Harmonics
The presence of harmonics in the waveform of the network voltage can be attributed to
various causes such as rectifiers, variable speed drives, thyristors, saturated transformer,
arc furnaces, etc.
The main problems caused by harmonics are:
• Interferences in telecommunications systems and equipment.
• Distortion of the Electricity Supply Voltage
• Erratic operation of control and protection relays
• Failures in transformers and motors due to overheating caused by core losses.
If the harmonic power is significant, i.e. THVD greater than 7 %, THID greater than
40 %, this may result in overvoltages and overloads, which may lead to the failure of the
capacitors, circuit breakers, contactors etc.