Functions
92
7UM62 Manual
C53000-G1176-C149-3
−
Rated current of the current transformer set in A (see above).
Winding 1 is defined as the reference winding and therefore needs no numeral; the
other windings are referred to winding 1.
The reference winding is normally that of the higher voltage. If not the higher voltage
side is used as reference winding, it must be considered that the vector group
changes: e.g. a Dy5 transformer is regarded from the Y side as Yd7.
If a transformer winding is regulated, then the actual rated voltage of the winding is not
used as U
N
, but rather the voltage which corresponds to the average current of the
regulated range.
If the setting of the protection should be performed with secondary values only (e.g.
because external matching transformers are present), the factory-set parameters for
transformer data can remain unchanged. The presets for transformer data apply for a
ratio of 1: 1 without phase displacement
Zero Sequence
Current
Treatment
The treatment of the winding starpoint is of no concern if the zero sequence currents
are eliminated from the phase currents. Because of the zero sequence current
elimination, fault currents which flow through the CTs during earth faults in the network
if there is an earthing point in the protected zone (transformer starpoint or starpoint
earthing transformer) are neutralized without any special measures from outside. The
elimination of the zero sequence currents is selected by setting
STARPNT SIDE*
=
earthed
(see Figure 2-34).
In networks with isolated or arc compensated starpoint, the elimination of the zero
sequence current may be set ineffective provided that the starpoint of the protected
transformer winding has no connection to earth, not even via a Petersen coil or a surge
arrester. In this case, each double earth fault with one base point in the protected zone
will be cleared by the relay, regardless of any double earth fault priority (see side title
”Isolated Starpoint” and Figure 2-33).
Increase of Pickup
Value on Startup
For additional security against overfunctioning when a non-energized protection
object is switched in, an increase of the pickup value on startup can be set at address
. As this option is mainly provided for generator and motor
protection, the default setting is
OFF
if a 2-winding transformer has been selected as
protected object.
The associated parameters can be found at addresses
and
.
Address
is used to set the pickup value for detecting a
startup. The function is disabled by setting I/I
nO
= 0. The
specifies the
increase factor of the pickup values on startup. For transformer protection, a setting of
2052A
=
1.0
is recommended. For switching of external loads such
as motors or transformers, it should be increased to
2.0
. Due to the high time
constants, branch b of the characteristic may well be exceeded for a short time.
Harmonic Restraint
The inrush restraint of the device can be activated and deactivated at address
. It is based on an evaluation of the 2nd harmonics present in the
inrush current. When the device is delivered from the factory, a ratio I
2fN
/I
fN
of 15 % is
set and can normally be maintained. However, the component required for restraint
can be parameterized. To provide for more restraint in exceptional cases, where
switch-on conditions are particularly unfavourable, a smaller value can be set at
address
U
N
2
U
max
U
min
⋅
U
max
U
min
+
---------------------------------
⋅
2
1
U
min
-------------
1
U
max
--------------
+
----------------------------------
=
=
Voltage to be set
