A new problem in electrical installations is the presence of high-frequency currents and voltages. These supraharmonics regularly lead to problems. As a result, this phenomenon desperately requires attention. High-frequency switching equipment is the source of numerous high-frequency disturbances .These can be found in many types of converters, such as in:
However, this list is not complete. Many devices with power electronics use high switching frequencies to achieve the desired goal. The figure below gives an example of the currents required by a charger for an electric car.
The switching frequency used is around 10 kHz (current of 1.08 A) and also results in the presence of currents with a frequency that is a multiple of this (20 kHz, 40 kHz). The following figure shows an analysis of the currents of a phase.
These high-frequency currents result in a high-frequency voltage in the installation (see frequency spectrum of the voltage). The impedance of the mains is high for this high frequency due to the inductance of the mains. In addition, many connected devices will be able to provide a path with low impedance due to the presence of capacitors in the various connected devices.
Source: Tim Slangen (TU/e)
Because the capacitors for the high-frequency voltage have a low impedance, a relatively large current will flow. Assuming the capacitor is designed for 1 mA at a voltage of 230V and a frequency of 50 Hz, the impedance of the capacitor will be a factor 200 times smaller at 10 kHz than at 50 Hz, after all:
At a voltage of 1.24 V (see spectrum of the voltage), a high-frequency current will flow with a frequency of 10 kHz of:
This will cause the capacitor to overload and eventually damage the capacitor.
The application of a high switching frequency and poor filtering, causing these currents to also occur in the installation and network, result in the occurrence high-frequency voltages. These, in turn, lead to high-frequency currents in devices, which can cause damage, malfunction or failure of devices.
It is, therefore, important to recognize this problem. Regarding regulations, a great deal also still needs to be arranged, on the one hand to obtain emission requirements for appliances (determining the allowed level of pollution) and on the other hand immunity requirements for appliances (determining what appliances must be able to withstand.)
