SC Library

Reports published by SC A1 that were not fully published in Electra are available on this page.

Motors for Nuclear Power Plants

Working Group A1.06-10

Convenor: Enzo Tortello (IT)

In 2002, as a result of re-licensing, nearly 700 MW of U.S. nuclear power capacity was added in 13 uprate programs. Over the following two years similar re-licensing efforts have resulted in 33 uprates which have increased nuclear capacity by over 1,700 MW. Uprates can increase capacity by as much as 20 percent and cost as little as $10 per kW.

Uprates include both reactor thermal power uprates and major component upgrades, such as turbine rotor replacements or control system upgrades
In extended power uprates, significant changes are required in balance of plant equipment such as main power transformers, steam turbines, turbine generators, electrical distribution system, and heater drain systems.
The present investigation is aimed at defining the impact on large motors in nuclear power plants.
Unfortunately, the answers to the questionnaire were very limited, probably due to the persisting uncertainty in the field of nuclear energy production in many countries.

Also where an increase in nuclear power capacity is considered the position of auxiliary motors is not so evident. As a result the increase in motors capacity is not strictly a consequence of the increase in power generation units.
Better rewinding than replacing motors? The answer is not univocal. Nevertheless two aspects are evident:

  • Safety is very important also in tackling the problem of motors;
  • The ASDs option is not so popular for motors in the field of nuclear application.

In conclusion, it is worthwhile mentioning that final considerations could be affected by the very limited answers received.
Published May 2009

Motors for Nuclear Power Plants – Final Report (Click to Download) (doc, 37kB)

Perception of Large Motors

Working Group A1.06-14

Convenor: Enzo Tortello (IT)

In recent years the impression given by operators in the field of energy production is of motors are being less considered than in the past.
As a consequence, the role of motors in power plants seems to become a minor one and motors are considered, very often, like a commodity.
On the other side some parameters (i.e. availability/reliability) are gaining new importance in favour of motors also in power plants.
The scope of the present questionnaire is to give an evidence to the still existing importance of large motors also in the field of energy production and in detail:
1. Define national policy in motors procurement (internal manufacturing vs. import);
2. Define parameters useful for selecting motors;
3. Define importance of availability/reliability of motors in power plants;
4. Determine the most probable reasons for failure of motors;
5. Determine the components more affected by failure in motors;
6. Define rules for managing failure data (record practice, report generation, etc.),
7. Find out recent improvements and future developments in motors;
8. Define repair and spare parts policy.

Answers have been received from 5 countries: Australia, Brazil, Italy, Japan and Serbia. The number of answering countries is not so large but they cover almost all continents.

Some conclusions may be drawn from the answers to the questionnaire:
1. the most important parameter for selecting motors in P.P.s is availability/reliability (especially in conventional and gas P.P.s)
2. ASDs applications are not so popular as expected in the field of energy production
3. the main reasons for failure in large motors are mechanical
4. the component affected more frequently by failure is the stator
5. records of failure are usually available c/o Users’
6. no significant improvements are present or foreseen in motors
7. repair shops are present almost in all countries
8. Cases of “to repair vs. to replace” are given; generally the criteria for selection are economic.
9. Generally spare policy suggests the availability of complete motors (better than stators and rotors) but does not exclude the availability of other parts.

From these conclusions it is possible to notice that the approach of Users’ to the motors is typically the one deserved to a commodity. Motors attract the attention mainly when they do not work or do not work correctly.
Another important point is that failure records are in the hands of Users rather than in the hands of Manufactures and feedbacks (probably) are not so frequent.
These are important point to take into consideration in order to finalise whatever activities in the field of investigations to be held by Committees and Working Groups in the future.
Published: May, 2009

Perception of Large Motors – Final Report (Click to Download) (doc, 51kB)

On-Line Condition Monitoring Tools for Large Turbine Generators

Working Group A1.01-1A

Convenors: Don Rose (AUS), Mal Park (AUS)

A large number of on-line monitoring systems are now available or becoming available for turbine-generators. Increasingly these systems are being seen as tools to help plan and minimise maintenance outages and to recognise developing failures in time to take corrective action.
This questionnaire sought first to define as many systems as could be recognised as applicable to hydrogen cooled generators with water cooled stator conductors, and then to determine the level of reliability, usefulness, acceptability and degree of present and likely future application in relation to each system.

TG Condition Monitoring (Click to Download) (doc, 511kB)

Final Report on Questionnaire "High-Efficiency Motors"

Convenor: Enzo Tortello Italy

The questionnaire on high-efficiency motors was launched in Paris on September, 1998. The questionnaire was then revised, after the 29th of August 2000 meeting in Paris, according to A1-06 Experts’ indications. The final report was consolidated in February, 2003. Answers were obtained from 13 countries: Australia, Canada, China, Czech Republic, Finland, France, Italy, Malaysia, Korea, RSA, Switzerland, UK, and USA.

The answers received show that the problem is still open. Direct requests for high-efficiency large motors do not seem so frequent and urgent. On the other side DOE in the USA by means of EPACT, the EC by the agreement with CEMEP, Australia and Korea by means of National Standards push for use of small and medium-size high-efficiency motors. Nevertheless also the impact of large high-efficiency motors on energy saving is judged of increasing interest. Another way to tackle the problem is to stress process design better than motor efficiency.

There is no strong suggestion of new motor design but the use of new materials inside a traditional design is preferred. Problems are also connected with measuring correct figures of efficiency (additional losses) and with evaluating efficiency improvement in tenders ( what are the rules/formulas and the parameters for saving evaluation?). As a conclusion no tailored standards for large motors are available at the moment even if IEC’s recent interest for high-efficiency motors of all types and sizes is highlighted by Responders.

