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 Ι
2
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 V
Nom
= 6600 V
Nominal current
Ι
MOTNom
= 126 A
Startup current (primary)
Ι
STARTUPw
= 624 A
Long-term current rating
Ι
max
= 135 A
Startup time (cold condition) T
Max.STARTUPc
= 15 s
Startup time (warm condition) T
Max.STARTUPc
= 8.5 s
Current transformer
Ι
NomCTWdl prim
/Ι
N omCTsec
= 200 A/1 A
The setting for address STARTUP CURRENT (Ι
STARTUP
) as a secondary value is calculated as follows:
[formel-maxanlauf-150502-kn, 1, en_US]
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 · Ι
STARTUP
= 2.5 A.
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:
[beispiel-anl-zulstrom-270602-kn, 1, en_US]
[formel-motoranlauf-260602-kn, 1, en_US]
For ratios deviating from nominal conditions, the motor tripping time changes:
2.8.1.2
Functions
2.8 Motor Protection
SIPROTEC 4, 7SJ62/64, Manual 147
C53000-G1140-C207-8, Edition 08.2016
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