# Design, Evaluation and Implementation of an Islanding Detection Method for a Micro-grid

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Islanding Detection Method for an MG Based on the Instantaneous Active and Reactive Power at the PCC

#### 2.1. Calculation of the Instantaneous Active and Reactive Power

_{3ph}) delivered from the MG to the dedicated line, which is defined and given in (1), can be calculated from the voltages (v

_{a}, v

_{b}and v

_{c}) and currents (i

_{a}, i

_{b}and i

_{c}) measured at the PCC.

_{3ph}) delivered from the MG to the dedicated line is calculated from the voltages (v

_{a}’, v

_{b}’ and v

_{c}’), which respectively lag v

_{a}, v

_{b}and v

_{c}by a quarter of period, and currents (i

_{a}, i

_{b}and i

_{c}) [25], as shown in (2).

#### 2.2. Islanding Detection Method Based on the Instantaneous Active and Reactive Power at the PCC

_{3ph}and q

_{3ph}is described. When the MG is disconnected from the distributed network by opening the circuit breakers at the grid side, p

_{3ph}and q

_{3ph}will be constant, which depend on the voltages at the PCC as well as the impedance of the dedicated line. p

_{3ph}will become almost zero because little resistance exists in the dedicated line. On the other hand, q

_{3ph}has some value corresponding to the series inductance and the shunt capacitance of the dedicated line. Since the parameters of the dedicated line can be obtained, these constant active and reactive powers can be easily calculated. Therefore, if the calculated instantaneous active and reactive powers converge to the pre-calculated constant values, the islanding inception will be detected.

**S**

_{ref}) is given by

**V**

_{PCC}and

**Z**

_{line}* represent the rated line-line voltage of the PCC and the impedance of the dedicated line, respectively.

_{1}and k

_{2}depend on the variation of the voltages at the PCC and the measurement ratio errors of the current transformer (CT) and the potential transformer (PT). The variation of the voltages at the PCC is ±20%, with the fully consideration of the voltage deviation both in the steady-state and the transient state after an islanding inception, and sufficient margin. Thus, k

_{1}and k

_{2}are set by

_{3}is set to be 15°, considering the limits of phase errors of both CTs and PTs, also with sufficient margin [26,27]. These three coefficients, k

_{1}, k

_{2}and k

_{3}, only depend on the limits of voltage variation and the limits of measurement errors of CTs and PTs defined in the IEC Standards [26,27]. Thus, when the proposed method is applied in another MG, k

_{1}, k

_{2}and k

_{3}will not be changed, and only

**S**

_{ref}should be pre-calculated considering the parameters of the new dedicated line.

_{3ph}, q

_{3ph}) moves into the islanding detection region, which is used to prevent the mal-detection for the transient disturbances.

## 3. Case Studies

^{2}, whose series resistance, series inductance and shunt capacitance are 0.8316 Ω/km, 0.0022 H/km and 0.0021 μF/km, respectively. The MG is composed of three DGs i.e., a 2 MW natural gas-fired generator, a 2 MW DFIG type wind generator, and a 1 MW photovoltaic generator, and some associated local loads. The system is modeled using the PSCAD/EMTDC simulator, where the sampling rate is 32 samples/cycle. The signals of the currents and voltages measured at the PCC are passed through anti-aliasing RC low-pass filters with the cutoff frequency of 960 Hz, which is half the sampling frequency.

#### 3.1. Islanding Conditions

_{a}(solid), v

_{b}(dashed), and v

_{c}(dotted) are shown in the upper subfigure and i

_{a}(solid), i

_{b}(dashed), and i

_{c}(dotted) are shown in the lower subfigure. After the islanding inception, the voltages decrease slightly whilst the currents decrease to nearly zero. p

_{3ph}and q

_{3ph}are respectively shown in the upper subfigure and lower subfigure of Figure 3b. After islanding inception, p

_{3ph}becomes almost zero after a slight fluctuation whilst q

_{3ph}becomes a very small value directly. Both p

_{3ph}and q

_{3ph}change and become stable again in several milliseconds after the island incepts. In Figure 3c, the trajectory of the point (p

