Sound Emission Measurement (Transformer, Switchgear, dB(A))

The measurement of the sound level emitted by transformers, circuit breakers, variable-frequency drives and other electrotechnical equipment, expressed in A-weighted decibels (dB(A), where the human ear is less sensitive to very low and very high frequencies than the measuring instrument would register without weighting), following a standardised measurement method (for example NEN-EN-ISO 3746 for the enveloping-surface method) with fixed measurement distances and points around the source. Transformer noise arises mainly from magnetostriction in the core (a slight shape change of the core material with every half-cycle of the mains frequency, producing a fundamental hum at 100 Hz and its multiples) and from cooling-system fans or oil pumps, and the measured sound pressure or sound power levels must be checked against both the manufacturer's warranty values and the local environmental permit (Activiteitenbesluit milieubeheer), where the night-time immission limit at nearby dwellings is often the decisive factor for siting and any required noise-mitigation measures (enclosures, acoustic screens, vibration-damping mountings).