Siemens SIPROTEC 7UT613 series Manual page 216

2 Functions
Thermal Tripping
Characteristic
216
This means that a pickup will only occur if an unbalanced load of about 1.1 times the
setting value of I2p (address 4021 or 4022) is present.
The corresponding time multiplier is accessible via address 4024 D I2p.
The time multiplication factor may also be set to ∞. If set to infinity, the pickup of this
function will be indicated but the stage will not trip after pickup. If the inverse time stage
is not required, select 140 = UNBALANCE LOAD in address Definite Time when
configuring the protection functions.
If under address 4025 I2p DROP-OUT the Disk Emulation has been set, dropout
is thus produced in accordance with the dropout characteristic, as described in the
function description of the asymmetrical load protection under margin heading „Drop-
out Behaviour".
The „Definite Time StagesI
inverse-time stage as alarm and tripping stages.
In case of generators and motors, the thermal stage permits a good adjustment of the
asymmetrical load protection to the thermal load capacity of the machine due to the
asymmetrical load. The first characteristic value is the maximum permanent permissi-
ble negative sequence current. For machines of up to 100 MVA with non-salient pole
rotors, this typically amounts to a value in a range from 6 % to 8 % of the nominal
machine current, and with salient-pole rotors at least 12 %. For larger machines and
in cases of doubt, please refer to the instructions of the machine manufacturer. Set
this value under address 4031 I2>.
As the relevant measuring location for asymmetrical load is usually assigned to the
side of the machine to be protected, a conversion of the pickup value is not required,
i.e. during permanent permissible asymmetrical load of, for example, 11% it can be set
directly under address 4031 I2>:
I2> = 0,11 [I/I
].
nSide
If, however, the asymmetrical load protection must be set in amps secondary during
operation, the machine values must be converted.
Example:
Machine
Current transformer
results under address 4033 in the secondary value
I2> = 0.53 [A].
This permanently permissible negative system current is simultaneously the pickup
threshold for the thermal asymmetrical load protection and also the limit for the asym-
metrical load warning stage. The delay of the warning indication can be set under
address 4033 T WARN. Usually approx. 20 s.
The asymmetry factor FACTOR K (address 4034) is a measure for the thermal stress
of the rotor. It indicates the time for which 100 % asymmetrical load are permissible
and corresponds with the permissible thermal energy loss (K = (I/I
by the machine manufacturer or it can be seen on the asymmetrical load diagram of
the machine.
>>, I
>" as discussed above can be used in addition to the
2 2
I = 483 A
N
I = 11 % (salient-pole machine)
2perm
500 A/5 A
2
) · t). It is indicated
N
7UT613/63x Manual
C53000-G1176-C160-2