_{3ph}, q

_{3ph}), which is shown with the marks of “o”, is located in the third quadrant prior to the islanding inception. This is because the power is delivered from the grid to the MG prior to the islanding inception, which can also be confirmed in Figure 3b. When the islanding incepts, p

_{3ph}is nearly zero and q

_{3ph}has the negative value because of the characteristics of the dedicated line. Therefore, the trajectory moves to the islanding detection region. In Figure 3d, where “0” and “1” respectively mean mode of interconnection and islanding, the islanding detection signal is activated at 22.53 ms after the islanding inception. The results indicate that the proposed method can successfully and quickly detect the islanding operation in 1.5 cycles after the islanding inception.

_{3ph}, q

_{3ph}). As seen in Figure 4d, the trajectory of the point moves into islanding detection region at 20.45 ms after islanding inception. In Case 3, the generating power of the MG is larger than the local loads of the MG. Thus, the point (p

_{3ph}, q

_{3ph}) is in the fourth quadrant prior to the islanding inception. As expected, the trajectory of the point (p

_{3ph}, q

_{3ph}) enters the islanding detection region from the fourth quadrant at 22.53 ms after the islanding inception, as shown in Figure 5c,d.

#### 3.2. Fault Conditions

#### 3.2.1. Faults with Different Position

_{3ph}and q

_{3ph}fluctuates after the fault incepts due to the large fault current. The point (p

_{3ph}, q

_{3ph}) is near the origin prior to the fault inception, since the generating power of the MG is same as the local loads. However, when the fault occurs, the point moves far away the origin, since the fault currents are considerably large. The proposed method does not activate the islanding detection signal (Figure 6d).

_{3ph}, q

_{3ph}) do not move into the islanding detection region, as shown in Figure 7c. Thus, the islanding detection signal is not activated.

#### 3.2.2. Faults with Different Inception Angle

_{3ph}, q

_{3ph}) moves far away the islanding detection region and consequently inactivates the islanding detection signal. In case of faults with different inception angle, even the magnitudes and waveforms of fault current in Cases 6 and 7 were different from those in Case 5, as seen in Figure 8a and Figure 9a, the fault currents were still considerably large. Finally, the islanding detection signal could not be activated as shown in Figure 8d and Figure 9d.

#### 3.2.3. Faults with Different Type

_{3ph}and q

_{3ph}fluctuate even when the transient state is finished, as seen in Figure 10b. Hence, the trajectory of the point (p

_{3ph}, q

_{3ph}) cannot remain stable at one point and move into the islanding detection region in Figure 10c. In addition, the islanding detection signal is not activated.

_{3ph}and q

_{3ph}fluctuate in Figure 11b and Figure 12b, and the trajectory of the point (p

_{3ph}, q

_{3ph}) does not move into the islanding detection region in Figure 11c and Figure 12c. As expected, the islanding detection signal is not activated.

#### 3.2.4. Faults with Different Fault Impedance

_{3ph}and q

_{3ph}fluctuate and the trajectory of the point (p

_{3ph}, q

_{3ph}) cannot remain stable at one point and move into the islanding detection region. The similar results and analysis can be easily drawn even the fault resistance exists in these unbalanced fault conditions. In addition, fault resistance has no effect on the magnitude and waveform of the fault current in the case of a balanced fault (3P fault). Hence, it could be easily concluded that the fault resistance would not affect the performance of the proposed islanding detection method.

## 4. Hardware Implementation

_{c}= 960 Hz) to the 16-bit A/D converters operating at a sampling rate of 32 s/c. All calculation and process of islanding detection are done in the IED.

_{3ph}, q

_{3ph}) cannot remain stable at one point even when the transient state is over. This is because p

_{3ph}and q

_{3ph}slightly fluctuate due to the noise signals in the voltages and currents. To prevent mal-operation due to these noise signals, the islanding detection region is appropriately expanded and set to be a circle. The results indicate that the proposed method can successfully and fast detect the islanding inception at 17.71 ms after the islanding inception. In Figure 17, even noise signals are contained in real voltage and current signals, the proposed islanding detection method does not activate the islanding detection signal due to large p

_{3ph}and q

_{3ph}after the fault inception.

