The effects of three-phase harmonics on circuits are similar to the effects of stress and high blood pressure on the human body. High levels of stress or harmonic distortion can lead to problems for the utility's distribution system, plant distribution system and any other equipment serviced by that distribution system. Effects can range from spurious operation of equipment to a shutdown of important plant equipment, such as machines or assembly lines. Harmonics can lead to power system inefficiency. Some of the negative ways that harmonics may affect plant equipment are listed below:
1. CONDUCTOR OVERHEATING: a function of the square RMS current per unit volume of the conductor. Harmonic currents on undersized conductors or cables can cause a “skin effect”, which increases with frequency and is similar to a centrifugal force.
2. CAPACITORS: can be affected by heat rise increases due to power loss and reduced life on the capacitors. If a capacitor is tuned to one of the characteristic harmonics such as the 5th or 7th, over-voltage and resonance can cause dielectric failure or rupture the capacitor.
3. FUSES AND CIRCUIT BREAKERS: harmonics can cause false or spurious operations and trips, damaging or blowing components for no apparent reason.
4. TRANSFORMERS: have increased iron and copper losses or eddy currents due to stray flux losses. This causes excessive overheating in the transformer windings. Typically, the use of appropriate “K factor” rated units is recommended for non-linear loads.
5. GENERATORS: have similar problems to transformers. Sizing and coordination is critical to the operation of the voltage regulator and controls. Excessive harmonic voltage distortion will cause multiple zero crossings of the current waveform. Multiple zero crossings affect the timing of the voltage regulator, causing interference and operation instability.
6. UTILITY METERS: may record measurements incorrectly, resulting in higher billings to consumers.
7. DRIVES/POWER SUPPLIES: can be affected by mis-operation due to multiple zero crossings. Harmonics can cause failure of the commutation circuits, found in DC drives and AC drives with silicon controlled rectifiers (SCRs).
8. COMPUTERS/TELEPHONES: may experience interference or failures.
1. CONDUCTOR OVERHEATING: a function of the square RMS current per unit volume of the conductor. Harmonic currents on undersized conductors or cables can cause a “skin effect”, which increases with frequency and is similar to a centrifugal force.
2. CAPACITORS: can be affected by heat rise increases due to power loss and reduced life on the capacitors. If a capacitor is tuned to one of the characteristic harmonics such as the 5th or 7th, over-voltage and resonance can cause dielectric failure or rupture the capacitor.
3. FUSES AND CIRCUIT BREAKERS: harmonics can cause false or spurious operations and trips, damaging or blowing components for no apparent reason.
4. TRANSFORMERS: have increased iron and copper losses or eddy currents due to stray flux losses. This causes excessive overheating in the transformer windings. Typically, the use of appropriate “K factor” rated units is recommended for non-linear loads.
5. GENERATORS: have similar problems to transformers. Sizing and coordination is critical to the operation of the voltage regulator and controls. Excessive harmonic voltage distortion will cause multiple zero crossings of the current waveform. Multiple zero crossings affect the timing of the voltage regulator, causing interference and operation instability.
6. UTILITY METERS: may record measurements incorrectly, resulting in higher billings to consumers.
7. DRIVES/POWER SUPPLIES: can be affected by mis-operation due to multiple zero crossings. Harmonics can cause failure of the commutation circuits, found in DC drives and AC drives with silicon controlled rectifiers (SCRs).
8. COMPUTERS/TELEPHONES: may experience interference or failures.