Wind Farm Electrical Protection Systems Explained

Protection Systems in Wind Farms

A wind farm is composed of the following: installation of low-voltage generators, BT/MT transformation, a medium-voltage distribution network, a substation, and evacuation lines. Generally, the wind generator produces low voltage (690 V) and connects to a transformer that increases the voltage (20–30 kV) to minimize cable losses while evacuating the power produced to the substation.

Evacuation Line Protection

The most common method to connect the wind farm substation to the utility network is through a dedicated line. Protections assigned to this line include:

• Overvoltage protection
• Directional overcurrent protection
• Earth leakage protection

Substation Transformer Systems

Substation transformers utilize load-voltage regulation to help maintain stability on the MT network and, consequently, within the generators, especially when evacuation lines are of considerable length. Protections assigned to the MV/AT transformers include:

• Differential overcurrent switch-fault relays
• Liquid or gas pressure relays
• Thermal overcurrent relays

Grounding and Neutral Configuration

The configuration of the main transformer is typically star-triangle, with the MT network neutral either isolated or grounded. The purpose of the grounding transformer is to ground the system neutral; otherwise, it would remain isolated. If a ground fault occurs in the line system, the grounding transformer allows the circulation of a current strong enough to trigger the neutral overcurrent relays. This scheme has the advantage of reducing surges and facilitating the detection of earth faults. Protections associated with the grounding transformer are primarily overcurrent protections.

Transformer Safety and Short Circuit Management

The transformer must be protected against overcurrent, usually via fuses. Fuses provide protection against faults in the transformer secondary. When switches are used, they must be designed to open at the maximum short-circuit current, including the contribution of adjacent generators. In this case, overcurrent relays are used.

Lightning Protection

Wind farms require specialized protection against lightning due to their location and height, which make them highly susceptible to strikes. Lightning protection reduces potential damage by providing a low-impedance path to the ground. This system consists of:

• Lightning conductors
• Grounding systems
• Surge protection devices