Source: https://docs.jmrp.io/phonometry/devices/emission/sound-power-turbines/
# Sound Power of Steam Turbine Sets (IEC 61063)
A steam turbine set is too large, too hot and too tied to its foundation to
be carried to a test room, and it is measured where it runs, in the turbine
hall, with the auxiliary plant of the station working around it. IEC 61063 is
the noise test code for that job. It takes the survey method of ISO 3746 and
fixes what the method leaves open for this one family of machines: the shape
of the enveloping surface around a turbine, a gear or a generator and an
exciter standing in a row on their operating floor, where the microphones go
on it, how the background and the hall are corrected, and what the report has
to say. This guide covers each step: the stepped measurement surface and its
area, the key and additional microphone positions, the background correction
of Table 2 and how it departs from the $K_{1\mathrm{A}}$ of ISO 3746, the
environmental correction of Figure A.3 and the qualification of the hall, the
surface sound pressure level and the sound power level, and the report. Which
route fits other machines is weighed in
[Sound Power](https://docs.jmrp.io/phonometry/devices/emission/sound-power/).
## 1. The test code (IEC 61063)
The standard applies to the part of a turbine set, the turbine, the driven
machinery and the components attached to them, that stands above the floor of
the turbine room, inside a continuous enveloping surface bounded by that floor
(clause 1.1.1). Which floor is the reflecting plane depends on how the set is
mounted. A continuous, reflecting operating floor is; an operating floor near
the horizontal centreline of a large set is too, as long as it has no openings
through which the noise radiated beneath it reaches the microphones
(1.1.2). An open grating, a floor with openings near the set, or walkways
around it are not, and the foundation floor becomes the plane (1.1.3); the
plant beneath then contributes so much at the microphones that the sound power
level is no longer valid, unless the openings are blocked with panels during
the test. Noise control treatments fitted to the set, enclosures or screens,
are reported by type, location and extent (1.1.5).
The method is the survey grade of ISO 3746 (Introduction), and Table 1 gives
the standard deviation its sound power levels tend to stay within: 5 dB for a
source with prominent discrete tones and 4 dB for one whose sound is spread
evenly over frequency. When the method compares similar machines that are
omnidirectional and radiate broadband noise, measured in similar halls, NOTE 1
puts the standard deviation of that comparison at 3 dB or less. IEC 61063 was
written against the 1979 edition of ISO 3746;
the library's ISO 3746 is the 2010 edition, and where this guide sets the two
side by side it says so.
### How the measurement goes
1. Enclose each part of the set in a **reference box**, the smallest box that
just holds it with its lagging and any screen, standing on the reflecting
plane (7.1). The **measurement surface** is the set of parallelepipeds 1 m
out from the boxes.
2. Place the **five key positions** of Figure 2 on it and the **additional
positions** between them, at equal distances, close enough that every
casing has a measurement section (7.2). The overhead ones may be left out if
a preliminary run shows they move the result by no more than 1.0 dB.
3. With the set in a steady operating condition under rated load (and, to find
the noisiest condition, at 25 %, 50 % and 75 % as well, 6.2), read the
A-weighted level at each position with a sound level meter to IEC 651 on
the slow time weighting, calibrated before each series with a calibrator
good to $\pm 0.5$ dB (5.1, 5.2, 7.4).
4. Get the **background** at each position. With the turbine running it can
rarely be measured, and NOTE 1 of 8.1 lets it be computed from the sound
power of the auxiliary plant and the reflections of the hall.
5. **Qualify the hall**: the environmental correction $K$, from its
reverberation time or from a calibrated reference sound source, may not
exceed 7 dB (Annex A). Outdoors $K$ is zero, and the wind has to stay below
6 m/s (4.3, A.4).
6. **Compute** the corrected levels (Table 2), the surface sound pressure
level (Equation (2)) and the sound power level (Equation (3)), and write the
report of clause 10.
