Almost in every wind farm a step-up substation is built to collect all the energy generated by the turbines and received through the MV cables. The exceptions are new wind farms or existing wind farms extensions built near a substation that can be upgraded to absorb the additional energy produced: in these cases, only a control center with the SCADA and the medium voltage system is realized.
Although there are different possible technical solutions, normally a substation will be composed by the following elements:
- Medium voltage system
- High voltage system
- Capacitors banks
- Auxiliary services
- Control, protection and metering system
- Communication system
- Fire protection and intruders protection systems
Medium voltage system is composed by the general busbar, disconnectors, circuit breakers and current transformer.
High voltage system is made of one or more transformers, together with earthing reactance, surge arresters, current transformer, voltage transformer, circuit breaker and disconnector with earthing switch.
Capacitors banks are installed to comply with the grid requirements regarding active and reactive power.
The auxiliary services supply energy both in AC/DC current, and count with a group of battery that can generate energy for several hours to operate the substation in case of emergency, a rectifier and often a backup diesel generator, with a tank big enough to provide energy for 3 days..
Control, protection and metering system allows the correct operation of the wind farm according to local regulations and grid requirements. Basically they are protection relays for the switchgear and power transformers
The communication system, must guarantee the correct communication with the adjacent substations and with the grid owner control center, in order to make possible the correct operation of the wind farm substation. Normally communications are through optical fiber/carried wire.
Fire protection system is normally composed by optical or infrared detectors, fire extinguisher, external bells or siren, while te intruders protection system are normally a fence plus a closed circuit TV.
Also the SCADA server is normally located inside the substation, together with a parabolic antenna to grant broad band connection.
There are several available solutions to connect with the existing high voltage distribution network: normally a dedicated line is used, while in other situations a tap off (or “T” connection) is used. A third solution is to open the existing line between 2 substations.
The 3 solution are shown on the following diagrams: