Duke Energy Substation Charlotte, North Carolina

Location: Charlotte, North Carolina
Owner/Operator: Duke Energy
Client: Vanquish Fencing Solutions

Duke Energy Substation Noise Assessment & Barrier Design Considerations

HGC Noise Vibration Acoustics was retained by Vanquish Fencing Solutions to complete a detailed noise assessment of a Duke Energy substation, located off Monroe Road in Charlotte. The study quantified existing transformer noise emissions, evaluated future noise levels associated with planned replacement equipment, and assessed compliance with the applicable Charlotte Noise Ordinance. Vanquish was supplying a new sound barrier to ensure long-term compliance at the facility property lines.

Using sound power data obtained through onsite acoustical measurements, manufacturer-supplied transformer data, and a full 3-D acoustical model, HGC demonstrated that with the new transformers and the proposed barrier, the substation is expected to meet both daytime and nighttime criteria.

Transformer Power Substation Site Context and Noise Sources

The substation operates continuously (24/7) and has residences in close proximity.

The facility currently operates three step-down power transformers, two of which are slated to be replaced with new Siemens Energy units. As part of the site refurbishment, Vanquish proposed an 8-ft-high noise barrier along the east property line, with an optional increase to 10 ft for additional attenuation.

Primary transformer noise sources include:

• Three transformer cores generating low-frequency hum
• Transformer radiator cooling fans generating broadband noise

Manufacturer’s test reports provided frequency-dependent sound power data for the new equipment, used for acoustical modelling purposes.

Applicable City of Charlotte Noise Criteria

Noise limits at the substation property line are governed by the Charlotte Noise Ordinance, established under Ordinance No. 9585, amending Chapter 15, Article III of the Charlotte City Code.

Applicable limits:

• 85 dBC — daytime
• 60 dBC — nighttime

These values were applied in all modelling scenarios to determine compliance.

Sound Power Measurement Methods

Sound power levels of the three transformers were measured onsite using sound intensity methods, which allows for accurate acoustical characterization of transformer components while minimizing the influence of ambient noise.

Measurements were collected in 1/3-octave bands both at source and in various positions around the site for use in determining transformer sound emission characteristics, and for calibrating the acoustical model.

Acoustical Modelling Approach

A full 3-D acoustical model of the substation and surrounding area was developed using ISO 9613-2 propagation methods, accounting for:

• Geometrical spreading
• Atmospheric absorption
• Ground attenuation
• Shielding by structures, topography, and proposed barriers

Four receptor locations at the east, north, west, and south property lines were used to represent the most sensitive assessment positions.

Three acoustic modelling scenarios were evaluated:

1. 1. No east property line barrier
   2. 8-ft-high east barrier
   3. 10-ft-high east barrier

Acoustical Analysis Results and Noise Mitigation Recommendations

HGC’s measurements, analysis and modelling found that:

• Replacement of transformers 2 and 3 with Siemens Energy units will reduce overall sound emissions relative to current conditions.
• Installation of an 8-ft or 10-ft barrier along the east property line will reduce noise levels to below the applicable Charlotte Noise Ordinance limits.

While the 8-ft barrier would meet the requirements, HGC recommended a 10-ft barrier to provide an additional margin of compliance and to minimize the potential for noise concerns from neighbouring residents.

HGC Noise Vibration Acoustics Consulting Services Provided

• Attended Acoustical Measurements
• Computational Acoustical Modelling
• Review of Local Noise Ordinances
• Noise Mitigation Analysis and Recommendations