## 5. Conclusions

_{3ph}, q

_{3ph}) moves into the islanding detection region, and the islanding detection signal is consequently activated. On the contrary, the trajectory of the point (p

_{3ph}, q

_{3ph}) would move to another point or fluctuates in a fault condition. The islanding detection region can be pre-defined considering the parameters of the dedicated line, variation of the voltage, and the possible measurement errors of CTs and PTs.

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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**Figure 3.**Results for Case 1. (

**a**) v

_{a}

_{,b,c}(upper) and i

_{a}

_{,b,c}(lower); (

**b**) p

_{3ph}(upper) and q

_{3ph}(lower); (

**c**) Trajectories of the point (p

_{3ph}, q

_{3ph}); (

**d**) Islanding detection signal.

**Figure 4.**Results for Case 2. (

**a**) v

_{a}

_{,b,c}(upper) and i

_{a}

_{,b,c}(lower); (

**b**) p

_{3ph}(upper) and q

_{3ph}(lower); (

**c**) Trajectories of the point (p

_{3ph}, q

_{3ph}); (

**d**) Islanding detection signal.

**Figure 5.**Results for Case 3. (

**a**) v

_{a}

_{,b,c}(upper) and i

_{a}

_{,b,c}(lower); (

**b**) p

_{3ph}(upper) and q

_{3ph}(lower); (

**c**) Trajectories of the point (p

_{3ph}, q

_{3ph}); (

**d**) Islanding detection signal.

**Figure 6.**Results for Case 4. (

**a**) v

_{a}

_{,b,c}(upper) and i

_{a}

_{,b,c}(lower); (

**b**) p

_{3ph}(upper) and q

_{3ph}(lower); (

**c**) Trajectories of the point (p

_{3ph}, q

_{3ph}); (

**d**) Islanding detection signal.

**Figure 7.**Results for Case 5. (

**a**) v

_{a}

_{,b,c}(upper) and i

_{a}

_{,b,c}(lower); (

**b**) p

_{3ph}(upper) and q

_{3ph}(lower); (

**c**) Trajectories of the point (p

_{3ph}, q

_{3ph}); (

**d**) Islanding detection signal.

**Figure 8.**Results for Case 6. (

**a**) v

_{a}

_{,b,c}(upper) and i

_{a}

_{,b,c}(lower); (

**b**) p

_{3ph}(upper) and q

_{3ph}(lower); (

**c**) Trajectories of the point (p

_{3ph}, q

_{3ph}); (

**d**) Islanding detection signal.

**Figure 9.**Results for Case 7. (

**a**) v

_{a}

_{,b,c}(upper) and i

_{a}

_{,b,c}(lower); (

**b**) p

_{3ph}(upper) and q

_{3ph}(lower); (

**c**) Trajectories of the point (p

_{3ph}, q

_{3ph}); (

**d**) Islanding detection signal.

**Figure 10.**Results for Case 8. (

**a**) v

_{a}

_{,b,c}(upper) and i

_{a}

_{,b,c}(lower); (

**b**) p

_{3ph}(upper) and q

_{3ph}(lower); (

**c**) Trajectories of the point (p

_{3ph}, q

_{3ph}); (

**d**) Islanding detection signal.

**Figure 11.**Results for Case 9. (

**a**) v

_{a}

_{,b,c}(upper) and i

_{a}

_{,b,c}(lower); (

**b**) p

_{3ph}(upper) and q

_{3ph}(lower); (

**c**) Trajectories of the point (p

_{3ph}, q

_{3ph}); (

**d**) Islanding detection signal.

**Figure 12.**Results for Case 10. (

**a**) v

_{a}

_{,b,c}(upper) and i

_{a}

_{,b,c}(lower); (

**b**) p

_{3ph}(upper) and q

_{3ph}(lower); (

**c**) Trajectories of the point (p

_{3ph}, q

_{3ph}); (

