IEEE - The Institute of Electrical and Electronics Engineers@ Inc.
Scope
Introduction This IR includes a description and a simplified single-line diagram for a typical utilityscale wind farm. As described and shown@ the collector system consists of mediumvoltage (34.5 kV) direct-buried cables with concentric neutrals bonded to the collector substation transformer grounded neutral point (34.5 kV side) and also bonded to the lowvoltage secondary neutral at each wind turbine step-up transformer. The IR did not state whether or not various classes and types of equipment (such as surge arresters@ step-up transformer cases and grounded neutral conductors) would be interconnected by means of a single grounding conductor. As well@ it did not state if the concentric neutral jacket is insulating or semi-conductive. The basic question asked is whether: (1) is the grounding of the collector system cables adequate as described@ or (2) must the cables also be grounded four times in each mile of cable run assuming that the described grounding points do not provide such grounding. Because large-scale wind farms are a relatively new and emerging form of cogeneration@ or in this situation renewable energy@ specific NESC rules have not been developed for wind farms. Consequently@ both careful consideration of all factors and good engineering judgment are required in the design and operation of wind farm systems to ensure that all applicable NESC rules are met. See also Rule 012C regarding items not specified in the NESC rules. Several factors must be considered to determine application of existing NESC rules to grounding of the described system. Note that this interpretation is limited to the system described in the IR