1. Harmonics degrade the operating characteristics of protective relays. Effect of harmonics on relay depends on the design features and principles of operation.
2. Some digital relays and algorithms operate on sample data and zero crossing moment. Harmonic distortion creates error on such operation.
3. Harmonics make higher di/dt at zero crossings and the current sensing ability of the thermal magnetic breakers and change trip point due to extra heating in the solenoid.
4. Current harmonic distortion affects the interruption capability of circuit breakers and fuses.
5. The fuses are thermally activated and inherently RMS over current devices. Fuse materials are also susceptible to extra skin effect of the harmonic frequencies.
However, the changes in operating characteristics are small and do not present a problem. Most studies say that it is difficult to predict relay performance without testing. A lot of studies have been published on electro-mechanical and electronic relays. Presence of harmonic current, particularly third harmonic, in a fault situation, results in considerable measurement errors relative to the fundamental based setting. Harmonic content increases the possibility of mal-operation, unless only the fundamental waveforms are captured.
2. Some digital relays and algorithms operate on sample data and zero crossing moment. Harmonic distortion creates error on such operation.
3. Harmonics make higher di/dt at zero crossings and the current sensing ability of the thermal magnetic breakers and change trip point due to extra heating in the solenoid.
4. Current harmonic distortion affects the interruption capability of circuit breakers and fuses.
5. The fuses are thermally activated and inherently RMS over current devices. Fuse materials are also susceptible to extra skin effect of the harmonic frequencies.
However, the changes in operating characteristics are small and do not present a problem. Most studies say that it is difficult to predict relay performance without testing. A lot of studies have been published on electro-mechanical and electronic relays. Presence of harmonic current, particularly third harmonic, in a fault situation, results in considerable measurement errors relative to the fundamental based setting. Harmonic content increases the possibility of mal-operation, unless only the fundamental waveforms are captured.