Configuration
6.2 Use of 3RA2 load feeders with highly energy-efficient motors (IE3)
SIRIUS - SIRIUS 3RA load feeders
Manual, 09/2016, A5E03656507520A/RS-AB/003
29
Rated motor current/setting scale
For motor protection, the motor's rated current must be set on the motor starter protector's
setting scale. The new IE3 motors generally have lower rated currents. This can lead to
situations in which a motor starter protector with a lower rated current has to be chosen for
the same motor rating. Thus, the short-circuit detection response value also drops and can
lead to tripping during motor starting.
Short-circuit detection (Page 28)
Optimization of 3RV2 motor starter protectors for IE3 motors
The motor starter protectors have been revised in relation to the higher locked rotor currents
and inrush currents as follows:
● Raising of the lower short-circuit detection response tolerances without changes to t
he
max
imum values.
→ No change to system dimensioning
● Increase in the making / breaking capacity.
→ Far-reaching avoidance of restrictions due to increased motor starting currents
and
i
nrush currents, see the chapter "Technical modifications/restrictions of 3RV2 motor
starter protectors (Page 31)".
● Adaptation of some motor starter protector versions' overload releases and setting
scales.
→ Avoidance of using smaller motor starter protectors due to lower rated motor currents
(see chapter "Technical modifications/restrictions of 3RV2 motor starter protectors
(Page 31)")
In the case of motors with very high locked rotor and inrush currents, problems can arise
despite adaptations, e.g. undesired tripping on starting. It is recommended that motor starter
protectors be selected such that the setting does not need to be made in the upper range of
the setting scale. This reduces power loss in the device (cost saving and reduced
temperature rise in the control cabinet) and increases the distance from the short-circuit
releases' response limits.
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