It persistently holds that network-related problems are essentially due to the utility company. This claim is only partially correct. The reality is much more complex. The source of network disturbances can be the energy supplier as well as the energy user. However, the fact is that 85% of the power quality disturbances are "home-made", ie caused by plant operators.
The switching on or off of larger loads on the part of energy providers may lead to voltage changes (under- or overvoltage) or to frequency fluctuations in the dynamic network. These network perturbations continue throughout the network and affect the operation of sensitive devices, such as cell phones. Rectifiers, networks or PLC systems.
Harmonics are used by non-linear consumers such as As thyristors, IGBTs and varistors caused. These components are u.a. in DC power supplies, computers, electronic ballasts and dimmers, and in converters and frequency converters in variable speed motor drives. The modern electronics work with low voltage. The incoming alternating current is first rectified by a bridge rectifier and smoothed out with a smoothing capacitor.
The current consumed by these consumers is pulsed. This comes from the jolting charging of the smoothing capacitor behind the rectifier. Due to the impulsive charging of the current is changed in its shape, it is no longer purely sinusoidal, but superimposed with harmonic currents. The consequence for the consumer is now that the load current can no longer be taken sinusoidally from the grid.
Since the frequencies of voltage and current are linked via the network impedance, they produce current distortions as well as voltage distortions at the terminals and vice versa. If the current at linear consumers is not distorted, ie sinusoidal, and the voltage has a different shape, ie not sinusoidal, then the current at the power terminals also assumes a non-sinusoidal shape. The following table describes the phenomena and their causes.
Lightning strikes, switching operations
| Phenomena | Main cause | Limited to | |
|---|---|---|---|
| Provider | Consumer | ||
| Frequency Fluctuations | Load changes Loss of production |
Yes | No |
| Slow voltage- Changes |
Load Changes | Yes | No |
| Fast voltage- Changes / Flicker |
Circuits, Special Loads |
No | Yes |
| Voltage unbalance | unbalanced Stress the phases |
partially | Yes |
| Harmonics and Interharmonics |
Special devices/td> | partially | Yes |
| Signal voltages | Information transfer | Yes | Yes |
| DC or voltages |
Special devices (Half-wave rectifier) |
No | Yes |
| Voltage dips and Interruptions |
Error in the supplier, Consumer network (Short circuits, interruptions) |
Yes | No |
| Temporary overvoltage | Error in the consumer network Resonances in the network |
No / Partially |
Partially / Yes |
| Transient overvoltage | No | No | |