| MONITOR | 2/2017 30 TECHNICAL APPLICATION Safety by means of insulation monitoring Fire safety in wind power stations A fire in a wind energy plant can have devastating consequences. Usually it is beyond repair and must be written off to the tune of a few million. With regard to this topic, the well-known VdS guideline on fire safety [1] mentions "Insufficient electrical protection concept with regard to insulation fault detection and selectivity of shutdown” as a main cause of fire. This conceals a high savings potential for operators, industrial managers and insurers. With the correct protection concept, which monitors the insulation properties of the electrical plant, faults can generally be detected and averted at an early stage. The insulation resistance gives some indication of the quality of the electrical plant and is an indication of potential faults. In this way, not only direct insulation faults, e.g. worn away cable insulation, can be discovered, but also other faults in the electrical system, which have an effect on the overall insulation resistance of the plant. The structure of the electrical systems and the selected system type are decisive when choosing the right protection method. TN systems (earthed systems) [2] are common and widely spread in Germany, although the advantages of an IT system (unearthed system) [3] for wind power stations in par- ticular are obvious: In an IT system, if the right dimensioning and low system leakage capacitances are used, when a fault first occurs there are neither high fault currents (high degree of fire safety) nor dangerous touch voltages for persons (protection against touching indirectly). Further operation is possible without any danger. Some German manufacturers of wind power stations have recognised these advantages and already operate their plants in an IT system. Some standards, such as DIN EN 61400-1 (wind turbines – Part 1: Design requirements), also recommend sensible monitoring methods. This standard stipulates that the dan- ger to people and animals has to be minimised, and that any possible damage during operation and maintenance of the WEA must be kept to a minimum. A suitable measurement concept must be available, regardless of whether the system is earthed or unearthed. In accordance with the require- ments of IEC 61557-8 for IT systems with an insulation moni- toring device, it is advisable to also install an insulation fault location system as well as fast and efficient fault localisation. In TN systems, monitoring with a residual current monitoring device (RCM) is a safe and economic alternative. Bender provides globally proven, field-tested and opera- tionally reliable equipment as well as integral solutions for detecting any potential electrical dangers at an early stage. The safety of persons and plants is thereby guaranteed, since critical operating and plant statuses can be detected and reported in good time. Preventive intervention provides a high degree of plant availability, and risks of failure and service interruptions are reduced to a minimum. [1] VdS: 3523 - Wind turbine guideline for fire safety, 2008, VdS Verlag [2] In TN systems (earthed systems), the neutral point of the supplying transformer is connected to earth [3] In IT systems (unearthed systems) the active lines have no conductive or low impedance connection to PE (earth) M. Sc. Michael Breuer, S-EMEA