Operate Curve For Asymmetrical Load - Siemens SIPROTEC 5 7UM85 Manual

3.2

Operate Curve for Asymmetrical Load

Various functions of the 7UM85 have applications for asymmetrical load. The protection function can deter-
mine the tripping time of the device in the shortest time according to the specific setting.
Protection for the Unbalanced Load
If a phase failure and asymmetry occur during operation or asymmetrical start when the rated currents are
smaller than 10 times the rated transformer current, the protection for the unbalanced load takes effect. The
2 stages of the function are typically set for a separate protection of a maximum permissible unbalanced load
and for a phase failure.
Overcurrent Protection, Ground
Measuring the ground current is effective to detect the asymmetric load. Depending on the setting, the Over-
current protection, ground function protects the unbalanced load in case of a phase failure and asymmetrical
load.
Thermal Overload Protection
The Thermal overload protection function calculates the overtemperature for each phase separately. The
maximum overtemperature of the phases is regarded as the tripping temperature. This means that the
maximum current of the 3 phase currents is always assumed. If there is an overload in one winding, the entire
protected object is switched off. Thus, the protection against asymmetrical load is guaranteed.
Motor-Starting Time Supervision
If the maximum current of all 3 phases of the motor is larger than the parameter Curr.thres.starting,
the motor changes to the
The Motor-Starting Time Supervision function supervises the starting time of each phase. If the current in
one of 3 phases exceeds the configured pickup threshold due to the unbalanced load, the function operates.
Undervoltage Protection
The device can use 2 undervoltage protection stages to detect a phase failure during operation or in case of a
2-phase motor start.
SIPROTEC 5, Additional Information on the Protection of Explosion-Proof Motors with Type of Protection Increased Safety e,
Manual
C53000-H5050-C078-1, Edition 03.2019
starting state.
Operate Curve
3.2 Operate Curve for Asymmetrical Load
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