prEN IEC 60953-1:2025

SLOVENSKI STANDARD
01-december-2025
Pravila za preskuse toplotne sprejemljivosti parne turbine - 1. del: Visoka
natančnost za velike kondenzacijske parne turbine
Rules for steam turbine thermal acceptance tests - Part 1: High accuracy for large
condensing steam turbines
Règles pour les essais thermiques de réception des turbines à vapeur - Partie 1: Haute
précision pour les turbines à vapeur à condensation de grande puissance
Ta slovenski standard je istoveten z: prEN IEC 60953-1:2025
ICS:
27.040 Plinske in parne turbine. Gas and steam turbines.
Parni stroji Steam engines
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

5/287/CDV
COMMITTEE DRAFT FOR VOTE (CDV)
PROJECT NUMBER:
IEC 60953-1 ED2
DATE OF CIRCULATION: CLOSING DATE FOR VOTING:
2025-11-07 2026-01-30
SUPERSEDES DOCUMENTS:
5/278/CD, 5/285/CC
IEC TC 5 : STEAM TURBINES
SECRETARIAT: SECRETARY:
China Mr Chang Fu
OF INTEREST TO THE FOLLOWING COMMITTEES: HORIZONTAL FUNCTION(S):

ASPECTS CONCERNED:
Energy Efficiency
SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING
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clauses to be included should this proposal proceed. Recipients are reminded that the CDV stage is the final stage for
submitting ISC clauses. (SEE AC/22/2007 OR NEW GUIDANCE DOC).

TITLE:
Rules for steam turbine thermal acceptance tests - Part 1: High accuracy for large condensing
steam turbines
PROPOSED STABILITY DATE: 2035
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IEC CDV 60953-1 © IEC 2025
CONTENTS
CONTENTS . 1
FOREWORD . 8
INTRODUCTION . 10
1 Scope . 11
1.1 General . 11
1.2 Object . 11
1.3 Matters to be considered in the contract . 11
2 Normative references . 12
3 Units, symbols, terms and definition . 12
3.1 General . 12
3.2 Symbols, units . 12
3.3 Subscripts, superscripts and definitions . 12
3.4 Guarantee parameters . 12
3.4.1 Guidance on guarantee parameters . 12
3.4.2 Thermal efficiency . 12
3.4.3 Heat rate . 12
3.4.4 Thermodynamic efficiency . 12
3.4.5 Steam rate . 12
3.4.6 Main steam flow capacity . 12
3.4.7 Power output . 12
3.4.8 Guarantee values for extraction and mixed-pressure turbines . 13
3.4.9 Thermal Load Capacity (for Nuclear applications) . 13
4 Guiding principles . 13
4.1 Advance planning for test. 13
4.2 Preparatory agreements and arrangements for tests . 14
4.3 Planning of the test . 14
4.3.1 Time for acceptance tests . 14
4.3.2 Direction of acceptance tests . 14
4.4 Preparation of the tests . 14
4.4.1 Condition of the plant . 14
4.4.2 Condition of the steam turbine . 15
4.4.3 Condition of the condenser . 15
4.4.4 Isolation of the cycle . 15
4.4.5 Checks for leakage of condenser and feed water heaters . 17
4.4.6 Cleanliness of the steam strainers . 17
4.4.7 Checking of the test measuring equipment . 17
4.5 Comparison measurements . 17
4.5.1 General . 17
4.5.2 Reduced uncertainty for comparison measurements . 17
4.6 Settings for test . 18
4.6.1 Load settings . 18
4.6.2 Special settings . 18
4.7 Preliminary tests . 18
4.8 Acceptance tests . 18
4.8.1 Constancy of test conditions . 18
4.8.2 Maximum deviation and fluctuation in test conditions . 18
IEC CDV 60953-1 © IEC 2025
4.8.3 Duration of test runs and frequency of readings . 19
4.8.4 Reading of integrating measuring instruments . 20
4.8.5 Alternative methods . 20
4.8.6 Recording of tests . 20
4.8.7 Additional measurement . 20
4.8.8 Preliminary calculations . 20
4.8.9 Consistency and number of tests . 20
4.9 Repetition of acceptance tests . 20
5 Measuring techniques and measuring instruments . 20
