Functions
2.6 Motor Protection
SIPROTEC, 7SJ61, Manual
C53000-G1140-C210-1, Release date 02.2008
106
The setting for address
STARTUP CURRENT
(
I
STARTUP
) as a secondary value is calculated as follows:
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
STARTUP
= 2.5.
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:
For ratios deviating from nominal conditions, the motor tripping time changes:
At 80% of nominal voltage (which corresponds to 80% of nominal starting current), the tripping time is:
After the time delay (
4104
LOCK ROTOR TIME
) has elapsed, the binary input becomes effective and generates
a trip signal. If the locked rotor time is set just long enough that during normal startup the binary input
„>Rotor
locked“
(FNo. 6805) is reliably reset during the delay time
LOCK ROTOR TIME
, faster tripping will be available
during motor starting under locked rotor conditions.