High Efficiency Motors (Click to Download) (doc, 77kB)

Final Report on Questionnaire “Experience in Vacuum Pressure Impregnated Machines to-date”

Convenor: Enzo Tortello Italy

Vacuum Pressure Impregnation is a very popular insulating technique today not only for motors but also for turbogenerators.
This technique has been used since the middle of the last century, mainly for small and medium size motors. More recently VPI has been extended successfully to large size turbogenerators too.

Such a long period of application makes it possible to try surveying this topic and summarizing important conclusions from this experience.
This questionnaire is mainly devoted and limited to investigating field-experience on VPI treatment of large motors.
As a consequence motors with power ratings of 800 kW and above and voltage ratings of 1kV and higher for power generation and industrial applications are within the scope of the questionnaire.

Even if the questionnaire was answered by Experts from four countries only ( Australia, Canada, Italy -two different answers- and US), the report was considered worthwhile publishing as an interesting reference.

VPI Motor Experience (Click to Download) (doc, 70kB)

Final Report on Questionnaire “Soft-start”

Convenor: Enzo Tortello Italy

The term “soft-start” here means the starting of turbo-generators, hydro-generators or motors via an electronic device which supplies variable frequency and/or voltage to the rotating electrical machine.
Please note that according to the technique used more specific terms like “voltage start” or “frequency start” may be encountered in literature.

The advantages of using an electronic device for starting large generators and motors are mainly: less over current, less mechanical stress, less thermal stress, and less vibrations.
Additional advantages are only one supply unit to be provided for consecutive starts of several generator/motor units and shorter length of the whole machine set (e.g. large single-shaft units - gas turbine/steam turbine/turbo-generator- can not afford a starting motor).

The questionnaire does not cover more traditional starting methods which imply the use of rotating machines (i.e. pony-motors).
Answers were received from 6 countries only: Australia, Canada, Korea (two answers), Malaysia, Russia and US.
Answers from two nations are substantially negative as there are no applications available in those countries: it is the case of Australia (only small-motor applications present ) and Canada.

Motor Soft Start (Click to Download) (doc, 78kB)

Final Report on Questionnaire "Variable Speed Drives"

Convenor: Enzo Tortello Italy

The questionnaire is divided into two parts: the first one devoted to the more technical aspects and the second one covering the more common applications.

Energy conservation is of great concern in the major parts of the world and the role of motors in energy saving may be very important, mainly due to the widespread use and popularity of electric motors. Energy saving in motors is a opportunity given by supply via adjustable speed drives (ASD) which offer nowadays improved efficiency, availability, and reliability. The above features are themselves higher than in the past years due to better electronic components and topology.

As known, ASDs generally comprise a frequency converter that supplies (more usually) a three-phase electric motor coupled to a driven machine. According to the voltage level of the grid and the voltage level of the frequency converter, converter transformer (step down or step up) may also be part of the system.

Variable Speed Drives (Click to Download) (doc, 109kB)

Summary Review of Responses to Questionnaire on: The Effect of Network Considerations on the Design of Large Turbine Generators

Working Group A1.01.4

Coordinator: Trevor Stokes (GB)

The questionnaire was developed in response to suggestions made at the 1999 meeting of the then Equipment Group 11.01 in Orlando and combined ideas from two contributors. The first was for a questionnaire on the subject of the effect of special operating regimes on generators connected to the network, and the second was to investigate the economic and technical relevance of turbine generator design parameter specification based on grid considerations.

Part I of the questionnaire looked at the effect of any mandatory design requirements imposed by system operators, such as reactance limitations, off-frequency operation, etc. Part II was intended to ascertain the effect of any special operating regimes such as two-shifting or load following on the generator design.

The Effect of Network Considerations on the Design of Large Turbine Generators (Click to Download) (pdf, 93kB)

Stressing Turbine Generators beyond their Established Thermal Limits - Report on Questionnaire

Working Group A1.01.03

Coordinator: Reinhard E. Joho- (CH)

Power delivery payments in liberalised/deregulated grids can be very progressive with demand. The known practice of peaking may thus become increasingly beneficial for the operator. Peaking corresponds to a temporarily increased thermal utilisation of the generator beyond the established rated continuous class 130 operation limit.

The concern in doing this is primarily about the electrical insulation. However, insulation technologies with enhanced performance have been introduced, allowing higher operation temperatures, increased electrical stress, or improved thermal conductivity. This can be of interest for both upgrading of existing plants, and for providing more economic generator solutions for new plants.
The questionnaire applies to generators having rated voltage 10kV and higher, rated power 40MW and above, and having a stator winding based on a mica-synthetic resin based stator insulation.

Stressing Turbine Generators beyond their Established Thermal Limits (click to Download) (pdf, 122kB)

Questionnaire Report On Condition Monitoring Tools For Hydro-generators

Working Group A1.02

Convenor: Gérard Hemery (F)

The objective of the questionnaire was to survey the water power generation industry's experience of condition monitoring tools. The answers and main analysis are given in the document.
The condition monitoring tools of this survey concern the main components of the generator, excluding the normal electrical or mechanical protection.

Questionnaire Report On Condition Monitoring Tools For Hydrogenerators (Click to Download) (pdf, 751kB)

The Impact Of The Change In The Characteristics On The Costs Of Hydro-Generators

Working Group A1.02

Convenor: P Wegscheider (A)

Due to organisational changes in the electricity supply industry it is becoming more and more important to specify exactly the interface between generating plant and the power system. There is a general wish to define more clearly the additional services required of the power system which are to be fulfilled by the generating units. It is also important to know the costs of the additional services.

The Impact Of The Change In The Characteristics On The Costs Of Hydro-Generators (Click to Download) (pdf, 295kB)