5.1 Overview . 20
5.1.1 Instrument accuracy requirements . 20
5.1.2 Measuring instruments . 22
5.1.3 Measuring uncertainty . 22
5.1.4 Calibration of instruments . 22
5.1.5 Alternative instrumentation . 23
5.2 Measurement of power. 23
5.2.1 Determination of mechanical turbine output . 23
5.2.2 Measurement of boiler feed pump power . 23
5.2.3 Determination of electrical power of a turbine generator . 23
5.2.4 Measurement of electrical power . 23
5.2.5 Electrical instrument connections. 24
5.2.6 Electrical instruments . 24
5.2.7 Instrument transformers . 24
5.2.8 recalibration of instruments and transformers . 24
5.3 Flow measurement . 24
5.3.1 Determination of flows to be measured . 24
5.3.2 Measurement of primary flow . 24
5.3.3 Installation and location of flow measuring devices . 26
5.3.4 Calibration of primary flow devices for water flow . 26
5.3.5 Inspection of flow measuring devices . 28
5.3.6 Differential pressure measurements . 28
5.3.7 Water flow fluctuation . 28
5.3.8 Secondary flow measurements . 28
5.3.9 Occasional secondary flows. 29
5.3.10 Density of water and steam . 30
5.3.11 Determination of cooling water flow of condenser . 30
5.4 Pressure measurement (excluding condensing turbine exhaust pressure) . 30
5.4.1 Pressures to be measured . 30
5.4.2 Instruments . 30
5.4.3 Main pressure measurements . 30
5.4.4 Pressure tapping holes and connecting lines . 30
5.4.5 Shut-off valves . 30
5.4.6 Calibration of pressure measuring devices . 30
5.4.7 Atmospheric pressure . 31
5.4.8 Correction of readings . 31
5.5 Condensing turbine exhaust pressure measurement . 31
5.5.1 General . 31
5.5.2 Plane of measurement . 31
5.5.3 Pressure taps . 31
IEC CDV 60953-1 © IEC 2025
5.5.4 Manifolds . 32
5.5.5 Connecting lines . 32
5.5.6 Instruments . 33
5.5.7 Calibration . 33
5.6 Temperature measurement . 33
5.6.1 Points of temperature measurement . 33
5.6.2 Instruments . 33
5.6.3 Main temperature measurements . 33
5.6.4 Feed train temperature measurements (including bled steam) . 33
5.6.5 Condenser cooling water temperature measurement . 33
5.6.6 Thermometer wells . 33
5.6.7 Precautions to be observed in the measurement of temperature . 34
5.7 Steam quality determination . 34
5.7.1 General . 34
5.7.2 Tracer technique . 34
5.7.3 Condensing method . 34
5.7.4 Constant rate injection method . 34
5.7.5 Extraction enthalpy determined by constant rate injection method . 34
5.7.6 Tracers and their use . 34
5.8 Time measurement . 34
5.9 Speed measurement . 35
6 Evaluation of tests . 35
6.1 Preparation of evaluation . 35
6.2 Computation of results . 35
6.2.1 Calculation of average values of instrument readings . 35
6.2.2 Correction and conversion of averaged readings . 35
6.2.3 Checking of measured data . 35
6.2.4 Thermodynamic properties of steam and water . 36
6.2.5 Calculation of test results . 36
7 Correction of test results and comparison with guarantee . 36
7.1 Guarantee values and guarantee conditions . 36
7.2 Correction of initial steam flow capacity . 36
7.3 Correction of output . 36
7.3.1 Correction of maximum output . 36
7.3.2 Correction of Output with specified initial steam flow . 36
7.4 Correction of the thermal performance . 36
7.5 Definition and application of correction values . 36
7.6 Correction methods . 36
7.6.1 General . 36
7.6.2 Correction by heat balance calculation . 36
7.6.3 Correction by use of correction curves prepared by the manufacturer . 37
7.6.4 Tests to determine correction values . 37
7.7 Variables to be considered in the correction of specific turbine cycles . 37
7.7.1 Scope of corrections . 37
