oSIST prEN IEC 60034-33:2026

SLOVENSKI STANDARD
01-oktober-2026
Električni rotacijski stroji - 33. del: Sinhronski hidrogeneratorji, vključno z motor-
generatorji - Posebne zahteve
Rotating electrical machines - Part 33: Synchronous hydrogenerators including motor-
generators - Specific requirements
Drehende elektrische Maschinen - Teil 33: Besondere Anforderungen an
Synchrongeneratoren, angetrieben durch hydraulische Turbinen, einschließlich Motor-
Generatoren
Machines électriques tournantes - Partie 33: Hydro-génératrices synchrones y compris
les groupes moteur-générateurs - Exigences spécifiques
Ta slovenski standard je istoveten z: prEN IEC 60034-33:2026
ICS:
29.160.20 Generatorji Generators
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

2/2319/CDV
COMMITTEE DRAFT FOR VOTE (CDV)
PROJECT NUMBER:
IEC 60034-33 ED2
DATE OF CIRCULATION: CLOSING DATE FOR VOTING:
2026-08-07 2026-10-30
SUPERSEDES DOCUMENTS:
2/2317/RR
IEC TC 2 : ROTATING MACHINERY
SECRETARIAT: SECRETARY:
United Kingdom Mr Charles Whitlock
OF INTEREST TO THE FOLLOWING COMMITTEES: HORIZONTAL FUNCTION(S):

ASPECTS CONCERNED:
SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING
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TITLE:
Rotating electrical machines - Part 33: Synchronous hydrogenerators including motor-
generators - Specific requirements

PROPOSED STABILITY DATE: 2028
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IEC 60034-33 ED2 © IEC 2026 2/2319/CDV

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IEC 60034-33 ED2 © IEC 2026 2/2319/CDV

CONTENTS
CONTENTS . 1
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 Site operation conditions . 11
5 Ratings and parameters . 11
5.1 Output . 11
5.1.1 Output rating of a hydrogenerator . 11
5.1.2 Output ratings of a motor-generator . 11
5.1.3 Increase in active power . 11
5.1.4 Under-excited operation . 12
5.2 Rated voltage . 12
5.3 Rated power factor . 12
5.4 Rated speed . 12
5.5 P-Q capability diagram . 12
5.6 Voltage and frequency variations during operation . 13
5.7 Efficiency and losses . 15
5.7.1 Weighted average efficiency . 15
5.7.2 Losses . 15
5.7.3 Determination of winding losses . 16
5.7.4 Windage Losses . 16
5.7.5 Determination of thrust bearing losses for vertical machines . 16
5.7.6 Tolerance of the total losses . 17
5.8 Electrical parameters and time constants . 17
5.8.1 Short-circuit ratio . 17
5.8.2 Direct axis transient and subtransient reactances . 17
5.8.3 General case . 18
5.9 Tolerances on reactance . 18
5.10 Total harmonic distortion (THD) . 18
5.11 Torques . 19
6 Temperature . 19
6.1 Temperature rise . 19
6.2 Measurements for the stator winding . 20
6.3 Measurements for the stator core . 20
6.4 Correction due to deviation from reference operation . 21
6.5 Bearing temperature . 21
7 Operating performances and electrical connections . 21
7.1 Special operational requirements . 21
7.1.1 Stator excess current . 21
7.1.2 Rotor excess current . 22
7.1.3 Continuous unbalanced load . 22
7.1.4 Short time unbalanced load . 22
7.1.5 Mechanical output overload . 23
IEC 60034-33 ED2 © IEC 2026 2/2319/CDV

