VDE publication series "Standards understandable". Vol. 114, 2nd edition. VDE-Verlag, Berlin / Offenbach 2007. ISBN 3-8007-3026-X

Individual evidence

  1. ↑ Protective measures and measurement technology. ( Memento of June 12, 2007 in the Internet Archive ) (accessed on February 13, 2012; PDF; 516 kB).
  2. ↑ a b c d e f Gerhard Kiefer: VDE 0100 and the practice. 1st edition. VDE-Verlag, Berlin / Offenbach 1984. ISBN 3-8007-1359-4 .
  3. ↑ a b c Wilfried Knies, Klaus Schierack: Electrical systems technology; Power plants, networks, switchgear, protective devices. 5th edition, Hanser Fachbuchverlag. 2006 ISBN 978-3-446-40574-5 .
  4. ^ A. Senner: Electrical engineering. 4th edition. Europe teaching aids. Willing, Wuppertal-Barmen 1964, 1965.
  5. ^ Rüdiger Kamme: Medical technology. 4th edition, Springer-Verlag, Berlin Heidelberg New York 2011, ISBN 978-3-642-16186-5 .
  6. ^ Günter Springer: Electrical engineering. 18th edition, Verlag Europa-Lehrmittel, Wuppertal, 1989, ISBN 3-8085-3018-9 .
  7. ↑ VdS Verlag: Guideline for the prevention of damage VdS 2349 Low-interference electrical installation. Online (accessed April 3, 2012; PDF; 367 kB).
  8. ↑ Protective measures in electrical systems. Online ( Memento of November 1, 2013 in the Internet Archive ) (accessed on February 13, 2012; PDF; 1.6 MB).
  9. ↑ Dangers of electrical current, protective measures and protective devices. Online (accessed February 13, 2012; PDF; 10.3 MB).
  10. ↑ Karl-Hans Kaul, Grünberg: Technologies for constant insulation monitoring . Online (accessed February 13, 2012; PDF; 1.8 MB).
  11. ↑ VdS Verlag: Guideline for the prevention of damage VdS 3501 insulation fault protection in electrical systems with electronic equipment. Online (accessed April 3, 2012; PDF; 837 kB).
  12. ↑ Bartec: Earth fault blocker 8SG1110 . Online (accessed April 3, 2012; PDF; 573 kB).
  13. ↑ Kurt Rode: Earth fault relay EA 2 . Online (accessed on April 3, 2012; PDF; 201 kB).
  14. ↑ Switchover and monitoring module. ( Memento of June 21, 2006 in the Internet Archive ) (accessed October 8, 2012; PDF; 1.1 MB).
  15. ↑ Protection system IT network with insulation monitoring . Online (accessed February 13, 2012; PDF; 173 kB).

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