Olsun Electrics’ Noise Attenuating (NA) transformers are designed for use in applications where the effects of distribution system (primary side) electrical noise must be limited (attenuated) prior to feeding a load (secondary). “Electrical noise” is the result of voltage transients or surge voltages brought about by equipment sharing the distribution system. Equipment utilizing contactors or vacuum interrupters, switching circuit apparatus like variable speed drives and other voltage surge producing devices can all be contributors to undesirable results with computers, medical, audio-visual and other surge sensitive equipment that may happen to be sharing a common distribution feed.
There are two noise mode types:
- Common Mode is the noise associated with phase-to-ground circuits.
- Transverse Mode or Normal Mode is the noise associated with line-to-line circuits.
Noise attenuation is a logarithmic expression in decibels (dB) and is the ratio of the input transient voltage (VTI) to the output transient voltage (VTO).
- 20log10 x ( VTI / VTO )
- 10:1 – 20dB
- 100:1 – 40dB
- 1000:1 – 60dB
- 1,000,000 – 120dB
Addressing Common Mode Noise
Olsun Electrics’ standard Noise Attenuating Transformers utilize a full winding height, copper foil electrostatic shield (E.S.S.) placed between the primary and secondary windings as well as between the inner winding and the core (dual shields). These shields are grounded and serve to short circuit to ground the capacitive noise that might otherwise be electrostatically coupled between the windings.
Addressing Transverse (Normal) Mode Noise
Transverse mode noise is more a function of electromagnetic coupling via the core as opposed to capacitive coupling between the windings as is the case with common mode noise. Because of this, Olsun Electrics standard Noise Attenuation Transformers utilize an appropriately rated metal oxide varistor surge suppressing device on the primary of the transformer to better address the problem of transverse mode noise.
Between the two approaches, the dual E.S.S. and the MOV Surge device, it is not unreasonable to expect attenuation values of not more than 120dB common mode and 60dB transverse mode using Olsun Electrics NA Transformers. However, it is important to note that these values are not absolute and will vary depending on, among other parameters, transformer loading and transient magnitude and frequency.