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2.36
Motor Starting Time Supervision (ANSI 48)
When using the 7UM62 to protect motors, the motor starting protection supplements the overload protection
described in Section 2.11 by protecting the motor against too long starting procedures. In particular, rotor-criti-
cal high-voltage motors can quickly be heated above their thermal limits when multiple starting attempts occur
in a short period of time. If the durations of these starting attempts are prolonged by excessive voltage surges
during motor starting, by excessive load moments, or by locked rotor conditions, a tripping signal will be initiated
by the device.
2.36.1
Functional Description
Motor Startup
The motor starting time monitoring is initiated by the motor starting recognition setting entered at address I
MOTOR START. This current releases the calculation of the tripping characteristic.
One characteristic is definite time while the other one is inverse time.
Inverse Time Characteristic
The inverse time-overcurrent characteristic is designed to operate only when the rotor is not blocked. With de-
creased startup current resulting from voltage dips when starting the motor, prolonged starting times are calcu-
lated properly and tripping can be performed in time. The tripping time is calculated based on the following for-
mula:
with
t
TRIP
t
Start max
I
I
StartCurr
I
Motor Start
Figure 2-114
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
Actual tripping time for flowing current I
Tripping time for nominal startup current I
Current actually flowing (measured value)
Nominal starting current of the motor (Parameter 6502, START. CURRENT)
Pickup value for recognition of motor startup (Parameter 6505, I MOTOR START)
Trip Time Depending on Startup Current
2.36 Motor Starting Time Supervision (ANSI 48)
(param. 6503, STARTING TIME)
StartCurr
Functions
251
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