## 2. The measurement surface
The parallelepipeds of the measurement surface run parallel to the reference
boxes at the measurement distance $d$, and "the measurement distance ($d$) is
1 m" (7.1): each is 2 m wider and 1 m taller than its box, and the first and
the last are 1 m longer, at the two ends of the set. Figure 2 dimensions them on
the measurement surface, and Equation (1) gives its area:
$$
S = 2\,h_\mathrm{max}\,b_\mathrm{max} + \sum_{i=1}^{Z} l_i\,(2 h_i + b_i),
$$
with $l_i$, $b_i$ and $h_i$ the length, width and height of the $i$-th of the $Z$
parallelepipeds. The sum is the tops and the long sides; the first term stands
for every transverse face, the two ends and the steps between neighbours. It
is the exact area when the sections shrink from one largest section towards
both ends, each containing the next, which is how both drawings of Figure 2
are built. Otherwise it is not: it counts too much when the tallest and the
widest boxes are different ones, and too little when a small section stands
between two large ones. `enveloping_area_m2` sums the stepped surface face by
face for that case. A single box gives the enveloping parallelepiped of
ISO 3746, $lb + 2lh + 2bh$.
The set of this guide is the one Figure 2 b draws: the HP and IP casings in
one box, the LP turbine in its own, then the generator and the exciter.
```python
from phonometry import emission
boxes = [ # length, width, height above the floor [m]
emission.TurbineReferenceBox(6.0, 4.0, 3.5, "HP-IP"),
emission.TurbineReferenceBox(5.0, 5.0, 4.5, "LP"),
emission.TurbineReferenceBox(7.0, 3.5, 3.0, "Generator"),
emission.TurbineReferenceBox(3.0, 2.5, 2.2, "Exciter"),
]
surface = emission.turbine_measurement_surface(boxes)
print(surface.lengths_m, surface.widths_m, surface.heights_m)
# [7. 5. 7. 4.] [6. 7. 5.5 4.5] [4.5 5.5 4. 3.2]
print(round(surface.area_m2, 1), round(surface.enveloping_area_m2, 1)) # 410.1 410.1
```
## 3. The microphone positions
Figure 2 prescribes five **key positions** (7.2.1): 1 and 5 at the centres of
the two ends, 2 and 4 on the two long sides and 3 overhead, the last three in
the plane between the turbine and the driven machinery. In Figure 2 a that is
the plane after the turbine box; in Figure 2 b, between the LP turbine and the
generator, so the library takes the number of boxes on the turbine side
(`turbine_boxes`) and puts 2, 3 and 4 at the outer corner of the wider (and
taller) of the two parallelepipeds that meet there, as both drawings do.
The **additional positions** start at the key positions and are "arranged at
equal distances", such "that there is at least one measurement section at
each casing" (7.2.2). The library walks two paths, as the plans and the
elevations of Figure 2 draw them: round the sides at the microphone height,
from 1 through 2, 5 and 4 back to 1, and the overhead line in the vertical
plane of the shaft, from 1 up the front end, across the top and its steps to
3, and on to the rear end and down it to 5 (both elevations put a position on
the front end above key position 1). It divides each run between key
positions into the fewest equal intervals no longer than `spacing_m`, and
stands a position at every division. The two paths are divided each on its
own, so their stations need not stand in the same transverse sections, as the
drawings of Figure 2 happen to put them; 7.2.2 asks only for equal distances.
The "measurement section at each casing" is checked per parallelepiped: a
spacing that leaves one without a position on its long sides emits a
`SoundPowerWarning`, and where one box holds two casings, as the HP and IP
turbines do here, whether both are reached is read from `positions_m`. The
height of the row round the sides is yours: Figure 2 draws it without
dimensioning it. The NOTE of 7.2.2
lets the overhead positions be deleted, for safety or cost, once a
preliminary run has shown they change the sound power level by no more than
1.0 dB (section 6), and `include_overhead=False` leaves them out.