7.7.2 Turbines with regenerative feed-water heating . 37
7.7.3 Turbines which have no provision for the addition or extraction of steam
after partial expansion . 37
7.7.4 Turbines with steam extraction for purposes other than feed-water
heating (extraction turbines) . 37
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7.7.5 Other types of turbine . 37
7.8 Guarantee comparison . 37
7.8.1 Tolerance and weighting . 37
7.8.2 Guarantee comparison with locus curve . 38
7.8.3 Guarantee comparison with guarantee point . 38
7.8.4 Guarantee comparison for turbines with throttle governing . 38
7.8.5 Guarantee comparison for extraction turbines . 38
7.9 Deterioration of turbine performance (ageing) . 38
7.9.1 Timing to minimise deterioration . 38
7.9.2 Correction with comparison tests . 38
7.9.3 Correction without comparison tests . 38
8 Measuring uncertainty . 38
8.1 General . 38
8.2 Determination of measuring uncertainty of steam and water properties . 38
8.2.1 Pressure . 38
8.2.2 Temperature . 38
8.2.3 Enthalpy and enthalpy difference . 38
8.3 Calculation of measuring uncertainty of output . 39
8.3.1 Electrical measurement . 39
8.3.2 Mechanical measurement . 39
8.3.3 Additional uncertainty allowance because of unsteady load conditions . 39
8.4 Determination of measuring uncertainty of mass flow . 39
8.4.1 Measuring uncertainty of mass flow measurements . 39
8.4.2 Measuring uncertainty of multiple measurements of primary flow . 39
8.4.3 Uncertainty allowance for cycle imperfections . 39
8.5 Calculation of measuring uncertainty of results . 39
8.5.1 General . 39
8.5.2 Measuring uncertainty of thermal efficiency . 39
8.5.3 Measuring uncertainty of thermodynamic efficiency . 39
8.5.4 Uncertainty of corrections . 39
8.5.5 Guiding values for the measuring uncertainty of results . 39
8.6 Example uncertainty calculation . 40
Annex A (normative) Feedwater heater leakage and condenser leakage tests . 44
A.1 Feedwater heater leakage tests . 44
A.2 Condenser leakage tests . 44
Annex B (normative) Evaluation of multiple measurements, compatibility . 45
Annex C (normative) Mass flow balances . 46
C.1 Multiple mass balances (normative) . 46
C.2 Flows for further evaluations (informative) . 46
Annex D (informative) Short-statistical definition of measuring uncertainty and error
propagation in acceptance test . 47
Annex E (informative) Temperature variation method . 48
E.1 Description of the problem . 48
E.2 Possibility to determine the leakage flow . 48
E.3 Applied example . 48
Bibliography . 49

IEC CDV 60953-1 © IEC 2025
Figure 1 – typical configuration of a flow section with an orifice and a throat tap nozzle
and flow straightener . 25
Figure 2 – Basket tip . 32
Figure 3 – Guide plate . 32

Table 1 – Maximum deviations and fluctuations in operating conditions . 18
Table 2 – Recommended uncertainties of measured variables . 21
Table 3 – Apportionment of unaccounted leakages . 36
Table 4 – Guiding values for the uncertainty of test results . 40
Table 5 – Example uncertainty calculation for reheat cycle with calibrated primary
flows measurements . 40
Table 6 – Example uncertainty calculation for wet nuclear cycle with calibrated primary
flow measurement . 42

IEC CDV 60953-1 © IEC 2025
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Rules for steam turbine thermal acceptance tests - Part 1: High accuracy
for large condensing steam turbines

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for
standardization comprising all national electrotechnical committees (IEC National Committees).
