Device for network monitoring with assigned switching devices

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A device for network monitoring with assigned switching devices ( ENS ) is an automatic disconnection point for small power generation systems up to 30  kW peak power . It guarantees that in the event of a power failure or grid shutdown, the inverter will in any case disconnect itself from the power grid, in order to prevent islanding and the resulting feedback into the power grid, which could potentially lead to dangerous effects. The requirements for an ENS were developed by the professional association for precision mechanics and electrical engineering , together with the VDEW project group "TAB for small power plants".

technology

The ENS is a safety device. If an unintentional island network occurs when a sub- network is disconnected , this is recognized and the generator is disconnected from the network. The electrical voltage , network frequency and the impedance of the network are monitored. Island formation is recognized either by a jump in the network impedance or when frequency or voltage limits are exceeded. With single-phase inverters, voltage monitoring can also be carried out in three phases. Then there is no impedance monitoring. In the case of inverters without a transformer, insulation monitoring and an AC / DC sensitive residual current circuit breaker (type B) are also required.

The ENS requirements call for a redundant implementation, i.e. H. the monitoring device is available twice. The probability that both (independent) monitoring systems fail is very low. Therefore, in systems with ENS, there is no need for a disconnection device that is accessible to the distribution network operator at any time and the annual inspection of this disconnection device. According to the pre-standard DIN V VDE V 0126-1-1 of February 2006 , the disconnection device is not required for small generating systems for electrical energy that feed into the public low-voltage network if they have an ENS.

designation

Since the 2005 version of VDE 0126, the disconnection point is no longer called “device for network monitoring with associated switching devices”, but rather: “automatic switching point between a network-parallel self-generation system and the public low-voltage network”. In the preliminary standard DIN V VDE V 0126-1-1, which came into effect on February 1, 2006, the term ENS is expressly no longer used.

The distribution network operators implement this standard through the supplementary notes to the VDEW guideline, Sept. 2005 "In-house generation systems on the low-voltage network 4th edition 2001" and state that the term "ENS" should be avoided in future as a synonym for the disconnection point, as previously after the draft standard E DIN VDE 0126 automatically meant the impedance measurement as a criterion for the detection of isolated operation.

The abbreviation ENS remained colloquially in use for network monitoring, also because there were providers who continued to use the abbreviation in the product name.

50.2 Hz problem

In VDE 0126, the limit for overfrequency protection of systems connected to the low-voltage network was set at 50.2 Hz. This was the reason for the 50.2 Hz problem. This involved the simultaneous shutdown of several gigawatts of generating capacity in the low-voltage network, should the frequency rise to over 50.2 Hz during a (rare) network failure, the so-called system split. Other threshold values ​​were entered for over 300,000 PV systems with an output greater than 10 kW and this retrofitting was legally accompanied by the System Stability Ordinance.

Follow Norms

It was not directly adopted in the European standards, although VDE 0126 was also used abroad (France, Belgium, the Czech Republic, etc.). For micro-generators up to 16 A, EN 50438: 2013 (requirements for the connection of small generators to the public low-voltage network) was developed at European level. This standard has meanwhile been incorporated into EN 50549-1: 2019 (Requirements for generating systems intended for parallel operation with a distribution network - Part 1: Connection to the low-voltage distribution network), which also covers generators on the low-voltage network with a rated current of over 16 A. The function of the ENS is taken over by the interface protection .

In Germany, most of the tasks of VDE 0126 are now described by VDE-AR-N 4105: 2011-08 (minimum technical requirements for connection and parallel operation of generating systems on the low-voltage network), the current second edition is VDE-AR-N 4105: 2018 -11. In application rule 4105, the term network and system protection, or NA protection for short, is used for network monitoring. In the follow-up version of VDE V 0126-1-1: 2013-08, the topic was no longer dealt with itself; instead, reference was made to application rule 4105 in many places. The document was still needed for some time for users of VDE 0126-1-1 abroad; after this user base ceased to exist, it was withdrawn.

Web links

Individual evidence

  1. ↑ ENS26NA - assembly and operating instructions. UfE Umweltfreund Energieanlagen GmbH, September 7, 2011, accessed on June 23, 2020 .
  2. ↑ Boemer et al .: Effects of a high proportion of decentralized generation systems on grid stability in the event of overfrequency & development of proposed solutions to overcome them , ecofys & IFK, Berlin / Stuttgart, September 2011.
  3. ↑ SysStabV
  4. ↑ 50.2 Hertz Problem: General Information. BDEW, July 27, 2012, accessed on June 22, 2020 .
  5. ↑ C. Duvauchelle, B. Gaiddon :: Evolution de la DIN VDE 0126 - De la version de 1994 à la DIN VDE 0126-1-1 de 2006. In: Projet ESPRIT - Etudes scientifiques prénormatives sur le réseau au raccordement of installations photovoltaïques . June 2010, accessed June 22, 2020 .
  6. ↑ DIN VDE V 0126-1-1: 2013-08 (automatic switching point between a network-parallel self-generation system and the public low-voltage network). In: DKE / K 373. VDE, August 2013, accessed on June 22, 2020 .