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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
The setting for address STARTUP CURRENT (I
For reduced voltage, the startup current is also reduced almost linearly. At 80 % nominal voltage, the startup
current in this example is reduced to 0.8 · I
The setting for detection of a motor startup must lie above the maximum load current and below the minimum
start-up current. If no other influencing factors are present (peak loads), the value for motor startup I MOTOR
START set at address 1107 may be an average value:
Based on the Long-Term Current Rating:
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
2.7 Motor Protection (Motor Starting Protection 48, Motor Restart Inhibit 66, Load Jam Protection)
STARTUP
STARTUP
V
= 6600 V
Nom
= 126 A
I
MOTNom
= 624 A
I
STARTUPw
I
= 135 A
max
T
= 15 s
TMax.STARTUPc
T
= 8.5 s
TMax.STARTUPw
/ I
= 200 A / 1 A
I
NomCTprim
NomCTsec
) as a secondary value is calculated as follows:
= 2.5.
Functions
131
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