A Study in Voltage Flickering

A Study of Voltage Flickering

As the light load increased, harmonic disturbance produced a “flicker” phenomenon throughout the facility that was detectable to the human eye.

Observations

The 34,000+ 1000W HID 347/400V HPS lighting drivers installed at our client’s greenhouse were collectively producing harmonic current disturbance in the 400V lighting power distribution systems facility that was severe enough to cause significant degradation of equipment lifespans.

Tests confirmed that multiple elements in the facility’s distribution and lighting load topology were interacting to exacerbate the disturbances seen at the plant.

There was a significant amount of conducted EMI on the 400V lighting feeders — a combination of both differential and common-mode noise.

The large number of nearly identical drivers exhibited a significant propensity for their harmonic noise to constructively interfere, exacerbating the effects of harmonic noise.

The facility’s 2MVA transformers were undersized and insufficiently rated to support the nonlinear profile of the load.

The lighting driver transients and harmonics coupling through the 2MVA transformers were inciting and driving a significant resonance in the 13.8kV distribution wiring.

Recommendations

Enginuity Global provided a robust set of electrical engineering solutions that would resolve the flicker phenomenon for our client.

Rework the Neutral wires in transformers to reduce coupling of phase conductor EM fields to any unutilized conductors. This is necessary to protect the transformers from HF noise being coupled to unused conductors and back to the transformers.

Install customized filtering at the individual lighting strings fed from the contactor panels throughout the plant, which rejects harmonic noise from the drivers locally and takes rejected energy to ground at each locale.

Rework the facility’s grounding topology to reduce the reactance of the ground paths, lowering the impedance to harmonic noise — as well as improving the ground bonding with building structural steel to improve overall noise rejection and protection throughout the facility.