Setting Notes - Siemens SIPROTEC 7UM62 Manual

2.36.2

Setting Notes

General
Startup Time Monitoring is only active and available if address 165 STARTUP MOTOR was set to Enabled
during configuration. If the function is not required, it is set to Disabled. Address 6501 STARTUP MOTOR
serves to switch the function ON or OFF or to block only the trip command (Block relay).
Pickup Values
The device is informed of the startup current values under normal conditions at address 6502 START.
CURRENT, and of the startup time at address 6503 STARTING TIME. This ensures timely tripping if the value
2
of I t calculated by 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 („>Rotor locked"). A locked rotor leads to a loss of ven-
tilation and therefore to a reduced thermal load capacity of the machine. For this reason the motor starting time
supervision is to issue a tripping command before reaching the thermal tripping characteristic valid for normal
operation.
A current above the threshold 6505 (address I MOTOR START) is interpreted as a motor startup. Consequent-
ly, 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:
Nominal voltage
Nominal current
Startup current
Permissible continuous stator current:
Starting time at I
CT Ratio I
N CTprim
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
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:
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
StartCurr
/I
N CTsec
2.36 Motor Starting Time Supervision (ANSI 48)
U
I
Mot.Nom
I
StartCurr
I
max
t
Start max
200 A/1 A
= 2.5 · I .
StartCurr N CTsec
= 6600 V
N
= 126 A
= 624 A
= 135 A
= 8.5 s
Functions
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