112
Two step definite and inverse time-
delayed residual
overcurrent protection (TEF1 and TEF2)
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The polarizing voltage for directional earth-fault overcurrent protection is obtained by
internal calculation (U
N
=UL1+UL2). The voltage contains a certain amount of harmon-
ics, especially when the protection is connected to CVTs.
Due to the bandpass filtering a polarizing voltage down to 1 percent of the rated voltage
will provide correct directional functionality. This is also valid when the protection is
connected to CVTs.
The minimum polarizing voltage to the protection (Umin) is calculated from the formu-
la:
(Equation 56)
To even secure operation in unfavorable cases, Umin must be equal to at least 2 volt
plus the maximum network frequency false voltage, due to measuring errors in the VT
circuits.
where:
I
F min
is the minimum primary operate fault current
Z
n min
is the minimum zero-sequence impedance seen from the relay
U
sec
, U
prim
are the rated phase voltages of connected CVTs (VTs)
U
min
I
F min
Z
n
min
U
sec
U
prim
---------------
⋅
⋅
=
Summary of Contents for REO 517
Page 10: ... RQWHQWV ...
Page 16: ...6 Introduction to the application manual KDSWHU QWURGXFWLRQ ...
Page 64: ...54 Blocking of signals during test KDSWHU RPPRQ IXQFWLRQV ...
Page 88: ...78 Scheme communication logic ZCOM KDSWHU LQH LPSHGDQFH ...
Page 146: ...136 Unbalance protection for capacitor banks TOCC KDSWHU XUUHQW ...
Page 166: ...156 Dead line detection DLD KDSWHU 3RZHU V VWHP VXSHUYLVLRQ ...
Page 378: ...368 Monitoring of DC analog measurements KDSWHU 0RQLWRULQJ ...
Page 384: ...374 Pulse counter logic PC KDSWHU 0HWHULQJ ...
Page 412: ...402 Serial communication modules SCM KDSWHU DWD FRPPXQLFDWLRQ ...
Page 440: ...430 LED indication module KDSWHU DUGZDUH PRGXOHV ...