Rotating electrical machines

Study Committee A1 is the global knowledge centre of rotating electrical machines with field of activities covering research, development, design, manufacturing, operation, conversion and de-commissioning of large rotating electrical machines and high efficiency motors. This includes the condition assessment of rotating machine components to develop a remaining life prediction methodology from which maintenance, refurbishment and power upgrades can be planned. SC A1 is active in the areas of Turbo-Generators, Hydro-Generators, Large Motors, High Efficiency Motors and New Technologies. Each of these technology groups is concerned with the international exchange of information, knowledge, practice and experience on rotating electrical machines.

SC A1 has 24 Regular Members, 3 Additional Regular Members dealing with distributed generation technologies and 15 observer members, 9 technical advisors, chairman and secretary and more than 300 experts from 41 countries contributing to A1 activities and attending A1 meetings and colloquiums. Members of our Study Committee are from Utilities, Manufacturers, Consultants, Research Centres and Universities.

One key focus area within Study Committee A1 is the effect of an ever-increasing growth in renewable generation on the present installed base-load conventional generation. Renewable generation introduce a high state of unpredictability, significantly impacting load controllability, resulting in significant load cycling which conventional base-load units are expected to balance out, and for which they were not designed for. Technical Brochure 743 – Guide on New Generator Grid Interaction Requirements was published to create awareness of this topic. A new Joint Working Group A1/C4.66 was created to develop a guide on the Assessment, Specification and Design of Synchronous Condensers for Power Systems with Predominance of Low or Zero Inertia Generators to support network developers in their task of developing stable networks using available decommissioned inertia.

Strategic Directions of SC A1

The activities of the Study Committee have been driven by the following six key main Strategic Directions:

• SD 1: Asset Management
• SD 2: Machine/System Interaction
• SD 3: Renewable Generation
• SD 4: Motors
• SD 5: Machine Monitoring, Diagnosis and Prognosis
• SD 6: Efficiency of Electrical Machines

SD 1: Asset Management

Asset management is a broad term that also includes other subjects such as: service and operating experience, availability, maintenance, failure modes, condition assessment, and all aspects of machine performance associated with asset ownership.

Asset management of power plants requires critical decisions to be made on different options available to improve asset reliability. Economic and technical decisions range from the repair of components, major refurbishment, or the total replacement of a generator or motor. The design life of a generator is normally about 30 years for turbo-generators and over 50 years for hydro-generators. Turbo-generators built in the 80’s and hydro generators built in the 50’s and 60’s has already reached the end of their useful life and nearly all show various technical problems caused by ageing which require decision on life extension or replacement. Alternatives such as: partial repairs, components replacement to extend the life of existing generators or even to recommend their complete replacement with due consideration to the time in which the machine is out-of-service without generating income to the owner and, as much as possible, using the existing foundations in order to exclude expenditures due to construction work and to maintain the dynamic stability and static loading of the power plant foundations, are considered in the decision process.

The following Work Groups deal directly or indirectly with the Strategic Direction – Asset Management:

• WG A1.33 is developing a guide for the proper storage and cleanliness of turbo-generators and their components. In the current economic climate, there has been a greater tendency to put turbo-generators into storage for either short or long periods of time before assembly on site, or to ‘mothball’ it after assembly before commissioning. This raises the question of what is considered good industry practice for the storage conditions, environmental control, type and frequency of testing/monitoring and cleanliness procedures put in place during the various storage and assembly periods to ensure a successful preservation of the equipment.
• The concept and design of a hydro generator aims to achieve a machine that maximizes the value seen from the perspective of the customer while at the same time allows the manufacturer to innovate, optimize their design and provide current state of art in generator manufacture. The starting point is the technical equipment specification, and if it is not properly developed, the design resulting from it will not achieve the objective of optimal value for both the customer and manufacturer. WG A1.42 seeks to achieve consensus between customer and supplier so that the requirements contained in the technical specification are not a mere continuation of practices originated in the past or even impractical requirements due to a lack of equipment knowledge but to incorporate the current state of the art in the field.
• WG A1.49 is surveying the magnetic core dimensioning limits for hydro-generators. Developments in the understanding of the ‘state of the art’ properties of laminated silicon-steel and current economic drivers are requiring generator designers to revisit design concepts related to dimensioning criteria and the limits related to their usage. Design constraints start with the standard BxH characteristic curves that currently are limited to 1.8T and sometimes one can find induction levels greater than this limit. As the machine saturation condition impacts on its efficiency and reactance values, and since some level of saturation may be welcomed in operation e.g. to mitigate unbalanced magnetic pull, there is a need to establish a consensus regarding the limits of modern magnetic core dimensioning procedures.
• WG A1.55 is doing a survey on split core stators: Site access limitations and the significant size of large hydro generators can make it impossible to transport them as integral units and make site installation very difficult. A split core stator is a practical compromise. The design of a split core stator is more critical than a single continuous stator core as a poor design can result in core vibrations, noise or shaft voltage and can even lead to core and/or winding damage, shortening the stator life. It is therefore imperative to investigate and summarize the state-of-the-art designs, manufacturing, transportation and installation of split core stators as it will add significant value to engineering applications in the hydro-generator market.
• A survey on lap and wave windings and their consequences on maintenance and performance is carried out by WG A1.56. The layout of a hydro-generator stator winding, i.e. choice of slot number and winding configuration, greatly influence the characteristics of the generator. Specific design differences between lap and wave winding can affect manufacturing and installation costs as well as life cycle costs. In some cases, material savings and installation time reduction can be obtained with wave windings depending on pole number, slot number and number of parallel current circuits. The focus of this WG will be to describe the different characteristics of lap and wave windings and give a guideline for the optimal choice with respect to the considerations described above.
• The purpose of WG A1.57 is to set out the generator visual inspection requirements for stator windings and cores of large turbo generators which should be complied with during outages when work is performed on generators. Inspections performed on generators and all of their components are some of the most important tasks expected of a person responsible for these state-of-the-art components and must be performed by adequately trained and experienced maintenance personnel, generator contractors and all other supporting staff. Generators are high capital equipment and perform an essential function in the power generation process. All safety aspects such as the high kinetic energy present in the rotating rotor shaft, the presence of hydrogen gas which can be extremely hazardous and the presence of high voltage on the stator terminals and stator winding require diligent scrutiny to ensure optimal performance. This working group will recommend an inspection regime and the necessary competencies that are necessary to avoid generator failure.
• WG A1.59 Stator windings are key components in a hydro-generator. When a fault to ground occurs in service it is not always possible to proceed immediately to the replacement of the faulted coil due to commercial or contractual reasons where the generator must be returned to service as soon as possible. The solution is often to cut out the faulted coil and to operate the generator with a voltage unbalance until a scheduled outage period in which the faulted coil can be replaced. The replacement of form-wound bars can be quite easy to perform with skilled personnel if spare bars are available. The situation is quite different when replacement of a multi-turn coil is required. The newly established WG A1.59 will evaluate different techniques and solutions in repairing failed stator windings.
• The increase in the need for electrical energy is demanding both high availability as well as maximum productivity from power plants. Operating plants at maximum productivity while still requiring plant to achieve maximum life expectancy poses reliability challenges from an asset management point of view. In the current challenging economic environment, asset management is usually confronted with the impact of ageing plant. Aged plant maintained using standard maintenance strategies often results in less reliable generators due to the inadequacy of these maintenance strategies to address unique problems associated with ageing. Subsequently unique non-standard strategic maintenance strategies are utilised which consider the increase or deferral of maintenance, type of repairs required or even if mothballing should be considered. All these decisions are driven by relative costs, with an associated financial risk assessment for generator life extension versus upfront investment for refurbishment or even complete replacement. WG A1.60 - Guide on economic evaluation for refurbishment or replacement decisions on hydro generators will develop guidelines and qualifying criteria in assisting Asset Management in the decision-making process regarding hydro generator refurbishment or replacement.
• Except for very small machines, the thrust bearings of hydroelectric units are hydrodynamic oil film tilting pad bearings. The utilization of a fluid film has several advantages such as low friction and almost no wear during continuous operation, the ability to remove the friction losses, and good damping. Even though oil has higher viscosity than, for example, water, the fluid film is very small in relation to the machines’ dimensions. Design features such as hydraulic or spring supports of the pads, which allow uniform load distribution and tilting, serve to maintain a stable oil film. White metal or plastic coatings on the pad improve the sliding in temporary absence of a fluid film and are enough to avoid wear or destruction of the parts. Such a component combines a multitude of physical effects such as fluid dynamics, tribology, heat conduction, heat convection, and solid body mechanics including thermo-mechanics. Failures in the design of these complex systems may lead to failures causing major outages. Various problems, root cause analysis and operational limits on these types of bearings are investigated by WG A1.62.
• Terminal bushings of stator windings of large turbine generators must conduct high winding current of several thousand Ampere through the generator housing and in addition have to seal the inner cooling gas atmosphere to avoid hydrogen gas leakage. These neutral and phase side bushings of the winding are connected to the circuit rings inside the generator and to phase bus ducts outside the generator housing. They are a vital part of each turbine generator with extremely high energy concentration which is assumed to operate for many years without any maintenance. WG A1.63 is investigating and will publish user experiences on terminal bushings and bushing flexible connections.
• Electric motors and the systems they drive account for between 43% and 46% of all global electricity consumption in the industrial sector. A large industrial plant may have more than a hundred motors. These motors operate all kinds of process equipment and their failure can result in losses in plant productivity and reductions in product quality. In power stations a motor failure may lead to difficulties in electricity generation or even led to complete failure of generation. Decisions to repair or replace a failed motor should be based on variables such as: the original stator and rotor must be in reasonably repairable conditions, a thorough evaluation of the root-cause of the failure, repair cost, motor power rating and efficiency, load duty, environmental conditions, load factor, energy efficient motor purchase price, annual operating hours, electricity price, and economic analysis. To assist with this decision making, WG A1.64 is developing a guide for evaluating the repair/replacement of standard efficiency motors.
• WG A1.67 - State of the Art in methods, experience and limits in end winding corona testing for Hydro Generators was established in 2019 to elaborate, through exchange of experience, a basic guide that comprises the main methods applied around the world, experience regarding the techniques, the devices and the test conditions and, finally, establish the limit values in determining that end winding corona test results are acceptable or not.