7.1.6 Sudden short circuit . 23
7.2 Connection to grid . 23
7.2.1 Synchronization . 23
7.2.2 Application of load . 24
7.3 Starting of motor-generator . 24
7.4 System earthing . 24
7.5 Neutral point leads . 25
7.6 Rotating direction and phase sequence. 25
7.7 Stator winding . 26
8 Winding insulation . 26
8.1 Winding insulation performance . 26
8.1.1 General . 26
8.1.2 Winding insulation resistance . 26
8.1.3 Dielectric dissipation factor measurements on new stator bars or coils . 27
8.1.4 Partial discharge measurements for stator winding . 27
8.1.5 Voltage withstand test for turn insulation of multi-turn coil for stator . 27
8.1.6 Quality inspection for Roebel bars . 27
8.2 Voltage withstand tests . 27
8.2.1 Stator bars/coils . 27
8.2.2 Inserted stator bars/coils . 28
8.2.3 Stator winding completed before rotor inserted . 28
8.2.4 Field winding before delivery . 28
8.2.5 Field winding completed . 28
8.2.6 Stator winding for completed machine . 29
8.2.7 Field winding for completed machine . 29
8.2.8 DC alternative tests . 29
8.2.9 Global VPI stators . 29
8.3 Breakdown test for insulation . 29
8.4 Voltage endurance test for insulation . 29
8.5 Thermal cycle test . 30
8.6 Stator winding terminals . 30
9 Mechanical structural performances and design . 30
9.1 Rotating part mass moment of inertia . 30
9.2 Maximum speed . 31
9.3 Structural strength . 31
9.4 Critical bending speed . 32
9.5 Start and stop of motor-generators. 32
9.6 Start and stop of hydrogenerators . 32
9.7 Over speed . 32
9.8 Fatigue verification . 32
10 Core vibration . 32
11 Noise . 33
12 Basic structural requirements . 34
12.1 General layout . 34
12.1.1 Structure and general layout of the machines . 34
12.1.2 Machine components . 34
12.1.3 Hydraulic or pneumatic braking system . 34
12.1.4 Hydraulic jacking system . 34
IEC 60034-33 ED2 © IEC 2026 2/2319/CDV

12.1.5 Dynamical (electrical) braking . 34
12.2 Stator . 35
12.2.1 Frame and core structure. 35
12.2.2 Stator frame connecting structure . 35
12.2.3 Stator end winding . 35
12.3 Rotor . 35
12.3.1 Damper winding . 35
12.3.2 Structure with one shaft or segmented shafts . 35
12.4 Structure tolerance . 35
12.5 Bearings . 36
12.5.1 Bearing alloy . 36
12.5.2 Bearing lubricant . 36
12.5.3 Shaft currents . 36
12.5.4 Bearing insulation resistance . 36
13 Ventilation and cooling system . 36
13.1 Cooling scheme . 36
13.1.1 General . 36
13.1.2 Air cooling system . 36
13.1.3 Evaporative cooling system . 37
13.1.4 Water cooling system . 37
13.2 Redundancy on the design of coolers and motor fans . 37
13.3 Cooling structure . 37
13.3.1 Materials . 37
13.3.2 Water supply and drainage . 37
13.3.3 Cooling water pressure . 37
14 Instrumentation required for protection and control . 37
14.1 General . 37
14.2 Stator and bearing temperature . 38
14.3 Bearing vibration and shaft displacement . 38
15 Instrumentation for condition monitoring of machines . 39
15.1 General . 39
15.2 Instrumentation required for condition monitoring . 39
16 Marking . 39
16.1 Information to be marked on machine nameplate: . 39
16.2 Repaired or refurbished machines . 40
17 Factory and site tests . 40
Annex A (informative) Special tools . 41
Annex B (informative) Correction of measured windage losses on the machines . 42
Annex C (informative) Correction of measured bearing losses for different oil bath
temperatures . 44
Annex D (informative) Scope of supply . 46
Annex E (normative) Test run and guaranteed period . 47
E.1 72 h test run . 47
E.2 15-day examination test run for motor-generators . 47
E.3 Handover and guarantee period . 47
Annex F (informative) Test items . 48
F.1 Inspection test for hydrogenerator and motor-generator in factory . 48
IEC 60034-33 ED2 © IEC 2026 2/2319/CDV

F.2 Site routine test of hydrogenerator and motor-generator . 48
F.3 Startup test run of hydrogenerator and motor-generator . 49
F.4 Performance test of hydrogenerator . 49
Annex G (informative) Condition monitoring . 50
G.1 Air gap distance . 50
G.2 Core and frame vibration. 50
G.3 Stator end winding vibration . 50
G.4 Partial discharge . 50
G.5 Air gap magnetic flux . 51
G.6 Others . 51
Bibliography . 52

Figure 1 – P-Q capability in p. u. . 13
Figure 2 – Voltage and frequency limits for hydro machines . 14
Figure 3 – Location of measuring points in the horizontal plane . 33

Table 1 – Preferred speed for 50 Hz machines - Unit: 1/min . 12
Table 2 – Preferred speed for 60 Hz machines - Unit: 1/min . 12
Table 3 – Reference temperature . 16
Table 4 – Temperature rise limits for machine’s main part . 19
Table 5 – Temperature rise limits for collector ring . 19
Table 6 – Permitted excess current multiple vs. time duration . 22
Table 7 – Permitted negative phase sequence current for the machines . 22
Table 8 – Permitted negative phase sequence current for the machines . 23
Table 9 – Material properties for grounding connectors . 25
Table 10 – Test voltage for insulating resistance measurement . 27
Table 11 – Dielectric dissipation factor . 27
Table 12 – Testing values for voltage withstand test of field winding . 29
Table 13 – Limits for vibration in the core . 33
Table 14 – Temperature sensor locations . 38
Table A.1 – Special tools . 41

