Functionality; Function Block; Signals - ABB RET650 Technical Manual

1MRK 504 135-UEN A
6.2.2
6.2.3
6.2.4
Technical manual

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.

Function block

REFPDIF
I3P* TRIP
I3PW1CT1* START
I3PW2CT1* DIROK
BLOCK BLK2H
IRES
IN
IBIAS
IDIFF
ANGLE
I2RATIO
IEC09000275_1_en.vsd
IEC09000275 V1 EN
Figure 44: REFPDIF function block

Signals

Table 36: Input signals for the function block REFPDIF (REF1-)
Signal
I3P
I3PW1CT1
I3PW2CT1
BLOCK
Table 37: Output signals for the function block REFPDIF (REF1-)
Signal
TRIP
START
DIROK
BLK2H
IRES
IN
IBIAS
Table continues on next page
Differential protection
Description
Group signal for neutral current input
Group signal for primary CT1 current input
Group signal for secondary CT1 current input
Block of function
Description
General trip signal
General start signal
Directional criteria has operated for internal fault
Block due to 2-nd harmonic
Magnitude of fundamental frequency residual current
Magnitude of fundamental frequency neutral current
Magnitude of the bias current
Section 6
111