What causes network disturbances?

There is a persistent opinion that grid-related problems are essentially the fault of the energy supplier. This assertion is only partially correct. The reality is much more complex. The source of grid disturbances can lie with the energy supplier as well as with the energy consumer. The fact is, however, that 85% of power quality disturbances are "home-made," i.e., caused by plant operators.

Energy suppliers:
Under certain circumstances, the connection or disconnection of larger loads on the part of the energy suppliers can lead to voltage changes (undervoltage or overvoltage) or to frequency fluctuations in the dynamic network. These network repercussions propagate throughout the network and influence the functioning of sensitive devices such as rectifiers, networks or PLC systems.

Operating equipment (consumers):
Harmonics are caused by non-linear loads such as thyristors, IGBT's and varistors. These components are installed, among others, in DC power supplies (power supplies), computers, electronic ballasts and dimmers as well as in power converters and frequency converters in motor drives with controllable speed. Modern electronics work with extra-low voltage. Here, the incoming alternating current is first rectified by a bridge rectifier and smoothed out by a smoothing capacitor. The current drawn by these consumers is pulse-shaped. This comes from the intermittent charging of the smoothing capacitor downstream of the rectifier. The intermittent charging changes the shape of the current, which is no longer purely sinusoidal but is superimposed with harmonic currents. The consequence for the consumer is now that the consumer current can no longer be taken from the mains in sinusoidal form. Since the frequencies of voltage and current are linked via the network impedance, they generate current distortions as well as voltage distortions at the terminals and vice versa. If the current at linear loads is not distorted, i.e. sinusoidal, and if the voltage has a different form, i.e. non-sinusoidal, the current at the mains terminals also assumes a non-sinusoidal form. The following table describes the phenomena and their causes.

Phenomenon	main cause	Limitably by
		Supplier	Consumer
Frequency variations	Load changes, loss of generation	yes	no
Slow voltage changes	Load changes	yes	no
Fast voltage changes / flicker circuits	Circuits, special loads	no	yes
Voltage unbalance	unbalanced loading of phases	partly	yes
harmonics and interharmonics	special devices	partly	yes
Signal voltages	Information transmission	yes	yes
DC currents or voltages	Special devices (half-wave rectifiers)	no	yes
Voltage dips and interruptions	Faults in the utility, consumer network (short circuits, interruptions)	no	no
Temporary overvoltage	Faults in the consumer network; resonances in the network	no/partial	partial/yes
Transient overvoltage	Lightning strikes, switching operations	no	no