Siemens SIPROTEC 7UT613 series, Руководство пользователя

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2.2 Differential Protection
133
7UT613/63x Manual
C53000-G1176-C160-2
The increase of the
pickup value on
startup The increase of the pickup value on startup serves as an additional safety against
overfunctioning when a non-energised protection object is connected. At address
1205 INC.CHAR.START
it can be switched to
ON
or
OFF
. Especially for motors or mo-
tor/transformer units in block connection it should be set to
ON
.
The restraint current value
I-REST. STARTUP
(address
1251
) is the value of the re-
straining current which is likely to be undershot before startup of the protected object
takes place. This parameter can only be set with DIGSI at
Additional Settings .
Please be aware of the fact that the restraint current is twice the traversing operational
current. The pre-set value of 0.1 represents 0.05 times the rated current of the protect-
ed object.
Address
1252 START-FACTOR
determines by which factor the pickup value of the
Diff>
stage is to be increased on startup. The characteristic of this stage increases by the
same factor. The I
Diff>>
stage is not affected. For motors or motor/transformer in unit
connection, a value of
2
is normally adequate. This parameter can only be set with
DIGSI under Additional Settings .
The increase of the pickup value is set back to its original value after time period
T
START MAX
(address
1253
) has passed.
Add-on Restraint In systems with very high traversing currents a dynamic add-on restraint is enabled for
external faults. The initial value is set at address
1261 I-ADD ON STAB.
. The value
is referred to the rated current of the protected object. The slope is the same as for
characteristic branch
b (
SLOPE 1
, address
1241
). This parameter can only be set with
DIGSI at Additional Settings . Please note that the fact that the restraint current is the
arithmetical sum of the currents flowing into the protected object, i.e. it is twice the tra-
versing current. The additional stabilisation does not influence the stage
I-DIFF>>
.
The maximum duration of the add-on restraint after detection of an external fault is set
to multiples of an AC-cycle (address
1262 T ADD ON-STAB.
). This parameter can
only be set with DIGSI at Additional Settings . The add-on restraint is disabled auto-
matically even before the set time period expires as soon as the device has detected
that the operation point
I
diff
/
I
stab
stationary (i.e. via at least one cycle) within the tripping
zone near the fault characteristic (
≥
80 % of the fault characteristic slope).
Add-on restraint operates individually per phase, but blocking can be extended to all
three phases (so-called crossblock function). By means of address
1263 CROSSB.
ADD ON
it can be determined how long the crossblock should be effective. This pa-
rameter can only be set with DIGSI at Additional Settings . Here, too, setting is in mul-
tiple of one AC-cycle. If 0 Per. cycle is set, crossblock is ineffective, i.e. only the phase
with detected external fault will be blocked. Otherwise all phases will be blocked. in
this case the same setting as for
1262 T ADD ON-STAB.
is advisable. When set to
∞
, the crossblock function is always effective.
Harmonic Restraint Restraint with harmonic content is available only when the device is used as trans-
former protection, i.e. the
PROT. OBJECT
(address
105
) is a
3 phase transf.
or
1 phase transf.
or
Autotransf.
or
Autotr. node
. This function is also used
for shunt reactors if current transformers are installed at both sides of the connection
points.
The inrush restraint function with 2nd harmonic can be switched in address
1206
INRUSH 2.HARM. OFF
and
ON
. It is based on evaluation of the 2nd harmonic present
in the switch-on inrush current. The ratio of 2nd harmonics to the fundamental (ad-
dress
1271
,
2. HARMONIC
) is set to
I
2fN
/
I
fN
= 15 % as default setting. It can be used
without being changed. To provide more restraint in exceptional cases, where ener-
gising conditions are particularly unfavourable, a smaller value can be set at the afore-