Siemens Siprotec 7UM611 Manual page 147

Example: Motor with the following data:
Rated voltage
Rated current
Starting current
Long-Term Current Rating
Startup Duration for I
CT Ratio I
The setting for address START. CURRENT 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
CTsec
The setting for detection of a motor startup must lie above the maximum load current
and below the minimum startup current. If no other influencing factors are present
(peak loads), the value for motor startup I MOTOR START set at address 6505 may
be set to an average value:
The tripping time of the starting time monitoring is calculated as follows:
Under nominal conditions, the tripping time is the maximum starting time T
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 for example:
After the delay time LOCK ROTOR TIME has expired, the binary input becomes effec-
tive and initiates a tripping signal. If the blocked rotor time is set to a value that the
binary input ">Rotor locked" (No. 6805) is reliably reset during the delay time
LOCK ROTOR TIME, faster tripping will be available during motor starting under locked
rotor conditions.
7UM61 Manual
C53000-G1176-C127-3
U = 6600 V
N
I
Mot.nom
I
StartCurr.
I
max
T
StartCurr. Startmax
/I 200 A / 1 A
N CTprim N CTsec
2.24 Motor Starting Time Supervision (ANSI 48)
= 126 A
= 624 A
= 135 A
= 8.5 s
= 2.5 · I
Startcurr. N
.
Max.STARTUP
147