Siemens SIPROTEC 4 7SJ61 Manual page 110

Functions
2.6 Motor Protection
Motor Protection Example
Figure 2-41 illustrates an example of a complete motor protection characteristic. Such characteristic usually
consists of different protection elements, and each element is responsible for special motor malfunctions.
These are:
•
Thermal overload protection: to avoid overheating of the motor due to inadmissible load
•
Load jam protection: to prevent overheating and mechanical damage due to a locked rotor
•
Motor starting protection: protects the motor against prolonged startup procedures and the consequent
thermal overload of the rotor
•
Overcurrent and high-current elements: for motor shutdown due to electrical faults
[motorbelastungsgrenze, 1, en_US]
Figure 2-41
Example:
Motor with the following data:
Nominal voltage
Nominal current
Long-term current rating
Startup duration
Current transformer
The setting for address 4402 Load Jam I> as secondary value is calculated as follows:
110
Example of a complete motor protection characteristic
U = 10 kV
Nom
= 436 A
Ι
Nom
= 135 A
Ι
max
T
startmax
Ι
NomCTprim
= 8.5 s
/ Ι = 500 A / 1 A
NomCTsec
SIPROTEC 4, 7SJ61, Manual
C53000-G1140-C210-6, Edition 05.2016