• Gossen Metrawatt
  • Camille Bauer

What causes power disturbances?

There’s a tenaciously prevailing opinion that mains-related problems can essentially be traced back to the power utility. This assertion is only partially correct. The truth is far more complex. Sources of power disturbances can be found at the power utilities as well as at the facilities of the power consumers. However, 85% of all power quality disturbances are indeed “homemade”, i.e. caused by the equipment operators themselves.

Power Utilities

Under certain circumstances, connecting and disconnecting large loads on the part of the power utility may result in voltage fluctuations (i.e. overvoltage or undervoltage) or frequency fluctuations in the dynamic network. This mains pollution spreads throughout the entire grid and influences the functioning of sensitive devices such as rectifiers, networks and PLC systems.

Operating Equipment (consumers)

Harmonics are caused by non-linear consumers such as thyristors, IGBTs and varistors. These components are used in, amongst other devices, DC power supplies (power packs), computers, electronic ballasts and dimmers, as well as in power converters and frequency converters for drive units using motors with adjustable speed. Modern electronics works with extra-low voltage. Incoming alternating current is first of all rectified by means of a bridge rectifier and smoothed by a smoothing capacitor.

Current consumed by these devices is pulsed. This results from intermittent charging of the smoothing capacitor downstream from the rectifier. The current’s waveform is changed by this intermittent charging: it’s no longer sinusoidal but rather superimposed with harmonic current. The consequence for the consumer is that sinusoidal current is no longer available from the mains.

Due to the fact that voltage and current frequencies are linked via line impedance, they cause current and voltage distortion at the terminals and vice versa. If current supplied to linear consumers is not distorted, i.e. if it’s sinusoidal, and if the voltage has a different waveform, i.e. not sinusoidal, the current at the mains terminals is also non-sinusoidal. The following table describes the various phenomena and their causes.

Phenomenon Primary Cause Can be Limited by
The Power Utility The Power Consumer
Frequency fluctuation Load changes,
generation failure
Yes No
Gradual voltage
changes
Load changes Yes No
Rapid voltage
changes / flicker
Switching,
special loads
No Yes
Voltage asymmetry Asymmetric
loading of the phases
To some extent Yes
Harmonics and
sub-harmonics
Special devices To some extent Yes
Signal voltages Data transmission Yes Yes
Direct current or
voltage
Special devices
(half-wave rectifiers)
No Yes
Voltage dips and 
interruptions
Faults in the power utility’s
or the power consumer’s network
(short-circuits, interruptions)
No No
Temporary overvoltage   Faults in the power consumer’s network,
power resonance
No /
to some extent
To some extent /
yes
Transient overvoltage Lightning, switching operations No No

 

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