Ground Fault Protection (GFP)
Different type of ground fault protections
(see Fig. F27)
Three types of GFP are possible dependind on the measuring device installed :
- “Residual Sensing” RS
The “insulation fault” current is calculated using the vectorial sum of currents of current transformers secondaries. The current transformer on the neutral conductor is often outside the circuit-breaker.
- “Source Ground Return” SGR
The « insulation fault current » is measured in the neutral – earth link of the LV transformer. The current transformer is outside the circuit-breaker.
- “Zero Sequence” ZS
The « insulation fault » is directly measured at the secondary of the current transformer using the sum of currents in live conductors. This type of GFP is only used with low fault current values.
Fig. F27: Different types of ground fault protections
Positioning GFP devices in the installation
| Type / installation level | Main-distribution | Sub-distribution | Comments |
|---|---|---|---|
| Source Ground Return (SGR) | [math]\displaystyle{ \definecolor{bggrey}{RGB}{234,234,234}\pagecolor{bggrey}\color{RoyalBlue}\Box }[/math] | Used | |
| Residual Sensing (RS) (SGR) | [math]\displaystyle{ \definecolor{bggrey}{RGB}{234,234,234}\pagecolor{bggrey}\color{RoyalBlue}\Box }[/math] | [math]\displaystyle{ \definecolor{bggrey}{RGB}{234,234,234}\pagecolor{bggrey}\color{RoyalBlue}\blacksquare }[/math] | Often used |
| Zero Sequence (SGR) | [math]\displaystyle{ \definecolor{bggrey}{RGB}{234,234,234}\pagecolor{bggrey}\color{RoyalBlue}\Box }[/math] | [math]\displaystyle{ \definecolor{bggrey}{RGB}{234,234,234}\pagecolor{bggrey}\color{RoyalBlue}\blacksquare }[/math] | Rarely used |
[math]\displaystyle{ \color{RoyalBlue}\Box }[/math] Possible
[math]\displaystyle{ \color{RoyalBlue}\blacksquare }[/math] Recommended or required