**d**) Islanding detection signal.

**Figure 13.**Results for Case 11. (

**a**) v

_{a}

_{,b,c}(upper) and i

_{a}

_{,b,c}(lower); (

**b**) p

_{3ph}(upper) and q

_{3ph}(lower); (

**c**) Trajectories of the point (p

_{3ph}, q

_{3ph}); (

**d**) Islanding detection signal.

**Figure 14.**Results for Case 12. (

**a**) v

_{a}

_{,b,c}(upper) and i

_{a}

_{,b,c}(lower); (

**b**) p

_{3ph}(upper) and q

_{3ph}(lower); (

**c**) Trajectories of the point (p

_{3ph}, q

_{3ph}); (

**d**) Islanding detection signal.

**Figure 16.**Hardware implementation results for Case 1. (

**a**) v

_{a}

_{,b,c}(upper) and i

_{a}

_{,b,c}(lower); (

**b**) p

_{3ph}(upper) and q

_{3ph}(lower); (

**c**) Trajectories of the point (p

_{3ph}, q

_{3ph}); (

**d**) Islanding detection signal.

**Figure 17.**Hardware implementation results for Case 4. (

**a**) v

_{a}

_{,b,c}(upper) and i

_{a}

_{,b,c}(lower); (

**b**) p

_{3ph}(upper) and q

_{3ph}(lower); (

**c**) Trajectories of the point (p

_{3ph}, q

_{3ph}); (

**d**) Islanding detection signal.

Scenario | Case No. | Description | Figure | Detection Signal |
---|---|---|---|---|

Islanding | Case 1 | Generating power of the MG < local loads of the MG | Figure 3 | Should be activated |

Case 2 | Generating power of the MG ≈ local loads of the MG | Figure 4 | ||

Case 3 | Generating power of the MG > local loads of the MG | Figure 5 |

Scenario | Case No. | Fault Position | Fault Inception Angle | Fault Type | Fault Impedance | Figure | Detection Signal |
---|---|---|---|---|---|---|---|

Fault | Case 4 | Distribution line of the MG | 0° | Three-phase | 0 Ω | Figure 6 | Should NOT be activated |

Case 5 | Dedicated line | 0° | Three-phase | 0 Ω | Figure 7 | ||

Case 6 | Dedicated line | 45° | Three-phase | 0 Ω | Figure 8 | ||

Case 7 | Dedicated line | 90° | Three-phase | 0 Ω | Figure 9 | ||

Case 8 | Dedicated line | 0° | Single line-to-ground | 0 Ω | Figure 10 | ||

Case 9 | Dedicated line | 0° | Double line-to-ground | 0 Ω | Figure 11 | ||

Case 10 | Dedicated line | 0° | Line-to-line | 0 Ω | Figure 12 | ||

Case 11 | Dedicated line | 0° | Single line-to-ground | 1 Ω | Figure 13 | ||

Case 12 | Dedicated line | 0° | Single line-to-ground | 5 Ω | Figure 14 |

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## Share and Cite

**MDPI and ACS Style**

Zheng, T.; Yang, H.; Zhao, R.; Kang, Y.C.; Terzija, V.
Design, Evaluation and Implementation of an Islanding Detection Method for a Micro-grid. *Energies* **2018**, *11*, 323.
https://doi.org/10.3390/en11020323

**AMA Style**

Zheng T, Yang H, Zhao R, Kang YC, Terzija V.
Design, Evaluation and Implementation of an Islanding Detection Method for a Micro-grid. *Energies*. 2018; 11(2):323.
https://doi.org/10.3390/en11020323

**Chicago/Turabian Style**

Zheng, Taiying, Huan Yang, Rongxiang Zhao, Yong Cheol Kang, and Vladimir Terzija.
2018. "Design, Evaluation and Implementation of an Islanding Detection Method for a Micro-grid" *Energies* 11, no. 2: 323.
https://doi.org/10.3390/en11020323