SD 2: Machine/System Interaction

Generators are always connected to a load to enable power transfer. The behaviour of generators directly influences the behaviour of the connected load, and vice versa the behaviour of connected load has a major effect and impact on generators. It is essential to clearly understand the effect both systems have on each other to enable effective management of a stable grid as well as to ensure prolonged life of generating equipment.

• JWG A1/C4.52 - As wind generation is becoming a significant component of the generation portfolio in many power systems, provision of frequency-active power control is being required for this technology in many regions. This joint working group between A1 and C4 will document the state-of-art in developing such capabilities for wind turbine generators, as well as the system technical performance aspects of such controls and the impact of such controls on equipment design and performance.
• Conventional power plants are increasingly required to operate flexibly to facilitate both, larger penetration of renewable energy and commercial considerations of operating in peak demand periods. Cyclic operation, including two-shifting, operating at minimum load, and fast ramp up/down have all become normal for many power plants; even from quite an early stage of plant life. Operational flexibility is crucial for commercial success of power plants. Cycling operation will result in more starting and stopping of auxiliary drives and this can result in several mechanisms which lead to deterioration of electric motor components. Typical failures that have been attributed to cycled operation include material fatigue arising from torque stresses on rotors during starting and stopping, and high starting currents causing thermal and electromagnetic effects. To study the effects of increased flexibility requirements on motors, WG A1.54 was created in 2015.
• The addition of inverter-based resources into the generation mix internationally over the past two decades, has led to the need for additional services to be provided from conventional generation, the majority of which is coal based globally. The coal-based generators were not designed for high ramp rates, quick response and provision of other ancillary services such as frequency and voltage support. There is also a requirement for minimum generation levels to be maintained for a period. It is therefore clear that flexible and minimum load operation should be achieved to effectively implement and support inverter-based resource generation. WG A1.65 will develop a guide for optimal management of coal generation in presence of significant inverter-based resources.