IEC 60034-33 ED2 © IEC 2026 2/2319/CDV

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Rotating electrical machines -
Part 33: Synchronous hydrogenerators including motor-generators -
Specific requirements
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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Standardization (ISO) in accordance with conditions determined by agreement between the two
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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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way in which they are used or for any misinterpretation by any end user.
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regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies
provide conformity assessment services and, in some areas, access to IEC marks of conformity.
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
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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 60034-33 ED2 © IEC 2026 2/2319/CDV

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
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 60034-33 has been prepared by IEC technical committee 2: Rotating machinery. It is an
International Standard.
This second edition cancels and replaces the first edition published in 2022. 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
2/XX/FDIS 2/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.
A list of all parts in the IEC 60034 series, published under the general title Rotating electrical
machines, 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 60034-33 ED2 © IEC 2026 2/2319/CDV

INTRODUCTION
IEC 60034-33 ED2 © IEC 2026 2/2319/CDV

1 Scope
This part of IEC 60034 applies to three-phase salient-pole synchronous generators and
synchronous motor-generators for hydraulic turbine and pump-turbine applications, that have
rated frequency of 50 Hz or 60 Hz, rated output of 10 MVA and above, pole pair number 3 and
above, and rated voltage of 6 kV and above.
This document supplements basic requirements for rotating machines given in IEC 60034-1.
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 60034-1, Rotating electrical machines - Part 1: Rating and performance
IEC 60034-2-1, Rotating electrical machines - Part 2-1: Standard methods for determining
losses and efficiency from tests (excluding machines for traction vehicles)
IEC 60034-2-2, Rotating electrical machines - Part 2-2: Specific methods for determining
separate losses of large machines from tests - Supplement to IEC 60034-2-1
IEC 60034-4-1, Rotating electrical machines - Part 4-1: Methods for determining electrically
excited synchronous machine quantities from tests
IEC 60034-15, Rotating electrical machines - Part 15: Impulse voltage withstand levels of form-
wound stator coils for rotating a.c. machines
IEC 60034-18-1, Rotating electrical machines - Part 18-1: Functional evaluation of insulation
systems - General guidelines
IEC 60034-18-32, Rotating electrical machines - Part 18-32: Functional evaluation of insulation
systems - Electrical endurance qualification procedures for form-wound windings
IEC 60034-27-1, Rotating electrical machines - Part 27-1: Off-line partial discharge
measurements on the stator winding insulation of rotating electrical machines
IEC 60034-27-3, Rotating electrical machines - Part 27-3: Dielectric dissipation factor
measurement on stator winding insulation of rotating electrical machines
IEC 60034-27-4, Rotating electrical machines - Part 27-4: Measurement of insulation resistance
and polarization index of winding insulation of rotating electrical machines
IEC 60034-33:2022, Rotating electrical machines - Part 33: Synchronous hydrogenerators
including motor-generators - Specific requirements
IEC 60050-411, International Electrotechnical Vocabulary - Chapter 411: Rotating Machines
IEC 60060-1, High-voltage test techniques - Part 1: General definitions and test requirements
IEC 60085, Electrical insulation - Thermal evaluation and designation
IEC 60034-33 ED2 © IEC 2026 2/2319/CDV

IEC 60287-3-1:2017, Electric cables - Calculation of the current rating - Part 3-1: Operating
conditions - Site reference conditions
IEC 60417, Graphical symbols for use on equipment - 12-month subscription to regularly
updated online database comprising all graphical symbols published in IEC 60417
IEC 60445, Basic and safety principles for man-machine interface, marking and identification -
Identification of equipment terminals, conductor terminations and conductors
IEC 63132-1, Guide for installation procedures and tolerances of hydroelectric machines - Part
1: Common
IEC 63132-2, Guide for installation procedures and tolerances of hydroelectric machines - Part
2: Vertical generator
ISO 7919-5:2005, Mechanical vibration — Evaluation of machine vibration by measurements
on rotating shafts — Part 5: Machine sets in hydraulic power generating and pumping plants
ISO 10816-5:2000, Mechanical vibration — Evaluation of machine vibration by measurements
on non-rotating parts — Part 5: Machine sets in hydraulic power generating and pumping plants
ISO 20816-1, Mechanical vibration - Measurement and evaluation of machine vibration - Part
1: General Guidelines
ISO 20816-5, Mechanical vibration - Measurement and evaluation of machine vibration - Part
5: Machine sets in hydraulic power generating and pump-storage plants
IEEE Std 1043: 1996, IEEE Recommended practice for voltage-endurance testing of form-
wound bars and coils
IEEE Std 1310: 2012, IEEE Recommended practice for thermal cycle for voltage-endurance
testing of form-wound bars and coils for large rotating machines
IEEE Std 1553: 2002, IEEE Trial-use standard for voltage-endurance testing of form-wound
coils and bars for hydrogenerators
EN 50522: 2010, Earthing of power installations exceeding 1 kV a.c.
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60034-1, IEC 60034-
2-1, IEC 60034-2-2, IEC 60050-411 and IEC 63132-1, as well as the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
3.1
hydrogenerator
synchronous machine operated as generator and driven by a hydraulic turbine
IEC 60034-33 ED2 © IEC 2026 2/2319/CDV

