6.2.2
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 low-impedance function is a percentage biased function with an additional zero
sequence current directional comparison criterion. This gives excellent sensitivity and
stability during through faults. The function allows the use of different CT ratios and
magnetizing characteristics on the phase and neutral CT cores. Unlike high impedance
restricted earth fault it allows for mixing with other functions and protection IEDs on
the same CT cores.
6.2.3
Function block
REFPDIF
I3P*
I3PW1CT1*
I3PW2CT1*
BLOCK
TRIP
START
DIROK
BLK2H
IRES
IN
IBIAS
IDIFF
ANGLE
I2RATIO
IEC09000275_1_en.vsd
IEC09000275 V1 EN
Figure 44:
REFPDIF function block
6.2.4
Signals
Table 36:
Input signals for the function block REFPDIF (REF1-)
Signal
Description
I3P
Group signal for neutral current input
I3PW1CT1
Group signal for primary CT1 current input
I3PW2CT1
Group signal for secondary CT1 current input
BLOCK
Block of function
Table 37:
Output signals for the function block REFPDIF (REF1-)
Signal
Description
TRIP
General trip signal
START
General start signal
DIROK
Directional criteria has operated for internal fault
BLK2H
Block due to 2-nd harmonic
IRES
Magnitude of fundamental frequency residual current
IN
Magnitude of fundamental frequency neutral current
IBIAS
Magnitude of the bias current
Table continues on next page
1MRK 504 135-UEN A
Section 6
Differential protection
111
Technical manual
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