Measurement of the utility frequency

- load shedding -  


When generating capacitys or large consumers get offgrig unexpectedly, then deviations from 800 mHz are allowed for a short (49,200 Hz to 50.800 Hz). At higher deviations a massive failure in the network is likely. In this case a defined gradual plan for load-shedding comes into force, to avoid problematic network conditions. When dropping of loads at lower frequency or dropping of generation a hight frequencies do not help to stabilize the frequency, then the network is switched off (black out) and then rebuilt without the failures.

Steps of load shedding

The definition of load shedding in Germany is described in the Technical requirements for automatic frequency relieve (Technische Anforderungen an die automatische Frequenz- entlastung) and is subject to the requirements of the Operation Handbook Policy 5 of the ENTSO-E. In the following, the exemplary implementation plan is represented with four stages:

FrequencyActionSum of loadTyp of activation
49,8 HzActivation of power reserves immediately
and shedding of pump accumulators (t<10s)
manually /
49,2 HzImmediate shedding of pump accumulators automatic
49,0 HzLoad Shedding Step 1, ca. 12.5 %ca. 12.5 %automatic
48,8 HzLoad Shedding Step 2, ca. 12.5 %ca. 25.0 %automatic
48,6 HzLoad Shedding Step 3, ca. 12.5 %ca. 37.5 %automatic
48,4 HzLoad Shedding Step 4, ca. 12.5 %ca. 50.0 %automatic
47,5 HzSeparation of power plants from the gridautomatic
Source: Technische Anforderungen an die automatische Frequenzentlastung of FNN

After the separation of the power plants from the network, the network is gradually built up again, which allows the identification of the disturbance and thus the workaround.