Setting Notes; Overcurrent Protection; Overload Protection - Siemens SIPROTEC 7SJ62 Handbuch

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Setting Notes

Overcurrent
protection
Unbalanced load
protection
Voltage Protection
Motor starting time
supervision
Restart inhibit
Overload
protection
7SJ62/63/64 Additional Information
C53000-B1174-C170-1
Setting notes and, if applicable, setting formulas for each protection function are
indicated in the device manual. The corresponding chapter numbers are bracketed.
The following paragraphs give additional hints particularly for application of the device
as protection of explosion proof motors.
(See Subsection 2.2 in the device manual)
Especially in such cases where no separate time-overcurrent protection/short-circuit
protection is provided for, the integrated time-overcurrent protection must be
configured available as overcurrent protection function and switched on (see
"example").
(See Subsection 2.7 in the device manual)
The operating range of the unbalanced load protection is between 0.1 ⋅ I
Unbalanced load protection thus becomes necessary in the current range of > 4 ⋅ I
Effective motor protection against phase failure and asymmetric load is achieved by
overcurrent protection of the ground system.
(See Subsection 2.6 in the device manual)
Also the undervoltage protection can be applied to detect an unbalanced load (phase
failure or inadmissible voltage surge) - provided voltage transformers are used.
(See Subsection 2.8.1 in the device manual)
Motor starting is detected if a (configurable) current threshold is exceeded. The same
threshold is used by the overload protection to "freeze" its thermal profile i.e., maintain
it at constant level. Therefore this threshold should not be set unnecessarily low as it
limits the operating range of the overload protection towards higher currents during
operation.
(See Subsection 2.8.2 in the device manual)
During normal operation explosion proof machines may be started twice from cold and
once from warm condition. Afterwards, a sufficiently long cooling time must be
observed.
This equilibrium time must not be set to zero for protection of explosion proof motors!
Caution!
When auxiliary voltage supply (larger than the admissible system failure bridging time)
fails while the restart inhibit is operating, the inhibit is aborted. This fact must be
considered during operation.
(See Subsection 2.10 in the device manual)
The thermal overload protection feature creates a thermal profile of the machine under
protection. If the first configurable threshold of the calculated overtemperature has
been exceeded, an alarm indication will be issued. If the second temperature
threshold has been reached, this alarm indication must be used as a trip command to
disconnect the machine from the power supply. Furthermore, the following special
cases must be considered:
Setting Notes
and 4 ⋅ I .
N N
.
N
25