Setting Notes - Siemens SIPROTEC 7SK80 Manual
Motor protection
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Functions
2.7 Motor Protection (Motor Starting Protection 48, Motor Restart Inhibit 66, Load Jam Protection)
Switching of Startup Times
The motor manufacturer provides startup time curves for both cold and warm motor conditions (see Figure 2-
33). The function Motor Starting Protection automatically performs a switching. The "warm motor" condition is
derived from the thermal storage of the restart inhibit (see Section 2.7.2). Therefore, this function must be en-
abled. The condition for the switching is determined by the parameter 4106 TEMP.COLD MOTOR. If the motor
temperature (actually the rotor temperature) exceeds the threshold value, then a switching from "cold motor"
to "warm motor" takes place (see logic diagram 2-34). The threshold values can be derived from the permitted
number of cold (n
value can be determined.
(Parameter 4106 TEMP.COLD MOTOR)
The setting value should always be lower than the limit value (see Setting Notes 2.7.1.2).
2.7.1.2 Setting Notes
General
Motor starting protection is only effective and accessible if address 141 48 = Enabled is set. If the function is
not required Disabled is set. The function can be turned ON or OFF under address 4101 48.
Startup Parameter
The device is informed of the startup current values under normal conditions at address 4102 STARTUP
CURRENT, the startup time at address 4103 STARTUP TIME. At all times this enables timely tripping if the value
2
I
t calculated in the protection device is exceeded.
If the startup time is longer than the permissible blocked rotor time, an external rpm-counter can initiate the
definite-time tripping characteristic via binary input („>48 Rot. locked"). A locked rotor leads to a loss of
ventilation and therefore to a reduced thermal load capacity of the machine. For this reason, the motor starting
time function is to issue a tripping command before reaching the thermal tripping characteristic valid for normal
operation.
A current above the current threshold 1107 I MOTOR START is interpreted as motor startup. Consequently,
this value must be chosen such that it is reliably attained by the actual starting current under any load or voltage
conditions during motor startup, but not during a permissible short-time overload.
Example: Motor with the following data:
Rated Voltage
Nominal current
Startup current (primary)
Long-term current rating
Startup time (cold condition)
Startup time (warm condition)
Current transformer
122
) and warm (n
) motor startups. By means of the following formula an approximate limit
cold
warm
V
= 6600 V
Nom
I
= 126 A
MOTNom
I
= 624 A
STARTUPw
I
= 135 A
max
T
= 15 s
TMax.STARTUPc
T
= 8.5 s
TMax.STARTUPw
I
/ I
= 200 A / 1 A
NomCTprim
NomCTsec
E50417-G1140-C344-A4, Release date 08.2010
SIPROTEC, 7SK80, Manual
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