Dispositivo de protección de falla a tierra

Diagrama de cableado de un sistema FV autónomo con un controlador de carga con control de iluminación de CC y un inversor para cargas de CA. (1) Dispositivo de protección de falla a tierra (GFPD).

Diagrama de cableado de un sistema FV autónomo con un controlador de carga con control de iluminación de CC y un inversor para cargas de CA. El sistema está tiene una falla a tierra de CC en un conductor no puesto a tierra en el cableado de la fuente FV.

Un dispositivo de protección de falla a tierra (GFPD) utiliza un interruptor automático de baja corriente (.5-1 A) para crear una conexión entre un conductor (cable) y tierra en el lado de CC de un sistema FV, lo que crea un conductor puesto a tierra. Este interruptor automático está conectado a otro interruptor automático a cual se conecta el conductor sin conexión a tierra. En el caso de una falla a tierra, el interruptor automático de baja corriente se disparará eliminando la conexión entre el conductor de tierra y la tierra, pero también abre o aisla el conductor no puesto a tierra del circuito de la fuente FV. Un GFPD mejorará la seguridad en todos los sistemas con una conexión a tierra de CC, pero son más vitales para los sistemas que tendrán módulos FV montados en el techo de una estructura. La construcción de un sistema montado en poste o en tierra minimizará el riesgo de incendio para las personas en caso de una falla a tierra y puede ser una forma de aumentar la seguridad de un sistema. Los dispositivos de protección contra fallas a tierra pueden ser un costo adicional significativo para los sistemas pequeños y pueden ser difíciles de encontrar en muchos lugares, lo que generalmente limita su uso en muchas partes del mundo.

A GFPD plays an important role in a PV system with a DC system ground by helping to prevent fires from ground faults that go undetected by overcurrent protection devices (OCPDs). A ground fault can go undetected because the OCPDs for the PV source are sized to the maximum current of the PV source, which means that OCPDs are often ineffective against DC ground faults occurring at the PV source as it doesn't exceed their current rating. This can lead to a fire because PV modules will continue to provide current as long as there is sunshine and a circuit. The diagram at right shows how a GFPD operates during a ground fault on an ungrounded DC conductor:

1. A fault occurs on a DC ungrounded conductor of a system.
2. The current from the fault follows the equipment grounding conductor (EGC) back to the busbar for the grounded conductor to complete the circuit. Current surges from the PV source.
3. The current of the GFPD on the connection between ground and the grounded conductor is exceeded. The device disconnects the DC system ground, opens the PV source circuit, and the fault is disabled.

This has the benefit of reducing the potential of a fire resulting from the ground fault, but also creates a new hazard. A grounded conductor, like the black DC wire in the diagram, will have a voltage of 0 V to ground - grounded conductors are generally safe to touch. An ungrounded conductor, like the red DC wire in the diagram, will have the voltage of the PV source relative to ground and is not safe to touch. The new hazard is created because of two things that happen when a GFPD activates during a ground fault:

1. The previously ungrounded (red) conductor with the PV source voltage relative to ground effectively becomes a grounded conductor with 0 V to ground.
2. The previously safe grounded (black) conductor with 0 V is turned into an ungrounded conductor by removing its ground, which means that it may have the full voltage of the PV source relative to ground.

This creates a hazard for system users or anyone troubleshooting the problem as the issue may not be readily apparent and safe/unsafe conductors of a system have switched roles due to the GFPD. Ground faults should be taken very seriously and any troubleshooting should be done by someone with experience dealing with ground faults.