1. Noise Measurement
Table of Content:
1 Objective..........................................................................................................
2 Scope...............................................................................................................
3 Referenced Documents....................................................................................
4 Definitions and Abbreviations...........................................................................
5 Description.......................................................................................................
5.1 General..............................................................................................
5.2 Measuring instruments used .............................................................
5.3 Remarks on noise measurement ......................................................
5.4 Impact of reflections and noise sources in the vicinity.......................
6 Measurement plans.........................................................................................
7 Proceeding in case of deviations......................................................................
8 Copyright .........................................................................................................
1 Objective
This written procedure gives a description of how to perform and evaluate noise
measurements. It is intended not only as an internal measuring instruction, but also for
explaining the procedure to the client. By means of measurement data acquired on a
unique basis, establishing a noise statistic for all generators and motors of division AG
shall be rendered possible.
2 Scope Organization
This procedure is valid for all functional units. These tests shall be performed by on each
Hydro generator during commissioning.
Evaluation w ill be done in the works, in the case of Hydro generators and for motors
and turbo generators by assigned personnel
Measured values may however be inspected by the customer after completion of the
Measurement and on request a test report with the measured data not yet evaluated
may be handed over.
Products
This QM-procedure defines the noise measurement on large machines of all types.
Safety
When performing a noise measurement with an emitted sound pressure level above 85
dB(A) ear plugs shall be used. Moreover, with live parts sufficient safety clearances must
always be kept. When there are measuring points high above the floor, take care of
danger of falling and secure appropriately during measurement.
3 Referenced Documents
EN ISO 1680:2000
EN ISO 3741:2001
IEC 1260
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2. 4 Definitions and Abbreviations
None.
5 Description
5.1 General
Before performing a noise measurement on large machines actual questions must be
clarified with the person in charge respectively. The test engineer will elaborate the
corresponding noise measurement plans, into which measurement results shall be
entered by the tester.
The calibrated noise level meter is put at disposal by department for the time of the
measurement. After returning the noise level meter with the stored data, the engineer
will read out the measured values and in the case of noise measurement on Hydro
generators for further evaluation.
According to the noise measurement plan, measurement of overall noise and octave
analysis shall be performed at the indicated points in a distance of 1m from the emitting
surface, giving however always priority to the distance which is required by safety
reasons.
5.2 Measuring instruments used
Precision noise level meter, accuracy class 1 acc. to IEC 1260
e. g.: B & K, type 2238 (basis SPM BZ7126 ver, 1,1,0) and microphone 2230584 (or
similar) with transmission factor of 30,7dB Read the operating instructions!
5.3 Remarks on noise measurement
If the greatest linear dimension l of the machine (not including stub shaft ends) is l >=
0,25m, measurement lines (i.e. the line linking the measuring points) will run at a
smallest distance of d = 1 m from the machine surface. When defining the surface, small
protruding parts which have no influence on noise emission are not considered (e.g.
lifting lugs, shaft ends, etc.).
If the greatest linear dimension is l < 0,25 m, the measuring distance shall be 4 l ≤ d ≤ 1
m, however 0,25 m at a minimum. For machines with horizontal shaft the measurement
line runs in shaft center height h of the machine, how ever in height of 0,25 m at a
minimum. With all machines the measurement line which lies in the vertical plane runs in
shaft plane level.
Admissible fluctuation of the noise pressure level during duration of the measurement at
each measurement point: < 1dB(A), otherwise measurement at this point has to be
repeated or adequate justification given.
Deviation between two adjacent measurement points: < 3dB(A), otherwise clarify with
additional measurement in more detail by locally halving of measurement point raster.
Measurements of interfering ambient noise (difference <10 dB to machine noise) have to
be recorded. Other additional measuring points (e.g. at openings to the turbine
basement, control room, turbines, oil pumps, turbine governor a.o.) must be recorded as
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3. well. Moreover, features of the building and machine configuration, like special set-up of
the group, noise reduction measures etc. must be reported by the tester in the noise
measurement report as remarks !