SD 3: Renewable Generation

Renewable energy technologies vary widely in their technical and economic maturity. Their common feature is that they produce little or no greenhouse gases and rely on virtually inexhaustible natural sources for their ‘fuel’. Wind generation presented a great growth in the last decade. The installed wind capacity has more than doubled every third year, in the last decade. According to the National Energy Agency Technology Roadmap for Wind Energy, wind power can make up 18% of the total energy production by 2050.

Due to this anticipated growth in wind power generation, it is essential to focus work groups in this area to ensure that we keep abreast the latest technologies available in the market with specific focus on efficiency, reliability and monitoring of wind turbine generators. As wind turbine generation is a relatively new technology in its present modern form, we need to influence the present and future technologies to ensure optimum power system reliability and availability. WG A1.51 and JWG A1/C4.52 are Work Groups that will focus on wind turbine generation. WG A1.51 (See SD 5) will do a survey on the monitoring, reliability and availability of wind generators and JWG A1/C4.52 (see SD 2) will focus on the Frequency-active power control of wind generation.

In 2019 Study Committees A1 and C4 will be forming JWG A1/C4.66 to prepare a guide on the assessment, specification and design of synchronous condensers for power systems with high levels of renewable generation. As part of carbon emission reduction mechanisms, many countries have adopted policies to increase the installed capacity of renewable generation to either supplement or replace existing thermal generation. Wind and solar have proven to be the most economical choices up to this point in time and have been deployed en-masse at both transmission and distribution voltage levels. Significant reductions in system inertia will impact network frequency control capability including observable rates of change of frequency (ROCOF) following credible and non-credible contingency events. At low inertia levels, there is likely to be a need to increase and possibly improve primary frequency control capabilities. The ability of under frequency load shedding and/or over frequency generation shedding schemes to operate correctly following non-credible events is also likely to be impeded if ‘minimum’ levels of inertia are not maintained. The main objective of this WG will be to produce an application guide which power network owners/operators and other parties can use to help determine network needs and thereby specify synchronous condenser design requirements to successfully maintain network inertia.

SD 4: Motors

Electrical motors perform almost all mechanical work in factories, offices, service centres, hospitals, households and schools. In auxiliary services of power plants and in industry, motors are used for driving compressors, fans and pumps, machine tools, robots, transport equipment and many other equipment. Historically the Advisory Group was focused on motors with ratings more than 800 kW and 1000 V for power stations, but the scope also now includes smaller ratings high efficiency motors used for dispersed generation considering their large potential for energy saving. The significant potential that energy saving by electrical motors can have on future power generation requirements is noted and by encouraging work groups to study the potential and effect of large-scale deployment of high efficiency motors, hopefully significant benefits for industry can be obtained.

Approximately half of the global electric energy demand is consumed by electric motor systems. Energy efficient electric motors represent one of the largest opportunities for cost-effective electricity savings and reduction of greenhouse gas emissions. In order to gain fast and efficient access to the energy efficiency improvements of electric motor systems, regulations mandating the energy labelling of products for minimum energy performance standards (MEPS) have been widely applied to three-phase electric motors and the MEPS efficiency has resulted in higher efficiency levels such as IE3 - premium efficiency type motors. The world can save up to 160 GW on global power generation by improving 5% of motor efficiency.

