Siemens SIPROTEC 4 7UT6 Series Manual page 195

Setting
Delay
The inverse curves (see below) permit a consideration of load imbalance per unit of time. However, especially
for generators and motors a better adjustment to the protected object can be achieved with the thermal stage
(see below under "Thermal Tripping Characteristic"
Inverse Time Element Ι2p bei IEC-Kennlinien
Having selected an inverse time tripping characteristic the thermal load of a machine caused by unbalanced
load can be simulated easily. Use the characteristic which is most similar to the thermal asymmetrical load
curve of the machine manufacturer.
With the IEC characteristics (address 140 UNBALANCE LOAD = TOC IEC) the following options are available
at address 4026 IEC CURVE:
•
Normal Inverse (inverse, type A according to IEC 60255-3),
•
Very Inverse (very inverse, type B according to IEC 60255-3),
•
Extremely Inv. (extremely inverse, type C according to IEC 60255-3).
The characteristics and equations they are based on are listed in the "Technical Data".
If an inverse-time characteristic is selected, it must be noted that a safety factor of about 1.1 has already been
included between the pickup value and the setting value. This means that a pickup will only occur if an unbal-
anced 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 4023 T I2p.
The time multiplication factor may also be set to ∞. If set to infinity, the pickup of this function will be indi-
cated but the stage will not trip after pickup. If the inverse time stage is not required, select Definite Time
in address 140 UNBALANCE LOAD, when configuring the protection functions.
If under address 4025 I2p DROP-OUT the Disk Emulation is 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 "Dropout Behaviour".
The definite time stages as discussed above under "Definite Time Stages I2>>, I2>" can be used in addition to
the inverse-time stage as alarm and tripping stages.
Definite Time Tripping Ι2p for ANSI Characteristics
The thermal behaviour of a machine can be closely replicated due to negative sequence by means of an
inverse time tripping curve. Use the characteristic which is most similar to the thermal asymmetrical load
curve of the machine manufacturer.
With the ANSI characteristics (address 140 UNBALANCE LOAD = TOC ANSI) the following is made available in
address 4027 ANSI CURVE:
•
Extremely Inv.,
•
Inverse,
•
Moderately Inv. and
•
Very Inverse.
The characteristics and the equations they are based on are listed in the "Technical Data".
If an inverse-time characteristic is selected, it must be noted that a safety factor of about 1.1 has already been
included between the pickup value and the setting value. This means that a pickup will only occur if an unbal-
anced 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 indi-
cated but the stage will not trip after pickup. If the inverse time stage is not required, select Definite Time
in address 140 UNBALANCE LOAD, when configuring the protection functions.
SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016
= 0.55 · 545 A = 300 A primary or
I2>>
0.55 · 545 A · (1/600) = 0.50 A secondary
= 1 s
T I2>>
Functions
2.8 Unbalanced Load Protection
195