Function
Range or value
Accuracy
Reset time at 5 to 0 x IdUnre
unrestrained function
Min. = 15 ms
Max. = 30 ms
-
Critical impulse time, unrestrained function
2 ms typically at 0 to 5 x
IdUnre
-
Impulse margin time unrestrained function
10 ms typically
-
Operate time at 0 to 5 x IMinNegSeq
Negative sequence unrestrained function
Min. = 25 ms
Max. = 35 ms
-
Reset time at 5 to 0 x IMinNegSeq
Negative sequence unrestrained function
Min. = 30 ms
Max. = 45 ms
-
6.4
Low impedance restricted earth fault protection
REFPDIF
6.4.1
Identification
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Restricted earth-fault protection, low
impedance
REFPDIF
IdN/I
SYMBOL-AA V1 EN
87N
6.4.2
Functionality
Restricted earth-fault protection, low-impedance function REFPDIF can be used on
all directly or low-impedance earthed windings. The REFPDIF function provides
high sensitivity and high speed tripping as it protects each winding separately and thus
does not need inrush stabilization.
The REFPDIF function is a percentage biased function with an additional zero
sequence current directional comparison criterion. This gives excellent sensitivity and
stability during through faults.
REFPDIF can also protect autotransformers. Five currents are measured at the most
complicated configuration as shown in Figure
1MRK502052-UEN B
Section 6
Differential protection
165
Technical manual
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