Specific protection of prosumer electrical installations
When you integrate PV production into a building electrical installation, some specific points need to be taken into account regarding the protection devices, in particular the ones described below.
Automatic disconnection (loss-of-mains protection)
When there is grid outage, and if no other local source can provide backup power, the grid-tie PV inverters disconnect rapidly, and the electrical installation is no longer supplied. Although this may at first seem counterintuitive, it addresses a serious safety concern. In case of utility supply loss, installations with local generation are required to guarantee that they do not inject power into the grid to keep utility workers safe.
For installations with PV production operating only grid-connected, this safety feature can be provided by a dedicated protection device, installed at the local sources’ feeders or at the electrical installation utility incomer, or can be provided by the PV inverters themselves.
Most PV inverters include an integrated loss-of-mains protection, which disconnects the PV inverter in the event of a power outage. The presence of this protection and its compliance to standards is to be checked with the PV manufacturer.
Another option is to use a dedicated protection device, generally located at the photovoltaic system feeder.
Location of overcurrent protection for the photovoltaic system
This protection should be coordinated with the main circuit-breaker to ensure selectivity.
Another safety measure is the AC overcurrent protection for the photovoltaic power supply system.
To isolate electrical faults on the photovoltaic installation, an overcurrent protection device must be located at the point where the photovoltaic system is connected to the building’s electrical installation. It is essential to include the overcurrent protection in this exact location, to avoid tripping the main circuit breaker, in case of fault in the photovoltaic feeder.
To ensure things work properly, this overcurrent protection should be coordinated with the main circuit-breaker to guarantee selectivity.
This selectivity may not be so easy to achieve, in particular when the photovoltaic production capacity is equivalent to or higher than the building installed power. In this case, the circuit breaker at the photovoltaic incomer has the same rating or higher than the main circuit breaker. Thus, to ensure selectivity between the two breakers, possible options include:
- oversize the main circuit breaker
- split the photovoltaic system into smaller systems, or
- consider time selectivity, for applications higher than 630 Amps
Isolation and switching of the photovoltaic power supply system
As described in the previous paragraph, an AC disconnection device must be located at the photovoltaic switchboard, to isolate the photovoltaic system from the rest of the electrical installation during maintenance. Moreover, an isolation function must be provided for the photovoltaic inverters, by disconnection means, on both the DC side and the AC side.