3.2
motor-generator
synchronous machine which can operate in motor mode and generator mode, generally used in
pumped-storage power plant
3.3
stator concentricity
radial distance from the reference centre to the best centre of stator bore
3.4
rotor concentricity
radial distance from the reference centre to the best centre of rotor outer circle
3.5
stator circularity
difference between the maximum and minimum radii, measured from the best centre of stator
bore
3.6
rotor circularity
difference between the maximum and minimum radii, measured from the best centre of rotor
outer circle
3.7
Air gap
3.7.1
nominal air gap
design air gap value between stator inner surface and rotor at the centre of poleshoe at rated
conditions
3.7.2
static air gap
air gap at standstill and in cold condition after full load rejection
Note 1 to entry: This value is used for the purposes of IEC 63132-1 and IEC 63132-2.
3.8
stress control coating
paint or tape on the surface of the main insulation that extends beyond the conductive slot
portion coating in high-voltage stator bars and coils
3.9
condenser
heat exchanger device by which cooling medium is changed to liquid phase from vapour in
evaporative cooling circulation system
3.10
grid
public electrical network or a local (e.g. industrial) network which is connected to the machine
either directly or through a transformer
3.11
SFC starting
operating mode in which synchronous machine is started in motor mode by the method of
regulating power frequency, using static frequency converter (SFC) as variable-frequency
power supply
IEC 60034-33 ED2 © IEC 2026 2/2319/CDV

3.12
back to back starting
synchronous starting method in which one machine is started in motor mode, driven by the
other electric connected machine that is started in generator mode
4 Site operation conditions
The machines shall be able to operate continuously at rated conditions (MVA, MW, voltage,
frequency and power factor) at the following site operation conditions:
a) The altitude does not exceed 1 000 m above sea level (based on coupling elevation for
vertical machine, centre line of shaft for horizontal machine);
b) The cooling air temperature (primary coolant) does not exceed 40 °C;
c) The inlet water temperature (secondary coolant) of air coolers, oil coolers and heat
exchangers (e.g. of direct water cooled stator windings) is not higher than 25 °C and not
less than 5 °C;
d) The inlet water temperature (primary coolant) of direct water cooled stator windings shall
be 30 °C to 40 °C, the water conductivity is in the range of 0,4 μS/cm to 2,0 μS/cm, the pH
value is 6,5 to 9,0, and the hardness is less than 2 μmol/l, at 25 °C of water temperature;
e) Relative humidity in powerhouse (generator floor) does not exceed 85 %;
f) Installed in covered powerhouse on proper foundation;
g) Structural strength of machine shall meet the requirement of seismic accelerations at the
location. Appropriate design measures shall be taken to prevent harmful damage to the
machine. The acceleration value may be different for different regions due to the local
geographical condition. The acceleration values in horizontal direction and vertical direction
shall be defined as a technical condition according to the seismic grade at the location by
the purchaser.
Site conditions different from the above shall be agreed between purchaser and manufacturer.
5 Ratings and parameters
5.1 Output
5.1.1 Output rating of a hydrogenerator
The output rating of a hydrogenerator preferable is the apparent power (in MVA) or the active
power (in MW), available continuously at the stator terminals (main leads) at rated frequency,
voltage and power factor.
5.1.2 Output ratings of a motor-generator
The output ratings of a motor-generator include two parts:
a) The apparent power (in MVA) or the active power (in MW), available continuously at the
stator terminals (main leads) at rated frequency, voltage and power factor during generator
mode;
b) Mechanical output power (in MW) available continuously at the shaft during motor mode.
5.1.3 Increase in active power
By agreement between purchaser and manufacturer, it is allowed to increase active power of
hydrogenerators to rated output (apparent power) by increasing power factor up to 1,0.
IEC 60034-33 ED2 © IEC 2026 2/2319/CDV

