The AC/DC conversion process gives rise to electromagnetic harmonics of various frequencies. These harmonics must be dealt with in order not to cause disturbances with communication equipment. A converter station also has equipment that generates acoustic noise that can be disturbing to people in the neighborhood.
HVDC Light operates with a higher frequency (1 - 2 kHz) than a classic HVDC converter (50 or 60 Hz). (See
HVDC Light AC harmonic spectrum.) Therefore the whole station is located in a screened building to avoid electromagnetic disturbances and also audible noise.
Telephone interference
Frequencies between 100 Hz and up to say 3 kHz, i.e. harmonics within the audible range, can cause telephone interference to people close to the AC lines coming from the HVDC Light converter station. In certain cases the DC cables can also generate disturbances in close parallel telephone cables. In order to prevent this
the converter reactor and AC filters suppress these frequencies. In certain projects, the DC capacitor is also turned into a DC filter. Telephone interference from HVDC stations is relatively rare. The cases that have occurred have mostly been due to ground faults in the telephone system.
PLC interference
If power line carrier communications (in the range from 20 - 40 kHz up to about 200 kHz) are used in the AC grid, high frequency noise from the HVDC Light converter might cause interference. To prevent this, a PLC filter can be installed.
Radio interference (RI)
High frequency noise from the HVDC Light converter might also cause radio interference in the AM bands (150 kHz - 30 Mhz) in the vicinity of the converter station. FM radio, TV and mobile phones occupy higher frequencies and are not disturbed. The fact that most of the equipment is inside a metal building takes care of most of the RI noise. In addition small RI-filters are normally provided.
Audible noise
The fact that practically all equipment is located in a building helps to control the audible noise. Sound barriers can relatively easily be fitted. The audible noise that a HVDC Light converter station emits to the surroundings therefore comes mainly from the transformer and the valve cooling fans. There are a number of methods to mitigate the noise:
- orient disturbing equipment away from the most sensitive sound direction
- use of low noise level equipment
- screening or enclosing equipment
The owner always specifies the permissible audible noise level.