```python
array = emission.turbine_microphone_positions(
surface, microphone_height_m=1.5, spacing_m=4.0, turbine_boxes=2)
print(array.count, int(array.overhead_mask.sum())) # 23 7
print(array.positions_m[array.key_mask])
# [[ 0. 0. 1.5] key position 1
# [12. 3.5 1.5] 2
# [23. 0. 1.5] 5
# [12. -3.5 1.5] 4
# [12. 0. 5.5]] 3
print(array.positions_per_box, array.every_box_sampled) # (2, 2, 2, 1) True
array.plot() # plan; array.plot(view="elevation") from the side
```
*The surface around the set of Figure 2 b, 410.1 m², and the 23 positions of
a 4 m spacing: 16 round the sides at 1.5 m and 7 on top. The plan shows both
long sides and the overhead line on the shaft; the elevation shows the side of
key position 4, as both elevations of Figure 2 do, and the top, which is where
key position 3 stands.*
## 4. The background correction: Table 2 against ISO 3746
Each position's level is corrected for the background before it is averaged
(8.1), and the correction is read from Table 2:
| Level with the source operating less the background (dB) | Correction to subtract (dB) |
| :--- | :--- |
| 3 | 3 |
| 4 | 2 |
| 5 | 2 |
| 6 | 1 |
| 7 | 1 |
| 8 | 1 |
| 9 | 0.5 |
| 10 | 0.5 |
| > 10 | 0.0 |
`turbine_background_correction` judges the last row first, on the difference
as measured: anything above 10 dB is "> 10" and takes no correction, 10.2 dB
as much as 11 dB. Between 3 and 10 dB the table is printed in whole decibels,
so the difference is rounded to the nearest one, halves upwards, before it is
read, and 9.5 to 10 dB takes the 0.5 dB of the row 10; the library reads the
stepped table of ISO/TS 7849-1 the same way. Below 3 dB there is no row: the
background "should be at least 3 dB below" (4.2), and under that "a valid
measurement of the machine under test cannot be made". The function returns
the 3 dB of the first row there, which still leaves an upper limit, since the
exact correction for a smaller difference is larger, and that is how the
NOTE of 4.2 lets such a result be used. It is also the value ISO 3746:2010
prints for the same case.
```python
print(emission.turbine_background_correction([3.0, 4.0, 5.0, 6.0, 9.0, 10.0, 11.0]))
# [3. 2. 2. 1. 0.5 0.5 0. ]
print(emission.turbine_background_correction([4.4, 4.5, 9.5, 10.0, 10.2]))
# [2. 2. 0.5 0.5 0. ]
```
ISO 3746:2010 corrects the background with a formula instead, Equation (12)
of clause 8.3.3,
$$
K_{1\mathrm{A}} = -10 \lg\left(1 - 10^{-0.1 \Delta L_{p\mathrm{A}}}\right),
$$
taken as zero above 10 dB and as 3 dB below 3 dB, and it applies it once, to
the difference between the surface-averaged levels, where IEC 61063 corrects
each position before the average. At the differences Table 2 prints, the two
agree within 0.35 dB: the steps lead the formula at 5 dB (2 against 1.65) and
at 8 dB (1 against 0.75), and trail it at 4 dB (2 against 2.20) and at 6 dB
(1 against 1.26). Between the rows, where a measured difference usually falls,
the rounding moves them further apart, from 0.57 dB below the formula at
3.5 dB to 0.56 dB above it just short of 5.5 dB. Above 10 dB neither
subtracts anything.
*The same background, two corrections. Table 2 read in whole decibels is a
staircase over the curve of ISO 3746:2010 Equation (12); its printed rows sit
within 0.35 dB of the curve, and the rounding between them within 0.6 dB.*
## 5. The environmental correction and the hall
The reflections of the hall raise the levels on the surface, and the
environmental correction $K$ takes them off (8.2). Figure A.3 prints the
curve and its formula,
$$
K = 10 \lg\left[1 + \frac{4}{A/S}\right],
$$
the $K_2$ of ISO 3744 and ISO 3746, with $A$ the equivalent absorption area of
the hall from its reverberation time, $A = 0.16\,V/T$, measured with
broadband noise or an impulse and A-weighting on the receiving side (A.3.1).