The following motor Work Groups are active in SCA1:

• WG A1.45 is compiling a guide for Determining the Health Index of Large Electric Motors.  With the axiom that all motors have inherent defects, it is necessary to quantify the defects’ severity in order to link it the likelihood/probability of the motor functional failure. Large electric motors need quantitative analysis of monitored motor data, which when normalised with operational and environmental conditions of the monitored motor, show the severity of the defect in relation to the level of functional in-service failure risk exposure. The guide will aid utilities in identifying the appropriate measurements that are necessary for statistical quantification of in-service failure risk for effectively planned predictive maintenance interventions.
• Environmental concerns have led industry to focus on energy saving measures. Variable frequency drives (VFD) have been widely used to save energy. VFDs are used for several applications in utilities and industry like induced draft fans, cooling tower fans, condensate extraction pumps, compressors, coal conveyors, coal feeders and ventilation system equipment. As the penetration of VFDs in industry and in power stations has increased, several motor failures have been reported worldwide and it has become clear that manufacturers do not have common design criteria for inverter grade motors. The variety of VFD technologies available stresses the motor insulation differently. The guide compiled by WG A1.53 shall elaborate on the design requirement of three phase induction motors for VFD applications including a user guide for retrofitting of existing installations.
• WG A1.54 – Impact of Flexible Operation on Large Motors. The scope of this topic is shared with Strategic Direction 2 where more information on the scope of this Work Group can be found.
• WG A1.58 was created in 2016 to compile a guide for the selection of copper versus aluminium rotors for induction motors. In industrial applications, squirrel cage induction motors are widely used. The materials used for the manufacturing of the rotor cage can be from different conductive metals, with the most used ones being aluminium alloys and copper. With these materials, the cage of the rotor can be manufactured by die-casting or welding processes. Both materials have advantages and disadvantages, which are not always clearly understood.
• WG A1.68, titled Evaluating Quality Performance of Electric Motor Manufacturing and Repair Facilities, was created in 2019. The WG will compile a guide covering the best available practices on evaluating the quality performance of motor manufacturing and repair facilities.

SD 5: Machine monitoring, diagnosis and prognosis

Condition Monitoring is becoming a vital instrument in any business as it can result in significant cost savings if done correctly and effectively. The field of condition monitoring is one of continuous evolution and development. The long-term goal of any plant owner is to effectively operate machines to achieve maximal performance, reliability and efficiency and to make intelligent maintenance decisions through understanding the behaviour and signs of deterioration. This is called Condition Based Maintenance, which is maintenance performed when it is optimally required. Short, medium and long-term risks can be evaluated with an effective condition monitoring system. The system can also be designed to provide diagnosis of machine condition allowing the prediction of problems, optimize operational efficiency and improve plant productivity. Some systems are based on expert systems and further development in this field is anticipated. There is an important link between monitoring, diagnosis, the life management and life extension processes (prognosis). The following work groups are performing work in this field:

