The harmonics in electrical systems are electrical currents or sinusoidal electrical voltages that have a frequency equal to an integer multiple of the frequency of the distribution system, called the fundamental frequency. By overlapping the Fundamental Current and the Fundamental Voltage respectively, they cause the distortion of the waveform.
When powering an electrical equipment in alternating current, it is expected that since the voltage has a sinusoidal shape, the current absorbed by the load is also sinusoidal, this is true only for some types of loads or linear loads, but not for non-linear loads in which the relationship between current and voltage is no longer represented by a straight line.
The extent of the deformation is defined by a parameter called total harmonic distortion of current THDi%. The drawbacks caused by the harmonics are manifold and include the malfunction of equipment, the increase in currents in the circuits, the increase in losses, noise frequency interference etc.
SINUSOIDAL POWER SUPPLY
MAINS SUPPLY WITH HARMONICS
High harmonic distortion values and anomalous voltage values of the neutral with respect to the earth potential can cause equipment failures, leading to production downtime and expensive repairs to the electrical distribution network.
It is essential that the user is aware of the expensive problems and dangers associated with high levels of harmonics, especially in consideration of the important increase in the use of non-linear devices.
Harmonic components can significantly affect the electrical distribution network by acting on all of the connected structures and equipment.
Harmonic distortions cause the following problems in an installation:
- Conductor overtemperatures, in particular the neutral one in presence of single-phase distorted loads;
- MV/LV Transformer over temperatures;
- Harmonic distortion of the voltage caused by the saturation of the MV/LV transformers;
- Overheating of standard power supply transformers with consequent expensive downtime and repairs or replacement of the transformer;
- Resonance with other reactive components on the same power line (e.g. power factor correction banks);
- Poor power factor;
- Resonance producing overvoltages;
- Increase in electricity supply costs due to harmonic losses;
- Interferences in telecommunication systems and equipment;
- Irregular operation of the control and protection relays;
- Intervention of automatic circuit breakers and other protective devices;
- Failure or malfunction of computers, motor drives, lighting circuits and other sensitive loads;
TO HARMONICS IN ELECTRIC POWER SUPPLY:
PASSIVE FILTERS FOR HARMONICS
Passive Filters (PHF) are additional filters usually installed on the power supply line of the drive.
The filters consist of a combination of inductor (filter inductor) -capacitor inserted in derivation from an asymmetrical series inductor (main inductor). The performance of the passive harmonic filters IREM PHF series are very high: they reduce the harmonic distortion in current from 100% of THDi to typical values lower than 5%; the filters are made up of capacitors that form a resonant circuit with a reactor that has a high impedance path at the fundamental frequency and a low impedance path at higher specific frequencies.
Passive filters are more commonly connected to individual loads in the system rather than to the common coupling point since the application requires a consistent load for effective harmonic mitigation.
The passive harmonic filter is installed in series with the line and therefore must be chosen according to the current absorbed by the load or by the group of loads. IREM passive harmonic filters guarantee excellent attenuation and do not need to be tuned with reference to the impedance parameters of the installation site.