The object of IEC is to promote international co-operation on all questions concerning
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as
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3) IEC Publications have the form of recommendations for international use and are accepted
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies
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IEC is not responsible for any services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including
individual experts and members of its technical committees and IEC National Committees for
any personal injury, property damage or other damage of any nature whatsoever, whether direct
or indirect, or for costs (including legal fees) and expenses arising out of the publication, use
of, or reliance upon, this IEC Publication or any other IEC Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced
publications is indispensable for the correct application of this publication.
9) IEC draws attention to the possibility that the implementation of this document may involve
the use of (a) patent(s). IEC takes no position concerning the evidence, validity or applicability
of any claimed patent rights in respect thereof. As of the date of publication of this document,
IEC [had/had not] received notice of (a) patent(s), which may be required to implement this
document. However, implementers are cautioned that this may not represent the latest
IEC CDV 60953-1 © IEC 2025
information, which may be obtained from the patent database available at https://patents.iec.ch.
IEC shall not be held responsible for identifying any or all such patent rights.
IEC 60953-1 has been prepared by subcommittee WG11/MT14: Thermal Acceptance Test, of
IEC technical committee TC 5: Steam turbines. It is an International Standard.
This second edition cancels and replaces the first edition published in 1990. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) .;
The text of this International Standard is based on the following documents:
Draft Report on voting
XX/XX/FDIS XX/XX/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
This part of IEC 60953 is to be read in conjunction with IEC 60953-0:2022, and the words 'high
accuracy acceptance test' should be read in place of 'acceptance test' IEC 60953-0:2022 is
taken as a Reference Standard.
A list of all parts in the IEC 60953 series, published under the general title Rules for steam
turbine thermal acceptance tests, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
IEC CDV 60953-1 © IEC 2025
INTRODUCTION
Following the publication of the Reference Standard IEC 60953-0:2022 it was considered
necessary to draw up a Supplementary Standard (this document) for guidance on the thermal
acceptance tests where a high degree of accuracy is required replacing the firs t edition of IEC
60953-1:1990.
However, a large number of the provisions and recommendations of IEC 60953-0:2022 are still
applicable and, therefore, in order to avoid a repetitive and bulky document, only the high
accuracy-specific addenda will be found in this document.
Although this document is intended to apply to large condensing steam turbines, it can
nevertheless be used for other types and sizes of turbines to define the basis of a specific
procedure to be agreed upon by the parties involved.
The structure and clause numbering of this document follow that of IEC 60953-0:2022.
Subclauses found in this document supersede the whole of the equivalent subclause in IEC
60953-0:2022. Subclause numbering has been extended whenever new items have been
included.
The main differences between this document and IEC 60953-0:2022 are listed below.
Clause 1: Scope
This document provides for very accurate testing of steam turbines to obtain the level of
performance with minimum test uncertainty. The operating conditions during the test are
stringent and compulsory.
This document is based on the exclusive use of the most accurate calibrated instrumentation
and the best measuring procedures currently available. The test uncertainty shall not be larger
than 0.3 % for a fossil fired unit and 0.4 % for a nuclear unit. To motivate both parties to achieve
the highest accuracy possible it is recommended that the test uncertainty is not considered in
the comparison between test result and guarantee value unless otherwise agreed in the
contract.
These criteria must be met to achieve a code compliant test.
Clause 4: Guiding principles
This document gives further guidelines on the timing of the tests, the test isolation and
necessary secondary flow measurements, the test duration and allowable test conditions.
Clause 5 Measuring techniques and measuring instruments
This document gives further advice regarding instrument accuracy and calibration requirements
with the aim to reduce the overall measurement uncertainty. A particular focus is given to the
selection, installation and inspection of primary power and flow meters.
