Noise prevention

 

Amprion plans and operates its high-voltage switchgear in such a way that disturbing noise emissions are prevented, and the permissible emissions levels adhered to.

The primary noise emitters are transformers (permanent noise) and, in isolated cases, possible impulse noise from switchgear, although this - because of the low switching frequency - is not generally perceived as disturbing. Only low-noise transformers and switchgear has been installed in recent years.

Open-air substations with an high-side voltage of 220 kV or more are subject to a licensing procedure under the Federal Emissions Control Act (BImSchG). The noise emissions from these installations are assessed under the Technical Instructions to Prevent Noise (TA-Lärm).

Transformers

The main source of transformer noise is the load-independent oscillation of the iron core as a result of magnetostrictive length changes of the laminated sheets. These oscillations are transmitted by the insulating oil and the core support structures to the transformer tank and from there are emitted acoustically as airborne noise. At a network frequency of 50 Hz, the transformer noise has a harmonic spectrum with level-determining frequencies at 100, 200, . . 600 Hz, which exhibit high frequency stability in line with the low network frequency fluctuations.

The noise emission key indicators are described in the VBI directive VDI 3739 (Emission key indicators for technical noise sources, transformers).Since the early 70's, Amprion has purchased only transformers in the lowest-noise version corresponding to the state of technology.

We reduce the noise levels of our transformers with the following measures to minimise noise:

  • Reduced induction
  • Use of grain-oriented sheet steel
  • Change of core structure (step-lap core)
  • Oscillation-insulated set-up of the active section in the tank

Secondary sound insulation, such as the installation of sound-walls or the use of sound insulation sheathings can further reduce noise emissions where necessary.

Transformers

When using a sound-wall, a noise-level reduction of up to 12 dB(A) (near field) can be achieved, which decreases with increasing distance, depending on the distance between transformer and emission impact location. A noise insulating sheathing developed by Amprion for high-voltage transformers (sheet-steel construction with noise insulation and absorption inserts) which, where necessary, can be placed onto the existing transformer stand, achieves noise level reductions of approx. 14 dB(A) at 100 Hz, approx. 16 dB(A) at 200 Hz and approx. 17 dB(A) at 300 Hz, 400 Hz.

Circuit breakers

Because of the low switching frequency - switching is only required in the event of failures or specifically for overhaul purposes - noise emissions from circuit breakers are negligible.

Circuit breakers emit impulse noise, whereby the duration of the noise impulse is in the order of approx. 49 - 100 ms

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