ERL F-PRO 116, Руководство пользователя

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D05125R01.20 F-PRO 116 User Manual 5-7
Table 5.7: 51G (IDMTL) Neutral Overcurrent Settings (No. of Stages – 1)
Setting Description Range
Function Activation Enable/disable
Pickup
0.05 to 10 (1 A)
0.25 to 50 (5 A)
Curve Type For details see Table 5.3 “I EC and IEEE Curves ”
TMS 0.01 to 10.00
Pickup DTL Delay 0.00 to 999.99 seconds if chosen for DTL characteristics
Reset Delay DTL/ANSI Decay (other than DTL selection)
Reset DTL Delay 0.0 to 99.9 seconds if DTL is chosen
A
0.0010 to 1000.0000 settable if chosen for user defined characteristics
B 0.0000 to 10.0000 settable if chosen for user defined characteristics
p 0.01 to 100.00 settable if chosen for user defined characteristics
TR 0.10 to 150.00 settable if chosen for user defined characteristics
Inrush Blocking Enable/disable
64/50/51 Instantaneous SEF
The sensitive earth fault protection works by measuring the residual current across the three
phases in a system or by measuring the transformer neutral current. The first one is done by
using a Core balanced current transformer (CBCT). In the event of a fault, the residual current
over the three phases will not be equal to zero as the current from the faulted phase flows
through the earth.
The sensitive earth fault protection is usually used in alternators and transformers with high
resistance grounding. High resistance grounding restricts the earth fault current to less than the
nominal value. High resistance grounding enables electrical systems to continue running when
one of the phases is faulted. This prevents interruptions to the power supply. This kind of
earthing system provides time to identify and isolate the fault.
Once an earth fault occurs in the high resistance grounding system, an alarm needs to be
generated and the fault needs to be traced. Undetected earth faults in the system are
dangerous as a second earth fault in another phase may result in a short- circuit. A residual
current earth fault relay may not be an accurate option for detecting an earth fault as it may
not have the sensitivity to detect such low fault current values.
The sensitive earth fault protection, as the name suggests, is a highly sensitive function. It can
sense currents as low as 0.5% of the CT secondary current. The sensitive earth fault relay may
be configured to generate an alarm and / or a trip signal.