100–% Stator Earth Fault Protection with 20 Hz Voltage Injection (ANSI 64G - 100%)
197
7UM62 Manual
C53000-G1176-C149-3
2.29.2 Setting Hints
General
The 100-% stator earth fault protection is only effective and accessible if it has been
set to
at address
during the configuration of the
protection functions. In addition, the function requires the following settings to be
made in Power System Data 1:
−
Address
:
; Sets the resistance transformation ratio (see side
title “Fault Resistances”)
−
Address
should be set to Load. resistor for this application.
The 20 Hz voltage is in this case picked up at the U
E
input, and the displacement
voltage for the 90-% stator earth fault protection (SEF) is calculated from the phase-
to-earth voltages. If the measured voltage (input U
E
is to be used for the 90-% SEF
as well, the address should be set to neutr. transf. or broken delta.
Address
is used to switch the function ON or OFF, or to block
only the trip command (Block relay).
Fault Resistances
The final setting values are determined in the primary test as described in Section 3.3.
Please note that the protection calculates the earth resistance from the secondary val-
ues U
SEF
and I
SEF
which are present at the device terminals. The association between
this calculated value and the actual (primary) stator earth resistance is determined by
the transformation ratio of the earthing and the neutral transformer. For the overall
transformation, the following formula applies:
Meaning:
R
Esec
Earth resistance, converted for the device side
R
Eprim
Primary earth resistance of the stator winding (= fault resistance)
ü
Transf
Transformation ratio of the earthing or neutral transformer
Earthing transformer (leg transformation divided by
3):
Neutral transformer:
ü
MinCT
Transformation ratio of the miniature CT
ü
Divider
Transformation ratio of the voltage divider
R
Esec
1
ü
Transf
2
-------------------
ü
MinCT
ü
Divider
--------------------
R
Eprim
⋅
⋅
=
ü
Transf
ü
EarthTransf
1
3
---
U
Nprim
3
------------------
U
Nsec
3
----------------
-------------------
⋅
1
3
---
U
Nprim
3
------------------
500V
3
--------------
-------------------
⋅
=
=
=
ü
Transf
ü
NeutralTransf
U
Nprim
3
------------------
U
Nsec
-------------------
=
=