Electricity + Control October 2019

EARTHING + LIGHTNING PROTECTION

Application examples Acknowledging that the protection of rooftop PV systems against lightning is imperative, the type of lightning protection system to be used differs for new and existing structures. For new structures, it is mandatory to carry out a lightning protection risk assessment in accordance with SANS 62305-2. Once the assessment has been conducted, the appropriate lightning protection level will be selected and the lightning protection system can be designed and installed to meet this, to protect both the structure and the rooftop PV system. For existing structures, the design and installation of an appropriate lightning protection system for the rooftop PV system will vary for: - Structures without an existing lightning protection system - Structures with an existing lightning protection system where adequate separation distances can be maintained - Structures with an existing lightning protection system where separation distances are inadequate. Structures without external lightning protection Once the required risk assessment has been carried out, if it indicates that a structural LPS is not required the following protection measures should be implemented: - Surge protection to PV system by means of Class 2 and 3 surge arresters - Equipotential bonding to electrical earthing systembymeans of 16mm² copper conductors.

- ac output of the inverter / TN-S system - LV input / TT/TNS system - Data interface / two pairs of data cables. Structures with external lightning protection If the assessment confirms that there is an existing structural lightning protection system in place, the level of protection provided should be verified by an inspection of the system.This should also serve to verify that the lightning protection system is intact, fully functional and in accordance with SANS 62305 Part 3. Any defects should be rectified to ensure that the LPS for the rooftop PV system will work properly. The inspection and verification of the existing LPS and the design of the LPS for the rooftop PV system should be performed by a lightning protection specialist. The lightning protection system should be installed in such a way that the PV panels are not vulnerable to direct lightning strikes. The method of protecting the rooftop PV installation is via the air termination system, with the preferred protection methods being either the angle of protection method or the rolling sphere method of protection. The size of the sphere and the size of the angle of protection are both dependent on the applicable lightning protection level. The designer of the lightning protection system should also consider which method of protection will be more economically viable. If possible, where the calculated separation distances are maintained, an isolated lightning protection system should be installed. Isolated lightning protection systems are far more effective than non-isolated systems. If the installation of an isolated lightning protection system is not possible then the installation of additional Class 1 lightning current arresters is required on both the ac and dc sides at the inverter boxes.

Surge protection recommendations apply for: - dc input of the inverter / for 2 MPPTs

Figure 3. On buildings where a structural LPS is not required, surge protection measures must be applied on the solar PV system and it must be bonded to the building’s electrical earthing system.

Figure 4. Equipotential bonding]

28 Electricity + Control

OCTOBER 2019