Clause 6 Evaluation of tests
This document gives further advice on the evaluation of the test results, test isolations and
allowable cycle leakages.
Clause 8 Measuring uncertainty
This document gives further guidance on reducing the overall test measurement uncertainty.
IEC CDV 60953-1 © IEC 2025
1 Scope
1.1 General
This part of IEC 60953 establishes a Supplementary Standard for thermal verification tests for
high accuracy for large condensing steam turbines.
The rules given in this document follow the guidance given in IEC 60953-0:2022 , but contain
amendments and supplements regarding guarantees and verification of the guarantees for high
accuracy thermal acceptance tests.
The rules given in this document are applicable primarily to thermal acceptance tests with high
accuracy for large condensing steam turbines for power generation applications. It can
nevertheless be used for other types and sizes of turbines to define the basis of a specific
procedure to be agreed upon by the parties involved. Only the relevant portion of these rules
will apply to any individual case.
The rules provide for the testing of turbines, whether operating with either superheated or
saturated steam.
Uniform rules for the preparation, carrying out, evaluation, comparison with guarantee and
calculation of measuring uncertainty of acceptance tests are defined in this standard. Details
of the conditions under which the acceptance test shall take place are included.
Should any complex or special case arise which is not covered by these rules, appropriate
agreement shall be reached by manufacturer and purchaser before the contract is signed.
1.2 Object
The purpose of the thermal acceptance tests of steam turbines and turbine cycles described in
this document is to verify guarantees given by the manufacturer of the equipment concerning
the following parameters.
Efficiency guarantees:
a) Thermal efficiency,
b) Heat rate,
c) Power output.
Capacity guarantees:
d) Maximum power output at specified steam conditions according to IEC 60045-1:2020 [1]
(other than steam flow),
e) Nuclear: thermal load capacity of the steam turbine under defined conditions.
The guarantees with their provisions are formulated completely and without contradictions (see
Error! Reference source not found.). The acceptance tests may also include such
measurements as are necessary for corrections according to the conditions of the guarantee
and checking of the results.
1.3 Matters to be considered in the contract
Subclause 1.3 of IEC 60953-0:2022 applies.
IEC CDV 60953-1 © IEC 2025
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60953-0:2022, Rules for steam turbine thermal acceptance tests - Part 0: Wide range of
accuracy for various types and sizes of turbines
IEC 60953-1:1990, Rules for steam turbine thermal acceptance tests. Part 1: Method A - High
accuracy for large condensing steam turbines
3 Units, symbols, terms and definition
Subclause of IEC 60953-0:2022, 3.0 applies.
3.1 General
Subclause of IEC 60953-0:2022, 3.1 applies.
3.2 Symbols, units
Subclause of IEC 60953-0:2022, 3.2 applies.
3.3 Subscripts, superscripts and definitions
Subclause of IEC 60953-0:2022, 3.3 applies.
3.4 Guarantee parameters
3.4.1 Guidance on guarantee parameters
Subclause of IEC 60953-0:2022, 3.4.1 applies.
3.4.2 Thermal efficiency
Subclause of IEC 60953-0:2022, 3.4.2 applies.
3.4.3 Heat rate
Subclause of IEC 60953-0:2022, 3.4.3 applies.
3.4.4 Thermodynamic efficiency
Subclause of IEC 60953-0:2022, 3.4.4 is not applicable.
3.4.5 Steam rate
Subclause of IEC 60953-0:2022, 3.4.5 is not applicable.
3.4.6 Main steam flow capacity
Subclause of IEC 60953-0:2022, 3.4.6 is not applicable.
3.4.7 Power output
Subclause of IEC 60953-0:2022, 3.4.7 applies.
IEC CDV 60953-1 © IEC 2025
3.4.8 Guarantee values for extraction and mixed-pressure turbines
Subclause of IEC 60953-0:2022, 3.4.8 is not applicable.
