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Small power plants must be disconnected from the grid immediately in the event of a network shutdown or network disruption to avoid any danger to people and equipment.

Converting renewable energy into electricity is a key element of stabilising the global climate. In the context of small and micro power plants we mainly see photovoltaic installations, small wind power generators, cogeneration plants or small hydropower plants being used. The energy produced in this way is used to cover own consumption needs, or fed into the public grid to generate a profit.

Requirements for good network and plant (NP) protection

To ensure network safety, an automatic interface monitors the transfer between small power plants and the grid of the energy supplier (ES). Large power plants are managed and monitored directly by the ES using telecontrol engineering. This is too expensive and therefore uneconomical for the many private producers of electricity.

In the event of a power cut or a disruption in the grid of the energy supplier, small private power plants immediately have to be disconnected from the public grid to prevent unwanted feed-in.

Failure to disconnect from the grid without delay puts maintenance personnel at risk, while consumers can also be exposed to improper voltages and frequencies. The monitoring and the automatic disconnection are carried out by an automated interface. Small power plants have to be equipped with an automatic isolation unit that is checked and permitted by an accredited body. Country-specific norms define how the interface should be realised and checked in detail.

To meet the requirements of the standards and of the energy supply companies, the market offers solutions as individual components, multinational components as well as integrated solutions.

The thresholds can even be adjusted outside the standard values if required by the network operator. Functionally safe devices also fulfil the monitoring function in the event of faults, recognise these faults and ensure a safe operating condition.

Characteristics of a good grid and system protection

  • Functional safety
  • Voltage drop protection
  • Overvoltage protection
  • Monitoring of voltage quality
  • Frequency drop protection
  • Frequency rise protection
  • Detection of off-grid operation by phase voltage monitoring, RoCoF (Rate of change of frequency) and/or vector shift
  • Non-volatile fault latch
  • Random thresholds and reconnection times for non-adjustable energy producer (e.g. combined heat and power plant (CHP))
  • Wide rated voltage and rated frequency range (up to 60Hz), adjustable rated voltage
  • Free, practically unlimited parameterability
  • Software update option on site
  • Interfacing
  • Monitoring of 1 and 3 phase grids (with and without N)

Country-specific standards

  • Germany: VDE-AR-N 4105
  • Germany – medium voltage: BDEW-RL
  • Denmark: VDE-AR-N 4105
  • Austria: ÖVE/ÖNorm E 8001-4-712/A1
  • Italy: CEI 021
  • France: DIN VDE 0126-1-1
  • Czech Republic: DIN VDE 0126-1-1
  • Greece: DIN VDE 0126-1-1
  • Norway: DIN VDE 0126-1-1
  • Belgium: C10/11
  • UK: G59/G83
  • Poland, Portugal, Turkey, Cyprus: EN50438 Tab. 2
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