Harmonic distortion in your manufacturing plant

Effect of Harmonics

Symptoms of problematic harmonic levels include overheating transformers, motors, and cables. Thermal protective devices keep tripping, and digital devices are operating abnormally and producing logic faults. Harmonics in your power can stress your electrical network and damage your equipment. Components can fail, increasing operating costs.

Energy-efficient equipment uses power electronics with non-linear load behavior. The results of non-linear loads are non-sinusoidal currents containing harmonic currents. These harmonic currents interact with the impedance of the electrical network.

Non-linear Loads

The figure above illustrates the voltage and current waveforms of an inductive load with non-linear characteristics.

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Measurements with a Jantiza 509-PRO

The power quality data showed that there were a lot of harmonic emissions and that the voltage dropped every so often when motors started up or when the weather was bad.

According to IEEE 519, harmonic voltage distortion on power systems 1.0kV and below is limited to 8% THDv with each individual harmonic limited to 5% at the PCC at the bus voltage. The current harmonic limits vary based on the short circuit strength of the system as per the IEEE 519 criteria.

The effects of voltage unbalance can also be severe on induction motors, power electronic converters, and VFDs. Voltage unbalances in induction motors reduces efficiency and could lead to premature motor failure. During voltage unbalance the negative sequence voltage will result in generating a negative (reversing) torque. This phenomenon results in a reduction in torque, increased pulsation, and increased motor noise.

Harmonic Correction Solutions

Omniverter provides three different harmonic correction solutions. Omniwave Active Harmonic Filter (AHF) offers harmonic correction up to the 50th harmonic frequency. Omniverter Dynamic Harmonic filter (DHF) filter specific low-order harmonics (5,7&11). The DHF traps both upstream and downstream harmonic currents. The Omniverter Resonance Harmonic Filter (REHF) filter higher-order harmonics. The REHF can be configured to eliminate resonance. The RHEF compensates for switching transient events due to upstream utility capacitor switching. ?

Results

A phased approach was followed at the specific manufacturing plant. The solution was to filter the 3rd, 5th, and 7th order harmonics using?an AHF active harmonic filter at a specific load. The second solution was the use of a REHF Harmonic Filter to reduce the higher-order harmonics on the voltage bus of the plant.

The REHF is designed to correct voltage spikes, capacitor-switching transients, and resonant conditions.