Page 34 - 4587
P. 34
Figure 6.1 - PLC implementation types of electrical power
distribution systems
A directly earthed neutral strongly limits over voltages but it
causes very high fault currents, here as an unearthed neutral limits
fault currents to very low values but encourages the occurrence of
high over voltages. In any installation, service continuity in the
event of an insulation fault is also directly related to the earthing
system. An unearthed neutral permits service continuity during an
insulation fault. Contrary to this, a directly earthed neutral, or low
impedance-earthed neutral, causes tripping as soon as the first
insulation fault occurs.
The choice of earthing system in both low voltage and medium
voltage networks depends on the type of installation as well as the
type of network. It is also influenced by the type of loads and
service continuity required.
The main objectives of an earthing system is to provide an
33
