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2021-01-14 study

Dielectric strength in the event of temporary voltage surges

The VDE FNN study investigates the effects of short-term exceedances of the maximum permissible operating voltage on equipment and thus closes a Knowledge gap.

Update, 07.01.2021: The study is now available in English.


The energy transition and the integration of new consumption and generation facilities are changing the energy system and making the operation of the power grid more challenging. In order to ensure a highly reliable power supply, an expansion of electrical networks is taking place an the limits in operation are being explored to a greater extent - including voltage. The specifications in the European Network Codes and in the VDE-Application Rules take into account the changes in the system and in the networks and allow, for example, temporary exceedances of the maximum permanently permissible voltage. VDE FNN has investigated whether the equipment in existing networks can meet these requirements in a new study entitled "Analysis and assessment of the requirements on the Performance of the Equipment in case of temporary Network conditions with voltages above Um", or also known as "Study of the Dielectric Strength of Power Equipment".

Function and aging of equipment

In the study, VDE FNN shows under which conditions a reliable network operation can be ensured considering temporary voltages higher than the maximum permissible voltage for equipment (Um) in the distribution and transmission network. The question is how short-term voltages higher than Um affect the function and aging of different power equipment:

  • Overhead lines
  • Switchgear and switching devices
  • Current and voltage transformers
  • Power transformers and reactors
  • Surge arresters
  • Cable systems

Results in brief

  • No permanent operation with increased voltage is allowed
  • "Reserves" may be built in the operating equipment, according to the specifications in the standards
  • Network operators are responsible to check whether an operation of 1.05 Um is sufficient the their power equipment and determine a corresponding procedure

The study is available in the VDE store in German and English. VDE FNN members can download the study in both languages free of charge.