• WG A1.43 focusses on state-of-the-art rotor temperature measurement systems. Protecting key generators and large industrial motors against premature failure due to rotor overheating has always been a demanding task. This is particularly true in cases where the rotor windings are inaccessible in operation and the respective winding temperatures cannot be determined with accuracy, e.g. brushless excitation systems. Unexpected component failure can result in forced outages and costly emergency repairs. In order to prevent unexpected component failure, some rotating machines today are equipped with temperature measurement instrumentation. This topic is of high importance, not just for machine monitoring and diagnostics purposes, but also for the purposes of machine design and construction improvements. The completed Technical Brochure for this work will be published in 2019.
• WG A1.44 is compiling a guideline on Testing of Turbo and Hydro-generators. Previously published TB 386 ‘Generator Maintenance, Inspection and Test Programs’ provided recommendations regarding maintenance, inspection and testing of turbo-generators in power plants. However, it was felt the necessity of having a new document in order to provide guidance to plant personnel on test procedures and practices to ensure equipment integrity, including hydro-generators, as well as an overall guidance regarding safety precautions, industry references, acceptable ranges of results, and, where appropriate, actions should the results be outside acceptable ranges.
• WG A1.51 is conducting a study on monitoring, reliability and availability of wind generators. Wind power assets are numerous (over 60,000 out of warranty assets in the EU by 2021) and dispersed over large geographical areas. Wind turbine generators are a high-cost, key component of the asset and therefore monitoring of generators could play an important part in OPEX reduction. The goal of this WG is to develop a best practice guide for monitoring of wind assets. As part of this, a key task will be the assessment of currently available methodologies and their effectiveness (diagnostic & prognostic capabilities, accuracy, robustness, IT and analytical overheads, associated costs, potential cost savings, logistical issues). Although a large amount of public domain information exists regarding monitoring systems (sensors, data processing methods, impact on maintenance scheduling & logistics) there is a lack of information regarding how operators utilize these systems. Part of the aim of the WG will be to bring operators together to share experience on this specific issue.
• The predictive diagnosis of winding insulation in large motors (more than 800 kW and 1000 V) is of great importance, for both technical and economic reasons. In October 2004 SC A1 published the technical brochure: “Application of On-line Partial Discharge Tests to Rotating Machines”, providing guidance on where it is appropriate to apply partial discharge (PD) measurements and providing a proper focus on what results could be expected. Since then IEC/TS 60034-27, IEC/TS 60034-27-2, IEEE Std 1434 concerning the subject of PD measurements on the stator winding insulation of rotating machines have all been updated (in 2006, 2012 and 2014 respectively). The technologies in this field have evolved fast and new measurement and diagnostic tools are now available, including new kinds of PD sensors and new signal processing tools for noise and disturbance suppression. Simultaneously, the industrial use of converter fed high-voltage machines is steadily growing. Particularly in motors, where the effects of motor drivers on the insulation aging process and in PD monitoring have a significant influence, there is still a lack of information, reference cases and standard procedures. WG A1.61 - Survey of Partial Discharge Monitoring in Large Motors is at task to fill this information gap.

SD 6: Efficiency of electrical machines

Generators and motors are the highest efficient components used in the power generation process, with power conversion efficiencies ranging from 98% to 99%. Further improvement on these efficiencies has proven possible, but requires highly advanced modelling requiring complex algorithms, making use of all technical knowledge and experience available, pushing technologies to its absolute safe limits. On a large turbo generator of 1000MWe output, a 0.1% improvement in efficiency can result 1MWe extra being available to the national grid, powering an additional 50 to 60 households, without any increase to operational costs. As design tools, insulation materials, steel forgings, silver bearing copper and cooling mediums are pushed to its limits as a result of industry needs for larger and more efficient machines, a whole new world for the development of new materials are opening.

The development of new materials can improve cooling and electrical insulation heat transfer characteristics in generators and motors, thereby directly contributing to the increase in efficiency of these electrical machines. Higher efficient electric motors, due to its widespread use and location at the centres of consumption, have a great impact on the reduction of losses in power systems, directly resulting in significant cost savings for large industrial users. The utilization of polymer nano-composite materials in electrical machines is promising for near-future HV electrical insulation by enamelling the conductors to be more resistant to partial discharges and improving their voltage and thermal endurance capacity contributing to an additional increase in efficiency.

Currently active Working Groups

Five WGs were disbanded in 2019, after completion of their activities, with publication of Technical Brochures and Electra Reports. Four new WGs were approved in 2019. At present there are 30 active WGs in the SC and 5 WGs near completion of their work and ready for publication in 2020. Present active Work Groups in SC A1 are covering the following topics:

Work starting in 2020

Completed work

The following list is a summary of Technical Brochures completed by Study Committee A1 in recent years available on e-cigre.org:

