Observations on the Certification Requirements of the IEC Code

aspects of the certification concerning materials, structures, machinery and electrical components and these are only covered in brief form. For this IEC 61400-3 states:

“When determining the structural integrity of elements of a wind turbine, national or international design codes for the relevant material may be employed. Special care shall be taken when partial safety factors from national or international design codes are used together with partial safety factors from this standard. It shall be ensured that the resulting safety level is not less than the intended safety level in this standard”.

There is no selected nationally accepted code for offshore wind farms and thus the application of this requirement cannot be directly applied from the IEC Code. The intended safety level is implied based on the return period selected for design checks and the load factor but not specifically stated as a reliability factor.

A number of the Technical Requirements of Certification appear to be difficult to carry out and the actions required do not themselves appear to be well specified though the spirit of the intent is strong in the document IEC 61400-22 as written. Several areas are pointed out on the issues of Certification to highlight the definition problems with the Code for a Certifier.

1.4.7.1 Load Cases (IEC 61400-22 8.3.3)

“the Certification body shall evaluate the loads and load cases for compliance…..by independent analysis.”

This appears to be a costly option and focuses on calculation error rather than errors of assumptions which are often the causes of failures. While there is a need for the Certifier to be qualified to run the independent analyses the concentration on that aspect may be something that needs to be examined. German requirements refer to the “plausibility check” to assure that the numbers are judged experientially.

1.4.7.2 Control and Protection System (IEC 61400-22 8.3.2)

“The Certification Body shall evaluate the documentation of a control and protection system, comprising:

o description of wind turbine modes of operation;

o design and functionality of all elements;

o fail-safe design of the protection system;

o system logic and hardware implementation;

o a test plan for the verification of the control and protection system functions”.

Since much of the control and protection system is run by computer it requires Certification of the software system as well as the logic.

It seems that with offshore wind farms they will be large and fairly complex projects;

there will be a number of systems and subsystems that have to be controlled, others that have to be monitored. The suppliers may potentially be significant in their number so each of the interfaces may have to be developed with good coordination. Some of this may be avoided if it were decided that the manufacturer’s owned system was part of the package. It may be that the manufacturers verify the software since the warranty

provisions that have to date been offered make not doing so a higher risk for the manufacturer: however the regulator may be prudent not to rely on the risk profile of others to determine acceptability.

In order to Certify the systems it would be necessary to review the systems, the simulations and review the network analysis, and assure that the owner/operator

responsible for the software kept a log of the changes and had a system to ensure it was known what version of the software was operating at any time, and that indeed it had been tested thoroughly and the operators trained thoroughly including potential glitches.

It should be clear at commissioning that there is document of the software version which is installed. A formal testing process needs to be in place at commissioning and it is necessary to define what tests should be run based on any changes to commissioned software. A change control process is important since the structural capability of the towers depends on the software working.

Code security: it should be defined who has authority to read the software and change it is another issue as well as the necessity to create notifications in case of change to the software.

The basis of ensuring the system has had a check would involve carrying out a Failure Mode and Effect Analysis on the hardware and software, among other things checking for single points of failure on the software and the hardware associated with control and monitoring. Interviews with those providing the software would be part of the process as would the operator training definitions and requirements.

Appendix E of 61400-22 does give guidance which is useful in the process of Certification on this subject.

1.4.7.3 Acoustic Noise Measurements (IEC 61400-22 8.8.3) The acoustic noise measurements are spelled out well in the IEC Code so it would be straightforward to certify according to the IEC requirements 61400-11 for this activity.

1.4.7.4 Tower, Nacelle and Spinner

These details are not specifically covered in the IEC Guidelines except that load conditions apply to the components so one must look to DNV for Tower and GL for Tower, Nacelle and Spinner or alternative certifier requirements.

1.4.7.5 Personnel Safety (IEC 61400-22 8.3.14)

The IEC code contains a section on Personnel safety and suggests several inclusions:

o safety instructions;

o climbing facilities;

o access ways and passages;

o standing places, platforms and floors;

o hand rails and fixing points;

o lighting;

o electrical and earthing system;

o fire resistance;

o emergency stop buttons;

o provision of alternative escape routes;

o provision for emergency stay in an for offshore wind turbine for one week;

and

o offshore specific safety equipment for an offshore wind turbine

There is insufficient guidance to reflect the specifics of how to consider these and to what standard.

GL state that EN 50308 Wind Turbines –Labor Safety as the document they use to Certify this aspect of Offshore Wind Farms and is quite prescriptive in many of the requirements: it is an excellent code and directly applicable to the offshore wind turbine industry. (Note: For further discussion a sections 3.5 and 4 of this Report and the Safety Management System Template directly addresses Personnel Safety).

1.4.7.6 Inspection of Personnel Safety (IEC 61400-22 (D.6))

The intent of the checks to be carried out are applaudable, however, the specifics need to be laid out for implementation e.g. “the existing of suitable lighting shall be checked”

and “the function of the emergency light shall be checked”. The Code, however, does not specify any details of what is suitable and whether indeed an emergency light is required though it appears to imply it.

What is clear from the above is that there was a tremendous amount of energy and effort that went into this code, but it requires a level of more detail for application with clarity of what is intended as mandatory in order that the result will be the quality of the certification process that is intended.