The hall qualifies when $K$ does not exceed 7 dB (8.3, A.3.3), which the
clause restates as $A/S \ge 1$. The two agree to the whole decibel the limit
is printed in: the curve gives $10 \lg 5 = 6.99$ dB at $A/S = 1$ and reaches
7 dB at $A/S = 0.997$. `check_turbine_test_environment` judges the 7 dB,
from the correction itself or from a bare `environmental_correction_db`
(0 outdoors).
A.3.2 offers a second route: a reference sound source calibrated in a free
field over a reflecting plane, whose sound power level $L_{W\mathrm{r}}$ is set against
the level $L_W$ it shows in the hall by the method of ISO 3746 with $K$ taken
as zero, so $K = L_W - L_{W\mathrm{r}}$. By its NOTE, $L_W$ is the mean of two
determinations, the source in the middle of each long side of the set, and a
machine longer than 10 m takes two more, at the ends. Outdoors, and in very
large halls or halls that are not closed, $K$ is zero (A.4), and the wind has
to stay below 6 m/s, with a windscreen above 1 m/s (4.3).
```python
room = emission.turbine_environmental_correction(
surface.area_m2, volume_m3=60_000.0, reverberation_time_s=3.2)
print(room.absorption_area_m2, round(room.ratio, 2),
round(room.environmental_correction_db, 2)) # 3000.0 7.32 1.89
print(emission.check_turbine_test_environment(room).passes) # True
source = emission.turbine_reference_source_correction(
[95.6, 96.3, 95.9, 96.8], calibrated_level_db=94.2, machine_length_m=21.0)
print(round(source.environmental_correction_db, 2)) # 1.95
```
*Figure A.3 with the hall of the example on it: 60 000 m³ and 3.2 s give
3000 m² of absorption, an $A/S$ of 7.3 and a $K$ of 1.89 dB, well inside the
7 dB of A.3.3.*
## 6. The surface level and the sound power level
The corrected levels are energy-averaged and $K$ is subtracted, Equation (2),
$$
\overline{L_{p\mathrm{A}}} = 10 \lg\left[\frac{1}{N}
\sum_{i=1}^{N} 10^{0.1 L_{p\mathrm{A}i}}\right] - K,
$$
and the surface term gives the sound power level, Equation (3),
$L_{W\mathrm{A}} = \overline{L_{p\mathrm{A}}} + 10 \lg(S/S_0)$ with
$S_0 = 1$ m². The level is recorded to the nearest whole decibel (9.4 g).
```python
import numpy as np
levels = np.array([ # dB re 20 uPa, in the order of array.positions_m
91.8, 93.1, 93.6, 94.2, 93.0, 90.4, 89.7, 88.2, 87.5, 88.6, 90.1, 90.9,
93.4, 94.6, 93.9, 92.7, 92.2, 94.0, 95.1, 93.8, 90.6, 89.3, 87.9])
background = np.array([ # computed from the auxiliary plant (8.1, NOTE 1)
84.0, 84.2, 84.5, 84.8, 85.0, 83.2, 82.5, 81.4, 80.6, 81.3, 82.9, 83.4,
85.0, 84.8, 84.5, 84.2, 83.0, 83.0, 83.0, 83.0, 83.0, 82.0, 81.0])
full = emission.turbine_sound_power(
levels, surface_area_m2=surface.area_m2, background_levels_db=background,
environmental_correction_db=room.environmental_correction_db,
overhead_mask=array.overhead_mask)
print(round(full.surface_pressure_level_db, 2),
round(full.sound_power_level_db, 2)) # 89.78 115.91
print(full.reported_sound_power_level_db) # 116.0
print(round(full.overhead_effect_db, 2), full.overhead_may_be_deleted) # 0.27 True
print(round(full.level_range_db, 1), full.arithmetic_mean_allowed) # 8.6 False
full.plot(position_labels=array.labels) # the key bars numbered as in Figure 2
```
The differences from the background run from 6.8 to 12.1 dB, so Table 2 takes
1 dB off thirteen positions, 0.5 dB off seven and nothing off three. The seven
overhead positions raise the level by 0.27 dB, well within the 1.0 dB that
would let a later run on the same set leave them out.
The NOTE of 8.3 allows a plain arithmetic average in place of Equation (2)
when the position levels span no more than 5 dB, and says the average should
not differ from Equation (2) by more than 0.7 dB. For a fixed range the energy
average leads the arithmetic one most when the levels sit at the two ends of
the range, and the worst of those sets, two levels 5 dB apart with the louder
at 41 % of the positions, puts them 0.707 dB apart: the NOTE's figure to its
one decimal. Here the levels span 8.6 dB, so the note does not apply
(`arithmetic_mean_allowed` is `False`).
A lighter load lowers the level without lowering the background. At a quarter
of the rated load, 4.5 dB quieter, eight positions come within 3 dB of the
background, and the result is only an upper limit:
```python
import warnings
with warnings.catch_warnings():
warnings.simplefilter("ignore", emission.SoundPowerWarning)
quarter = emission.turbine_sound_power(
levels - 4.5, surface_area_m2=surface.area_m2,
background_levels_db=background,
environmental_correction_db=room.environmental_correction_db)
print(quarter.upper_limit, quarter.conforms) # True False
```
*The full-load run position by position, and the report of the two loads.
The Table 2 correction has already come off each bar; the gap between the
dashed and the red line is the environmental correction of the hall.*
## 7. The report
Clause 10 asks the report to state that the A-weighted sound power level "has
been obtained in full conformity with the procedures of this standard and
that this level is expressed in decibels above 1 pW", and to give at least:
the turbine with its noise control screens and enclosures, the operating
conditions, the A-weighted levels at each position corrected for the
background, the surface sound pressure level, the sound power level, and the
date and time of the measurements. `turbine_noise_declaration` builds it from
one determination per operating condition. It keeps each sound power level as
determined and gives it in the report to the whole decibel, finds the loudest
condition on the levels before that rounding, so two loads that round to the
same decibel are still told apart, and carries the standard deviation of
Table 1 for the kind of sound. A determination that is not in full conformity,
an upper limit or a hall beyond 7 dB, cannot carry the statement and is
refused with a `ValueError`.
```python
half = emission.turbine_sound_power(
levels - 1.5, surface_area_m2=surface.area_m2, background_levels_db=background,
environmental_correction_db=room.environmental_correction_db,
overhead_mask=array.overhead_mask)
report = emission.turbine_noise_declaration(
{"50 % load": half, "100 % load": full},
turbine="Three-casing condensing set, 60 MW, with generator and exciter",
noise_control="none",
measured_at="2026-09-25, 10:30 to 12:10",
tonal=True)
print(report.reported_sound_power_levels_db) # (114.0, 116.0)
print(report.loudest_condition, report.standard_deviation_db) # 100 % load 5.0
print(report.statement)
report.plot()
```
### `turbine_sound_power()` parameters
| Parameter | Type | Units | Range / default | Notes |
| :--- | :--- | :--- | :--- | :--- |
| `pressure_levels_db` | 1D array | dB | at least 4 positions | $L_{p\mathrm{A}i}$ with the set operating |
| `surface_area_m2` | float | m² | positive | $S$ of Equation (1) |
| `background_levels_db` | 1D array or `None` | dB | required | One per position; `None` states that none was determined |
| `environmental_correction_db` | float | dB | required | $K$; 0 outdoors; a value above 7 dB warns |
| `overhead_mask` | bool array | | `None` | For `overhead_effect_db` (NOTE of 7.2.2) |
## What this guide covers
**Covered.** The IEC 61063:1991 determination of the A-weighted sound power level of a
steam turbine set: the stepped measurement surface 1 m out and its area by
Equation (1) (with the exact stepped area beside it), the five key positions
of Figure 2 and the additional positions at equal distances with the check
of 7.2.2 made per reference box, the stepped background correction of Table 2
per position,
the environmental correction of Figure A.3 from the reverberation time or
from a reference sound source (A.3.2), the 7 dB qualification of A.3.3 and
the wind limit of 4.3, the surface sound pressure level and the sound power
level of Equations (2) and (3), the arithmetic average of the NOTE of 8.3,
the overhead deletion test of 7.2.2, the whole-decibel rounding of 9.4 g, the
report of clause 10 and the standard deviations of Table 1.
