What causes the GFPE to operate in a zero-sequence type system?

The operation of the Ground Fault Protection Equipment (GFPE) in a zero-sequence type system is fundamentally linked to the concept of zero-sequence currents, which occur when there is an imbalance among the phase conductors and the neutral. In a zero-sequence system, the current flowing through the neutral conductor becomes significant when there is an unbalanced load or a fault condition, such as a ground fault.

When there is an imbalance between the phase conductors and the neutral, it leads to a situation where the currents in the three phases do not sum to zero, causing a resultant current to flow through the neutral. This is particularly critical for safety, as any ground fault will also produce an unequal distribution of current across the phases, contributing to the zero-sequence current flow. The GFPE is designed to sense this zero-sequence current and operate accordingly to disconnect the power, thereby providing a protective measure against electrical shock and fire risks associated with ground faults.

This understanding of zero-sequence currents highlights the importance of maintaining balanced loads in a system and illustrates why the GFPE acts in response to imbalances in phase and neutral currents.