Impact of Distributed Generation during the European 2006 Disturbance

The requirements for disconnection of generation units connected to the distribution grid (especially wind generation and CHP) are usually less strict than for the units connected to the transmission grid, i.e. they are disconnected at a smaller frequency deviation. When the frequency deviation reaches the threshold values of the units’ protection, they are automatically disconnected from the grid as happened immediately after the split of the UCTE system in three areas as shown in Figure 2. This resulted in areas where units had tripped due to under-frequency (in the Western area) and due to over-frequency (in the North-Eastern area). Such a behavior worsened the situation in the Western area (increased imbalance) while in the North Eastern area this reaction reduced power imbalance during the first seconds after the splitting.

Recovering the frequency to its nominal value required an increase of generation output in the Western area and a decrease of generation output in the North-Eastern area. After a few minutes, wind farms were automatically reconnected to the grid, being out of the TSOs’ control. This unexpected reconnection had a very negative impact, preventing the dispatchers in both areas from managing the situation.

Additionally, certain TSOs in the North-Eastern area were not able to reduce the power output from generation connected to the transmission and distribution grid in a sufficiently short time necessary for the frequency restoration.

These are examples of insufficient TSO control over the generation behavior. This needs to change in the future in order to eliminate the negative impact of distributed generation on the grid as reflected in Recommendation #5 of the Final report which states that the regulatory or legal framework has to be adapted in terms of the following aspects:

  • TSOs should have the control over generation output (changes of schedules, ability to start/stop the units)
  • Requirements to be fulfilled by generation units connected to the distribution grid should be the same in terms of behavior during frequency and voltage variations as for the units connected to the transmission network. These requirements should be applied also to units already connected to transmission and distribution grids
  • Operators of generation units connected to the transmission grid must be obliged to inform the TSO about their generation schedules and intra-day changes of programs prior to their implementation

TSOs should receive on-line data of generation connected to DSOs grids (at least 1-minute data)
The Final report - System disturbance on November 4th 2006 is available at


Let?s start with organization in protection testing