**3. Configuration of wind farm**

A wind farm composed of six 1.5 MW wind turbines is connected to a 25 kV distribution system that exports electricity to a 120 kV network via a 25 km long feeder from a 25 kV bus 4. Three 1.5 MW wind turbines pairs simulate the 9-MW wind farm. Wind turbines use squirrel cage induction generators (SCIG) [5].

**Figure 4.** *9 MW—Wind farm connected to the grid.*

**Figure 4** shows the system considered for protection in which three wind turbine generators are connected to the grid.

The stator winding is connected directly to the 60 Hz grid, and a controllable-pitch windmill drives the rotor [6, 7]. The pitch angle is controlled to limit the generator's output power to its nominal value for winds exceeding the little velocity (9 m/s). A protection system is installed at each wind generator from W1 to W3, which measures voltage, current, and speed. Reactive power absorbed by the IGs is partly compensated by capacitor banks connected at each wind turbine low voltage bus [8–10]. The rest of the reactive power required to maintain the 25-kV voltage at bus B4 close to 1 pu is provided by a 3-Mvar STATCOM with a 3% droop setting. Modeling of Wind Turbine Generator is carried in MATLAB Software [11]. The data of wind turbine generator modeling is shown in Appendix A.

### **4. Protection of wind turbine generator**

The digital protection system installed on W1 to W3 consist of following protections covers in single digital relay for wind turbine generator [12].



**Table 1.**

*Desired operation of digital relay R1, R2, and R3 at W1, W2, and W3 respectively.*

The desired protection for relay 1 at W1, relay 2 at W2, and relay 3 at W3 are shown in **Table 1** for different fault locations.

#### **4.1 Protection algorithm**

The relay R1, R2, and R3 are located at Bus 1, Bus 2, and Bus 3. The algorithm is explained in this section by considering Relay R1 to protect W1 against internal faults F1. For faults F4, F5 and F6 at POC at Bus 4, R1 reacts instantaneously as both these three faults impact the W1 directly. On the other hand, the relay R1 remains stable for F2, F3 and F7 and maybe operate as a backup to the primary relay addressing these faults. Here, F2 and F3 are parallel feeder faults considered external faults for F1. F7 is a external fault in the grid system. The protection algorithm for such desired operation as per **Table 1** is shown in **Figure 5**. As per the Algorithm, relay R1 measured threephase voltage and current *Vabc* and *Iabc* with the help of PT and CT in the beginning [13]. Using the symmetrical component method, Positive sequence, negative

**Figure 5.** *Protection algorithm for WTG.*

sequence, and zero sequence voltage and current are *V*1, *V*2, *V*<sup>0</sup> and *I*1, *I*2, *I*<sup>0</sup> respectively have been calculated. Based on the different conditions as shown in **Figure 5**, the tripping commands have been sent to the circuit breaker of W1. The next section will describe how the Algorithm detects LG, LL, LLL, LLLG faults for internal and external fault conditions.