3.4.9 Thermal Load Capacity (for Nuclear applications)
Subclause of IEC 60953-0:2022, 3.4.9 applies.
4 Guiding principles
4.1 Advance planning for test
The parties to any test under these rules shall reach agreement, when the plant is being
designed, as to the testing procedure, the interpretation of guarantees, the number, location
and arrangement of measuring points and measuring devices, valves and piping arrangements.
This especially applies to steam turbines in nuclear power stations where subsequent
modifications are often impracticable and the measuring points are not always accessible once
the plant has started to operate. It is recommended that for the most important measurements
special connection facilities such as flanges and thermometer wells be provided for the
measuring equipment so that the acceptance tests can be carried out without impairing the
instruments for normal operation.
The instrumentation has to be selected in such a way that power and heat flows which enter
and leave the "system", as defined in the contract, and the conditions at its boundaries, can be
determined. It is the responsibility of the steam turbine supplier to propose the required
accuracy of all instrumentation including that which is supplied by others.
By testing in accordance with this document the parties interested in the test agree to achieve
a high accuracy test by:
a) Improving instrument accuracy and calibration
b) Minimise deviations from guarantee reference conditions
c) Minimise cycle deviations from design intent including cycle imperfections and internal and
external leakages
d) Minimise fluctuations of the plant operating conditions
e) Minimise the operating time before the test is conducted
The following is a list of typical items upon which agreement should be reached during the plant
design:
f) Type and location of the primary and secondary flow measuring devices upon which the test
calculations are based, considering the upstream and downstream piping arrangements
including flow straightening devices and in relation to the sensitivity of the mea sured flow
to the test result.
g) Number and location of valves required to ensure as far as practicable that no unaccounted -
for flow enters or leaves the test cycle or bypasses any cycle component. In a nuclear plant
there may be some make-up line or emergency valving that cannot be isolated and for which
the method of accounting the leakage has to be agreed.
h) Number and location of temperature wells and pressure connections required to ensure
correct measurements at all measurement points.
i) Number of multiple instrument connections required to improve the accuracy for high
sensitivity test points.
j) Handling of leak-off flows to avoid complications in testing or the introduction of errors.
___________
Mixed pressure turbines - several inlets at different pressures during the expansion.
IEC CDV 60953-1 © IEC 2025
k) Means of measuring pump shaft leakages, if necessary.
l) Method of determining steam quality, including sampling technique as required. The
recommended methods are given in the RS.
1) Method in order to determine steam turbine internal leakage flows has to be defined and
agreed by both parties considering the sensitivity of the internal leakage to the test result
(direct measurement, values determined from the heat balance diagram or conducting a
temperature variation test see RS).
4.2 Preparatory agreements and arrangements for tests
Subclause of IEC 60953-0:2022, 4.2 applies.
4.3 Planning of the test
Subclause of IEC 60953-0:2022, 4.3 applies.
4.3.1 Time for acceptance tests
Acceptance tests on site shall be carried out as soon as possible and preferably within 8 weeks
after the first synchronization.
It is the intent during this period to minimize performance deterioration and risk of damage to
the turbine. Enthalpy drop tests or preliminary tests (see IEC 60953-0:2022 4.5) should be made
during this period to monitor HP and IP turbine section performance. However, these tests do
not provide LP section performance and for this reason it is imperative to conduct the
acceptance tests as soon as possible.
If the tests are conducted within 8 weeks adjustment of the test results for the effects of ageing
is not permitted.
If there are indications of deposits or damages it is recommended to postpone the tests until
after an inspection outage. If deposits or damages are present these must be rectified before
testing can proceed. The test can proceed if the absence of deposits and damages can be
verified.
In the event of delays beyond 8 weeks the test may proceed by agreement with the application
of one of the following degradation correction methods:
a) Measured degradation from turbine comparison tests (see IEC 60953-0:2022 7.9.1). Due
considerati
...