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