• 776 - Factory Quality Assurance Testing Requirements for Turbo-Generator Components - Stator Bars
• 774 - State of the Art of Stator Winding Supports in Slot Area and Winding Overhang of Hydro Generators
• 772 - Turbo-generator stator windings support system experience
• 769 - Dielectric Dissipation Factor Measurements on New Stator Bars and coils
• 743 - Guide on New Generator Grid Interaction Requirements
• 729 - Technological Feasibility Studies for Super and Ultra-Premium Efficient Motors
• 724 - Guide on Use of Premium Efficiency IE3motors for Determining Benefits of Greenhouse Gas Emission Reduction
• 690 - Vibration and Stability Problems met in New, Old and Refurbished Hydro Generators, Root Causes and Consequences
• 682 - Survey on Hydro Generator Instrumentation and Monitoring
• 665 - Hydro-generator Behaviour Under Transient Conditions
• 641 - Guide on Economic Evaluation of Refurbishment / Replacement decisions on Turbo-generators
• 621 - Generator On-Line Over and Under Excitation Issues
• 582 - Survey on Hydro Generator Cleaning
• 581 - Guide - Corona Electromagnetic Probe Tests (TVA)
• 574 - Guide for Consideration of Duty on Windings of Generators
• 573 - Guide for Minimizing the Damage from Stator Winding Ground Faults on Hydro-generators
• 558 - Guide for the Monitoring, Diagnosis and Prognosis of Large Motors
• 552 - Guide of methods for determining the condition of stator winding insulation and their effectiveness in large motors
• 551 - Feasibility of Updating from Class 155 (F) to Class 180 (H) the Electrical Insulation Systems in Electrical Rotating Machines
• 522 - Generator Stator Winding Stress Grading Coating Problem
• 517 - Guide for the Prevention of Over-fluxing of Generators
• 503 - State of the Art and Capacity for Robotic Inspection of Turbo-generators
• 491 - Generator End-Winding Retaining Rings – A Literature Survey and Care Guideline
• 480 - Guide on Stator Water Chemistry Management
• 470 - Life Extension of Large Electric Motors in Nuclear Power Plants
• 469 - State of the Art in Efficiency of Hydro Generators Commissioned since 1990
• 454A - Hydro-generators Fire Protection – Update (Annex)
• 454 - Hydro-generators Fire Protection – Update
• 437 - Guide for On-Line Monitoring of Turbo-Generators
• 397 - Guide for minimizing the damage from stator winding grounds on Turbo-generators
• 392 - Survey of Hydro-generator Failures
• 386 - Generator Maintenance, Inspection and Test Programmes
• 258 - Application of On-Line Partial Discharge Tests to Rotating Machines
• 257 - EL CID Testing of Large Steam-Turbine-Driven Generators

SC A1 Indian Colloquium and Paris Session

SC A1 had a very successful Colloquium in India in 2019. The Colloquium took place on the 26 and 27 September 2019 in Hotel Taj Vivanta situated in New Delhi. The Colloquium was attended by more than 170 delegates.

The following Preferential Subjects was the topic for the Colloquium:

Preferential Subject 1: High Renewable Penetrated Networks

1. Methods and experiences for the evaluation of existing base load plant to handle new grid requirements such as cyclic loads, high values in the rate of change of frequency (Hz/s), fault ride through capability, extended U/f requirements, higher power factor requirements.
2. Usage of new as well as decommissioned power plant generators as synchronous condensers to solve power quality issues due to large scale renewable integration & comparison with other FACTs devices.
3. Design improvements, technological advancement and operational experience of Hydro generators for prolonged and efficient operation as low and very low speed generators, synchronous condensers and pump-motors.
4. Innovative trends in the field of Turbo generators, Hydro generators, wind turbine generators, large motors and high efficiency motors.
5. Suitability of generators and motors in a renewable energy mix environment from a harmonics point of view.
6. Latest designs implemented or proposed for Rotating Electrical Machines to endure severe load cycling.
7. Wind Turbine generator experience: Failures, design challenges, maintenance philosophies and maintenance challenges.
8. Concentrated solar power, solid waste and Biomass power plants: Design, specification, construction, efficiency, operation and maintenance experience.

