Table 57. Numerical stabilized low impedance restricted earth-fault protection (LREFPNDF)
Characteristic Value
Operation accuracy Depending on the frequency of the current measured: 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 x set
Operate value
38 ms 40 ms 43 ms
Reset time < 40 ms
Reset ratio Typical 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 x f
n
, where n = 2, 3, 4, 5, …
1) Current before fault = 0.0, f
n
= 50 Hz, results based on statistical distribution of 1000 measurements
2) Includes the delay of the signal output contact
Table 58. Numerical stabilized low impedance restricted earth-fault protection (LREFPNDF) main settings
Parameter Function Value (Range) Step
Operate value LREFPNDF 5...50 % 1
Restraint mode LREFPNDF None
2nd harmonic
-
Start value 2.H LREFPNDF 10...50 % 1
Minimum operate time LREFPNDF 40...300000 ms 1
Operation LREFPNDF Off
On
-
Table 59. High-impedance based restricted earth-fault protection (HREFPDIF)
Characteristic
Value
Operation accuracy At the frequency f = f
n
±1.5% of the set value or ±0.002 × I
n
Start time
1)2)
I
Fault
= 2.0 × set
Operate value
I
Fault
= 10.0 × set
Operate value
Typical 22 ms (±5 ms)
Typical 15 ms (±5 ms)
Reset time < 60 ms
Reset ratio Typical 0.96
Retardation time < 60 ms
Operate time accuracy in definite time mode ±1.0% of the set value or ±20 ms
1) Current before fault = 0.0 × I
n
, f
n
= 50 Hz
2) Includes the delay of the signal output contact
Table 60. High-impedance based restricted earth-fault protection (HREFPDIF) main settings
Parameter
Function Value (Range) Step
Operate value HREFPDIF 1.0...50.0 % 0.1
Minimum operate time HREFPDIF 40...300000 ms 1
Operation HREFPDIF Off
On
-
Transformer Protection and Control 1MRS757846 A
RET620
Product version: 2.0
38 ABB
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