• Overheating and sustained damage to bearings, stator and rotor laminations and winding insulation on generators, causing early life failure. Similar effects on power transformers; in the US and Japan harmonics have resulted in fires in distribution transformers

• Overheating and destruction of power factor correction capacitors. Danger of resonance (i.e. harmonic amplification of voltage or current) if ‘detuning reactors’ are not fitted to the capacitor banks, causing catastrophic damage to equipment. Even with detuning, capacitors can be damaged by harmonic currents

• Overheating of the stator and rotor of fixed speed electric motors; risk of bearing collapse due to ‘hot’ rotors (i.e. on double cage or deep bar rotor designs). This is especially problematic on fixed speed explosion proof motors with increased risk of explosion. If the voltage distortion is over the prescribed limit (2% or 3% VTHD maximum for IEC motors, depending on specific explosion proof protection concept), the motor is no longer certified, losing any third party assurance as to its safety.

• Spurious tripping of circuit breakers and rupturing of fuses. Interference with electrical, electronic and control system equipment, including computers, radio communications, measuring devices, lighting, etc. Errors introduced in some types of monitoring equipment process systems dependent on such accurate measurements

• Overheating of cables and additional risk of failure due to resonance. Decreased ability to carry rated current due to ‘skin effect’, which reduces a cable’s effective cross sectional area

Note - The effects of harmonics on generators (including those on standby applications) are significantly more pronounced than on utility or plant power transformers. For the same magnitude of harmonic current the resultant voltage distortion can be three to four times higher due to the increased source impedance.