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056-019 Earth fault protection Issue 2 - ADM

Earth fault protectionDSE7300 and DSE5500 series controllers include an Earth fault protection alarm that is configured using the PCconfiguration software.

Restricted Earth fault protectiono Can be restricted to detecting earth faults upstream (generator protection) or

downstream (load protection) of the neutral CTo 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 wouldrequire your equipment to protect the generator

o The diagram below shows typical connection of a DSE7300 series controller configuredfor restricted earth fault protection.

NOTE : Upstream and downstream protection are both shown though the neutral must only be connected toearth in one place!

Earthing theneutral beforethe CT willdetect earthfaults onlyafter the CT(load)

Earthing the neutral after theCT will detect earth faults onlybefore the CT (generator)

7/30/2019 Earth Fault Protection

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056-019 Earth fault protection Issue 2 - ADM

Unrestricted Earth fault protectiono 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.

Detectiono 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 earthfault, the curve is followed. The curve makes larger earth faults cause faster tripping ofthe generator.

o DSE Earth Fault Detection is intended for relatively large earth leakage only and cannotbe used to provide 30mA personnel earth leakage protection.

Typical settingso Its 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 faultandthese must be allowed for when the alarm is being configured.

o Higher curve values give slower reaction and can be used to prevent spurious tripscaused by (for instance) transformers being energised.

o For unrestricted earth fault protection and upstream restricted protection, the alarmshould be shutdownto stop the system immediately.

o For downstream restricted protection, the alarm can be electrical tripto allow a coolingtrip 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.

CT in theneutral toearth link willdetect earthfaults in thegenerator andin the load