4.3.4.10 Technical data
Table 687: LREFPNDF Technical data
Characteristic Value
Operation accuracy Depending on the frequency of the measured
current: f
n
±2 Hz
±2.5% of the set value or ±0.002 x I
n
Start time
1, 2
Minimum Typical Maximum
I
Fault
= 2.0 × set
Oper-
ate value
37 ms 41 ms 45 ms
Reset time Typically 40 ms
Reset ratio Typically 0.96
Retardation time <35 ms
Operate time accuracy in definite time mode ±1.0% of the set value or ±20 ms
Suppression of harmonics DFT: -50 dB at f = n × f
n
, where n = 2, 3, 4, 5, …
4.3.5 High-impedance based restricted earth-fault protection
HREFPDIF (ANSI 87NHI)
4.3.5.1 Identification
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
High-impedance based restricted
earth-fault protection
HREFPDIF dIoHi> 87NHI
4.3.5.2 Function block
Figure 431: Function block
4.3.5.3 Functionality
The high-impedance based restricted earth-fault protection function HREFPDIF
is used for the restricted earth-fault protection of generators and power
transformers.
The function starts when the differential neutral current exceeds the set limit.
HREFPDIF operates with the DT characteristic.
1
Current before fault = 0.0, f
n
= 50 Hz, results based on statistical distribution of 1000 measure-
ments
2
Includes the delay of the signal output contact
1MRS759142 F Protection functions
REX640
Technical Manual
759
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