5.4 Impact of reflections and noise sources in the vicinity
Reflection at nearby surfaces:
Sound waves are always reflected at surfaces and noise pressure level is
correspondingly increased as compared to a source in an open space (free field):
plane reflecting surface: +3dB (directly at the reflecting surface: +6dB !),
corner line: +6dB (crossing of 2 reflecting planes),
spacial corner: +9dB (crossing of 3 reflecting planes) !
Superposition of N noise sources L1, L2, L3,...LN :
Supersition of 2 noise sources :
When two noise sources emit noise with same energy and the measurement position is
in the same distance from both sources, the sound pressure level of one singular source
can be calculated from the total level Lsum as per L1 = L2 = Lsum – 3dB. If the noise levels
of both sources differ in amplitude, they can be separated as follows (L1 being the
higher value):
Subtraction of noise sources:
a) measurement of total noise Lsum (level L emitted by running machine is superposed
with background noise Lnoise)
b) measurement of background noise Lnoise separately (with machine at rest)
c) separation by subtraction (background noise must differ at least by 3dB to max.
10dB!)
6 Measurement plans
Attached below are samples of measurement plans for various generator types:
Bulb generator
Vertical generator
Horizontal generator
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4. Page 4 of 10

5. Required measurements
Standstill :
Measurement of sound pressure level LAeq at MP1, MP2, MP3, MP4
Frequency analysis of the loudest measurement point out of MP1, MP2, MP3
Rated load :
Measurement points MP1, MP2, MP3 above closed pit covers
Measurement of sound-pressure LAeq at MP1, MP2, MP3
Measurement points MP7, MP8, MP9 above opened pit covers
Measurement of sound-pressure LAeq at MP7, MP8, MP9
Frequency analysis of the loudest measurement point out of MP1, MP2, MP3 resp. MP7,
MP8, MP9
Frequency analysis of MP4, MP5, MP6
If significant sound pressure changes are noted at further measurement points (standard
distance is approx. 1m to emitting surface), these have to be recorded and entered into
the measurement diagram.
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6. Page 6 of 10

7. Required measurements
Standstill:
Measurement of sound pressure level LAeq at MP1, MP3, MP5, MP7
Frequency analysis of the loudest measurement point out of MP1 through MP7
Storage no.001, M23
Rated load:
Measurement of sound-pressure LAeq at MP1, MP2, MP3, MP4, MP9
Measurement of sound-pressure LAeq at MP5, MP6, MP7, MP8
Frequency analysis of the loudest measurement point out of MP1 to MP9, store no.002,
M23
Measurement of sound-pressure LAeq at MP10
Frequency analysis of measurement point MP10, storage no.003, M23
If significant sound pressure changes are noted at further measurement points (standard
distance is approx. 1m to emitting surface), these have to be recorded and the
measurement diagram complemented (e.g. additional measurement points on the
generator covers, outside in front of the closed door of the generator ring room, in front
of the closed turbine access, ...)
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8. Noise Measurement Report Horizontal Generator
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9. Required measurements
Standstill:
Measurement of sound pressure level LAeq at MP2,20,22,23,30,31,32
Frequency analysis of the loudest point out of MP2,20,22,23,30,31
Frequency analysis of MP32
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10. Rated load:
Measurement of sound pressure level LAeq at MP1 through MP31
Measurement of sound pressure level LAeq at MP32
Frequency analysis of the loudest point out of MP1 through MP31
Frequency analysis of MP32
If significant sound pressure changes are noted at further measurement points (standard
distance is approx. 1m to emitting surface), these have to be recorded and the
measurement diagram complemented (e.g. additional measurement points on the
generator covers, in front of the closed turbine access, ...)
7 Proceeding in case of deviations
Any nominal value, minimum value, maximum value, tolerance etc given in an instruction
is intended to serve for quality control purposes only. In the case of deviations, a
nonconformity report has to be written according to PNG Power Standard.
8 Copyright
This Document is properly of PNG Power internal use only and must neither be copied.
Neither is it to be handed over nor in other way communicated to a third party.
Infringement will lead to prosecution.
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