Preferential Subject 2: Operational Experience and New Developments

1. Operational experience on state-of-the-art technologies used for large turbo generators, hydro generators, wind turbine generators, high voltage motors and high efficiency motors.
2. Latest designs and maintenance practices to improve efficiency, reliability, availability, robotic inspections, and reduce maintenance costs.
3. Performance and reliability comparison of different designs of large motors of same ratings and duty cycles with regards to heating, efficiency, mean time to failure, life cycle costs.
4. Advanced and optimised condition monitoring and analysis making use of latest technologies, taking digitization, big data, advanced analytics, etc. into consideration.
5. Experience with renovation, modernization and up-rating of aged power plants.
6. Novel techniques to overcome known operational and design problems of hydro power plants especially for operation in silt prone water.

There were 24 papers presented covering large turbo generators, machine insulation system, hydro generators and motors. These papers were presented in six sessions.

The next Study Committee Meeting will take place in Paris, France on the 26th of August 2020. The Preferential Subjects for the Group Discussion Meeting in Paris are as follows:

PS 1: Generation Mix of the Future

• Effect and risk of an increasing renewable power mix on existing legacy generators, generator auxiliaries, and motors
• Improvement in designs and maintenance practices to comply with new and future grid requirements
• Evolution and trends in new machines for renewable generation

PS 2: Asset Management of Electrical Machines

• Experience with refurbishment, replacement, design improvements, power up-rating, and efficiency improvement of aged generators and motors
• Optimised condition monitoring, diagnosis, prognosis, and maintenance practices to improve reliability and extend operational life
• Operational and project experience: installations, failure analysis; robotic inspections; recovery options; cost and time reduction initiatives; and effects of torsional electromechanical oscillations for synchronous compensators, wind turbine generators, turbo-generators, hydro-generators, and motors

PS 3: Latest Developments

• Designs, specifications, materials, manufacturing, maintenance, performance, and efficiency improvement of electrical machines
• Condition monitoring techniques and equipment

Tutorials and Workshops

Tutorials are regarded as a valuable initiative to disseminate knowledge from work done by work groups within the study committee. The sharing of knowledge by experts in Study Committee A1 is encouraged and invitations from National Committees to present tutorials at regional meetings will be welcomed. Four tutorials were delivered by SCA1 experts during the SCA1 2019 Colloquium in India. The topics covered were:

• Magnetic core dimensioning limits in Hydro-Generators - Johnny Rocha
• Application of dielectric dissipation factor measurements on new stator coils and bars - Monique Krieg-Wezelenberg
• Guidance on the Requirements for High speed Balancing/over speed testing of turbine Generator Rotors following Maintenance or Repair - Ben Adams
• Guide for Cleanliness and Proper storage of Generators and Components - Kevin Mayor

A tutorial will take place in Paris in the Palais des Congress on Monday morning the 24th of August 2020 starting at 08h30 in Salle Maillot. The topic of the tutorial is ‘Specification vs Value of new hydro-generators – A cause and consequence trade-off’ to be delivered by Johnny Rocha.

Future Activities

SC A1 is conducting studies and international surveys on new developments and technologies to improve the performance of electrical rotating machines in order to increase their availability and reliability for the supply of electrical power systems. The following subjects will guide the future activities of the SC:

• Improvements in design, materials, insulation, cooling, bearings, availability, reliability, efficiency and maintenance of rotating electrical machines.
• Life management
• Large Generators and Motors
• Renewable generation
• Machine/System Interaction
• Machine monitoring, diagnosis and prognosis
• New developments in excitation systems
• Superconducting machines.
• Utilization of polymer nano-composites is promising as near-future HV electrical insulation in rotating machines.

Publications

Published in 2019

Publications

To come in 2020

The following Technical Brochures and Reports are programmed to be published in 2020: