Technical requirements for high-penetration wind : What system operators need, and what wind technology can deliver

As wind penetration levels increase, the effects on the electricity system increase, and therefore the technical characteristics of the wind generation become more important. In addition, many modern wind turbines could in principle behave unlike conventional synchronous generators, raising new problems and perhaps providing new benefits to the system. Electricity system operators are responsible for the satisfactory operation of their electricity systems in normal and abnormal conditions. In order to achieve this, they define technical requirements which all parties connected to their system must follow. These technical requirements can take several forms but are commonly referred to as ´grid codes´. This paper approaches the issues by considering the fundamental technical requirements of system operators. This is compared with current and possible future technical capabilities of wind turbine technology. The technical issues discussed are: 1. voltage and frequency operating ranges; 2. reactive power; 3. voltage control; 4. power quality; 5. frequency response; 6. stability (fault ride-through); 7. the process of grid code development; 7. and system operation issues. This paper supports the initiative led by the European wind energy association to achieve ´structural harmonisation´ of grid codes, i.e. to achieve common definitions, terminology and methodology. Due to the differing characteristics of electricity systems, a set of requirements applicable everywhere would be unnecessarily onerous in most countries, and agreement would be very difficult to achieve. The paper proposes that it is appropriate for some technical requirements to be activated only when wind penetration reaches some threshold which is technically justifiable. These thresholds should be clearly defined in advance by the system operators or energy regulators. The authors believe that the important technical issues are now known and relatively well understood. Interest will increasingly move- to methods for validating compliance with the requirements, especially testing. The authors also believe that there may be opportunities for system operators to make use of the presence of a large number of fully-controllable sources of real and reactive power distributed across their networks, in ways that have not yet been considered.