The new Service Specification applying to type certification of wind turbines as well as for component certification was introduced in our last newsletter. The experiences gathered from certification projects specifically component and type certification of on- and offshore wind turbines realised over the last years has been taken into account for this new certification scheme. Correspondingly the type and component certification schemes have been adapted to meet market needs and expectations.
In course of the update of the whole scheme much more effort was taken to get to the next level of certification and standardization; beyond modules and elements of certification this includes all technical aspects laid down in standards and recommended practices. This article focuses on the aspects of electrical installations and rotor blades.
The DNV GL standard DNVGL-ST-0076 “Design of electrical installations for wind turbines” provides principles and technical requirements for design and construction of electrical installations for wind turbines onshore and offshore. The standard can be applied as part of the technical basis for carrying out a DNV GL certification of wind turbines and it is also intended to cover the requirements implied when using IEC-related certification schemes. All systems and components mentioned therein and listed below can undergo a component certification as per DNVGL-SE-0441.
The standard is applicable to the design of electrical components and electrical systems for the complete wind turbine, including main components, cable systems and, control and protection systems.
Electrical installations shall be so designed that:
- the maintenance of normal operational conditions will be ensured without recourse to any emergency source of electrical power
- the operation of emergency equipment required for machinery and personal safety will be ensured under various defined emergency conditions
- the safety of personnel and installations from electrical hazards will be ensured and risks of injury to human life will be reduced to a minimum
- the equipment and installations will reach the expected lifetimes
- sufficient levels of reliability are reached for the entire system.
The standard 0076 covers the certification of:
- rotating electrical machines
- power transformers (dry-type and liquid-immersed)
- frequency converters
- high voltage switchgear
- back-up power supply systems
- low-voltage switchgear, control gear and switchboards including safety-related parts
- cables, lines and accessories
- lightning protection, earthing and bonding
- electrical pitch and yaw drives
- selection and interconnection of electrical equipment
- electrical control and protection systems
- testing, installation, commissioning and maintenance
- corrosion protection
- fire protection systems
- extreme environmental conditions, offshore applications
- ventilation and cooling systems
- grid parallel and island operations.
The DNV GL standard DNVGL-ST-0376 „Rotor blades for wind turbines“ provides principles and technical requirements for rotor blades for wind turbines onshore and offshore. This standard can be applied as part of the technical basis for carrying out DNV GL type certification of wind turbines or DNV GL component certification of rotor blades.
The standard is applicable to all types of wind turbines and rotor blades, even though many requirements have been formulated specifically for blades made from fibre-reinforced plastics for operation on horizontal axis wind turbines. It is applicable to the structural and functional design, and manufacturing, of rotor blades for wind turbines, including requirements for materials, testing, repair and operation.
Rotor blades shall be designed so that:
- the maintenance of normal operational conditions will be ensured
- the safety of personnel and installations will be ensured and risks of injury to human life will be reduced to a minimum
- the rotor blades will reach the expected life time
- sufficiently high reliability is reached for the entire system.
Newly introduced is the test pyramid including its options for future rotor blade tests, see Figure 1.
Figure 1: Test pyramid
In many cases, it may be appropriate or even necessary to supplement material coupon tests and full scale blade tests by further testing on an intermediate level. When certifying a rotor blade for compliance with the present standard, such intermediate level testing may be applied as part of the design verification process, by using test results as design values in structural verification analyses, and as partial substitute for full scale blade testing.
These days, manufacturing inspections and surveillance are an important part of the certification process. The inspections should be based on witnessing as the majority of the manufacturing process for the blade in question. The intention of the inspections is to gain sufficient confidence that the quality management, works office/area and shop floor documentation and procedures used by the concerned manufacturing site staff, to ensure compliance with the approved component certified design documentation and that the design can be repeatedly transferred into production. This standard gives guidance and provides the full scope of manufacturing inspections.
For all standards all requirements specified therein shall be fulfilled. However deviations from these requirements or the application of alternative means of complying with these requirements, may be acceptable after consultation and agreement with DNV GL. It is essential that an equivalent level of safety and reliability can be demonstrated while applying alternative methods, tests, analysis or solutions.
Starting with the publication of the electrical engineering standard exactly one year ago, the meanwhile famous rotor blade standard was published at the end of last year. End of May 2016 our DNV GL standard for loads started hearing. With that the last piece of the puzzle for the full DNV GL scheme for on- and offshore wind energy went to the public. The documents on control and protection systems, support structures or extreme temperatures complete the full scheme. Expect the final document on machinery components and mechanical engineering soon. They are all glued together by our service specifications for component, type and project certification and can be amended with documents on e.g. lifetime extension, corrosion protection or shop approvals – just to name some.
The latest revision of all DNV GL documents can be found in the ”rules and standards” pages on the DNV GL website.
The certification services are adjusted to follow the wind turbine or component development phases from concept to serial production and beyond, see figure 2. These development phases may be supported during the wind turbine development by respective certification deliverables.
Figure 2: Certification services aligned with the development process
The main differentiators of the DNV GL certification scheme to other existing schemes are:
- more guidance and descriptions to facilitate application
- all wind turbine relevant topics addressed in one service specification
- all wind turbine development phases are supported by the certification scheme
- certification may be tailored by adding multiple optional services, e.g. based on additional SE.
The benefits of applying this service specification are:
- independent approval of the wind turbine and component to reduce own risk in developing and designing
- reducing costs by early detection of non-conformities
- confidence in technical integrity
- confirmation of requirements as stated by project developers, investors, operators, manufacturers, governmental and non-governmental organisations
- proof by an independent body to meet the national and international acknowledged state-of-the-art and to ease market entry
- utilise statements and certificates for authorisation by governmental institutions
- proof to investors or insurer that third party approval is successfully performed
- securing sustainable energy production throughout the lifecycle
- minimising technical risks
- document stepwise the maturity of the wind turbine development project
- mitigate risks to environment and people.
Component certification as a term used in this service specification covers e.g. major and minor components, systems, single parts or assemblies used in a wind turbine or attached to it. The mandatory certification modules comprise design, manufacturing and testing at different stages of the wind turbine development process.
The specification together with the respective DNV GL standards and recommended practices represents a completely revised and expanded version of the GL-IV-1 “Guideline for the Certification of Wind Turbines”, Edition 2010 and GL-IV-2 “Guideline for the Certification of Offshore Wind Turbines”, Edition 2012; both with a history of 30 years. Get your own copy here.
Read the previous article about this topic 'Preview of a new RC Service Specification' published on 31 March 2016.
If you are interested in finding out more about our new service documents wind energy, please feel free to contact directly: Mike Wöbbeking, Director and Service Area Leader, Renewables Certification DNV GL - Energy.