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and earth.
2. If the neutral is not accessible, the overvoltage limiter is
installed between a phase and earth.
3. It runs off external over voltages, transmitted by the
transformer, to the earth and protects the low voltage network from
a voltage increase due to flashover between the transformer’s
medium voltage and low voltage windings.

Advantages

1. System provides the best service continuity during use.
2. When an insulation fault occurs, the short-circuit current is very
low.
3. Higher operational safety only a capacitive current flows, which
is caused by the system leakage capacitance if an earth fault
occurs.
4. Better accident prevention the fault current is limited by the
body impedance, earthing resistance and the high impedance of the
earth fault loop.

Disadvantages
1. Requires presence of maintenance personnel to monitor and
locate the first fault during use.
2. Requires a good level of network insulation (High leakage
current must be supplied by insulating transformers).
3. Overvoltage limiters must be installed.
4. Requires all the installation’s exposed conductive parts to be
Same Voltage level. If this is not possible RCDs (residual-current
device) must be installed.
5. Locating faults is difficult in widespread networks.
6. When an insulation fault with reference to the earth occurs, the
voltage of the two healthy phases in relation to the earth take on
the value of the phase-to-phase voltage So when Select Size of
equipments it is need to higher insulation level of the Equipments.
7. The risk of high internal over voltages makes it advisable to
reinforce the equipment insulation.
8. The compulsory insulation monitoring, with visual and audible
indication of the first fault if tripping is not triggered until the
second fault occurs.
9. Protection against direct and indirect contact is not guaranteed.

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