Earth fault protection
DSE7300 and DSE5500 series controllers include an “Earth fault protection” alarm that is configured using the PC
configuration software.
• Restricted Earth fault protection
o Can be ‘restricted’ to detecting earth faults upstream (generator protection) or
downstream (load protection) of the neutral CT
o Upstream or downstream protection depends upon the location of the neutral to earth
link.
o Earth the neutral conductor before the neutral CT (generator side) to detect earth faults
after the CT (load side)
o Earth the neutral conductor after the neutral CT (load side) to detect earth faults before
the CT (generator side) – This is more common. As a generator supplier you would
require your equipment to protect the generator
o The diagram below shows typical connection of a DSE7300 series controller configured
for restricted earth fault protection.
Earthing the
neutral ‘before’
the CT will
detect earth
faults only
‘after’ the CT
(load)
Earthing the neutral ‘after’ the
CT will detect earth faults only
‘before’ the CT (generator)
NOTE : Upstream and downstream protection are both shown though the neutral must only be connected to
earth in one place!
056-019 Earth fault protection Issue 2 - ADM
• Unrestricted Earth fault protection
o By placing the earth fault CT in the neutral to earth link, we provide earth fault detection
that is unrestricted, we detect earth faults in the load and in the generator.
o The diagram below shows typical connection of a DSE7300 series controller configured
for unrestricted earth fault detection.
CT in the
neutral to
earth link will
detect earth
faults in the
generator and
in the load
• Detection
o The DSE controller summates outgoing and incoming current. A mismatch indicates
earth fault. If the measured earth fault current (mismatch) is above the setting for earth
fault, the ‘curve’ is followed. The curve makes larger earth faults cause faster tripping of
the generator.
o DSE Earth Fault Detection is intended for relatively large earth leakage only and cannot
be used to provide 30mA personnel earth leakage protection.
• Typical settings
o It’s impossible to give a typical setting for the trip level as it depends upon many things,
including the makeup of the load. Many loads have a small amount of earth fault and
these must be allowed for when the alarm is being configured.
o Higher ‘curve’ values give slower reaction and can be used to prevent spurious trips
caused by (for instance) transformers being energised.
o For unrestricted earth fault protection and ‘upstream’ restricted protection, the alarm
should be shutdown to stop the system immediately.
o For ‘downstream’ restricted protection, the alarm can be electrical trip to allow a cooling
trip after breaker opening before the set is stopped. Opening the breaker removes the
fault from the alternator as the fault must be ‘load side’.
Further details of earth fault protection wiring and configuration can be found in the relevant operator and PC software manuals.
056-019 Earth fault protection Issue 2 - ADM