**Not covered.** The instruments are assumed right: the IEC 651 sound level meter on the slow
time weighting, the calibrator of 5.2 and the placement that keeps steam,
air and fields off the microphone (7.4) are the operator's. The reflecting
plane is not checked against A.2.1 (absorption below 0.1, 4 m beyond the
surface), the height of the row of microphones is the caller's because
Figure 2 does not dimension it, and the $L_W$ determinations of a reference
source are made with the ISO 3746 method
(`sound_power_pressure(grade="survey")`) before they are passed. How the
plant below the operating floor or around the set reaches the microphones
(1.1.3) is outside the standard, and so outside the library. Every reference
box is taken as centred on one shaft line, so a set whose boxes are flush on
one long side and step only on the other, as Figure 2 a draws one, is
modelled symmetrically; Equation (1) does not change. The side row and the
overhead line are divided each on its own, not in the aligned transverse
sections the drawings of Figure 2 show, and a reference box that holds several
casings is checked as one.
## See also
- [Sound Power](https://docs.jmrp.io/phonometry/devices/emission/sound-power/): choosing among the
determination routes and the ISO 4871 declaration.
- [Sound Power by Pressure Methods (ISO 3744 / ISO 3746 / ISO 3745)](https://docs.jmrp.io/phonometry/devices/emission/sound-power-pressure/):
the enveloping-surface survey method this test code is built on, and its
$K_1$ and $K_2$.
- [Sound Power in Situ by Comparison (ISO 3747)](https://docs.jmrp.io/phonometry/devices/emission/sound-power-in-situ/):
the other route for a machine that cannot leave its installation.
- API reference: [`emission.turbine_noise`](https://docs.jmrp.io/phonometry/reference/api/power/turbine-noise/).
## References
- International Electrotechnical Commission. (1991). *Acoustics — Measurement
of airborne noise emitted by steam turbines and driven machinery* (IEC
61063:1991). Read in its English adoption, BS EN 61063:1996, the text of EN
61063:1996, which is IEC 1063:1991 without modification. Equations (1) to
(3), Tables 1 and 2, Figure 2, the Figure A.3 of Annex A and the report of
clauses 9 and 10 that this guide implements.
- International Organization for Standardization. (2010). *Acoustics —
Determination of sound power levels and sound energy levels of noise sources
using sound pressure — Survey method using an enveloping measurement surface
over a reflecting plane* (ISO 3746:2010).
[ISO](https://www.iso.org/standard/52056.html). The survey method IEC 61063
is built on (it cites the 1979 edition), and the background correction K1A
of Equation (12), clause 8.3.3, that Table 2 is compared with.
## Standards
IEC 61063:1991, *Acoustics — Measurement of airborne noise emitted by steam
turbines and driven machinery*: the measurement surface and its area of
Equation (1), the microphone positions of Figure 2, the background correction
of Table 2, the environmental correction of Figure A.3 with the qualification
of A.3.3, the surface sound pressure level and sound power level of Equations
(2) and (3), and the report of clauses 9 and 10 with the standard deviations of
Table 1.
