8.3 ELECTRICAL CONCEPT DESIGN
development (during this electrical study) and approximate locations (with red crosses) of existing onshore grid substations.
8.3.1 Introduction
8.3.2 Onshore Substation
This section provides the outcomes of a preliminary investigation into the electrical layouts of the onshore substation and offshore cabling. It also provides indicative costing and sizing for the electrical equipment.
DNV GL has prepared a preliminary schematic electrical diagram showing the electrical system for the onshore substation. This is shown in Figure 8-2.
It is assumed that the Tamil Nadu offshore wind farm development will not include an offshore substation. The onshore substation will be the central location for the collection of energy from the Wind Turbine Generators (WTGs) located offshore. For the purpose of the electrical concept design the following configuration has been considered, 84 WTGs each of 6 MW capacity. The overall installation capacity is therefore calculated as 504 MW. For the remaining project configurations Turbine.Architect has been used to validate and scale the results from this concept design study. 66 kV array cables have been assumed for all turbines 4 MW, 6 MW and 10 MW. The offshore wind farm location within zone A is assumed at 15 km away from the shore during this electrical study. The wind farm being near to the shore and with 66 kV collection system voltage level, FOWIND estimates the possibility of direct HVAC connection of the offshore wind farm to the onshore substation. This arrangement reduces the overall CAPEX and future operation and maintenance cost. However, towards the detail engineering if the offshore wind farm is finally located more than 20 km from the shore, then the requirement of having an offshore substation should be assessed. As 220 kV is an operational network voltage in Tamil Nadu, 220 kV is utilised as the operating voltage for the connection to the network at the onshore substation. Figure 8-1 illustrates the assumed location of the 504 MW Tamil Nadu offshore wind farm
This conceptual design represents a typical solution for an onshore substation based on the use of standard components. Both active power and reactive power requirements should be considered during detailed design so that grid code requirements can be met at the point of connection. Compensation equipment will be required at the different operating voltages to address the capacitive effects of the cabling as well as to satisfy the requirements of the grid code. The normal running arrangement is with all onshore transformers in service. The following main equipment has been assessed and determined as being suitable for the onshore substation configuration:
4 x 160 MVA Offshore Transformers 2 x 90 MVAr Dynamic Reactive Compensation (approximate value) 4 x 30 MVAr Shunt Reactors (approximate value) 2 x Harmonic Filters 8 x feeder circuits operated at 66 kV The maximum apparent power and current flow in the transformer connected circuit breakers are calculated as: 160 MVA and 0.420 kA on 220 kV winding 160 MVA and 1.4 kA on 66 kV winding
Considering the above apparent power values, the transformer connected circuit breakers should be selected with appropriate capacity. The following are recommendations as a preliminary design:
Circuit breaker with a capacity of 2500 Amps on 66 kV winding Circuit breaker with a capacity of 3150 Amps on 220 kV winding
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