The Harmonic Filter resistors are used to eliminate the dangerous distortions (harmonics) generated inside the network due to connection of more and more number of electronic power converters.
The main problems caused by harmonics, that are sinusoidal currents with different frequencies and amplitudes compared with the rated 50/60 Hz network currents, are:
increment of losses on the line
malfunctioning of the test equipments
interferences with radio and phone systems
resonances
high currents at neutral point
These Harmonic Filter resistors , used together with reactors and capacitors, help to reduce and filter the harmonics. The main characteristics of TELEMA resistors are:
low variation of resistance value at hot condition
low working overtemperature
high reliability
high insulations, internal and to ground
specific insulation design to guarantee the integrity of the unit in the event of overvoltages for atmospheric discharges or switching in the network
supported impulse test up to 400 kV
all conductive parts are connected to a well-known potential