**4. Impact on distribution networks of DG ground current contribution**

The distribution network considering DG, shown in Fig. 12, has been modelled to analyze the effects of wind farms and PV solar installations ground current contribution to the network. The DG is based on capacitive coupling models of a 1 MW PV solar installation and a 1.4 MW wind farm with the electric parameters shown in Table 1 and Table 2, respectively.

This distribution network feeds two loads through a multi-terminal ring topology. These loads are connected to bus 2 and 5 with a rated power of 500+ *j 25* kVA each one.

In steady state conditions, the wind farm generates a total active power of 1370 kW, and the PV solar installation delivered 940 kW to the distribution network. To analyse the capacitive coupling effect over the ground current in DG systems, it has been noticed the voltage and current waveforms seen at node 5 through the capacitive coupling of the line.

Fig. 12. Distribution network based on capacitive coupling model of wind farms and solar installations.


The electric parameters of the network grid are shown in Table 3.

Table 3. Electric parameters of the network grid.

274 Power Quality Harmonics Analysis and Real Measurements Data

Capacitive cooupling model |Z|

15 kV 50 Hz

Zth

Network grid

1

Simplified model |Z|

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

Frequency (Hz)

Fig. 11. Resonance frequency of the wind farm model without considering capacitive

**4. Impact on distribution networks of DG ground current contribution** 

wind farm with the electric parameters shown in Table 1 and Table 2, respectively.

loads are connected to bus 2 and 5 with a rated power of 500+ *j 25* kVA each one.

current waveforms seen at node 5 through the capacitive coupling of the line.

P= 500 kW Q= 25 kvar

Fig. 12. Distribution network based on capacitive coupling model of wind farms and solar

*5 km*

3 2

Wind generator 1400 kVA

*3.1 km*

4 5

*2.5 km*

The distribution network considering DG, shown in Fig. 12, has been modelled to analyze the effects of wind farms and PV solar installations ground current contribution to the network. The DG is based on capacitive coupling models of a 1 MW PV solar installation and a 1.4 MW

This distribution network feeds two loads through a multi-terminal ring topology. These

In steady state conditions, the wind farm generates a total active power of 1370 kW, and the PV solar installation delivered 940 kW to the distribution network. To analyse the capacitive coupling effect over the ground current in DG systems, it has been noticed the voltage and

> P= 500 kW Q= 25 kvar

> > *10.5 km*

*15.1 km*

coupling (dashed line) and with capacitive couplings (solid line).

Solar PV 1000 kW

installations.

Impedance

 |Z| (

)

In node 5, the phase voltage waveform meets the standard regulation of harmonic distortion (THD=5.4%) with a fundamental component of 8.72 kV, as shown in Fig. 13.

Fig. 13. Simulation result of the distribution network: (a) phase voltage waveform and (b) FFT analysis of the waveform obtained, at node 5.

Harmonic Distortion in Renewable Energy Systems: Capacitive Couplings 277

3.80 3.81 3.82 3.83 3.84 3.85 3.86

Time (s)

(a)

(b)



Bellini A., Bifaretti S., Iacovone V. & Cornaro C. (2009). Simplified model of a photovoltaic

Chayawatto N., Kirtikara K., Monyakul V., Jivacate, C. & Chenvidhya D. (2009). DC/AC

module, *International Conference on Applied Electronics*, pp. 47–51, ISBN 978-80-7043-

switching converter modeling of a PV grid-connected system under islanding phenomena, *Renewable Energy,* Vol. 34, No. 12, (2009), pp. 2536–44, ISSN 0960-1481

Fig. 15. Simulation result of the distribution network: (a) current waveform and (b) FFT

analysis of the waveform obtained, at node 5.

to be exposed to a high amount of ground current.

781-0, Pilsen, Bohemia, Czech Republic, Sept. 9-10, 2009

model.

**6. References** 


Current (kA)

Although voltage waveform meets standard regulations, it has been observed an important ground current contribution through the admittance of the underground cables. The ground voltage waveform has a considerable magnitude with peaks reaching 7 V, as shown in Fig. 14. Likewise, the ground current measurement due to the capacitive coupling of these underground cables is also significant as shown in Fig. 15.

The fundamental component of the current waveform is 313 mA, and the THD of this waveform is 190.78%. The most predominant harmonic components are harmonic 72 with 145.22% of the fundamental component, followed by harmonic 70 and 76 with 98.29% and 58.75%, respectively, as shown in Fig. 15a.

Fig. 14. Simulation result of the distribution network ground voltage waveform at node 5.

These observations point to the importance of controlling the capacitive coupling in load installations connected to networks with DG. Otherwise, end users equipments can be exposed to malfunctioning and lifetime reduction due to the capacitive ground current. Moreover, GPR can reach values of unsafe work conditions.