5.1.4 Under-excited operation
Hydrogenerators and motor-generators when operating in generator mode shall be able to
operate continuously in under-excited mode at power factor 0,9 with rated active power at rated
voltage.
5.2 Rated voltage
The rated voltage (line to line voltage U at stator terminals) of the machine shall be defined by
N
purchaser and manufacturer according to rated output, rated speed of machine, as well as other
conditions in the system.
5.3 Rated power factor
The power factor shall be agreed upon between purchaser and manufacturer. Preferred rated
power factors at generator terminals are 0,85; 0,875; 0,9; 0,925 or 0,95 overexcited.
Rated power factor of motor-generators in motor mode shall be defined as a design condition
by purchaser.
5.4 Rated speed
The rated speed (1/min) shall be:
3000/ p for 50 Hz machines;
3000/ p for 60 Hz machines.
where p is the number of pole pairs.
NOTE The preferred speeds in Table 1 and Table 2 are convenient to design electrical symmetric and balanced
windings for the machines.
Table 1 – Preferred speed for 50 Hz machines - Unit: 1/min
1 000 750 600 500 428,6 375 333,3 300 250
214,3 200 187,5 166,7 150 142,9 136,4 125 115,4
107,1 100 93,8 88,2 83,3 75 71,4 68,2 62,5
Table 2 – Preferred speed for 60 Hz machines - Unit: 1/min
1 200 900 720 600 514,3 450 400 360 300
257,1 240 225 200 180 171,5 163,7 150 138,5
128,5 120 112,6 105,8 100 90 85,7 81,8 75
5.5 P-Q capability diagram
The manufacturer shall supply a P-Q capability diagram indicating the limits of operation as
shown in Figure 1, where:
Curve A represents operation limits with rated stator current and constant apparent power
output, which is restricted by temperature rise of the stator winding;
IEC 60034-33 ED2 © IEC 2026 2/2319/CDV

Curve B represents operation limits with rated field current, which is restricted by temperature
rise of the field winding;
Curve C1 and C2 indicates the theoretical and practical limits set by the effects of end region
heating, steady-state stability, etc.
Curve D indicates the limits of minimum excitation current to prevent instability issues (usually
defined by a minimum excitation current of 10 % of the no-load excitation current).
Curve E indicates the reluctance circle. Although possible, the operation within the reluctance
circle needs special care and a special design of the excitation and control systems.

Figure 1 – P-Q capability in p. u.
NOTE Figure 1 shows the limitation of the electrical machine only and does not consider operational limitation of
the hydraulic machine.
5.6 Voltage and frequency variations during operation
For generators and motor-generators, combinations of steady state voltage variation and
frequency variation are classified as being either zone A or zone B (maximum case outside of
zone A), in accordance with Figure 2.
Synchronous hydrogenerators and synchronous motor-generators shall be capable of deliver
continuous rated output at the rated power factor, over the ranges of ±5 % in voltage and ±2 %
in frequency, as defined by the shaded area of Figure 2 (zone A), but need not fully comply with
its performance at rated voltage and frequency (see rated point in Figure 2), and may exhibit
some deviations. Temperature rises may be higher than the condition for rated voltage and
frequency.
The temperature rise or temperature limits in accordance with this document, such as Table 4
and Table 5, apply at the rated point only and may progressively be exceeded as the operating
point moves away from the rated point. For conditions at the extreme boundaries of zone A, the
temperature rises, and temperature typically exceed the limits specified in this document.
IEC 60034-33 ED2 © IEC 2026 2/2319/CDV

A machine shall be capable of operation within zone B, and reaching the rated output, but will
exhibit greater deviations from its performance at rated voltage and frequency than in zone A.
Temperature rises will be higher than at rated voltage and frequency and most likely will be
higher than those in zone A. Temperature limits for insulation systems may be exceeded.
Extended operation at the perimeter of zone B is not recommended at all.
Excursions into zone B shall be limited in value, duration no longer than 10 minutes, recurrence
not below 6 hours and frequency of occurrence no higher than 2 times per month. Requiring
permanent operation in zone B without negative impact on lifetime will inevitably lead to a non-
economical design and can require a volume increase of the machine in the range of 10% or
more.
For other conditions of duration, recurrence and frequency of occurrence, corrective measures
should be taken where practical, within a reasonable time if possible, for example, a reduction
in output (reactive or active po
...